Season 4, Episode 13: The Truth

In a flash-forward to the year 2043, David is facing an inquiry about Bob's clone, Robert Melnikov, Jr. At that time, it had just been discovered that an outbreak of the Spanish Flu in 2010 had caused a reactivation of endogenous retroviruses in the DNA of Bob Jr., who was two years old at the time. Unaware of this "reawakening," Bob Jr. had set up a fertility clinic when he was eighteen, through which he had sold his sperm to over 3 million women, so that they could have children - through in vitro fertilization - with an active Jacobsen's Organ. Seventeen years later, David's daughter, Lilith, who is a paleovirologist in 2043, discovered that a number of infectious disease pandemics between 2010 and 2043 were all caused by reactivated "fossilized" viruses in the DNA of Robert's offspring.

Image provided courtesy of Shaftesbury Films.

David testifying in 2043.

CAN A FLU EPIDEMIC REACTIVATE FOSSIL VIRUSES?

What are fossil viruses?

Retroviruses, such as HIV or the herpes virus, store their genetic material as RNA, but they're able to convert this to DNA, which then integrates into the DNA of the cell they infected. If this happens in a germ-line cell (that is, a sperm or egg cell) the DNA of the retrovirus is passed on to the next generation.

When the human genome was sequenced, scientists discovered that over the course of human evolution many retroviruses had integrated into our DNA. In fact, about 8% of our DNA consists of human endogenous retroviruses, or HERVs. Many of these viruses have been in our genome for millions of years, and we share some fossil viruses with other species that evolved from the same common ancestors. The study of fossil viruses is called paleovirology.

Can endogenous retroviruses be reactivated?

Most of the endogenous retroviruses in our genome have been there for so long and have acquired so many mutations that they are no longer functional. The viral genetic material is partially lost, or has moved to different parts of the genome, or no longer codes for functional viral proteins. These retroviruses can't be reactivated anymore. Others have integrated into the genome more recently and are mostly intact. Some of these newer HERVs can indeed still express viral proteins. So far, none of the endogenous retroviruses have been spontaneously reactivated to form a complete infectious virus.

However, scientists have been able to reconstruct one of these fossil viruses in the lab. The virus had been mutated over time and there were several versions of the virus present in the human genome. The researchers puzzled together the sequence of the original virus, and were able to recreate an active virus that could infect cells. The main reason for reactivating these ancient viruses in the lab is to understand how current retroviruses, such as HIV, work. By figuring out what happened to the fossil viruses, scientists can learn a lot about how to fight those that infect humans today.

Image provided courtesy of AXS Studio Inc and Shaftesbury Films.

Artists' rendition of reactivated ancient retroviruses.

Can another virus reactivate endogenous retroviruses?

Elements of human endogenous retroviruses can indeed be activated when the cell is infected by a virus. HIV, herpes virus, and Influenza A are all able to reactivate HERVs. The reactivation of HERVs by HIV can be used as a potential drug target: HIV itself keeps mutating, so it's very difficult to develop drugs against it. But if HERVs are activated in the same cells that also contain HIV, drugs against HERVs would attack the infected cell.

None of the reactivated HERVs are themselves infectious, though. If they are activated at all, they only express some of their proteins - not the entire virus. And most of the HERVs are mutated to the point where none of their components can be activated anymore.

So?

It's possible that some endogenous retroviruses in Robert Melnikov Jr.'s DNA were reactivated when he contracted the Spanish Flu as a kid…in 2010. However, as of 2008, no reactivated HERVs have produced complete working viruses unless they were pieced together in a lab. Furthermore, for Bob Jr.'s offspring to have reactivated multiple infectious viruses, something in the DNA of his sperm cells would had to have been altered to program the activation of multiple retroviruses that each, in turn, became wildly infectious. This is extremely unlikely; the high mutation rate of HERVs means that most of them can't be reactivated at all, and those that can are not fully functional infectious viruses.

DID YOU KNOW?

In this episode we learn that, in the future, Mayko has received artificial skin transplants and had several internal organs and even her leg regenerated from stem cells. Artificial skin is already being used to treat severe burn victims who do not have enough skin left for the standard procedure of skin grafting (where skin is taken from one part of the body and transplanted to the burnt region). Currently, research is underway to improve artificial skin so it more closely resembles real skin, using biopsies from the patient's own skin.

Image provided courtesy of Shaftesbury Films.

Thanks to regenerative medicine, Mayko looks as young as she did 35 years earlier!

Regenerating organs from stem cells is not yet routine, but the field of Regenerative Medicine is studying how various organs could be (partially) regrown from stem cells. For example, experiments have shown that liver tissue can be regrown by injecting stem cells into patients' livers. Researchers are also studying how stem cells can be used to grow parts of organs (for example heart tissue) in the lab, which could then be used for transplantation.

-- Eva Amsen

Want to read and learn more?

Read an article about fossil viruses and the emerging field of paleovirology:
http://www.newyorker.com/reporting/2007/12/03/071203fa_fact_specter

Find out how endogenous retroviruses can be used to develop anti-HIV drugs:
http://www.cbc.ca/health/story/2007/11/09/hiv-vaccine.html

Learn how artificial skin can be improved:
http://www.worldhealth.net/news/on_artificial_skin

Visit the website of the McEwen Centre for Regenerative Medicine to learn how stem cells can repair organs:
http://www.mcewencentre.com/res_prog_rr.asp