Effects of BCR-ABL inhibitors on anti-tumor immunity

In chronic myeloid leukemia (CML), BCR-ABL-mediated oncogenic signaling can be successfully targeted with the BCRABL- inhibitors imatinib, nilotinib, and dasatinib leading to complete cytogenetic (Philadelphia chromosome not detectable upon cytogenetic testing of bone marrow) and even complete molecular (BCR-ABL not detectable by PCR in peripheral blood) responses. However, CML apparently can not be cured by BCR-ABL inhibitors alone, likely due to treatment-resistance of CML stem/progenitor cells, which provokes a relapse of disease after cessation of therapy. Evidence from patients treated with allogenic stem cell transplantation or IFN-α points to an important role of anti-tumor immunity for durable control of CML disease. Data from multiple in vitro and ex vivo studies indicate that BCR-ABL inhibitors may also influence anti-tumor immunity. Varying effects on different immune effector cell subsets and of the different compounds have been reported, the latter being due to their particular and diverse potency and spectrum of target kinases. As multiple approaches presently aim to combine BCR-ABL inhibition with immunotherapeutic strategies to improve disease control in CML, immunomodulatory effects of the available BCR-ABL inhibitors may be of direct clinical relevance. Here we review the available data regarding the effects of imatinib, nilotinib, and dasatinib on dendritic cells, T cells and natural killer cells as important cellular components of anti-tumor immunity.