A DNA vaccine encoding a single-chain trimer of HLA-A2 linked to human mesothelin peptide generates anti-tumor effects against human mesothelin-expressing tumors

Mesothelin is highly expressed in a majority of ovarian cancer cells and is expressed at low levels in normal cells. Therefore, mesothelin represents a potential target antigen for ovarian cancer vaccine development. DNA vaccines employing single-chain trimers (SCT) have been shown to bypass antigen processing and presentation and result in significant enhancement of DNA vaccine potency. In the current study, we created a DNA vaccine employing an SCT targeting human mesothelin and characterized the ensuing antigen-specific CD8⁺ T cell-mediated immune responses and anti-tumor effects against human mesothelin-expressing tumors in HLA-A2 transgenic mice. Our results showed that vaccination with DNA employing an SCT of HLA-A2 linked to human mesothelin epitope aa540-549 (pcDNA3-Hmeso540-β2m-A2) generated strong human mesothelin peptide (aa540-549)-specific CD8⁺ T cell immune responses in HLA-A2 transgenic mice. Vaccination with pcDNA3-Hmeso540-β2m-A2 prevented the growth of HLA-A2 positive human mesothelin-expressing tumor cell lines in HLA-A2 transgenic mice in contrast to vaccination with DNA encoding SCT linked to OVA CTL epitope. Thus, the employment of SCT of HLA-A2 linked to the human mesothelin epitope aa540-549 represents a potential opportunity for the clinical translation of DNA vaccines against human mesothelin-expressing tumors, particularly ovarian cancer cells.