Recent evidence shows PD-1 expression on CD4+ and CD8+ T-cells, including on CML-reactive PR1-CTL in TKI-naive but also TKI-treated remission CML patients (124–126), which suggests T-cell exhaustion also in deep molecular remission, this provides a rationale for the treatment with checkpoint blocking antibodies to PD-1/PD-L1. This evidence concerns the gene PDCD1 and chronic myelogenous leukemia, BCR-ABL1 positive.