Abstract 3576: FT500, an off-the-shelf NK cell cancer immunotherapy derived from a master pluripotent cell line, enhances T-cell activation and recruitment to overcome checkpoint blockade resistance

The development of PD1/PDL1 targeting checkpoint inhibitors (CI) has transformed the oncology landscape, providing long term remissions in multiple indications. However, many tumor subtypes are resistant to checkpoint blockade therapy, and relapse remains a significant concern. Novel therapeutic approaches with the ability to overcome CI resistance are needed, and there is significant opportunity for therapies capable of additively or synergistically enhancing T-cell activation and recruitment when combined with CI. Adoptive transfer of NK cells from healthy donors has the potential to recruit T cells to the tumor microenvironment and augment T-cell activation at the tumor site. NK cells have both direct anti-tumor activity and the capacity to secrete inflammatory cytokines and chemokines upon activation, enabling the cells to play a unique and critical role in regulating anti-tumor T cell activity. We sought to determine whether FT500, an off-the-shelf NK cell product derived from a clonal master pluripotent cell line, could synergize with CI to relieve local immunosuppression and enhance T-cell activation and recruitment to the tumor site. FT500 is universally negative for cell surface PD1, and expression of PDL1 on tumor lines had no discernable effect on FT500 cytotoxicity. Similarly, addition of PDL1 blocking antibody had no effect on FT500 cytotoxicity or degranulation, suggesting that FT500 is inherently resistant to PDL1-PD1 mediated inhibition. Additionally, activation of FT500 induced the secretion of soluble factors capable of enhancing T-cell activation, as evidenced by increased upregulation of CD69. We hypothesized that FT500 might also enhance CI by promoting recruitment of T cells to the tumor site. Using conventional in vitro transwell migration assays, we found that FT500 produced soluble factors that promoted the migration of activated T cells. Additional profiling confirmed FT500 production of a range of chemokines, including CCL3, CCL4, CXCL10 and CCL22. Furthermore, using an in vivo recruitment model, FT500 was able to recruit T cells out of the circulation and into the peritoneal cavity. Similarly, utilizing a three-dimensional tumor spheroid model in vitro, infiltration of T cells into tumor spheroids was significantly enhanced when combined with FT500, suggesting that FT500 can enhance tumor infiltration of T cells. Our data suggest that FT500 is a potent producer of chemokines and can facilitate the recruitment of T cells to the tumor site. In addition to its direct cytotoxic potential, FT500 is also able to enhance T-cell activation, suggesting an ability to synergize with CI to reduce tumor burden. Together, our data provide evidence supporting the combination of FT500, an off-the-shelf NK cell cancer immunotherapy, with CI to overcome checkpoint blockade resistance. Citation Format: Ryan Bjordahl, Sajid Mahmood, Svetlana Gaidarova, Ramzey Abujarour, Raedun Clarke, Laurel Stokely, Paul Rogers, Moyar Ge, Megan Robinson, Betsy Rezner, Tom Tong Lee, Bahram Valamehr. FT500, an off-the-shelf NK cell cancer immunotherapy derived from a master pluripotent cell line, enhances T-cell activation and recruitment to overcome checkpoint blockade resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3576.