key: cord-0323056-q903kxmm
authors: Li, W.; Syed, F.; Yu, R. X.; Yang, J.; Xia, Y.; Relich, R. F.; Zhang, S.; Khalili, M.; Huang, L.; Kacena, M. A.; Zheng, X.; Yu, Q.
title: Soluble immune checkpoints are dysregulated in COVID-19 and heavy alcohol users with HIV infection
date: 2021-12-30
journal: nan
DOI: 10.1101/2021.12.22.21268218
sha: f3cbcbc4c622192285312f9a30adc4f71cabeb83
doc_id: 323056
cord_uid: q903kxmm

Immune checkpoints (ICPs) consist of paired receptor-ligand molecules that exert inhibitory or stimulatory effects on immune defense, surveillance, regulation, and self-tolerance. ICPs exist in both membrane and soluble forms in vivo and in vitro. Imbalances between inhibitory and stimulatory membrane-bound ICPs (mICPs) in malignant cells and immune cells in the tumor immune microenvironment (TIME) have been well documented. Blockades of inhibitory mICPs have emerged as an immense breakthrough in cancer therapeutics. However, the origin, structure, production regulation, and biological significance of soluble ICPs (sICPs) in health and disease largely remains elusive. Soluble ICPs can be generated through either alternative mRNA splicing and secretion or protease-mediated shedding from mICPs. Since sICPs are found in the bloodstream, they likely form a circulating immune regulatory system. In fact, there is increasing evidence that sICPs exhibit biological functions including (1) regulation of antibacterial immunity, (2) interaction with their mICP compartments to positively or negatively regulate immune responses, and (3) competition with their mICP compartments for binding to the ICP blocking antibodies, thereby reducing the efficacy of ICP blockade therapies. Here, we summarize current data of sICPs in cancer and infectious diseases. We particularly focus on sICPs in COVID-19 and HIV infection as they are the two ongoing global pandemics and have created the world's most serious public health challenges. A storm of sICPs occurs in the peripheral circulation of COVID-19 patients and is associated with the severity of COVID-19. Similarly, sICPs are highly dysregulated in people living with HIV (PLHIV) and some sICPs remain dysregulated in PLHIV on antiretroviral therapy (ART), indicating these sICPs may serve as biomarkers of incomplete immune reconstitution in PLHIV on ART. We reveal that HIV infection in the setting of alcohol abuse exacerbates sICP dysregulation as PLHIV with heavy alcohol consumption have significantly elevated plasma levels of many sICPs. Thus, both stimulatory and inhibitory sICPs are present in the bloodstream of healthy people and their balance can be disrupted under pathophysiological conditions such as cancer, COVID-19, HIV infection, and alcohol abuse. There is an urgent need to study the role of sICPs in immune regulation in health and disease.

Immune checkpoints (ICPs) consist of paired receptor-ligand molecules that exert inhibitory or stimulatory effects on immune defense, surveillance, regulation, and self-tolerance [1] [2] [3] [4] [5] . Under normal circumstances, ICPs regulate the breadth, magnitude, and duration of the immune responses against malignancy and infection while protecting tissues from excessive insult. However, in certain pathological situations such as cancer or persistent infection, the balance between ICP stimulatory and inhibitory signals becomes dysregulated [1] [2] [3] [4] [5] [6] [7] inhibitory ICPs including CTLA-4, PD-1, TIM-3, and LAG-3 on total and HIV-specific CD4 and CD8 T cells [6] [7] [8] [17] [18] [19] [20] [21] , which is associated with an accelerated decline in the number of CD4 T cells in PLHIV 8, 22 . Following ART, expression of these ICPs on the surface of T cells declines, but remains elevated when compared with healthy controls [8] [9] [10] . Importantly, expression of inhibitory ICPs can be used as surrogate immunological biomarkers of ART effectiveness. In ART-treated PLHIV, PD-1 expression on CD8 T cells has been associated with impaired reconstitution of CD4 T cells and a shorter time to viral rebound after stopping ART 23, 24 . In addition, CD4 T cells expressing high levels of PD-1, LAG-3, and TIGIT alone or in combination are enriched for integrated HIV DNA during ART 25, 26 . Furthermore, most CD4 T cells expressing at least one of these ICPs, carry inducible and replication-competent HIV genomes 25 ICP molecules exist in both membrane and soluble forms in vivo and in vitro [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] . Similar to membrane-bound ICPs (mICPs), soluble ICPs (sICPs) are also present in normal physiological conditions and highly dysregulated in patients with cancer, viral infections, or ALD (alcoholassociated liver disease) [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] . Soluble ICPs can be generated through either alternative mRNA splicing and secretion or protease-mediated shedding from mICPs by actions of matrix metalloproteinases (MMPs) 44, 46 . Although the detailed structure, production regulation, function, and clinical relevance of sICPs largely remain unknown, many sICPs exist in native forms that exhibit biological functions such as regulation of antibacterial immunity 42, 46 . Since sICPs are paired receptor-ligand molecules and circulate in the bloodstream, they likely form a circulating immune regulatory system. In addition, increasing evidence has shown that sICPs interact with their mICP compartments to positively or negatively regulate immune responses 43 . Furthermore, sICPs can compete with their mICP compartments for binding to the ICP blocking antibodies, thereby interrupting the efficacy of ICP blockade therapies. Thus, there is an urgent need to study the role of sICPs in immune regulation in health and disease. Here, we summarize current data of sICPs in cancer and infectious diseases. We particularly focus on sICPs in COVID-19 and HIV infection as they are the two ongoing global pandemics and have created the world's most serious public health and development challenges.

As described in our recent report 45 , we used a multiplex immunoassay (the Human Immuno-Oncology Checkpoint Protein Panel, MilliporeSigma, Burlington, MA) to simultaneously quantify plasma concentrations of 16 sICPs (sBTLA, sCD27, sCD28, sCD40, sCD80/B7-1, sCD86/B7-2, sCTLA-4, sGITR, sGITRL, sHVEM, sICOS, sLAG-3, sPD-1, sPD-L1, sTIM-3, and sTLR-2) in healthy blood donors. Plasma levels of two additional ICPs (sCD160 and sLIGHT) were quantified using the Human CD160 Matched ELISA Antibody Pair Set (Sino Biological, Beijing, China) and the Human LIGHT Duoset ELISA Kit (R&D Systems, Minneapolis, MN), respectively. We found that, except for sGITR and sLIGHT, which were only detected in 30-50% of plasma samples, all other 16 sICPs were steadily detected in plasma samples from all healthy blood donors (Table 1) . These sICPs could be generated through either alternative mRNA splicing and secretion or protease-mediated shedding from mICPs by actions of MMPs 44, 46 . Several studies have demonstrated that sICPs are present in the peripheral blood as the native polypeptide products of their genes and have biological functions. For example, CTLA-4, also known as CD152, is a member of the immunoglobulin (Ig) gene superfamily 47 .

CTLA4 is constitutively expressed in regulatory T cells but can be upregulated in conventional T cells after activation 47, 48 . CTLA-4 and CD28 are homologous receptors that share a pair of ligands (B7-1 and B7-2) expressed on the surface of antigen-presenting cells (APCs), but mediate opposing functions in T-cell activation 48 . CTLA-4 interacts with its ligands to inhibit T-cell responses 48 , while CD28 acts as a major co-stimulatory receptor in promoting full activation of T cells in response to T cell receptor (TCR) engagement 49 . As shown in Table 1 , plasma levels of sCTLA-4 in healthy individuals were detected at a median concentration of 31 pg/mL with the interquartile ranges of 12 -81 pg/mL (n=39), which are higher than the detection limit (9.3 pg/mL) of the multiplex immunoassay. These results argue against a previous report showing that circulating CTLA-4 was undetectable in healthy volunteers using an enzyme immunoassay (EIA) 44 . This is because the EIA has limited detection sensitivity (≥ 4 ng/mL) 44 , which is insufficiently sensitive for the detection of sCTLA-4 concentrations in healthy people.

Immunoprecipitation and Western blotting analyses of serum sCTLA-4 revealed a polypeptide consistent with the predicted size (23 kDa) from an alternative transcript of the CTLA-4 gene, suggesting sCTLA-4 is present as a native molecule rather than a product of proteolytic digestion or shedding of mCTLA-4 44 . Functional studies have shown that sCTLA-4 immunoreactivity can be blocked by B7.1 (also known as CD80), one of its known ligands. This supports the notion that sCTLA-4 is present as a soluble functional molecule. Thus, sCTLA-4 likely has important immunoregulatory functions, which is similar to soluble cytokine receptors such as soluble forms of TNF receptor, IL-2α receptor, IL-4 receptor, and IL-7 receptor that exist in the biological fluids and regulate cytokine activity in vitro and in vivo [50] [51] [52] [53] [54] [55] .

In contrast to sCTLA-4, several sICPs including sHVEM (also known as TNFRSF14 or CD270), sCD160, sLAG-3, and sTIM-3 were present at high concentrations (Table 1) in healthy people. These are potent inhibitory ICPs. HVEM was initially identified as the receptor of herpes simplex virus 1 (HSV-1) through binding to the HSV-1 glycoprotein D (gD) 56 . Since then, HVEM has been identified as a co-signaling molecular switch through interacting with BTLA (also known as CD272), CD160, and LIGHT 57 . In addition, HVEM can bind to SALM5 (synaptic adhesion-like molecule 5) to regulate neuroinflammation 58 . We have recently reported that recombinant sHVEM affects TNF-α and IFN-γ production by anti-CD3/anti-CD28-stimulated T cells from healthy volunteers 45 , indicating sHVEM may act as a circulating immune regulator.

Like sCTLA-4 and sHVEM, other sICPs such as sLAG-3, sTIM-3, sPD-1, and sPD-L1 are biologically active and participate in immune regulation 39, [59] [60] [61] . Thus, the majority (if not all) of ICPs have soluble forms that are detectable in the peripheral blood of healthy individuals.

Different sICPs are likely produced at different levels and at distinct checkpoints to fine-tune immune homeostasis in health, although their origin, production regulation, and biological

function are yet to be discovered. Of note, these data related to plasma sICPs were obtained from adults with a median age of 42 years (26-52) and 64% were from males 45 . Future study is needed to investigate whether sICP levels and functions in healthy people are affected by age, gender, and race.

ICPs act as gatekeepers for immune responses and play a central role in immune homeostasis that is maintained by a precise balance between stimulatory and inhibitory ICPs on the surface of effector and regulatory immune cells. The immune homeostasis is a tightly regulated network which fails during tumor development due to an imbalance between inhibitory and stimulatory ICPs. Indeed, high levels of inhibitory ICPs on the surface of tumor cells is a hallmark of the tumor immune microenvironment (TIME) that is infiltrated with many types of innate and adaptive immune cells 62 . Increased inhibitory ICPs are responsible for tumor immune escape and thereby have become major targets for cancer immunotherapy 5,13-15 .

While mICPs have been extensively studied in cancer immunity and cancer immunotherapy, the origin, production regulation, and biological significance of sICPs largely remains elusive. Due to their function in both positive and negative immune regulation, sICPs and their levels change in the peripheral blood, which may affect the development, prognosis, and treatment of cancer. Studies have shown that plasma or serum levels of sICPs can serve as biomarkers and/or predictors of cancer patient outcomes or therapeutic responses 43, 63 .

Plasma or serum levels of numerous sICPs including sPD-L1, sPD-1, sLAG-3, sTIM-3, sCTLA-4, sHVEM, sCD80, sCD86, sCD27, sCD40, and sBTLA are highly elevated in patients with various types of tumors and serve as prognostic markers for solid tumors such as non-small cell lung cancer, gastric cancer, colon cancer, and cervical cancer 42, 60, [64] [65] [66] [67] . Soluble ICPs are also biologically active in cancer patients. Studies have revealed that plasma/serum levels of sCD40L are highly elevated in patients with lung cancer and undifferentiated nasopharyngeal carcinoma 68, 69 . The elevated sCD40L in cancer patients is likely derived from activated platelets rather than T cells, because cancer patients have significant platelet activation, but inadequate T-cell activation [70] [71] [72] . A functional study has shown that the upregulated sCD40L seen in cancer patients exerts an immunosuppressive effect through enhancement of MDSC (myeloid-derived suppressor cell)-mediated suppression of T cell proliferation and IFN-γ production, expansion of regulatory T cells (Treg), and enrichment of PD-1 + T cells 73 . On the other hand, sPD-1 is likely generated through mRNA splicing and secretion, as four PD-1 splice variants have been identified 74 . In vitro and in vivo studies have shown sPD-1 is able to bind its membrane-bound ligands (mPD-L1 and mPD-L2) to block mPD-1/mPD-L1/mPD-L2 interaction, thereby restoring T cell immunity 60 . Indeed, local delivery of sPD-1 in the tumor microenvironment through adenoassociated virus-mediated delivery vector induces antitumor immunity through improving T cell function 75, 76 . The origin, production regulation, function, and biological significance of sICPs in tumors have been systematically reviewed 43, 60, 77, 78 . Collectively, the levels of sICPs in the peripheral circulation in cancer patient are frequently altered, which likely has clinical significances. That said, a better understanding of the underlying mechanisms of the sICP network could lay the foundation for the development of new strategies for treating cancers with immunotherapies.

Two recent studies, reported by Kong have demonstrated that a "storm" of sICPs occurs in COVID-19 patients and is associated with All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this this version posted December 30, 2021. ;  the severity of COVID-19 79, 80 . The Kong study quantified 14 sICPs including sBTLA, sCTLA-4, sGITR, sHVEM, sIDO, sLAG-3, sPD-1, sPD-L1, sPD-L2, sTIM-3, sCD27, sCD28, sCD80, and s4-1BB in the serum samples from patients with asymptomatic, mild/moderate, and severe/critical COVID-19 using the ProcartaPlex Human ImmunoOncology Checkpoint Panel (Invitrogen, Carlsbad, CA) 79 , while the Avendano-Ortiz study quantified 9 sICPs including sCD25, sCD86, sCTLA-4, Galectin-9, sLAG-3, sPD-1, sPD-L1, sTim-3, and s4-1BB using the LEGENDplex HU Immune Checkpoint Panel 1 (BioLegend, San Diego, CA) 80 . After merging the overlapping 6 sICPs that were detected in both studies, a total of 17 sICPs including sBTLA, sCTLA-4, sGalectin-9, sGITR, sHVEM, sIDO, sLAG-3, sPD-1, sPD-L1, sPD-L2, sTIM-3, sCD25, sCD27, sCD28, sCD80, sCD86, and s4-1BB were studied in the serum or plasma samples from COVID-19 patients 79, 80 . The Kong study showed that, except for sPD-L2, each of the other 13 sICPs was significantly higher in the severe/critical group than in the mild/moderate and asymptomatic groups 79 . On the other hand, the Avendano-Ortiz study showed that plasma levels of sCD25, sCD86, Galectin-9, sPD-1, sPD-L1, and sTim-3, but not sLAG-3, sCTLA-4, and s4-1BB, were significantly higher in the severe/critical group than in the mild/moderate groups 80 .

Therefore, both studies demonstrated that the serum or plasma levels of sPD-1, sPD-L1, and sTIM-3 were significantly higher in the severe/critical group than in the mild/moderate and asymptomatic groups, but their data conflicted regarding the serum or plasma levels of sLAG-3, sCTLA-4, and s4-1BB between healthy controls and COVID-19 patients 80 . The Kong study also showed that serum levels of 11 sICPs (sGITR, s4-1BB, sTIM-3, sCD27, sLAG-3, sPD-1, sCD28, sCTLA-4, sBTLA, sHVEM, and sCD80) were persistently higher in severe/critical patients than in mild/moderate cases during hospitalization. In addition, the levels of 8 sICPs (sIDO, sGITR, s4-1BB, sTIM-3, sCD27, sLAG-3, sPD-1, and sCD28) were negatively correlated with absolute counts of CD4 and CD8 T cells. The Avendano-Ortiz study also demonstrated that plasma levels of sCD25, sTIM-3, Galectin-9, and sPD-L1, but not sCD86, showed a negative correlation with the absolute lymphocyte count (ALC). These results suggest that sICPs are dysregulated in All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. We also used a multiplex immunoassay (the Human Immuno-Oncology Checkpoint Protein Panel, MilliporeSigma, Burlington, MA) to simultaneously quantify the concentrations of 16 sICPs in plasma samples from healthy controls (n=23) and patients with asymptomatic All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this this version posted December 30, 2021. ; https://doi.org/10.1101/2021.12.22.21268218 doi: medRxiv preprint (n=15) or hospitalized (severe/critical) COVID-19 (n=24). Among these 16 sICPs, 4 (sCD40, sGITRL, sICOS, and sTLR-2) were not previously studied in COVID-19 patients, while 12 were already tested in the two studies by Kong and Avendano-Ortiz et al. In our studies, the healthy control subjects were matched with the COVID-19 patients in terms of age, sex, and race. We found that plasma levels of the majority of 16 sICPs were significantly higher in COVID-19 patients when compared with healthy controls (data not shown). The 4 sICPs (sCD40, sGITRL, sICOS, and sTLR-2) that had not previously been studied in COVID-19 were significantly higher in the plasma from patients with asymptomatic or severe/critical COVID-19 when compared with healthy controls (Fig. 1A) . Plasma levels of sGITRL, sICOS, and sTLR-2, but not sCD40 were further elevated in severe/critical COVID-19 patients than in asymptomatic cases (Fig. 1A) . We also found that sCTLA-4 and sLAG-3, 2 sICPs that were studied by Kong and Avendano-Ortiz et al. with conflicting results, were elevated in plasma from patients with severe/critical COVID-19 when compared with healthy controls (Fig. 1B) , which is in agreement with Kong's results.

Taken together, a storm of sICPs occurs in the peripheral circulation of COVID-19 patients and is associated with the disease severity. The circulating sICP levels on admission appear to be better mortality predictors than inflammatory cytokines and chemokines 80 , and thereby can potentially serve as biomarkers of COVID-19 progress and outcome. Given that some, if not all, sICPs are biological active, they may also serve as circulating immune regulators or pharmaceutical targets for COVID-19 therapy. To this end, mechanistic studies and large-scale, cross-sectional and longitudinal studies are needed to investigate the origin, production regulation, and clinical significance of sICPs in patients with COVID-19.

Chronic immune activation and exhaustion are important features of persistent viral infections such as infection with HIV. Indeed, immune exhaustion represents a barrier to effective and specific immunity against HIV infection. Chronic immune activation and exhaustion All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. Here, we simultaneously quantified plasma levels of 16 sICPs from 23 healthy controls, 46

PLHIV who were ART-naïve, and 65 PLHIV who were on ART using a multiplex immunoassay as detailed above. These three groups of study subjects were matched in terms of demographic parameters including age, gender, and race. As shown in Fig. 2 , except GITR which was only detected in 34.8% (8/23) of healthy controls, each of the other 15 sICPs was detectable in the plasma samples from healthy controls, indicating that they could play biological roles in immune homeostasis under physiologic conditions. Compared to healthy controls, ART-naïve PLHIV had significantly higher plasma levels of the 15 sICPs tested. Specifically, only sTIM-3 was not elevated in ART-naïve PLHIV. In comparison to healthy controls, PLHIV on ART only had higher plasma levels of 3 sICPs (sCD40, sCTLA-4, and sHVEM) (Fig. 2) . These findings appear to indicate that ART effectively, but not completely, restores ICP homeostasis. Among these 3 sICPs that remained at higher levels in the peripheral blood of PLHIV on ART, sHVEM and sCD40 were not affected by ART, while sCTLA-4 was dramatically reduced, but did not return to a normal level (Fig. 2) . Both CD40 (also known as TNFRSF5) and HVEM (also known as TNFRSF14) are members of the tumor necrosis factor receptor superfamily. CD40 is a costimulatory molecule that is mainly expressed on the surface of APCs such as dendritic cells, monocytes/macrophages, and B cells. CD40 is required for APC activation via binding to CD154 (also known as CD40 ligand or CD40L) on T cells. CD40-CD40L interaction leads to the All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this this version posted December 30, 2021. ;  initiation of bidirectional intracellular signaling in both CD40 + APCs and CD40L + T cells, resulting in APC activation and T cell responses [108] [109] [110] . Dysregulation of CD40/CD40L expression and interactions contributes to the severity in numerous diseases such as HIV infection [111] [112] [113] , cancer 108, 114 , and autoimmune disorders [115] [116] [117] . However, the role of sCD40 in the peripheral circulation of PLHIV largely remains elusive. We found that ART-naïve PLHIV had excessive production of sCD40, which was minimally affected by ART, suggesting that circulating sCD40 may represent an indicator of dysregulation of APC and T cell function that is a hallmark of HIVassociated deficiency in cell-mediated immunity.

Similar to sCD40, sHVEM was also excessively produced in PLHIV and was barely affected by ART (Fig. 2) . HVEM serves as a shared receptor/ligand for stimulatory and inhibitory ligands/receptors, including LIGHT, BTLA, and CD160 that are expressed on both hematopoietic and non-hematopoietic cells. HVEM acts as a bifunctional ligand/receptor that exhibits costimulatory signals upon binding to LIGHT and co-inhibitory signals upon binding to BTLA or CD160 118, 119 . Due to its role of bifunctional ligand/receptor, HVEM serves as a molecular switch between stimulatory and inhibitory signaling 120,121 , thereby playing a unique role in immune homeostasis. We have recently reported that expressions of both sHVEM and mHVEM were highly dysregulated in heavy alcohol users with ALD, specifically alcoholic hepatitis (AH), when compared with heavy alcohol users without AH 45 . Plasma levels of upregulated sHVEM in AH patients remained high for 6 months of complete alcohol abstinence 45 , indicating sHVEM might serve as a prognostic marker for AH. We also found that sHVEM-his, consisting of the soluble extracellular domain of human mHVEM linked to a polyhistidine tag at the C-terminus, significantly inhibited TCR-induced TNF-α production by both CD4 T cells and CD8 T cells from AH patients and healthy controls 45 , indicating sHVEM plays an inhibitory role in HVEM axis-mediated TNF-α production. Currently, the regulation and function of sHVEM in HIV immunopathogenesis is not known. Thus, studies are needed to All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this this version posted December 30, 2021. ; https://doi.org/10.1101/2021.12.22.21268218 doi: medRxiv preprint elucidate the mechanisms of action for the sHVEM axis and the interplay between sHVEM and mHVEM in HIV infection.

Alcohol abuse and HIV infection are both major health issues worldwide. Globally, more than 2 billion people consume alcohol on a regular basis, and approximately 76 million suffer from alcohol-related disorders 122, 123 . Long-term heavy alcohol users develop a spectrum of ALD, ranging from AH, fibrosis/cirrhosis, to hepatocellular carcinoma (HCC) 124 . Alcohol overconsumption contributes to 5.1% of the global burden of diseases and causes approximately 3.3 million deaths every year 125, 126 . HIV is the causative agent of AIDS and has claimed over 36 million lives with an estimated 38 million PLHIV worldwide at the end of 2020 127 . Alcohol overconsumption is common among PLHIV and adversely influences the health outcomes by increasing HIV-associated comorbidities such as liver disease, cardiovascular disease, pulmonary disease, bone disease, and cancer [128] [129] [130] . It is well known that alcohol overconsumption and HIV infection independently damage the gastrointestinal (GI) tract mucosal barrier, leading to a leaky gut that allows microbial translocation and accumulation of microbial components such as lipopolysaccharide (LPS) in the blood. Specifically, alcohol disrupts gap junction integrity of gut mucosal epithelial cells, leading to increased GI permeability and translocation of microbial components such as LPS from the GI tract into the blood and liver [131] [132] [133] . Alcohol-induced microbial translocation has been considered a major driver of chronic immune activation and inflammation in AH patients [134] [135] [136] [137] . In PLHIV, microbial translocation is a cause of chronic immune activation and inflammation, which is a hallmark of progressive HIV infection and a stronger predictor of disease outcome compared to plasma viral load 138, 139 . We therefore hypothesize that alcohol overconsumption and HIV infection exacerbate microbial translocation, immune dysregulation, and inflammation, thereby accelerating disease progression of HIV infection and ALD. To test this hypothesis, we All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this this version posted December 30, 2021. ; https://doi.org/10.1101/2021.12.22.21268218 doi: medRxiv preprint established a cohort of heavy alcohol users with and without HIV infection. We analyzed and compared the profiles of sICPs in the peripheral blood in heavy drinkers without overt ALD (HDC) versus PLHIV on ART (HIV) versus PLHIV on ART who were heavy drinkers, but did not have ALD (HDC+HIV). We found that plasma levels of all 16 sICPs were similar between HDC and HIV groups ( Table 2 ). Fourteen out of sixteen sICP examined were dramatically elevated in the peripheral blood in HDC+HIV when compared with either HDC or HIV ( Table 2 ). sCD27 and sTIM-3 were not elevated in HDC+HIV compared with either HDC or HIV ( Table 2 ). These results indicate that sICPs were highly dysregulated in HDC+HIV even though these individuals had no clinical evidence of overt ALD and their liver enzyme parameters including the circulating levels of AST and ALT and AST:ALT ratio were similar to healthy individuals (data not shown).

Previous studies from our group and others have demonstrated that chronic excessive drinking leads to immune abnormalities in heavy drinkers even when there are no obvious signs of clinical liver disease 137, [140] [141] [142] . HDCs have increased bacterial translocation as they have higher serum levels of LPS and markers of monocyte/macrophage activation (sCD14 and sCD163) than non-excessive drinkers 141 . In addition, mucosal-associated invariant T (MAIT) cells in the peripheral blood are significantly decreased in HDCs compared to healthy controls 142 . Moreover, HDCs have increased levels of MAIT activation-associated cytokines such as IL-18 and IL-12 142 .

MAIT cells are innate-like lymphocytes that are highly enriched in liver, mucosa, and peripheral blood, and play a protective role in antimicrobial immunity 143, 144 . These results highlight the presence of immune dysregulation in HDCs. HIV infection and alcohol abuse dramatically exacerbate immune abnormalities such as sICP dysregulation. Future study is needed to investigate the mechanisms underlying exacerbated sICP dysregulation in heavy drinkers with HIV infection.

All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this this version posted December 30, 2021. ; infected individuals without symptoms (Asym), and healthy controls (HCs). Red lines represent the mean and the standard error of the mean. ns, no significant; *p<0.05; **p<0.01; ***p<0.001. All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. 

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CD28 Costimulation: From Mechanism to Therapy

Molecular cloning and expression of a receptor for human tumor necrosis factor

Demonstration of two distinct forms of released low-affinity type interleukin 2 receptors

The murine interleukin-4 receptor: molecular cloning and characterization of secreted and membrane bound forms

Cloning of the human and murine interleukin-7 receptors: demonstration of a soluble form and homology to a new receptor superfamily

Soluble cytokine receptors: their role in immunoregulation

Mechanisms of soluble cytokine receptor generation

Herpes simplex virus-1 entry into cells mediated by a novel member of the TNF/NGF receptor family

HVEM, a cosignaling molecular switch, and its interactions with BTLA, CD160 and LIGHT

Neuron-specific SALM5 limits inflammation in the CNS via its interaction with HVEM

Soluble TIM3 and Its Ligands Galectin-9 and CEACAM1 Are in Disequilibrium During Alcohol-Related Liver Disease and Promote Impairment of Antibacterial Immunity

Soluble PD-1: Predictive, Prognostic, and Therapeutic Value for Cancer Immunotherapy

Soluble PD-L1 generated by endogenous retroelement exaptation is a receptor antagonist

Understanding the tumor immune microenvironment (TIME) for effective therapy

Clinical significance of circulating soluble immune checkpoint proteins in sorafenib-treated patients with advanced hepatocellular carcinoma

Serum levels of soluble programmed death-ligand 1 (sPD-L1) in patients with primary central nervous system diffuse large B-cell lymphoma

Soluble LAG3 acts as a potential prognostic marker of gastric cancer and its positive correlation with CD8+T cell frequency and secretion of IL-12 and INF-gamma in peripheral blood

Highly elevated soluble Tim-3 levels correlate with increased hepatocellular carcinoma risk and poor survival of hepatocellular carcinoma patients in chronic hepatitis B virus infection

A soluble form of CTLA-4 is present in paediatric patients with acute lymphoblastic leukaemia and correlates with CD1d+ expression

Soluble CD40 ligand plasma levels in lung cancer

High serum levels of soluble CD40-L in patients with undifferentiated nasopharyngeal carcinoma: pathogenic and clinical relevance

CD40 ligand on activated platelets triggers an inflammatory reaction of endothelial cells

Platelet activation in patients with advanced gastric cancer

Alterations in signal transduction molecules in T lymphocytes from tumor-bearing mice

Elevated serum soluble CD40 ligand in cancer patients may play an immunosuppressive role

Alternative splice variants of the human PD-1 gene

Reconstructed adeno-associated virus with the extracellular domain of murine PD-1 induces antitumor immunity

Eliminating mesothelioma by AAVvectored, PD1-based vaccination in the tumor microenvironment

Soluble immune checkpoint molecules: Serum markers for cancer diagnosis and prognosis

Development of immune checkpoint therapy for cancer

Storm of soluble immune checkpoints associated with disease severity of COVID-19

The immune checkpoints storm in COVID-19: Role as severity markers at emergency department admission

Clinical course and outcomes of critically ill patients with SARS-CoV-2 pneumonia in Wuhan, China: a single-centered, retrospective, observational study

Clinical predictors of mortality due to COVID-19 based on an analysis of data of 150 patients from Wuhan, China

Clinical features of patients infected with 2019 novel coronavirus in Wuhan

Complex Immune Dysregulation in COVID-19 Patients with Severe Respiratory Failure

Lymphopenia predicts disease severity of COVID-19: a descriptive and predictive study

Clinical and immunological features of severe and moderate coronavirus disease 2019

Lymphopenia in severe coronavirus disease-2019 (COVID-19): systematic review and meta-analysis

Deep immune profiling of COVID-19 patients reveals distinct immunotypes with therapeutic implications

Selective CD8 cell reduction by SARS-CoV-2 is associated with a worse prognosis and systemic inflammation in COVID-19 patients

Lymphopenia during the COVID-19 infection: What it shows and what can be learned

Neutrophils in COVID-19

Reduction and Functional Exhaustion of T Cells in Patients With Coronavirus Disease 2019 (COVID-19)

Relationships among lymphocyte subsets, cytokines, and the pulmonary inflammation index in coronavirus (COVID-19) infected patients

Immunology of COVID-19: Current State of the Science

Infection of human lymphomononuclear cells by SARS-CoV-2. bioRxiv

T cell responses in patients with COVID-19

Distinct inflammatory profiles distinguish COVID-19 from influenza with limited contributions from cytokine storm

Rethinking interleukin-6 blockade for treatment of COVID-19

Cytokine Levels in Critically Ill Patients With COVID-19 and Other Conditions

Excessive matrix metalloproteinase-1 and hyperactivation of endothelial cells occurred in COVID-19 patients and were associated with the severity of COVID-19

Is a "Cytokine Storm" Relevant to COVID-19?

Warriors of SARS-CoV-2 Infection

Pathological study of the 2019 novel coronavirus disease (COVID-19) through postmortem core biopsies

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

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

COVID-19 severity correlates with airway epithelium-immune cell interactions identified by single-cell analysis

Soluble PD-L1: a potential immune marker for HIV-1 infection and virological failure

Multiple effects of CD40-CD40L axis in immunity against infection and cancer

Molecular mechanism and function of CD40/CD40L engagement in the immune system

CD40/CD40L and Related Signaling Pathways in Cardiovascular Health and Disease-The Pros and Cons for Cardioprotection

The emerging role of CD40 ligand in HIV infection

Role of CD40 ligand dysregulation in HIV-associated dysfunction of antigen-presenting cells

Contrasting Roles of the PD-1 Signaling Pathway in Dendritic Cell-Mediated Induction and Regulation of HIV-1-Specific Effector T Cell Functions

CD40 Agonist Antibodies in Cancer Immunotherapy

CD40 and autoimmunity: the dark side of a great activator

Targeting the CD40-CD40L pathway in autoimmune diseases: Humoral immunity and beyond

The CD40-CD40L Dyad in Experimental Autoimmune Encephalomyelitis and Multiple Sclerosis

HVEM/LIGHT/BTLA/CD160 cosignaling pathways as targets for immune regulation

HVEM, a cosignaling molecular switch, and its interactions with BTLA, CD160 and LIGHT

HVEM pathway: a bidirectional switch regulating T-cell activation

CD160 inhibits activation of human CD4+ T cells through interaction with herpesvirus entry mediator

Global statistics on addictive behaviours: 2014 status report

Alcohol: taking a population perspective

Practice Guideline Committee of the American Association for the Study of Liver, D. & Practice Parameters Committee of the American College of, G. Alcoholic liver disease

Alcohol consumption: monitoring, regulation and impact on public health

Health Warnings on Alcoholic Beverages: Perceptions of the Health Risks and Intentions towards Alcohol Consumption

WHO. HIV data and statistics. HIV/AIDS fact sheets

Veterans Aging Cohort Study Project, T. HIV/AIDS, comorbidity, and alcohol: can we make a difference?

Effects of alcohol and HIV infection on the central nervous system

Immune activation and neuroinflammation in alcohol use and HIV infection: evidence for shared mechanisms

Ethanol disrupts intestinal epithelial tight junction integrity through intracellular calcium-mediated Rho/ROCK activation

Activation of the innate immune system and alcoholic liver disease: effects of ethanol per se or enhanced intestinal translocation of bacterial toxins induced by ethanol?

Alcoholic liver disease: pathogenesis and new therapeutic targets

Impact of Alcohol Abuse on the Adaptive Immune System

Innate immunity in alcoholic liver disease

Molecular mechanisms of alcoholic liver disease: innate immunity and cytokines

Alcohol abstinence ameliorates the dysregulated immune profiles in patients with alcoholic hepatitis: A prospective observational study

Microbial translocation is a cause of systemic immune activation in chronic HIV infection

Intestinal microbiota, microbial translocation, and systemic inflammation in chronic HIV infection

The circulating microbiome signature and inferred functional metagenomics in alcoholic hepatitis

Quantity of alcohol drinking positively correlates with serum levels of endotoxin and markers of monocyte activation

Alcohol Abstinence Does Not Fully Reverse Abnormalities of Mucosal-Associated Invariant T Cells in the Blood of Patients With Alcoholic Hepatitis

The role of mucosal-associated invariant T cells in infectious diseases

MAIT cells: new guardians of the liver

Effects of Age, Sex, Body Weight, and Quantity of Alcohol Consumption on Occurrence and Severity of Alcoholic Hepatitis