Agonism of 41BB (CD137), a costimulatory molecule in the TNFR family, has profound consequences on the metabolic state of CD8+ T cells, as revealed by Menk et al. Signaling through p38-MAPK and upregulation of PCG1α leads to increased mitochondrial mass, mitochondrial fusion, and increased available ADP, positioning the cell for a rapid metabolic response. 41BB agonism, even transiently, enhances the impact of anti-PD-1 therapy and adoptive T cell therapy, highlighting the importance of metabolic sufficiency of antitumor T cells.

Despite remarkable responses to cancer immunotherapy in a subset of patients, many patients remain resistant to these therapies. The tumor microenvironment can impose metabolic restrictions on T cell function, creating a resistance mechanism to immunotherapy. We have previously shown tumor-infiltrating T cells succumb to progressive loss of metabolic sufficiency, characterized by repression of mitochondrial activity that cannot be rescued by PD-1 blockade. 4-1BB, a costimulatory molecule highly expressed on exhausted T cells, has been shown to influence metabolic function. We hypothesized that 4-1BB signaling might provide metabolic support to tumor-infiltrating T cells. 4-1BB costimulation of CD8(+) T cells results in enhanced mitochondrial capacity (suggestive of fusion) and engages PGC1alpha-mediated pathways via activation of p38-MAPK. 4-1BB treatment of mice improves metabolic sufficiency in endogenous and adoptive therapeutic CD8(+) T cells. 4-1BB stimulation combined with PD-1 blockade results in robust antitumor immunity. Sequenced studies revealed the metabolic support afforded by 4-1BB agonism need not be continuous and that a short course of anti-4-1BB pretreatment was sufficient to provide a synergistic response. Our studies highlight metabolic reprogramming as the dominant effect of 4-1BB therapy and suggest that combinatorial strategies using 4-1BB agonism may help overcome the immunosuppressive metabolic landscape of the tumor microenvironment.

Author Info: (1) Tumor Microenvironment Center, UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA. (2) Tumor Microenvironment Center, UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh

Author Info: (1) Tumor Microenvironment Center, UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA. (2) Tumor Microenvironment Center, UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA. Department of Immunology, University of Pittsburgh, Pittsburgh, PA. (3) Tumor Microenvironment Center, UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA. Department of Immunology, University of Pittsburgh, Pittsburgh, PA. (4) Department of Cell Biology, University of Pittsburgh, Pittsburgh, PA. (5) Tumor Microenvironment Center, UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA. Department of Immunology, University of Pittsburgh, Pittsburgh, PA. (6) Tumor Microenvironment Center, UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA. (7) Department of Immunology, University of Pittsburgh, Pittsburgh, PA. Department of Cell Biology, University of Pittsburgh, Pittsburgh, PA. (8) Tumor Microenvironment Center, UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA gdelgoffe@pitt.edu. Department of Immunology, University of Pittsburgh, Pittsburgh, PA.

Less