IL21 and neoplasm: We next investigated the effect of distinct TIL culture conditions on the expansion of tumor-reactive T cells, including concentration of IL-2 (stimulates expansion of both conventional T cells and Treg), and presence of IL-21 (plays a key role in the development and maintenance of memory CD8+ T cells, inhibits Treg proliferation), anti-PD-1 antibody (blocks inhibitory interaction of T cells’ PD-1 with PD-L1), and IFNγ (activates antigen presentation and supports type 1 immune response).