key: cord-264646-d7qexyav authors: Raza, Syed Shadab; Khan, Mohsin Ali title: Mesenchymal Stem Cells: A new front emerge in COVID19 treatment: Mesenchymal Stem Cells therapy for SARS-CoV2 viral infection date: 2020-07-15 journal: Cytotherapy DOI: 10.1016/j.jcyt.2020.07.002 sha: doc_id: 264646 cord_uid: d7qexyav Currently, treating coronavirus disease 2019 (COVID19) patients, particularly those afflicted with severe pneumonia, is challenging, as no effective pharmacotherapy for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) exists. Severe pneumonia is recognized as a clinical syndrome, characterized by hyper induction of proinflammatory cytokine production, which can induce organ damage followed by edema, dysfunction of air exchange, acute respiratory distress syndrome, acute cardiac injury, secondary infection, and increased mortality. Owing to the immunoregulatory and differentiation potential of mesenchymal stem cells (MSCs), we aimed to outline current insights into the clinical application of MSCs in the patients of COVID19. Based on results from preliminary clinical investigations, one predicts that MSCs therapy for SARS-CoV-2 infected patients is safe and effective although multiple clinical trials with a protracted follow-up will be necessary to determine the long term effects of the treatment on COVID19 patients. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has garnered global attention as the causative agent for the coronavirus disease 2019 (COVID19) pandemic and its associated morbidity and mortality worldwide. As of today, approximately 6.9 million confirmed cases of COVID19 have been reported in more than 213 countries and territories with an estimated 53,000 critically ill and 4,02,000 deaths (https://www.worldometers.info/coronavirus/). First detected in a cluster of patients with pneumonia of unknown cause in the city of Wuhan, China, in December 2019, within two months the outbreak was declared a public health emergency of international concern by the World Health Organization (WHO). Clinical data suggest that the elderly and people with chronic underlying health issues are more prone to SAR-CoV-2 associated illness and death than young individuals. Currently, there is no specific antiviral treatment or effective vaccines available for COVID19. The available therapies include non-specific anti-viral, antibiotics to treat bacterial infections and sepsis, and corticosteroids to lower inflammation. However, these measures fail in patients with severe disease, which is characterized by a cytokine storm. The clinical manifestations of viral infection especially SARS, include mild prodrome of fever and myalgias lasting 3-7 days, during which viral replication occurs. Cough, respiratory symptoms, dyspnea, and hypoxemia are the common appearances during the second week of the illness. Finally, dyspnea may progress to respiratory failure, progressive pneumonia, and ARDS. Interestingly, clinical worsening occurs during the time of decreasing viral load [1] , and in several cases, the cause for the determination seems to be immunopathologic injury rather than direct injury from the virus [2] . Identifying the SARS-CoV-2 virus receptor recognition mechanism, which regulates its virulence and pathogenesis, holds the key to tackle the COVID19 epidemic [3] . The pathogenesis of SARS-CoV-2 depends on the recognition and engagement of SARS-CoV receptor angiotensin I converting enzyme 2 receptor (ACE2) as an entry receptor and the serine protease transmembrane protease, serine 2 (TMPRSS2) for S protein priming [4] . The efficiency of ACE2 usage was found to be a vital factor for SARS-CoV-surface, especially the Alveolar Type II cells (AT2) of the lungs and capillary endothelial cells [6] . It has been reported that usually over-activated immune system of infected patients kills the virus thereby releasing inflammatory mediators resulting in a cytokine storm, with elevated levels of multiple proinflammatory cytokines that cause edema, persistent pain and pressure in the chest, shortness of breath, acute respiratory distress, secondary bacterial infection and increased mortality [7] . Interestingly, consistent absence of ACE2 in immune cells such as T and B-lymphocytes, and macrophages in bone marrow, lymph nodes, thymus, and spleen [8] , suggests that immunological therapy could be a potential therapeutic option for infected patients. Considering the seriousness of this deadly pandemic and its impact on the global economy there is an urgent need to develop effective therapies against COVID19. Herein, we proposed Mesenchymal Stem Cells (MSCs) as a possible therapeutic candidate against the SARS-CoV-2 infection. MSCs are an attractive approach for treating both acute and chronic lung pathological conditions like COVID19, mainly because these cells offer multiple protective mechanisms to defend and repair pulmonary damage. Further, MSCs exhibit broad immune regulatory function, which makes them suitable for anti-viral therapy as safety and effectiveness of these cells have been documented in clinical trials of severe lung infections [9, 10, 11] . Results of preliminary investigations on SARS-CoV-2 infected patients treated with MSCs have revealed a noteworthy reversal of pathological symptoms, further indicating the potential of MSCs in lung infection [7, 12] . To date, one clinical case study and a single center open-label pilot investigation have been reported on COVID19 patients employing MSCs as a therapy [7, 12] . Apart from the above-published preliminary studies, forty-one clinical trials that employ MSC-based therapies have been approved (including seven withdrawn) and are summarized in Table 1 . Results from these trails are expected to shed light on the pathophysiology of the disease, and the interventions offered by MSCs post-treatment. Here, briefly, we have summarized the outcome of the two papers published from China. The first study was a case report [12] , in which a critically ill 65-year-old female with severe pneumonia, respiratory failure, moderate anemia, hypertension, and multiple organ failure received three infusions of umbilical cord MSCs (UCMSCs, 5X10 7 cells/infusion), three days apart. Before receiving UCMSCs, the clinical laboratory examination showed an abnormal percentage of white blood cells, neutrophils and lymphocytes in peripheral blood and the patient received antiviral therapy. During cell therapy, antibiotic was given to manage the bacterial infection, and to modulate the immune system thymosin α1 was injected. Twenty-four hours after the second UCMSCs administration, serum bilirubin, CRP, (AST)/(ALT) and other vital signs began to get stabilized and therefore, the patient no longer required mechanical ventilation. After receiving the second cell infusion, the white blood cell, neutrophil and lymphocyte counts together with T subsets returned to normal levels. Two days after the third injection the patient tested negative for SARS-CoV-2. Consecutive CT scanning pre and post cell administration revealed that pneumonia had resolved. Further, from the first day of UCMSCs infusion till the third day no side effects were observed, signifying the cells were well tolerated. Another study by Leng et al., 2020 reported that the intravenous administration of clinical-grade human MSCs in SARS-CoV-2 infected patients resulted in improved clinical outcomes [7] . In this study seven patients (one critically severe, four severe, and two having common symptoms of pneumonia) were enrolled in the treatment group and three patients served as placebo controls (all displaying severe symptoms). All treated patients received a single dose of 1X10 6 MSCs/kg body weight and remarkably all seven showed improvement over a period of two weeks with no noticeable adverse effect. However, within the control group, just one showed improvement, one exhibited ARDS symptoms, and the other died. The overall improvement in the MSCs infused group was striking as within 2 days after treatment pulmonary functions and symptoms of all the seven patients significantly improved, and most tested negative for the SARS-CoV-2 nucleic acid test over two weeks after MSCs infusion. After 6 days of treatment, the cellular immune response showed an elevated peripheral lymphocyte count, decline in C-reactive protein, and the disappearance of activated CXCR3 + CD4 + T cells, CXCR3 + CD8 + T cells, and CXCR3 + natural killer cells (NK cells). As expected, the number of CD14 + CD11c + CD11b mid regulatory DC cells also returned to normal, levels of the pro-inflammatory cytokine TNF-α was decreased, and the ratio of chemokine IL-10 increased significantly in the MSCs treatment group compared to the placebo control group. Furthermore, the gene expression profile showed that MSCs did not express ACE2 and TMPRSS2 indicating they were free from COVID-19 infection. Finally, the RNA sequencing and gene expression analysis showed that MSCs were closely involved in the anti-viral pathways, and had anti-inflammatory trophic activities [7] . While both of the above studies have provided new insights into the protective mechanism of MSCs during viral infection, a few shortcomings in these treatments, however, could be noticed. For example, severity and mortality largely correspond to age, and therefore it looks curious to have old patients in the placebo group in the study by Leng et al. Further, there is a lack of information on MSCs processing and screening before infusion, and also the long-term follow-up of patients is missing in both of the abovecited studies. For a protocol to be implicated in a larger cohort, optimal information regarding MSCs as well as patients needs to be investigated in a rationally designed controlled setting. To understand lung pathophysiology associated with SARS-CoV-2 infection it is important to recognize the behavior of the virus within the host (humans). Clinically, the immune reaction induced by SARS-CoV-2 infection has two-stages: i) the immune protective phase (Incubation phase) and ii) Inflammation-driven damage phase (Severe phase) [13] . During non-severe stages, a particular adaptive immune response is required to remove the virus and to prevent disease progression to severe stages. However, when a protective immune response is impaired, the virus will spread, thus, enormous destruction of not just lung but all ACE2 expressing tissues is imminent. The damaged cells will induce innate inflammation that is largely mediated by proinflammatory macrophages and granulocytes [13] . As MSCs can immunomodulate cells from both the innate and adaptive immune systems [14, 15, 16, 17] , MSCs could offer a new therapeutic approach to COVID19 patients. However, a major concern is when to initiate MSCs treatment. An argument can be made for stratifying patients based on disease severity and focusing specifically on those that present with a cytokine storm and require ventilation [18] . Interestingly, in a recent study, displaying results from the responder vs. non-responder towards MSC treatment in GvHD, based on the results obtained, the authors argued that the severity of the disease could help stratify the patients for MSC treatment [19] . Anyhow, the existing pre-clinical data [20] and that from clinical trials in non-viral ARDS patients support the use of MSCs in moderate or mild disease although this remains disputable [21] . However, because of the limited understanding of the pathogenesis of COVID-19, an optimal approach for administration of MSC-based therapies has yet to be established. The cytokine storm is a systematic inflammatory response associated with a variety of broader allocations in humans [7] , and possibly this may explain why some COVID19 patients present with multiple complications. In these cases, MSCs with the potential for broad in vivo distribution may be applied. Additionally, combination therapies may be explored to enhance the MSCs effect in vivo. For example, the combinational of the sphingosine 1 phosphate analog FTY720 and UCMSC attenuates acute lung injury and affords better survival in mice that each monotherapy [60] . Similarly, combining adipose-derived mesenchymal stem cells with pre-activated, disaggregated shapechanged platelets provides more protection to the rat lung from acute respiratory distress syndrome (ARDS) complicated by sepsis [61] . Nebulized Heparin along with MSCs inhibits coagulation and inflammatory pathways and modulates alveolar macrophages [62]. All the above-enlisted approaches seem advantageous, but whether they apply to COVID19 remains to be determined. The pandemic outbreak of COVID19 is rapidly spreading all over the world posing great health and economic challenges. So far available data suggest that the most vulnerable to infection are people age 65 or older and those with existing serious health issues [63] . In severely affected patients, lung inflammation is characterized by invasion of neutrophils and macrophages into the alveolar space, which together with overactivated pro-inflammatory cytokines results in impairment to the lung endothelial and epithelial [26] . In the absence of any specific therapies, the best way to manage COVID19 currently is to reduce the infection rate and mortality rate. Thus, there"s a pressing need for the treatments that are effective in treating infection-induced cytokine storm, which is associated with increased mortality, but also prevent damage that may killing [71] , suggesting their anti-bacterial potential. MSCs also can transfer mitochondria and microvesicles that modulate immunity and epithelial response to injury [72] . These data, coupled with the fact that MSCs can be readily procured in large numbers from various tissue including adipose tissue, cord blood, liver, placenta and dental pulp [73] makes them an excellent candidate for cell therapy. Accumulating evidence suggests that a subgroup of patients with severe COVID19 shows signs of cytokine storm syndrome [26] . The virally induced cytokine storm has been linked to uncontrolled pro-inflammatory responses that persuade significant pulmonary immunopathology. Thus, understanding the inter-relationship of the events between incubation and severe phases of the disease progression holds the key for therapeutic interventions. The plasma level of COVID19 patients showed a higher level of IL-6, IL-10, TNF-α, IL-2, IL-7, IL-10, GCSF, MCP-1, MIP-1α, and TNF-α [26], an indication of uncontrolled systematic cytokine storm, which was reportedly attenuated by treatment with MSCs [7] although the mechanism remains unclear. As in hyperinflammation, the immunosuppressive measures are likely to be beneficial, thus, MSCs may exert effect through inhibiting the pro-inflammatory cytokines by the virtue of its immunosuppressive potential [7] . Further, by making direct cell-to-cell contact with immune cells or by secretion of a range of anti-inflammatory factors, MSCs can target immune cells and affect their function. Moreover, MSCs expresses several cell adhesion molecules like ICAM-1 and VCAM-1 to attract activated immune cells [74] thereby increasing their exposure to anti-inflammatory signals from MSCs. Further, IL-6 is a vital initiator of an uncontrolled cytokine storm [75] , and is also a significant correlate in severe patients of COVID19 [76] . Previous studies indicated that MSCs have significantly inhibited cytokine storm by inhibiting the overproduction of the IL-6 [77] . Thus, it is reasonable to assume that to some extent MSCs may suppress the activated cytokines by suppressing the activation of IL-6 production. In any case, blocking IL-6 could also be an effective strategy. Licensing-approach is another robust The authors declare no conflicts of interest. SSR designed, drafted and edited the manuscript. MAK reviewed the manuscript. Both authors have approved the final article. 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