To begin to evaluate whether Tregs in breast tumors are mainly recruited from peripheral blood (PB) or converted in situ from other CD4+ lymphocyte subtypes, we isolated Tregs (CD4+CD25+CD127−/low), naive CD4+ T cells (CD4+CD45RA+CD25−) and memory CD4+ T cells (CD4+CD45RO+CD25−) from breast cancers (tumor infiltrating, TI), PB and ipsilateral draining lymph nodes (LN) of 5 breast cancer patients and used next-generation sequencing to compare their TCR-β/α repertoires (Figure 1A). Here, CD4 is linked to breast cancer.