Luo, Yan

AbstractThe challenge of disease relapsed/refractory (R/R) remains a therapeutic hurdle in chimeric antigen receptor (CAR) T‐cell therapy, especially for hematological diseases, with chronic lymphocytic leukemia (CLL) being particularly resistant to CD19 CAR T cells. Currently, there is no approved CAR T‐cell therapy for CLL patients. In this study, we aimed to address this unmet medical need by choosing the B‐cell activating factor receptor (BAFF‐R) as a promising target for CAR design against CLL. BAFF‐R is essential for B‐cell survival and is consistently expressed on CLL tumors. Our research discovered that BAFF‐R CAR T‐cell therapy exerted the cytotoxic effects on both CLL cell lines and primary B cells derived from CLL patients. In addition, the CAR T cells exhibited cytotoxicity against CD19‐knockout CLL cells that are resistant to CD19 CAR T therapy. Furthermore, we were able to generate BAFF‐R CAR T cells from small blood samples collected from CLL patients and then demonstrated the cytotoxic effects of these patient‐derived CAR T cells against autologous tumor cells. Given these promising results, BAFF‐R CAR T‐cell therapy has the potential to meet the long‐standing need for an effective treatment on CLL patients.

While acknowledging that newer therapies have improved survival rates in chronic lymphocytic leukemia (CLL), patients with high-risk disease features are at an increased risk of treatment failure. Allogeneic hematopoietic cell transplantation (allo-HCT) was traditionally offered as front-line consolidation in high-risk CLL; however, with the emergence of targeted therapies like Bruton tyrosine kinase (BTK) and B-cell lymphoma 2 (BCL-2) inhibitors, the role of allo-HCT has been relegated to later stages of the disease. Patients with relapsed/refractory (R/R) CLL who have failed both BTK and BCL-2 inhibitors represent a therapeutic challenge owing to a poor prognosis. Chimeric antigen receptor T-cell (CAR T) therapies targeting CD19 have improved response rates and overall survival in various types of R/R B-cell non-Hodgkin lymphomas. For CLL, no approved CAR T-cell therapies are yet available. Emerging data appear to show a therapeutic benefit of CAR T-cell therapy in patients with R/R CLL, even after failing an allo-HCT.

e19501 Background: Relapsed and/or refractory (R/R) disease is observed in patients who receive CD19 targeting chimeric antigen receptor (CAR)-T cells to treat B-cell lymphoid leukemias and lymphomas. We generated a novel CAR, MC10029 that targets B-cell activating factor receptor (BAFF-R) to address this unmet medical need. Methods: We engineered a second-generation BAFF-R CAR (MC10029 CAR). The construct includes the single chain variable fragment (scFv) of our newly developed BAFF-R antibody with CD28 costimulatory and CD3ζ signaling domains. We confirmed MC10029 CAR-T cell antigen-specific activation with in vitro degranulation assays and a direct cytolytic assay. We used BAFF-R positive leukemia and lymphoma cell lines in both in vitro and in vivo models to further characterize MC10029 CAR-T cells, and finally, we enriched tumor primary cells from chronic lymphocytic leukemia (CLL) patients as a target for MC10029 CAR-T cells. In preparation for our Phase I clinical trial, we have manufactured three batches of CAR-T cells using a MC10029-encoding lentiviral vector produced under GMP conditions. The production batches of MC10029 CAR-T cells were evaluated for product quality with Viability, Identity and Potency as well as Safety from adventitious viral agents. Antigen specific cytotoxicity of the MC10029 CAR-T cells was confirmed using our standard degranulation assay. Results: MC10029 CAR-T cells elicited in vitro antigen-specific cytotoxicity against Nalm-6 cells, Z138 cells, MEC-1 cells, and a CD19 knock out Nalm-6 model designed to mimic CD19-negative R/R disease. We demonstrated in vivo antitumor effects of MC10029 CAR-T cells in NSG mice challenged with these same cell lines. We showed cytotoxicity of MC10029 CAR-T cells against CLL patients’ tumors. We also showed our quality control results to highlight our clinical trial trajectory. Conclusions: Novel MC10029 CAR-T cells showed broad utility against BAFF-R positive B-cell lymphoid malignancies in a series of in vitro, in vivo, and ex vivo models. With these robust data, we have moved forward to generate clinical grade MC10029 CAR-T cells using cGMP manufacturing and quality protocols in preparation of a MC10029 CAR-T cell Phase I clinical trial.