Thirty years of baculovirus-insect cell protein expression: from dark horse to mainstream technology.

In December 1983, a seminal paper appeared on the overexpression of human IFN-β in insect cells with a genetically engineered baculovirus. The finding that baculoviruses produced massive amounts of two proteins (polyhedrin and p10) by means of two very strong promoters and that the corresponding genes were dispensable for virus propagation in insect cells was crucial in the development of this expression system. During the next 30 years, major improvements were achieved over the original baculovirus expression vector (BEV) system, facilitating the engineering of the baculovirus vectors, the modification of the sugar moieties of glycoproteins expressed in insect cells and the scale-up of the cell culture process. To date, thousands of recombinant proteins have been produced in this successful expression system, including several protein-based human and veterinary vaccines that are currently on the market. Viral vectors based on adeno-associated virus are being produced using recombinant baculovirus technology and the first gene therapy treatment based on this method has been registered. Specially adapted BEVs are used to deliver and express heterologous genes in mammalian cells, and they may be used for gene therapy and cancer treatment in the future. The purpose of this review is to highlight the thirtieth 'anniversary' of this expression system by summarizing the fundamental research and major technological advances that allowed its development, whilst noting challenges for further improvements.