Abstract C242: Development of adoptive-T-cell therapy for prostate cancer incorporating a novel chimeric cytokine receptor

Abstract

Abstract Introduction: Prostate cancer is the most common cancer in men. Standard therapy incorporates surgery, radiotherapy, anti-androgen therapy and chemotherapy. Once anti-androgen resistance occurs, median survival is only 18 months. Consequently, there is a pressing need for novel therapies. One promising strategy involves genetic re-targeting of T-cells using chimeric antigen receptor (CAR) technology. These fusion receptors are directed against native tumor antigens, thereby bypassing the need for either HLA expression or antigen processing. In prostate cancer, prostate specific membrane antigen (PSMA) represents a highly attractive target for this approach. However, one key limitation of this strategy is poor longevity of reinfused T-cells. While parenteral interleukin-2 (IL-2) may help to circumvent this, it is not selective for engineered T-cells and is frequently highly toxic. To address this need, we have developed a novel chimeric receptor, which enables T-cells to receive an IL-2 intracellular signal in response to IL-4. Methods: The PSMA specific CAR, P28z was expressed in human T-cells and the murine IL-2 dependent cell line CTLL2 using the oncoretroviral vector SFG. A fusion receptor of IL4-R and the intracellular domain of IL-2R (MOHAIR) was co-expressed with P28z using the T2A system. CAR grafted T-cells were co-cultured with antigen positive and negative tumor cell lines. Proliferation of CTLL2 cells or human T-cells was determined by trypan exclusion. Production of IFN was measured by ELISA. Results: To test the function of MOHAIR, initial studies were performed using the IL-2-dependent CTLL2 cell line. We observed that all MOHAIR-expressing CTLL2 cell lines proliferated equally well in human IL-4 or IL-2, unlike control cells which only proliferated in IL-2. CTLL2s expressing MOHAIR and secreting IL4 became cytokine independent Next we tested function using primary human T-cells. P28z and P28z-MOHAIR (MOP) transduced T-cells destroyed PSMA expressing prostate cancer cell lines and release IFN in a strictly antigen-specific manner. Both T-cell populations proliferated following multiple stimulations on PSMA positive cell lines in the presence of IL-2. By contrast, these T-cells died upon re-stimulated in the absence of antigen or IL-2. Uniquely, MOP transduced T-cells proliferated over multiple antigen stimulations in the presence of IL-4, whereas P28z transduced T-cells died rapidly when cultured in IL-4. When grown in the absence of antigen, MOP T-cells expand preferentially in IL-4, compared to MOP or P28z T-cells grown in IL-2. Conclusions: P28z confers PSMA antigen specificity on transduced human T-cells. Mohair enables delivery of a potent IL-2 intracellular signal in response to the weakly mitogenic cytokine, IL-4. This provides a convenient system to achieve selective expansion of PSMA retargeted human T-cells in response to exogenous IL-4. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C242.