Melanoma Evolves Complete Immunotherapy Resistance through the Acquisition of a Hypermetabolic Phenotype.

Despite the clinical success of T cell checkpoint blockade, most cancer patients still fail to have durable responses to immunotherapy. The molecular mechanisms driving checkpoint blockade resistance, whether pre-existing or evolved, remain unclear. To address this critical knowledge gap, we treated B16 melanoma with the combination of CTLA-4, PD-1, and PD-L1 blockade and a Flt3 ligand vaccine (≥75% curative), isolated tumors resistant to therapy, and serially passaged them in vivo with the same treatment regimen until they developed complete resistance. Using gene expression analysis and immunogenomics, we determined the adaptations associated with this resistance phenotype. Checkpoint resistance coincided with acquisition of a "hypermetabolic" phenotype characterized by coordinated upregulation of the glycolytic, oxidoreductase, and mitochondrial oxidative phosphorylation pathways. These resistant tumors flourished under hypoxic conditions whereas metabolically starved T cells lost glycolytic potential, effector function, and the ability to expand in response to immunotherapy. Further, we found that checkpoint resistant versus sensitive tumors could be separated by non-invasive MRI imaging based solely on their metabolic state. In a cohort of melanoma patients resistant to both CTLA-4 and PD-1 blockade, we observed upregulation of pathways indicative of a similar hypermetabolic state. Together these data indicated that melanoma can evade T cell checkpoint blockade immunotherapy by adapting a hypermetabolic phenotype.