Therapeutic Synergy of Human Papillomavirus E7 Subunit Vaccines plus Cisplatin in an Animal Tumor Model: Causal Involvement of Increased Sensitivity of Cisplatin-Treated Tumors to CTL-Mediated Killing in Therapeutic Synergy

Abstract

Purpose: The goal of this study was to investigate the therapeutic potentials of combining chemotherapy with human papillomavirus (HPV) E7 subunit vaccines in an animal tumor model and to determine the underlying therapeutic mechanisms. Experimental Design: Animals bearing HPV E6/E7^expressing tumors were treated intratumorally with a selected cytotoxic drug, cisplatin, twice at 1-week interval and s.c. with E7 subunit vaccines thrice at 1-week interval. Tumor chemoimmunoresponse was measured by tumor size. Ag-specific CTL activities and tumor histology were checked in mice under treatments. Apoptosis, in vivo T-cell subset depletion, adoptive CTL transfer, and tumor regression were used to determine the mechanisms for antitumor therapeutic effects. Results: Combined therapy using cisplatin plus E7 subunit vaccines improved cure and recurrence rates of tumors and long-term antitumor immunity dramatically more than single therapy alone. In particular, both components of E7 subunit vaccines were required for induction of Ag-specific CTL as well as therapeutic synergy when combined with cisplatin. This therapeutic synergy was abrogated by depletion of CD8 + Tcells in vivo and was concomitant with histologic changes (such as heavy infiltration of lymphocytes and reduced tumor cell density). Finally, the increased sensitivity of cisplatin-treated tumors to CTL-mediated killing was found to be responsible for therapeutic synergy. Conclusions: E7 subunit vaccines plus cisplatin mediate antitumor therapeutic synergy through the increased sensitivity of cisplatin-treated tumors to CTL-mediated killing. Moreover, E7-based therapeutic vaccines have the potential to improve chemotherapy in patients with cervical cancer.Cervical cancer of the uterus is caused mainly by infection with human papillomavirus (HPV; ref. 1). Presently, HPV virus-like particle-based prophylactic vaccination against HPV infection is expected to reduce cervical cancer incidence. In women already infected with HPV, however, therapeutic vaccines are one promising option for control of cervical cancer incidence. To date, HPV E6 and E7 proteins have been a major target for immune-based therapeutic strategies against HPV-derived cervical cancers as they are expressed constantly in cervical cancer cells (2, 3). In particular, a variety of E6-or E7-targeted vaccine types have been tested preclinically and in humans. These include peptide vaccines (4 -6), DNA vaccines (7 -10), recombinant proteins (11 -13), dendritic cell -based vaccines (14 -17), and viral/bacterial delivery of vaccines (18 -20). These studies have shown the importance of T-cell responses, particularly CTL in clearing cervical lesions in humans or tumors in animals. In our recent findings, tumor burden is inversely related to E7 subunit vaccine-induced antitumor therapeutic efficacy (21). For instance, E7 subunit vaccines were able to cure tumors of a smaller size (2 mm in diameter) but not larger tumors (6-8 mm in diameter). This prompted us to evaluate whether E7 subunit vaccines...

Vaccine-Induced Tumor Necrosis Factor–Producing T Cells Synergize with Cisplatin to Promote Tumor Cell Death

“…6), and other (carboplatin and topotecan) but not all chemotherapeutics. Previously, it was observed that HPV16 E7-specific immune responses combined with cisplatin treatment can enhance apoptotic tumor cell death (37,38). Here, we confirm these observations and additionally show that TNFa has a key function in this enhanced cell death, indicated by the decreased synergy between cisplatin and vaccination in antitumor responses when TNFa was neutralized by systemic antibody treatment.…”

“…We postulate that both mechanisms can be involved in previous studies in which synergy was observed between cisplatin and efficient T cell-based immunotherapy (9,37,38,(41)(42)(43)(44).…”

“…Because cisplatin with TNFamediated apoptosis is induced after a minimum of 10 hours, this mechanism is likely not involved in short in vitro cytotoxicity assays as performed us (Fig. 6C) and others (37,39). However, the synergy is relevant when TNFa-producing T cells and cisplatin are together with tumor cells for a longer period as occurs in the in vivo situation.…”

Pretreatment with Cisplatin Enhances E7-Specific CD8+ T-Cell–Mediated Antitumor Immunity Induced by DNA Vaccination

“…Previously, Bae et al (21) have shown that cisplatin combined with HPV E7 peptidebased subunit vaccines improved the cure of established E7-expressing tumors as well as the long-term antitumor immunity in tumor-bearing mice. Their data also suggest that treatment with cisplatin increased the sensitivity of the tumors to CTL-mediated killing, which agrees with our current data (see Fig.…”

DNA Vaccines against Infectious Diseases and Cancer

“…Using IM-EP, we observed that E7 DNA vaccines induced 29 times higher IFN-γ production from CD8+ T cells than IM alone, thus displaying more potent antitumor therapeutic efficacy (our unpublished data). It can be further speculated that antitumor therapeutic activity of EP-delivered E7 DNA vaccines could be enhanced greatly by combining DNA vaccination with chemotherapy or radiation, based upon our preclinical data showing therapeutic synergy between chemotherapy/radiotherapy with E7 subunit vaccine-based immune therapy (Bae et al, 2007;Ye et al, 2007;Sin et al, 2009a).…”