Development of new vaccines and diagnostic reagents against tuberculosis

Tuberculosis (TB) is a major infectious disease problem with one-third of the world population infected, 8 million people developing the active disease and 2 million dying of TB each year. The attenuated Mycobacterium bovis Bacillus Calmette Guerin (BCG) is the only available vaccine against TB. However, the trials conducted in different parts of the world have shown that this vaccine doe not provide consistent protection against TB. The purified protein derivative (PPD) of Mycobacterium tuberculosis is the commonly used reagent for the diagnosis of TB. However, PPD lacks specificity because of the presence of antigens crossreactive with M. bovis BCG and other mycobacteria. The studies to identify M. tuberculosis antigens and epitopes as candidates for new protective vaccines and specific diagnostic reagents against TB have led to the identification and characterization of several major antigens of M. tuberculosis including heat shock proteins (hsp) and secreted antigens present in the culture filtrate (CF) of M. tuberculosis. Some of these antigens have shown promise as new candidate vaccines (hsp60, Ag85 and ESAT-6, etc.) and specific diagnostic reagents (ESAT-6 and CFP10, etc.) for TB. Moreover, in the mouse model of TB, vaccination with DNA-hsp60 has immunotheraputic effects and helps in eradication of persisters. In addition, identification of proper adjuvant and delivery systems has shown the promise to overcome the problem of poor immunogenicity associated with subunit and peptide based vaccines. More recently, the comparison of the genome sequence of M. tuberculosis with M. bovis BCG and other mycobacteria has led to the identification of M. tuberculosis-specific genomic regions. Evaluation of these regions for encoding proteins with immunological reactivity can lead to the identification of additional antigens of M. tuberculosis useful as new vaccines and reagents for specific diagnosis of TB.