CD4 and peripheral arterial disease: In this study, we report, perhaps, the most comprehensive phenotypic analysis of various subpopulations of CD4+ T cells, CD8+ T cells, TFH cells, B cells, and CD4Treg, CD8Treg, TFR, and Breg in PAD patients following two doses of the mRNA SARS-CoV-2 vaccine and changes in these subsets in a small number of CVID patients before and following the 1st dose and 2nd dose of the SARS-CoV-2 vaccination.