PDCD1 and acute myeloid leukemia: Notably, when co-cultured with recombinant human PD-L1, PD-1-positive CD71+ red lineage progenitor cells and PD-1-positive CD34+ hematopoietic stem progenitor cells (HSPCs) activate caspase-3 in myelodysplastic syndromes (MDS)-pre-AML lesions, resulting in apoptosis and ineffective hematopoiesis (58).