1. ¹Department of Pathology, Johns Hopkins Medical Institutions, Baltimore, MD, USA
2. ²Department of Obstetrics and Gynecology, Johns Hopkins Medical Institutions, Baltimore, MD, USA
3. ³Department of Oncology, Johns Hopkins Medical Institutions, Baltimore, MD, USA
4. ⁴Department of Obstetrics and Gynecology, Division of Gynecologic Oncology, University of Alabama at Birmingham, Birmingham, AL, USA
5. ⁵Department of Molecular Microbiology and Immunology, Johns Hopkins Medical Institutions, Baltimore, MD, USA

Correspondence: Dr T-C Wu, Department of Pathology, Johns Hopkins Medical Institutions, CRB II Room 309, 1550 Orleans Street, Baltimore, MD 21231, USA. E-mail: wutc@jhmi.edu

Received 2 November 2007; Revised 11 December 2007; Accepted 30 January 2008; Published online 10 April 2008.

Abstract

Intradermal administration of DNA vaccines via a gene gun represents a feasible strategy to deliver DNA directly into the professional antigen-presenting cells (APCs) in the skin. This helps to facilitate the enhancement of DNA vaccine potency via strategies that modify the properties of APCs. We have previously demonstrated that DNA vaccines encoding human papillomavirus type 16 (HPV-16) E7 antigen linked to calreticulin (CRT) are capable of enhancing the E7-specific CD8⁺ T-cell immune responses and antitumor effects against E7-expressing tumors. It has also been shown that cluster (short-interval) DNA vaccination regimen generates potent immune responses in a minimal time frame. Thus, in the current study we hypothesize that the cluster intradermal CRT/E7 DNA vaccination will generate significant antigen-specific CD8⁺ T-cell infiltrates in E7-expressing tumors in tumor-bearing mice, leading to an increase in apoptotic tumor cell death. We found that cluster intradermal CRT/E7 DNA vaccination is capable of rapidly generating a significant number of E7-specific CD8⁺ T cells, resulting in significant therapeutic antitumor effects in vaccinated mice. We also observed that cluster intradermal CRT/E7 DNA vaccination in the presence of tumor generates significantly higher E7-specific CD8⁺ T-cell immune responses in the systemic circulation as well as in the tumors. In addition, this vaccination regimen also led to significantly lower levels of CD4⁺Foxp3⁺ T-regulatory cells and myeloid suppressor cells compared to vaccination with CRT DNA in peripheral blood and in tumor-infiltrating lymphocytes, resulting in an increase in apoptotic tumor cell death. Thus, our study has significant potential for future clinical translation.