Leukemia-Derived DC for T-Cell Therapy against AML Progenitor Cells
Authors: Schmetzer Helga , Liepert Anja , Grabrucker Christine , Fischbacher Dorothea , Freudenreich Markus , Merle Marion , Reibke Roland , Schuster Friedhelm , Reuther Susanne , Kremser Andreas , Loibl Julia , Schmid Christoph , Kroell Tanja , Borkhardt Arndt , Kolb Hans-Jochem 
Published: April 2020

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 &gt;67% of all cases gained an antileukemic T cell cytotoxicity after DC training if &gt;45% proliferating/&gt;65% CD4+/&gt;42% memory T cells or &gt;40% mature DC/&gt;65% DCleu were in the DC training setting. Moreover, 90% of DC trained T cells gained a lytic activity if &gt;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.