Recombinant bacillus Calmette–Guérin (BCG) vaccines expressing theMycobacterium tuberculosis30-kDa major secretory protein induce greater protective immunity against tuberculosis than conventional BCG vaccines in a highly susceptible animal model

Abstract

Tuberculosis (TB) continues to ravage humanity, causing 2 million deaths per year. A vaccine against TB more potent than the current live vaccine, bacillus Calmette-Gué rin (BCG), is desperately needed. Using two commercially available strains of BCG as host strains, BCG Connaught and Tice, we have constructed two recombinant BCG vaccines stably expressing and secreting the 30-kDa major secretory protein of Mycobacterium tuberculosis (M. tb.), the primary causative agent of TB. We have tested the efficacy of the two strains in the highly susceptible guinea pig model of pulmonary TB, a model noteworthy for its close resemblance to human TB. Animals immunized with the recombinant BCG vaccines and challenged by aerosol with a highly virulent strain of M. tb. had 0.5 logs fewer M. tb. bacilli in their lungs and 1 log fewer bacilli in their spleens on average than animals immunized with their parental conventional BCG vaccine counterparts. Statistically, these differences were highly significant. Paralleling these results, at necropsy, animals immunized with the recombinant BCG vaccines had fewer and smaller lesions in the lung, spleen, and liver and significantly less lung pathology than animals immunized with the parental BCG vaccines. The recombinant vaccines are the first vaccines against TB more potent than the current commercially available BCG vaccines, which were developed nearly a century ago.

A novel live recombinant mycobacterial vaccine against bovine tuberculosis more potent than BCG

“…The vaccines tested were the parental Mycobacterium bovis BCG Tice (BCG), rBCG30 (pSMT3-MTB30 or pMTB30) Tice [12], and rBCG30Mb (pSMT3-MB30) Tice, a recombinant BCG Tice expressing large amounts of the homologous M. The challenge strain was the Mycobacterium bovis Type strain (ATCC 19210), prepared as described for M. tuberculosis in previous studies [12].…”

“…Specific-pathogen free 250-to 300-g outbred male Hartley strain guinea pigs from Charles Rivers Breeding Laboratories were injected intradermally with 10 3 CFU of parental BCG, rBCG30, or rBCG30Mb prepared as previously described [12,13]. The preparation of the vaccines entailed washing the bacteria by centrifugation, enumerating them in a Petroff-Hausser chamber, and resuspending them in phosphate-buffered saline (PBS); such bacteria had a very high (>90%) CFU:particle ratio.…”

“…Moreover, compared with BCG-immunized animals, who were highly protected compared with sham-immunized animals, rBCG30-immunized animals had ~10-fold fewer lung lesions, significantly less lung pathology, and significantly longer survival after M. tuberculosis aerosol challenge [12,13]. rBCG30 is currently in human clinical trials.…”

“…We have previously described a live recombinant BCG vaccine, rBCG30, that is significantly more potent than BCG in protecting against M. tuberculosis aerosol challenge in the guinea pig model of pulmonary tuberculosis [12,13].…”

“…rBCG30 expresses large amounts of the M. tuberculosis 30 kDa major secretory protein, a mycolyl transferase [12].…”