Isolation and Analysis of Tumor-Infiltrating Treg

Besides their important function in immune homeostasis, autoimmunity, and peripheral tolerance, regulatory T cells (Tregs) also play a crucial role in cancer immune evasion, by assisting tumors to shield from antitumor responses by effector cells. Tregs are recruited to infiltrate tumors and upon finding favourable conditions in the tumor microenvironment, proliferate and suppress effector T cell function thereby promoting tumor escape and growth. In human cancer patients and mouse models, a low ratio of effector T cells to Tregs is a key feature of this immune-suppressive tumor microenvironment and correlates with poor prognosis. This chapter describes protocols for the isolation of tumor-infiltrating lymphocytes (TILs) from solid tumors, their quantification, and phenotyping via flow cytometry to assess the effector T cell:Treg ratio and the expression of relevant markers.