Abstract LB009: A BCMA-specific allogeneic CAR-T cell therapy (CB-011) genome-engineered to express an HLA-E fusion transgene to prevent immune cell rejection

Abstract The approval and commercial launch of multiple first-generation CD19- or BCMA-directed, autologous CAR-T cell products have laid the foundation and opened a path for the development of more advanced cellular therapeutics, including CAR-T cell products with next-generation capabilities. Among these newer designs, allogeneic cell therapies are positioned to unlock the broad potential of engineered immune cells as a leading therapeutic modality. However, expansion, persistence, armoring, and trafficking of allogeneic CAR-T cells are critical to achieving long-term efficacy. Caribou Biosciences is advancing a BCMA-specific allogeneic CAR-T cell product candidate, CB-011, with an immune cloaking approach that includes both the removal of the endogenous B2M protein and the insertion of a B2M-HLA-E-peptide (B2M-HLA-E) fusion protein transgene. This strategy is designed to blunt CAR-T cell rejection by both recipient T cells and NK cells, and CB-011 is in preclinical development for relapsed or refractory multiple myeloma (r/r MM). We used Cas12a chRDNA guides in the manufacture of CB-011 to make four edits, including site-specific insertion of a proprietary humanized anti-BCMA CAR into the TRAC locus with high specificity and efficiency, thus eliminating TCR expression to prevent graft-versus-host disease (GvHD). In addition, we inserted a gene encoding a B2M-HLA-E fusion protein into the native B2M gene locus. This method simultaneously prevents the expression of the native B2M protein and expresses a minor HLA class I antigen HLA-E to blunt both T- and NK-mediated rejection of the CAR-T cells by the recipient’s immune system. B2M is a protein that stabilizes all HLA class I antigens on the cell surface, therefore its knockout eliminates endogenous HLA class I presentation on the surface of the CAR-T cells. To demonstrate that the B2M-HLA-E fusion protein expression protects CB-011 from NK-mediated cell killing, we developed an in vitro competition assay in which CB-011 cells are co-incubated with NK cells. We observed that CAR-T cells expressing the B2M-HLA-E fusion have a survival advantage over cells that do not express the fusion in the presence of NK cells in vitro, indicating that they could resist killing by a recipient’s NK cells and potentially circulate longer. The BCMA-specific CAR leads to long-term survival in mice bearing established orthotopically-engrafted MM tumor cells. Furthermore, mice treated with high doses of CB-011 did not experience symptoms typical of GvHD. This strategy should enable CB-011 CAR-T cells to remain in circulation longer in recipients, providing for increased potential of antitumor activity. Citation Format: Elizabeth Garner, Emilie Degagne, Suparna Roy, Paul Donohoue, Tristan Fowler, Morena Stanaway, Vanina Vicena, Devin Mutha, Benjamin Schilling, McKay Shaw, Mara Bryan, Leslie Edwards, Stephen Smith, Bryan Kohrs, Lynda Banh, Kyle McSweeney, Justin Skoble, Steven Kanner. A BCMA-specific allogeneic CAR-T cell therapy (CB-011) genome-engineered to express an HLA-E fusion transgene to prevent immune cell rejection [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB009.