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Published on: March 8, 2012
Characterization of HLA-A2-restricted HPV-16 E7-specific CD8(+) T-cell immune responses induced by DNA vaccines in
1Department of Pathology, The Johns Hopkins University School of Medicine, The Johns Hopkins Medical Institutions, Baltimore, MD 21205, USA.
Abstract:
We have recently demonstrated that linkage of DNA-encoding calreticulin to DNA-encoding human papillomavirus-16 E7 antigen strongly enhances the efficacy of DNA vaccines against E7-expressing tumors in animal models. In this study, as a prelude to clinical translation, we characterized the ability of DNA-encoding calreticulin linked to DNA-encoding E7 antigen to generate HLA-A2-restricted E7-specific CD8(+) T-cell responses in HLA-A2 (AAD) transgenic mice, as well as antitumor effects against an E7(+) HLA-A2(+) tumor cell line, TC-1/A2. Our results show that while vaccination with CRT/E7 DNA generates strong H-2D(b)-restricted E7 (amino acid (aa)49-57)-specific CD8(+) T-cell immune responses in both C57BL/6 and HLA-A2 (AAD) transgenic mice, no such responses were generated to HLA-A2-restricted epitopes in either type of mouse. In contrast, vaccination with DNA-encoding calreticulin linked to DNA encoding a mutant version of E7 with a deleted aa49-57 epitope leads to the generation of an HLA-A2-restricted E7 (aa11-20)-specific CTL response in HLA-A2 (AAD) transgenic mice. More importantly, vaccination with CRT/mtE7 (del aa49-57) DNA protects against a lethal challenge with TC-1/A2 tumor cells in HLA-A2 (AAD) transgenic mice. Furthermore, our in vitro studies demonstrate that the presence of the E7 (aa49-57) epitope does not suppress presentation of the HLA-A2-restricted E7 (aa11-20) epitope through MHC class I molecules. Thus, the predominant E7 aa49-57-specific CD8+ T-cell immune response in HLA-A2 transgenic mice vaccinated with CRT/E7 is likely due to preferred expansion of E7 aa49-57-specific CD8(+) T cells in vaccinated mice. These results highlight the importance of epitope immunodominance in the evaluation of immune responses in HLA-A2 (AAD) transgenic mice.
Insights
DNA vaccines linking calreticulin to human papillomavirus-16 E7 antigen show promise. Modifying the E7 antigen to focus on specific epitopes generates HLA-A2-restricted T-cell responses and provides protection against tumors in mice.
Area of Science:
- Immunology
- Vaccinology
- Oncology
Background:
- DNA vaccines encoding calreticulin (CRT) linked to human papillomavirus-16 E7 antigen (E7) enhance anti-tumor efficacy in preclinical models.
- Translating these findings to clinical applications requires understanding the generated immune responses in specific human leukocyte antigen (HLA) contexts.
Purpose of the Study:
- To characterize the ability of DNA encoding CRT linked to E7 antigen (CRT/E7) to generate HLA-A2-restricted E7-specific CD8(+) T-cell responses and antitumor effects in HLA-A2 (AAD) transgenic mice.
- To evaluate the impact of epitope immunodominance on vaccine efficacy.
Main Methods:
- Vaccination of C57BL/6 and HLA-A2 (AAD) transgenic mice with DNA encoding CRT/E7 or a modified version (CRT/mtE7) lacking the immunodominant E7 aa49-57 epitope.
- Assessment of H-2D(b)-restricted and HLA-A2-restricted E7-specific CD8(+) T-cell responses.
- Evaluation of antitumor effects against an E7(+) HLA-A2(+) tumor cell line (TC-1/A2).
Main Results:
- CRT/E7 DNA vaccination induced strong H-2D(b)-restricted E7 aa49-57-specific CD8(+) T-cell responses in both mouse strains, but no HLA-A2-restricted responses.
- Vaccination with CRT/mtE7 DNA generated HLA-A2-restricted E7 aa11-20-specific CD8(+) T-cell responses in HLA-A2 (AAD) transgenic mice.
- CRT/mtE7 DNA vaccination conferred protection against a lethal TC-1/A2 tumor challenge in HLA-A2 (AAD) transgenic mice.
Conclusions:
- The immunodominance of the E7 aa49-57 epitope can overshadow the generation of HLA-A2-restricted T-cell responses when using the wild-type E7 antigen.
- Modifying the vaccine construct to target subdominant epitopes, like E7 aa11-20, can elicit protective, HLA-A2-restricted CD8(+) T-cell immunity.
- These findings underscore the critical role of epitope selection and immunodominance in designing effective DNA vaccines for HLA-A2-positive individuals.
