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.

Angiotensin-Converting Enzyme 2 (ACE2) is cell surface receptor responsible for SARS-CoV-2 entry highly expressed in maternal-fetal interface including placenta cells e.g. stromal cells, prevascular cells of deciduas, cytotrophoblast, syncytotrophoblast. Several studies reported lack of transplacental transmission of SARS-CoV-2 from a COVID-19 positive mother to fetus suggests that the SARS-CoV-2 may not be transmitted from mother to her child due to some placenta barriers but may be replicating inside the placenta. Our earlier studies demonstrated that human placenta organ culture supports the replication of Japanese Encephalitis(JE) virus indicating their susceptibility and possibility to support propagation of other viruses. Based on our previous experience and present work, we propose that human Placental organ culture will be an ideal in vitro model for propagation of COVID-19 as it has the requisite receptors and tissue architecture needed for virus replication and vaccine development.