Efficient MHC class I-peptide binding is required but does not ensure MHC class I-restricted immunogenicity

Area of Science:

• Immunology
• Molecular Biology
• Computational Biology

Background:

• Cytotoxic T lymphocyte (CTL) epitopes are peptides presented by major histocompatibility (MHC) class I molecules.
• Candidate CTL epitopes are often identified by their ability to bind efficiently to MHC class I molecules in vitro.
• The relationship between MHC class I-peptide binding affinity and actual immunogenicity requires systematic investigation.

Purpose of the Study:

• To investigate the relationship between MHC class I-peptide binding affinity and peptide immunogenicity.
• To determine if in vitro MHC class I binding is a valid approach for identifying immunogenic CTL epitopes.
• To identify factors beyond binding affinity that influence CTL epitope immunogenicity.

Main Methods:

• Tested 15 known CTL epitopes for MHC class I binding affinity.
• Compared binding affinities of known CTL epitopes with 83 non-epitope peptides sharing MHC class I motifs.
• Induced peptide-specific CTL responses in mice using high and low affinity Kb binding peptides.

Main Results:

• Peptides containing known CTL epitopes exhibited higher MHC class I binding affinity compared to non-epitope peptides.
• High-affinity MHC class I binding was required for inducing peptide-specific CTL responses.
• Only a subset of high-affinity binding peptides elicited reproducible CTL responses, indicating additional factors are involved.

Conclusions:

• Efficient peptide-MHC class I binding is a necessary but not sufficient condition for immunogenicity.
• Selecting candidate CTL epitopes based on MHC class I binding affinity is a valid strategy, minimizing the risk of missing immunogenic peptides.
• Additional factors beyond binding affinity play a role in determining CTL epitope immunogenicity.