Eradication of established HPV16-transformed tumours after immunisation with recombinant Semliki Forest virus expressing a fusion protein of E6 and E7

Preventative and therapeutic vaccines for cervical cancer

"High-risk" genotypes of the human papillomavirus (HPV), most commonly HPV genotype 16, are the primary etiologic agents of cervical cancer. Indeed HPV DNA is detected in 99% of cervical carcinomas. Thus, cervical cancer and other HPV-associated malignancies might be prevented or treated by the induction of the appropriate viral-antigen-specific immune responses. Transmission of papillomavirus may be prevented by the generation of antibodies to capsid proteins L1 and L2 that neutralize viral infection. HPV L1 virus-like particles (VLPs) show great promise as prophylactic HPV vaccines in ongoing clinical trials but L2-based preventative vaccines have yet to be tested in patients. Since the capsid proteins are not expressed at detectable levels by infected basal keratinocytes or in HPV-transformed cells, therapeutic vaccines generally target the nonstructural early viral antigens. Two HPV oncogenic proteins, E6 and E7, are critical to the induction and maintenance of cellular transformation and are co-expressed in the majority of HPV-containing carcinomas. Although other early viral antigens show promise for vaccination against papillomas, therapeutic vaccines targeting E6 and E7 may provide the best opportunity to control HPV-associated malignancies. Various candidate therapeutic HPV vaccines are currently being tested whereby E6 and/or E7 are administered in live vectors, as peptides or proteins, in nucleic acid form, as components of chimeric VLPs, or in cell-based vaccines. Encouraging results from experimental vaccination systems in animal models have led to several prophylactic and therapeutic vaccine clinical trials. Should this new generation of HPV preventative and therapeutic vaccines function in patients as demonstrated in animal models, oncogenic HPV infection and its associated malignancies could be controlled by vaccination. Importantly, recent advances in HPV detection and continued improvements in screening further enhance our opportunities to systematically eradicate HPV-associated malignancy.

Vaccination strategies for the treatment and prevention of cervical cancer

PURPOSE OF REVIEW

Immunotherapy of HPV-induced premalignant anogenital lesions and cervical cancer has made impressive progress. HPV as causative agent is targeted by prophylactic and therapeutic vaccination strategies. Preclinical and clinical studies have shown induction of natural and/or vaccine-induced immune responses. This review will summarize the status of vaccine development and clinical testing published since March 2003.

RECENT FINDINGS

For prophylactic vaccines there is first clinical evidence of effectivity (ie, 100% protection from HPV infection and dysplasia by virus-like particle (VLP) vaccine-induced neutralizing antibodies). Also, therapeutic vaccines have entered clinical evaluation. While prophylactic VLP vaccines are immunogenic per se, therapeutic vaccines will need further adjuvants to guide T cell differentiation, expansion, survival, and homing to tumor sites. To enhance clinical outcome of successful T cell induction in patients, the susceptibility of the tumor cells for lysis must be addressed in the future, since tumor immune evasion is a severe problem in cervical cancer.

SUMMARY

While successful prophylactic HPV vaccines have entered large clinical trials, therapeutic HPV vaccines, in spite of T cell induction, lack clinical responses due to the problem of tumor immune evasion. Adjuvants for systemic and local immune modulation will be mandatory for effective therapy.

Size-Dependent Immunogenicity: Therapeutic and Protective Properties of Nano-Vaccines against Tumors

Infection can protect against subsequent disease by induction of both humoral and cellular immunity, but inert protein-based vaccines are not as effective. In this study, we present a new vaccine design, with Ag covalently conjugated to solid core nano-beads of narrowly defined size (0.04-0.05 microm) that localize to dendritic cells (DEC205(+) CD40(+), CD86(+)) in draining lymph nodes, inducing high levels of IFN-gamma production (CD8 T cells: precursor frequencies 1/5000 to 1/1000) and high Ab titers in mice. Conjugation of Ag to these nano-beads induced responses that were significantly higher (2- to 10-fold) than those elicited by other bead sizes, and higher than a range of currently used adjuvants (alum, QuilA, monophosphoryl lipid A). Responses were comparable to CFA/IFA immunization for Abs and ex vivo peptide-pulsed dendritic cell immunization for CD8 T cells. A single dose of Ag-conjugated beads protected mice from tumors in two different model challenges and caused rapid clearance of established tumors in mice. Thus, a range of Ags conjugated to nano-beads was effective as immunogens in both therapeutic and prophylactic scenarios.

Superior Therapeutic Efficacy of Alphavirus-Mediated Immunization against Human Papilloma Virus Type 16 Antigens in a Murine Tumour Model: Effects of the Route of Immunization

In our efforts to develop a strong, effective immune response against cervical carcinoma and premalignant disease, we study the use of recombinant Semliki Forest virus (SFV) encoding the oncoproteins E6 and E7 from high-risk human papilloma viruses (HPVs). Optimal immunization conditions are required for immunotherapeutic treatment of cervical cancer as it has been postulated that cervical cancer patients are immune-suppressed and/or immunologically tolerant for HPV. We previously generated an optimized construct encoding a fusion protein of HPV16 E6 and E7 and a translational enhancer (enhE6,7). Immunization of mice with SFV-enhE6,7 was shown to induce cytoxic T cell (CTL) responses and resulted in the eradication of established tumours. We now demonstrate, using HPV16-specific MHC class I tetramers, that high pCTL frequencies can be induced. However, this induction is strongly influenced by the route of immunization applied. Whilst in bulk CTL assays, requiring in vitro restimulation, CTL activity can be observed upon sc, ip, iv and im immunization, detectable pCTL frequencies, without in vitro restimulation, are only induced upon im and iv immunization. The route of immunization also strongly influences the dose of viral vector needed to induce CTLs and tumour therapy. As few as 5x104 SFV-enhE6,7, primed and boosted iv, are needed to eradicate tumours in six out of seven mice treated. Furthermore, exponentially growing tumours of approximately 500 mm3 in size were seen to completely resolve and even tumours as large as 1500 mm3 decreased to one-third of their size. Apart from this potency, SFV vectors can safely be used for the expression of oncoproteins such as E6 and E7, since the viral RNA is not integrated in the host genome. Thus SFV-enhE6,7 meets with the criteria that a vaccine against cervical cancer should be safe and induce a very strong, long-lasting CTL response, strong enough to eradicate existing tumours.

Vaccines for cervical cancer

Human papillomaviruses (HPVs) are responsible for the nearly 450,000 cervical cancers that occur each year throughout the world. In the United States, the cancer rate is low (13,500 cases per year); nevertheless, HPVs affect millions of men and women annually in the form of genital warts and preinvasive diseases of the cervix and anogenital region. The expense of cancer prevention via precancer and cancer management is high, yet most HPV infections resolve spontaneously as a result of a successful host immune response. Recently, the discovery of methods to reproduce HPV virions (viral-like particles) in vitro has resulted in a successful clinical trial of preventing HPV infection and its associated precursor lesions. Although prevention is type-specific and duration of immunity is unknown, these results validate a vaccine strategy targeting prepubertal children that could prevent a significant proportion of genital warts and cervical precancers and cancers from occurring during reproductive life. Reversing advanced preinvasive and invasive cervical neoplasia with immunotherapeutics is a more difficult challenge, inasmuch as little or no evidence for natural immune-mediated regression of these diseases exists. Nonetheless, recent controlled trials have shown some success in inducing precursor regression with vaccines targeting viral oncoproteins. Anecdotal reports of therapies that augmentcellular immunity raise hopesthattherapeutics targeting multiple pathways of anti-viral or anti-tumor immunity will be beneficial to women with established cervical cancer. However, success will require identifying and circumventing the mechanisms by which tumor cells evade the immune system.

Antitumor efficacy of Venezuelan equine encephalitis virus replicon particles encoding mutated HPV16 E6 and E7 genes

An effective vaccine for treating human papillomavirus (HPV)-associated malignancies such as cervical cancer should elicit strong T cell-mediated immunity (CMI) against the E6 and/or E7 proteins necessary for the malignant state. We have developed Venezuelan equine encephalitis (VEE) virus replicon particle (VRP) vaccines encoding the HPV16 E6 and E7 genes and tested their immunogenicity and antitumor efficacy. The E6 and E7 genes were fused to create one open reading frame and mutated at four or at five amino acid positions to inactivate their oncogenic potential. VRP encoding mutant or wild type E6 and E7 proteins elicited comparable cytotoxic T lymphocyte (CTL) responses to an immunodominant E7(49-57) epitope and generated comparable antitumor responses in several HPV16 E6(+)E7(+) tumor challenge models: protection from either C3 or TC-1 tumor challenge was observed in 100% of VRP-vaccinated mice. Eradication of C3 tumors was observed in approximately 90% of mice following therapeutic VRP vaccination. Eradication of HLF16 tumors lacking the E7(49-57) epitope was observed in 90% of human leukocyte antigen (HLA)-A(*)0201 transgenic mice following therapeutic VRP vaccination. Finally, the predicted inactivation of E6 and E7 oncogenic potential was confirmed by demonstrating normal levels of both p53 and retinoblastoma proteins in human mammary epithelial cells (MEC) infected with VRP expressing mutant E6 and E7 genes. These promising results support the continued development of mutant E6 and E7 VRP as safe and effective candidates for clinical evaluation against HPV-associated disease.

Cervical cancer vaccines: recent advances in HPV research

Carcinomas of the anogenital tract, particularly cancer of the cervix, account for almost 12% of all cancers in women, and so represent the second most frequent gynecological malignancy in the world (48). It is well established that chronic infection of cervical epithelium by human papillomaviruses (HPV) is necessary for the development of cervical cancer. In fact, HPV DNA has been demonstrated in more than 99.7% of cervical cancer biopsy specimens, with high-risk HPV16 and HPV18 sequences being most prevalent (45,73). Therefore, an effective vaccine that would mount an immune response against HPV-related proteins might contribute to the prevention or elimination of HPV expressing lesions. This review will concentrate on the most recent advances in vaccine-mediated prevention and immunotherapy of HPV-induced cervical cancer, including presentations from the 20(th) International HPV Conference held in October 2002 in Paris.