T-cell responses in COVID-19 survivors six to eight months after infection: a longitudinal cohort study in Pune
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The SARS-CoV-2 immune response is crucial for disease management, although diminishing immunity raises the possibility of reinfection. In matched samples collected at one month and six to eight months after infection, we examined the immunological response to SARS-CoV-2 in a group of convalescent critically ill COVID-19 patients. The PBMCs were isolated from enrolled study participants and flow cytometry analysis was done to assess the lymphocyte subsets of naive, effector, central memory, and effector memory CD4+ or CD8+ T cells in COVID-19 patients at one month and six to eight months after infection. Immunophenotypic characterization of immune cell subsets was performed on individuals who were followed longitudinally for one month (n=44) and up to 6-8 months (n=25) after recovery from COVID infection. We observed that CD4+ T cells in hospitalized SARS-CoV-2 patients tended to decrease, whereas CD8+ T cells steadily recovered after one month, while there was a sustained increase in the population of effector T cells and effector memory T cells. Furthermore, COVID-19 patients showed persistently low B cells and a small increase in the NK cell population. In conclusion, our findings show that T cell responses were maintained at 6-8 months after infection. This opens new pathways for further research into the long-term effects in COVID-19 immunopathogenesis.