Rapid identification and sorting of viable virus-reactive CD4+ and CD8+ T cells based on antigen-triggered CD137 expression

Current methods for the detection and isolation of antigen-specific CD4(+) and CD8(+) T cells require the availability of peptide/MHC multimers or are restricted to cells that produce cytokines after antigen contact. Here we show that de novo cell surface expression of the TNF-receptor family member CD137 (4-1BB) identifies recently activated, but not resting, human CD4(+) and CD8(+) memory T cells. Maximum CD137 expression level is uniformly observed in both T-cell subsets at 24h after stimulation with antigen. In experiments with CMV and EBV-reactive T cells, we confirmed the specificity of CD137 expression by co-staining with peptide/HLA tetramers. Substantial proportions of CD137(+) T cells did not produce IFN-gamma, suggesting that CD137 detects a broader repertoire of antigen-specific T cells. Activated CD137(+) T cells could be easily purified by MACS and expanded in vitro thereafter. This CD137-based enrichment method was capable of isolating 2-fold higher numbers of anti-viral CD4(+) and CD8(+) T cells compared to the IFN-gamma secretion assay. In conclusion, antigen-triggered CD137 expression allows the rapid detection and sorting of virus-reactive CD4(+) and CD8(+) T cells. The CD137 assay is most attractive for the simultaneous targeting of anti-viral T helper and effector cells in monitoring studies and adoptive immunotherapy trials.