In 2003, a research team inserted genes into the brain for the first time. They used liposomes coated in a polymer called polyethylene glycol, which unlike viral vectors, are small enough to cross the blood–brain barrier.
Short pieces of double-stranded RNA (short, interfering RNAs or siRNAs) are used by cells to degrade RNA of a particular sequence. If a siRNA is designed to match the RNA copied from a faulty gene, then the abnormal protein product of that gene will not be produced.
Gendicine is a cancer gene therapy that delivers the tumor suppressor gene p53 using an engineered adenovirus. In 2003, it was approved in China for the treatment of head and neck squamous cell carcinoma.