While down-regulation in the fraction of IL-4-positive within BTLA-positive CLL T cells may suggest sustained T cell inhibition mediated by BTLA, substantially elevated levels of IL-4 in these cells strengthen the assumption regarding BTLA dysfunction in CLL T cells manifested by the ineffective inhibition of T cell proliferative capacity and IL-4 cytokine secretion. This evidence concerns the gene BTLA and B-cell chronic lymphocytic leukemia.