Abstract 555: Allogeneic Natural Killer cells engineered to express HER2 CAR, Interleukin 15 and TGF beta dominant negative receptor effectively control HER2+ tumors
Authors: Richardson Celeste , Moore Finola , Alvarez Andres , Barandiaran Alexia , Barron Luke , Choi Eugene , Ezell Tucker , Franco Charlotte , Hamza Bashar , Johnson Jennifer , Khamhoung Annie , Kyung Taeyoon , Marques Marilyn , Picarella Dominic , Sewell Jared , Storer Alex , Walsh Meghan , Suri Vipin 
Published: June 2022

Abstract
Despite the success of HER2 targeted therapies in HER2+ breast and gastric cancer, additional therapies are needed to address treatment-resistant metastatic disease. Adoptive immune cell therapy is a promising therapeutic modality given the remarkable clinical responses seen with autologous chimeric antigen receptor (CAR) T cells in hematological malignancies. However, success of cell therapy in solid tumors has been more limited. Three major impediments to the success of adoptive cell therapies in solid tumors are the heterogeneity of antigen expression, the immunosuppressive tumor microenvironment (TME), and the inherent challenges of manufacturing autologous cells and consequent variability of these cell products. Engineered, off-the-shelf, allogeneic Natural Killer (NK) cells provide a solution to these challenges. We describe here CAT-179, a novel engineered CAR-NK cell therapeutic for HER2+ solid tumors. CAT-179 cells express three transgenes: a HER2-directed CAR to effectively eliminate tumor cells, a Transforming Growth Factor (TGF) β dominant negative receptor (DNR) for resistance to TGFβ -mediated immunosuppression in the TME, and Interleukin 15 (IL15) cytokine to enhance NK cell persistence and activity for durable response. High efficiency engineering of the large (~3.7Kb) cargo containing CAR, IL15, and DNR in CAT-179 is enabled by the non-viral TC Buster™ Transposon System. Transposon engineering of CAT-179 results in high and stable expression of CAR (45% CAR at day 7 post gene delivery) without the need for post-engineering selection. CAT-179 demonstrates both CAR-dependent and innate NK receptor-dependent tumor cell killing in vitro, reducing the likelihood of tumor escape through antigen loss. CAT-179 effectively kills in vitro both high HER2-expressing SKOV3 cells as well as lower HER2-expressing HT-29 cells. CAT-179 also demonstrates resistance to TGFβ mediated immunosuppression, as evidenced by 75% reduction in TGFβ -induced phosphorylation of SMAD2 as well as prevention of TGFβ induced downregulation of NK cell activating receptors and restoration of NK cell cytotoxic activity. These data suggest CAT-179 cells will be protected from TGFβ -mediated immune suppression in the TME. Finally, the addition of IL15 in CAT-179 significantly enhances persistence for at least fourteen days in vitro without the need for exogenous cytokines. Moreover, CAT-179 administration to NSG mice showed expansion and persistence of the transferred cell product. CAT-179 addresses key hurdles to allogeneic cell therapy for solid tumors and is a promising new therapeutic approach for HER2 expressing breast, gastric and other tumors.
Citation Format: Celeste Richardson, Finola Moore, Andres Alvarez, Alexia Barandiaran, Luke Barron, Eugene Choi, Tucker Ezell, Charlotte Franco, Bashar Hamza, Jennifer Johnson, Annie Khamhoung, Taeyoon Kyung, Marilyn Marques, Dominic Picarella, Jared Sewell, Alex Storer, Meghan Walsh, Vipin Suri. Allogeneic Natural Killer cells engineered to express HER2 CAR, Interleukin 15 and TGF beta dominant negative receptor effectively control HER2+ tumors [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 555.