CRISPR positioned to eliminate human papilloma viruses that cause cervical cancer

  • A 2018 clinical study in China is the first to use CRISPR to edit cells inside the human body in an attempt to eliminate the human papilloma virus (HPV) and is hugely significant for millions of women
  • Nearly all sexually active people get an HPV virus at some point in their lives and persistent high-risk HPV infections are the main cause of cervical cancer
  • Respectively 34,800 and 256,000 women in the UK and US live with cervical cancer and each year about 3,200 and 12,200 new cases of cervical cancer are diagnosed in the UK and US respectively nearly all related to HPV
  • Cervical cancer is increasing in older women not eligible for the HPV vaccine and not availing themselves of Pap test screening programs
  • A new study suggests that cervical cancer mortality among older women could increase by 150% in the next 20 years

CRISPR positioned to eliminate human papilloma viruses that cause cervical cancer

January 2018 marked the beginning of the first CRISPR clinical study to attempt to edit cells while they are in the body of women in the hope to eliminate the human papilloma virus (HPV), which is the main cause of cervical cancer. The study, led by Zheng Hu of the First Affiliated Hospital, Sun Yat-Sen University, Guangzhou, Guangdong, China, is the first to edit human cells while inside the body. Zheng Hu will apply a gel that carries the necessary DNA coding for the CRISPR machinery to the cervixes of 60 women between the ages of 18 and 50. The study’s aim is to prevent cervical cancers by targeting and destroying the HPV genes that cause tumor growth while leaving the DNA of normal cells untouched. Current estimates suggest that every year 527,624 women are diagnosed with cervical cancer and 265,672 die from the disease. Zheng Hu’s study is expected to be completed by November 2018 and findings reported in January 2019.
 
In this Commentary

This Commentary describes the Chinese CRISPR study and the etiology and epidemiology of cervical cancer. It also describes the current cervical cancer vaccination possibilities and the challenges they face. Further, the significance of the Chinese study is demonstrated by an English study, published in December 2017 in the Lancet Public Health, which warns that although HPV vaccination programs have significantly reduced the incidence of cervical cancer among young women, the incidence of the disease is increasing significantly among older women who do not qualify for the cervical cancer vaccine, and fail to avail themselves of regular Pap tests (A Pap test is a simple, quick and essentially painless screening procedure for cancer or precancer of the uterine cervix). The latter part of the Commentary describes advances that CRISPR technology has made over the past decade as well as describing its main ethical and technical challenges.
 
Human papilloma virus (HPV)

There are over 200 different types of HPV related viruses. Viruses are the etiological agents of approximately 15% of human cancers worldwide, and high-risk HPVs are responsible for nearly 5% of cancers worldwide. It is estimated that about 75% of the reproductive-age population has been infected with 1 or 2 types of genital HPV. About 79m Americans are currently infected with HPV, and about 14m people become newly infected each year. The American Centers for Disease Control and Prevention estimates that more than 90 and 80% of sexually active American men and women respectively will be infected with at least one type of HPV at some point in their lives. Most HPV infections are harmless, they last no more than 1 to 2 years, and usually the body clears the infections on its own. More than 40 HPV types can be easily spread by anal, oral and vaginal sex. About 12 HPV types are high risk, and it is estimated these persist in only about 1% of women. However, a central component of the association between HPV and cervical carcinogenesis is the ability of HPV to persist in the lower genital tract for long periods without being cleared. These persistent high-risk types of HPV can lead to cell changes, which if untreated, may progress to cancer. Other HPV types are responsible for genital warts, which are not sexually transmitted.
 
Etiology of cervical cancer
 
 “The way that the HPV causes cancer informs us about how cancer occurs in other settings. Virus particles insert foreign DNA into a person’s normal cells. This virus then turns off the “off-switch” and allows the oncogenes [Genes that can transform a cell into a tumor cell] to progress unchecked and create an oncogenic virus. So, in this case the 'insult' is known: it’s an HPV virus. However, in many circumstances we’re not sure what that initial switch is that upsets the balance between a tumor suppressor and an oncogene,” says Whitfield Growdon, of the Massachusetts General Hospital and Professor of Obstetrics, Gynecology and Reproductive Biology at the Harvard University Medical School: see video below:
 
 
HPV and cervical cancer

The association of risk with sexual behavior has been suggested since the mid-19th century, but the central causal role of HPV infection was identified just 40 years ago. HPV infection is the main etiologic agent of cervical cancer. 99% of cervical cancer cases are linked to genital infection with HPV and it is the most common viral infection of the reproductive tract. HPV types 16 and 18 are responsible for about 70% of all cervical cancer cases worldwide. Further, there is growing evidence to suggest that HPV also is a relevant factor in other anogenital cancers (anus, penis, vagina and vulva) as well as head and neck cancers. The importance of prevention and cervical cytological screening was established in the second half of the 20th century, which preceded and even advanced etiologic understanding.
 
Epidemiology of cervical cancer
 
Cervical cancer is one of the most common types of gynecological malignancies worldwide. It ranks as the 4th most frequent cancer among women in the World, and the 2nd most common female cancer in women between 15 and 44. According to the World Health Organization there were some 630m cases of HPV infections in 2012, and 190m of these led to over 0.5m new diagnoses of cervical cancer. The World has a population of some 2,784m women aged 15 and older who are at risk of developing cervical cancer. Each year about 3,200 and 12,200 new cases of cervical cancer are diagnosed in the UK and US respectively; nearly all related to HPV. There is estimated to be 34,800 and 256,000 women in the UK and US respectively living with cervical cancer. Each year some 890 and 4,200 women die from cervical in the UK and US respectively.
 
HPV vaccines
 
HPV vaccines, which prevent certain types of HPV infections, are now available to females up to the age of 26, and have the potential to reduce the incidence of cervical and other anogenital cancers. “Vaccinations work by using your own immune system against foreign pathogens such as viruses and bacteria. Vaccination against some high risk sub-types of cancer-causing HPV viruses is one of the most meaningful interventions we’ve had since the development of the Pap test,” says Growdon: see video below.
 
 
Gardasil and Cervarix

Gardasil, an HPV vaccine developed by Merck & Co., and licenced by the US Food and Drug Administration (FDA) in 2006, was the first HPV vaccine recommended for girls before their 15th birthday, and can also be used for boys. In 2008 Cervarix, an HPV vaccine manufactured by GlaxoSmithKline,  was introduced into the UK’s national immunization program for girls between 12 and 13. Both vaccines have very high efficacy and are equally effective to immunise against HPV types 16 and 18, which are estimated to cause 70% of cervical cancer cases. Both vaccines significantly improve the outlook for cervical cancer among women living in countries where it is routinely administered to girls before they become sexually active. “Both Gardasil and Cervarix vaccines have been shown to be incredibly effective at preventing the development of high-grade dysplasia, which we know, if left unchecked, would turn into cervical cancer,” says Growdon: see video above.

Gardasil also protects against HPV types 6 and 11, which can cause genital warts in both men and women. Second-generation vaccines are under development to broaden protection against HPV. In 2014 the FDA approved Gardasil 9, an enhanced vaccine, which adds protection against an additional 5 HPV types that cause approximately 20% of cervical cancers.
Global challenge

Despite the availability of prophylactic vaccines, HPVs remain a major global health challenge due to inadequate vaccine availability and vaccination coverage. Despite the promise, vaccine uptake has been variable in developed nations, and limited in developing nations, which are most in need. The available vaccines are expensive, require a cold chain to protect their quality, and are administered in 2 to 3 doses spanning several months. Thus, for a variety of practical and societal reasons (e.g., opposition to vaccination of young girls against a sexually transmitted agent, fear of vaccination), coverage, particularly in the US has been lower than would be optimal from a public health perspective.
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Success among young women

Notwithstanding, a study referred to above and published in the Lancet Public Health suggests cervical cancer cases are expected to fall by 75% among young women for whom vaccination is now the norm. Death from cervical cancer among the generation who were 17 or younger in 2008 when the UK vaccination program was introduced is expected to virtually disappear.
 
Challenges for older women

Notwithstanding the success of HPV vaccines for young women, there are continuing challenges for older women who, because of their age, do not qualify for HPV vaccines, and do not attend their Pap screening test when invited. “Pap tests involve scraping the cervix on the outside for cells, which then udergo microscopic examination. Today this is carried out by a computer. Further examination is carried out by a cytopathologist who determines status . . . . . . . . . . Pap tests do not diagnose cancer, but tell you whether you are at high risk of either having pre-cancerous or cancerous cells. Actual diagnosis of cervical cancer involves a colposcopy. This is a simple procedure, which uses a specific type of microscope called a colposcope to look directly into the cervix, magnify its appearance, and helps to take biopsies of abnormal areas,” says Growdon: see videos below.
 

What is a Pap smear test?


Diagnostic tests for cervical cancer
 
Older women and Pap tests

Pap tests, which are offered by NHS England to women between 25 and 64, is the most effective way of preventing cervical cancer; yet data show that in 2016 there was a significant drop in Pap test screening as women’s age increased. If such screening covered 85% of women, it is estimated that it would reduce deaths from cervical cancer by 27% in 5 years, and the diagnosis of new cases of cervical cancer by 14% in 1 year. According to the authors of the 2017 Lancet study, “The risk of acquiring an HPV infection that will progress to cancer has increased in unvaccinated individuals born since 1960, suggesting that current screening coverage is not sufficient to maintain – much less reduce – cervical cancer incidence in the next 20 years.”
 
Cervical cancer projected to increase in older women

Over the next 2 decades, diagnoses of cervical cancer in women between 50 and 64 are projected to increase by 62%, which could increase mortality from the disease by nearly 150%. “The main reason for this is that the population is ageing and women currently 25-40 will not benefit from vaccination – and they are in the age range where the likelihood of getting an HPV infection is quite high,” saidAlejandra Castanon one of the authors of the Lancet study.
 
Chinese study extends CRISPR technology

The Chinese study mentioned above to eliminate the HPV virus employs an innovative extension of CRISPR, which is a ‘game-changing’ technology. Over the past decade CRISPR has become a significant tool for genetic manipulation in biomedical research and biotechnology.  
 
CRISPR and genome editing

CRISPR is a complex system that can recognize and cut DNA sequences in order to provide organisms a strong defence against attacks and make them immune from further assaults. CRISPR has been adapted for both in vitro and in vivo use in eukaryotic cells to perform highly selective gene silencing or editing. Eukaryotic cells are those that contain a nucleus surrounded by a membrane and whose DNA is bound together by proteins into chromosomes.  CRISPRs are specialized stretches of DNA, and "CRISPR-Cas9" provides a powerful tool for precision editing due to its highly efficient targeting of specific DNA sequences in a genome, and has become the standard for genetic editing. Cas9 protein is an enzyme that acts like a pair of molecular scissors capable of cutting strands of DNA. The genomes of organisms encode messages and instructions within their DNA sequences. Genome editing involves changing those sequences, thereby changing the messages. This is achieved by making a break in the DNA, and tricking a cell's natural DNA repair mechanisms to make desired changes; CRISPR-Cas9 provides a means to do this. The technology’s ease of use and low cost have made it popular among the scientific community, and the possibility of its use as a clinical treatment in several genetically derived pathologies has rapidly spread its significance worldwide.
 
Changing ethical concerns

Despite CRISPRS promise there have been significant ethical concerns to genome editing, which center around human germline editing. This is because germline editing entails deliberately changing the genes passed on to children and future generations; in other words, creating genetically modified people. The debate about genome editing is not a new one, but has regained attention following the discovery that CRISPR has the potential to make such editing more accurate and even "easy" in comparison to older technologies. As of 2014, there were about 40 countries that discouraged or banned research on germline editing, including 15 nations in Western Europe. There is also an international effort, launched in December 2015 at the International Summit on Human Gene Editing and led by the US, UK, and China, to harmonize regulation of the application of genome editing technologies. 
 
After initially being opposed to using CRISPR in humans, in June 2016, the US National Institutes of Health advisory panel approved the technology for a study designed to target three types of cancer and funded by the Parker Institute for Cancer Immunotherapy at the University of Pennsylvania. In 2017 the UK approved the use of CRISPR for research in healthy human embryos. 
 
Off-target effects

Soon after scientists reported that CRISPR can edit DNA in 2012, experts raised concerns about “off-target effects,” meaning either CRISPR changes a gene scientist did not want changed or it fails to change a gene that they do. Although CRISPR-Cas9 is known for its precision a study, published in 2017 in the journal Nature Methods, raised concerns that because of the potential for “off-target effects” testing CRISPR in humans may be premature. Non-intended consequenes can happen because one molecule in the CRISPR system acts like a “molecular bloodhound”, searching the genome until it finds a match to its own sequence of  genetic letters; but there are 6bn genetic letters of the human genome, which suggests that there may be more than one match. Scientists anticipate and plan for this by using a computer algorithm to predict where such flaws might occur, then they search those areas to see if such off-target effects did occur. Notwithstanding such procedures and despite CRISPR’s precision, substantial efforts still are required to make the technology a common device safe for human clinical treatments.
 
Advances using CRISPR
 
The first clinical study using CRISPR began in October 2016 at the West China Hospital in Chengdu. Researchers, led by oncologist Lu You from Sichuan University, removed immune cells from the blood of a person with lung cancer, used CRISPR to disable a gene called PD-1, and then returned the cells to the body. This study is part of a much larger CRISPR genome editing revolution. Today, there are about 20 human clinical studies taking place using CRISPR technology most of which are in China. Different studies focus on different cancers including, breast, bladder, oesophageal, kidney, and prostate cancers. Further, a 2017 paper published in the journal Cell describes a number of innovative ways CRISPR being used; including editing cells while inside the body.
 
Takeaways
 
Despite the efficacy of HPV vaccines, immunization against cervical cancer still has significant challenges. Vaccines only target young people before they become sexually active, and are not recommended for slightly older and sexually active women. There is an urgent and growing concern about older women therefore who were not eligible for HPV vaccination, and are not availing themselves of regular Pap tests, and in whom the incidence of cervical cancer is increasing significantly. This makes Zheng Hu’s clinical study extremely important because it holds out the potential to substantially dent this large and rapidly increasing burden of cervical cancer.

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