CD4 and breast cancer: Figure 1 shows a representative strategy for flow cytometric immunophenotyping of CD3+CD4+CXCR5+CD25− TFH and CD3+CD4+CXCR5+CD25+ follicular regulatory T (TFR) TIL in fresh BC tissue. Furthermore, the active state of these specialized CD4+ T cell subpopulations can be achieved using PD-1 and ICOS expression levels to identify functional PD-1hiICOSint TFH and functional PD-1intICOShi TFR TIL (Shi et al., 2018; Xing et al., 2020; Noël G., in press).