PDCD1 and B-cell chronic lymphocytic leukemia: Ibrutinib, a Bruton's tyrosine kinase inhibitor, was shown to down-regulate PD-L1 expression on tumor cells and PD1 in CD4+ and CD8+ T cells via inhibition of STAT3 and also decreased IL-10 production by chronic lymphocytic leukemia (CLL) cells in patients (69).