Abstract 3149: Chimeric antigen receptor-modified T cells against several target antigens in multiple myeloma
Authors: Chang Lung-Ji , Liu Yuchen , Kuo Hao-Hsiang , Tsao Shih-Ting , Moreb Jan S. 
Published: August 2015

Introduction: Multiple myeloma (MM) is an incurable plasma cell dyscrasia involving the bone marrow (BM), accounting for about 10% of all hematologic malignancies. With novel drugs and autologous stem cell transplantation, the average survival has significantly improved. Nevertheless, most patients experience resistant relapses and eventually succumb to their disease. Thus, there is an urgent need for more effective treatments. Targeted CAR-T cells that can completely eradicate residual MM cells might be a highly effective immunotherapy strategy for MM patients.

Materials and Methods: We generated lenti-CAR vectors targeting several known MM surface antigens: CS1, CD317 (hm1.24), CD138, and B cell maturation antigen (BCMA, CD269 or TNFRSF17). MM patients’ BM and peripheral blood T cells were transduced with these lenti-CAR vectors, and killing efficacy was assessed in short term and long term co-incubation experiments by flow cytometry using green fluorescent protein-labeled MM cells and annexin V/PI staining.

Results: Patients’ T cells transduced with the above four lenti-CARs displayed similar MM-specific killing activities when co-cultured 1:1 with Molp2 MM cell line. All four CAR-Ts killed &gt;70% of MM cells after 24 hr, with CS1 and BCMA CARs showing the highest killing (&gt;80%). After 72 hr, all MM cells were killed. Then ten times more MM cells were added to the CAR-T cultures to examine continued killing effect. Except for CD317 CAR-Ts, all other MM-specific CAR-Ts displayed complete killing effect in the 2nd round of 5-day co-cultures. Primary MM cells from two previously treated patients were also tested, and we observed similar killing effect from these CAR-Ts. We observed that expression of CS1 and CD317 CAR resulted in self killing of these CAR-Ts. Therefore we checked and confirmed the expression of these antigens on the surface of T cells. This surprising observation explains the self killing as well as the limitations of these specific CAR-Ts, and renders these targets less suitable for clinical application. We further engineered a novel dual CD138/BCMA CAR and examined its functionality in targeting MM cells. The results demonstrated that the dual CD138/BCMA CAR-Ts displayed prolonged killing compared to the single CAR-Ts, and continued to be effective even after four rounds of MM-targeting co-cultures spanning &gt;30 days.

Conclusion: CAR-modified T cells specific for several MM surface antigens have demonstrated variable effective killing of both established MM cell lines and primary MM tumors. Targeting two antigens by dual CD138/BCAM CAR T cells showed significantly more effective and consistent killing of MM cells. Such approach may overcome the issue of antigen escape seen in single CAR strategy, and might be a more suitable treatment modality for future clinical trials.

Citation Format: Lung-Ji Chang, Yuchen Liu, Hao-Hsiang Kuo, Shih-Ting Tsao, Jan S. Moreb. Chimeric antigen receptor-modified T cells against several target antigens in multiple myeloma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3149. doi:10.1158/1538-7445.AM2015-3149