Dendritic cells pulsed with leukemia blasts elicit jw vitro potent anti-leukemia cytotoxic t-cell response in patients given allogeneic bone marrow transplantation and in their donors

The success of adoptive immunotherapy for treatment of leukemia depends on the generation of T cells that can specifically react with malignant cells. Dendritic cells (DCs) are the most effective antigen-presenting cells for development of T-cell responses. In this study, we analysed the antileukemia activity generated by pulsing DCs with leukemia blasts (LB) of 4 children with acute myeloid leukemia (AML). Briefly, LB-pulsed DCs, generated from PBL of bone marrow donors through stimulation with GM-CSF and IL-4. were used, together with rIL-7 and rIL-12, to elicit in vitro leukemia-specific CDS T cell response. Effector cells were either CD4-dep!eted PBL of the 4 patients given allogeneic BMT or CD4-depleted PBL and bone marrow cells (BMC) of their donors. Autologous irradiated CD4-enriched lymphocytes were also added to the cultures. Cultures were restimulated every week, using autologous irradiated adherent PBL and patients'irradiated LB. We found that, in all bulk cultures tested, after the second restimulation, effector cells displayed a sizeable cytotoxic activity towards autologous LB (range 20-50% at an effector target ratio of 10:1), but very low or absent reactivity against patient normal BMC or PHA-blasts. Notably, cytotoxic activity was maintained or augmented through repeated re-stimulations and effector cells showed a variable, but continuous expansion. Phenotypic analysis demonstrate that the majority of effector cells both in PBL and BMC were CD3+ (range 80-97%)/CD8+ (range 73-88%) lymphocytes. CD4+ lymphocytes were always less the 10%. In some samples, expansion of 78+ cells was observed. Cryopreservation of effector cells did not affect their cytotoxic activity. Further experiments are in progress in order to better characterise this cell population. Altogether, these results demonstrate that CTL directed against LB can be elicited and expanded not only in the PBL of transplanted patients, but also in BMC and PBL of their donors. Since these CTL display a negligible reactivity against host normal cells, our results seem to suggest a possible application of this approach in protocols of adoptive immunotherapy in patients with AML.