Updated Analysis of a Phase 1, Open-Label Study of LCAR-B38M, a Chimeric Antigen Receptor T Cell Therapy Directed Against B-Cell Maturation Antigen, in Patients with Relapsed/Refractory Multiple Myeloma

Abstract LCAR-B38M is a bispecific chimeric antigen receptor T cell (CAR T) therapy directed against B-cell maturation antigen (BCMA). The bi-epitope BCMA binding moieties confer high avidity binding and distinguish LCAR-B38M from other BCMA CAR constructs. Preliminary results of LCAR-B38M in patients (pts) with relapsed/refractory (R/R) multiple myeloma (MM) showed encouraging efficacy and manageable safety (Fan et al.JCO 2017;35:18_suppl LBA3001). Here we present updated safety and efficacy results of the trial. LEGEND-2 (NCT03090659) is an ongoing phase 1, single-arm, open-label multicenter study evaluating LCAR-B38M in pts (18-80 years) with R/R MM. Lymphodepletion was performed using 3 doses of cyclophosphamide 300 mg/m2 on days -5, -4, and -3. Five days after lymphodepletion, LCAR-B38M CAR T cells (median CAR+ cell dose = 0.5x106 cells/kg, [range, 0.07-2x106]) were given in 3 infusions (20, 30, and 50% of total dose). The primary objective is to evaluate the safety of LCAR-B38M CAR T cells; the secondary objective is to evaluate the anti-myeloma response of the treatment. Adverse events (AEs) were graded using the Common Terminology Criteria for AE, v.4.03, and cytokine release syndrome (CRS) was assessed according to Lee et al. (Blood 2014;124:188-95). Response was evaluated using International Myeloma Working Group criteria. This analysis presents data from a single institution. As of June 25, 2018, 57 pts have been infused with LCAR-B38M CAR T cells. The median age was 54 years (range, 27-72), median number of prior therapies was 3 (range, 1-9), and 74% of pts had stage III disease by Durie-Salmon staging. The median duration of follow-up for all pts was 12 months (range, 0.7-25). AEs were reported by all pts; most common were pyrexia (91%), CRS (90%), thrombocytopenia (49%), and leukopenia (47%). Grade ≥3 AEs were reported by 65% of pts; most common were leukopenia (30%), thrombocytopenia (23%), and increased aspartate aminotransferase (21%). CRS was mostly grade 1 (47%) and 2 (35%); 4 pts (7%) had grade 3 cases. Liver function abnormalities were the most common signs of end organ injury among pts with CRS. The median time to onset of CRS was 9 days (range, 1-19). All but 1 CRS events resolved, with a median duration of 9 days (range, 3-57). No clear relationship was demonstrated between dose and CRS; there may be some effect at higher doses, but conclusions are limited by the small number of pts in the grade 3 CRS group (n=4; Figure 1A). Neurotoxicity was observed in 1 pt who had grade 1 aphasia, agitation, and seizure-like activity. The overall response rate (partial response [PR] or better) was 88% (95% confidence interval [CI], 76-95). Complete response (CR) was achieved by 42 pts (74%; 95% CI, 60-85), very good partial response was achieved by 2 pts (4%; 95% CI, 0.4-12), and PR was achieved by 6 pts (11%; 95% CI, 4-22; Figure 1B). Among pts with CR, 39/42 were minimal residual disease (MRD) negative by 8-color flow cytometry. The median time to initial response was 1 month (range, 0.4-4). No clear relationship between LCAR-B38M CAR T cell dose and response was observed (Figure 1C). BCMA expression did not correlate with clinical response. The median duration of response (DOR) was 16 months (95% CI, 12-not reached [NR]). The median DOR for pts who achieved a CR was 22 months (95% CI, 14-NR). At data cutoff, 18 pts (36%) who achieved PR or better progressed. The median progression-free survival (PFS) for all treated pts was 15 months (95% CI, 11-NR); median PFS for pts who achieved CR was 24 months (95% CI, 15-NR). The median overall survival was not reached. Overall, 17 pts died during the study and follow-up period; causes of death were progressive disease (PD; n=14), suicide after PD (n=1), esophagitis (n=1), and pulmonary embolism and acute coronary syndrome (n=1). Peak levels of LCAR-B38M (≥1x104 copies/µg genomic DNA) were observed in a majority of pts with blood samples for analysis (n=32). LCAR-B38M CAR T cells were not detectable in peripheral blood in 71% of pts at 4 months; 5 pts showed CAR T cell persistence up to 10 months. This ongoing first-in-human study has provided initial proof-of-concept that bispecific LCAR-B38M CAR T cells may be a highly effective therapy for R/R MM. LCAR-B38M CAR T cell therapy displayed a manageable safety profile consistent with its known mechanism of action and demonstrated deep and durable responses in pts with R/R MM. A phase 1/2 study of LCAR-B38M in R/R MM has been initiated in the US (NCT03548207). Disclosures Zhuang: Nanjing Legend Biotech: Employment. Fan:Nanjing Legend Biotech: Employment.