PDCD1 and neoplasm: Several studies in pre-clinical mouse models have indicated the critical role of the CXCR5/TCF1+ subset of CD8+ T cells in sustaining a prolonged response to ICB immunotherapy.213–217 Studies have demonstrated stem cell-like properties in these cells, characterized by lower expression levels of inhibitory checkpoint molecules such as PD-1, LAG3, TIM-3, and 2B4, and potent self-renewal capacity in the tumor niche.