Imatinib mesylate minimally affects bcr-abl+ and normal monocyte-derived dendritic cells but strongly inhibits T cell expansion despite reciprocal dendritic cell-T cell activation

In chronic myeloid leukemia, bcr-abl(+) monocytes provide a unique opportunity to generate dendritic cells (DC) expressing a broad spectrum of leukemic antigens, and bcr-abl(+) DC vaccines may allow immunological eradication of leukemic cells persisting under treatment with the tyrosine kinase inhibitor imatinib. However, the efficiency of bcr-abl(+) DC vaccines will critically depend on the absence of deleterious effects of bcr-abl and of imatinib on DC functions. We show that ber-abl(+) monocytes, devoid of contamination of CD14(low) granulocytic precursors, differentiate into DC with typical immunophenotypical and functional features, and bcr-abl transcription decreases simultaneously. During differentiation, imatinib induces a slight increase of DC apoptosis and prevents CD1a up-regulation in a dose-dependent manner in ber-abl(+) and normal monocyte-derived DC, but at most, 25% of DC fail to acquire CD1a. When DC maturation is induced in the presence of imatinib, ber-abl(+) and normal monocyte-derived DC up-regulate major histocompatibility complex and costimulatory molecules, CC chemokine receptor 7 and CD83. However, secretion of interleukin-12p70 is decreased in a dose-dependent manner. Imatinib exposure of bcr-abl(+) and normal monocyte-derived DC during differentiation and maturation is not detrimental to T cell immunostimulatory functions of DC. In sharp contrast, imatinib, when added to DC-T cell cultures, profoundly suppresses DG-mediated T cell proliferation, despite reciprocal DC-T cell activation attested by up-regulation of CD25 on T cells and of CD86 on DC. Our findings demonstrate that T cells, not normal or bcr-abl(+) monocyte-derived DC, are major targets for imatinib immunomodulatory effects. It can be envisioned already that imatinib-free windows will be required to enable vaccination-induced, leukemia-specific T cell expansion.