Targeting a non-canonical STING signaling pathway in T cells to improve antitumor immunity.
Authors: Meier Jeremy , Petrova Aleksandra , Hurst Katie , Gandy Evelyn , Thaxton Jessica , Serody Jonathan Stuart 
Published: June 2024

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Background: While chimeric antigen receptor (CAR) T cell therapies have revolutionized the treatment of hematologic malignancies, they are less effective in treating solid tumors, which is in part due to the poor persistence and decreased survival of these cells in the tumor microenvironment (TME). The stimulator of interferon genes (STING) signaling axis has emerged as a promising target to remodel the TME to make it more immune favorable, and work from our group previously demonstrated that STING agonists could improve the persistence and antitumor activity of CAR T cells in an immunocompetent murine breast tumor model. Yet, the T cell intrinsic effect of STING activation is thought to decrease T cell proliferation and lead to T cell death. Thus, we sought to better understand the impact of activating STING in different T cell subsets to be able to more effectively target STING as an adjunct to cellular therapies. Methods: Primary T cell cultures generated from murine splenocytes and human peripheral blood mononuclear cells were polarized in vitro towards either a Th/Tc1 or Th/Tc17 lineage and treated with the mammalian STING agonist 2’3’-cGAMP. Cells were subsequently characterized by immunophenotyping, bioenergetic analysis, and RNA sequencing. Adoptive cell transfer experiments in a murine melanoma model and an immunocompetent murine breast cancer model utilizing an anti-Neu CAR T cell were employed to determine the differential impact of STING agonism on T cell subsets in vivo. Results: While treatment of Th/Tc1 cells with cGAMP led to impaired proliferation and T cell death, Th/Tc17 cells were immune to this effect. Instead, cGAMP triggered activation of a non-canonical STING pathway in Th/Tc17 cells resulting in metabolic reprogramming in favor of fatty acid oxidation over glycolysis. Th/Tc17 cells treated with cGAMP assumed more of a stem like memory T cell phenotype and displayed a more favorable bioenergetic profile with improved mitochondrial health and decreased reactive oxygen species production. Adoptive transfer of cGAMP conditioned Th/Tc17 memory like cells enhanced tumor control in an aggressive murine melanoma model, which was secondary to improved persistence of T cells in the TME. Further, while intratumoral delivery of STING agonists augmented the antitumor activity of Th/Tc17 cells, the function of Th/Tc1 cells was impeded by activating STING. Conclusions: STING activation in T cells leads to differential responses within T cell subsets as Th/Tc17 cells uniquely shift to a more fit T cell with improved antitumor properties. As cGAMP is found in the tumor microenvironment and can be secreted by tumor cells, CAR T cells with a greater Th/Tc17 footprint may be able to better subsist in the TME. Our findings also provide insight into how to engineer cellular therapies to take advantage of this non-canonical pathway to optimize the integration of STING based therapeutics into patient treatments.