The invention is directed to methods for determining antigen-specific T cells. In some embodiments, methods of the invention may be implemented by the steps of reacting under interaction conditions one or more antigens with T cells in a plurality of subsets of a tissue sample, such as peripheral blood; sorting antigen-interacting T cells from other T cells; separately sequencing for each subset recombined nucleic acid encoding a segment of a TCR chain from a sample of T cells prior to exposure to antigen and from a sample of T cells isolated based on their interaction with antigen, thereby forming a clonotype profile for the former sample and the latter sample for each subset; and identifying as antigen-specific T cells those T cells associated with a clonotype whose frequency increases in the latter sample relative to its frequency in the former sample.