Cutting edge: Characterization of allorestricted and peptide-selective alloreactive T cells using HLA-tetramer selection

The vast majority of alloreactive T cells recognize foreign MHC molecules i n a peptide-dependent manner. A subpopulation of these peptide-dependent al loreactive T cells is peptide-specific and contains T cells that are of int erest for tumor immunotherapy. Allorestricted T cells (i.e., peptide-specif ic and alloreactive) specific for tumor-associated Ags can be raised in vit ro. However, it is technically difficult to distinguish between peptide-spe cific and peptide-nonspecific alloreactive T cells by functional assays in vitro. Here we show for the first time that allorestricted T cells specific ally bind HLA-peptide tetrameric complexes, as nominal Ag-specific T cells would do. In consequence, fluorescent HLA-peptide tetrameric complexes can be used for sorting and cloning of allorestricted CTLs specific for a pepti de of interest. We also show by the mean of HLA-peptide tetramers the exist ence of peptide-selective alloreactive T cells that recognize a conformatio n on the foreign-MHC brought about by some but not all peptides bound.