Abstract B021: Treatment with a novel targeting module, redirecting UniCAR T cells against PSCA, delays subcutaneous tumor growth and prolongs survival of tumor-bearing NSG mice

Abstract Background: The adoptive transfer of T cell engineered with chimeric antigen receptors (CARs) is currently considered a highly promising therapeutic option for treating so far incurable malignant diseases. In order to reduce adverse reactions associated with CAR engineered T cells, a flexible modular universal chimeric antigen receptor (UniCAR) platform is developed, which allows a precise control of CAR T cell reactivity to manage side effects while preserving efficacy. The UniCAR technology splits the signaling and antigen-binding aspects of conventional CARs into two individual components. The UniCAR is structurally similar to second-generation CARs, however the single chain variable fragment (scFv) does not recognize a cell surface antigen but a short peptide motif derived from a human nuclear autoantigen. Antigen-specificity and crosslinking of UniCAR expressing T cells to target cells is provided by a separate targeting module (TM) compromising a scFv, binding to specific cell surface antigens, fused to the aforementioned peptide motif. Thus, T cells engineered to express UniCARs remain inactivated after infusion, since the UniCAR target is not available for binding under physiological conditions. Only in the presence of the TM, antigen specific activation of UniCAR T cells occurs, which allows for a more sophisticated regulation. Methods: We developed a novel radio-immune target module (TM), which consists of an anti-PSCA (prostate stem cell antigen) scFv for redirecting of UniCARs to PSCA expressing tumor cells. Three different tags are fused in a row to the C-Terminus of the scFv to functionalize the molecule for combined immune- and radiotherapy. First, a ten amino acid (aa) long tag mediates the crosslink to T cells genetically modified with the UniCAR. Further downstream, a peptide tag (Rx) for enhanced conjugation of radionuclides and finally, a 6xhistidine (His) tag are located. TM-Rx efficacy was evaluated for target cell killing in-vitro and compared to a TM without Rx-tag. In-vivo efficacy of the TM-Rx was also investigated in a high and low-tumor burden mouse model. Results: Rx-TM and TM equivalently kill PSCA-expressing tumor cells in-vitro in presence of UniCARs in an E:T (Effector:Target) ratio of 1:1 after 24 hours. UniCAR T cell engrafted NSG (NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ) mice show no clinical signs of autoimmunity neither in presence nor absence of the TM. One week treatment with TM delays subcutaneous tumor growth and prolongs survival of tumor bearing, UniCAR T cell engrafted NSG mice. Longterm infiltration of tumor tissue by UniCARs could be observed over 16 weeks in the high and low-tumor burden ectopic carcinoma model. Conclusion: The UniCAR technology shows efficacy both in-vitro and in-vivo. Extension of the TM with an additional tag does not impair functionality of the UniCAR platform. Short-treatment prolongs survival of tumor bearing mice but does not lead to cure, therefore combination with other treatment modalities e.g. radiation oncology seems reasonable. Citation Format: Elham Pishali Bejestani, Malte von Bonin, Marc Cartellieri, Armin Ehninger, Mechthild Krause, Michael Baumann, Gerhard Ehninger, Michael Bachmann. Treatment with a novel targeting module, redirecting UniCAR T cells against PSCA, delays subcutaneous tumor growth and prolongs survival of tumor-bearing NSG mice. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B021.