5-Aza-2'-Deoxycytidine Promotes Cytotoxic Effect of CART-Cells on Leukaemia Cells

T cells modified to express CD19-specific chimeric antigen receptors (CAR) have shown anti-tumour efficacy in early phase clinical trials in patients with relapsed and refractory B-cell malignancies. In addition to direct cytotoxicity, chemotherapeutic drugs can have an immunomodulatory effect both through enhancing the tumour-specific immune response and increasing the tumour’s susceptibility to immune mediated destruction. Hence, combining immunomodulatory chemotherapy and CAR T-cells is an attractive approach for eliminating tumours, particularly in advanced stages. 5-aza-2'-deoxycytidine (5-AZA) is a hypomethylating agent that induces terminal differentiation, senescence or apoptosis in haematological malignancies. Here, we have explored a CAR-based immunotherapy combined with 5-AZA to maximise the effect of the CAR T-cells against CD19+ B-cell leukaemia. A second generation CAR including CD3zeta and the CD28 co-stimulatory domain was cloned into the PiggyBac-transposon vector and was used to generate CAR19 -T cells. Cord blood -derived mononuclear cells (MNC) were transfected with CAR19-transposon/transposase plasmids and expanded with CD3/28 beads for 2 weeks in the presence of 20ng/ml IL2 and 10ng/ml IL7. CAR19 T-cells efficiently induced cytolysis of CD19+ leukaemia cells in vitro and exhibited anti-tumour activity in vivo in a xenograft mouse model of leukaemia. Pre-treatment with 5-AZA produced greater leukaemia cell cytolysis in vitro and maximised anti-tumour activity of CAR19 T-cells in vivo against xenograft primary leukaemia compared to 5-AZA or CAR19 T-cells alone. In vitro analysis revealed that pre-treatment with 5-AZA up-regulates CD19 expression in leukaemia cells and improves CAR19 T-cell recognition of target cells increasing the formation of effector/ target cell conjugates and target cell cytolysis. Therefore using 5-AZA pre-treatment can be particularly useful for B-cell leukaemias with reduced expression of CD19. We have also demonstrated that pre-treatment of target cells with 5-AZA potentiates the effect of CAR19 T-cells used at low dose or low effector:target (E:T) suggesting that even small numbers of CAR19 T-cells can mediate a potent antitumor effect when combined with 5-AZA pre-treatment of target cells. This is particularly important for patients receiving limited numbers of CAR T-cells or for patients with large leukaemic burden. In addition, we speculate that the enhanced cellular cytotoxicity produced by 5-AZA-conditioning may allow the infusion of decreased numbers of CAR19 T-cells.