Multiplexed Engineered, Off-the-Shelf T Cells Carrying Three Tumor-Associated Antigen-Targeting Modalities: CAR + Pan-Tumor Targeting TCR + CD16 Fc Receptor
Authors: Nguyen Cokey , Peralta Eigen , Chang Chia-Wei , Yeh Wen-I , Pan Yijia , Lu Dan , Sumi May , Pribadi Mochtar , Yang Bi-Huei , Sung Eric , Witty Alec , Lee Tom 
Published: November 2020

Autologous chimeric antigen receptor (CAR)-T cell therapy has shown great promise in various hematologic malignancies. However, the complexities associated with immune cell evasion are prevalent causes of disease relapse in many cancers. With the advent of pluripotent stem cell (iPSC)-derived CAR-T cells, many factors that hamper therapeutic efficacy of CAR-T cells can be addressed through multiplexed engineering at the clonal level. This includes enhanced potency, increased capacity for multi-antigen targeting, and the consistency of a clonally derived engineered cellular product for off-the-shelf patient administration. In particular, strategies to mitigate antigen escape and address tumor heterogeneity may help promote durable responses.
To combine the potent targeted therapy of the CAR with universal targeting of secondary and tertiary antigens, we expressed an MR1 clonal T cell receptor (TCR) and a high-affinity, non-cleavable CD16 Fc receptor (hnCD16) in our iPSC-derived CAR19 T cells (CAR19-iT cells) directed to leukemia and lymphoma and CAR-MICA/B T cells directed to solid tumors. The MR1-TCR allows highly specific recognition of tumor associated antigen presented by the MR1 protein. The non-polymorphic MHC class I-related protein MR1 is widely expressed with minimal variability among patients and enables the unique prospect to be a universal cancer immunotherapy by using the cognate MR1-TCR. The hnCD16 Fc receptor has been shown to improve antibody-dependent cellular cytotoxicity (ADCC) leveraging the broad range of available therapeutic monoclonal antibodies to target clinically validated tumor antigens. A preliminary assessment demonstrated that MR1-TCR overexpressed in T cells allowed for enhanced recognition of multiple hematological and solid tumor cell lines. Notably, prominent target specific killing was seen in A549 lung carcinoma cells (&gt;75% reduction in total viable cells) with the directed cytotoxicity specifically inhibited by an MR1 blocking antibody. Next, in vitro functional testing was performed on the engineered CAR19-iT cells in co-culture assays where we measured killing of tumor cells via MR1-TCR engagement and via hnCD16 mediated ADCC. Specifically, we show that CAR19-iT cells expressing hnCD16 can be efficiently directed to lyse CD20+ Raji cells in the presence of rituximab or HER2+ SKOV3 cells in the presence of Herceptin, demonstrating the potential to target both hematological malignancies and solid tumors with one target modality in combination with various monoclonal antibodies. Moreover, CAR19-iT cells expressing either MR1-TCR or hnCD16 show the ability to control growth of CD19 KO lymphoma cells in the co-culture assays, further highlighting the unique ability to elicit multiple ways to target antigen escape. Further in vitro and in vivo combinatorial targeting studies focused on antigen escape and tumor heterogeneity are ongoing and will be discussed. In summary, the advances presented here demonstrate that both the MR1-TCR and hnCD16 modalities synergize with CAR-iT cells as an off-the-shelf therapeutic that can provide durable responses and enable broad applicability for targeting of additional tumor antigens where single-agent therapeutics fail to provide clinical benefit for patients.

Disclosures
Nguyen: Fate Therapeutics, Inc.: Current Employment. Peralta:Fate Therapeutics, Inc.: Current Employment. Lu:Fate Therapeutics, Inc.: Current Employment. Sung:Fate Therapeutics, Inc.: Current Employment. Lee:Fate Therapeutics, Inc.: Current Employment.