Simian Virus 40 (SV40) is a polyomavirus that was first discovered in the 1960s in rhesus monkey kidney cells. It is a small, double-stranded DNA virus with a circular genome of approximately 5,200 base pairs. Although SV40 naturally infects monkeys and can cause tumors in them, it does not typically cause disease in humans. However, the virus has been extensively studied due to its ability to transform cells in culture and induce tumors in rodents, making it a valuable model for understanding the molecular mechanisms of cellular transformation and tumorigenesis.

SV40 infection can lead to the expression of two main viral proteins: the large T-antigen (LT) and the small t-antigen (st). The large T-antigen plays a crucial role in viral replication, as it interacts with cellular proteins, such as the tumor suppressors p53 and retinoblastoma protein (pRb), resulting in the deregulation of the cell cycle and promoting cellular transformation.

The discovery of SV40 has led to significant advancements in molecular biology and virology. For example, the SV40 promoter and enhancer elements have been widely used as tools for driving gene expression in eukaryotic cells, and the study of SV40’s ability to transform cells has provided insights into the molecular basis of cancer.

It is worth noting that during the 1950s and 1960s, some polio vaccines were inadvertently contaminated with SV40 due to the use of monkey kidney cells in vaccine production. Later investigations have shown that SV40 exposure from these contaminated vaccines likely did not significantly increase the risk of cancer in humans, and modern polio vaccines are now produced using cell lines free of SV40.