Colorectal cancer (CRC) has the third highest incidence rate of any cancer in New Zealand. Immune cells play an important role in determining CRC disease progression. T cell infiltration, in particular, is associated with disease outcome. However, T cell populations are highly diverse and recent work in our laboratory has demonstrated that the infiltration frequency of specific population of regulatory T cells (Tregs) improved prognostic stratification. This population of Tregs expresses the transcription factor BLIMP-1. The underlying mechanism of protection, however, has not yet been elucidated.
Here, mass cytometry was used to assess the frequency and phenotype of BLIMP-1+ Tregs in tumour and non-tumour bowel (NTB) obtained fresh from CRC patients undergoing bowel resection. This data was analysed using network cluster analyses including SCAFFoLD, VORTEX and CITRUS. These analyses revealed a significant increase in the frequency of both total Tregs and BLIMP-1+ Tregs in the tumour compared to NTB. Further, CITRUS analysis revealed that an increase in BLIMP-1+ Tregs was a classifying, significant feature of the tumour tissue compared to NTB; two of seven T cell populations that were present at a greater abundance in the tumour than the NTB were BLIMP-1+ Tregs. These analyses also revealed expression of ICOS, CD45RO and a variety of exhaustion markers on BLIMP-1+ Tregs indicating a more activated phenotype than conventional Tregs. These findings were validated on the same tissue samples using conventional flow cytometry, and further, IL-2 was demonstrated to be an important factor in promoting this Treg phenotype in vitro. Together, this work highlights the complexity of T cell responses in colorectal cancer and demonstrates the strength of mass cytometry and network analyses for resolving these populations.