REGN5458, a Bispecific BCMAxCD3 T Cell Engaging Antibody, Demonstrates Robust In Vitro and In Vivo Anti-Tumor Efficacy in Multiple Myeloma Models, Comparable to That of BCMA CAR T Cells

Abstract

Improving therapies for multiple myeloma (MM) remains a high medical need because of the significant morbidity and mortality of the disease. Targeted immunotherapies represent a promising opportunity to fill this clinical need. B cell maturation antigen (BCMA) is an attractive cell-surface target for MM due to its consistent expression on MM patient malignant plasma cells and expression limited in normal tissue primarily to plasma cells. Redirection of a patient's T cells to recognize tumors by CD3-binding bispecific molecules or through the generation of chimeric antigen receptor (CAR) T cells, has shown preliminary evidence of clinical activity. Bispecific antibodies concurrently engage a tumor antigen on cancer cells and the CD3 signaling machinery on T cells, bringing the tumor cell and T cell into proximity and facilitating T cell activation and tumor cell killing. By contrast, CAR T cell therapy involves re-infusion of the patient's own T cells after ex vivo engineering to express CARs targeting tumor antigens and triggering T cell signaling. Here we describe the generation of REGN5458, a human bispecific antibody that binds to BCMA and CD3. In vitro, REGN5458 efficiently activates T cells and induces polyclonal T cell killing of myeloma cell lines with a range of BCMA cell-surface densities, and also induces cytotoxicity of primary human plasma cells. Similar to gamma-sectretase inhibitors, incubation of myeloma cell lines with REGN5458 increased surface levels of BCMA. In xenogenic studies, after BCMAhigh NCI-H929 and BCMAlow MOLP-8 MM cells were co-implanted with PBMC and grown subcutaneously in immunodeficient NOD/SCID/L2Rgamma-deficient (NSG) mice, REGN5458 doses as low as 0.4 mg/kg significantly suppressed the growth of both tumors. Using aggressive, systemic xenogenic tumor models, in which NSG mice were engrafted with PBMC and intravenously injected with BCMAhigh OPM-2 cells or BCMAlow MOLP-8 cells expressing luciferase, REGN5458 reduced tumor burden and suppressed tumor growth at doses as low as 0.4 mg/kg. In immunocompetent mice genetically engineered to express human CD3, REGN5458 inhibited the growth of syngeneic murine tumors expressing human BCMA at doses as low as 0.04 mg/kg. Finally, as REGN5458 binds to cynomolgus CD3 and BCMA and mediates cytotoxicity of primary cynomolgus plasma cells, the pharmacology of REGN5458 was evaluated in cynomolgus monkeys. REGN5458 administration was well-tolerated, resulting in a mild inflammatory response characterized by transiently increased CRP and serum cytokines. Importantly, REGN5458 treatment led to the depletion of BCMA+ plasma cells in the bone marrow, demonstrating cytotoxic activity in non-human primates. The anti-tumor efficacy of REGN5458 was compared to BCMA-specific CAR T cells using 2nd generation CAR lentiviral constructs containing a single-chain variable fragment binding domain from REGN5458's BCMA binding arm and 4-1BB and CD3z signaling domains. Human PBMC-derived T cells were transduced to express this CAR and expanded. Both REGN5458 and the BCMA CAR T cells demonstrated similar targeted cytotoxicity of myeloma cell lines and primary patient blasts in vitro, and were capable of clearing established systemic OPM-2-luciferase myeloma tumors in NSG mice, but with different kinetics: treatment with REGN5458 resulted in rapid clearance of tumors within 4 days, whereas treatment with BCMA CAR T cells allowed tumors to continue to grow for 10-14 days following injection before rapidly inducing tumor clearance. Thus, REGN5458 exerts its therapeutic effect rapidly after injection, using effector T cells that are already in place. In contrast, BCMA CAR T cells require time to traffic to the tumor site and expand, before exerting anti-tumor effects. Collectively, these data demonstrate the potent pre-clinical anti-tumor activity of REGN5458 that is comparable to that of CAR T cells, and provide a strong rationale for clinical testing of REGN5458 in patients with MM. Disclosures Dilillo: Regeneron Pharmaceuticals: Employment. Olson:Regeneron Pharmaceuticals: Employment. Mohrs:Regeneron Pharmaceuticals: Employment. Meagher:Regeneron Pharmaceuticals: Employment. Bray:Regeneron Pharmaceuticals: Employment. Sineshchekova:Regeneron Pharmaceuticals: Employment. Startz:Regeneron Pharmaceuticals: Employment. Retter:Regeneron Pharmaceuticals: Employment. Godin:Regeneron Pharmaceuticals: Employment. Delfino:Regeneron Pharmaceuticals: Employment. Lin:Regeneron Pharmaceuticals: Employment. Smith:Regeneron Pharmaceuticals: Employment. Thurston:Regeneron Pharmaceuticals: Employment. Kirshner:Regeneron Pharmaceuticals: Employment.

Bispecific Antibodies for Multiple Myeloma: A Review of Targets, Drugs, Clinical Trials, and Future Directions

“…In cynomolgus monkey studies, REGN5458 depleted BCMA + plasma cells in the BM (117). The REGN5458 treatment induced a mild inflammatory response in the cynomolgus monkeys characterized by transiently increased C-reactive protein and serum cytokines, but was otherwise well-tolerated (117). In a comparative study with CAR T cells, REGN5458 displayed targeted cytotoxicity of MM cells lines and primary plasmablasts.…”

“…REGN5458 is an anti-BCMA x anti-CD3 BsAb, with an Fc domain and anti-BCMA/anti-CD3 Fab domains (116). In preclinical studies, REGN5458 increased surface levels of BCMA on MM cell lines, in addition to inducing T cell killing of MM cells and cytotoxicity in primary human plasma cells (117). In NSG mice, REGN5458 inhibited xenografted tumor growth at doses of 0.4 mg/kg, and at ten times lower doses in immunocompetent mouse models (117).…”

“…In preclinical studies, REGN5458 increased surface levels of BCMA on MM cell lines, in addition to inducing T cell killing of MM cells and cytotoxicity in primary human plasma cells (117). In NSG mice, REGN5458 inhibited xenografted tumor growth at doses of 0.4 mg/kg, and at ten times lower doses in immunocompetent mouse models (117). In cynomolgus monkey studies, REGN5458 depleted BCMA + plasma cells in the BM (117).…”

“…In NSG mice, REGN5458 inhibited xenografted tumor growth at doses of 0.4 mg/kg, and at ten times lower doses in immunocompetent mouse models (117). In cynomolgus monkey studies, REGN5458 depleted BCMA + plasma cells in the BM (117). The REGN5458 treatment induced a mild inflammatory response in the cynomolgus monkeys characterized by transiently increased C-reactive protein and serum cytokines, but was otherwise well-tolerated (117).…”

“…Additionally, administration of REGN5458 to NSG mice led to clearance of systemic OPM-2 myeloma tumors within 4 days (compared with CAR T cells, which required 10-14 days for tumor clearance) (117). A clinical trial (NCT03761108) of a firstin-human study of the drug was initiated in January 2019, in patients with R/R MM.…”