Development of an Allogeneic Anti-Bcma T Cell Therapy Utilizing a Novel Dimeric Antigen Receptor (DAR) Structure
Authors: Ding Bei Bei , Gray John Dixon , Zhang Nan , Zhang Yanliang , Cao Xia , Krapf Irina , Deng Qingdong Mark , Wei Angel , Zeldis Jerome B. , Knight Robert D. , Kaufmann Gunnar F. , Ji Henry , Guo Wenzhong 
Published: November 2019

Background: Multiple myeloma remains an incurable malignancy of plasma cells. Adoptive transfer of chimeric antigen receptor (CAR)-expressing T cells is a promising new therapy for hematologic malignancies. B-cell maturation antigen (BCMA) is a protein that is selectively expressed by B-lineage cells, including Multiple Myeloma (MM) cells, and represents a suitable target for T cell therapy. We have developed an allogeneic T cell therapy approach utilizing genetic engineering of donor-derived T cells to express an anti-BCMA Dimeric Antigen Receptor (DAR) using a proprietary non-viral vector Knock out/knock in (KOKI) technology. Preclinical data demonstrate potent anti-tumor activity both vitro and in vivo against BCMA-expressing MM cell lines.
Methods: Anti-BCMA DAR-T cells were generated through genetic engineering of T cells derived from healthy donors by inserting the anti-BCMA DAR construct into the TRAC gene locus, resulting in loss of endogenous TCR expression while expressing the DAR. Distinct DAR constructs were utilized differing only in their intracellular signaling components, namely combinations of 4-1BB, CD28, and CD3zeta. The anti-BCMA DAR-T cells were expanded and purified for subsequent preclinical studies. Using in vitro assays, the different anti-BCMA DAR-T cells were evaluated against multiple myeloma cell lines for specific cytotoxicity as well as stimulus-induced cytokine secretion and cell expansion. The in vivo anti-tumor activity was assessed using luciferase-expressing RPMI8226 cells in NSG mice in a model of disseminated disease. A single dose of anti-BCMA DAR-T cells or relevant control cells was administered, and tumor burden was assessed weekly using bioluminescence imaging.
Results: After purification, the anti-BCMA DAR T cells population contained less than 1% TCR-expressing ab T cells. The DAR-positive T cell population was between 20-50%. All anti-BCMA DAR-T cells exhibited BCMA-specific activation, including cytokine production, proliferation, cytotoxicity, and in vivo tumor eradication. The DAR-T cells using a third generation signaling configuration containing components from 4-1BB, CD28 and CD3zeta signaling domains performed best overall.
Conclusions: All tested anti-BCMA DAR-T cells exhibited effective anti-tumor activity. Direct comparison of different cytoplasmic signaling compositions of the DAR allowed for selection of the most potent construct, namely the anti-BCMA DAR utilizing a 3rd generation signaling domain configuration. Based on these data, further development of anti-BCMA DAR-T therapy for hematological malignancies is warranted. These allogeneic abTCR-negative anti-BCMA DAR-T cells have been selected for clinical development.

Disclosures
Ding: Sorrento Therapeutics, Inc.: Employment, Equity Ownership, Patents & Royalties. Gray:Sorrento Therapeutics, Inc.: Employment, Equity Ownership, Patents & Royalties. Zhang:Sorrento Therapeutics, Inc.: Employment, Equity Ownership. Zhang:Sorrento Therapeutics, Inc.: Employment, Equity Ownership, Patents & Royalties. Cao:Sorrento Therapeutics, Inc.: Employment, Equity Ownership, Patents & Royalties. Krapf:Sorrento Therapeutics, Inc.: Employment, Equity Ownership. Deng:Sorrento Therapeutics, Inc.: Employment, Equity Ownership. Wei:Sorrento Therapeutics, Inc.: Employment, Equity Ownership. Zeldis:Sorrento Therapeutics Inc: Employment, Equity Ownership. Knight:Sorrento Therapeutics, Inc.: Employment, Equity Ownership. Kaufmann:Sorrento Therapeutics, Inc.: Employment, Equity Ownership, Patents & Royalties. Ji:Sorrento Therapeutics Inc: Employment, Equity Ownership, Patents & Royalties; Celularity, Inc.: Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Guo:Sorrento Therapeutics, Inc.: Employment, Equity Ownership, Patents & Royalties.