CD27 and COVID-19: The analysis of T-helper differentiation in peripheral blood revealed a relative loss of ‘naïve’ CD4 T cells (with CD45RA+CD27+CCR7+CD95− phenotype) but a significant increase in the amount of EM2 (CD45RA−CD27−CCR7+) and EMRA (CD45RA+CD27−CCR7−) cells in COVID-19 patients compared to controls [57].