Medicine Innovates are the news series of Global Medical Discovery that highlighted the research excellence service in medical and biomedical research worldwide. The high prevalence and mortality associated with tuberculosis in different parts of the world has made this infectious disease a major public health concern. Recently, it was discovered that the BCG vaccine does not provide complete protection against tuberculosis. Thus, researchers have sought to improve the effectiveness of the BCG vaccine via overexpression of immunologically relevant genes and biotechnological manipulations. The pathogenicity and virulence of the causative organism Mycobacterium tuberculosis have been attributed to the possession of several genes, which code for intracellular and extracellular lipases. Previous studies on the role of lipases produced by pathogens have identified these enzymes as virulence factors. Therefore, there is a need to conduct an extensive investigation into the virulence of mycobacterial lipases.
Dr. Vipul K. Singh (now Postdoctoral Fellow at McGovern Medical School, UTHealth, Houston, Texas, USA) and colleagues demonstrated that the overexpression of Rv3097c in Mycobacterium bovis BCG vaccine impaired the effectiveness of the vaccine against Mycobacterium tuberculosis infection in mice. The work is published in the peer-reviewed journal: Vaccine 29 (2011) 4754-4760.
The authors observed that the expression of Rv3097c was upregulated in sense strains BCG (pMV361::rv3097c-s) and downregulated in antisense strains BCG (pMV361::rv3097c-as) compared to the vector control BCG (pMV361). Also, they observed the overexpression of Rv3097c in sense strains and downregulation in antisense strains. However, a 4-fold and 11-fold upregulation of LipY was noticed ex vivo in macrophages cell line infected with BCG (pMV361) and BCG (pMV361::rv3097c-s).
Additionally, the research team discovered that BCG (pMV361) vaccinated mice gained weight while BCG (pMV361::rv3097c-s) vaccinated mice lost weight after seven days. This weight loss was evident in BCG (pMV361::rv3097c-s) vaccinated mice compared to BCG (pMV361::rv3097c-as) and BCG (pMV361) vaccinated mice. The authors documented that a high bacillary load was observed in unimmunized and BCG (pMV361::rv3097c-s) vaccinated mice compared to BCG (pMV361) vaccinated mice. The bacillary load in BCG (pMV361::rv3097c-as) vaccinated mice was significantly lower than the bacillary load of BCG (pMV361::rv3097c-s) vaccinated mice.
Furthermore, it was also found that the lung tissues of BCG (pMV361::rv3097c-s) vaccinated mice was characterized by a high bacillary burden, areas of necrosis, peribronchial and alveolar leucocytic infiltration, disappearance of air spaces, vascular congestion and edema while the lung tissues of BCG (pMV361) vaccinated mice were characterized by a low bacillary burden, small lesions and little areas of necrosis.
Dr. Singh and colleagues also were first to discover that the overproduction of lipase by BCG (pMV361::rv3097c-s) resulted in the increased hydrolysis of apolar lipids, poor immune response, and survival of infected mice. BCG vaccinated mice exhibited the best protection from Mycobacterium tuberculosis infection, followed by LipY vaccinated mice and TG vaccinated mice. The immune response induced by LipY and TG divalent vaccine was better than TG alone but worse than LipY alone. In addition, improved IL-2, IL-6, TNF and IFN-γ responses were observed in BCG (pMV361) vaccinated mice compared to BCG (pMV361::rv3097c-s) vaccinated mice. The IL-2, TNF and IFN-γ responses of LipY and TG vaccinations were better than TG vaccinations but worse than LipY vaccinations.
The study was indeed the first to demonstrate that the immunogenicity of BCG vaccines was inhibited by LipY-induced hydrolysis of certain lipids. The novel findings documented in this study is a cornerstone for further research studies on the inhibition of therapeutic targets that reduce the protective immune response of BCG vaccines.
In real life situation if LipY lipase is a cell wall associated protein interacting with effector molecules of the immune system, then immunization of subjects with subunit antigen LipY would generate an immune response against mycobacterial lipase, causing host immune system to remain effective. We would share our experience in the quest for a booster antigen. Rv3097c of M. tuberculosis encoding a lipase (LipY) has been studied in a mice model of tuberculosis which appears to be a good candidate protective antigen to counter infection of M. tuberculosis.
Singh, V.K., Srivastava, V., Singh, V., Rastogi, N., Roy, R., Shaw, A.K., Dwivedi, A.K., Srivastava, R., and Srivastava, B.S. Overexpression of Rv3097c in Mycobacterium bovis BCG abolished the efficacy of BCG vaccine to protect against Mycobacterium tuberculosis infection in mice, Vaccine 29 (2011) 4754-4760.