Abstract
AIM: To clarify the immune cellular changes in critically ill patients recovering from coronavirus disease 2019 (COVID-19). METHODS: The immune response of peripheral blood mononuclear cells from patients with severe COVID-19 in different stages of recovery (3, 6, and 12 months from hospitalization) was evaluated by single-cell mass cytometry. Immunological changes in patients were compared with those in age-matched healthy donors. RESULTS: Three patients with severe COVID-19 were compared with four healthy donors. In the patients, there was an increase in the cell density of CD4- and CD8-positive T lymphocytes, and B cells, over the course of the recovery period. CD4- and CD8-positive T lymphocytes expressing T-bet and granzyme B (Gzm B) in patients were abundant during all recovery periods. The level of regulatory T cells remained high throughout the year. The levels of natural killer (NK) cells in patients were higher than in those in the healthy donors, and the frequency of CD16(+) NK cells expressing Gzm B increased throughout the year. CONCLUSION: Patients recovering from severe COVID-19 showed persistence of cytotoxic lymphocytes, NK cells, and regulatory T cells throughout the posthospitalization year of recovery.