RNA interference, or RNAi, is a powerful mechanism used to regulate gene expression. It is the application of a biological process originally observed in plants and subsequently studied in C. elegans. In these organisms, naturally occurring double-stranded RNAs are able to silence or knockdown expression of specific genes. Because of the specificity of the RNAi system, an incredible level of genetic control can be achieved in model systems via introduction of double-stranded RNAs targeting desired genes. The ability to exercise precise control over a gene, not just to turn it on and off but also to control the level of expression, is an incredible tool. It provides the ability to look at effector functions as a result of expression level and is a possible window into the early stages of disease. Those who develop novel therapeutic strategies look to RNAi as a possible way to silence deleterious genes in cancer, hepatitis, and other diseases.

In 2003 Dr. Gregory Hannon of Cold Spring Harbor Laboratory reported a new technique that allowed RNAi to be used in mammalian cells as well as in a mammalian model system. By knocking down Trp53, a well characterized tumor suppressor gene, Hannon was able to cause lymphomas in mice. Not only could the expression of Trp53 be virtually eliminated, but it could be scaled to produce variable degrees of disease.