T-cell Receptor Specificity Maintained by Altered Thermodynamics<inline-graphic xlink:href="sbox.jpg"/>

Background: The molecular principles governing T-cell specificity are poorly understood. Results: High affinity binding of a melanoma-specific T-cell receptor (TCR) is mediated through new MHC contacts and distinct thermodynamics. Conclusion: A novel thermodynamic mechanism upholds TCR-peptide specificity. Significance: TCRs can maintain peptide specificity using a mechanism that may enable widespread, safe enhancement of TCR binding affinity in therapeutic applications. The T-cell receptor (TCR) recognizes peptides bound to major histocompatibility molecules (MHC) and allows T-cells to interrogate the cellular proteome for internal anomalies from the cell surface. The TCR contacts both MHC and peptide in an interaction characterized by weak affinity (KD = 100 nm to 270 mu m). We used phage-display to produce a melanoma-specific TCR ( alpha 24 beta 17) with a 30,000-fold enhanced binding affinity (KD = 0.6 nm) to aid our exploration of the molecular mechanisms utilized to maintain peptide specificity. Remarkably, although the enhanced affinity was mediated primarily through new TCR-MHC contacts, alpha 24 beta 17 remained acutely sensitive to modifications at every position along the peptide backbone, mimicking the specificity of the wild type TCR. Thermodynamic analyses revealed an important role for solvation in directing peptide specificity. These findings advance our understanding of the molecular mechanisms that can govern the exquisite peptide specificity characteristic of TCR recognition.