Tumor-infiltrating PD-L1+ T cells have diverse immunosuppressive effects within the TME through both inhibitory PD-L1 signaling into CD4+ and CD8+ T cells and PD-1 engagement on other tumor-infiltrating immune cells.55 We found that splenic CD4+ (Figure 2E) but not CD8+ T cell (Figure 2F) subsets in aged versus young had higher PD-L1 expression prevalence, whereas PD-L2 expression prevalence and MFI (Figure S1D) were similar. Here, CD274 is linked to neoplasm.