SV40

SV40 is an abbreviation for simian vacuolating virus 40 or simian virus 40, a polyomavirus that is found in both monkeys and humans. Like other polyomaviruses, SV40 is a DNA virus that sometimes causes tumors in animals, but most often persists as a latent infection. SV40 has been widely studied as a model eukaryotic virus, leading to many early discoveries in eukaryotic DNA replication and transcription. The hypothesis that SV40 might cause cancer in humans has been a particularly controversial area of research. It is currently unclear whether SV40 has any role in causing tumors. As a result of these uncertainties, academic opinion remains divided, with some arguing that this hypothesis is not supported by the data and others arguing that some cancers may involve SV40. The US National Cancer Institute announced in 2004 that although SV40 does cause cancer in some animal models, "substantial epidemiological evidence has accumulated to indicate that SV40 likely does not cause cancer in humans". This announcement was based on two studies. This 2004 announcement is in contrast to a 2002 study performed by The National Academy of Sciences Immunization Safety Review committee that stated, "The committee concludes that the biological evidence is moderate that SV40 exposure could lead to cancer in humans under natural conditions". SV40 may act as a co-carcinogen with crocidolite asbestos to cause mesothelioma. The mechanism may involve suppression of the transcriptional properties of tumor suppressor p53 in humans by the SV40 large T antigen and SV40 small T-antigen. Tumor suppressor p53 is responsible for initiating regulated cell death ("apoptosis"), or cell cycle arrest when a cell is damaged. A mutated p53 gene may contribute to uncontrolled cellular proliferation, leading to a tumor. Vaccine contamination with SV40 Some vaccines made in the US between 1955 and 1961 were found to be contaminated with SV40, from the growth medium and from the original seed strain.