Development of new vaccines and drugs for TB: Limitations and potential strategic errors

Department of Microbiology, Immunology & Pathology, Colorado State University, Colorado, CO 80523, USA.
Future Microbiology (Impact Factor: 4.28). 02/2011; 6(2):161-77. DOI: 10.2217/fmb.10.168
Source: PubMed


The concomitant HIV and TB epidemics pose an enormous threat to humanity. After invading the host Mycobacterium tuberculosis initially behaves as an intracellular pathogen, which elicits the emergence of acquired specific resistance in the form of a T-helper-1 T-cell response, and involves the secretion of a myriad of cytokines and chemokines to drive protective immunity and granuloma formation. However, after that, a second phase of the disease process involves survival of bacilli in an extracellular state that is still poorly understood. This article briefly reviews the various strategies currently being used to improve both vaccination and drug therapy of TB, and attempts to make the argument that current viewpoints that dominate [both the field and the current literature] may be seriously flawed. This includes both the choice of new vaccine and drug candidates, and also the ways these are being tested in animal models, which in the opinion of the author run the risk of driving the field backwards rather than forward.

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    • "We strongly suspect that neutrophils are the main cause of necrosis in both the mouse and guinea pig models of tuberculosis [3,5,34], and this is further emphasized by studies in humans [21,22]. To date we were assuming that our observations in NOS2 -/- and other murine models were due to the influx of neutrophils, based on simply measuring “Gr1-positive” cells, but clearly our current concept needs to be significantly modified based on the observations here that Gr1hi and Gr1int cells represent two distinct granulocyte subsets. "
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    ABSTRACT: Tuberculosis is one of the world's leading killers, stealing 1.4 million lives and causing 8.7 million new and relapsed infections in 2011. The only vaccine against tuberculosis is BCG which demonstrates variable efficacy in adults worldwide. Human infection with Mycobacterium tuberculosis results in the influx of inflammatory cells to the lung in an attempt to wall off bacilli by forming a granuloma. Gr1(int)CD11b(+) cells are called myeloid-derived suppressor cells (MDSC) and play a major role in regulation of inflammation in many pathological conditions. Although MDSC have been described primarily in cancer their function in tuberculosis remains unknown. During M. tuberculosis infection it is crucial to understand the function of cells involved in the regulation of inflammation during granuloma formation. Understanding their relative impact on the bacilli and other cellular phenotypes is necessary for future vaccine and drug design. We compared the bacterial burden, lung pathology and Gr1(int)CD11b(+) myeloid-derived suppressor cell immune responses in M. tuberculosis infected NOS2-/-, RAG-/-, C3HeB/FeJ and C57/BL6 mice. Gr-1(+) cells could be found on the edges of necrotic lung lesions in NOS2-/-, RAG-/-, and C3HeB/FeJ, but were absent in wild-type mice. Both populations of Gr1(+)CD11b(+) cells expressed high levels of arginase-1, and IL-17, additional markers of myeloid derived suppressor cells. We then sorted the Gr1(hi) and Gr1(int) populations from M. tuberculosis infected NOS-/- mice and placed the sorted both Gr1(int) populations at different ratios with naïve or M. tuberculosis infected splenocytes and evaluated their ability to induce activation and proliferation of CD4+T cells. Our results showed that both Gr1(hi) and Gr1(int) cells were able to induce activation and proliferation of CD4+ T cells. However this response was reduced as the ratio of CD4(+) T to Gr1(+) cells increased. Our results illustrate a yet unrecognized interplay between Gr1(+) cells and CD4(+) T cells in tuberculosis.
    PLoS ONE 11/2013; 8(11):e80669. DOI:10.1371/journal.pone.0080669 · 3.23 Impact Factor
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    • "Thus, the development of a more effective TB vaccine is required to combat the global threat of TB (Hawkridge and Mahomed, 2011). Several alternative TB vaccine candidates are currently being tested experimentally as pre-exposure or post-exposure or booster preparations, including subunit, live attenuated, recombinant BCG, and DNA vaccines (Hawkridge and Mahomed, 2011; Orme, 2011; Walzl et al., 2011; Yuan et al., 2011). DNA vaccines represent novel vaccine approach for TB, and are currently under rigorous investigation (Liu et al., 2008; Ly and McMurray, 2008; Lowrie, 2006; Saha et al., 2011; Yuan et al., 2011). "
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    ABSTRACT: Tuberculosis remains one of the major causes of global public health problems. There is no effective vaccine for the disease until now. Many reports show that DNA vaccines are promising to induce protection against Mycobacterium tuberculosis (M. tb); however, the efficiency of DNA vaccine is limited due to inadequate delivery systems. Among others, live attenuated bacterial vectors such as Salmonella enterica typhimurium (S. typhimurium) have significant promise as efficient mucosal delivery vehicles for DNA vaccines. In this study, we constructed recombinant attenuated S. typhimurium DNA vaccines carrying genes encoding resuscitation promoting factor (Rpf)-like proteins of M. tb on eukaryotic expression plasmid agianst latent tuberculosis and evaluated the plasmid stability and growth curve assays of the recombinant Salmonella vaccine constructs in vitro. Four Rpf gene fragments (RpfB, RpfC, RpfD, RpfE) associated with latency were amplified from genomic DNA of the H37Rv strain of M. tb, cloned into eukaryotic expression plasmid (pVR1020) and verified by sequencing. In later studies, we will demonstrate the potential use of the Salmonella-mediated DNA constructs as candidate post-exposure vaccines against tuberculosis through testing their immunogenicity and effectiveness for oral delivery in eukaryotic systems.
    AFRICAN JOURNAL OF BIOTECHNOLOGY 07/2012; 11(50):11150-11159. · 0.57 Impact Factor
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    • "For this reason, there is great interest in developing new vaccines to prevent TB infection. A number of alternative living and nonliving TB vaccines, including genetic vaccines, are currently being investigated [11] [12] [13]. For example, DNAhsp65 is a genetic vaccine containing the gene of mycobacterial 65 kDa heat shock protein that has also been used in prime-boost protocols as an attempt to improve BCG efficacy. "
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    ABSTRACT: Cellular immunity is critical for protection against tuberculosis, but its integrity is compromised during undernutrition. The present study was designed to evaluate if the attenuated mycobacterium BCG is a safe vaccine for undernourished individuals. An experimental model of undernutrition was established by subjecting BALB/c mice to dietary restriction. These animals received 70% of the amount of food consumed by the healthy control group and exhibited physiological alterations compatible with malnutrition, including body weight loss, reduced levels of triglycerides and glucose, and reduced lymphocyte numbers. Undernourished mice were immunized with BCG, and the mycobacterial loads in lymph nodes, spleen, liver, lungs, and thymus were determined. A much higher proportion of undernourished mice exhibited bacterial dissemination to the lymph nodes, spleen and liver. In addition, only undernourished animals had bacteria in the lungs and thymus. Concomitant with higher mycobacterial loads and more widespread BCG dissemination in undernourished mice, production of TNF-α, IFN-γ, and IL-10 was also diminished in these mice. Taken together, these results indicate that BCG infection is more severe in undernourished mice. Whether a similar phenomenon exists in undernourished children or not remains to be thoroughly investigated.
    Clinical and Developmental Immunology 04/2012; 2012(3):673186. DOI:10.1155/2012/673186 · 2.93 Impact Factor
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