Empty conformers of HLA-B preferentially bind CD8 and regulate CD8⁺ T cell function.

Area of Science:

• Immunology
• Molecular Biology
• Cellular Biology

Background:

• Human leukocyte antigen (HLA) class I (HLA-I) molecules present peptides to CD8+ T cells, initiating immune responses.
• Peptide binding is typically essential for stable HLA-I surface expression and T cell receptor (TCR) interaction.
• Certain HLA-I alleles, like HLA-B*35:01, can form stable, peptide-deficient (empty) heterodimers on the cell surface.

Purpose of the Study:

• To investigate the binding characteristics and functional implications of peptide-deficient HLA-B*35:01 molecules.
• To determine the role of empty HLA-I in CD8+ T cell interactions and activation.
• To elucidate the influence of HLA-I peptide occupancy on CD8 binding and T cell responses.

Main Methods:

• Utilized tetramer binding assays to assess the interaction of peptide-deficient HLA-B*35:01 with CD8 and CD8+ T cells.
• Performed functional studies involving immunological synapse formation and T cell activation assays.
• Analyzed the impact of empty HLA-I on CD8 binding affinity and T cell responses in antigen-specific contexts.

Main Results:

• Peptide-deficient HLA-B*35:01 tetramers exhibit preferential binding to CD8 and a significant proportion of blood-derived CD8+ T cells via a CD8-dependent mechanism.
• Empty HLA-B*35:01 conformers do not directly activate CD8+ T cells but accumulate at the immunological synapse during antigen-induced responses.
• These peptide-deficient conformers enhance cell adhesion and CD8+ T cell activation in response to cognate peptides.

Conclusions:

• HLA-I peptide occupancy critically influences CD8 binding affinity.
• Empty HLA-I molecules represent a novel regulatory mechanism for CD8+ T cell activation through their interaction with CD8.
• These findings expand our understanding of HLA-I function beyond peptide presentation and highlight a new pathway for modulating T cell immunity.