Reprogramming of exhausted T cells in pancreatic cancer with SBRT/IL-12 therapy

Pancreatic ductal adenocarcinoma (PDAC) has a poor 13% 5-year survival rate and is the 3 rd leading cause of cancer related deaths in the US. Current treatment options include surgical resection, chemotherapy, and radiation. Surgical resection is the only treatment with curative potential, however, few PDAC patients are eligible, and recurrence rates are high. The limited efficacy of targeted interventions is largely attributed to the highly immunosuppressive tumor microenvironment (TME) in PDAC. The PDAC TME has a dense stromal peripheral layer that restricts effector cell infiltration and a myeloid cell compartment that suppresses the anti-tumor function of intratumoral T cells. Chronic antigen presentation to T cells also induces T cell exhaustion in the PDAC TME, further limiting anti-tumor responses. T cell exhaustion is typically described by increased expression of inhibitory receptors and limited cytotoxic potential and is a major barrier to effective PDAC therapeutics. Our lab has developed a pre-clinical orthotopic KP2 PDAC mouse model that recapitulates the immunosuppressive PDAC TME. However, the functionality and subsets of exhausted T cells (Tex cells) present in this model have not been fully understood. To examine Tex cell dynamics in the PDAC TME, we have used flow cytometry to identify progenitor, intermediate, and terminally exhausted T cells based on their differential expression of PD-1, Ly108, and Tim3. Using additional markers of exhaustion and activation, we show that the intermediate Tex population (PD-1+, Ly108+, Tim3+) has the most effector-like phenotype in the PDAC TME, suggesting a potential role of intermediate Tex cells in tumor control. To target the PDAC TME, we developed a novel therapeutic that combines stereotactic body radiation therapy (SBRT) and IL-12 immunotherapy. SBRT/IL-12 therapy repolarizes the PDAC TME and results in abrogation of PDAC tumor burden and long-term survival. Single-cell RNA sequencing reveals a decrease in the exhausted T cell phenotype after SBRT/IL-12 therapy, and cytotoxicity assays demonstrate restoration of anti-tumor functions of T cells post-therapy. Flow cytometry analysis of Tex subsets in the PDAC TME demonstrates repolarization towards cytotoxicity and activation of each subset, including the most severely exhausted terminally exhausted T cells. These findings suggest that the reprogramming of Tex cells in the PDAC TME is important for the efficacy of SBRT/IL-12 therapy. This work also informs the broader application of SBRT/IL-12 therapy to other solid tumors.