- 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, 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.