Use of CFSE to monitor ex vivo regulatory T-cell suppression of CD4+ and CD8+ T-cell proliferation within unseparated mononuclear cells from malignant and non-malignant human lymph node biopsies.

Regulatory T-cells (Tregs) play a critical role in the inhibition of self-reactive immune responses and as such have been implicated in the suppression of anti-tumor immunity. A clearer understanding of the mechanisms by which Tregs suppress effector T-cell responses within the context of anti-tumor immunity may lead to more effective treatments. The study of Tregs, particularly in the context of ongoing active immune responses, has been challenging due to the lack of surface molecules truly unique to these cells. Several surface markers have been shown to be constitutively expressed by Tregs, such as high levels of CD25, GITR and CTLA-4, and thus have been useful for their study. However, the heterogeneity of surface marker expression still makes identifying Tregs ex vivo challenging. As such, the only means available, currently, to accurately identify Tregs ex vivo is through functional suppression assays. Tregs have been shown to inhibit a variety of cellular functions including T-cell proliferation and as such, in vitro inhibition of proliferation is routinely used as a measure of Treg-mediated suppression. Several assays currently exist to assay cellular proliferation, including [(3)H]thymidine incorporation and CFSE dilution. However, a limitation of using [(3)H]thymidine is the difficulty differentiating between proliferation of the target cells and that of the Tregs themselves. Due to the ability to differentiate by flow cytometric analysis between labeled and unlabelled cells using CFSE, in contrast to [(3)H]thymidine, it is possible to analyze the proliferation of labeled target cells separate from unlabeled Tregs in co-culture experiments. In addition, the use of multi-color flow cytometry allows for the analysis of different T-cell subsets simultaneously without the necessity to separate these cells. Thus, CFSE has several advantages to [(3)H]thymidine for analysis of cellular proliferation. Herein we describe our work utilizing CFSE labeling to assess, (1) proliferative responses of CD4(+) and CD8(+) T-cells in unseparated single cell suspensions from human lymph nodes and, (2) the ability of tumor infiltrating suppressive populations, including Tregs, isolated from neoplastic lymph nodes to suppress in vitro proliferation of allogeneic CD4(+) and CD8(+) T-cells isolated from peripheral blood of healthy donors.