Anti-tumor immunotherapy is mainly based on the activation of cytotoxic T lymphocytes (CTL). CTL recognize peptides derived from tumor antigens and presented at the tumor cell surface in association with HLA class I molecules (HLA-I).
Two types of peptides have been described in the international scientific publications: (i) dominant peptides, which exhibit high HLA-I affinity and which are abundant at the cell surface and (ii) cryptic peptides which have low HLA-I affinity, are weekly presented at the cell surface and are therefore non-immunogenic.
So far vaccination against cancer has been tried with dominant peptides. However these vaccines are relatively unsuccessful because immune system is tolerant against dominant peptides. This tolerance does not concern cryptic peptides, which are in essence good candidates for tumor vaccination. However, because of their low affinity for HLAs, cryptic peptides are incapable of generating a significant immune response. VAXON’s proprietary technology has succeeded in optimizing immunogenicity of cryptic peptides (optimized cryptic peptides) presented by the most frequent HLA-I molecules (HLA-A2, HLA-B7, HLA-A24 and HLA-A3).  Importantly vaccination of humanized mice with optimized cryptic peptides protects them against tumor growth while vaccination with dominant peptides does not.

Efficacy of hTERT optimized cryptic peptides versus dominant peptides on the survival of tumor-bearing mice (Gross et al. J. Clin. Invest. 113, 425, 2004)

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