CD8A and infection: During the COVID-19 pandemic, a large body of studies using scRNA-seq of PBMCs had revealed detailed changes in gene expression in different immune cell subtypes including different types of T and B cells, NK cells, monocytes, dendritic cells, etc. during and after infection, results from which indicated greatly reduced CD4+ and CD8+ T-cell numbers and T-cell exhaustion upon SARS-CoV-2 infection.