Abstract C021: Targeted delivery of neoantigens to pancreatic cancer to enable immunotherapy
Authors: Sun Siming , Patel Jay , Wascher Alexis , Mose Evangeline S. , Jaquish Dawn , Brightman Spencer , Schoenberger Stephen , Lowy Andrew M. , de Mendoza Tatiana Hurtado 
Published: November 2022

Abstract
Immunotherapy has become a standard of care treatment for many cancer types. Anti-tumor immune responses are elicited against neoantigens that arise from genetic alterations within tumor cells, and high tumor mutational burden increases the likelihood of response to immune checkpoint blockade. Pancreatic duct adenocarcinoma, has relatively modest mutational burden, often accompanied by an immunosuppressive microenvironment, rendering them resistant to immunotherapy. Introduction of neoantigens by transduction of tumor cells or by intra-tumoral injection have been shown to lead to tumor rejection or delayed growth, and to sensitization to immunotherapy. iRGD is a tumor-targeting peptide that binds to av integrins expressed on tumor vasculature. It is proteolytically processed to expose a motif (R/KXXR/K) that interacts with neuropilin-1, leading to extravasation into the tumor. Therapeutics conjugated or co-administered with iRGD can be delivered to the tumor. Here we have explored the concept of iRGD mediated delivery of neoantigens to tumors to promote antitumor immune responses. This concept was initially tested in a model of breast cancer by delivering the ovalbumin antigen SIINFEKL ( OVAI) to tumors followed by adoptive T cell transfer of OVAI specific T cells (OTI). In this model, we observed tumor regression in 70% of the mice treated with iRGD+OVA. Within the responders, 42% had a complete response without apparent toxicity. In order to adapt this strategy to pancreatic cancer, we tested KPC derived tumor cell lines for the potential of presenting OVAI in their MHCI followed by CTL assays that showed the ability of OTI T cells to kill tumor cells presenting OVAI. The initial treatment studies in pancreatic cancer were performed by injecting 1199 KPC cells into the pancreas of C57B6 mice. One week post injection, mice were treated with a one-time intravenous injection of OTI CD8 and OTII CD4 T cells plus OVAI, OVAII (ISQAVHAAHAEINEAGR) and iRGD. Unfortunately, no differences in tumor volume or survival were observed compared to controls. We hypothesized that the immunosuppressive environment of the pancreas could be inhibiting T cell responses and next combined the T cell therapy with low dose gemcitabine (5mg/kg). The rationale for this combination comes from recent data from our laboratory showing that low dose gemcitabine reduces the percentage of MDSCs and increases DCs in tumors, leading to increased T cell activation. We therefore treated mice with low dose gemcitabine alone (2 times per week), iRGD+OVAI+OTI T cells (1 time) or the combination. Mice were sacrificed at 3 weeks post tumor cell implantation. We observed that the combination group had the lowest tumor weight and volume compared to either treatment alone. These preliminary experiments suggest a potential benefit for combining strategies that relieve immunosuppression by reducing MDSCs with strategies that induce T cell activation by neoantigen delivery to the tumor.
Citation Format: Siming Sun, Jay Patel, Alexis Wascher, Evangeline S. Mose, Dawn Jaquish, Spencer Brightman, Stephen Schoenberger, Andrew M. Lowy, Tatiana Hurtado de Mendoza. Targeted delivery of neoantigens to pancreatic cancer to enable immunotherapy [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C021.