Peptide-pulsed T2 cells are routinely used to study T-cell activation by MHC-restricted peptides derived from tumor-associated antigens (TAAs). Nevertheless, the capacity of T2 cells to present antigenic epitopes remains to be precisely quantified, primarily due to the detection limits imposed by available methods. Since naturally-processed TAA-derived epitopes have been shown to be displayed at levels as low as 10-150 copies per cell, highly sensitive detection and quantification techniques are essential to assess the natural degree of T-cell sensitivity. Here, we report the use of soluble, high-affinity T-cell receptors (TCRs) coupled with single-molecule fluorescence microscopy to quantify three reported TAA-derived epitopes on peptide-pulsed T2 cells, dissecting the relationship between concentration of exogenous peptide, number of epitopes presented, and activation of epitope-specific T cells. Our findings indicate that peptide concentrations in the low nanomolar range are required for T2 cells to present TAAs in extents that are comparable to those of malignant cells.
Keywords: T-cell activation; T-cell receptor; T2 cells; antigen presentation; fluorescence microscopy; monoclonal TCR; tumor-associated antigens.