Abstract A30: Novel T-cell engaging antibodies against L1CAM for neuroblastoma

Background: T cell-mediated immunotherapy has shown great promise in the treatment of human cancers. Bispecific antibodies (BsAbs) that engage CD3 on T cells and a tumor antigen on target cells can induce polyclonal T cell-mediated cytotoxicity against both leukemia (expressing CD19) and solid tumors (expressing HER-2 or GD2), unrestricted by MHC. The L1 cell adhesion molecule (L1CAM) is a glycoprotein consisting of 6 Ig-like domains and 5 fibronectin-like repeats in the ectodomain. In normal tissues, L1CAM expression is restricted to neurons, renal tubules, and skin at low levels and plays an important role in brain development, including neuronal migration and differentiation. Interestingly, L1CAM is also overexpressed on various pediatric cancers including neuroblastoma (NB), and stimulates tumor proliferation, migration, and metastasis. Chimeric IgG1 antibody, chCE7, targeting the 6th Ig-like domain of human L1CAM, had high affinity (KD = 0.63 nM) and when 131I-labeled, had superior sensitivity and specificity over 131I-MIBG in patients with metastatic NB. However, chCE7 lacked ADCC ability in preclinical studies and no major clinical responses have been reported for anti-L1CAM chimeric antigen receptor (CAR) modified T cells (NCT02311621). Methods: By CDR grafting, the murine antibody E71 (specific for 2nd Ig-like domain with KD = 2.23 nM) was humanized to huE71, and huE71-BsAb using the IgG(L)-scFv BsAb platform previously described (Xu et al., Can Immunol Res 2016) was generated and compared to huE72 (the humanized version of CE7)-BsAb. The BsAbs were produced in CHO-S cells and purified by protein A affinity chromatography. Size homogeneity was confirmed by SEC HPLC. Binding to L1CAM and CD3, or to tumors and T cells was measured by SPR (Biacore) or by FACS, respectively. In vitro T-cell activation and cytokine release were assessed by FACS and by ELISA, respectively. In vitro tumor cytotoxicity was measured by 4-hour 51Cr release at an E:T ratio of 10:1. In vivo antitumor effect was assessed in Balb/c-Rag2-/-IL-2R-c-KO (DKO) mice xenografted with subcutaneous (s.c.) NB cell lines or patient-derived xenografts (PDX). Tumor targeting was performed by using 89Zr-labeled huE71 and huE72 IgG1 in xenografted nude mice. Results: Both BsAbs showed a molecular size of 210kDa with >90% purity. When assessed by SPR for binding to the L1CAM, huE71-BsAb retained its parental affinity, while that of huE72-BsAb decreased by 8-fold (KD of 5.15nM and 5.28nM, respectively). As expected from the IgG(L)-scFv design, both BsAbs showed lower binding to CD3(+) T cells when compared with huOKT3 IgG1. Both BsAbs induced CD25 expression on CD4(+) or CD8(+) T cells after 96 hours of culture in the presence of L1CAM(+) IMR32 NB cell line, and CD8(+) T cells showed more activation in the presence of huE72-BsAb. Both BsAbs induced similar level of Th1 cytokine (e.g. TNFα) from PBMCs following 24 hours of culture in the presence of IMR32. Both BsAbs mediated T-cell cytotoxicity on L1CAM(+) cell lines with pM EC50s. In nude mice xenografted with s.c. L1CAM(+) cancer cell line, intravenous (i.v.) huE71 IgG1 showed higher tumor targeting efficiency than huE72 IgG1. In DKO mice xenografted with s.c. IMR32 (carrying luciferase reporter gene) and s.c. PBMCs, i.v. huE71-BsAb significantly suppressed tumor growth while huE72-BsAb had no antitumor effect. Similar results were observed in an s.c. L1CAM(+) NB PDX model when PBMCs were injected i.v. Conclusions: Despite near-identical in vitro binding characteristics, BsAbs targeting different epitopes on the same target have strikingly different antitumor properties in vivo. HuE71-BsAb is a potential T cell engaging immunotherapeutic for NB and other L1CAM(+) solid tumors. Citation Format: Maya Suzuki, Hong Xu, Hongfen Guo, Brandon Nemieboka, Zhihao Wu, Jason Lewis, Nai-Kong V. Cheung. Novel T-cell engaging antibodies against L1CAM for neuroblastoma [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr A30.