Zombies in our genes helped us evolve, and could help battle cancers Premium

Retroviruses can reshape human genomes, influencing evolution, placental development, cancer, and more.

Viruses are ubiquitous entities that have long plagued humans, often presenting in pesky, self-limiting infections, like a bout of the common cold. While most viral encounters are transient and merely inconvenient, some can have devastating or chronic consequences, leading to severe disease or even death. The recent COVID-19 pandemic and other emerging infectious diseases around us are good examples.

However, this battle between host and pathogen churns up a fascinating question: could viral infections have reshaped the human genome in the process?

Most viruses can’t really affect the genome. However, retroviruses buck this trend: they are a group of viruses that can integrate and reshape the genomes of the hosts they infect. Retroviruses have an RNA genome; can reverse-transcribe it to DNA and thus insert it into the host’s genome.

Their name comes from a unique enzyme they possess, called reverse transcriptase. It’s the one with the ability to convert the virus’s RNA into a corresponding DNA sequence. Teams led by Howard Temin at the University of Wisconsin–Madison and David Baltimore at the Massachusetts Institute of Technology reported its discovery in 1971. It spawned a widespread search for viruses that have this enzyme.

The knowledge that these viruses could cause cancer was even then well-known, even if the mechanism wasn’t clear until the 1971 teams’ reports. Oluf Bang and Vilhelm Ellermann had discovered the viral cause of chicken leukosis back in 1908 while Ludwik Gross isolated a leukaemia-causing virus in mice in 1957.

But it wasn’t until 1980 that researchers — Robert C. Gallo & co. — found the first human retrovirus. Dr. Gallo had extensively worked on the human T lymphotropic virus (HTLV) and his group isolated it from a patient with cutaneous T-cell lymphoma. This work was later published in the Proceedings of The National Academy of Sciences.

As if in quick succession, in 1983, Françoise Barré-Sinoussi, working closely with Luc Montagnier at the Institut Pasteur in Paris, reported the discovery of a retrovirus from the lymph node of a patient suffering from acquired immune deficiency syndrome (AIDS).