Immunoprofiling of patients with chronic myeloid leukemia at diagnosis and during tyrosine kinase inhibitor therapy

Tyrosine kinase inhibitors (TKIs) are the current standard treatment in chronic myeloid leukemia (CML). In addition to the BCR-ABL target oncoprotein, they also inhibit off-target kinases (e.g. c-KIT, TEC, SRC), some of which have physiological functions in immune responses. In vitro studies have implied immunosuppressive effects of TKI treatment. As comprehensive in vivo data are missing, we aimed at analyzing the detailed immunoprofile of patients with CML at diagnosis and during therapy. We collected 88 peripheral blood (PB) and 73 bone marrow (BM) samples from 54 patients with CML at diagnosis, during imatinib and dasatinib therapies. Leukocytes and lymphocyte subclasses were analyzed with an extensive flow cytometry panel including markers for activation, differentiation and memory status. At diagnosis, a lower proportion of B cells and dendritic cells and an increased amount of NKT-like cells were detected in the BM. During imatinib therapy, all these changes normalized and the immunoprofile resembled healthy controls. However, dasatinib patients were clearly divided into two distinct groups: one similar to healthy controls and the other showing immunoactivation characterized by significant elevations of CD8+, NK- and NKT-like cells in PB. T cells of the latter group strongly expressed CD57+, HLA-DR and CD45RO and had low CD62L antigen levels characteristic of late memory cytotoxic lymphocytes. Our results indicate that while both TKIs show immunosuppressive effects in vitro, they have a significant and differential effect on the numbers and proportions of immune effector cells in vivo. In particular, in a distinct subgroup of dasatinib-treated patients, immune reactivity is markedly enhanced warranting careful follow-up.