Anales RANF

P7. P URINERGIC S IGNALING IN THE T UMOR G ROWTH AND M ETASTASIS P.68 CHARACTIZATION OF CD39 EXPRESSION ON T CELLS IN ACUTE MYELOID LEUKEMIA F. Brauneck*, P. Ahmadi*, A. Rissiek, N. Wildner, J. Wellbrock, F. Haag, W. Fiedler and J. Schulze zur Wiesch University Medical Center Hamburg-Eppendorf, Hamburg, Germany. * These authors equally contributed. Acute myeloid leukemia (AML) is the most prevalent acute leukemia among adults. Even after initially successful therapy most patients experience relapses that might be due to immune escape. In order to overcome immune escape in AML it is pivotal to identify relevant immune cell subsets and checkpoints. We performed multicolor flow cytometry on peripheral blood mononuclear cells (PBMCs) and AML blasts of 14 patients with newly diagnosed AML and 9 healthy donors (HDs), focusing on differentiation, exhaustion markers (e.g. PD-1) and the two ectoenzymes CD39 and CD73. We observed an increased frequency of PD1+CD8+ T cells in AML patients compared to HD (11.2% vs. 3.9%; p=0.08). Similarly, in the CD4-compartement we found on both subsets, conventional (CD4+CD25lo, CD4cons) and regulatory (CD4+CD127loCD25hi) CD4+ T cells, an increase of PD1-expressing cells from AML patients as compared to HD (CD4cons: 11.1% vs. 2.3%; p=0.05; Tregs: 24.4% vs. 11.7%; p=0.05). Concomitantly, the expression of CD39 was also increased on CD4cons and Tregs from AML patients as compared to HD (Tcons: 11.1% vs 2.3%; p=0.05; Tregs: 67.9% vs 39.2%; p=0.01). Of note, the overall frequency of Tregs did not differ between PBMCs from AML and HD. Based on these data we aim to investigate the role of CD39 on the inhibitory capacity of Tregs, activation status and the proliferative capacity of T effector cells. Currently, we are investigating further functional assays to assess the role of CD39 and other purinergic mediators in the progression of AML.