The present invention relates to a method for the detection of epitope-specific T-cells and target epitopes of reactive T-cells. Furthermore, the present invention relates to vectors comprising a first promoter which is specifically inducible by the epitope-specific contact with a T-cell in antigen-presenting cells, a nucleic acid which is functionally linked to this first promoter and which encodes a marker gene, a second promoter which is constitutive in antigen-presenting cells, and a nucleic acid which is functionally linked to said second promoter. Furthermore, the present invention relates to antigen-presenting cells which are transduced with the vectors according to the invention.