CD4 and breast cancer: In vitro stimulation of peripheral blood mononuclear cells (PBMCs) with EVs from HV, TNBC, ER+HER2−, ER-HER2+, and ER+HER2+ groups demonstrated a general trend for an increase in the CD4+ T cell (Figure 3A) and a statistically significant decrease in CD8+ T cell (Figure 3B) populations of PBMCs when co-cultured with BC-derived serum EVs as compared to nonstimulated PBMCs.