PDCD1 and cancer: Prior studies have demonstrated the importance of stem-like T cells in the anti-PD-1/L1 stimulated response to chronic viral infections and cancer.10,11 Additionally, our group and others have shown that the tumor-draining lymph node (TdLN) is an important reservoir for stem-like T cells which supply the tumor.21,22,25,26 Tumor antigen specific cells are primarily found in the TdLN rather than the non-TdLN or other secondary lymphoid organs like the spleen (Figure S2A).