Interferon Gamma (IFNγ) Interferes with the Effects of Tyrosine Kinase Inhibitors (TKI) In CML Cells.

Chronic myeloid leukemia (CML) is a myeloproliferative disease which resolves in the constitutive activity of the BCR-ABL protein. Since the introduction of imatinib as first line therapy for CML, the overall survival of patients could be significantly extended. However, mutations of the BCR-ABL protein and environmental effects mediated by adhesion molecules, cytokines and growth factors were shown to induce resistance to TKIs. For the development of immunotherapeutic approaches that combine TKIs with vaccination strategies or donor lymphocyte infusions it is important to understand the mechanisms of possible interactions and inhibition. Therefore, we thought to determine the role of activated T cells and to analyze a possible antiapoptotic effect of released IFNγ on the CML cells.

CML cell lines and primary cells from patients with CML were treated with imatinib or nilotinib and incubated with activated (PMA/ionomycin) or resting T cells in transwell experiments. Induction of apoptosis was analyzed by flow cytometry. In addition, IFNγ was used together with TKIs and apoptotic cell death and proliferation was determined. Immunoblotting was performed to analyze the involved pathways.

Incubation of CML cells in transwell assays with activated but not resting T lymphocytes resulted in significant inhibition of the apoptosis induction by imatinib and nilotinib. To further determine the mechanisms mediating these effects, CML cells were treated with IFNγ in addition to the TKIs. In line with the results from previous experiments, IFNγ reduced the rate of cell death and proliferation inhibition mediated by imatinib and nilotinib. Interestingly, in contrast to IFNα, IFNγ inhibited the TKIs induced downregulation of MHC-class I molecules on CML cells. In line with these results, Western blot analysis of K-562 cells incubated with imatinib or nilotinib showed an increased caspase-3 activation and PARP cleavage as well as reduced down regulation of anti-apoptotic molecules such as xIAP as compared to IFNγ treated cells. Furthermore, we observed a diminished TKI induced downregulation of Jak-2 and STAT-5 phosphorylation as well as increased nuclear expression of RUNX-1 in cells treated with IFNγ.

Our results demonstrate that IFNγ released by activated T-cells can interfere with the action of TKIs in CML patients and might have important implications in the development of immunotherapeutic approaches.

No relevant conflicts of interest to declare.