CD4 and medical procedure: As the percentage of CD25+FOXP3+ cells within the CD4+ subpopulation was reduced in kidney transplant patients (Figure S2 in Supplementary Material), for the suppression assays a gate was set to sort Tregs containing >85% of CD4+CD25hiFOXP3+ T cells similar to the control group (CD4+CD25veryhi gate, Figure S3A in Supplementary Material).