CD27 and COVID-19: Furthermore, staining the PBMCs of the COVID-19 convalescents with MHC-I multimers revealed that SARS-CoV-2-specific CD8+ T cells had effector memory (CD45RA−CCR7−) or central memory (CD45RA−CCR7+) phenotypes with early (CD27+CD28+) or intermediate (CD27+CD28−) differentiation [27].