1. ¹Department of Pathology, The Johns Hopkins University School of Medicine, The Johns Hopkins Medical Institutions, Baltimore, MD, USA
2. ²Department of Obstetrics and Gynecology, The Johns Hopkins University School of Medicine, The Johns Hopkins Medical Institutions, Baltimore, MD, USA
3. ³Department of Obs/Gyn, Chang Gung Memorial Hospital, Taipei, Taiwan
4. ⁴Department of Oncology, The Johns Hopkins University School of Medicine, The Johns Hopkins Medical Institutions, Baltimore, MD, USA
5. ⁵Department of Molecular Microbiology and Immunology, The Johns Hopkins Medical Institutions, Baltimore, MD, USA

Correspondence: Dr T-C Wu, Department of Pathology, The Johns Hopkins University School of Medicine, Richard Ross Research Building, Room 512, 720 Rutland Avenue, Baltimore, MD 21205, USA. E-mail: wutc@jhmi.edu

Received 21 November 2004; Revised 17 May 2005; Accepted 8 July 2005; Published online 18 August 2005.

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.