TCRs with Distinct Specificity Profiles Use Different Binding Modes to Engage an Identical Peptide-HLA Complex

Area of Science:

• Immunology
• Structural Biology
• Molecular Biology

Background:

• T-cell receptor (TCR) cross-reactivity is crucial for adaptive immunity but its molecular underpinnings remain poorly understood.
• The extent to which TCRs recognizing the same antigen (Ag) also recognize shared off-target peptides is unclear.
• This knowledge gap limits our understanding of how the immune system recognizes a vast array of foreign and self-peptides.

Purpose of the Study:

• To elucidate the molecular basis of TCR cross-reactivity.
• To determine the peptide specificity profiles of human TCRs targeting the cancer-testis antigen NY-ESO-1_157-165 presented by HLA-A2.
• To reconcile how a limited TCR repertoire can recognize a broad antigenic pool.

Main Methods:

• Determined TCR-peptide-HLA crystal structures.
• Utilized a single-chain peptide-HLA phage library to generate peptide specificity profiles.
• Analyzed three newly identified human TCRs specific for NY-ESO-1_157-165-HLA-A2.

Main Results:

• Two TCRs recognized the same central peptide feature but differed in peripheral peptide binding, showing partially overlapping specificity profiles.
• A third TCR adopted a flipped peptide conformation, recognizing off-target peptides with low similarity to the cognate peptide.
• Structural and binding data revealed distinct peptide recognition modes among TCRs specific for the same antigen.

Conclusions:

• TCRs specific for a cognate peptide recognize discrete, albeit sometimes overlapping, peptide repertoires.
• The observed TCR binding modes explain how a limited TCR repertoire can recognize a vastly larger pool of antigenic peptides.
• These findings provide molecular insights into TCR cross-reactivity and its implications for immune surveillance and autoimmunity.