Coronavirus derived expression systems

Both helper dependent expression systems, based on two components, and sing le genomes constructed by targeted recombination, or by using infectious cD NA clones, have been developed. The sequences that regulate transcription h ave been characterized mainly using helper dependent expression systems and it will now be possible to validate them using single genomes. The genome of coronaviruses has been engineered by modification of the infectious cDNA leading to an efficient (> 20 mug ml(-1)) and stable (> 20 passages) expre ssion of the foreign gene. The possibility of engineering the tissue and sp ecies tropism to target expression to different organs and animal species, including humans, increases the potential of coronaviruses as vectors. Thus , coronaviruses are promising virus vectors for vaccine development and, po ssibly, for gene therapy. (C) 2001 Elsevier Science B.V. All rights reserve d.