Moreover, in chronic myeloid leukemia (CML), while the EURO-SKI trial sub-analysis focused on P-gp (ABCB1) expression in peripheral blood leukocytes as a predictor for treatment-free remission after TKI discontinuation, the baseline P-gp expression levels on T cells and NK cells might also influence the initial immune response to the leukemia and potentially the long-term success of TKI therapy, even if not directly an ‘immunotherapy’ in the classic sense [75]. This evidence concerns the gene PGP and leukemia.