Humanized NOG mice as a model for tuberculosis vaccine-induced immunity: a comparative analysis with the mouse and guinea pig models of tuberculosis.

The humanized mouse model has been developed as a model to identify and characterize human immune responses to human pathogens and has been used to better identify vaccine candidates. In the current studies, the humanized mouse was used to determine the ability of a vaccine to affect the immune response to infection with Mycobacterium tuberculosis. Both human CD4+ and CD8+ T cells responded to infection in humanized mice as a result of infection. In humanized mice vaccinated with either BCG or with CpG-C, a liposome-based formulation containing the M. tuberculosis antigen ESAT-6, both CD4 and CD8 T cells secreted cytokines that are known to be required for induction of protective immunity. In comparison to the C57BL/6 mouse model and Hartley guinea pig model of tuberculosis, data obtained from humanized mice complemented the data observed in the former models and provided further evidence that a vaccine can induce a human T-cell response. Humanized mice provide a crucial pre-clinical platform for evaluating human T-cell immune responses in vaccine development against M. tuberculosis.

Heat killed Saccharomyces cerevisiae as an adjuvant for the induction of vaccine-mediated immunity against infection with Mycobacterium tuberculosis.

The use of novel vaccine delivery systems allows for the manipulation of the adaptive immune systems through the use of molecular adjuvants that target specific innate pathways. Such strategies have been used extensively for vaccines against cancer and multiple pathogens such as Mycobacterium tuberculosis. In the current study we used heat killed non-pathogenic recombinant Saccharomyces cerevisiae expressing M. tuberculosis antigen Rv1886c (fbpB, mpt59, Ag85B) as a delivery system in conjunction with its ability to stimulate innate immunity to determine its ability to induce immunity. We established that the recombinant yeast induced activated antigen specific T cells are capable of reducing the mycobacterial burden. Inoculation of the recombinant yeast after vaccination with BCG resulted in a systemic alteration of the phenotype of the immune response although this was not reflected in an increase in the reduction of the mycobacterial burden. Taken together the data suggest that heat killed yeast can induce multiple cytokines required for induction of protective immunity and can function as a vehicle for delivery of M. tuberculosis antigens in a vaccine formulation. In addition, while it can enhance the effector memory response induced by BCG, it had little effect on central memory responses.

BCG sub-strains induce variable protection against virulent pulmonary Mycobacterium tuberculosis infection, with the capacity to drive Th2 immunity.

The hallmark of a vaccine is to induce long-term protective immunity against the pathogen. The use of Mycobacterium bovis BCG as a vaccine against tuberculosis has been problematic in that immunity induced by BCG wanes over time and it may be less effective against more virulent strains of Mycobacterium tuberculosis. Thus it is important to determine what factors might be associated with waning or inefficient immunity. One such factor has been associated with the difference in many types of BCG that are used around the world, or more specifically due to the loss of genomic material in the various sub-strains used in vaccination programs. To address this issue we investigated the long-term immune response generated by 3 sub-strains BCG in the C57BL/6 mouse model of experimental tuberculosis. Mice vaccinated with these diverse strains of BCG were assessed at 6 and 12 months post-vaccination. All BCG sub-strain induced elevated levels of IFN-γ-producing cells at each time point as determined by ELISpot assay. However, when mice were challenged at 6 and 12 months with either M. tuberculosis H37Rv or HN878 the ability of the BCG sub-strains to protect vaccinated mice varied, depending on the time of challenge and on the strain used to infect mice. BCG Pasteur was then used to vaccinate guinea pigs, which were subsequently infected with either H37Rv or HN878. Data showed that BCG Pasteur prolonged the survival of guinea pigs against infection with both strains. Taken together these data suggest that longevity of the immune response generated by BCG is not related to the loss of genetic material and that BCG can induce a protective immune response to infection with a clinical strain of M. tuberculosis.

Role for matrix metalloproteinase 9 in granuloma formation during pulmonary Mycobacterium tuberculosis infection.

Recent studies have shown that matrix metalloproteinases (MMPs) are induced by Mycobacterium tuberculosis during pulmonary infection. Here, expression of MMP-9 during pulmonary M. tuberculosis infection was characterized to determine whether its production correlated with disease resistance in vivo and to determine what role, if any, MMP-9 might have in granuloma formation. Following aerosol infection with M. tuberculosis, dissemination of bacilli occurred earlier in the C57BL/6 resistant mouse strain than in the susceptible CBA/J strain, as was evident from an increased number of bacteria in the blood, spleen, and liver at day 14 after infection. In addition, early dissemination of the bacilli was associated with early induction of protective immunity as assessed from gamma interferon levels. Nonspecific blocking of MMPs in C57BL/6 mice early during infection reduced hematogenous spread of the bacilli, suggesting that MMPs indeed play a role in facilitating dissemination, likely via extracellular matrix degradation. The concentration of active MMP-9, specifically, was greater in the lungs of C57BL/6 mice than in those of the CBA/J mice at day 28, thereby suggesting that MMP-9 is not one of the MMPs directly involved in promoting early dissemination of M. tuberculosis. Instead, however, histological lung sections and flow cytometric analysis of lung cells from MMP-9-knockout mice showed that MMP-9 is involved in macrophage recruitment and granuloma development. These combined data support the idea that early MMP activity is an essential component of resistance to pulmonary mycobacterial infection and that MMP-9, specifically, is required for recruitment of macrophages and tissue remodeling to allow for the formation of tight, well-organized granulomas.