Introduction: Pancreatic Cancer (PC) has a highly immunosuppressive microenvironment with a low mutational burden and has so far been resistant to immunotherapy. Irreversible electroporation (IRE) is a non-thermal method of inducing tumor cell death, without damage to adjacent blood vessels, that is being used clinically for selected patients with locally advanced PC. Despite local control rates greater than 90%, most IRE patients develop distant recurrence, emphasizing the need for better methods to treat micrometastatic disease. Using an immunocompetent mouse model of PC, we have previously shown that IRE induces complete regression in 25-33% of subcutaneous tumors, and complete responders are protected from a tumor rechallenge. However, IRE alone did not produce significant therapeutic immunity (abscopal effects) against concomitant distant tumors. We hypothesized that combination of IRE with innate immune stimulators would also enhance the adaptive immune response.

Methods: We used a cell line generated from a genetically engineered (KPC) mouse establish bilateral flank tumors. The “primary” tumor was treated with IRE alone or in combination with local delivery of a toll-like receptor 7 (TLR7) agonist (1V270) and CD40 agonistic antibody (CD40Ab). 15 parameter procartaplex (Thermo) was used for cytokine analysis and RNA-Seq was performed using an Illumina MiSeq 1000 platform with total RNA from excised tumor all on day 7 post procedure.

Results: We observed complete regression in 8/10 tumors treated with the combination (Combo) of IRE, 1V270 and CD40Ab compared to 3/10 in IRE alone. However, the combo was much more effective than IRE alone at inducing regression of the untreated secondary flank tumor, including complete regression of 7/10 untreated tumors. CD40Ab alone had minimal effect on local or secondary tumor growth. Analysis of systemic cytokines using multiplex analysis showed 112 fold increase in IFNy levels in plasma with the Combo compared to untreated mice (P<0.001) and a 39 fold increase compared to IRE alone (P<0.001). Other factors of Th1 response such as IP-10 and IL12-P70 were also significantly (P<0.001) higher in the Combo group compared to IRE alone along with TNFa (elevated 3.2 fold vs IRE). RNA-Seq of the whole tumor followed by gene set enrichment analysis showed significant elevation in Type II interferon, (P<0.0001), IL2 (P<0.0001), and apoptosis (P=0.0001) pathways in the Combo group. Both IRE alone and the Combo group complete responders were protected from tumor growth after immediate rechallenge (14 days) and delayed rechallenge (180 days). However, flow cytometric analysis of the splenocytes revealed that the combo group had more CD44+CD62L+CD8+ central memory T-cells (16%) in contrast to IRE alone (11%).

Conclusion: These data suggest that local delivery of CD40Ab and TLR7 agonists augment the systemic immune effects of IRE and have the potential to improve the overall survival of patients undergoing IRE for locally advanced PC by reducing distant recurrence.

Citation Format: Jayanth Surya Narayanan Shankara Narayanan, Diego Vicente, Partha Ray, Thomas Whisenant, Rebekah White. Combining irreversible electroporation with TLR7 and CD40 agonists confers systemic anti-tumor immunity in a murine pancreatic cancer model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2221.