IMMU-22. ALLOGENEIC NK CELLS SECRETING IL15 AND RESISTANT TO TGF-β Show Antitumor Activity Against Gliobastoma

INTRODUCTION: High grade brain cancers, like most solid tumors, often relapse and are resistant to current therapies. Limited efficacy to cell therapy may be related to intratumoral heterogeneity and the suppressive tumor microenvironment. Hence, we aimed to modify allogeneic natural killer (NK) cells, which can recognize expressed tumor stress ligands, to resist TGF-β and secrete IL15. METHODS: Cord blood-derived NK cells were expanded and modified to express IL15 and a dominant negative receptor (DNR) against TGF-β. NK cell product activity against the GBM cell line U87MG were evaluated in vitro and in vivo. The behavior of these cells were also analyzed ex vivo, to evaluate the impact (including potential toxicity) of increasing the potency of this allogeneic NK cell product. RESULTS: While animals injected with NK cells secreting IL15 and expressing DNR successfully cleared tumors 6 days after T cell infusion, we did not observe significant differences in survival between the groups (no treatment control mice vs treated with mock-transduced NK cell vs DNR-transduced NK cells vs IL-15/DNR-transduced NK cells). Therefore, we sought to determine whether cytokine-related toxicity was responsible for death in the setting of tumor clearance. We compared no treatment control mice vs mice treated with mock-transduced or IL-15/DNR-transduced NK cell products. Elevated levels of IL-15 were detected in the plasma of mice treated with IL-15/DNR-transduced NK cells. These elevated IL-15 levels corresponded with NK cell persistence in the brain measured by ddPCR. However, no other cytokines were upregulated. CONCLUSIONS: We observed improved tumor clearance when NK cells were both protected against immune suppressive TGF-β and were capable of secreting the stimulatory cytokine IL15. We are currently performing additional experiments to determine whether toxicity from IL15 secretion occurs. To potentially mitigate this toxicity we plan to engineer a suicide gene into these constructs.