THU0036 FIRST-IN-HUMAN TRIAL OF BCMA-CD19 COMPOUND CAR IN THE TREATMENT OF AUTOANTIBODY MEDIATED DISORDERS

Background: Donor-specific anti-HLA antibodies (DSAs) are antibodies in the recipient directed against donor class I/II HLA antigens. The existence of DSAs before allogenic hematopoietic stem cell transplantation (AHSCT) are known to cause primary graft failure. Currently there’s no established method of DSA desensitization due to the long half-life of plasma cells. Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disease involving in multiple organ systems mediated by numerous autoantibodies. Recent results have shown that depletion of B cells by CD19 CAR-T cells effectively reversed some manifestations in two SLE mouse models. However, plasma cells could be spared with single CD19 CAR-T cells, and peripheral circulating anti-DNA IgG and IgM autoantibodies remain elevated or increased in treated mice. Objectives: We present the efficacy of BCMA-CD19 compound CAR (cCAR), which target on antibody- producing “root”, both B cells and plasma cells in preclinical study and in our first-in-human phase 1 clinical trial. Methods: We constructed a BCMA-CD19 cCAR composed of a complete BCMA-CAR fused to a complete CD19 CAR, separated by a self-cleaving P2A peptide. We assessed the functional activity of cCAR in co-culture assay with multiple cell lines. We also verified cCAR efficacy with two mouse models, injected with either BCMA-expressing MM.1S cells or CD19-expressing REH cells. In our phase 1 clinical trial, we enrolled patients with hematologic malignancies with antibody mediated disorders. Results: BCMA-CD19 cCAR exhibited robust cytotoxic activity against the K562 cells engineered to express either CD19 or BCMA in co-culture assays, indicating the ability of each complete CAR domain to specifically lyse target cells. In mouse model study, cCAR-T cells were able to eliminate tumor cells in mice injected with MM.1S cells and REH cells, indicating that both BCMA and CD19 are specifically and equally lysing B cells and plasma cells in vivo, making BCMA-CD19 cCAR a candidate for clinical use. In our first-in-human clinical trial, the first case is a 48-year-old female patient having resistant B-ALL with high DSA titers. She exhibited complete remission of B-ALL at day 14 post-CAR T treatment. MFI of DSA dropped from 7800 to 1400 at 8 weeks post cCAR treatment, the reduction percentage was approximately 80% (Figure 1). The patient had no CRS, and no neurotoxicity was observed. Figure 1. 1. A) MFI of DSA and other HLA antibodies before and at different time points after cCAR T infusion. B) the percent reduction post-transfusion of cCAR T cells at different time points. The second case is a 41-year-old female patient having a refractory diffuse large B cell lymphoma with bone marrow (BM) involvement. Furthermore, she has a 20 years of SLE, with manifestation of fever dependent of corticosteroids. On day 28 after cCAR treatment, PET/CT scan showed CR, and BM turned negative. In addition, she is independent of steroids, has no fever and other manifestations, C3/C4 are within normal ranges, and all the ANA dropped significantly, especially the nuclear type ANA, which turned from> 1:1000 to be negative at day 64. She had Grade 1 CRS but with no neurotoxicity observed. The absence of B cells and plasma cells persisted more than 5 months post CAR therapy. Conclusion: Our first in human clinical trial on BCMA-CD19 cCAR demonstrated profound efficacy in reducing DSA levels in an AHSCT candidate and ANA titer in a SLE patient. There was strong clinical evidence of depletion of antibody-producing roots, B-cells and plasma cells in both patients. Our results further suggested that BCMA-CD19 cCAR has the potential to benefit patients receiving solid organ transplants or those with other antibody-mediated diseases. Figure 2. Reduction of different type of ANA titer at different time points. Acknowledgments: patients and their families Disclosure of Interests: Fang liu: None declared, Hongyu Zhang: None declared, Xiao Wang: None declared, Jia Feng: None declared, Yuanzhen cao Employee of: Employee of iCell Gene Therapeutics LLC, Yi Su: None declared, Masayuki Wada Employee of: employee of iCell Gene Therapeutics LLC, Yu Ma Employee of: employee of iCAR Bio Therapeutics Ltd, Yupo Ma Shareholder of: shareholder of iCell Gene Therapeutics LLC