PDCD1 and neoplasm: Further analysis of these CD8+ T-cells revealed that there were reduced terminally-differentiated PD-1+CD44+Tim3+TCF1−CD8+ T-cells but significantly increased stem-like PD-1+CD44+Tim3−TCF1+CD8+ T-cells [41] in the tumor of Prdm1fl/flFoxp3YFP-Cre mice compared to WT mice (Additional file 12d).