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

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/m 2 on days -5, -4, and -3. Five days after lymphodepletion, LCAR-B38M CAR T cells (median CAR+ cell dose = 0.5x10 6 cells/kg, [range, 0.07-2x10 6 ]) 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 (≥1x10 4 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.