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Gastrin vaccine improves response to immune checkpoint antibody in murine pancreatic cancer by altering the tumor microenvironment

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Pancreatic cancer has been termed a ‘recalcitrant cancer’ due to its relative resistance to chemotherapy and immunotherapy. This resistance is thought to be due in part to the dense fibrotic tumor microenvironment and lack of tumor infiltrating CD8 + T cells. The gastrointestinal peptide, gastrin, has been shown to stimulate growth of pancreatic cancer by both a paracrine and autocrine mechanism. Interruption of gastrin at the CCK receptor may reduce tumor-associated fibrosis and alter tumor immune cells. Polyclonal Ab Stimulator (PAS) is a vaccine that targets gastrin and has been shown to prolong survival of patients with pancreatic cancer. Here, we report that PAS vaccination monotherapy elicits both a humoral and cellular immune response when used in immune competent mice-bearing pancreatic tumors and that PAS monotherapy produced a marked T-cell activation and influx of CD8 + lymphocytes into pancreatic tumors. Isolated peripheral lymphocytes elicited cytokine release upon re-stimulation with gastrin in vitro demonstrating specificity of immune activation for the target peptide. Combination therapy with PAS and PD-1 Ab activated CD4 −/CD8 − TEMRA cells important in T-cell-mediated tumor death and memory. Tumors of mice treated with PAS (250 μg) or PAS (100 and 250 μg) in combination with a PD-1 Ab were significantly smaller compared to tumors from PBS or PD-1 Ab-treated mice. When PAS was given in combination with PD-1 Ab, tumors had less fibrosis, fewer inhibitory Treg lymphocytes, and fewer tumor-associated macrophages. These findings reveal a novel approach to improve treatment strategies for pancreatic cancer.

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Polyclonal antibody stimulator


100 µg Polyclonal antibody stimulator


250 µg Polyclonal antibody stimulator


Pancreatic ductal adenocarcinoma




Tumor-associated macrophages


Terminally differentiated T cells


Tumor microenvironment


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We appreciate the technical support from the staff in the Lombardi Georgetown Comprehensive Cancer Center Core Histology laboratory and Flow cytometry facilities. We also appreciate the staff in the animal care facility. All the investigations in this project were done at Georgetown University School of Medicine in the research laboratory of Dr. Smith, comparative medicine animal facility, and core labs (above) in the Lombardi Georgetown Comprehensive Cancer Center.


The study was funded in part by a grant from Cancer Advances, Inc. and its subsidiary Vaccicure, and NIH CA051008 to the Georgetown Lombardi Cancer center Core facilities.

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Authors and Affiliations



JPS, NO, RS, LS and AC conceived and designed research; JPS, JB, HC, and XL performed experiments; JPS, NO, RS, JB, HC, XL, AHK, LS and AC analyzed data; JPS, NO, RS, JB, HC, AHK, LS, and AC interpreted results of experiments; JPS, XL, and HC prepared figures; JPS drafted manuscript; NO, RS, JB, HC, XL, AHK, LS, AC, and JPS edited and revised manuscript; ALL authors approved the content of the final version of manuscript.

Corresponding author

Correspondence to Jill P. Smith.

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Conflict of interest

Cato Research, Durham NC has intellectual property rights for PAS. PAS compound was transferred to Georgetown University by a Material Transfer agreement with Vaccicure Limited, Liverpool, UK for this research project. All authors work for Cato Research or Georgetown University.

Ethical approval and ethical standards

All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All procedures performed in studies involving animals were in accordance with the ethical standards of the Georgetown University. The IACUC Protocol Number was 2016-1193 and the protocol approval date was 10/05/2017.

Animal source

C57BL/6 mice were purchased from Charles River Laboratories (Maryland).

Cell line authentication

Murine pancreatic cancer cells, mT3, were a gift from the Tuveson lab (Cold Spring Harbor, NY). Authentication of mT3 murine cells was performed by the investigator that developed the cells [33] and further IMPACT-III testing was performed by IDEXX BioResearch (Columbia, MO) to ensure the cells were pathogen-free.

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Osborne, N., Sundseth, R., Burks, J. et al. Gastrin vaccine improves response to immune checkpoint antibody in murine pancreatic cancer by altering the tumor microenvironment. Cancer Immunol Immunother 68, 1635–1648 (2019).

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