CD8 T cell function and cross-reactivity explored by stepwise increased peptide-HLA versus TCR affinity.

Area of Science:

• Immunology
• Cancer Immunotherapy
• T Cell Biology

Background:

• CD8 T cell activation relies on T cell receptor (TCR) binding to peptide-human leucocyte antigen (pHLA) complexes.
• Both peptide:HLA affinity and TCR:pHLA affinity influence T cell responses, but their combined effects on immunogenicity are not fully understood.
• Investigating these affinities is critical for designing effective cancer vaccines and immunotherapies.

Purpose of the Study:

• To systematically investigate the impact of peptide:HLA and TCR:pHLA binding affinities on CD8 T cell functional outcomes and cross-reactivity.
• To compare the immunogenicity of native tumor epitopes versus affinity-optimized variants in cancer patients.
• To provide insights into rational epitope selection for cancer vaccines.

Main Methods:

• Developed and utilized the 'blue peptide assay' for precise measurement of peptide:HLA affinity.
• Generated and characterized human tumor peptide variants with differing HLA affinities.
• Assessed the functionality and cross-reactivity of CD8 T cell clonotypes from cancer patients vaccinated with native or optimized epitopes, and from tumor-infiltrated lymph nodes (TILNs).

Main Results:

• Vaccines with native Melan-A/MART-1 epitopes induced CD8 T cells with superior functionality and cross-reactivity compared to affinity-optimized epitopes.
• Melan-A/MART-1-specific TILN cells showed heterogeneous functional and cross-reactive profiles dependent on the specific T cell clone.
• Both peptide:HLA and TCR:pHLA affinities significantly and additively impacted T cell responses, without hierarchical dominance.

Conclusions:

• Native tumor epitopes may elicit more robust and broadly reactive CD8 T cell responses than affinity-optimized ones in cancer immunotherapy.
• Understanding the interplay between peptide:HLA and TCR:pHLA affinities is key for designing effective cancer vaccines.
• The developed assay and findings offer new strategies for selecting tumor-specific epitopes to enhance T cell-mediated tumor control.