M
any authors date the first report of an infectious etiology of cervical cancer to the year 1842, when Domenico Antonio Rigoni-Stern presented the incidence of cancer-related mortality in Verona. However, a careful analysis of the original publication, now available in English translation, revealed that this conclusion – based on the different frequency in nuns compared to married women – is unsustainable because of the failure to differentiate between corpus and cervix cancer, and also because Rigoni-Stern never in fact postulated such a relationship in his study (1).Human pathogenic papillomaviruses (HPV) came into the picture many decades later, when in the 1970s Harald zur Hausen focused attention on the family of papillomaviruses which were well documented as etiologically implicated in benign tumors (warts, condylomata acuminata) and malignancies of animals, such as rabbits. The role of these viruses in the development of tumors was confirmed by the discovery of characteristic papillomavirus particles in the coilocytes pathognomonic for preneoplastic cervical lesions. After it had been shown that there is not only one human papillomavirus (formerly known as "wart virus") but in fact a heterogeneous group – today we are aware of more than 100 human pathogenic representatives (the so-called HPV types) – experimental strategies were developed to search for related viruses (2). These investigations led to the identification of the first mucosotropic papillomaviruses (HPV 6 and 11) and the HPV 16 and 18 subsequently classified as the prototypes of human pathogenic high risk papillomaviruses, which together are responsible for around 70% of cases of cervical cancer worldwide (squamous and adenocarcinomas).
SUMMARY
Introduction: In the 70 years since Harald zur Hausen postulated the human papillomavirus (HPV) as an etiological factor in the formation of cervical dysplasia and invasive cervical cancer, further studies have confirmed that the high risk strains HPV 16 and 18 are implicated in about 70% of cervical dysplasias and cancer. Cell culture experiments have shown the potential of these viruses for malignant transformation. Epidemiological studies conducted during the 80s have since confirmed the association between HPV and cervical cancer. In the early 90s, genetic engineering technologies allowed for the successful development of so-called virus-like particles (VLP), consisting only of nucleic acid free non-infectious virus capsule. This was followed by the first industrial scale vaccine development. The tetravalent vaccine was licensed first in the USA in June 2006, and then in Europe in September 2006. The German Standing Vaccination Committee (Ständige Impfkommission, STIKO) approved the vaccine in March 2007 for Germany. The approval of the bivalent vaccine by EMEA (European Agency for the Evaluation of Medical Products) occured in September 2007. Methods: Selective literature review of recent vaccination studies of HPV-associated dieseases. Results and discussion: All recently published studies show the high effectiveness of the bivalent (HPV 16 and 18) and the quadrivalent vaccine (HPV 16, 18 and 6,11) in the prevention of cervical intraepithelial neoplasia. The vaccine has also been shown to be highly effective in HPV- associated preneoplasias of the vulva, vagina and anus. Studies published to date show protection for at least 5 years. The highest vaccination effectivity is observed in non-infected young humans. Dtsch Arztebl 2007; 104(41): A 2806–10
Key words: cervical carcinoma, HPV, vaccination, vaccine, virus-like particle
Klinik für Frauenheilkunde und Geburtshilfe, UKS-H Campus Lübeck: PD Dr. med. Löning, Prof. Dr. med. Diedrich; Fakultät für Biowissenschaften, Deutsches Krebsforschungszentrum Heidelberg: Prof. Dr. rer. nat. Gissmann; Klinik und Poliklinik für Frauen-heilkunde und Geburtshilfe, München: Prof. Dr. med. Friese; Universitätsfrauenklinik Ulm: Prof. Dr. med. Kreienberg; Allgemeine Gynäkologie und Geburtshilfe; Medizinische Hochschule Hannover: Prof. Dr. med. Peter Hillemanns
ORIGINAL ARTICLE
Human Papillomavirus
and Cervical Cancer
Current Status of Vaccination Against Human Pathogenic
Papillomavirus
Martin Löning, Lutz Gissmann, Klaus Diedrich, Klaus Friese,
Rolf Kreienberg, Peter Hillemanns
Shortly after the DNA of HPV 16 and 18 was isolated from biopsies of cervical cancers, various research teams confirmed that these genomes frequently are present in tumors. It was discovered in 1992 that "persuasive data exist for a causal association between HPV and cervical cancers" (3).
Development of prophylactic vaccines
The possibility of developing a vaccine was already being considered even before a general awareness of a causality had developed.
To confer subsequent immunity, it was assumed that only complete virus particles – and not a monomeric protein – could be considered for use as a vaccine. A "conventional viral vaccine" consisting of inactivated viruses or viruses adapted in cell culture was not an option because papillomaviruses – unlike many other viruses – can only be multiplied very inefficiently in cell cultures. An elegant solution was found in the form of genetic engineering production of so-called virus-like particles (VLP) which had already been produced for other viruses (hepatitis B vaccine).
Furthermore, this type of vaccine offers unsurpassable safety because no infectious particles can be formed. About 10 years ago, various companies began to develop an interest in HPV vaccines. The first quadrivalent vaccine was licensed in Mexico and the USA in early June 2006 for the 9 to 26 year age group, while European approval was granted by the EMEA (European Agency for Evaluation of Medical Products) in September 2006 for children and adolescents aged 9 to 15 years and for women aged 16 years or older.
The concurrently developed bivalent vaccine has recently become available in Europe. The German Cancer Research Center (Deutsches Krebsforschungszentrum, DKFZ) in Heidelberg together with the American National Institute for Health (NIH) have been recognized as the originators of a patent for the manufacture of the VLPs of HPV 16 which has been licensed to both companies.
Clinical studies
Both the bivalent and the quadrivalent vaccines consist of VLPs of HPV 16 and HPV 18, the two virus types most commonly associated with cervical cancer. The quadrivalent vaccine additionally contains types 6 and 11 VLPs for protection against condylomata acuminata. The bivalent vaccine contains as adjuvant not only aluminium salts but also AS04 (monophosphoryl lipid A) to enhance immune response. AS04 induces consistently higher and longer-persisting antibody levels than the same vaccine with a conventional aluminium salt formulation. VLPs are produced in a yeast expression system (quadrivalent vaccine) or insect cells (bivalent vaccine). The recommended vaccination schedules are very similar: threefold intramuscular administration of month 0, 1 (bivalent vaccine) and 2 (quadrivalent vaccine) and month 6. The single vaccine dose of 0.5 ml contains 20 and 40 µg antigen of the individual VLPs respectively.
Following a series of phase I studies to test for possible side effects, efficacy was evaluated for the first time in a double-blind, multicenter phase II study. Altogether 2392 women aged 16 to 23 years received either the HPV 16 VLP vaccine or placebo. After a mean follow-up of 17.4 months, persisting HPV 16 infections and 9 cases of HPV 16 associated cervical intraepithelial neoplasia (CIN) were diagnosed in 41 women. All of these subjects belonged to the placebo group. The vaccine has therefore been shown to be highly effective in a phase II study (4).
Bivalent vaccine against HPV 16 and 18
1113 girls and adult women between the ages of 15 and 25 years were recruited into a double-blind, placebo-controlled phase II study (5).
The most important inclusion criteria were the absence of HPV16/18 DNA in the PCR (polymerase chain reaction) and the non-presence of HPV 16/18 L1 specific antibody together with normal cervical cytology. The follow-up was 18 months to a maximum 27 months. 100% total IgG seroconversion for HPV 16 and 99.7% total IgG conversion for HPV 18 was recorded after 7 months. The serum titers were 80 to 100 fold higher than after a natural infection. 91.6% protection against initial infection with HPV 16/18 was achieved. Efficacy against persisting infection was 100%, as was protection against histologically confirmed CIN.
Quadrivalent vaccine against HPV 6, 11, 16 and 18
In the placebo-controlled study, 552 women aged between 16 and 23 years from the USA, Europe and Brazil with a history of normal cervical cytology received vaccine or placebo on day 1 and after 2 and 6 months (6). Two and a half years after vaccination with the quadrivalent vaccine, persisting infections with HPV 6, 11, 16 or 18 and the associated diseases were reduced by 90% compared to the women vaccinated with placebo (p < 0.001). In a 35 month follow-up, persisting HPV infections were diagnosed in 36 cases in the placebo group, but in only one case in the active vaccine group.
The quadrivalent vaccine prevented cervical precanceroses caused by HPV 16, 18, 6 and 11 to an extent of 100%. Minor injection site reactions were somewhat rarer in the placebo group, and the commonest side effects were pain at the needle insertion site and headache, although these effects did not prompt any of the subjects to discontinue participation.
The neutralizing antibody titers were markedly higher after immunization (month 7) in the women who received the active vaccine than in the placebo group after natural infection. However, after 36 months the antibodies were still higher than in the women who had previously had a natural HPV infection.
Phase III results for the quadrivalent vaccine
The recently published results of the phase III clinical studies of the quadrivalent vaccine demonstrate with high significance the prophylactic efficacy of up to 100% for all primary end points over a period of 3 years (protection against cervical cancer, cervical adenocarcinoma in situ, precancerous and potentially precancerous lesions of the cervix, vulva and vagina, the corresponding cancers, and genital warts) (7, 8).
The FUTURE I and II studies are prospective, double-blind, placebo-controlled, randomized studies in which more than 17 000 women aged between 16 and 26 years were enrolled (9). In the per protocol population for prophylactic efficacy of the quadrivalent vaccine compared to placebo, women were studied who were HPV type 6, 11, 16, 18 negative up to the end of the vaccination series, received all 3 vaccine doses on schedule and had not violated the study protocol.
The FUTURE I study demonstrated 100% efficacy of the quadrivalent vaccine for each of the primary end points caused by the HPV types 6, 11, 16, 18. The FUTURE II study showed 98% efficacy in preventing potentially precancerous cervical lesions (CIN2/3), adenocarcinoma in situ and cervical carcinomas caused by HPV types 16, 18. One case of CIN 2/3 occurred in the active vaccine group. This subject was persistingly HPV high risk type 52 positive and transiently HPV type 16 positive since enrollment.
Potential effects of HPV 16/18 vaccination on the reduction of the number of cervical cancer cases in dependence on the vaccination rate (30 to 100%)
An extended analysis of the efficacy of the quadrivalent vaccine compared to placebo was performed on the total study population, regardless of whether the women were HPV positive on enrollment (including HPV type 6, 11, 16, 18) or already had an HPV-associated anogenital disease. Protocol violations were accepted (intention-to-treat population).
The purpose of this extended analysis was also to demonstrate the effect of the vaccination on every prevalent or incident HPV-related infection or lesion, independently of the HPV type. The FUTURE I study revealed still 34% efficacy against every HPV-related vulvar, vaginal or anogenital lesion and 20% efficacy against every HPV-related cervical lesion.
Even in this population, the FUTURE II study showed 44% efficacy against HPV type 16, 18 related high-grade cervical lesions and 17% efficacy against every HPV-related cervical lesion (7).
Another, recently published study confirms these results. In all HPV 16 and 18 negative women the study revealed 100% effectiveness against the development of VIN 2–3 (vulvar intraepithelial neoplasia) and VaIN 2–3 (vaginal intraepithelial neoplasia) within 3 years. The effectiveness on including the women who were already HPV positive at the time of first vaccination was 71% for HPV 16/18 associated VIN and VaIN (10).
Overall, these results show that a reduction in anogenital diseases including cervical cancer is already observed in all the vaccinated women in the first 3 years after the vaccination. However, an HPV infection already present before vaccination in many cases evidently develops into a lesion within 3 years and cannot be prevented by vaccination. The difference in the disease incidence has increased continuously in the study population between the active treatment and the placebo group over the entire follow-up period.
Duration of vaccination protection
The vaccination protection period so far documented in published studies is 4.5 and 5 years (11, 12).
In the follow-up investigation of the multicenter, randomized, placebo controlled double-blind study of the bivalent HPV 16/18 L1 VLP AS04 vaccine, 383 women from the active vaccine group were compared with 393 women from the placebo group for HPV-DNA, PAP findings, and long-term immunity. Besides the high vaccine effectiveness of 100% against HPV 16/18 CIN lesions, persisting seropositivity of the HPV 16/18 vaccine titers of above 98% was observed (11).
In a multicenter, randomized, placebo controlled double-blind study with the quadrivalent HPV 6/11/16/18 vaccine, 1158 women between 16 and 23 years of age without a previous abnormal PAP smear were enrolled.
5 years after the start of the study, the combined incidence of HPV 6/11/16/18 associated persisting infections or diseases was reduced by 96% in the active vaccine group (n=276) (2 cases in the vaccine group versus 46 in the placebo group, n=275).
The active vaccine group contained no cases of HPV 6/11/16/18 associated precancerous cervical dysplasias or genital warts compared to 6 cases in the placebo group (effectiveness = 100%; 95% CI: 12–100%). The vaccine-induced anti-HPV vaccine titers remained for 5 years at or above the level observed after natural infections (12).
Under the auspices of the Nordic Cancer Registry, a cohort of vaccinated subjects is to be monitored centrally for vaccine non-responders over the next 10 years to clarify the aspect of vaccination protection over this period. Study programs with a booster vaccination are being conducted concurrently.
Effectiveness of vaccination in adolescents
Interestingly, adolescents exhibit an immune response superior to that of young women. Altogether 506 girls and 510 boys (age 10 to 15 years) and 513 young women (age 16 to 23 years) were treated with the quadrivalent vaccine. Besides the very low complication rate (mainly injection-related skin irritations), seroconversion of more than 99% against all 4 HPV types was observed in every group after completion of vaccination (month 7). The antibody titers were significantly 1.7 to 2.7 fold higher for all 4 HPV types in the 10 to 15 year olds compared to the 16 to 23 year old women.
Cross immunity against other HPV types
Besides the strictly type specific immunization against HPV 16/18 with the bivalent HPV16/18 L1 VLP AS04 vaccine, the evaluation of the clinical study showed 54.5% cross protection against the HPV 16 related type 31 and 94.2% against the HPV 18 related type 45 (11).
In another recently published phase III study, the bivalent vaccine against HPV 16 and 18 was found to provide 60% cross protection against HPV 45, 36% against HPV 31 and 32% against HPV 52. The bivalent vaccine was found to have an overall effectiveness of 27% after one year against all oncogenic HPV types not contained in the vaccine (14).
It remains to be seen whether these data are confirmed by further studies and whether the cross protection is maintained in the long-term course.
Introduction of the vaccination in Germany
The research results so far obtained for HPV vaccination are without doubt impressive. In 2006, the Advisory Committee of the US Center of Disease Control (CDC) included the quadrivalent HPV vaccine in the list of vaccines recommended by the government for preadolescent girls. In Germany, the Standing Vaccination Committee (Ständige Impfkommission, STIKO) recommended the vaccination of 12 to 17 year old girls in March 2007.
Over the long term, a fall in the rate of cervical cancer is to be expected, and in the medium term a reduction of the very much more common precanceroses (CIN).
The benefits for Germany will consist primarily in a marked reduction of abnormal swab specimens detected during screening and the subsequently necessary diagnosis, treatment and follow-up. The expected long-term reduction in the cancer rate, therefore, is not only expected to provide benefits for women, the introduction of vaccination could already become cost-effective within a few years. Many health insurers granted reimbursement of the costs, around 500 euros for a complete vaccination, even before the STIKO recommendation.
The proposed level of protection of the population, however, will require a high level of vaccination coverage which in the absence of vaccination programs for adolescents represents a social challenge in the German context (diagram). It is therefore very important to initiate in these target groups information and education programs driven by cooperation between various societies (German Cancer Society [DKG], gynecological and pediatric societies, Zervita Project Group, Cancer Information Service [KID], German Green Cross, and others).
Even after the introduction of HPV vaccination, many questions remain unresolved (HPV type replacement, breakthrough infections, protective antibody titers, duration of vaccination protection) which can only be clarified in population-based studies. The cervical cancer early detection program remains essential despite vaccination and must be optimized. Some 160 000 unclarified and abnormal cytological findings (PAP III to IV) are diagnosed annually in Germany. With a reduced prevalence of cervical neoplasia and thus a poorer positive predictive value of conventional cancer smears in the vaccinated population, the introduction of the highly sensitive HPA-DNA test in cancer screening is to be expected. Conflict of Interest Statement
Prof. Dr. rer. nat. Lutz Gissmann receives remuneration from the sale of the vaccines of MSD/SP and GSK.
PD Dr. med. Martin Löning, Prof. Dr. med. Klaus Diedrich, Prof. Dr. med. Klaus Friese, Prof. Dr. med. Rolf Kreienberg and Prof. Dr. med. Peter Hillemanns have over the last 5 years received lecture and consulting fees as well as travel expense remunerations from several companies operating in the field of cytology/molecular diagnostics/vaccines. They hold no shares in these companies and are in no relationship of employment towards them.
Manuscript received on 11 December 2006, final version accepted on 1 August 2007. Translated from the original German by mt-g.
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Correpsonding author PD Dr. med. Martin Löning
Klinik für Frauenheilkunde und Geburtshilfe UKS-H Campus Lübeck
Ratzeburger Allee 160 23562 Lübeck, Germany loening@gmx.de
