The clinical study of anti-BCMA CAR-T with single-domain antibody as antigen binding domain.

Abstract

8025 Background: Relapsed/refractory (RR) multiple myeloma (MM), RRMM, remains as an incurable disease and has a 5-year survival rate of nearly 50%. To address the unmet medical need, an autologous CAR-T cell therapy was developed previously with a humanized single-domain antibody (sdAb) targeting BCMA as the antigen binding domain, 4-1BB and CD3ζ as cytoplasmic domain. Methods: An investigator-initiated clinical trial (IIT) was conducted in China to assess the safety and efficacy of the sdAb-based CAR-T. The trail was started in June 2018 and the last patient infused in June 2019. As of 1 February 2021, 34 were treated and followed up. The patients had received multiple lines of prior treatment (including bortezomib, lenalidomide, and others). Following a lymphodepleting regimen of cyclophosphamide (300-600 mg/m2, d-5, -4) and fludarabine (25-30 mg/m2, d-5 to d-3), patients were infused with 2.5-10.0 × 106 CAR+ cells/kg body weight. CAR-T was infused immediately after preparation and quality control performed in all patients except one, who was infused a 10.0 × 106 CAR+ cells/kg dose of frozen cells. Efficacy was assessed based on the IMWG criteria, toxicity was graded by CTCAE 4.02, and CRS grading was based on the grading system by CARTOX working group. Results: All 34 patients had the tumor burden of plasma cells in bone marrow, or M protein or free light chains (FLCs) in serum, 7 patients were accompanied with extramedullary diseases. The efficacy shows the best ORR is 88.2% (30/34), sCR rate is 55.9% (19/34). The mPFS was 12.1 months, several patients shows continuous sCR after 2 years. No obvious correlation between efficacy and dosage were found in three dose groups of 2.5×106 CAR+ cells/kg (6 pts), 5.0×106 CAR+ cells/kg (23 pts) or 10.0×106 CAR+ cells/kg (5 pts). The observed adverse events include thrombocytopenia (≥grade 3, 38.2%), neutropenia (≥grade 3, 44.1%), leukopenia (≥grade 3, 32.4%), lymphopeniPa (≥grade 3, 26.5%), and anemia (≥grade 3, 20.6%). CRS was monitored occurring in 29 patients (any grade, 85.3%, ≥grade 3, 2.9%). Conclusions: Our result demonstrates that the CART employing one humanized sdAb targeting BCMA is safe and efficacious for clinical application. The phase I clinical trial has been initiated in China for searching the RP2D using the cryopreserved CAR-T cells. Clinical trial information: NCT03661554.