Human papillomavirus vaccines for the treatment of cervical cancer

Optimized Gemcitabine Therapy in Combination with E7 Peptide Immunization Elicits Tumor Cure by Preventing Ag-Specific CTL Inhibition in Animals with Large Established Tumors

The role of chemotherapeutic agents in tumor immunotherapy is still controversial. In this study, we test using a TC-1 tumor model whether gemcitabine plus E7 peptide vaccine regimens (E7 peptides+CpG-ODN+anti-4-1BB Abs) may result in tumor cure in mice with large established tumors, with a focus on their effects on Ag-specific cytotoxic T lymphocyte (CTL) and myeloid-derived suppressor cell levels. Gemcitabine inhibited tumor growth by its direct cytotoxicity to tumor cells in vivo. E7 peptide vaccine regimens enhanced Ag-specific CTL lytic and antitumor therapeutic activity. Initial combination therapy using gemcitabine and E7 peptide vaccine regimens resulted in tumor regression with tumor relapse in animals with large established tumors, which appeared to result from the suppression of Ag-specific CTL activity by gemcitabine treatment. However, optimization of gemcitabine therapy by reducing its dose and frequency led to complete tumor regression without any recurring tumors in all tested mice even after discontinuation of therapy, possibly due to Ag-specific CTL responses. Thus, this study shows that the optimal dose and therapy frequency of gemcitabine are critical for achieving tumor cure in tumor-bearing animals undergoing E7 peptide vaccine regimen therapy, mainly by preventing CTL suppression. These findings may have implications for designing peptide-based therapeutic vaccines in cancer patients undergoing chemotherapy.

Combined stimulation of IL-2 and 4-1BB receptors augments the antitumor activity of E7 DNA vaccines by increasing Ag-specific CTL responses

Human papillomavirus (HPV) infection is a major cause of cervical cancer. Here, we investigate whether concurrent therapy using HPV E7 DNA vaccines (pE7) plus IL-2 vs. IL-15 cDNA and anti-4-1BB Abs might augment antitumor activity against established tumors. IL-2 cDNA was slightly better than IL-15 cDNA as a pE7 adjuvant. Co-delivery of pE7+IL-2 cDNA increased tumor cure rates from 7% to 27%, whereas co-delivery of pE7+IL-2 cDNA with anti-4-1BB Abs increased tumor cure rates from 27% to 67% and elicited long-term memory responses. This increased activity was concomitant with increased induction of Ag-specific CTL activity and IFN-γ responses, but not with Ag-specific IgG production. Moreover, the combined stimulation of IL-2 and 4-1BB receptors with rIL-2 and anti-4-1BB Abs resulted in enhanced production of IFN-γ from Ag-specific CD8+ T cells. However, this effect was abolished by treatment with anti-IL-2 Abs and 4-1BB-Fc, suggesting that the observed effect was IL-2- and anti-4-1BB Ab-specific. A similar result was also obtained for Ag-specific CTL activity. Thus, these studies demonstrate that combined stimulation through the IL-2 and 4-1BB receptors augments the Ag-specific CD8+ CTL responses induced by pE7, increasing tumor cure rates and long-term antitumor immune memory. These findings may have implications for the design of DNA-based therapeutic vaccines against cancer.

Antitumor therapeutic and antimetastatic activity of electroporation-delivered human papillomavirus 16 E7 DNA vaccines: a possible mechanism for enhanced tumor control

DNA vaccines are known to be lacking in immunogenicity in humans. Presently, electroporation (EP) is thought to overcome this limitation. Here, we investigate whether human papillomavirus 16 E7 DNA vaccines delivered by EP might elicit potent antitumor activity in animal cervical cancer models, with a focus on the underlying mechanism(s). Intramuscular (IM)-EP delivery of E7 DNA vaccines induced more potent antitumor therapeutic and antimetastatic activity compared with IM delivery. Moreover, the tumor-controlled animals by IM-EP possessed long-term memory responses to parental tumor cells. This improved antitumor effect was concomitant with augmented Ag-specific CTL activities. IM-EP also induced IgG and Th-cell responses higher than IM delivery. Finally, IM-EP resulted in more antigen production in and more attraction of immune cells into the site of DNA injection, suggesting that these biological and immunological changes made by IM-EP might be responsible for enhanced CTL activities and antitumor resistance. Thus, this study shows that IM-EP can induce more potent antitumor activity by augmenting CTL responses possibly through more antigen production in and more attraction of immune cells into the muscle sites. This study also suggests that IM-EP of E7 DNA vaccines might be a potential approach toward treating patients with cervical cancer.

Adoptive transfer of human papillomavirus E7-specific CTL enhances tumor chemoresponse through the perforin/granzyme-mediated pathway

Adoptive cytotoxic T lymphocyte (CTL) therapy has an important implication in treating cancer patients. Here, we investigate whether adoptive transfer of human papillomavirus (HPV) E7-specific CTL can enhance tumor chemoresponse using an established cervical cancer animal model. Cisplatin-based chemotherapy plus CTL therapy showed an improved therapeutic effectiveness, along with antitumor protective responses to a parental tumor cell rechallenge. Cisplatin treatment dose-dependently increased the expression of Fas, intercellular adhesion molecule (ICAM)-1, and major histocompatibility complex (MHC) class I antigens (Ags) on tumor cells in vitro. However, CTL-expressing FasL failed to improve antitumor activity in vitro and in animals, resulting from nonfunctional Fas expressed on tumor cells. In contrast, ethylene glycol tetraacetic acid (EGTA) treatment blocked increased sensitivity of cisplatin-treated tumor cells to CTL-mediated killing in vitro, suggesting an important role of the perforin/granzyme-mediated pathway for improved therapeutic effectiveness. This notion was further confirmed by perforin knockout animal studies. Thus, this study shows that (i) modulation of Ag (Fas, ICAM-1) expression by tumor cells has little effect on their increased sensitivity to CTL-mediated killing, (ii) improved therapeutic effectiveness is mediated mainly through the perforin/granzyme-mediated tumor killing pathway, and (iii) a combination of chemotherapy and adoptive E7-specific CTL transfer augments antitumor therapeutic activity in vivo. This finding may have important implications for treating HPV-associated cervical cancer.

Suppression of antitumour protective cytotoxic T lymphocyte responses to a human papillomavirus 16 E7 DNA vaccine by coinjection of interleukin-12 complementary DNA: involvement of nitric oxide in immune suppression

Interleukin-12 (IL-12) has been shown to enhance cellular immunity in vitro and in vivo. The beneficial roles of IL-12 as a DNA vaccine adjuvant have been commonly observed. Here the impact of IL-12 complementary DNA (cDNA) as an adjuvant for a human papillomavirus (HPV) type 16 E7 DNA vaccine is investigated in a mouse tumour model. Coinjection of E7 DNA vaccine with IL-12 cDNA completely suppressed antigen-specific cytotoxic T-lymphocyte (CTL) responses, leading to a complete loss of antitumour protection from a tumour cell challenge. In addition, antigen-specific antibody and T helper cell proliferative responses were also suppressed by IL-12 cDNA coinjection. This inhibition was observed over different IL-12 cDNA doses. Furthermore, separate leg injections of IL-12 and E7 cDNAs suppressed antigen-specific CTL and tumour protective responses, but not antibody and T helper cell proliferative responses, suggesting different pathways for suppression of these two separate responses. Further knockout animal studies demonstrated that interferon-gamma and nitric oxide are not directly associated with suppression of antigen-specific antibody responses by IL-12 cDNA coinjection. However, nitric oxide was found to be involved in suppression of antigen-specific CTL and tumour protective responses by IL-12 cDNA coinjection. These data suggest that coinjection of IL-12 cDNA results in suppression of E7-specific CTL responses through nitric oxide, leading to a loss of antitumour resistance in this DNA vaccine model. This study further shows that the adjuvant effect of IL-12 is dependent on the antigen types tested.

Development of prophylactic recombinant HPV58-attenuated Shigella live vector vaccine and evaluation of its protective efficacy and immunogenicity in the guinea pig keratoconjunctivitis model

To develop a prophylactic recombinant HPV58L1-attenuated Shigella live vector vaccine and evaluate its protective efficacy and immunogenicity in the guinea pig keratoconjunctivitis model, the HPV58L1 gene was cloned into vector pUCmt, and then subcloned into the suicide vector pCVD442. The recombinant plasmid pCVD442-HPV58L1 was introduced into attenuated Shigella (sf301:deltavirG) with the helper plasmid PRK2013 by filter mating. The positive colonies were harvested and confirmed by polymerase chain reaction. The expression of the HPV58L1 protein with a molecular weight of 60 kDa was confirmed by western blot. The ability of the interested protein to self-assemble into virus-like particles was identified by transmission electron microscope, and murine erythrocyte hemagglutination assay. The guinea pig keratoconjunctivitis model was used to evaluate the protective efficacy and immunogenicity of the vaccine. Animal experiments showed that there was no keratoconjunctivitis occurred in the immunized group (HPV58-attenuated Shigella), and the serum levels of anti-HPV58L1-IgG and -IgA were obviously increased (P < 0.05), but the anti-sf301 LPS-IgG just slightly increased (P > 0.05). Enzymelinked immunosorbent spot assay showed that HPV58L1-specific IgA-antibody-secreting cells (ASC) and IgG-ASC of spleen and lymph nodes were also obviously increased (P < 0.01). In this study, a recombinant HPV58L1-attenuated Shigella live vector vaccine was successfully constructed, and it could induce strong humoral immune responses in the immunized animals, and induce protective antibody production.

Increased sensitivity of radiated murine cervical cancer tumors to E7 subunit vaccine-driven CTL-mediated killing induces synergistic anti-tumor activity

The development of therapeutic vaccines has important implications for the treatment of cancer patients. Here we investigate whether human papillomavirus (HPV) E7 subunit vaccines can enhance tumor radioresponse using an established cervical cancer animal model. Radiation plus E7 subunit vaccines improved complete response, cure, and recurrence rates of tumors dramatically compared with single therapy alone. In particular, both components of the E7 subunit vaccines (E7 protein and CpG-oligodeoxynucleotide) were required for the induction of antigen (Ag)-specific cytotoxic T-lymphocyte (CTL) responses and for therapeutic synergy with radiotherapy. Moreover, with combined therapy the radiation dose could be reduced by 16 Gy to achieve an equivalent anti-tumor efficacy to radiation treatment alone. This therapeutic synergy was found to be mediated by CD8(+) CTLs and was concomitant with histological changes (presence of apoptotic bodies and multinucleated giant cells; heavy infiltration of lymphocytes), as determined by in vivo T-cell depletion and histological analysis. Finally, phenotypic changes of radiated tumors and their increased sensitivity to CTL-mediated killing appeared to be responsible for therapeutic synergy. These results show that E7 subunit vaccines act as a potent enhancer of tumor radioresponse and that this is mediated by increased sensitivity of radiated tumors to CTL-mediated killing. This study further suggests that E7-targeted therapeutic vaccines have the potential to improve radiotherapy in patients with cervical cancer.