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Background: Demethylating agents like 5-Azacytidine (5-Aza) have entered treatment for myeloid dysplastic syndrome (MDS) and acute myeloid leukaemia (AML). Beyond the effect of differentiation, one suggested mechanism is that 5-Aza demethylates antigens such as Cancer-Testis Antigens (CTA) which will then be presented in order to induce immune response by immunocompetent cells. While a lot of attention was paid to the effects of 5-Aza in the myeloid cells, less is known about the impact of 5-Aza on immune cells. We therefore investigated the effects of 5-Aza on T cells. Materials and methods: T-cells were isolated from buffy coats using magnetic beads. Cells were stimulated and cultured for 1 week in the presence of IL-2. Thereafter cells were treated with or without 5 μM 5-Aza or 20 μM for 48h. mRNA was isolated and used for cDNA synthesis. qPCR was done under standard conditionings for expression of IL-10, FoxP3, and TGF-beta normalized for GAPDH. T cells were analyzed by fl ow cytometry using the following antibodies: CD3, CD4, CD8, HLA-DR, FoxP3, CD 127, and CD25. Functional killing of an AML cell line (HL60) was measured using a LDH release assay. Results: We observed a signifi cant (P = 0.03) growth delay of the 5-Aza treated T cells compared to untreated control cells. Only the highest dosage (20 μM) of 5-Aza increased the fraction of apoptotic cells. 5-Aza did not infl uence the expression of CD3, but caused a change in the distribution of T cell subpopulations: percentages of CD8 + T cells decreased from 46% to 35% whereas CD4 + T cells increased from 57% to 68%. When stained for activation marker HLA-DR, a reduced expression was observed after 5-Aza treatment (57%, 48%, and 44% respectively). By screening different mRNA levels we found that the mRNA expression of IL10, FoxP3, and TGF-beta was upregulated (P = 0.02, P = 0.003 and P = 0.02 respectively). Strikingly, we also found an upregulation of CD4 + FoxP3 + Treg cells from 4.8% to 9.6% to 10.9% respectively. In a cytotoxicity assay we observed a signifi cantly reduced capability of Aza-treated T cells to lyse target cells (P = 0.02). Conclusions: Our data indicate that 5-Aza inhibits the activity of T cells by: 1. reducing the number of CD8 + T killer cells, 2. upregulating the subpopulation of Tregs as well as increasing the expression of inhibitory cytokines like IL-10. We therefore conclude that 5-Aza treatment may constrain the distribution and function of immune cells. R1243 Dendritic-cell based tumour vaccination in prostate and renal cell cancer: systematic review and meta-analysis A. Draube (1), N. Klein-González (1), S. Rademacher (1), C. Brillant (2), M. Hellmich (3), M. von Bergwelt-Baildon (1) (1)Stem Cell Transplantation Program Cologne (Cologne, DE); (2)University Hospital of Cologne (Cologne, DE); (3)University of Cologne (Cologne, DE)