T cell subsets and colorectal cancer: discerning the good from the bad.

Tumor-specific T cells must overcome a multitude of suppressive mechanisms to destroy cancerous cells effectively. Furthermore, it appears that the tumor microenvironment facilitates the development of highly immunosuppressive T cells, which may also allow subsequent tumor progression. In colorectal cancer, the relationship between regulatory T cells (e.g. FoxP3(+) Tregs) and tumor prognosis and progression is less clear, despite their well-documented ability to impinge on anti-tumor immune responses. Here we explore our current knowledge of colorectal TIL heterogeneity, deciphering subsets which may be of benefit or detriment.