Targeting T Cell Dynamics with IL12mRNA Nanotechnology-Enhanced SBRT to Overcome Immune Suppression in Pancreatic Cancer

Abstract public domain (NIH RePORTER)

Pancreatic ductal adenocarcinoma (PDAC) is the most lethal of all major cancers, largely due to a tumor microenvironment (TME) that fosters immune suppression and treatment resistance. Minimal clinical progress has been made against this malignancy over the past 50 years, therefore our laboratory has investigated an alternative treatment strategy that administers two therapies directly to the TME: local radiotherapy and intratumoral immunotherapy. This approach concentrates the therapeutic payload within the tumor, which we hypothesized could overcome the immunosuppressive PDAC TME. To test this, a novel technology was generated in which a modified monomeric mRNA sequence of the potent immunostimulatory cytokine interleukin-12 (IL12) was encapsulated in a lipid nanoparticle (LNP) designed to maximize intratumoral uptake and endosomal release of the ribonucleic acid when administered directly to the TME. This immunotherapeutic was combined with localized stereotactic body radiotherapy (SBRT), an emerging radiotherapeutic for PDAC that we and others have recently shown augments the efficacy of immunotherapy. The treatment schedule of SBRT (6Gy/day over 4 consecutive days) followed by a local injection of IL12mRNA resulted in remarkable tumor elimination and long-term survival in multiple preclinical models of PDAC. The success of this local combinatorial approach was attributed to a profound repolarization of the PDAC TME that was now capable of supporting potent antitumor T cell responses. This application will focus on three cardinal features of SBRT/IL12mRNA therapy that are typically absent in PDAC, but are present only with this treatment strategy. First, combined therapy led to a complete loss of a specific subset of T cells commonly called “exhausted”, which are prevalent in the untreated PDAC TME and lack the ability to destroy tumor cells. Instead, an activated, effector T cell population was present following therapy. Second, these intratumoral T cells displayed a robust proliferative signature that afforded clonal expansion against SBRT-induced tumor antigens. Third and finally, this profound local T cell response accompanied an unprecedented systemic response that was able to eradicate distal hepatic metastases. The rarity of generating each of these distinguishing characteristics in PDAC following any treatment cannot underscore the importance of deciphering mechanism of this promising therapy, which we will accomplish by devoting separate aims to investigate each cardinal feature listed above. This knowledge will guide the development of a new generation of therapies that emphasize the repolarization of arduous TMEs in difficult-totreat malignancies and demonstrate that even the recalcitrant PDAC TME can be overpowered when the correct combination of therapies (e.g. SBRT and IL12mRNA) are administered locally. These studies require vertebrate animal models, as the complex and immunosuppressive PDAC tumor microenvironment cannot be recapitulated in vitro. Furthermore, evaluation of systemic antitumor immunity and T cell trafficking between primary and metastatic sites necessitates an intact physiological system.

Public health relevance public domain (NIH RePORTER)

Project Narrative: Pancreatic cancer remains a lethal malignancy resistant to most therapies, however we have discovered a preclinical strategy that results in the complete elimination of this difficult-to-treat cancer. The combination of radiotherapy followed by a mRNA-mediated immunotherapeutic induces a profound immunostimulatory cascade within the tumor microenvironment, which can now support potent antitumor T cell immunity. This application will investigate three distinguishing features that drive the unprecedented response we observe against pancreatic cancer.