Characterization of regulatory T cells in tumor suppressive microenvironments.

Increasing evidence suggests that immunotherapy is a promising strategy for treating patients with invasive and metastatic cancers, but clinical trails are discouraging so far. Recent studies showed that several subsets of regulatory tumor-infiltrating lymphocytes (TILs), such as naturally occurring CD4(+)CD25(+) regulatory T cells (Treg), and adaptively induced Treg cells of Tr1, Th3, CD8(+), as well as gammadelta Treg cells, have been identified in human cancers. These Treg-cell subsets form a tumor suppressive microenvironment that presents a major barrier to successful anti-tumor immunotherapy. Thus, how to modulate the Treg-cell function in tumor microenvironments is essential for cancer treatment and elimination. To date, there is no unique and selective marker for all subsets of Treg cells, and a combination of assays for Treg-associated markers and suppressive activity is still the most common way used to define these tumor-associated Treg cells. In this chapter, we describe protocols to purify and characterize tumor-associated Treg cells from peripheral blood and TILs of cancer patients, which is critical for predicting clinical outcomes and monitoring the effects of tumor immunotherapy.