Preclinical Evaluation of Allogeneic Anti-Bcma Chimeric Antigen Receptor T Cells with Safety Switch Domains and Lymphodepletion Resistance for the Treatment of Multiple Myeloma
Authors: Boldajipour Bijan , Galetto Roman , Sommer Cesar , Pertel Thomas , Valton Julien , Park Yoon , Gariboldi Annabelle , Chen Amy , Geng Tao , Dong Hong H , Boucher Gregory R , Van Blarcom Thomas J , Chaparro-Riggers Javier , Rajpal Arvind , Smith Julianne , Kuo Tracy , Sasu Barbra 
Published: November 2019

Abstract
Multiple myeloma (MM) is a hematological disease of plasma B cells that remains incurable despite the availability of numerous therapies. The plasma cell-specific expression of the TNF superfamily receptor BCMA may allow targeting of normal and malignant plasma cells. Genetically engineered chimeric antigen-receptor T cells (CAR T) have shown tremendous promise in the treatment of several hematological diseases, including MM. However, conventional autologous CAR T therapies use patient-derived T cells and the logistics of on-demand CAR T manufacture limits their availability to a broad patient pool.
Here we describe the preclinical evaluation of an allogeneic CAR T therapy targeting BCMA that has the potential for a readily available, off-the-shelf therapy for MM and other malignancies expressing BCMA. Human T cells were transduced with recombinant lentiviral vectors encoding three BCMA CAR candidates designed with fully human anti-BCMA scFvs, CD8a transmembrane domains and the intracellular signaling domains of 4-1BB and CD3zeta. All CAR T efficiently killed BCMA-expressing multiple myeloma cell lines (KMS12BM, MM1.S, Molp-8 and OPM-2), but not BCMA-negative REH cells in vitro and in vivo. Whereas 2 of the 3 candidates exhibited target-independent cytokine production, accelerated T cell differentiation and reduced target cell-induced expansion in vitro, the third candidate did not exhibit this scFv-induced autoactivation and was chosen as the lead molecule.
Due to the allogeneic nature of this T cell therapy, the possibility of graft-versus-host (GvH) reactions can be a safety concern. We applied Cellectis' know-how and TALEN® technology for the gene inactivation of the T cell receptor (TCR) alpha chain to significantly reduce the probability for TCR-mediated GvH reactions and found that TCR knockout did not affect CAR T activity in vitro or in vivo. Furthermore, we incorporated intra-CAR rituximab-recognition domains into the CAR molecule to enable depletion of CAR T cells from patients when necessary. We found that this modified CAR retained anti-BCMA CAR T activity and enabled CAR T depletion by rituximab.
Another aspect of allogeneic CAR T therapies is the rejection of the CAR T by host-versus-graft (HvG) reactions. Lymphodepletion prior to CAR T infusion enhances CAR T efficacy in autologous CAR T trials and may also prevent anti-CAR HvG reactions in allogeneic therapy settings. Engineering lymphodepletion resistance into CAR T cells could therefore enable sustained lymphodepletion for enhanced allogeneic CAR T persistence and efficacy. CD52 is expressed on all lymphocytes and administration of the anti-CD52 antibody alemtuzumab for prolonged lymphodepletion is an approved treatment for multiple sclerosis. TALEN®-mediated knockout of CD52 protected BCMA CAR T from alemtuzumab-induced cytotoxicity and did not alter BCMA CAR T anti-tumor activity.
Taken together these results support allogeneic BCMA CAR T as an off-the-shelf adoptive immunotherapy for the treatment of multiple myeloma and other BCMA-positive malignancies.

Disclosures
Boldajipour: Pfizer: Employment. Galetto:Cellectis SA: Employment. Sommer:Pfizer Inc.: Employment. Pertel:Pfizer Inc.: Employment. Valton:Cellectis Inc.: Employment. Park:Pfizer Inc.: Employment. Gariboldi:Cellectis SA: Employment. Chen:Alexo Therapeutics: Employment. Geng:Kodiak Sciences: Employment. Dong:Pfizer Inc.: Employment. Boucher:Pfizer Inc.: Employment. Van Blarcom:Pfizer Inc.: Employment. Chaparro-Riggers:Pfizer Inc.: Employment. Rajpal:Pfizer Inc.: Employment. Smith:Cellectis SA: Employment. Kuo:Pfizer Inc.: Employment. Sasu:Pfizer Inc.: Employment.