A NEW SERIES OF MYCOBACTERIAL EXPRESSION VECTORS FOR THE DEVELOPMENT OF LIVE RECOMBINANT VACCINES

Recombinant BCG (bacillus Calmette-Guerin) is a promising candidate as a live vaccine delivery system. Thus far, however, only autoreplicati ve plasmids carrying the heterologous genes to be expressed in BCG, to gether with antibiotic-resistance genes, have been successfully used. This could potentially lead to the spreading of antibiotic resistance among other bacteria, and might therefore be unsafe for the environmen t. In this study, we present a series of three Escherichia coli-Mycoba cteria shuttle vectors which enable expression and secretion of antige ns without the use of antibiotic-resistance markers. All these plasmid s confer mercury resistance to the host bacteria as the only selectabl e marker and contain a unique restriction site to allow for single-ste p in-frame cloning of open reading frames downstream from the Mycobact erium tuberculosis 85A antigen promoter and export signal. The system was used to express the free beta-subunit of human chorionic gonadotro pin (hCG beta), a potential target of an immunotherapeutic vaccine.