Immunotherapy of Acute MYELOID LEUKEMIA: ANTI-LEUKEMIC EFFECTS by Unprimed or Primed, Selected or Unselected Effector T-CELLS.
Authors: Schmetzer Helga , Schuster Friedhelm R , Buhmann Raymund , Freudenreich Markus , Doessinger Georg , Liepert Anja , Grabrucker Christine , Steger Brigitte , Reuther Susanne , Kremser Andreas , Loibl Julia , Fischbacher Dorothea , Schmid Christoph , Kroell Tanja , Busch Dirk , Borkhardt Arndt , Kolb Hans-Jochem 
Published: October 2019

Abstract
Abstract 5122
T-cells are the most important mediators of antileukemic reactions after allogeneic stemcelltransplantation (SCT) or donorlymphocyte-infusions (DLI) in patients (pts) with myeloid leukemias (AML,MDS), although relapses occur. Presentation of leukemic antigens (LAA) is improved by conversion of leukemic cells to leukemia derived DC (DCleu). Our hypothesis is, that myeloid blasts convert in vivo spontaneously to DCleu and prime CTL; moreover DCleu can be generated ex vivo from blasts and be used to prime T-cells enabling the generation of leukemia-specific CTL. Therefore (unprimed or primed) antileukemic effector T-cells have to be identified, characterized, optimized or selected.

Results
1) Blast- and DC-characterization: Blasts can be characterized by blast phenotypes or LAA-RNA-PCR(WT1,PR1 or PRAME).An LAA-overexpression was found in 70-94% of 88AML-samples compared to healthy controls. Ex vivo DCleu can regularly be generated independent from karyotypes and quantified in every AML-case and used to prime T-cells(Schmetzer 2005-2009).
2) Effectorcell characterization : a)In 6 patients after preemptive DLI-therapy between 0.1 and 0.5% LAA-specific T-cells with a highly Vβ-restricted T-cellprofil were found(Tetramer/Spectratyping). B)Compared to unprimed T-cells (with no or low antileukemic ex vivo function) selected from a patient after SCT IFNg-selected unprimed and even more primed T-cells have an improved antileukemic function compared to non-IFNg-selected primed T-cells. C) DC-priming (more than blast-priming) increases the antileukemic T-cell reactivity (shown in 20 cases) and is associated with highest Vβ-restriction, but is not in every case successful C) By spectratyping identical clone was found after DC-priming ex vivo and in vivo prepared from patient proving the value of DC-culturing for ‘simulating’ in vivo reactions.
3)Predictive and prognostic significance: a)Composition of DC-subtypes (high proportions of mature and leukemia-derived DC) and of T-cells (ratios>1 of CD4:CD8 and CD45RO:CD45RA)and microenvironment (high concentrations of CXCL8 and CCL2 in DC-culture supernatans,IL6 and IFNg in DC/T-MLC-supernatans) arepredictive for effectful antileukemic functionalityof primed T-cells b) Composition of DC-subtypes (high proportions of mature, leukemia-derived DC and convertibility of blasts to DC) predicts the clinical response to immunotherapy (SCT (n=18) or DLI-relapse therapy (n=17)):cases with higher proportions of mature DC/ DCleu /better blastconvertibility to DCleu had a higher chance to respond to immunotherapy (SCT/DLI) and had an improved overall survival.
In summary blasts can be characterized (LAA/blast phenotype) and DC/DCleu be generated in any given case independent from karyotype. A DC priming of T cells improves the antileukemic CTL, but not in every case. The composition of DC and T cells and the microenvironment in MLC are predictive for the ex vivo lytic efficiency of DC-primed T cells and for patients' response to immunotherapy (SCT or DLI). Effector T-cells can be identified, characterized or selected by their Vβ-profil, their LAA-specifity or IFNg-release (before or after blast- or DC-priming). Although the reactive differences or the therapeutic benefit of those different T-cellsubsets are not clear at the moment we hope to contribute to understand biological mechanisms behind cytotoxic reactions, to identify reactive T-cells (and identify best stemcell donors), to learn about escape mechanisms and to develop adoptive immunotherapies with specific, antileukemia directed T-cells without side effects.

Disclosures
No relevant conflicts of interest to declare.