Current status of tuberculosis and recombinant bacillus Calmette-Guérin vaccines

Tuberculosis (TB) is an infectious disease and a global concern of enormous proportions. One-third of the world's population is latently infected with Mycobacterium tuberculosis, and 2 million people die from TB annually. The only currently available vaccine-bacillus Calmette-Guerin (BCG)-is the most extensively used vaccine ever, with a record 3 billion doses administered during the last 4 decades. Because BCG is a live attenuated vaccine, it can be developed by genetic engineering to serve as a foreign antigen-producing multivalent vaccine. A new antibiotic-free host-vector system has been developed that expresses the foreign antigen from BCG by using a thymidylate synthase ThyX-deletion mutant of BCG and a plasmid harboring the thyX gene. This host-vector system is stable and can be useful for clinical purposes.