Abstract 2828: A novel synthetic stealth receptor that redirects host immune cell alloreactivity and potentiates functional persistence of adoptively transferred off-the-shelf cell-based cancer therapy

Abstract Chimeric antigen receptor (CAR) T-cell therapies have revolutionized the treatment of hematologic malignancies and have shown significant potential in solid tumor indications. However, logistical complexities associated with patient-specific CAR T-cell therapies often limit broad accessibility. Many of these challenges can be overcome with an allogeneic cellular product, but immune cell-mediated rejection of allogeneic cellular therapies remains a significant concern. Both allogeneic and autologous cell therapies currently rely on lymphodepleting conditioning to modulate the immune system and create greater access to homeostatic cytokines. However, protracted lympho-conditioning has been associated with poor immune reconstitution and increased susceptibility to opportunistic infections. Therefore, an ideal allogeneic cell therapy would be able to avoid immune rejection while reducing or eliminating the need for chemotherapeutic conditioning to deplete host lymphocytes. To address many of these challenges, we engineered our novel alloimmune defense receptor (ADR) that targets 41BB+ alloreactive immune cells while providing a CD3z signaling boost into our off-the-shelf iPSC derived NK cells expressing anti-CD19 CAR (CAR iNK). The ability of ADR+ CAR iNK cells to resist alloimmune rejection was tested by co-culturing ADR+ CAR iNK cells with allogeneic PBMCs from ten donors in a mixed lymphocyte reaction assay. Notably, ADR+ CAR iNK cells co-cultured with allogeneic PBMCs persisted to similar levels as the PBMC-free culture while ADR negative CAR iNK cells were eliminated when co-cultured with allogeneic PBMCs. Furthermore, all PBMC donors screened in ADR+ CAR iNK cell co-cultures showed ablation of reactive 41BB+ NK and T cells, with non-activated T cells remaining intact. CAR iNK cells +/- ADR were then compared in a Nalm6 disseminated in vivo model for anti-tumor efficacy. ADR+ CAR iNK cells and their ADR negative counterparts were found to equivalently control tumor. Building on this tumor model, we co-infused allogeneic T cells to mimic an immuno-competent setting. The data demonstrated that ADR negative CAR iNK cells were depleted and were unable to control tumor growth while significant levels of allogeneic T cells persisted. In contrast, ADR+ CAR iNK cells were able to resist allogeneic T cell attack, control tumor, and persist when compared to the ADR negative control. Collectively, our preliminary data suggest that ADR-armed CAR iNK cells withstand immune cell-mediated rejection with uncompromised effector function. We are actively developing models to confirm our initial finding that ADR+ effector cells also benefit from their engagement with alloreactive cells in immuno-competent settings to promote enhanced anti-tumor responses, proliferation, and persistence. Citation Format: Alan M. Williams, Ken Hayama, Yijia Pan, Brian Groff, Rina Mbofung, Lauren Fong, Nicholas Brookhouser, Berhan Mandefro, Ramzey Abujarour, Tom Lee, Quirin Hammer, Karl-Johan Malmberg, Maksim Mamonkin, Ryan Bjordahl, Jode Goodridge, Bahram Valamehr. A novel synthetic stealth receptor that redirects host immune cell alloreactivity and potentiates functional persistence of adoptively transferred off-the-shelf cell-based cancer therapy [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 2828.