Abstract CT013: Safety and efficacy from the phase 1/2 first-in-human study of REGN5459, a BCMA×CD3 bispecific antibody with low CD3 affinity, in patients with relapsed/refractory multiple myeloma
Authors: Suvannasankha Attaya , Kapoor Prashant , Pianko Matthew J. , Richter Joshua , D'Souza Anita , Anderson Larry D. , Magyar Andrew , Aina Oluwaseun , Boyapati Anita , Cronier Damien , Singh Nikhil , Rodriguez-Lorenc Karen , Kroog Glenn S. , Lee Hans C. 
Published: May 2023

Background: MM remains incurable and new tx options are needed, especially in heavily pre-treated R/R pts. REGN5459, a BCMAxCD3 bispecific Ab, binds to BCMA on MM cells and with low affinity to CD3 on T cells, triggering T-cell activation and plasma cell depletion with low cytokine release preclinically. This first-in-human study aimed to assess the safety, tolerability, and preliminary anti-tumor activity of REGN5459 monotherapy in pts with R/R MM.

Methods: Eligible pts had received ≥3 prior lines of tx including an anti-CD38 Ab, proteasome inhibitor, and immunomodulatory drug, and had exhausted all available tx options. Pts could receive REGN5459 until progression/intolerable toxicity. Primary objectives were to assess safety, tolerability, dose limiting toxicities (DLTs), and determine the recommended Ph 2 dose (RP2D) of REGN5459 (Ph 1) and assess efficacy of REGN5459 (Ph 2) per ORR.

Results: As of June 9, 2022, 43 pts were enrolled (Ph 1, 33; Ph 2, 10): median age 67 yrs (range, 26-85), 51% female, 16% high cytogenetic risk, 14% extramedullary plasmacytoma, 37% R-ISS Stage III disease, 61% triple-class refractory, and median of 5 (range, 2-9) prior lines of tx. In Ph 1, one DLT was reported in a pt receiving the highest dose (900 mg; Gr 3 hypoxia, pt later found to have primary lung cancer). RP2D was identified as 480 mg. All pts enrolled had ≥1 TEAE, 74% had Gr ≥3 TEAEs. TEAEs all-Gr in ≥30% of pts were CRS (54%), fatigue (44%), neutropenia (37%), anemia (35%), cough (30%), and diarrhea (30%). Gr ≥3 TEAEs in ≥15% of pts were neutropenia (37%), anemia (26%), lymphopenia (23%), thrombocytopenia (19%), and hypertension (16%). CRS Gr 1, 2, and 3 were reported in 47%, 2%, and 5%, respectively; there was no Gr 4 or 5 CRS. No Gr 3 CRS with RP2D. Tocilizumab was used in 19% and steroids in 9% of pts. One pt developed ICANS (2%, Gr 2). Incidence of serious TEAEs and TEAEs leading to tx discontinuation was 63% and 16%. Infections occurred in 61% (37% Gr ≥3). After data-cutoff, two deaths due to COVID pneumonia and COVID infection have been reported. ORR was 67% (58% ≥VGPR) for the entire cohort and 100% (85% ≥VGPR; 15% sCR; 39% CR) among pts receiving the RP2D (n=13). Median follow-up was 7 mos (range, 1-26) with longest response ongoing for 22+ mos. Median time to response was 0.8 mos. Median DOR was NR (95% CI, 12-NE); 12-mo DOR for RP2D was 66.7% (95% CI, 5.4-94.5). Of pts in ≥CR with available MRD results (n=8), 50% were MRD negative at the 10−5 threshold.

Conclusion: These initial data show that REGN5459 has acceptable safety/tolerability in R/R MM with most CRS of low grade and low incidence of ICANS. Modulation of CD3 affinity on bispecific Abs to maximize tumor killing, and mitigate CRS and T-cell exhaustion, warrants further research. Efficacy in this heavily pre-treated cohort was encouraging, with 100% ORR with the RP2D. Updated data will be presented at the meeting.

Citation Format: Attaya Suvannasankha, Prashant Kapoor, Matthew J. Pianko, Joshua Richter, Anita D'Souza, Larry D. Anderson, Andrew Magyar, Oluwaseun Aina, Anita Boyapati, Damien Cronier, Nikhil Singh, Karen Rodriguez-Lorenc, Glenn S. Kroog, Hans C. Lee. Safety and efficacy from the phase 1/2 first-in-human study of REGN5459, a BCMA×CD3 bispecific antibody with low CD3 affinity, in patients with relapsed/refractory multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT013.