RNA interference (RNAi) is a naturally occurring phenomenon by which cells guard themselves against viruses. The process involves post-transcriptional gene silencing in which specific RNA sequences get chopped into small pieces after binding to complementary short interfering RNAs (siRNA). These siRNAs can target either host mRNAs or viral genomic or messenger RNAs. As a consequence, gene expression and protein synthesis are blocked, inhibiting viral infection. Researchers at Harvard Medical School and the Massachusetts Institute of Technology have used RNA interference to inhibit HIV infection in host cells, raising hopes that the technology can be developed to complement available antiretroviral therapies. “It is interesting that this ancient, natural defense mechanism against viruses can be harnessed against HIV,” said Premlata Shankar, an HMS assistant professor of pediatrics at the Center for Blood Research and a lead author on the study, which appeared in print in the July 2002 issue of the journal Nature Medicine.