HPV: Stem Cell Division Determines Cancer or Cure

The chance of anyone getting infected with the sexually transmitted human papillomavirus (HPV) over the course of a lifetime is estimated at about 80%. Some HPV infections will clear themselves up in a year or two, with little or no medical intervention. Others will linger; the longer the virus lingers in the body, the greater the chance the viral infection will evolve into cancer.

The reason why some people find their HPV infections go away while others develop cancer has remained a mystery to medical science although the strength of the individual’s immune system has been thought to play a major role. A recent study suggests immune system may not be a significant factor after all. The study suggests the pure chance of how stem cells divide after they’ve become infected with HPV determines who gets cured and who gets cancer.

HPV Transmission

The virus is spread when the skin of an infected person comes in contact with the skin of someone not yet infected. Since HPV is a sexually transmitted infection, the site of infection is usually the genitals, anal area, and mouth-throat cavity.

Upon exposure, the virus burrows through the epithelium (multi-layered tissue that lines the body’s alimentary canal and reproductive organs) to reach the lining’s basal (innermost) layer, where stem cells are created.

Stem Cells and Daughter Cells

Stem cells are somewhat like blank cells, they become whatever type of cell is needed at a given location. Most of the time, stem cells divide in asymmetrical fashion: one new cell remains in the basal layer as a stem cell while the other (daughter) cell becomes the appropriate cell for the specific organ of the body, such as the cervix, anus, or tongue.

When the stem cell is infected, so is the daughter cell. The daughter cell then travels up through the epithelium to the outermost layer, where it can pass on the HPV infection to an uninfected partner. When each daughter cell eventually dies, the person’s viral load is reduced, indicating a clearing of infection.

Symmetrical Division

In random cases, stem cell division is symmetrical, producing either two new stem cells or two new daughter cells. The more daughter cells produced, the sooner the infection will die out and the person becomes cleared of HPV infection.

The more infected stem cells that remain in the basal layer, where they divide to make more infected cells, the longer the infection remains in the body. The longer the infection remains, the higher the likelihood of cancer.

Dr. Evan R. Myers led the study from the Duke University Medical School’s Department of Obstetrics and Gynecology in Durham, North Carolina. He worked with members of the university’s mathematics department to determine the rate of symmetrical versus asymmetrical stem cell division. They matched their mathematical models to a population of 313 teenage girls who were tested for HPV twice a year for four years.

The researchers discovered random cell division patterns played a critical role in self-eradication of the virus or long-term infection. They attribute the body’s ability to clear itself of infection is about 83% due to random cell division and roughly 20% to immune system strength.


Sources:

1. Ryser, Marc D., Evan R. Myers, and Rick Durrett. "HPV Clearance and the Neglected Role of Stochasticity." PLOS / Computational Biology. PLOS, 13 Mar. 2015. Web. 7 Apr. 2015.
2. "Human Papillomavirus (HPV): HPV and Cancer." CDC / Centers for Disease Control and Prevention. US Department of Health & Human Services, 22 Jan. 2015. Web. 7 Apr. 2015.