In 1975, Caltech President David Baltimore, former Caltech faculty member and Salk Institute researcher Renato Delbucco, and Caltech alumnus Howard Temin (Ph.D. 1960) were awarded the  Nobel Prize in Physiology or Medicine “for their discoveries concerning the interaction between tumour viruses and the genetic material of the cell.”

Studies of virus-induced changes of the growth characteristics of a normal cell to that of tumour cells – a phenomenon referred to as transformation – was facilitated during this decade due to the availability of methods for cultivating cells under laboratory conditions.

This technique combined with the discovery of several viruses which could cause transformation in animals and in cell cultures provided facilities for studies of the role of the virus in this process. It was found that both viruses which contain genetic material of the same type as that present in chromosomes of cells i.e. deoxyribonucleic acid (DNA) and also viruses containing a different type of genetic material, ribonucleic acid (RNA) could cause transformation.