key: cord-0934282-q1f23ipa
authors: Felsenstein, Susanna; Reiff, Andreas Otto
title: A hitchhiker's guide through the COVID-19 galaxy
date: 2021-09-24
journal: Clin Immunol
DOI: 10.1016/j.clim.2021.108849
sha: e135ecc9c03be13bb1f302a2d95f7672d849fb24
doc_id: 934282
cord_uid: q1f23ipa

Numerous reviews have summarized the epidemiology, pathophysiology and the various therapeutic aspects of Coronavirus disease 2019 (COVID-19), but a practical guide on “how to treat whom with what and when” based on an understanding of the immunological background of the disease stages remains missing. This review attempts to combine the current knowledge about the immunopathology of COVID-19 with published evidence of available and emerging treatment options. We recognize that the information about COVID-19 and its treatment is rapidly changing, but hope that this guide offers those on the frontline of this pandemic an understanding of the host response in COVID-19 patients and supports their ongoing efforts to select the best treatments tailored to their patient's clinical status.

Therefore, a thorough understanding of the immunopathology in COVID-19 is critical for selecting the most appropriate therapeutic interventions and preventing patient exposure to unnecessary or potentially harmful treatments.

The key immunologic processes of COVID-19 include:

 an initial rapid increase in viral load  excessive and prolonged innate immune activation  epi-and endothelial barrier dysfunction  a pro-coagulant state  excessive pulmonary neutrophil recruitment and formation of neutrophil extracellular traps (NETs)

These processes are also implicated in other infectious and inflammatory conditions. It remains to be determined if and to what extent the immune mechanisms observed in COVID-19 indeed differ from infectious and non-infectious conditions such as SIRS, inflammatory ARDS, and other systemic hyperinflammatory states.

To classify disease severity and assist in standardizing of research protocols, the WHO has developed an ordinal 9 point scale ( Figure 1 ) reflecting the various stages of disease progression [64, 65] . Applying this scale, this article attempts to match the underlying immunopathology of COVID-19 with evidencebased treatment modalities published in the peer-reviewed literature. We recognize that during the progression of the disease to severe COVID-19, these processes overlap, influence one another, and are causally linked. As the clinical picture evolves, different processes emerge and therapeutic targets change.

Our knowledge of the immunopathology and therapeutic options in COVID-19 is expanding daily. Best up to date advice will be found online through resources, such as the regularly revised websites of the NIH and WHO.

Until vaccines achieve protection at a population level, social distancing, face masks, and hand hygiene are effective and necessary measures mitigating infection risk [66] .

Over 114 vaccine candidates utilizing a diverse set of technologies are currently in clinical development [67] . Vaccination with mRNA constructs targeting influenza, rabies, zika or chikungunya virus have been subject to research efforts for some time and are now applied to SARS-CoV-2 [68] [69] [70] . Of those, two mRNA based vaccines, mRNA1273 from Moderna, Tozinameran from the BioNTech/Pfizer partnership and two adenovirus-vector vaccines, AZD1222 from AstraZeneca and the single-dose Janssen/Johnson & Johnson vaccine, have been granted Emergency Use Authorization (EUA) as COVID-19 vaccines in the US since December 2020. In addition, an adjuvanted inactivated virus vaccine by Sinovac and the heterologous recombinant adenovirus vaccine Sputnik V have been in widespread use.

Vaccines provide high-level protection from SARS-CoV-2 infection and severe disease and elicit a robust antibody and B-and T-cell response [71, 72] . However, despite the effective initial humoral vaccine response, neutralization activity declines over time. To what extent serum antibody titers are a proxy for reinfection risk remains to be determined, but evidence for neutralizing activity and protection from (re)infection is emerging [73] . A recent large study demonstrated that antibody titers in response to the two most widely used mRNA vaccines decreased significantly after six months [74] . In addition, vaccine-induced efficacy against emerging viral variants is reduced [75, 76] , supporting recent discussions for the need for booster vaccines.

In summary, the observation of breakthrough infections in vaccinated people, decreasing antibody titers following vaccination and emergence of new escape variants all highlight the ongoing need for close surveillance of this highly dynamic situation.

Since vaccines have become available, other prophylactic measures have become less relevant. However, they may remain of importance for select high-risk individuals, especially when suboptimal vaccine responses may be expected, such as in the immunocompromised.

The use of the monoclonal antibody combination casirivimab plus imdevimab (see below) as postexposure prophylaxis has been shown to result in a significant reduction of symptomatic SARS-CoV-2 infections compared with placebo (1.5% vs 7.8%; OR 0.17; p<0.001) [77] . As a result of these findings, the Food and Drug Administration (FDA) has issued an Emergency Use Authorization (EUA) for this combination as post-exposure prophylaxis within seven days [78] .

Type 1 Interferon is critically involved in the early antiviral response [79, 80] (see below). Prophylactic use of IFN-1 nasal drops four times daily in 3000 uninfected health care workers (HCWs) resulted in no symptomatic SARS-CoV-2 infections in any of the patient-facing staff [81] . Controlled studies investigating the role of IFN-1 in preventing COVID-19 are underway (NCT04552379, NCT04320238) [82] .

During the incubation period, patients are asymptomatic, and many will never develop symptoms as described above. In others, epithelial infection and local inflammation may result in symptoms consistent with a mild viral infection [83] .

High-risk patients should be monitored closely to initiate therapeutic interventions at the first signs of disease progression. SARS-CoV-2 replication peaks early, at symptom onset, so the timing of virostatic therapies is critical. Delayed antiviral treatment may shorten viral shedding but not significantly affect the viral load (VL) [84] . Outpatients with a higher VL one week after symptom onset are more likely to be hospitalized and prolonged shedding of replication-competent virus is associated with more severe disease [21, 85, 86] . This suggests that early antiviral treatment may curb the rapid early replication and possibly influence the risk of disease progression.

GCs may downregulate ACE2 in respiratory epithelia [165] and reduces airway inflammation, possibly impacting the beginning of epithelial and macrophage-driven host response. The STOIC trial of and agestratified cohort with mild COVID-19 symptoms for less than seven days. Intervention was open-label, 800mcg Budesonide dry powder inhalation BD until symptom resolution compared to SOC. Medically attended visits and hospitalizations were fewer (14% vs 1%; p=0.004), and symptom resolution faster (7 vs 8 days, p=0.007) [166] . The treatment was well-tolerated, encouraging larger placebo-controlled trials that target mildly affected outpatients.

 Convalescent plasma (CP) CP has been widely administered to patients with COVID-19, often with advanced disease. Patients may have already seroconverted and have neutralizing anti-SARS-CoV2 concentrations equivalent to those contained in CP [167] (Table 1) . CP may contain pro-inflammatory and pro-coagulant factors [168] . Further, SARS-CoV2 specific antibody titers vary greatly [169] . Antibody kinetics in COVID-19 differ: nonsurvivors have a delayed antibody response, whereas survivors produce neutralizing antibodies more rapidly [170] . Based on this observation and considering the abovementioned caveats, the timing of exogenous antibody administration seems critical. As the majority of studies on CP use have been uncontrolled, it is not surprising that efficacy assessments of a metanalysis including 30 studies and RCTs with 17.225 patients [171] were inconclusive (-very uncertain‖) and found no effect on mortality or clinical improvement at 28 days. 81) in patients who had been receiving ACEi when contracting SARS-CoV-2. Since then, several studies assessing the impact of discontinuing ACEi treatment upon COVID-19 diagnosis have not identified a difference in disease severity or death. Discontinuation of ACEi/ARB treatment in those already using these agents is therefore not justified.

Besides its antimicrobial properties, AZM has immunomodulatory effects. It repolarizes macrophages towards tissue-restorative M2 and inhibits pro-inflammatory NF B and STAT1 signaling [174, 175] . However, in patients with a moderate oxygen requirement (WHO stage 4), AZM did not impact progression to MV or death [176] . As macrolides prolong the QTc interval, their use should be carefully monitored, especially in older patients or in combination with other pro-arrhythmogenic agents. Most studies have investigated AZM in combination with HCQ and repeatedly identified an increased mortality risk associated with this combination [133] . AZM is therefore not recommended in the treatment of COVID-19.

Hospitalization becomes necessary in approximately 4.7% of infected individuals. The risk in patients over 60 years is higherapproximately between 10 and 20% [30] . The decision to admit patients not requiring O 2 will be informed by a comprehensive assessment of clinical, laboratory and imaging findings [177] , with more pro-active management of risk groups and the availability of healthcare resources.

Several clinical scores have been developed to distinguish those at risk for disease progression at the time of hospitalization ( Table 2) . A moderately accurate prediction of future severe COVID-19 disease can be achieved by combining the results of CT findings of the lung, inflammatory markers (C-reactive protein, ferritin, neutrophils, lymphocytes, albumin), evidence of tissue injury (transaminases, LDH, Troponin, D-Dimer) and evidence of electrolyte imbalance (blood urea, electrolytes) [178] . Lymphopenia and neutrophilia, expressed as elevated NLR (neutrophil/lymphocyte ratio) on admission are consistently associated with disease progression and death [179, 180] . A metanalysis of 5699 patients showed that an elevated NLR on admission increased the risk of death almost threefold (RR2. 74 [0.98-7.66 ] [181] . Leukocytosis, elevated LDH, procalcitonin, and transaminitis were associated with increased risk of ICU admission and death [32], while lymphopenia, elevated CRP and fibrinogen on admission predicted an O 2 requirement [182] . Another metanalysis including 4969 patients found that neutrophilia and lymphopenia on admission was associated with a significantly increased risk of progression to severe COVID-19 (OR 7.99; 1.77-36.14 resp. OR 4.2; 3.46-5.09,) and death (OR 7.87; 1.75-35.4, resp. OR 3.71; 1.63-8.44) [183] .

Biomarkers that may be helpful to assess risk for disease progression at this stage reflect activation of innate immunity, immune cell recruitment, and beginning damage to epithelial and endothelial barriers and tissue injury.

Blood samples of COVID-19 patients show significantly higher levels of circulating endothelial cells (CECs) on admission than those with other respiratory infections, demonstrating early and extensive endothelial injury [184] . Epithelial and endothelial damage begins long before a patient is admitted to the ICU, and CECs, if available, may be of prognostic value now [185] . Other markers of endothelial activation with discriminatory value at this stage are von Willebrand Factor (vWF), angiopoietin (Angpt-1/Angpt-2 ratio, see below) and soluble urokinase plasminogen activator receptor (suPAR). Early discharge and mild disease trajectory have been predicted by a suPAR of ≤2ng/mL with high specificity [186] .

Of all cytokines measured in over 1400 COVID-19 patients at hospitalization [187] , IL-6 and TNFα levels independently predicted disease severity and death, outperforming CRP, D-Dimers and ferritin. Higher CRP, IL-6, IL-8, IL-10, TNFα and IL-2R levels on admission were found in those patients later progressing to critical illness and/or death [188] . Hospitalization and progression to severe disease could also be predicted by a decision algorithm integrating demographic risk factors and comorbidities with immune cell profiling [189] . At this stage, replicating virus may rarely be present in blood [190, 191] . Viremia and RNAemia in COVID-19 increase the risk of critical disease and death six-to elevenfold [192] [193] [194] .

Considering more widely available markers, the combination of elevated LDH, CRP and decreased lymphocyte counts predicted ten-day mortality [195] . The combined analysis of the patient's age, CD4 + lymphocyte counts and LDH was a clinically useful composite for disease progression (AUC 0.92) [196] . In summary, markers of inflammation (CRP, ferritin), cardiac (troponin, BNP), epithelial (Angpt-2) and endothelial injury (CECs), combined with pre-existing clinical risk factors, may provide the best assessment for disease progression. Angpt-2 and CECs may also be helpful biomarkers in patients at risk for disease progression before an O 2 requirement develops but may not be widely available.

The Lung Injury Prediction Score (LIPS) assessed the risk of ARDS at time of hospitalization in a variety of conditions [197] [198] [199] [200] [201] . Even though not validated for COVID-19 ARDS, its positive predictive value for this indication was enhanced significantly when Angiopoietin 2 (Angpt-2), CRP, and the FiO2/SpO2 ratio within 6h of admission were included.

Multiorgan involvement, including coagulopathy, myocardial, liver, intestinal and kidney injury, may all precede respiratory manifestations [202, 203] . Myocardial injury on admission in particular predicts poor outcome, especially if both troponin and proBNP are elevated. Higher troponin levels on admission are accompanied by higher D-Dimers, fibrinogen, creatinine, WBC, and procalcitonin levels, reflecting organ involvement beyond the respiratory and cardiac systems. In a metanalysis published by Figliozzi et al., evidence of acute cardiac injury was by far most predictive for poor outcome (OR 10 [5-22.4]), followed by renal injury and low platelet and lymphocyte count [204] . Metadata from 10 clinical studies generated two predictive equations including CRP, neutrophil, lymphocyte count +/-D dimer, resulting in a sensitivity of 0.76 (0.68) and specificity of 0.79 (0.83) when applied to a cohort of patients [205] .

Future works must emphasize parameters that predict deterioration at a time point when therapeutic interventions can counteract disease progression. Based on a recent UK study on COVID-19 patients presenting to the emergency department, strict implementation of simple clinical observations while considering demographic risk factors outperforms the prognostic value of laboratory biomarkers [206] .

J o u r n a l P r e -p r o o f Finally, a recent study reports that Anti-DNA and anti-phosphatidylserine antibodies, determined at hospital admission, correlated strongly with progression to severe disease (PPV 85.7% and 92.8%). Antiphospholipid antibodies have been observed in COVID-19 patients since the very beginning of the pandemic [207] . This suggests that autoantibodies following the initial viral insult contribute to the pathology at later stages of COVID-19.

Based on published evidence about this disease stage, therapeutic recommendations include:

1. Antiviral therapy. The WHO no longer recommends antivirals for hospitalized patients. NIH guidelines however suggest that RDV may be used in hospitalized patients at high risk of disease progression with or without oxygen requirement (WHO stage 3, 4).

RECOVERY assessed dexamethasone in hospitalized patients of varying severity. There was no benefit seen in patients who did not require ventilatory support (OR 1.19; 0.91-1.55) [208] or in those with early disease (symptom duration <7days) [208] . Concerns for early steroid use would include immunosuppression at a time when viral replication may still be very active [209, 210] . In a metanalysis of five RCTs including 7692 patients, steroid use in patients without O 2 requirement was even associated with an increased mortality risk (RR 1.23 [1.00-1.62]; p=0.05) [211] . In summary, there is presently no evidence to support the use of steroids at WHO stage 3.

Interferons (IFN), produced by lymphocytes (Type II: IFN-) and epithelia (Type III: IFN-) are some of the most effective antiviral defense mechanisms. Type I IFNs (IFN , IFN ) initiate an antiviral response through their receptors INFAR1/2, widely expressed on epithelial, endothelial and myeloid cells. INFAR engagement activates Janus Kinase (JAK1), which mediates inflammation and antiviral effects [212] . While the use of a pro-inflammatory signaling molecules seems counterintuitive initially, the timing of IFN-I administration in relation to viral replication is critical. The replication of SARS-CoV-2 is reported to peak already at symptom onset. A rapid IFN-1 response controls viral replication, whereas a delayed IFN-1 rise results in excessive inflammation and tissue damage instead [82, [213] [214] [215] . In critically ill COVID-19 patients, IFN-1 and responses are impaired, virus persistence is prolonged and systemic inflammatory markers are comparatively high [216, 217] . SARS-CoV-2 produces only a weak early IFN-1 response in vitro [217] . A suppressed early IFN-1 response may allow viral replication to peak unopposed and contributes to the excessive inflammation seen in patients with severe disease [213, 214] . It follows that exogenous IFN-1 should be beneficial early, while delayed administration could easily be harmful [218] . Results of important IFN trials are summarized in Table 3 . The Solidarity trial assessed IFN-β1a therapy at WHO stages 3-6. It failed to demonstrate a survival benefit overall and suggested worse outcomes among ventilated patients. Three trials in hospitalized patients (WHO stages 3-5) treated with either IFN-β1b s.c. for two weeks or nebulized IFN-β1a resp. IFN-α2b within five days of admission suggested accelerated clinical improvement, reduced ICU admissions and lower mortality [219] . Treatment more than five days after admission however increased mortality (aHR 0.05 [0.01-0.37] early treatment, 6.8 [1.41-40.8] p=0.2 late treatment) [220] . In a phase II placebo-controlled study of nebulized IFN-β1a [221] in hospitalized patients, at WHO stages 3 and 4, IFN treatment still reduced the risk of severe disease or death significantly even though median symptom duration was ten days (OR 0·21 [0·04-0·97]; p=0·046). IFN-I may therefore retain a benefit for longer than suggested, at least in the noncritically ill [222] .

The International Society for Thrombosis and Hemostasis (ISTH) recommends low molecular weight heparin prophylaxis for all hospitalized patients with COVID-19 and supports its continuation for 2-6 weeks following discharge [223, 224] . The benefit of heparinization leading to improved organ support free survival in noncritically ill hospitalized patients has now been backed up by results from ATTACC/ACTIV-4a/REMAP-CAP and CORIST studies (see below). In the noncritically ill hospitalized group, therapeutic anticoagulation may be superior to prophylactic dosing, but more data is required [225, 226] .

Monoclonal antibodies failed to demonstrate a benefit in hospitalized patients [227, 228] , and are no longer recommended regardless of oxygen requirement, except in patients with humoral immunodeficiency [229].

The reported rate of patients progressing to stage 4 varies widely, but a large proportion of those admitted will require oxygen supplementation. Mortality in this group can be significant, even in those not dyspneic at presentation [230] . In a subset of patients, the controlled antiviral response transitions to a dysregulated immune response during this WHO stage, possibly even earlier. The clinical presentation is now characterized by ongoing respiratory epithelial and endothelial damage, followed by excessive recruitment of activated innate and adaptive immune cells. The most relevant immunopathologic processes, which in our opinion characterize stage 4 and overlap in many aspects with stages 3 and 5, are outlined below.

a. Disrupted AT2/ACE2 homeostasis The downregulation of ACE-2 in cells infected by SARS-CoV2 leads to elevated AT2 levels, vasomotor disturbance, increased ventilation-perfusion (V/Q) mismatch (ventilation of non-perfused lung areas), microcapillary leaks, and epithelial apoptosis [143] [144] [145] . AT2's pro-inflammatory effects via NFkB [141] enhance leukocyte-endothelial interactions through upregulation of ICAM-1 and VCAM-1, setting the stage for NETosis and thrombotic complication (see below) [231, 232] .

Monocytes and macrophages are key elements of the early antiviral response, dominate the developing dysregulated inflammatory process, and are the drivers for cytokine excess, neutrophil and lymphocyte recruitment, development of barrier dysfunction and tissue fibrosis [233, 234] . Depending on their environment, macrophages exist on a spectrum from pro-inflammatory M1, responsible for pathogen killing, production of reactive oxygen species (ROS) and proinflammatory cytokines (IL1b, TNFα, IL6, IL18) [235] , to M2 cells with a focus on phagocytic activity, promoting immune tolerance, fibrosis and tissue repair [236] [237] [238] . Non-inflammatory removal of apoptotic immune cells, efferocytosis, is a unique feature of M2 macrophages [239] . Activated alveolar macrophages (AM) [138, 140] recruit bone-marrow derived monocytes to the lung [240, 241] , where they adopt an M1 phenotype, complementing the antiviral response but also amplifying tissue damage [242] and initiate massive neutrophil recruitment and activation of Th1 and Th17 cells [243] . Histopathology of autopsied lungs of patients with COVID-19 ARDS implies a crucial role for macrophage activation and the subsequent neutrophil migration [244, 245] . The persistence and prolonged activation of M1 macrophages result in an excess of pro-inflammatory mediators, reactive oxygen species, enzymes and accumulating cellular debris all of which is detrimental to epi/and endothelial integrity [235, [246] [247] [248] . Once the inflammatory stimulus is removed, M1 must revert to M2 macrophages to begin a -clean up and repair program‖ and deactivate the previous -proinflammatory program‖. Otherwise, the inflammatory process will persist [249, 250] . One of the factors inhibiting the repolarization to M2 is netosis, thereby exacerbating tissue damage [251] .

c. Activation of the VEGF-Angpt-1/2-Tie2 system High Angpt-2 levels predict ICU admission at the time of hospitalization [252] . Patients with Angpt-2 levels above 5000pg/mL were 10 times more likely to require ICU care (OR 9.33 [2.35-44.9]). Angpt-2 was the only blood parameter correlating with compliance measures during MV (mL/cmH 2 O, r = − 0.46, p = 0.01) and renal function, emphasizing the prognostic relevance of biomarkers of endothelial activation and microvascular damage during this stage. Pulmonary neutrophil recruitment may be associated with further significant clinical deterioration and escalation of respiratory support [244] . Therefore, a high NLR as well as markers of epithelial and endothelial damage (low VEGF2R levels and low Angpt-1/2 ratio (see below) is expected to have prognostic value at this stage [202, [253] [254] [255] [256] .

1. Antiviral therapy: see recommendations as detailed under prior WHO stages 2. Steroids: GCs have many anti-inflammatory properties, including the repolarization of macrophages towards M2 and inhibition of neutrophil recruitment [257, 258] . The RECOVERY trial yielded landmark data on the role of GCs in COVID-19, and its results emphasize the importance of timing of therapeutic interventions. It studied hospitalized patients at WHO stages 3, 4 and 5ff treated with dexamethasone (6mg OD i. [211] . In summary, data is consistent showing that steroids are beneficial at later disease stages, in patients requiring oxygen or MV (see below). [267] .

In summary, Tocilizumab is recommended in combination with steroids for recently hospitalized patients at WHO stage 4-5, with rapid disease progression or who require MV for less than 24 hours [268].

A double-blinded RCT including 457 and 1365 patients randomized and treated in phases 2 and 3, respectively, assessed the use of sarilumab. Among the 20% of phase 3 patients receiving MV, a third of whom also received steroids, the proportion with ≥1-point improvement in clinical status at day 22 was 43.2% for sarilumab and 35.5% for placebo (RRR 21.7%). In analyses combining phase 2 and 3 patients requiring MV, the mortality risk was reduced, though non-significantly (HR 0.76; [0.51 to 1.13]). Again patients receiving GCs concomitantly showed more pronounce risk reduction (OR 0.49 [0.25 to 0.94]).

IL-1-inhibitors in the form of the endogenous receptor antagonist IL-1ra (anakinra) or as monoclonal antibody against IL-1 (canakinumab) showed promise in cohort and observational studies [269] [270] [271] [272] [273] [274] that triggered further investigations. Evidence remains controversial, but the timing of administration yet again seems crucial. A randomized trial [275] compared the addition of anakinra to SOC in patients at WHO stage 4ff. No difference was seen between the groups in mortality by 28 days (22% vs 24%, aHR 0.77 [0.33-1.77]), oxygen wean, or time to discharge. When patients requiring oxygen were randomized to receiving anakinra within ≤4days from admission, early treatment reduced 28-day mortality by 74% (aHR 0.26 [0.1-0.66], p<0.001) compared to SOC. No survival benefit was seen in patients not in the early treatment group who may have received anakinra as late rescue therapy (aHR 0.82, p=0.7). These results allow some attribution of benefit to use at earlier disease stages [276] and illustrate how critical the clinical status at the time of treatment allocation is. A recent metanalysis of IL-1 inhibition in COVID-19 could not proceed due to the data heterogeneity between studies [277] . A suPAR level of >6ng/mL heralds the development of respiratory failure in COVID-19 [278] and may assist biomarker-guided IL-1 inhibition [279] .

Two recent studies failed to demonstrate a benefit of IL-1 inhibition with canakinumab compared to SOC. Patients were included at WHO stages 4 and 5, and neither MV free survival nor risk of COVID-19 related death differed significantly [280] . Additional reasons for the lack of canakinumab benefit in COVID-19 are likely based on the pharmacokinetic profile of this drug and its selective inhibition of IL-1 , leaving IL-1 unopposed [281] . At present, pending further data collection, IL-1 inhibition is not recommended as SOC in COVID-19 management.

Many immune reactions responsible for the inflammatory response in COVID-19 (including IFN-1a,b) are transcriptionally regulated by the JAK-STAT pathway [282, 283] . A metanalysis [284] of five studies investigating JAK inhibition in COVID-19 demonstrated a significant reduction in mortality (HR 0.12 [0.03-0.39]), and ICU admission (OR 0.05 [0.01-0.26]). Table 5 .

In two early studies in hospitalized patients, most of whom with an O 2 requirement but not requiring MV, treatment with Baricitinib, an oral JAK1/JAK2 inhibitor, for seven days on LPV/r +/-HCQ background, demonstrated a faster reduction in O 2 requirement and a lower mortality rate (1/20 (5%) vs 25/56 (45%) compared to SOC [285] . A follow-up study mainly included patients at WHO stages 3/4 [286] . Here, the need for intensive level care at 14 days was significantly reduced in the treatment group, and patients were more likely to be discharged by two weeks (77.8% vs 12.8%, p<0.0001).

TACTIC-R [289] is assessing the combination of baricitinib with ravulizumab (a C5 inhibitor) in WHO stages 3-5. Although treatment with ruxolitinib, an oral JAK1/2 inhibitor, was shown to be safe, it did not reduce mortality or progression to MV in patients at WHO stages 4 and 5 [290].

In a recent study assessing tofacitinib in the treatment of hospitalized patients at WHO stages 3, 4 and 5 (including high flow O2 only) [291] , the cumulative incidence of death or respiratory failure through day 28 was reduced by 37% (RR 0.63; [0.41 to 0.97] p=0.04). All-cause mortality was observed in 2.8% of tofacitinib and 5.5% of placebo-treated patients, but the effect was not significant (HR 0.49; 95% CI, 0.15 to 1.63). Serious adverse events were not significantly more common in the treatment group (14.1% vs 12.0%). Potential safety concerns for JAKi include a rise in creatinine kinase, transaminases, and myelosuppression, which may increase the risk of opportunistic infections. The complete blood count should be monitored during treatment.

Data on the use of TNFi in COVID-19 is limited. In a small study including seven patients, three of which were already mechanically ventilated, Infliximab at a dose of 5mg/kg iv on days one and three [292] , resulted in a rapid decrease of pro-inflammatory cytokines and a clinical improvement in six of seven patients. In comparison, the mortality rate in the 17 control patients at a similar stage of hospitalization was 35%. The ACTIV trial (NCT04593940) recruits hospitalized patients with moderate to severe COVID-19 (WHO stage 4ff) and will, in addition to infliximab, assess abatacept and cenicriviroc, an inhibitor of chemokine receptors CCR2 and CCR5, for this indication.

GM-CSF, among other functions as overall pro-inflammatory cytokine and growth factor, polarizes macrophages towards M1 and upregulates integrin expression by neutrophils, mediating their adhesion to and migration across endothelium. Higher serum levels of GM-CSF in ARDS correlate with a higher risk of death [293] . Antagonizing GM-CSF, therefore, appears to be an attractive target in COVID-19 [213] . The best time for GM-CSF inhibition, based on immunopathology, would be prior to the recruitment of peripheral monocytes. GM-CSF inhibition has an established safety record [294] , but neutropenia, alveolar proteinosis, and impaired viral clearance remain concerns. In addition, lack of GM-CSF inhibits phagocytosis, efferocytosis by M2 macrophages and impairs the removal of NETs which may delay macrophage repolarization. Conversely, GM-CSF is critical for AM survival, surfactant removal, epithelial protection and the antiviral response. Higher GM-CSF levels in ARDS bronchoalveolar lavage fluid are associated with better outcomes [295] [296] [297] , contrasting the association of higher serum levels with a worse prognosis [298, 299] . Despite initial concerns for excessive granulocyte mobilization and recruitment of neutrophils to the lung [295] , first data assessing inhaled GM-CSF (sargramostim 125mcg, BD, for 5 days) in hypoxemic patients are encouraging [300] .

Addition of sargramostim for five days to SOC in patients at WHO stages 4 and 5 was associated with a P(A-a)O 2 improvement by ≥ 33% compared to SOC alone (54% vs 26%, p<0.001, NCT04326920). In a second cohort, including patients at WHO stage 4 and those requiring high flow oxygen but not NIV, oxygenation was also improved (treatment group 84%, SOC group 64% p=0.02) [301] .

Amplifying pulmonary neutrophil recruitment might worsen the patient's respiratory status. Under this premise, GM-CSF receptor blockade is also under investigation in COVID-19. Mavrilimumab (i.v. 6mg/kg once) showed some promise in a small prospective cohort study from Italy in patients at WHO stages 4 and 5 [302] . A double-blinded RCT recruited 40 patients in WHO stages 4 and 5 (n=21 receiving mavrilimumab) and found no significant difference in mortality or oxygen wean to placebo. However, mortality was high overall (43% and 53%, respectively) [303] . An ongoing study comparing mavrilimumab to placebo in hospitalized patients at WHO stages 4 and 5 reported in an interim analysis of n=166 that MV-free survival was higher in the treatment arm (86.7% vs 74.4%, p=0.1), equivalent to a 65% risk reduction, with final results outstanding [485] .

Netosis is probably one of the most important yet underrecognized mechanisms in the pathophysiology of COVID -19. The release of Neutrophil Extracellular Traps, or NETosis, is a defense system utilized by neutrophils against bacteria, viruses or protozoa. During the formation of neutrophil extracellular traps (NETs), the neutrophil nuclear membrane is dissolved and NETs consisting of chromatin, citrullinated histones (CitH3), neutrophil elastase (NE) and oxidative enzymes such as myeloperoxidase are released into the extracellular space [304] [305] [306] . Excessive NETosis damages epithelial [307] and endothelial [308] cells. NET removal by two extracellular enzymes, DNase I and DNaseIL3, expressed by dendritic cells and macrophages, is critical for tissue homeostasis [309] . NETs promote M1 persistence in COVID-19 and delay macrophage repolarization, which prevents the degradation of cellular debris by M2, facilitated by C1q [251] . As a result, efferocytosis, a hallmark feature of M2 cells, cannot occur effectively. Pro-inflammatory cytokines continue to be released, which prevents a timely switch to tissue-restorative repair processes [247, 248, 310] . NETs are also highly prothrombotic. They entrap erythrocytes and platelets and can form intravascular NET clots [309, 311] . Autopsies of COVID-19 victims show this, featuring thrombotic occlusion of pulmonary, cardiac, renal, and hepatic vasculature by aggregated NETs [312, 313] . NETosis can be quantified by measuring specific biomarkers (cell-free DNA, myeloperoxidase [MPO]-DNA, and citrullinated histone H3 [Cit-H3]) [314] . These correlate closely with SOFA scores [315, 316] and may be useful for risk stratification at earlier disease stages. Dornase alfa is commonly used in inhaled form for patients with cystic fibrosis where it cleaves extracellular DNA, mainly from leukocytes, thereby decreasing the viscosity of respiratory secretions [317] . Beneficial effects on recovery in small case series in critically ill COVID-19 patients with ARDS have been published, additional trials are underway [318] , [319] , [320, 321] . Other DNAse enzymes for the treatment of hospitalized patients with acute moderate to severe SARS-CoV-2 infection are currently in development.

The ATTACC trial compared therapeutic-dose heparinization as an initial strategy in noncritically ill patients, most at WHO stage 4 with SOC thromboprophylaxis. There was a trend favoring therapeuticdose heparinization (survival to discharge: 76.4% vs 80.2%), exclusive to this earlier disease stage[225], but more data is required. It inhibits glycolytic ATP production and is used to sensitize tumor tissue to chemo-and radiotherapeutic agents. 2-DG administration followed by low dose radiation was suggested as a means to reduce lung inflammation in COVID-19 [323] . The agent accumulates in metabolically active, virus-infected cells and results in their apoptosis. Phase 3 trials recruited patients at WHO stage 4ff, without adding radiation. Early oxygen wean was more frequently possible (42% vs 31%), but more evidence to support this treatment is needed, and detailed data on safety is lacking.

Driven by inflammatory cell recruitment and barrier dysfunction, patients at this stage have progressed to severe pneumonia, and their gas exchange is more severely affected. They require high flow oxygen, and approximately one fifth will require noninvasive pressure support [324] . The three main immunologic mechanisms during this stage include:

1. Disruption of endothelial and epithelial integrity Worsening capillary leakage and alveolar edema now contribute to poor gas exchange [325, 326] . The main determinants of endothelial and epithelial permeability are the VEGF and Ang/Tie2 systems. The primary stimulant of VEGF production by AECs is IL-1 [327] [328] [329] . Under normal physiologic conditions, pulmonary VEGF levels of capillary and alveolar lumens are strictly compartmentalized [330] . During an infection with SARS-CoV-2 this compartmentalization is lost, resulting in worsening epithelial damage [331] and release of alveolar-side VEGF into the bloodstream across the damaged barrier [332] . This promotes endothelial Angpt-2 release [331] , amplifying capillary leakage [333] . Therefore, an increase of VEGF in the alveolus (as detectable in bronchoalveolar lavage fluid) indicates improved barrier function and predicts recovery from ARDS [334] while increasing plasma levels are associated with worsening pulmonary edema [335, 336] . Angpt-1 is the main agonist of the endothelial Tie2 receptor [337, 338] . Their interaction seals endothelial tight junctions and protects against capillary leakage [339] [340] [341] [342] [343] [344] [345] . It opposes Angpt-2 action on Tie2 [342, 346] , which increases capillary permeability [342, 347, 348] and leads to epithelial apoptosis [325, 346, [349] [350] [351] [352] [353] . Increased Angpt-2 and low VEGF2R levels in plasma predict ARDS severity and 28d mortality [336] . In mechanically ventilated patients, serum Angpt-2 correlates with the severity of pulmonary vascular leakage and predicts the likelihood of ICU admission, development of ARDS and resulting fatality in COVID-19 [252, [354] [355] [356] [357] [358] [359] [360] . A low Angpt-1/Angpt-2 ratio is a marker for endothelial dysfunction and a consistent feature of adverse outcomes in sepsis, DIC and ARDS [361] [362] [363] [364] [365] [366] [367] [368] [369] .

Take home messages for this disease stage:

1. Data strongly support the use of GCs at this stage. Careful monitoring for secondary infections in these patients is critical. 2. JAK-inhibitors offer a benefit in terms of preventing progression to MV and survival 3. IL-6 inhibition, in combination with GCs, is recommended at this and later disease stages 4. While results from larger trials with IL-1 inhibitors are lacking, data available from observational cohorts suggests that they may have a benefit on clinical outcome and survival in this but not later disease stages. 5. The administration of GM-CSF antibodies can currently not be recommended while the use of inhaled GM-CSF may be of benefit at this and later stages 6. Enzymatic therapy with DNAse 1 or recombinant DNAse1L3 to counteract Netosis may play an important role in preventing progression of COVID-19 in this disease stage. However, data of clinical trials are still pending.

J o u r n a l P r e -p r o o f

Much of COVID-19-associated inflammatory pulmonary damage is mediated by M1 macrophages and the neutrophils they recruit [55, [370] [371] [372] . Neutrophilia, especially in the BAL fluid, is a consistent feature of severe COVID-19 and predicts mortality [28, 190, 202, 253, 255, [373] [374] [375] . Autopsies of COVID-19 patients have demonstrated the accumulation of neutrophils and M1 macrophages associated with microangiopathic and thrombotic changes in pulmonary capillaries [376] [377] [378] . Especially in patients who require respiratory support, the neutrophil population contains immature, lower density granulocytes (LDGs) [256] . LDGs are ineffective phagocytes [256, 312, [379] [380] [381] [382] , produce large amounts of proinflammatory cytokines (IL17, IFN-I) and have a propensity to form NETs [383, 384] . CXCL5 concentration in BAL fluid correlates with the extent of neutrophil infiltration of lung parenchyma [385, 386] . The damaged alveolar epithelium, in turn, activates the endothelium, which upregulates adhesion molecules [387] [388] [389] , and mechanically entraps primed neutrophils [390] [391] [392] . This close interaction with the activated endothelium activates the neutrophils, which causes them to release inflammatory mediators, form NETs [312, 390] and enter the alveolus [371] .

In summary, neutrophils home to the COVID-19 lung, interact with the damaged endothelium and contribute to tissue damage. Because of NETosis-induced impairment of macrophage repolarization, efferocytosis is defective. Accumulating NETs may not be adequately removed and sustain inflammation and neutrophil recruitment, further exacerbating inflammatory tissue injury.

Thromboembolism complicates up to a third of COVID-19 admissions to ICU [393] [394] [395] [396] [397] . Generalized endothelial damage and thrombotic microvascular injury of lungs, kidneys, liver and heart and frequent pulmonary embolism [396] and stroke [398] , characterize severe disease.

Evidence for endothelial dysfunction is present as early as WHO stage 3. Levels of FVIII, vWF:Ag, D-Dimers at the time of hospitalization correlate with risk of thromboembolic complications and mortality in COVID-19 patients [182, 399, 400] . Not all markers of endothelial damage have equal prognostic value, and more data are required in this area. Thrombomodulin, selectin, Angpt-2 and CEC levels were all significantly elevated in patients with more severe COVID-19, but in a comparative analysis, only vWF antigen discriminated disease severity of outpatients, non-critical (WHO stage 3,4,5) and critical (WHO stages 5,6,7) COVID-19 [401, 402] . Other selected markers of endothelial damage may predict inpatient mortality (glycocalyx damage (AUC 0.74), ADAMSTS13 (AUC 0.75) and VEGFA (AUC 0.73)), but will not be readily accessible to most clinicians [403] .

The complement system has antiviral properties [404] but can also result in tissue injury through activation of Netosis and pro-coagulant effects. The pivotal role of complement activation in COVID-19 was identified early [405] . Histopathology of skin, kidney and lung biopsies from COVID-19 patients (n=5) showed extensive deposition of C5b-9 in the microvasculature [406] . Complement pathways are highly induced in the COVID-19 lung, which correlate with disease severity [407] [408] [409] .

1. Antiviral therapy: remains indicated as discussed above 2. Steroids: remains indicated as discussed above 3. Heparin: remains indicated as discussed above 4. Cytokine inhibitors: As discussed above, IL-6 inhibition can be expected to be of benefit. The data for IL-1 inhibition is less clear but on balance would favor earlier use (WHO stage 4) J o u r n a l P r e -p r o o f

Based on the ACTT-2 and COV-barrier results, JAK inhibition has most impact at this stage. ACTT-2, a double-blinded, placebo-controlled RCT enrolled over 1,000 inpatients at WHO stage 4ff to assess efficacy and safety of baricitinib 4mg OD for 14 

Vanucizumab, a bispecific monoclonal antibody directed against Angpt-2 and VEGF, usually used as an angiogenesis inhibitor in solid tumors [410] , is currently undergoing trials in COVID-19.

Similarly, inhibition of VEGF as the main factor stimulating Angpt-2 release may be of value, especially as it enters the circulation in severe lung injury. Bevacizumab, a monoclonal VEGF-A antibody, has now been repurposed for use in COVID 19 (NCT04275414; NCT04305106) in patients meeting ARDS criteria. In a study of 26 patients, treatment with i.v. bevacizumab resulted in improved PaO2/FiO2 within 24h and rapid normalization of inflammatory markers [411] . However, the clinical status of the cohort was very diverse, complicating the interpretation of these findings. A case series in COVID-19 patients requiring ICU level care [412] included n=25 receiving bevacizumab, and n=21 receiving a combination of TCZ/ bevacizumab. 23/25 (93%) of bevacizumab treated individuals recovered to discharge, as did 14/21 patients receiving a combination treatment. Dosing and WHO stages of the patients were not reported, and more research is required before an assessment of its benefit can be made.

Vasculotide, a Tie2 mimetic improved survival in animal models of viral pneumonia and ARDS and reduced pulmonary edema and endothelial apoptosis [413] [414] [415] . Clinical trials investigating AV-001/Vasculotide and similar products in human ARDS and COVID-19 are planned . . The addition of simvastatin to SOC in patients with ARDS due to a variety of pathologies showed that only those with a hyperinflammatory phenotype, defined by IL-6 and sTNFr1 levels, benefited from statins. In this subgroup, the improvement achieved in 28 day mortality and ventilator-resp. organ support-free survival was significant [424] . While this does not address whether or not adding statins acutely would be of benefit, these findings may be relevant to future research on COVID-19 related ARDS.

Imatinib is a Bcr-Abl tyrosine kinase inhibitor and approved chemotherapeutic agent for Philadelphia chromosome positive CML and ALL. Experimental and early clinical evidence suggests that imatinib protects the integrity of the vascular barrier [425, 426] . It has been studied in severe COVID-19 with the rational of mitigating damage to the barrier of the alveolo-capillary unit. In a double-blinded placebocontrolled RCT [427] , 400 patients at WHO stages 4ff were assigned to either placebo or imatinib at a loading dose of 800mg followed by 400mg OD for nine days. Three-quarters of participants received concomitant GCs, a fifth RDV; no other immunomodulatory agents were used. Time to discontinuation of MV or oxygen wean did not differ, while time spent on MV was shorter (survivors 7 vs 12 days, p=0.02) and 28-day survival improved (mortality risk aHR 0·52 [0·26-1·05]; p=0·068).

At this stage, patients progress from requiring high flow oxygen to intubation and MV. The clinical deterioration at this stage is a direct consequence of the inflammatory and immunologic mechanisms initiated at stages 3 and 4 that are now leading to respiratory failure. In over 10,000 hospitalized COVID-19 patients from Germany, mortality was 53% among those who progressed to MV, compared to 16% who did not [324, 428] . Autopsy results in mechanically ventilated patients who had rapidly progressed to severe respiratory failure demonstrated neutrophilic invasion of the alveolar spaces and microvasculature, epithelial injury and microthrombi, likely related to excessive neutrophil recruitment to the lung [244] .

Take home messages for this disease stage: 1. Risk stratification based on clinical findings and biomarkers is critical 2. Currently available data strongly support the use of GCs in patients at this disease stage. 3. Heparin: remains indicated as discussed above 4. JAK inhibitors remain indicated as discussed above 5. Although data remain limited, monoclonal antibody directed against Angpt-2 and VEGF may play an a role in preventing the progression to MV in this disease stage 6. IL-6 inhibitors are recommended under certain conditions at this stage 7. Data is not sufficient to recommend the use of complement inhibitors or imatinib at this disease stage, but new data on a potential role for these agents is emerging 

Prolonged immunosuppression in the critically ill must be navigated with caution. Secondary bacterial and fungal superinfections frequently complicate severe COVID-19, and patients must be closely monitored. Increasingly, COVID-19 associated invasive mycoses are being recognized, due to profound lymphopenia, prolonged significant illness, and immunosuppressive therapies [429] .

There is a high incidence of isolated pulmonary artery thrombi in critically ill COVID-19 patients suggesting the possibility that some thrombotic events in these patients are formed in situ rather than representing dislodged emboli [430] . While thromboembolism is very common in COVID-19, heparinization does not completely abolish this risk [431] [432] [433] , and thromboembolic events despite prophylactic, and even therapeutic heparinization occur.

Biomarkers of NETosis such as cell-free DNA are significantly elevated in patients at WHO stage 5. Many factors contribute to the prothrombotic state in severe COVID-19, with NET formation and antiphospholipid antibodies emerging as important contributors [312] . Lastly, heparin resistance is not uncommon in severe COVID-19 [434] , and alternative strategies for anticoagulation may have to be pursued, such as direct thrombin inhibition with argatroban [435] . There was early recognition that anticoagulation should be administered in COVID-19 patients, but heparin dosing has been controversial [436, 437] ( Table 6 ). The International Society on Thrombosis and Haemostasis (ISTH) suggests risk stratification with dose escalation to intermediate (50% increase of prophylactic dose) for those with a BMI ≥30 or very high D-Dimers (≥3000) and discourages the use of therapeutic doses for primary prevention [223] . The ATTACC/ACTIV-4a/REMAP-CAP trial[438], where therapeutic anticoagulation was inferior to usual care thromboprophylaxis in the outcome of organ-support free survival, with a higher incidence of major bleeding complications, lends support to this approach. This sets critically ill COVID-19 patients apart from those with moderate illness (WHO stages 3,4,5) in whom therapeutic heparinization was not inferior (see above).

ASA has a favorable anti-inflammatory effect on the neutrophil-platelet-endothelial interaction which results in microthrombi, VQ mismatch and NETosis. The data on treatment with ASA in non-COVID-19 ARDS in at-risk individuals is controversial [439, 440] . One study even showed an association with an increased risk of MI, VTE and stroke [440] .

In addition to the use of IL-6 inhibitors as discussed under WHO stage 4, siltuximab (in one to two doses) was used in a small cohort study including 30 patients on either NIV support or MV matched to patients receiving SOC [441] . The majority received concomitant GCs (18/30). The 30-day mortality rate was significantly lower in the treatment group (HR 0·46, 95% CI 0·22-0·97); p=0·04). Though not all patients had completed the follow-up period, 16/30 were discharged, four remained on mechanical ventilation, and ten patients died. This contrasts the findings of the much larger Recovery trial on TCZ, and evidence on siltuximab will have to be revisited as more information becomes available.

In a cohort study comparing TCZ, Sarilumab and anakinra in patients at stages 5 and 6, IL-1 and IL-6 inhibition improved long-term (180 days) survival when initiated before the establishment of severe ARDS (PaO2/FiO2 < 100 mmHg). Notably, in this cohort that did not co-medicate patients with GCs, all three agents offered a survival benefit in patients requiring MV (180- 

Stages 6 and 7 are pathophysiologically similar and characterized by gradual deterioration of widespread endothelial damage [443] . Approximately 33% of hospitalized patients may progress to COVID-19 associated ARDS [444] . Acute respiratory distress syndrome (ARDS) is the result of dysregulated inflammation in response to a pulmonary or systemic insult that impacts the endothelial and epithelial integrity of the alveolocapillary unit [445] . Clinical data suggest ARDS endotypes with distinct clinical features and disparate outcomes [445, 446] . The clinical course of ARDS is described as occurring in two stages [361, 447] :

a. an inflammatory exudative phase characterized by alveolar-epithelial damage, recruitment of inflammatory cells with subsequent alveolar flooding with proteinaceous fluid, formation of hyaline membranes, and resultant hypoxemic respiratory failure (week 1-2) b. a fibroproliferative phase characterized by lung fibrosis and vascular remodeling (week 2-3ff) The Berlin ARDS criteria define an international diagnostic standard [447, 448] .

COVID-19 associated ARDS, as evidenced by autopsy studies, is consistently characterized by  extensively affected microcirculation, alveoli infiltrated with neutrophils and/or monocytes/macrophages  peripheral neutrophilia and decrease of most lymphocyte subsets (i.e., a high NLR), correlating with poor outcome, higher sequential organ failure assessment (SOFA) scores and death [28, 190, 202, 253, 255, 373, 374] .  a highly inflammatory pulmonary response, often in combination with ongoing viral RNA presence  extensive diffuse alveolar damage  widespread endothelial damage and thromboembolic events

The pandemic has put a spotlight on the fact that despite therapeutic advances, the overall mortality of ARDS remains unacceptably high [36] . Therefore, the most critical strategy in COVID-19 management is addressing the evolving inflammation-mediated tissue damage early. Ventilatory strategies, fluid balance and positioning are the most important points and foundations of ARDS management once it occurs but are well beyond the scope of this review. Pharmacologically, in addition to steroid administration, the therapeutic focus shifts to addressing the epithelial and endothelial barrier dysfunctionespecially if the Angpt2/1 ratio or circulating VEGFR2 levels remain elevated. The patient's prognosis may be reflected in Take home messages for this disease stage:

1. The use of GCs in patients with COVID-19 has been found to be most beneficial for patients in this disease stage. Careful monitoring for secondary infections in these patients is critical 2. Starting antiviral therapy in this disease stage is no longer recommended 3. Heparin at prophylactic dose remains indicated. A proposed risk stratification guiding heparin dosing is discussed above. The additional use of ASA and NSAIDs cannot be recommended 4. The use of IL-6 inhibitors may be beneficial 5. Drugs targeting Netosis might be critical in this disease stage but data from clinical trials are still pending. 6. Despite limited data the use of complement inhibitors for this stage cannot be recommended J o u r n a l P r e -p r o o f NLR, coagulation parameters, D-Dimers, von Willebrand factors, Troponin, BNP, renal and liver function, CECs (circulating endothelial cells), and NETosis markers such as cell free DNA (see above).

Treatment recommendations in this disease stage are essentially identical to those for WHO stage 6. 1. Steroids are of benefit in COVID-19 patients who are mechanically ventilated 2. Antibiotic and Antifungal treatment: Prolonged immunosuppression in the critically ill will have to be navigated with caution. Secondary bacterial and fungal superinfections frequently complicate severe COVID-19. Patients must be closely monitored for secondary infections. Increasingly, COVID-19 associated aspergillosis (CAPA) is being recognized, resulting from profound lymphopenia, and as a complication of immunosuppressive therapies [449] .

The use of MSC in severe ARDS is experimental and only included here for completeness and to introduce this novel treatment concept. It is a common misperception that MSCs in ARDS replace damaged alveolar cells. In fact, the proposed clinical benefit is ascribed to their immunomodulatory properties, skewing macrophages to M2, and exerting an antifibrotic effect. Available data is minimal. The COVID-19 Treatment Guidelines Panel of the NIH recommends against the use of mesenchymal stem cells for the treatment of COVID-19 outside of clinical trials.

Therapeutic options for patients with COVID-19 are rapidly evolving, and knowledge gained from currently ongoing clinical trials may change future treatment recommendations. We believe that sound treatment decisions are based on a thorough understanding of the immunopathology of COVID-19. This understanding will enable clinicians to develop a well-defined treatment strategy based on clinical risk scores, immune cell profiling, disease-stage specific biomarkers, laboratory and imaging findings. We recognize that during disease progression, pathological processes overlap, influence each other, and new ones may emerge. Especially at earlier disease stages, treatment target the prevention of a dysregulated hyperinflammatory state. We believe this occurs at the latest at WHO stage 4 in predisposed individuals. Once patients require mechanical ventilation, treatment becomes increasingly challenging with fewer effective treatment options and a higher risk of adverse outcomes. Consequently, a disease-stage specific treatment selection should not be made empirically but follow published evidence from the literature as summarized above. [461] Progression to severe disease Dyspnea 3.7 Progression to ITU Dyspnea 6.5 Li [188] hsTrop, CK, LDH See text Caricchio [178] Six criteria predicting cytokine storm, see text Predicted cytokine storm/ use of cytokine blockade 

A Novel Coronavirus from Patients with Pneumonia in China

World Health Organization. WHO Coronavirus (COVID-19) Dashboard

Data on SARS-CoV-2 variants in the EU/EEA 2021 [updated 09

Centers for Disease Prevention and Control. COVID Data Tracker

Receptor Recognition by the Novel Coronavirus from Wuhan: an Analysis Based on Decade-Long Structural Studies of SARS Coronavirus

Focus on Receptors for Coronaviruses with Special Reference to Angiotensin-Converting Enzyme 2 as a Potential Drug Target -A Perspective

SARS-CoV-2 Reverse Genetics Reveals a Variable Infection Gradient in the Respiratory Tract

Single-Cell RNA Expression Profiling of ACE2, the Receptor of SARS-CoV-2

The digestive system is a potential route of 2019-nCov infection: a bioinformatics analysis based on single-cell transcriptomes

Tissue distribution of ACE2 protein, the functional receptor for SARS coronavirus. A first step in understanding SARS pathogenesis

Recombinant ACE2 Expression Is Required for SARS-CoV-2 To Infect Primary Human Endothelial Cells and Induce Inflammatory and Procoagulative Responses

Inhibition of SARS-CoV-2 Infections in Engineered Human Tissues Using Clinical-Grade Soluble Human ACE2

Clinical Characteristics of Coronavirus Disease 2019 in China

Early Transmission Dynamics in Wuhan, China, of Novel Coronavirus-Infected Pneumonia

The Incubation Period of Coronavirus Disease

From Publicly Reported Confirmed Cases: Estimation and Application

Repeat COVID-19 Molecular Testing: Correlation with Recovery of Infectious Virus

Duration of infectiousness and correlation with RT-PCR cycle threshold values in cases of COVID-19

Viral cultures for COVID-19 infectivity assessment: Systematic review

Virological assessment of hospitalized patients with COVID-2019

COVID-19 and the liver

Effects of COVID-19 on the Nervous System

Prevalence and impact of acute renal impairment on COVID-19: a systematic review and meta-analysis

COVID-19 and Venous Thromboembolism: A Meta-analysis of Literature Studies

COVID-19 pneumonia: relationship between inflammation assessed by whole-body FDG PET/CT and short-term clinical outcome

WHO Working Group on the Clinical Characterization and Management of COVID-19 infection. A minimal common outcome measure set for COVID-19 clinical research

Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis

World Health Organization. COVID-19 vaccine tracker and landscape 2021

Safety and immunogenicity of a mRNA rabies vaccine in healthy adults: an open-label, non-randomised, prospective, first-in-human phase 1 clinical trial

Zika virus protection by a single low-dose nucleosidemodified mRNA vaccination

A lipid-encapsulated mRNA encoding a potently neutralizing human monoclonal antibody protects against chikungunya infection

Broad and strong memory CD4(+) and CD8(+) T cells induced by SARS-CoV-2 in UK convalescent individuals following COVID-19

mRNA vaccine-elicited antibodies to SARS-CoV-2 and circulating variants

Evidence for antibody as a protective correlate for COVID-19 vaccines

Comparison of two highly-effective mRNA vaccines for COVID-19 during periods of Alpha and Delta variant prevalence 2021

Effects of SARS-CoV-2 variants on vaccine efficacy and response strategies

Impact of the Delta variant on vaccine efficacy and response strategies

Administration FaD. FDA authorizes REGEN-COV monoclonal antibody therapy for postexposure prophylaxis (prevention) for COVID-19 2021

In vitro susceptibility of 10 clinical isolates of SARS coronavirus to selected antiviral compounds

Broad-spectrum antivirals for the emerging Middle East respiratory syndrome coronavirus

The Effect of Recombinant Human Interferon Alpha Nasal Drops to Prevent COVID-19 Pneumonia for Medical Staff in an Epidemic Area‖

Leveraging the antiviral type I interferon system as a first line of defense against SARS-CoV-2 pathogenicity

Signs and symptoms to determine if a patient presenting in primary care or hospital outpatient settings has COVID-19 disease

Potency and timing of antiviral therapy as determinants of duration of SARS-CoV-2 shedding and intensity of inflammatory response

Viral dynamics in mild and severe cases of COVID-19

COVID-19 pulmonary pathology: a multiinstitutional autopsy cohort from Italy and New York City

An orally bioavailable broad-spectrum antiviral inhibits SARS-CoV-2 in human airway epithelial cell cultures and multiple coronaviruses in mice

Remdesivir is a direct-acting antiviral that inhibits RNA-dependent RNA polymerase from severe acute respiratory syndrome coronavirus 2 with high potency

Adenine C-Nucleoside (GS-5734) for the Treatment of Ebola and Emerging Viruses

Controlled Trial of Ebola Virus Disease Therapeutics

Tolerability, and Pharmacokinetics of Remdesivir, An Antiviral for Treatment of COVID-19, in Healthy Subjects

Rethinking Remdesivir: Synthesis of Lipid Prodrugs that Substantially Enhance Anti-Coronavirus Activity

Development of Remdesivir as a Dry Powder for Inhalation by Thin Film Freezing

Remdesivir in adults with severe COVID-19: a randomised, double-blind, placebo-controlled, multicentre trial

Remdesivir for the Treatment of Covid-19 -Final Report

Effect of Remdesivir vs Standard Care on Clinical Status at 11 Days in Patients With Moderate COVID-19: A Randomized Clinical Trial

Remdesivir for 5 or 10 Days in Patients with Severe Covid-19

Repurposed Antiviral Drugs for Covid-19 -Interim WHO Solidarity Trial Results

Therapeutic Management of patients with COVID-19 2020

SARS-CoV-2 infection is effectively treated and prevented by EIDD-2801

Reduction in infectious SARS-CoV-2 in treatment study of COVID-19 with molnupiravir 2021

Molnupiravir, an Oral Antiviral Treatment for COVID-19

Biotherapeutics Provide Update on Progress of Clinical Development Program for Molnupiravir, an Investigational Oral Therapeutic for the Treatment of Mildto-Moderate COVID-19 2021

AVIFAVIR for Treatment of Patients with Moderate COVID-19: Interim Results of a Phase II/III Multicenter Randomized Clinical Trial

Early Treatment Arm Favirpiravir (GETAFIX) for adults with early stage COVID-19: A structured summary of a study protocol for a randomised controlled trial

A pilot clinical trial of recombinant human angiotensinconverting enzyme 2 in acute respiratory distress syndrome

Function, and Antigenicity of the SARS-CoV

Nafamostat Mesylate Blocks Activation of SARS-CoV-2: New Treatment Option for COVID-19

The Anticoagulant Nafamostat Potently Inhibits SARS-CoV-2 S Protein-Mediated Fusion in a Cell Fusion Assay System and Viral Infection In Vitro in a Cell-Type-Dependent Manner

Inhibition of SARS-CoV-2 entry through the ACE2/TMPRSS2 pathway: a promising approach for uncovering early COVID-19 drug therapies

Camostat cuts recovery time in half for mild COVID-19 patients 2021 [updated 30

Efficacy of the TMPRSS2 inhibitor camostat mesilate in patients hospitalized with Covid-19-a double-blind randomized controlled trial

Clinical improvement in a patient with severe coronavirus disease 2019 after administration of hydroxychloroquine and continuous hemodiafiltlation with nafamostat mesylate

Preventing thrombosis in a COVID-19 patient by combinatorial therapy with nafamostat and heparin during extracorporeal membrane oxygenation

Potential of heparin and nafamostat combination therapy for COVID-19

Glecaprevir and Maraviroc are high-affinity inhibitors of SARS-CoV-2 main protease: possible implication in COVID-19 therapy

CCR5 Antagonist Maraviroc Inhibits Acute Exacerbation of Lung Inflammation Triggered by Influenza Virus in Cigarette Smoke-Exposed Mice

REGN-COV2, a Neutralizing Antibody Cocktail, in Outpatients with Covid-19

Vir Biotechnology and GSK announce VIR-7831 reduces hospitalisation and risk of death in early treatment of adults with COVID-19

Nanobodies from camelid mice and llamas neutralize SARS-CoV-2 variants

Potent neutralization of clinical isolates of SARS-CoV-2 D614 and G614 variants by a monomeric, sub-nanomolar affinity nanobody

A Randomized Trial of Hydroxychloroquine as Postexposure Prophylaxis for Covid-19

Hydroxychloroquine as Postexposure Prophylaxis for Covid-19

Hydroxychloroquine in Nonhospitalized Adults With Early COVID-19 : A Randomized Trial

Hydroxychloroquine for treatment of nonsevere COVID-19 patients: Systematic review and meta-analysis of controlled clinical trials

Effect of Hydroxychloroquine in Hospitalized Patients with Covid-19

Hydroxychloroquine with or without Azithromycin in Mild-to-Moderate Covid-19

Update I. A systematic review on the efficacy and safety of chloroquine/hydroxychloroquine for COVID-19

Effect of hydroxychloroquine with or without azithromycin on the mortality of coronavirus disease 2019 (COVID-19) patients: a systematic review and meta-analysis

Mortality outcomes with hydroxychloroquine and chloroquine in COVID-19 from an international collaborative meta-analysis of randomized trials

A systematic review of experimental evidence for antiviral effects of ivermectin and an in-silico analysis of ivermectin's possible mode of action against SARS-CoV-2

Ivermectin for the treatment of COVID-19: A systematic review and meta-analysis of randomized controlled trials

Ivermectin for Prevention and Treatment of COVID-19 Infection: A Systematic Review, Meta-analysis, and Trial Sequential Analysis to Inform Clinical Guidelines

Elevated interleukin-1 release by human alveolar macrophages during the adult respiratory distress syndrome

Alveolar macrophages: plasticity in a tissue-specific context

A critical function for CD200 in lung immune homeostasis and the severity of influenza infection

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

Angiotensin III: a physiological relevant peptide of the renin angiotensin system

Age-and gender-related difference of ACE2 expression in rat lung

The pivotal link between ACE2 deficiency and SARS-CoV-2 infection

Individual variation of the SARS-CoV-2 receptor ACE2 gene expression and regulation

Angiotensin II and the fibroproliferative response to acute lung injury

Angiotensin II and vascular inflammation

Angiotensin-converting enzyme 2 (ACE2) as a SARS-CoV-2 receptor: molecular mechanisms and potential therapeutic target

Angiotensin II subtype AT1 and AT2 receptors regulate microvascular hydraulic permeability via cAMP and cGMP

Angiotensin-converting enzyme in innate and adaptive immunity

Macrophage polarization by angiotensin II-type 1 receptor aggravates renal injury-acceleration of atherosclerosis

Angiotensin III increases MCP-1 and activates NF-kappaB and AP-1 in cultured mesangial and mononuclear cells

Clinical Relevance and Role of Neuronal AT1 Receptors in ADAM17-Mediated ACE2 Shedding in Neurogenic Hypertension

Angiotensin II activates the Smad pathway during epithelial mesenchymal transdifferentiation

Factors associated with COVID-19-related death using OpenSAFELY

Living risk prediction algorithm (QCOVID) for risk of hospital admission and mortality from coronavirus 19 in adults: national derivation and validation cohort study

SARS2 simplified scores to estimate risk of hospitalization and death among patients with COVID-19

CoVA: An Acuity Score for Outpatient Screening that Predicts Coronavirus Disease 2019 Prognosis

Longitudinal COVID-19 profiling associates IL-1RA and IL-10 with disease severity and RANTES with mild disease

Aerosolized nanoliposomal carrier of remdesivir: an effective alternative for COVID-19 treatment in vitro

A multicentre, randomized study to evaluate the safety and efficacy of histamine dihydrochloride and interferon-alpha-2b for the treatment of chronic hepatitis C

Type I and Type III Interferons -Induction, Signaling, Evasion, and Application to Combat COVID-19

Peginterferon lambda for the treatment of outpatients with COVID-19: a phase 2, placebo-controlled randomised trial

Peginterferon Lambda-1a for treatment of outpatients with uncomplicated COVID-19: a randomized placebo-controlled trial

Inhaled corticosteroids downregulate the SARS-CoV-2 receptor ACE2 in COPD through suppression of type I interferon

Inhaled budesonide in the treatment of early COVID-19 (STOIC): a phase 2, open-label, randomised controlled trial

Effects of potent neutralizing antibodies from convalescent plasma in patients hospitalized for severe SARS-CoV-2 infection

Severe Acute Respiratory Syndrome Coronavirus 2

Neutralizing Antibody Titers in Convalescent Plasma and Recipients in New Mexico: An Open Treatment Study in Patients With Coronavirus Disease

Convalescent plasma for hospitalized patients with COVID-19: an open-label, randomized controlled trial

Angiotensin converting enzyme inhibitors and angiotensin II receptor blockers and outcomes in patients with COVID-19: a systematic review and meta-analysis

Azithromycin Polarizes Macrophages to an M2 Phenotype via Inhibition of the STAT1 and NF-kappaB Signaling Pathways

Impact of azithromycin treatment on macrophage gene expression in subjects with cystic fibrosis

Azithromycin in addition to standard of care versus standard of care alone in the treatment of patients admitted to the hospital with severe COVID-19 in Brazil (COALITION II): a randomised clinical trial

Development and Validation of a Clinical Risk Score to Predict the Occurrence of Critical Illness in Hospitalized Patients With COVID-19

Preliminary predictive criteria for COVID-19 cytokine storm

Early prediction of level-of-care requirements in patients with COVID-19

Early predictors of in-hospital mortality in patients with COVID-19 in a large American cohort

Neutrophil-to-lymphocyte ratio on admission to predict the severity and mortality of COVID-19 patients: A meta-analysis

Coagulation biomarkers are independent predictors of increased oxygen requirements in COVID-19

Lymphopenia and neutrophilia at admission predicts severity and mortality in patients with COVID-19: a meta-analysis

Endothelial cell infection and endotheliitis in COVID-19

Potential value of circulating endothelial cells for the diagnosis and treatment of COVID-19

Soluble Urokinase Plasminogen Activator Receptor as a Decision Marker for Early Discharge of Patients with COVID-19 Symptoms in the Emergency Department

An inflammatory cytokine signature predicts COVID-19 severity and survival

Longitudinal correlation of biomarkers of cardiac injury, inflammation, and coagulation to outcome in hospitalized COVID-19 patients

Profiling of immune dysfunction in COVID-19 patients allows early prediction of disease progression

Clinical features of patients infected with 2019 novel coronavirus in Wuhan

Autopsy Findings and Venous Thromboembolism in Patients With COVID-19: A Prospective Cohort Study

SARS-CoV-2 RNA in serum as predictor of severe outcome in COVID-19: a retrospective cohort study

Quantitative assessment of SARS-CoV-2 RNAemia and outcome in patients with coronavirus disease 2019

Early risk markers for severe clinical course and fatal outcome in German patients with COVID-19

An interpretable mortality prediction model for COVID-19 patients

A simple algorithm helps early identification of SARS-CoV-2 infection patients with severe progression tendency

Predictive Value of Combined LIPS and ANG-2 Level in Critically Ill Patients with ARDS Risk Factors

Lung injury prediction scores: Clinical validation and Creactive protein involvement in high risk patients

SpO2/FiO2 ratio on hospital admission is an indicator of early acute respiratory distress syndrome development among patients at risk

Early identification of patients at risk of acute lung injury: evaluation of lung injury prediction score in a multicenter cohort study

Acute lung injury prediction score: derivation and validation in a population-based sample

Clinical Characteristics of 138 Hospitalized Patients With

Novel Coronavirus-Infected Pneumonia in Wuhan

Clinical Insights into the Gastrointestinal Manifestations of COVID-19

Predictors of adverse prognosis in COVID-19: A systematic review and meta-analysis

A meta-analysis of SARS-CoV-2 patients identifies the combinatorial significance of D-dimer, C-reactive protein, lymphocyte, and neutrophil values as a predictor of disease severity

Predicting outcomes of COVID-19 from admission biomarkers: a prospective UK cohort study

Coagulopathy and Antiphospholipid Antibodies in Patients with Covid-19

Dexamethasone in Hospitalized Patients with Covid-19 -Preliminary Report

Efficacy of Corticosteroids in Patients with SARS, MERS and COVID-19: A Systematic Review and Meta-Analysis

Clinical evidence does not support corticosteroid treatment for 2019-nCoV lung injury

Corticosteroids for Patients With Coronavirus Disease 2019 (COVID-19) With Different Disease Severity: A Meta-Analysis of Randomized Clinical Trials

Jaks and STATs: biological implications

Dysregulated Type I Interferon and Inflammatory Monocyte-Macrophage Responses Cause Lethal Pneumonia in SARS-CoV-Infected Mice

IFN-I response timing relative to virus replication determines MERS coronavirus infection outcomes

Dynamic innate immune responses of human bronchial epithelial cells to severe acute respiratory syndrome-associated coronavirus infection

Impaired type I interferon activity and inflammatory responses in severe COVID-19 patients

Comparative Replication and Immune Activation Profiles of SARS-CoV-2 and SARS-CoV in Human Lungs: An Ex Vivo Study With Implications for the Pathogenesis of COVID-19

World Health Organization. Solidarity clinical trial for COVID-19 treatments

Interferon beta-1b in treatment of severe COVID-19: A randomized clinical trial

Retrospective Multicenter Cohort Study Shows Early Interferon Therapy Is Associated with Favorable Clinical Responses in COVID-19 Patients

Interferon beta-1a for COVID-19: critical importance of the administration route

Safety and efficacy of inhaled nebulised interferon beta-1a (SNG001) for treatment of SARS-CoV-2 infection: a randomised, double-blind, placebo-controlled, phase 2 trial

Scientific and Standardization Committee communication: Clinical guidance on the diagnosis, prevention, and treatment of venous thromboembolism in hospitalized patients with COVID-19

COVID-19) Treatment Guidelines. National Institutes of Health. 2021. 225. ATTACC Investigators; ACTIV-4a Investigators

Therapeutic Anticoagulation with Heparin in Noncritically Ill Patients with Covid-19

Heparin in COVID-19 Patients Is Associated with Reduced In-Hospital Mortality: The Multicenter Italian CORIST Study

Anti-SARS-CoV-2 neutralizing monoclonal antibodies: clinical pipeline

Clinical course of COVID-19 patients needing supplemental oxygen outside the intensive care unit

Role of the renin-angiotensin system in vascular inflammation

A novel role for calpain in the endothelial dysfunction induced by activation of angiotensin II type 1 receptor signaling

Contribution of monocytes and macrophages to the local tissue inflammation and cytokine storm in COVID-19: Lessons from SARS and MERS, and potential therapeutic interventions

Evaluation of Activation and Inflammatory Activity of Myeloid Cells During Pathogenic Human Coronavirus Infection

Identification of interferon-gamma as the lymphokine that activates human macrophage oxidative metabolism and antimicrobial activity

Interleukin 4 potently enhances murine macrophage mannose receptor activity: a marker of alternative immunologic macrophage activation

Macrophage plasticity, polarization, and function in health and disease

Macrophage Polarization

The clearance of dead cells by efferocytosis

Pathogenesis of influenza-induced acute respiratory distress syndrome

Novel concepts of acute lung injury and alveolar-capillary barrier dysfunction

Origin of monocytes and macrophages in a committed progenitor

IFN-gamma selectively suppresses a subset of TLR4-activated genes and enhancers to potentiate macrophage activation

COVID-19 pulmonary pathology: a multiinstitutional autopsy cohort from Italy

Alveolar macrophage dysfunction and cytokine storm in the pathogenesis of two severe COVID-19 patients

Protective and pathogenic functions of macrophage subsets

Phenotypic characterization of alveolar monocyte recruitment in acute respiratory distress syndrome

A novel subpopulation of monocyte-like cells in the human lung after lipopolysaccharide inhalation

Transcriptional profiling identifies novel regulators of macrophage polarization

Macrophage polarization and its role in the pathogenesis of acute lung injury/acute respiratory distress syndrome

NETs promote ALI/ARDS inflammation by regulating alveolar macrophage polarization

Angiopoietin-2 as a marker of endothelial activation is a good predictor factor for intensive care unit admission of COVID-19 patients

Neutrophil to CD4+ lymphocyte ratio as a potential biomarker in predicting virus negative conversion time in COVID-19

Neutrophil-to-lymphocyte ratio as an independent risk factor for mortality in hospitalized patients with COVID-19

Neutrophil-to-lymphocyte ratio predicts critical illness patients with 2019 coronavirus disease in the early stage

Severe COVID-19 Is Marked by a Dysregulated Myeloid Cell Compartment

Glucocorticoid attenuates acute lung injury through induction of type 2 macrophage

Association Between Administration of Systemic Corticosteroids and Mortality Among Critically Ill Patients With COVID-19: A Meta-analysis

IL-6 serum levels predict severity and response to tocilizumab in COVID-19: An observational study

Tocilizumab for patients with COVID-19 pneumonia. The single-arm TOCIVID-19 prospective trial

TOCIVID-19 -A multicenter study on the efficacy and tolerability of tocilizumab in the treatment of patients with COVID-19 pneumonia. Study protocol

Historically controlled comparison of glucocorticoids with or without tocilizumab versus supportive care only in patients with COVID-19-associated cytokine storm syndrome: results of the CHIC study

Association Between Administration of IL-6 Antagonists and Mortality Among Patients Hospitalized for COVID-19: A Meta-analysis

Efficacy and safety of tocilizumab in COVID-19 patients: a living systematic review and meta-analysis

Anakinra for severe forms of COVID-19: a cohort study

Interleukin-1 blockade with high-dose anakinra in patients with COVID-19, acute respiratory distress syndrome, and hyperinflammation: a retrospective cohort study

Evaluation of 17 patients with COVID-19 pneumonia treated with anakinra according to HScore, SOFA, MuLBSTA, and Brescia-COVID respiratory severity scale (BCRSS) scoring systems

Anakinra after treatment with corticosteroids alone or with tocilizumab in patients with severe COVID-19 pneumonia and moderate hyperinflammation. A retrospective cohort study

Anakinra combined with methylprednisolone in patients with severe COVID-19 pneumonia and hyperinflammation: An observational cohort study

Anakinra in hospitalized patients with severe COVID-19 pneumonia requiring oxygen therapy: Results of a prospective, open-label, interventional study

Effect of anakinra versus usual care in adults in hospital with COVID-19 and mild-to-moderate pneumonia (CORIMUNO-ANA-1): a randomised controlled trial

Efficacy of early anti-inflammatory treatment with high doses of intravenous anakinra with or without glucocorticoids in patients with severe COVID-19 pneumonia

Systematic review and meta-analysis of anakinra, sarilumab, siltuximab and tocilizumab for COVID-19

Soluble urokinase plasminogen activator receptor (suPAR) as an early predictor of severe respiratory failure in patients with COVID-19 pneumonia

An open label trial of anakinra to prevent respiratory failure in COVID-19

Effect of Canakinumab vs Placebo on Survival Without Invasive Mechanical Ventilation in Patients Hospitalized With Severe COVID-19: A Randomized Clinical Trial

Calming the cytokine storm in COVID-19

The type I interferon response in COVID-19: implications for treatment

COVID-19: combining antiviral and anti-inflammatory treatments

JAK-inhibitor and type I interferon ability to produce favorable clinical outcomes in COVID-19 patients: a systematic review and meta-analysis

Baricitinib therapy in COVID-19: A pilot study on safety and clinical impact

Beneficial impact of Baricitinib in COVID-19 moderate pneumonia; multicentre study

Baricitinib plus Remdesivir for Hospitalized Adults with Covid-19

Repurposed immunomodulatory drugs for Covid-19 in pre-ICu patients -mulTi-Arm Therapeutic study in pre-ICu patients admitted with Covid-19 -Repurposed Drugs (TACTIC-R): A structured summary of a study protocol for a randomised controlled trial

Tofacitinib in Patients Hospitalized with Covid-19

Infliximab against severe COVID-19-induced cytokine storm syndrome with organ failure-a cautionary case series

Uncontrolled Innate and Impaired Adaptive Immune Responses in Patients with COVID-19 ARDS

GM-CSF in inflammation

Modulation of neutrophil apoptosis by granulocyte colony-stimulating factor and granulocyte/macrophage colony-stimulating factor during the course of acute respiratory distress syndrome

The relative balance of GM-CSF and TGF-beta1 regulates lung epithelial barrier function

Lung epithelial GM-CSF improves host defense function and epithelial repair in influenza virus pneumonia-a new therapeutic strategy?

A randomized trial of recombinant human granulocyte-macrophage colony stimulating factor for patients with acute lung injury

Innate immune function and mortality in critically ill children with influenza: a multicenter study

Sargramostim to treat patients with acute hypoxic respiratory failure due to COVID-19 (SARPAC): A structured summary of a study protocol for a randomised controlled trial

GM-CSF blockade with mavrilimumab in severe COVID-19 pneumonia and systemic hyperinflammation: a single-centre, prospective cohort study

Mavrilimumab in patients with severe COVID-19 pneumonia and systemic hyperinflammation (MASH-COVID): an investigator initiated, multicentre, double-blind, randomised, placebo-controlled trial

Neutrophil extracellular traps kill bacteria

NETosis, complement, and coagulation: a triangular relationship

A novel cell-based assay for dynamically detecting neutrophil extracellular traps-induced lung epithelial injuries

Neutrophil extracellular traps directly induce epithelial and endothelial cell death: a predominant role of histones

Activated endothelial cells induce neutrophil extracellular traps and are susceptible to NETosis-mediated cell death

Anti-beta2GPI/beta2GPI induces human neutrophils to generate NETs by relying on ROS

Vascular occlusion by neutrophil extracellular traps in COVID-19

Association of Coronavirus Disease

With Myocardial Injury and Mortality

Neutrophil extracellular traps (NETs) as markers of disease severity in COVID-19

Neutrophil extracellular traps contribute to immunothrombosis in COVID-19 acute respiratory distress syndrome

Neutrophil more than platelet activation associates with thrombotic complications in COVID-19 patients

Dornase alfa for cystic fibrosis

Consideration of dornase alfa for the treatment of severe COVID-19 acute respiratory distress syndrome

Preliminary report of In vitro and In vivo Effectiveness of Dornase alfa on SARS-CoV-2 infection

Efficacy and safety of aerosolized intra-tracheal dornase alfa administration in patients with SARS-CoV-2-induced acute respiratory distress syndrome (ARDS): a structured summary of a study protocol for a randomised controlled trial

The Use of Dornase Alfa in the Management of COVID-19-Associated Adult Respiratory Distress Syndrome

A combinatorial approach of a polypharmacological adjuvant 2-deoxy-D-glucose with low dose radiation therapy to quell the cytokine storm in COVID-19 management

The prevalence of symptoms in 24

COVID-19): A systematic review and meta-analysis of 148 studies from 9 countries

The angiopoietin-Tie2 signaling axis in the vascular leakage of systemic inflammation

Alveolar fluid clearance is impaired in the majority of patients with acute lung injury and the acute respiratory distress syndrome

IL-1 and IFN-gamma increase vascular permeability

IL-1 Family Cytokine Regulation of Vascular Permeability and Angiogenesis

Vascular endothelial growth factor in acute lung injury and acute respiratory distress syndrome

Compartmentalization of vascular endothelial growth factor to the epithelial surface of the human lung

Vascular endothelial growth factor and related molecules in acute lung injury

Decreased VEGF concentration in lung tissue and vascular injury during ARDS

Vascular endothelial growth factor increases GEnC permeability by affecting the distributions of occludin, ZO-1 and tight juction assembly

A role for vascular endothelial growth factor in acute and resolving lung injury

Vascular endothelial growth factor may contribute to increased vascular permeability in acute respiratory distress syndrome

The role of angiogenic factors and their soluble receptors in acute lung injury (ALI)/ acute respiratory distress syndrome (ARDS) associated with critical illness

Angiopoietin and Tie signaling pathways in vascular development

Tek/Tie2 signaling: new and old partners

The antiinflammatory endothelial tyrosine kinase Tie2 interacts with a novel nuclear factor-kappaB inhibitor ABIN-2

Angiopoietin-1 inhibits endothelial permeability, neutrophil adherence and IL-8 production

COMP-Ang1 ameliorates leukocyte adhesion and reinforces endothelial tight junctions during endotoxemia

Excess circulating angiopoietin-2 may contribute to pulmonary vascular leak in sepsis in humans

Leakage-resistant blood vessels in mice transgenically overexpressing angiopoietin-1

Endothelial destabilization by angiopoietin-2 via integrin beta1 activation

Protective role of angiopoietin-1 in endotoxic shock

Hyperoxia causes angiopoietin 2-mediated acute lung injury and necrotic cell death

Angiopoietin-2 stimulation of endothelial cells induces alphavbeta3 integrin internalization and degradation

Endothelial glycocalyx breakdown is mediated by angiopoietin-2

Lentivirus-mediated angiopoietin-2 gene silencing decreases TNFalpha induced apoptosis of alveolar epithelium cells

Hyperoxia causes miR-34a-mediated injury via angiopoietin-1 in neonatal lungs

Angiopoietin-2 sensitizes endothelial cells to TNFalpha and has a crucial role in the induction of inflammation

tek, a novel tyrosine kinase gene located on mouse chromosome 4, is expressed in endothelial cells and their presumptive precursors

Angiopoietin-2, permeability oedema, occurrence and severity of ALI/ARDS in septic and non-septic critically ill patients

ANGPT2 genetic variant is associated with trauma-associated acute lung injury and altered plasma angiopoietin-2 isoform ratio

Plasma angiopoietin-2 as a potential causal marker in sepsisassociated ARDS development: evidence from Mendelian randomization and mediation analysis

Circulating angiopoietin 2 correlates with mortality in a surgical population with acute lung injury/adult respiratory distress syndrome

Plasma angiopoietin-2 outperforms other markers of endothelial injury in prognosticating pediatric ARDS mortality

Plasma angiopoietin-2 predicts the onset of acute lung injury in critically ill patients

Plasma angiopoietin-2 in clinical acute lung injury: prognostic and pathogenetic significance

Chronology of histological lesions in acute respiratory distress syndrome with diffuse alveolar damage: a prospective cohort study of clinical autopsies

Acute respiratory distress syndrome

Angiopoietin Level Trajectories in Toddlers With Severe Sepsis and Septic Shock and Their Effect on Capillary Endothelium

Excess circulating angiopoietin-2 is a strong predictor of mortality in critically ill medical patients

Excess circulating angiopoietin-2 levels in sepsis: harbinger of death in the intensive care unit? Crit Care

Microcirculatory perfusion disturbances following cardiac surgery with cardiopulmonary bypass are associated with in vitro endothelial hyperpermeability and increased angiopoietin-2 levels

Dysregulation of the angiopoietin-Tie-2 axis in sepsis and ARDS

Angiopoietin-2, a regulator of vascular permeability in inflammation, is associated with persistent organ failure in patients with acute pancreatitis from the United States and Germany

Angiopoietin-2 is critical for cytokine-induced vascular leakage

Single-cell landscape of bronchoalveolar immune cells in patients with COVID-19

Neutrophil recruitment and function in health and inflammation

Tissue damage from neutrophil-induced oxidative stress in COVID-19

Is neutrophilia associated with mortality in COVID-19 patients? A meta-analysis and meta-regression

Neutrophil to lymphocyte ratio as prognostic and predictive factor in patients with coronavirus disease 2019: A retrospective cross-sectional study

Pulmonary and cardiac pathology in African American patients with COVID-19: an autopsy series from New Orleans

Neutrophils and Neutrophil Extracellular Traps Drive Necroinflammation in COVID-19

Modeling COVID-19 with Human Pluripotent Stem Cell-Derived Cells Reveals Synergistic Effects of Anti-inflammatory Macrophages with ACE2 Inhibition Against SARS-CoV-2

Neutrophil subset responses in infants with severe viral respiratory infection

Functional heterogeneity and differential priming of circulating neutrophils in human experimental endotoxemia

A subset of neutrophils in human systemic inflammation inhibits T cell responses through Mac-1

The counter-intuitive role of the neutrophil in the acute respiratory distress syndrome

Netting neutrophils induce endothelial damage, infiltrate tissues, and expose immunostimulatory molecules in systemic lupus erythematosus

Post-Translational Modifications in NETosis and NETs-Mediated Diseases

Synchronized integrin engagement and chemokine activation is crucial in neutrophil extracellular trap-mediated sterile inflammation

Inflammatory cytokines in patients with persistence of the acute respiratory distress syndrome

Heterogeneous expression of cell adhesion molecules by endothelial cells in ARDS

The beta2, alpha4, alpha5 integrins and selectins mediate chemotactic factor and endotoxin-enhanced neutrophil sequestration in the lung

The alpha

CD49d/CD29) and alpha 5 beta 1 (VLA-5, CD49e/CD29) integrins mediate beta 2 (CD11/CD18) integrin-independent neutrophil recruitment to endotoxin-induced lung inflammation

Pulmonary retention of primed neutrophils: a novel protective host response, which is impaired in the acute respiratory distress syndrome

Priming and de-priming of neutrophil responses in vitro and in vivo

A Granulocytic Signature Identifies COVID-19 and Its Severity

Incidence of thrombotic complications in critically ill ICU patients with COVID-19

High risk of thrombosis in patients with severe SARS-CoV-2 infection: a multicenter prospective cohort study

Pulmonary Embolism and Deep Vein Thrombosis in COVID-19: A Systematic Review and Meta-Analysis

Pulmonary Embolism in Patients With COVID-19: Awareness of an Increased Prevalence

Incidence of venous thromboembolism in hospitalized patients with COVID-19

Large-Vessel Stroke as a Presenting Feature of Covid-19 in the Young

Von Willebrand factor (vWF): marker of endothelial damage and thrombotic risk in COVID-19

Low ADAMTS 13 plasma levels are predictors of mortality in COVID-19 patients

Circulating Von Willebrand factor and high molecular weight multimers as markers of endothelial injury predict COVID-19 in-hospital mortality

Von Willebrand factor with increased binding capacity is associated with reduced platelet aggregation but enhanced agglutination in COVID-19 patients: another COVID-19 paradox?

Microvascular dysfunction in COVID-19: the MYSTIC study

Complement Evasion Strategies of Viruses: An Overview

Complement C5 inhibition in patients with COVID-19 -a promising target?

Human kidney is a target for novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection

Proteomic and Metabolomic Characterization of COVID-19

Association of COVID-19 inflammation with activation of the C5a-C5aR1 axis

SARS-CoV-2 drives JAK1/2-dependent local complement hyperactivation

First-in-Human Phase I Study of Singleagent Vanucizumab, A First-in-Class Bispecific Anti-Angiopoietin-2/Anti-VEGF-A Antibody, in Adult Patients with Advanced Solid Tumors

Efficacy and tolerability of bevacizumab in patients with severe Covid-19

Extraordinary Survival Benefits of Severe and Critical Patients with COVID-19 by Immune Modulators: The Outcome of a Clinical Trial in Bangladesh

The Tie2-agonist Vasculotide rescues mice from influenza virus infection

Effects of a synthetic PEG-ylated Tie-2 agonist peptide on endotoxemic lung injury and mortality

Vasculotide, an angiopoietin-1 mimetic, reduces pulmonary vascular leakage and preserves microcirculatory perfusion during cardiopulmonary bypass in rats

Eculizumab as an emergency treatment for adult patients with severe COVID-19 in the intensive care unit: A proof-of-concept study

Eculizumab treatment in patients with COVID-19: preliminary results from real life ASL Napoli 2 Nord experience

Alexion Provides Update on Phase 3 Study of ULTOMIRIS® (ravulizumab-cwvz) in Hospitalized Patients with Severe COVID-19 2021

Anti-C5a antibody IFX-1 (vilobelimab) treatment versus best supportive care for patients with severe COVID-19 (PANAMO): an exploratory, open-label, phase 2 randomised controlled trial

Role of C5a in inflammatory responses

Meta-analysis of Effect of Statins in Patients with COVID-19

Acute respiratory distress syndrome subphenotypes and differential response to simvastatin: secondary analysis of a randomised controlled trial

Imatinib attenuates inflammation and vascular leak in a clinically relevant two-hit model of acute lung injury

Targeting Abl kinases to regulate vascular leak during sepsis and acute respiratory distress syndrome

Imatinib in patients with severe COVID-19: a randomised, double-blind, placebo-controlled, clinical trial

Case characteristics, resource use, and outcomes of 10 021 patients with COVID-19 admitted to 920 German hospitals: an observational study

Defining and managing COVID-19-associated pulmonary aspergillosis: the 2020 ECMM/ISHAM consensus criteria for research and clinical guidance

High rates of pulmonary artery occlusions in COVID

A meta-analysis

Anticoagulant treatment is associated with decreased mortality in severe coronavirus disease 2019 patients with coagulopathy

A meta-analysis of the incidence of venous thromboembolic events and impact of anticoagulation on mortality in patients with COVID-19

Venous Thromboembolism in Hospitalized COVID-19 Patients

Heparin resistance in COVID-19 patients in the intensive care unit

Heparin Resistance -Clinical Perspectives and Management Strategies

The management of venous thromboembolism in hospitalized patients with COVID-19

Therapeutic Anticoagulation with Heparin in Critically Ill Patients with Covid-19

Prevention or Treatment of Ards With Aspirin: A Review of Preclinical Models and Meta-Analysis of Clinical Studies

Effect of Aspirin on Development of ARDS in At-Risk Patients Presenting to the Emergency Department: The LIPS-A Randomized Clinical Trial

Siltuximab downregulates interleukin-8 and pentraxin 3 to improve ventilatory status and survival in severe COVID-19

Respiratory Impairment Predicts Response to IL-1 and IL-6 Blockade in COVID-19 Patients With Severe Pneumonia and Hyper-Inflammation

COVID-19 is, in the end, an endothelial disease

Incidence of ARDS and outcomes in hospitalized patients with COVID-19: a global literature survey

Recent advances in the understanding and management of ARDS

Patterns of Care, and Mortality for Patients With Acute Respiratory Distress Syndrome in Intensive Care Units in 50 Countries

Acute respiratory distress syndrome: the Berlin Definition

The Berlin definition of ARDS: an expanded rationale, justification, and supplementary material

Epidemiology of invasive pulmonary aspergillosis among COVID-19 intubated patients: a prospective study

Effect of Convalescent Plasma Therapy on Time to Clinical Improvement in Patients With Severe and Life-threatening COVID-19: A Randomized Clinical Trial

Convalescent plasma in the management of moderate covid-19 in adults in India: open label phase II multicentre randomised controlled trial

Clinical efficacy of convalescent plasma for treatment of COVID-19 infections: Results of a multicenter clinical study

A Randomized Trial of Convalescent Plasma in Covid-19 Severe Pneumonia

Effect of Convalescent Plasma on Mortality among Hospitalized Patients with COVID-19: Initial Three-Month Experience. medRxiv

Convalescent Plasma Antibody Levels and the Risk of Death from Covid-19

Convalescent plasma or hyperimmune immunoglobulin for people with COVID-19: a living systematic review

Early predictors of clinical outcomes of COVID-19 outbreak in

Early detection of elevated cardiac biomarkers to optimise risk stratification in patients with COVID-19

High mortality in COVID-19 patients with mild respiratory disease

Early prediction of disease progression in COVID-19 pneumonia patients with chest CT and clinical characteristics

Predictive symptoms and comorbidities for severe COVID-19 and intensive care unit admission: a systematic review and meta-analysis

A Randomized Clinical Trial of the Efficacy and Safety of Interferon beta-1a in Treatment of Severe COVID-19

Clinical evaluation of IFN beta1b in COVID-19 pneumonia: a retrospective study 2020

Triple combination of interferon beta-1b, lopinavir-ritonavir, and ribavirin in the treatment of patients admitted to hospital with COVID-19: an open-label, randomised, phase 2 trial

Therapeutic Effectiveness of Interferon-alpha2b Against COVID-19: The Cuban Experience

Interferon-alpha2b Treatment for COVID-19

Tocilizumab in Hospitalized Patients with Severe Covid-19

Tocilizumab in Patients Hospitalized with Covid-19 Pneumonia

Efficacy of Tocilizumab in Patients Hospitalized with Covid-19

Effect of Tocilizumab vs Usual Care in Adults Hospitalized With COVID-19 and Moderate or Severe Pneumonia: A Randomized Clinical Trial

Baricitinib restrains the immune dysregulation in patients with severe COVID-19

Experience With the Use of Baricitinib and Tocilizumab Monotherapy or Combined

Ruxolitinib in treatment of severe coronavirus disease

A multicenter, single-blind, randomized controlled trial

Combination of Ruxolitinib and Eculizumab for Treatment of Severe SARS-CoV-2-Related Acute Respiratory Distress Syndrome: A Controlled Study

Baricitinib plus Remdesivir for Hospitalized Adults with Covid-19

Venous thromboembolism and bleeding in critically ill COVID-19 patients treated with higher than standard low molecular weight heparin doses and aspirin: A call to action

Aspirin Use is Associated with Decreased Mechanical Ventilation, ICU Admission, and In-Hospital Mortality in Hospitalized Patients with COVID-19

Mortality and pre-hospitalization use of low-dose aspirin in COVID-19 patients with coronary artery disease

Meta-Analysis of the Effect of Aspirin on Mortality in COVID-19

Venous thromboembolism in critically ill COVID-19 patients receiving prophylactic or therapeutic anticoagulation: a systematic review and meta-analysis

Effects of Recombinant Human Angiotensin-Converting Enzyme 2 on Response to Acute Hypoxia and Exercise: A Randomised, Placebo-Controlled Study. Pulm Ther

Adverse events associated with nafamostat mesylate and favipiravir treatment in COVID-19 patients

Efficacy and safety of baricitinib for the treatment of hospitalised adults with COVID-19 (COV-BARRIER): a randomised, double-blind, parallel-group, placebo-controlled phase 3 trial

Mavrililumab improves outcomes in phase 2 trial in nonmechanically ventilated patients with severe COVID-19 pneumonia and systemic hyperinflammation

VTE in prophylactic VTE in therapeutic (and prophylactic)

VTE incidence) 5 observational (VTE and mortality) Incidence VTE (pooled, all) Incidence VTE (pooled, ICU) Incidence PE (pooled, all) Incidence PE (pooled ICU) Incidence DVT (pooled, all) Incidence DVT (pooled ICU) Mortality (with/without heparinization n=2886/5647) 255/ 1808

J o u r n a l P r e -p r o o f