Imatinib mesylate, a potent and selective inhibitor of the BCR-ABL tyrosine kinase, has been shown to induce durable haematological and major cytogenetic responses in a high percentage of CML patients. However in most patients the disease recurs, when imatinib is discontinued. In contrast, allogeneic stem cell transplantation (ASCT) is considered to be curative by the immune effect of donor T cells against CML progenitor cells. In this context, the role of imatinib is controversial; it may improve the results of ASCT by reducing the tumour load, it may also reduce the effect of donor lymphocyte transfusions (DLT) by impairing the function of T cells and the capacity of myeloid cells to present antigen. Patient derived CML-cells were studied for the stimulation of allogeneic HLA-matched and mismatched T-cells in the presence and absence of imatinib. In a 5 day culture the proliferative response of HLA-mismatched T cells was evaluated in presence of different concentrations of imatinib (0, 1, 2, or 5 micro M) and various responder-to-stimulator ratios. Thereby, proliferation was detected via a CFDA based assays and the activation profile (CD25, CD69) of the T-cells was determined by FACS. Cr51-release assays were performed after a 7 day culture of CML cells with HLA-matched T cells to test cytotoxicity of CD8+ T-cells. In addition, we characterized the antigen-presenting profile (CD14, CD33, HLA-DR, CD40, CD80, CD86, CD54, CD58) of the CML cells over a 5 day culture with and without imatinib. The presence of imatinib inhibited the proliferative capacity of allogeneic T-cells in a dose-dependent manner. Also, the expression of T cell activation markers was reduced in the presence of the different imatinib concentrations. Preincubation of CML cells with imatinib for 48 hours strengthened the effect on proliferation and activation of T cells. Moreover, imatinib impaired the cytotoxic function of T-cell (HLA-matched setting; CR51-release assay) also in a dose-dependent manner. Finally, the antigen-presenting profile of the myeloid leukemia cells was down regulated by increasing concentrations of imatinib. In summary, imatinib may interfere with the T cellular immune response and the antigen presenting profile on the CML cells in vitro. These results may have an impact on new strategies of treatment of CML with immunotherapy.
Disclosure:Research Funding: Novartis.