That recent ideas about immunosuppressive drugs, auto-immune syndromes and tumour viruses should join together to express themselves as a disease seems only to be expected.

An interesting consequence of this process is that the mice are then resistant to infection with exogenous mammary tumour viruses.

It was independently isolated by David Baltimore in 1970 at MIT from two RNA tumour viruses.

Leder and his colleagues were working on tumour viruses that cause cancer, when they noticed that one of the mice infected with the virus had a limb deformity.

Vidarabine is an antiviral, active against herpes viruses, poxviruses, rhabdoviruses, hepadnaviruses and some RNA tumour viruses.

The RNA tumour viruses have been studied extensively, and have been used to carry the human adenosine deaminase gene successfully into children with severe combined immunodeficiency.

He was particularly interested in the genetic and cellular-biological building blocks that switch genetic programmes on and off in tumour viruses and in the course of embryonic development.

It seems likely that the tumour viruses originally 'stole' their cancer genes from cellular DNA, and it may be that the transfer of genes between viruses and cells is a very common event.

He was awarded the Gabor Medal of the Royal Society in 2005 "in recognition for his work on the small DNA tumour viruses, specifically the papova virus group, papilloma, polyoma and SV40".

In 1975 Dr Renato Dulbecco, then Deputy Research Director of the Laboratories shared the Nobel Prize for Physiology or Medicine for his work on the interactions between DNA tumour viruses and cells.

In the late 1950s, he took Howard Temin as a student, with whom, and together with David Baltimore, he would later share the 1975 Nobel Prize in Physiology or Medicine for "their discoveries concerning the interaction between tumour viruses and the genetic material of the cell."