ABSTRACT
Induction of epitope-specific T-cell responses may provide an effective means of protecting against diseases for which no conventional vaccines exist. Unlike B cells, which only recognize epitopes directly on the surface of free antigens, T lymphocytes recognize peptide fragments bound to class I or class II molecules encoded by the major histocompatibility complex (MHC). A peptide that binds MHC and is recognized by the T-cell receptor (TCR) constitutes a T-cell epitope. In humans, MHC class I molecules include HLA-A, HLA-B, and HLA-C. The MHC class II molecules include HLA-DR, HLA-DP, and HLA-DQ.
