Identification of AH1-specific T cells in a mouse model of colorectal cancer

Abstract

Colorectal cancer (CRC) causes approximately 1.4 million new cases of disease and 700,000 deaths worldwide annually. To overcome limitations of studying CRC in humans, mouse models are used to test therapeutics such as cancer vaccines. These therapies aim to modulate the immune response, making detection of changes to the immune response vital to measuring the efficacy of candidate therapeutics.

Previous research in our lab demonstrated vaccination with chitosan gel containing ovalbumin (OVA) antigen could induce an antigen-specific anti-tumour CD8+ T cell response in an ectopic B16-OVA mouse model. However, this model utilized a melanoma cell line (B16) with a highly immunogenic model antigen (OVA). The CT26 cell line is a murine colorectal adenocarcinoma that expresses the MHC-I restricted endogenous cancer peptide AH1. Endogenous AH1-specific CD8+ T cells may produce a targeted cytotoxic response, eliminating CT26 cancerous cells. We are currently unable to determine to what extent an AH1-specific T cell response occurs after vaccination. The aim of this study was to identify AH1-specific T cells by two methods; (1) in vitro stimulation with a CT26 peptide (AH1), and (2) ex vivo identification of AH1-specific T cells using an antigen-specific MHC multimer.

It was shown that use of bone marrow derived dendritic cells pulsed with AH1 peptide, in combination with the growth factors interleukin (IL)-7 and IL-15 stimulated expansion of total, activated (CD62L-) and proliferating (Ki67+) CD8+ T cells compared to unstimulated cells. In addition, an MHC multimer was used to identify AH1-specific T cells in a vaccinated CT26 mouse model of CRC.

Through these experiments, I have developed and optimised methods that allow detection and identification of antigen-specific T cells in our mouse model, which is crucial for measuring vaccine-specific efficacy and protection. Following this study, we propose to activate endogenous AH1-specific CD8+ T cells by prophylactic and therapeutic vaccination with AH1 peptide, inducing expansion of AH1-specific IFNᵧ+ T cells to stimulate an effective cytotoxic anti-tumour response.