Characterization of Human CD8αβ Interaction With Classical and Unconventional MHC Molecules

Area of Science:

• Immunology
• Molecular Biology
• Biophysics

Background:

• The CD8 co-receptor is crucial for T-cell function, existing as CD8αα homodimers and CD8αβ heterodimers.
• CD8αβ is the canonical co-receptor on cytotoxic T-cells, regulating T-cell receptor (TCR) selection and peripheral antigen responses.
• The biophysical properties of human CD8αβ binding to MHC molecules remain largely uncharacterized.

Purpose of the Study:

• To determine the binding affinities of human CD8αβ and CD8αα to classical MHC class I (MHCI) alleles.
• To investigate the interactions of CD8αα and CD8αβ with unconventional MHC-like molecules.
• To explore the relationship between CD8 binding affinity and TCR selection.

Main Methods:

• Generation of soluble human CD8αβ and CD8αα using hetero-dimerized Fc-fusions.
• Assessment of binding affinities to various MHCI alleles and MHC-like molecules using biophysical techniques.
• Analysis of the association between CD8 binding affinity and TCR affinity.

Main Results:

• Both CD8αβ and CD8αα displayed weak binding affinities to multiple MHCI alleles, with variations observed across different alleles.
• CD8αα and CD8αβ bound to MHCI-related protein 1 with similar affinities as to classical MHCI.
• No binding was detected between CD8 and CD1a, CD1b, CD1c, or CD1d molecules.
• A significant inverse correlation was found between TCR affinity and CD8 co-receptor affinity for different MHCI alleles.

Conclusions:

• This study provides the first characterization of human CD8αβ binding to MHCI and related molecules.
• CD8 binding affinity to MHCI alleles is allele-specific and influences TCR selection in the thymus.
• The findings reveal a novel relationship between CD8-MHCI interactions and the development of the T-cell repertoire.