Abstract 1885: Potent tumoricidal activity of a FGFR4 CART in rhabdomyosarcoma

Abstract Despite decades of multi-module therapies, RMS remains incurable once it has metastasized, thus new therapeutic strategies are warranted. FGFR4 is a developmentally regulated cell surface receptor tyrosine kinase, overexpressed in virtually all, mutationally activated in about 10% of RMS, and directly activated by PAX3-FOXO1 fusion protein which makes it a tractable target for immunotherapy. We generated fifteen binders against FGFR4 and characterized them further as candidate molecules for immune therapy. We found that 3A11, a mouse IgG antibody, bound to FGFR4 positive cell lines. The VL and VH domain of 3A11 was cloned and made into scFvFc format (mouse Fv and Human IgG1 Fc). The chimeric form of 3A11 antibody was successfully produced in vitro and retained its FGFR4 specificity with an observed binding affinity at nanomolar range. By ELISA using the extra cellular domain of human FGFR1, FGFR2, FGFR3 or FGFR4, 3A11 scFvFc showed dose dependent binding to FGFR4 only. We then made 3A11 into a second generation CAR. Human T cells transduced with 3A11 CAR construct were found to be highly potent at inducing IFN-γ, TNF-α, IL-2 and cytotoxicity when the FGFR4-CART was co-cultured with RMS cells, but not with RMS cells with FGFR4 knocked out and FGFR4 negative cells. Our in vivo testing also found that 3A11 CART was able to eliminate RMS cells in murine xenograft metastatic models. Here we report the successful generation of binders specific to human FGFR4. FGFR4 CAR developed from 3A11 was able to kill FGFR4 positive target cells both in-vivo and in-vitro. Thus, 3A11 CAR T cells targeting FGFR4 may provide effective immune therapies for rhabdomyosarcoma and other FGFR4 expressing cancers and clinical trials are planned. Citation Format: Adam Cheuk, Meijie Tian, Jeetendra Kumar, Peter Azorsa, Nityashree Shivaprasad, Dina Schneider, Berkley Gryder, Jun Wei, Young Song, Xinyu Wen, Sivasish Sindiri, Joon-Yong Chung, Zhongyu Zhu, Dimiter Dimitrov, Stephen Hewitt, Boro Dropulic, Rimas Orentas, Javed Khan. Potent tumoricidal activity of a FGFR4 CART in rhabdomyosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1885.