A Novel and Highly Potent CAR T Cell Drug Product for Treatment of BCMA-Expressing Hematological Malignances

Abstract

Recently, B cell maturation antigen (BCMA) expression has been proposed as a marker for identification of malignant plasma cells in patients with multiple myeloma (MM). Nearly all MM and some lymphoma tumor cells express BCMA, while normal tissue expression is restricted to plasma cells and a subset of mature B cells. Targeting BCMA maybe a therapeutic option for treatment of patients with MM and some lymphomas. We are developing a chimeric antigen receptor (CAR)-based therapy for the treatment of BCMA-expressing MM. Our anti-BCMA CAR consists of an extracellular single chain variable fragment (scFv) antigen recognition domain derived from an antibody specific to BCMA, fused to CD137 (4-1BB) co-stimulatory and CD3zeta chain signaling domains. Selection of our development candidate was based on the screening of four distinct anti-BCMA CARs (BCMA01-04) each comprised of unique single chain variable fragments. One candidate, BCMA02 (drug product name bb2121) was selected for further studies based on the robust frequency of CAR-positive cells, increased surface expression of the CAR molecule, and superior in vitro cytokine release and cytolytic activity against the MM cell lines. In addition to displaying specific activity against MM (U226-B1, RPMI-8226 and H929) and plasmacytoma (H929) cell lines, bb2121 was demonstrated to react to lymphoma cell lines, including Burkitt's (Raji, Daudi, Ramos), chronic lymphocytic leukemia (Mec-1), diffuse large B cell (Toledo), and a Mantle cell lymphoma (JeKo-1). Based on receptor density quantification, bb2121 can recognize tumor cells expressing less than 1000 BCMA molecules per cell. The in vivo pharmacology of bb2121 was studied in NSG mouse models of human MM and Burkitt's lymphoma. NSG mice were injected subcutaneously (SC) with 107 RPMI-8226 MM cells. After 18 days, mice received a single intravenous (IV) administration of vehicle or anti-CD19Δ (negative control, anti-CD19 CAR lacking signaling domain) or anti-BCMA CAR T cells, or repeated IV administration of bortezomib (Velcade®; 1 mg/kg twice weekly for 4 weeks). Bortezomib, which is a standard of care for MM, induced only transient reductions in tumor size and was associated with toxicity, as indicated by substantial weight loss during dosing. The vehicle and anti-CD19Δ CAR T cells failed to inhibit tumor growth. In contrast, treatment with bb2121 resulted in rapid and sustained elimination of the tumors, increased body weights, and 100% survival. Flow cytometry and immunohistochemical analysis of bb2121 T cells demonstrated trafficking of CAR+ T cells to the tumors (by Day 5) followed by significant expansion of anti-BCMA CAR+ T cells within the tumor and peripheral blood (Days 8-10), accompanied by tumor clearance and subsequent reductions in circulating CAR+ T cell numbers (Days 22-29). To further test the potency of bb2121, we used the CD19+ Daudi cell line, which has a low level of BCMA expression detectable by flow cytometry and receptor quantification analysis, but is negative by immunohistochemistry. NSG mice were injected IV with Daudi cells and allowed to accumulate a large systemic tumor burden before being treated with CAR+ T cells. Treatment with vehicle or anti-CD19Δ CAR T cells failed to prevent tumor growth. In contrast, anti-CD19 CAR T cells and anti-BCMA bb2121 demonstrated tumor clearance. Adoptive T cell immunotherapy approaches designed to modify a patient's own lymphocytes to target the BCMA antigen have clear indications as a possible therapy for MM and could be an alternative method for treatment of other chemotherapy-refractory B-cell malignancies. Based on these results, we will be initiating a phase I clinical trial of bb2121 for the treatment of patients with MM. Disclosures Chekmasova: bluebird bio, Inc: Employment, Equity Ownership. Horton:bluebird bio: Employment, Equity Ownership. Garrett:bluebird bio: Employment, Equity Ownership. Evans:bluebird bio, Inc: Employment, Equity Ownership. Griecci:bluebird bio, Inc: Employment, Equity Ownership. Hamel:bluebird bio: Employment, Equity Ownership. Latimer:bluebird bio: Employment, Equity Ownership. Seidel:bluebird bio, Inc: Employment, Equity Ownership. Ryu:bluebird bio, Inc: Employment, Equity Ownership. Kuczewski:bluebird bio: Employment, Equity Ownership. Horvath:bluebird bio: Employment, Equity Ownership. Friedman:bluebird bio: Employment, Equity Ownership. Morgan:bluebird bio: Employment, Equity Ownership.

Preclinical Evaluation of Invariant Natural Killer T Cells Modified with CD38 or BCMA Chimeric Antigen Receptors for Multiple Myeloma

“…CD38B1-CAR (in short CD38-CAR) constructs containing different costimulatory domains were previously described in detail [ 42 , 43 ]. The BCMA-CAR contained the 4-1BB costimulatory domain and was constructed using the published murine scFv sequence derived from BCMA02 CAR (product name bb2121, WO 2016/094304 A2) [ 55 ]. In the SFG retroviral construct, the scFv was followed by a CD8a transmembrane domain and the 4-1BB and CD3ζ signaling domains or a CD28 transmembrane domain and intracellular sequence as described in Zhao et al [ 45 ].…”

Current advances in chimeric antigen receptor T-cell therapy for refractory/relapsed multiple myeloma

“…BCMA is uniformly present on MM cells, but its expression has shown a variable intensity in clinical samples of patients (Seckinger et al, 2017). As anti-BCMA CAR T cells have exhibited robust efficacy in myeloma control in preclinical studies (Chekmasova et al, 2015), BCMA CARs have set the stage for the rapid growth of worldwide clinical trials, and they have provided the most important clinical experience to date in MM.…”

Immunotherapeutics in Multiple Myeloma: How Can Translational Mouse Models Help?

“…CAR-T constructs have been created for use in MM against B cell maturation antigen (BCMA), CD19, and kappa light chains. Whilst a 100% cure rate was achieved in xenograft murine models with anti-BCMA constructs [78, 79], only very modest effects have been achieved in phase 1 trials in humans [80, 81]. Engineered NK cells specific to CD138 [82] and CS-1 [83] have also been effective in vitro and in vivo mouse models of human MM.…”