Leukemic cells stimulate naive T cells and induce Th2 polarization.

CD45RA⁺CD4⁺ allogeneic naive T-lymphocyte response to increasing numbers of irradiated leukemic cells or mo-DCs was measured after a 6-day MLC by 18-hour [³H]thymidine incorporation (upper panels). Fresh tumor cells (closed diamonds) were capable (CAT) or not (GEN and GUE) of stimulating naive CD4⁺ T-lymphocyte proliferation. Conversely, in all 5 cases analyzed, the day-6 IL-3–cultured tumor cells (open squares) were able to activate the proliferation of allogeneic naive T cells, with the same potency as mo-DCs (stars). IFN-γ and IL-4 production in T cells primed by stimulation with IL-3–cultured leukemic pDCs or mo-DCs was analyzed by flow cytometry (lower panels). The percentages of IL-4– or IFN-γ–producing cells are indicated in the plots and show the Th2 polarizing capacity of leukemic DCs, whereas mo-DCs induced a Th1 polarization.