Abstract B59: Transnuclear mice as models of the immune response to pancreatic cancer
Authors: Dougan Stephanie K. , Bilate Angelina , Jaenisch Rudolf , Ploegh Hidde L. 
Published: October 2015

Somatic cell nuclear transfer (SCNT) allows the efficient generation of mice that will serve as a source of T cells of defined specificity. By harvesting primary T cells from animals that are at the peak of an anti-tumor response, and by transfer of the nucleus from such antigen specific T cells into an enucleated oocyte, embryonic stem cells that harbor the TCR rearrangements of that T cell may be obtained and used for the construction of cloned mice. These animals contain T cells of the appropriate tumor specificity, have no genetic alterations other than the physiological TCR rearrangements and are the closest approximation of the tumor-specific CTLs that contribute to tumor resolution in vivo. Importantly, the generation of transnuclear mice is rapid, requiring approximately 6 weeks from T cell harvest to obtaining chimeric animals.

No good animal models are available for studying the immune response to pancreatic cancer, unlike in melanoma and prostate cancer for which we have excellent models. We are addressing this problem by generating a panel of transnuclear mice from pancreatic tumor infiltrating CD4 and CD8 T cells. These mice will 1) allow us to characterize the optimal CD8 and CD4 immune response necessary for rejection of pancreatic tumors; 2) define the spectrum of antigens seen by pancreatic tumor-infiltrating regulatory T cells; 3) address possible synergy of anti-tumor CD8 T cells with costimulatory blockade, silencing of anergy-related genes, or combination therapy with small molecule based chemotherapy; and 4) generate further interest in the community for studying immune-based therapies for pancreatic cancer.

One of the best characterized pancreatic tumor antigens in both mice and humans is mesothelin. We have generated a TN mouse line from a mesothelin-specific CD8 T cell. However, the resulting mouse shows downregulation of CD8 in the thymus, and produces CD8 T cells that are functionally anergic. This anergy can be overcome by prolonged culture with anti-CD3/CD28 coated beads, and the resulting activated Mes358 TN cells accumulate in the pancreatic tumor environment and block the early stages of pancreatic tumor growth. As a second approach, we used CRISPR technology to generate mesothelin-/- mice. When immunized with mesothelin, these mice will provide a robust source of Mes358 tetramer+ CD8 T cells for use as a donor population for SCNT to generate a second line of mesothelin-specific TN mice with higher affinity for mesothelin.

Immune-based therapies show a variable degree of success across different tumor types, with melanoma being highly amenable to anti-CTLA and other checkpoint blockade therapies while pancreatic cancer has been more refractory although combination of Ipilimumab with GVAX has shown modest efficacy. Many factors could contribute to this disparity, notably stroma and poor vascular density that limit drug delivery to pancreatic tumors. Understanding the requirements for CD8 T cell priming, trafficking and function in the context of stromal depletion is likely key to the success or failure of immunotherapies for pancreatic cancer.

Citation Format: Stephanie K. Dougan, Angelina Bilate, Rudolf Jaenisch, Hidde L. Ploegh. Transnuclear mice as models of the immune response to pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B59.