CD38 and COVID-19: In the acute phase of COVID-19, SARS-CoV-2-specific MHC-I multimer+CD8+ T cells express activation markers (CD38 and HLA-DR), Ki-67, IRs (PD-1, TIM-3, and LAG-3), and cytotoxic proteins (perforin and granzyme B), indicating that these cells are activated and proliferate with a high cytotoxic capacity [16].