Characterization of Human Cellular Immune Responses to NovelMycobacterium tuberculosisAntigens Encoded by Genomic Regions Absent inMycobacterium bovisBCG

Abstract

Comparative genomics has identified several regions of differences (RDs) between the infectious Mycobacterium tuberculosis and the vaccine strains of Mycobacterium bovis BCG. We aimed to evaluate the cellular immune responses induced by antigens encoded by genes predicted in 11 RDs. Synthetic peptides covering the sequences of RD1, RD4 to RD7, RD9 to RD13, and RD15 were tested for antigen-induced proliferation and secretion of Th1 cytokine, gamma interferon (IFN-␥), by peripheral blood mononuclear cells (PBMC) obtained from culture-proven pulmonary tuberculosis (TB) patients and M. bovis BCG-vaccinated healthy subjects. Among the peptide pools, RD1 induced the best responses in both donor groups and in both assays. In addition, testing of TB patients' PBMC for secretion of proinflammatory cytokines (tumor necrosis factor alpha Mycobacterium tuberculosis is among the most successful human pathogens and is the primary cause of human tuberculosis (TB) in the world. Globally, about 2 billion people are infected with M. tuberculosis, 8 to 10 million develop active disease, and 2 million die from TB every year (53). An overwhelming majority of TB patients reside in the developing countries, which suffer from marked poverty, lack of healthy living conditions, and inadequate medical facilities (53).The global control of TB requires effective vaccines and reagents for specific diagnosis. The only vaccine currently available for humans is Mycobacterium bovis bacillus CalmetteGuérin (BCG), a live attenuated strain of M. bovis. In spite of being the most used vaccine in the world, with proven efficacy against childhood TB meningitis and miliary TB (41, 49), BCG has failed to reduce the global burden of TB (43). The efficacy of BCG against pulmonary TB in adults has varied between 0 and 80% (16). Furthermore, vaccination with M. bovis BCG faces two additional problems. First, it induces a delayed-type hypersensitivity response that cannot be distinguished from infection with M. tuberculosis, and therefore, it compromises the use of purified protein derivative (PPD) of M. tuberculosis in skin tests for diagnostic or epidemiological purposes (25,26). Second, M. bovis BCG, as a live vaccine, is contraindicated in human immunodeficiency virus-infected patients for fear of causing disease (11). PPD, the commonly used diagnostic reagent, is nonspecific because of the presence of antigens crossreactive with M. bovis BCG and environmental mycobacteria (14, 25). Thus, there is a need to identify M. tuberculosisspecific antigens to develop new protective vaccines and specific diagnostic reagents against TB.Comparative genome analyses of the M. tuberculosis genome and M. bovis BCG have shown that 16 genomic regions of M. tuberculosis are deleted or lacking in some or all strains of M. bovis and/or M. bovis BCG (9). Among these regions of differences (RDs), 11 regions (RD1, RD4 to RD7, RD9 to RD13, and RD15) covering 89 open reading frames (ORFs) of M. tuberculosis H37Rv are absent in all M. bovis BCG substrains currently used as vaccin...

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Diagnostic and Vaccine Potentials of ESAT-6 Family Proteins encoded by M. tuberculosis genomic regions absent in M. bovis BCG

“…The results have suggested the presence of immunodominant antigens in RD7 and RD9 [49][50][51][52][53]. However, peptide pools of these RDs were also recognized in the same assays by cells from M. bovis BCG-vaccinated healthy subjects [49,53]. Further testing of the individual proteins present in RD7 and RD9, identified two immune dominant proteins from both regions, i.e.…”

Immune Responses to Candidate Vaccine Antigens Delivered Through Naked Plasmid and Mycobacterial Vectors

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