Leukemia-Derived DC for T-Cell Therapy against AML Progenitor Cells

Abstract

Presentation of leukemic antigens (LAA) can be improved by conversion of leukemic cells to leukemia derived DC (DCleu), thereby enabling the generation of leukemia specific CTL. DC/DCleu can be generated and quantified from every AML case with at least one of 3 different DC generating methods (Schmetzer 2007/2008). We want to enlight the role of the composition and quality of DC and (DC or blast trained) T cells to mediate leukemia cytotoxic reactions or to predict the clinical response to therapy. Autologous patients’, allogeneic donor T cells or T cells at relapse after SCT were trained with DC or blasts from 25 AML-cases in a ‘Mixed lymphocyte culture’ (MLC) and DC/T cell profiles and antileukemic Tcell cytotoxicity evaluated. We generated DC/mature DC/DCleu from every patient (Ø27/45/83%). DC training of T cells increased proliferating, CD4+ and memory T cells and decreased CD8+ T cells; blast training did not increase memory T cells. An antileukemic, very efficient T cell cytotoxicity was achieved in 47% of cases after DC/DCleu training but only in 24% after blast training of T cells. A comparison of cases with a gain of antileukemic T cell cytotoxicity to those without a lytic activity showed higher proportions of mature DC/DCleu and CD4/memory T cells and higher amounts of secreted IFNgamma and IL 6 in the lytically active, DC trained group. The differences were most distinct in the group with DC trained T cells prepared at relapse after SCT. Cases with a response to therapy showed higher proportions of DCleu, proliferating, memory or CD4+ T cells. We showed that >67% of all cases gained an antileukemic T cell cytotoxicity after DC training if >45% proliferating/>65% CD4+/>42% memory T cells or >40% mature DC/>65% DCleu were in the DC training setting. Moreover, 90% of DC trained T cells gained a lytic activity if >65% DCleu were in the MLC. AML patients presenting with a relapse after SCT showed better ex vivo convertibility of blasts to DCleu if they had responded to a GM CSF/DLI based therapy of their relapse after SCT compared to cases with no response (72 vs 36% blasts convertible to DCleu; 44 vs 29% generable DC). By spectratyping of the Vβ TCR region in an AML case we demonstrated a more extended clonal restriction of donor T cells after DC training of T cells compared to blast trained T cells. Moreover, the restricted pattern was also found in T cells from the patient after SCT. In summary, DC/DCleu can be generated in any given case independent from karyotype. A DC training of T cells improves the antileukaemic CTL, but can also mediate a T cell anergy. The composition of DC and T cells is predictive for the lytic efficiency of the trained T cells: A successful DC training of T cells is associated with high mature DC/DCleu counts and high rates of proliferating, CD4+ and memory T cells. Patients responding to a DLI/GM CSF based therapy are characterized by a better convertibility of blasts to DCleu and more mature DC. Identical clonal restrictions of T cells were found in blast trained and even more in DC trained T cells. Identical clonal patterns were found in ex vivo trained and in vivo selected T cells. We can contribute to understand biological mechanisms behind cytotoxic reactions and escape mechanisms and to develop adoptive immunotherapies with specific, antileukemia directed LAA specific T cells, e.g. selected by multimers from SCT donors or with specifically trained and selected T cells after DC training without side effects.