Antigen peptides

Tumor-associated antigens (TAAs) act as target peptides to induce cytotoxic T lymphocyte (CTL) responses for the development of cancer vaccines, a promising approach for cancer immunotherapy.
Tumor-associated antigens are selected based on their, immunogenicity, role in oncogenicity, number of antigenic epitopes and their expression level in antigen-positive cancer cells¹.
Receptors of CD8+ T cells usually recognize antigenic peptides presented in association with MHC class I molecules. Peptides displayed on the HLA-A*0201 molecules are the most frequently used since this HLA allele (HLA-A group, MHC class I) is expressed by 45% of the human population and the peptide binding motifs are well-charaterized¹.
To validate the efficacy of a tumor-associated antigen as a T-cell epitope, CD8+ T cells are usually induced in vitro using peptide-pulsed dendritic cells (DCs), generated from peripheral blood mononuclear cells (PBMCs), as antigen-presenting cells (APCs). Upon primary in vitro immunization, peptide-responding T cells are analyzed for their capacity to recognize tumor cell lines expressing the candidate tumor-associated antigen and to trigger an antigen-specific and HLA-A*02-restricted cytolytic activity against the target tumor cells. This approach is nammed reverse immunology. It has been successfully used to identify several antigenic peptides that are recognized by CD4+ or CD8+ T lymphocytes.
Tumour-associated antigens that have the potential to elicit immune responses are classified into different categories² :

• Antigens of high tumoural specificity
  Antigens derived from oncogenic viruses
  Antigens encoded by mutated genes
  Antigens encoded by cancer-germline genes
• Antigens of low tumoural specificity
  Tissue/Lineage-restricted differentiation antigens
  Antigens derived from overexpressed proteins