中国妇产科网（China-OBGYN）在《2016中国 HPV 论坛》期间就HPV的相关问题有幸采访到了Tom Broker教授（国际HPV学会主席；阿拉巴马大学伯明翰分校（UAB）的生物化学系综合癌症中心病毒学项目共同负责人，并被任命为ADIS研究中心、口腔癌症研究中心和囊性纤维化中心的资深科学家；美国冷泉港实验室电子显微镜实验室的科长兼长期聘用的资深科学家），现将采访内容整理与大家分享。
中国妇产科网：Tom Broker先生，大量的流行病调查证实HPV16/18是导致宫颈癌的最主要的两个型别， 是否除HPV16//18外需要做具体的型别区分？
Tom Broker教授：在癌症前期或癌症期，确定在病变位置上存在哪些HPV类型，这是绝对必要的。原因有多个方面。癌症中最常见的病毒确实是HPV 16和HPV 18，这个结论已获得了大量实验结果支持。但是，如果观察病人早20或30年的感染情况，HPV 16型和18型感染并不常见，其他类型比较常见。所以从良性感染或低度病变发展为癌症的过程中体现了对HPV 16和HPV 18型的选择倾向。尽管如此，高达30％的子宫颈癌的是由其他类型引起的。因此不能局限观察HPV 16和18型，否则会导致遗漏30％的（子宫颈癌）案例，此数量全球每年约100000名妇女。基因分型不可忽视的两点，主要与病情发展阶段有关。如果是做早期筛查，主要可以确定16型或18型感染的妇女，或确定其他的14或16种易致癌HPV病毒亚型，便于跟踪感染情况。显然感染HPV 16和18型的妇女存在着致癌高风险。但是，其余30％的可能致癌感染也不能忽略。另一个重要原因是多重感染是非常常见的。妇女可能不是单一HPV类型感染，她可能有2，3个或多重的（HPV类型）感染。在我对女性HIV艾滋病者的研究中，他们的免疫系统薄弱。其中有些患者在生殖道粘膜有11种不同的HPV亚型，她病得非常严重。我们发现，在同一时间伴随2，3，4，或5种类型的感染预示着癌症发展的更大风险。其他病毒类型似乎增补了HPV 16和18的活性。因此多重感染的妇女有更高的患癌风险。
China Obstetrics and Gynecology Network (China-OBGYN) Interview with Professor Tom Broker (Former President of the International Papillomavirus Society, Professor of Biochemistry and Molecular Genetics, University of Alabama) during The China Academy HPV Forum 2016
Transcripts of Professor Tom Broker
1. The United States has 2 different parallel plans in place. Historically it has been pap smear cytology for the last 65 years, which has been a reasonably successful program in reducing cervical cancer incidence by about 80% compared to before the pap smear screening. However for the last 15 to 20 years, molecular based screening technologies have proven that they are far more affordable, specific, sensitive and predictive. So the trend now is to convert from cytology to molecular probe technologies. The preferable approach (would be):
One of the economic challenges is that you have a large number of people who do cytology, who collect pap smears and interpret pap smears. That is a large number of people. And they have to be displaced, to be replaced by people with greater familiarity with molecular technology, so basically the transition of the work force from cytology to molecular screening capabilities. That occurs not only in the work place, but at the universities - the educational level. The new generation of medical technologist is much more familiar with molecular biology.
The immediate transition to molecular probe technologies would be most helpful. When there is not an established work force of cytologists and other pathologists, who are established in their methodology, the optimal approach would be to quickly train the new generation of people with skills in understanding of DNA, RNA, nucleic acids, technologies like PCR, and DNA and RNA hybridization, and the use of electronic instrumentation, as compared to the specialists who are experts in microscopy. I will simply say at a personal level, I began as a microscopist, but in parallel became a molecular biologist with expertise in DNA and RNA structure and hybridization. I found that each had their value in a complementary way, but ultimately the molecular biology is usually the most definitive.
2. The primary objective at this point is to truly understand the natural history of HPV infection and diseases. To do so, it is absolutely essential to understand the HPV genotypes. That would the highest priority. The reason is multiple folds. One is that the different HPV types infect different parts of the body. Some are in the external skin, some are in the oral cavity, genital tracks and so forth. It took decades of research to determine what HPV types were specific to different parts of the body and the different types of epithelia.
We call that the tropisms of the virus. An important point is that human papillomaviruses now numbered more than 205 kinds. They were determined by isolating whatever HPV was associated with different parts of the body and different stages of disease. So the way we could have known that is by gradually identifying more and more of the types. When we started out in 1980, my laboratory, there were only 6 known types. By 1983, there were 18 known types. But by 1985 or 1986, they were more than 40 known types, and it has continued to grow each year with the improved technology, and having an open mind to what is important. The other thing I want to say on this subject is the necessity to understand which of the viruses are associated with diseases that progress towards cancer. We have learnt to divide or categorize the HPV types according to low risk and high risk. The low risk can cause primary infection and lesion, but it will spontaneously resolve or it will be maintained, but it will not be ultimately kill. In contrast, the high risk oncogenic viruses really have a possibility progressing towards cancer. Again, you had to know which HPV types were present to determine if they were of the low risk types, or the higher risk (types), or the very high risk types. So typing was absolutely crucial.
The additional part of your question was with respect to quantification, or measurement of copy number, or the amount of DNA or RNA. We found over the years that the copy number, or the viral load was less important in the cancer evaluation at the level of DNA. But that was very important was the amount of messenger RNA from oncogenes, the cancer-causing genes. So quantification mattered more at the level of RNA transcription and gene expression. But DNA copy number mattered less. Quite specifically our lab discovered, unexpectedly, that in a cancer associated with HPV, that only a single genomic copy of the HPV was transcriptionally active. Every other copy was silenced using epigenetic suppression of gene expression. And so it did not matter if you had 500 copies, because only was been expressed. That completely changed the paradigm of whether DNA copy number matters. It does not.
3. It is absolutely essential to identify which HPV types might be present in any lesion, of pre-cancer or an invasive cancer. The reason is multiple folds. The most common viruses found in cancers that have already been developed indeed are HPV 16 and HPV 18. But if you look in early stage infections, 20 or 30 years earlier in that person’s life time, type 16 and 18 are not very common at all. Other types are. So the risk of progression from benign infection and low grade lesion towards cancer has a selection process towards HPV 16 and 18. Having said that, about 30% of cervical cancers are caused by other types that are also high risk. You cannot limit yourself to look in HPV 16 and 18. You are going to miss 30% of the (cervical cancer) cases, which (are) approximately 100000 women globally each year. There is two points for the genotyping, and it largely depends on the stage. If you are doing early screening, you want to identify those women who have type 16 or 18, or the other fourteen or sixteen viruses that are likely to cause cancer. So that you can follow them. Clearly the women with HPV 16 and 18 are going to be at high risk. But you cannot leave the other 30% behind. But the other important reason is that multiple infections are very common. A woman does not just have a single HPV type. She might have 2 or 3 (types). In my own research looking at women with HIV AIDS, who have a very weak immune system. I found one woman who had 11 different HPV types in the genital mucosa. She was very very sick. We found that co-infections with 2, 3, 4, or 5 types at the same time is a greater predictor of progression towards cancer. The other virus types seem to complement or supplement HPV 16 and 18 activities. So the multiply infected women were at much greater risk of abnormal pap smears and progression towards cancer.
4. Self-screening is a very important component of a public health approach to reducing HPV disease for a great variety of reasons. Women either are reluctant to go to a gynecologist or other family practitioner for annual evaluation, or she may not even have access to such a clinic. On the other hand, in the privacy of your own home, self-collection offers every woman the opportunity to be screened and tested. There are a variety of ways in which the collections can be made. At this point, they are very effective. Essentially as good as what would be carried out in a physician office. They can be packaged up and centrally evaluated in testing labs. Self-collection is an extraordinarily important aspect. It is a time saver. It enables higher level of privacy. And very often the woman would be more thorough in swabbing different parts of the genital tracks to capture potentially infected cells. So the success rate is very high. It is also very economical, and allows for much greater coverage. And also because there is a record of mailing and testing in central lab, there is a better opportunity for data management, which becomes extremely important.
5. I think vaccines are an important component of prevention, but are not sufficient to enable an entire society to eradicate HPV or have protection. In my opinion, there is a 5 fold strategy to preventing and managing HPV disease. Prophylactic vaccines are clearly one component. (But) at this point, they are too expensive, too controversial. A lot of people don’t feel that they are necessary. The overall acceptance rate in most countries is quite low, unfortunately. Because the vaccines are safe, effective, and absolutely do prevent HPV infection. But there are so many other social and political forces at work that a very high fraction of young people are not getting vaccinated. The second essential thing, perhaps even more important is the screening. Effective national molecular screening programs are absolutely essential to identifying early stage disease. In my personal opinion, screening ought to begin at a relatively young age, within 5 years of onset of sexual activity. And at least monitor who is acquiring HPV infection, and who might be at risk of persistent infection that could lead to progressive disease. The third area is still under research and development, and that is therapeutics. Once a HPV lesion is been identified, in the ideal world that will eventually arrive, we need to have treatments – simple, effective, topical treatment - that can make the infection go away. The forth important thing is public education and physician education. So that people are aware of a range of HPV diseases and what can done to prevent, control, manage and treat them. The final thing is public policy that comes from regulatory level, government level, and media relations to advocate for healthcare delivery capabilities, which go back to HPV screening and appropriate therapeutic care. You cannot control HPV with only one of the 5 aspects, you need all 5. And through the media and the general public, but ultimately the government regulatory side of approvals for clinical trials or founding for implementation of vaccines and screening programs all become crucial. One more thing in response to the question about males. Males are very likely to get HPV infections. HPV is a gender neutral infectious agent and men can get serious disease just as women can. Vaccine programs that included boys and young men would be a great public health policy and cost effective both in breaking the cycle of transmission between men and women, but also because men could get the disease. So I think all the pursuit whether it is the screening or vaccination should be available to the males as they are to the females. I would like to also add one other point, (which) is risk factors. Clearly the HPV associated diseases necessarily involve one or more HPV types, but there (are) other susceptibility risks that people are necessarily exposed to as a part of living. HPV is a part of human condition. The viruses are everywhere. They are unavoidable, and considering the wide range of HPV types, every body on earth has some HPV some where in their bodies, cutaneous or mucosa or both. So the idea that some how it is avoidable is impossible. HPV is everywhere and people will get it. The second thing is risk. There is ample evidence that early sexual activity is a high-risk situation for acquiring HPV in the genital track, boys or girls, especially girls. And the delayed onset of sexual activity is more and more protective depending on age. The youngest girls, if they are exposed, have a very high risk of not only primary infection but (also) future progression towards cancer. The second major risk factor in my opinion is repeated wounding and healing of the epithelium that harbors the HPV. We know from experiments and from natural history that repeated wounding and healing of a HPV infected tissue is more likely to progress towards cancer. And the third great risk factor is the immune status of the individual. And there are many many things that can cause immune insufficiency in the course of life. This is maybe my most important statement. I want to elaborate on the types of immunosuppressive events in human life. One of them is simply stress - emotional stress, physical stress, nutritional stress, and sunburn - all can activate HPV that is latent and sub-clinical. The second one, which it is a very frequent cause of activation, is pregnancy. A woman gets pregnant, she is immuno-modulated so she does not reject the developing fetus, embryonic fetus, but at the same time she is more susceptible to the activation of the persistent HPV in the genital track. The third thing is aging. All of us have our immune systems getting weaker and weaker with time. One of the periods of greatest emergence of cervical cancer is in people (who are) 55, 60, and 70 years old, because the immune system is getting weaker. But there are other important reasons such as solid organ transplantation. People who receive a new kidney or a liver or a heart or a lung or a pancreas and so forth who are on immunosuppressive drugs invariably will break out with whole body warts after about 10 years of immunosuppression. Another is people (with) auto-immune diseases, rheumatoid arthritis, lupus erythematosus, Crohn's disease, who are taking immunosuppressive drugs to control their auto-immune disease, will activate latent HPV. And of course HIV AIDS is immunosuppressive. And yet another one is people undergoing chemotherapy for cancer who have a depletion of their immune capabilities and their HPV will activate. So if you add it all together, it is impossible to go through life without experiencing an immunosuppressive event, or many times in the course of life. That is why HPV has become such a big medical problem. Every one is likely to carry it. Every one is likely to express it at some point in life.
6. Databases on HPV disease are essential. Even though HPV has been studied around the world rather intensively since the mid 1970s, we are still continuing to learn about the natural history of the infections, the risks, and the possible outcomes. Crucial to that is HPV genotyping and evaluation of multiple co-infections, as well as the other risk factors that individuals might be presenting them, increased or decreased their susceptibility to infection. The only way we could understand the detail of natural history is through databases, tumor registries that evaluate people who have progressed towards cancer. That is part of the learning process that the biomedical community can contribute and certainly should be supportive.