MHC I tetramer staining tends to overestimate the number of functionally relevant self-reactive CD8 T cells in the preimmune repertoire

Abstract

Previous studies that used peptide-MHC (pMHC) tetramers (tet) to identify self-specific T cells have questioned the effectiveness of thymic-negative selection. Here, we used pMHCI tet to enumerate CD8 T cells specific for the immunodominant gp33 epitope of lymphocytic choriomeningitis virus glycoprotein (GP) in mice transgenically engineered to express high levels of GP as a self-antigen in the thymus. In GP-transgenic mice (GP⁺ ), monoclonal P14 TCR⁺ CD8 T cells that express a GP-specific TCR could not be detected by gp33/D^b -tet staining, indicative of their complete intrathymic deletion. By contrast, in the same GP⁺ mice, substantial numbers of polyclonal CD8 T cells identifiable by gp33/D^b -tet were present. The gp33-tet staining profiles of polyclonal T cells from GP⁺ and GP-negative (GP^- ) mice were overlapping, but mean fluorescence intensities were ∼15% lower in cells from GP⁺ mice. Remarkably, the gp33-tet⁺ T cells in GP⁺ mice failed to clonally expand after lymphocytic choriomeningitis virus infection, whereas those of GP^- mice did so. In Nur77^GFP -reporter mice, dose-dependent responses to gp33 peptide-induced TCR stimulation revealed that gp33-tet⁺ T cells with high ligand sensitivity are lacking in GP⁺ mice. Hence, pMHCI tet staining identifies self-specific CD8 T cells but tends to overestimate the number of truly self-reactive cells.

Keywords: Clonal deletion; MHC-tetramers; Self-reactive T cells; gp33 epitope.