Multimeric MHC molecules have opened a new field not only for the analysis of antigen-specific T cells, but also to use in other applications such as expansion and isolation of antigen-specific T cells for adoptive T cell therapy. Schneck and coworkers have recently demonstrated that MHC class I-Ig dimers coated onto beads together with anti-CD28 form very potent artificial antigen-presenting cells (26). Interestingly using MHC-Ig dimers they were able to amplify CMV and MART-1 specific T cells to cell numbers at least equal to what they obtained using dendritic cells as stimulators. These amplified T cells also lysed antigen expressing tumor cells specifically. Thus, MHC-Ig dimeric molecules have now become a powerful tool in the field of tumor immunology not only for the detection of antigen specific T cells before and after different vaccination protocols but also for adoptive T cell transfer therapy. In addition, a different study has demonstrated the use of MHC class I dimers for in vitro stimulation of gp100 specific T cells, when precursor frequencies are too low in peripheral blood to be detected without in vitro stimulation (21).
We have chosen in our laboratory a different approach to generate MHC-Ig dimeric molecules that are even more sensitive for the detection of peptide-specific T cells. We have generated peptide-P2-microglobulin-MHC-Ig single chain dimers (Figure 3), which have the advantage that every MHC is loaded with the correct peptide leading to a decrease in non-specific background staining. In addition, we have used the MHC-Ig single chain in combination with paramagnetic IgG binding beads, which only bind cells with an immunoglobulin molecule bound on their cell surface. This technology enhances the detection limit of antigen-specific T cells, allows for the enrichment of antigen-specific T cells from stimulated cultures and peripheral blood, as well as generation of T cell lines and clones (5).
Finally, MHC-Ig dimers have been used with recombinant T cell receptors bound onto plasmon resonance surface for binding studies (27). These experiments have helped in understanding peptide-MHC/T cell receptor interactions.
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