Tumor or rumor viruses? Newly emerging retrovirus infections in human

The current pandemic of acquired immunodeficiency syndrome is, in fact, a zoonosis: simian immunodeficiency viruses (SIV) crossed the interspecific barriers between chimps and humans and developed into what we call now human immunodeficiency viruses type 1 and 2 (HIV-1 and -2). The enormous variability of HIVs is caused, in part, by multiple and repeated infections with different SIV types. Far from being a historical oddity, the transmission of retroviruses from non-human primates to humans is a regular and ongoing process. For example, SIVs, SIV-related viruses, simian T-lymphotropic viruses, and simian foamy viruses were detected in bush-meat hunters from Cameroon and primate keepers in zoos and primate centers worldwide.

Another example of newly emerging retroviral infections to be discussed is the XMRV, a human retrovirus related to the xenotropic murine leukemia virus. In several but not all recent studies, XMRV was documented to be present in patients with certain type of prostatic carcinoma and even in cohorts of patients with chronic fatigue syndrome (CFS). It remains to be understood whether XMRV plays a role in the patogenesis of prostatic carcinoma and CFS. Similarly, HMTV, retrovirus related to the mouse mammary tumor virus is associated with autoimmune primary biliary cirrhosis and certain types of mammary carcinoma.

A possible source of a new zoonosis might be the xenotransplantation of porcine organs or tissues. Porcine endogenous retroviruses (PERV), particularly recombinant PERV-A-C, infect human cells in vitro and impose a potential rise on therapeutic xenotransplantation. Although PERV transmission to the grafted humans or experimental baboons was not detected so far in vivo, the use of genetically modified GALKO pigs will require new prospective studies. Thanks to the integration polymorphism, some PERV copies can be eliminated during the breeding of donor pigs and, therefore, the identification of highly expressed and recombinogenic PERV-A and PERV-C copies is urgently needed.

Last but not least, infectious retroviruses might emanate even from human endogenous retroviruses (HERV) integrated in the human genome, which form 8% of our DNA. This is the case of multiple sclerosis-related virus (MSRV) similar to HERV type W. MSRV is considered as a proinflammatory agent in several human neurological disorders like optic neuritis, multiple sclerosis, and CFS. The diagnostic and prognostic value of XMRV, HMTV, and MSRV detection in blood and cerebrospinal fluid will be discussed.

This abstract refers to the research supported by the grant No. 301/09/2031 awarded by the Czech Science Foundation and Framework Program 6 project XENOME by the European Committee.