New viruses have been popping up in industrial water-cooling towers, in Antarctica and salty deserts. Erwin van Meir, from Winship Cancer Institute of Emory University, and his collaborators managed to find two inside someone’s metastatic tumor.
Working with Terry Fei Fan Ng and Eric Delwart from UCSF, Van Meir identified two new species of anellovirus, a family of viruses first discovered in the 1990s. The new viruses come from a patient with a melanoma that had metastasized to the brain and was operated on at Emory University Hospital.
The results were recently published in Oncotarget.
“We have no evidence that these two viruses were involved in the tumor’s formation, but the data are proof of principle that the metagenomics method used can discover more unknown viruses in human brain tumors,” Van Meir says.
Metagenomics is the study of genetic material obtained directly from the environment. The approach is often used to study bacteria, but it is equally valid for viruses. In this paper, investigators used enzymes to chew up human and bacterial DNA, enriching for viral DNA protected by the viral capsid.
Estimates from the USAID’s PREDICT program point to thousands or even millions of viruses, present in mammals and birds, which remain unknown to humans. According to Annual Review of Virology from this summer, Viruses with Circular Single-Stranded DNA Genomes are Everywhere! – and that includes Anelloviridae, for which there is “still no convincing direct causal relation to any specific disease.”
Anelloviruses are relatively primitive in that they do not encode a viral polymerase (the enzyme that copies DNA) and thus need to rely upon the host cell and replicate inside the nucleus. The new ones were named Torque teno mini virus Emory1 (TTMV Emory1) and Torque teno mini virus Emory2 (TTMV Emory2). The research team gave a nod to Emory by using its colors in the virus genome cartoons accompanying the publication.
The project came from a casual visit in the summer of 2013. I was a postdoc in Eric Delwart’s lab and was visiting the CDC to give a talk and stop by Emory. During my visit with Erwin, we talked about “A road map to the human virome” and came to a realization that brain tumors are the most under-characterized tissue, in terms of viruses. Potential virus identification in these samples could significantly increase our understanding, and with the state-of-the-art next generation sequencing techniques, these questions can now be answered.
Viruses aren’t major drivers for most cancers, but they are responsible for a subset. Human papilloma viruses, which cause cervical and head and neck cancers, and hepatitis B virus, which increases the likelihood of liver cancer, are good examples. Identification of viruses as causes for human cancer could be important because it opens up the possibility of vaccination, as has been successfully applied to HPVs.
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