Published online Mar 27, 2022. doi: 10.4331/wjbc.v13.i2.47
Peer-review started: November 6, 2021
First decision: December 27, 2021
Revised: December 28, 2021
Accepted: March 6, 2022
Article in press: March 6, 2022
Published online: March 27, 2022
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the coronavirus disease 2019 (COVID-19) pandemic, which was initiated in December 2019. COVID-19 is characterized by a low mortality rate (< 6%); however, this percentage is higher in elderly people and patients with underlying disorders. COVID-19 is characterized by mild to severe outcomes. Currently, several therapeutic strategies have been evaluated, such as the use of anti-viral drugs, prophylactic treatment, monoclonal antibodies, and vaccination. Advanced cellular therapies are also investigated, thus representing an additional therapeutic tool for clinicians. Mesenchymal stromal cells (MSCs), which are known for their immunoregulatory properties, may halt the induced cytokine release syndrome mediated by SARS-CoV-2, and can be considered as a potential stem cell therapy.
Currently, a great number of clinical trials, which include the intravenous infusion of MSCs in COVID-19 patients, are performed worldwide. Preliminary data of those studies are providing encouraging results regarding the application of MSCs for better management of COVID-19. However, the exact mechanisms by which MSCs exert their beneficial properties is not fully understand. Moreover, the majority of the currently performed studies are focusing primarily to the final outcome. In this study, an initial evaluation of the immunoregulatory properties of MSCs stimulated by COVID-19 patient serum was performed. The results of this study will provide significant insights into the role of MSCs as novel immunoregulatory players.
The main objective of this study was to evaluate the immunoregulatory properties of WJ and BM-MSCs, which may be used as a potential advanced cellular therapy against COVID-19. The secondary objectives were to determine any discrepancies between WJ- and BM-MSCs regarding the secretion of the immunoregulatory agents (such as cytokines and growth factors) and their ability to perform M2 phenotype switch of macrophages derived from COVID-19 patients.
Initially, WJ and BM-MSCs were isolated, expanded, and characterized according to the criteria provided by the ISCT. Then, stimulation of MSCs with a culture medium containing COVID-19 patient serum was performed. After 48 h, the COVID-19 culture medium was removed, and extensive washes of MSCs cultures were performed. Finally, new culture medium (without FBS) was added for another 48 h. Cytokine levels (IL-1Ra, IL-6, IL-10, and IL-13), growth factor levels (TGF-β1, FGF, VEGF, and PDGF), and the immunoregulatory molecule (IDO) were measured in the conditioned medium of stimulated MSCs. Also, using molecular and protein assays, the HLA-G isoforms (HLA-G1, G5, and G7) were determined. Finally, the ability of stimulated WJ and BM-MSCs to modulate the M2 macrophage phenotype was also investigated.
WJ and BM-MSCs were successfully expanded and characterized, before the performance of the stimulation experiments. MSCs from both sources exhibited a spindle-shaped morphology and successfully expressed CD73, CD90, CD105, CD29, and CD340, but did not express CD34 or CD45. Furthermore, MSCS were successfully differentiated to “osteocytes”, “chondrocytes”, and “adipocytes”, and therefore fulfilled the minimum criteria as defined by the ISCT. Then, the well-defined MSCs were stimulated with culture medium containing COVID-19 patient serum. Stimulated WJ and B-MSCs expressed increased levels of IL-1Ra, IL-6, IL-10, and IL-13 (P < 0.05) compared to unstimulated MSCs. Also, increased levels of TGF-β1, FGF, VEGF, and PDGF were observed in stimulated MSCs (from both sources) in comparison to the control group (P < 0.05). Co-culturing experiments of stimulated MSCs with macrophages obtained from COVID-19 patients showed the successful switch towards the M2 phenotype. Interestingly, M2 macrophages were characterized by high levels of CD206 and CD29 and low level of CD80, while CD11b was stable expressed.
MSCs were successfully activated by COVID-19 patient serum and secreted anti-inflammatory cytokines and growth factors, in response towards to the initial stimuli. It has been shown that this specific set of anti-inflammatory cytokines and growth factors can efficiently modulate the overactivated immune responses in a paracrine manner. In this way, the “cytokine storm” may be halted in critically ill COVID-19 patients. Besides that, MSCs can exert key regenerative properties and thus can reverse the lung alveolar damage. This study provided evidence regarding the beneficial application of MSCs in immune-related disorders such as COVID-19.
The next step of this study will be focused on performing more experiments under both in vitro and in vivo conditions. Specifically, the RNA-seq and proteomic analysis in unstimulated and stimulated WJ and BM-MSCs will provide further evidence regarding the differentially expressed proteins. Furthermore, the infusion of stimulated MSCs in animal models exhibiting acute respiratory distress syndrome will provide significant data for their immunoregulatory properties. To this direction, well-defined MSCs may represent an additional therapeutic tool for critically ill COVID-19 patients.