Leukemic Blasts Secondary to Myelodysplastic Syndromes Are Molecularly Programmed To Differentiate into Functionally Mature Dendritic Cells.

Adoptive immunotherapy of leukemia aims at eradicating the disease through the transfer of leukemia-reactive lymphocytes. Donor lymphocytes infusions (DLI) after allogeneic hemopoietic cell transplantation (allo-HCT) have shown to cure chronic myelogenous leukemia (CML). Unfortunately, when applied to acute leukemias, the DLI approach is far less successful. Strategies to increase the efficacy of adoptive immunotherapy for the cure of acute leukemias are therefore urgently needed. To this aim, blasts from acute myeloid leukemias (AML) can be differentiated in vitro into dendritic cells (leukemic DC or LDC) that directly present leukemic antigens to T lymphocytes. This is commonly achieved by culturing AML blasts with cytokines such as GM-CSF, IL-4 and TNF-α for 7–14 days. LDC can be further induced to functional maturation by exposure to CD40L. The efficacy of these protocols is, however, suboptimal, since a large proportion of AML sub-types do not differentiate into LDC. The addition of calcium ionophore (A23187) has been shown to rescue some of the cases. The aim of this study is to identify the characteristics associated with the ability of blast from AML to differentiate into functionally mature LDC. To this, we studied a cohort of 17 consecutive AML patients. AML blasts were induced to differentiate into LDC either by GM-CSF, IL-4 and TNF- α or by cytokines and A23187. LDC were further matured with CD40L. LDC differentiation was defined by expression of MHC class II, costimulatory (CD80, CD86, CD40, CD70) and adhesion molecules (CD54, CD58). The overall efficacy of LDC differentiation by cytokines was 20%. Maturation of LDC induced by cytokines failed, as ascertained by the lack of up-regulation of CD83 and the chemokine receptor CCR7. Upon exposure of AML blasts to cytokines and A23187, we observed LDC differentiation in more than 90% of the cases. LDC differentiation occurred in 24–48 hrs and was associated with the maintenance of disease markers expression (c-kit, CD34). Interestingly, blasts derived from AML secondary to myelodysplastic syndromes directly differentiated into mature LDC. On the other hand, LDC derived from primary AML were insensitive to the maturative stimulus CD40L. Accordingly, LDC from secondary AML were the most potent inducers of allogeneic T-cell proliferation. The efficacy of the combination of calcium ionophore and cytokines in differentiating myelodysplastic blasts into LDC provides the rational for novel adoptive immunotherapeutic approaches to treat high risk AML. Furthermore, the differential ability of primary leukemic blasts and blasts secondary to myelodysplastic syndromes to rapidly differentiate into functionally mature LDC suggest the existence of molecular factors committing AML cells to the DC lineage. The identification of such factors and their exploitation, for example by gene transfer, will enable the generation of LDC from all cases of AML for the stimulation of the immune system against leukemia.