Blimp-1+ regulatory T cells in human colorectal cancer

Abstract

Analysis of tumour infiltrating immune cells in colorectal cancer (CRC) is superior to the current staging at predicting disease-free survival. The Immunoscore has been proposed as a way to use CD3+ and CD8+ T cell infiltrates to stage disease; however, T cell heterogeneity is not taken into account. Unlike in many cancers, a high frequency of tumour infiltrating FOXP3+ regulatory T cells (Tregs) are associated with good patient outcomes in colorectal cancer. Blimp-1+ Tregs are a population of T cells shown to be potently suppressive in mice and, while present in human CRC, their role in patient outcome is unknown. Immunofluorescence was used to analyse immune cell infiltrates in early stage (II) CRC patients and to compare those with recurrent and non-recurrent disease (n=32). CD3 and CD8 were used for the Immunoscore. FOXP3, Blimp-1 and CD3 were used to quantify Blimp-1 regulatory T cells. Flow cytometry was used to determine the phenotype of Blimp-1+ Tregs in CRC. Patients with a high Immunoscore (high T cell infiltrate) had higher/longer disease-free survival than patients with a low Immunoscore (low T cell infiltrate, Log-rank test p<0.001). The ability to predict patient outcome was improved by measuring the infiltrate of CD4+FOXP3+Blimp-1+ cells (Blimp-1+ Tregs, Log-rank test p<0.0001). Patients with a low Immunoscore but high infiltrate of CD4+FOXP3+Blimp-1+ cells at the invasive margin had increased disease-free survival than those with a low Immunoscore and a low infiltrate of CD4+FOXP3+Blimp-1+ cells. Blimp-1+ Tregs produced IL-10 and displayed an activated Treg phenotype in CRC tumours. These results indicate that Blimp-1+ Tregs may play an important role in patient outcome in CRC. Incorporation of Blimp-1+ Tregs into the Immunoscore may help to identify patients at high risk of recurrent disease.