Phenotypic and functional cell properties are usually analyzed at the level of defined cell
populations but not single cells. Yet, large differences between individual cells may have
important functional consequences. It is likely that T-cell–mediated immunity depends on the
polyfunctionality of individual T cells, rather than the sum of functions of responding T-cell
subpopulations. We performed highly sensitive single-cell gene expression profiling,
allowing the direct ex vivo characterization of individual virus-specific and tumor-specific T …