The quality and quantity of leukemia-derived dendritic cells from patients with acute myeloid leukemia and myelodysplastic syndrome are a predictive factor for the lytic potential of dendritic cells-primed leukemia-specific T cells.

Adoptive immunotherapy is an important therapy option to reduce relapse rates after stem-cell transplantation in patients suffering from acute myeloid leukemia and myelodysplastic syndromes. Myeloid leukemic cells can regularly be induced to differentiate into leukemia-derived dendritic cells (DC(leu)), regaining the stimulatory capacity of professional dendritic cells (DCs) while presenting the known/unknown leukemic antigen repertoire. So far, induced antileukemic T-cell responses are variable or even mediate opposite effects. To further elicit DC/DC(leu)-induced T-cell-response patterns, we generated DC from 17 Acute myeloid leukemia (AML) and 2 myelodysplastic syndrome cases and carried out flowcytometry and (functional) nonradioactive fluorolysis assays before/after mixed lymphocyte cultures of matched (allogeneic) donor T cells (n=6), T cells prepared at relapse after stem-cell transplantation (n=4) or (autologous) patients' T cells (n=7) with blast containing mononuclear cells ("MNC") or DC(leu) ("DC"). Compared with "MNC", "DC" were better mediators of antileukemic-activity, although not in every case effective. We could define DC subtypes and cut-off proportions of DC subtypes/qualities (mature DC/DC(leu)) after "DC" priming, which were predictive for an antileukemic activity of primed T cells and the clinical course of the disease after immunotherapy (allogeneic stem-cell transplantation/donor lymphocytes infusion/therapy). In summary, our data show that the composition and quality of DC after a mixed lymphocyte culture-priming phase is predictive for a successful ex vivo antileukemic response, especially with respect to proportions of mature and leukemia-derived DC. These data contribute not only to predict DC-mediated functions or the clinical course of the diseases but also to develop and refine DC-vaccination strategies that may pave the way to develop and modify adoptive immunotherapy, especially for patients at relapse after allogeneic stem-cell transplantation.