Establishment of an expression cloning system for CD4+ T cell epitopes

Area of Science:

• Immunology
• Molecular Biology
• Biotechnology

Background:

• The invariant chain (Ii) is crucial for MHC class II molecule presentation.
• The pCI vector allows substitution of the CLIP region with antigenic peptides.
• Identifying CD4+ T cell epitopes is vital for understanding immune responses and developing therapies.

Purpose of the Study:

• To develop and validate a new expression cloning system for identifying CD4+ T cell epitopes.
• To isolate novel cross-reactive epitopes using a randomized peptide library.
• To assess the utility of the system for detecting unknown T cell epitopes.

Main Methods:

• Utilized a modified invariant chain (Ii) expression vector (pCI) for epitope presentation.
• Constructed an epitope-presenting library by inserting randomized 13-mer peptides.
• Loaded peptides onto HLA class II molecules coexpressed in COS-7 cells.
• Screened the library using a T cell clone from a patient with insulin-dependent diabetes mellitus.

Main Results:

• Successfully identified a novel epitope (PVQLSNQWHVVGATF) recognized by a GAD65-autoreactive T cell clone.
• The newly identified epitope showed cross-reactivity and comparable T cell stimulation to the original GAD65 epitope (p116-128).
• The identified epitope sequence was significantly different from the original GAD65 epitope.

Conclusions:

• The developed expression cloning system is effective for identifying CD4+ T cell epitopes, including cross-reactive ones.
• The system can identify epitopes for T cells with known specificities and potentially for those with unknown epitopes.
• This approach holds promise for advancing research in autoimmune diseases and T cell-mediated immunity.