Retroviruses are not only important in immunity of an organism but also with thier evolution. Some retroviruses, known as endogenous retroviruses, have even been successful to get incorporated into our genome and represent roughly 8% of human genome. Last month, a colleague of mine at UCSF in collaboration with University of Toronto published a paper in Plos Pathogens regarding the role of Human Endogenous Retroviruses on HIV infection.
The collaborating team found increased levels of HERV production in HIV-1 infected patients and showed that HIV-1 virus causes expression of HERV particles on cells which are recognized by cytotoxic immune cells. These HERV specific cytotoxic (CD8 T cells) that recognize HERV may end up increasing immune response against HIV-1 virus. The increased immunity by HERV can be indirect or direct. The cells that are expressing HERV are killed by immune cells and thus the HIV replicating inside these cells are also killed. This is the indirect effect of HERV on HIV. Also, some of the HERV proteins, very similar to HIV-1 proteins causes some cytotoxic immune cells to recognize cells expressing HIV-1 proteins and kill them directly. Thus, there is a serious potential of using HERV for vaccines.
This news must have been very big because the article was featured by The San Francisco Chronicle and CBC news of Canada. I even found the same work quoted by Michael Specter in a recent issue of The New Yorker. Interestingly Michael’s article, although in a non scientific journal is one of the best reviews on HERV that I have ever read. However, the article does not discuss the impact of HERV in the area of evolution.
Recently some scientists have started using HERV to track human ancestry as well. HERVs once used to be exogenous but somehow got incorporated into the human DNA of germline cells (ova or sperm) and thus became endogenous. However, most HERV are truncated such that they are not able to replicate once they become endogenous. Therefore, they are passed on from parents to offsprings from one generation to another. If two people have the same HERV, we know they are related because it is rare that the same virus incorporated itself at the same locus in the DNA of two different people at two different locations. Also, since the original sequence of the HERV can be known, the age of any mutations accumulated in a HERV sequence can be calculated.
Screening for HERV, a process known as Hervotyping, can be beneficial for vaccine development as well because different more effective vaccines can be designed for various populations based on presence or absence of a particular HERV.
In conclusion, HERV can be a very effective tool for vaccine development and it can also be a novel means to track human ancestry.
