Monitoring multifunctionality of immune-exhausted CD8 T cells in cancer patients.

CD8 T cells play a critical role in the host defense against cancers and infectious diseases. However, the presence of antigen-specific CD8 T cells does not always imply that cancers and/or pathogens are efficiently eliminated in the body. Concerning this point, the recent studies suggest the concept of immune exhaustion of CD8 T cells, characterized by their decreased production of IL-2, TNFα, and IFNγ even after antigen stimulation. Thus, continuous stimulation of CD8 T cells by the persistent antigens results in immune exhaustion, which eventually causes immune tolerance against cancers and chronic infections. The identification of immune effector and/or exhausted CD8 T cells by monitoring multiple parameters including T cell exhaustion markers such as PD-1 and Tim-3 and intracellular cytokines is, therefore, crucial to understand the real-time, ongoing immune status. For this purpose, polychromatic flow cytometry is the most common and reliable tool to monitor T cell functions. We describe here the method for detection of immune-exhaustion status of CD8 T cells from human peripheral blood mononuclear cells (PBMCs). By stimulation of PBMCs with PMA/ionomycin for 6 h, more than 1-2 % of total CD8 T cells are identified as positive in terms of multifunctionality, thus producing multiple cytokines--IL-2, TNFα, and IFNγ--at single-cell level in case of all healthy donors. By contrast, CD8 T cells from certain populations of cancer patients are significantly less effective; less than 0.5 % of CD8 T cells are positive in producing such multiple cytokines. The cutoff value around 0.5 % of CD8 T cells might distinguish patients who would receive beneficial effect by cancer vaccine from those who would not respond to the vaccine. Thus, the remaining capacity to produce multiple cytokines of CD8 T cells might be a critical parameter determining the outcome of cancer patients who receive various kinds of cancer vaccines. The method to monitor the state of multifunctionality of CD8 T cells, as described here, would become more important to understand the immune statues in cancers and chronic infectious diseases such as AIDS and malaria infections.