Abstract
Immune checkpoint inhibitors (ICIs) have shown superior clinical responses and significantly prolong overall survival (OS) for many types of cancer. However, some patients exhibit long-term OS, whereas others do not respond to ICI therapy at all. To develop more effective and long-lasting ICI therapy, understanding the host immune response to tumors and the development of biomarkers are imperative. In this study, we established an MC38 immunological memory mouse model by administering an anti-PD-L1 antibody and evaluating the detailed characteristics of the immune microenvironment including the T cell receptor (TCR) repertoire. In addition, we found that the memory mouse can be established by surgical resection of residual tumor following anti-PD-L1 antibody treatment with a success rate of > 40%. In this model, specific depletion of CD8 T cells revealed that they were responsible for the rejection of reinoculated MC38 cells. Analysis of the tumor microenvironment (TME) of memory mice using RNA-seq and flow cytometry revealed that memory mice had a quick and robust immune response to MC38 cells compared with naïve mice. A TCR repertoire analysis indicated that T cells with a specific TCR repertoire were expanded in the TME, systemically distributed, and preserved in the host for a long time period. We also identified shared TCR clonotypes between serially resected tumors in patients with colorectal cancer (CRC). Our results suggest that memory T cells are widely preserved in patients with CRC, and the MC38 memory model is potentially useful for the analysis of systemic memory T-cell behavior.