Regulation of Immunometabolism by the Integrated Stress Response in Cancer

Metabolic stress in the tumor microenvironment (TME) has emerged as a barrier to CD8+ tumor infiltrating lymphocyte (TIL) antitumor function in solid cancers. The integrated stress response (ISR) is an evolutionarily conserved pathway intrinsic to all mammalian cells poised to sense and respond to diverse metabolic stressors. However, it is poorly understood how the ISR integrates and regulates CD8+ TIL function in the stress of the TME. Activating transcription factor 4 (ATF4) is the central node of the ISR. In states of chronic stress, persistent ATF4 activity results in loss of cell metabolic homeostasis. Our recent work demonstrated that hypoxia in the TME enforces chronic ATF4 activity in CD8+ TILs, resulting in robust loss of tumor control. Pharmacologic inhibition of ATF4 enabled complete response to immune checkpoint inhibitor (ICI) therapy in therapy-resistant mouse models. However, the mechanism through which chronic ATF4 programs loss of CD8+ TIL metabolic homeostasis in the hypoxic TME remains elusive. Here we reveal preliminary data that position ATF4 as the central TME stress-responsive regulator of lipid metabolism in CD8+ TILs. We find that chronic ATF4 activity transcriptionally programs lipogenesis in CD8+ T cells, resulting in robust accumulation of intracellular lipid stores that we have previously shown govern CD8+ TIL cell metabolism. Due to elevated risk factors of alcohol and tobacco use, head and neck squamous cell carcinomas (HNSCCs) are a tumor type predominantly afflicted by hypoxia and lipogenesis across the TME and ICIs show only modest efficacy in HNSCC patients. Our preliminary data show that CD8+ TILs isolated from ICI therapy-resistant HNSCC patients display a gene signature indicative of chronic ATF4 activity. This proposal will test the central hypothesis that chronic ATF4 activity orchestrates steatosis in CD8+ TILs and serves as a primary metabolic checkpoint for ICI response in HNSCC patients. Aim 1 of this proposal will use T cells deficient in ISR kinases, mouse models with varied expression of ATF4, and CD8+ T cells isolated from HNSCC patients paired with metabolic imaging, scRNA-seq, CHIP-seq, metabolomics, lipidomics, and Seahorse bioanalysis to define the mechanisms upstream and downstream of chronic ATF4 activity that regulate steatosis in CD8+ TILs. Results from this aim will establish a radical new paradigm for ISR regulation of CD8+ TIL metabolism. Aim 2 of this proposal will use single-cell spatial transcriptomics, single-cell ultrahigh-plex spatial phenotyping, and pharmacologic inhibition of the ISR to determine the association between ATF4-regulated lipogenesis and ICI response in HNSCC patients. Results from this aim will elucidate a regulatory network of chronic ISR activity and metabolic fate in human CD8+ TILs, providing new avenues for clinical trial development. Project Number: 1R01CA310022-01 | Fiscal Year: 2026 | NIH Institute/Center: National Cancer Institute (NCI) | Principal Investigator: Jessica Thaxton | Institution: UNIV OF NORTH CAROLINA CHAPEL HILL, CHAPEL HILL, NC | Award Amount: $624,194 | Activity Code: R01 | Study Section: Cellular Immunotherapy of Cancer Study Section[CIC] View on NIH RePORTER: https://reporter.nih.gov/project-details/11319932