BCG has been integrated into the Expanded Immunization

BCG has been integrated into the Expanded Immunization Program of WHO since 1974 and neonatal vaccination with BCG is still used to prevent TB in countries with a high burden of TB (Marais et al., 2016). Correspondingly, adolescents and adults with LTBI always occur epidemiologically following inoculation with BCG after birth. To mimic the occurrence of LTBI, mice were vaccinated with BCG and then infected with M. tuberculosis to create the mouse model of LTBI (Nuermberger, 2008; Zhang et al., 2009; Ma et al., 2016), characterized by at least 1000CFU of M. tuberculosis and the pre-establishment of PND-1186 manufacturer in the lung. In this study, BCG as a booster resulted in a lower bacterial load in both lung and spleen than in the PBS-control mouse LTBI model. It is surprising that repeat BCG vaccination benefits the control of LTBI, while the regimen cannot block the reactivation of dormant M. tuberculosis in mice. Although WHO does not recommend adult vaccination with BCG, some countries in Eastern European still practice the strategy of BCG repeat vaccination in adults. Moreover, the commercial WBIA technologies, such as T-SPOT TB, may allow the screening and diagnosis of LTBI. Therefore, clinical evaluation of the preventive effect elicited by BCG repeat vaccination is needed to prevent latent infection. Importantly, mice boosted with A1D4-DMT also displayed stronger efficacy against latent infection than those with CTT3H-DMT, while the strongest protection was conferred by the CMFO-DMT subunit vaccine. More importantly, only CMFO-DMT could control the reactivation of the latent infection in mice, which was evaluated by enumeration of persisting M. tuberculosis in the lung and spleen after immunosuppressive treatment. Although vaccine-induced mechanisms to eliminate LTBI are still not fully understood, the pathogenesis of M. tuberculosis largely depends on the ability to delay the time of the antigen-specific CD4+ Th1 cells homing to the infected lung (Wolf et al., 2008; Griffiths et al., 2016), which benefits the replication of M. tuberculosis in the lung during early 3weeks after primary infection and promotes the establishment of a latent infection (Ernst, 2012). Moreover, reactivation of LTBI that progresses to active TB is more likely in persons co-infected with human immunodeficiency virus. Therefore, CD4+ Th1 type responses can be thought of as key in the control of TB (Cooper, 2009) and also play important roles in the containment of the LTBI. Rv2073c is absent from the genome of BCG (Behr et al., 1999). Rv2875 (Charlet et al., 2005) and Rv0577 (Huard et al., 2003) were presently expressed at a lower level in BCG than in M. tuberculosis. Although BCG also elicited CMFO-specific CD4+ Th1 type immune responses and induced CD8+ T cells in the spleen of vaccinated mice, more IFN-γ+ or IL-2+CD4+ T cells and IFN-γ+ CD8+ TEM cells against CMFO in the spleen were induced by CMFO-DMT compared to that induced by BCG, which were associated with the protection induced by CMFO-DMT against primary infection. The stronger protection conferred by CMFO-DMT than that conferred by A1D4-DMT and CTT3H-DMT might be the result of more comprehensive immunity elicited by each multistage antigen of CMFO-DMT against different status of M. tuberculosis in vivo. In particular, systemic antigen-specific IFN-γ + CD4+ TEM and IL-2+ TCM cells induced by CMFO-DMT could more easily home to the infected lung, which is also closely related with stronger protection against latent infection and more significant ability of CMFO-DMT as a booster to thwart the reactivation of LTBI than BCG repeat vaccination. Therefore, promoting the homing of T cells to the lung after vaccination might be an important vaccine development strategy. As previously reported in the treatment of TB with ID93 (Coler et al., 2013), infected animals that received a boost with subunit vaccine or BCG did not show any adverse effects during the entire experimental period. No Koch-like pathological changes were evident in the lungs of mice. Still, the safety of CMFO-DMT needs to be comprehensively evaluated.