Mycobacterium tuberculosis multistage antigens confer comprehensive protection against pre- and post-exposure infections by driving Th1-type T cell immunity

Abstract

There is an urgent need for a vaccine against tuberculosis (TB) that is more effective than the current sole licensed option. However, target antigens of Mycobacterium tuberculosis with the vaccine potential remain elusive. Five immunodominant antigens with characteristic expressions at the stages of primary infection (Ag85A), the regulation of nutrition and metabolism when transferring from rapid growth to latency (PhoY2 and Rv3407), latency (Rv2626c), and reactivation (RpfB) were selected to construct the fusion polyprotein WH121, which has better immunogenicity and protection than each multistage antigen. DMT adjuvanted WH121 vaccinated C57BL/6 mice could confer persistent and significant protection against the respiratory challenge with 80 CFU of virulent M. tuberculosis H37Rv at 9 and 18 weeks after immunization, as the BCG vaccine did. Moreover, WH121/DMT could boost the BCG primed mice against post-exposure infection, and more significantly inhibit the growth of M. tuberculosis in the spleen than BCG repeat vaccination. The protection elicited by WH121/DMT is attributed to the WH121-specific Th1-type biased immune responses, characterized by increased antigen-specific IgG2a/IgG1 ratio and high levels of IFN-γ secreted by the splenocytes of vaccinated mice. In particular, high levels of IFN-γ+ TEM cells in the spleen are an effective biomarker for the vaccine-induced early protection, and the persistent protection mainly depends on the increasing IL-2+IFN-γ+CD4+ and CD8+ T cells, especially IL-2+ TCM cells. These findings demonstrate that multistage-specific antigens might be promising targets for the next generation TB vaccine, and a combination of these antigens such as WH121/DMT is required for further preclinical evaluation.

A Multistage Subunit Vaccine Effectively Protects Mice Against Primary Progressive Tuberculosis, Latency and Reactivation

“…The vaccine-induced early and persistent protection against primary infection is respectively associated with the number of IFN-γ + T EM cells and IL-2 + T CM cells in the spleen ( Ma et al, 2016 ). At week 10 after immunization, CMFO-specific IFN-γ- or IL-2 secreting T cells ( Fig.…”

“…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 1000 CFU of M. tuberculosis and the pre-establishment of cell-mediated immunity 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.…”

“…Subsequently, the construction of two-stage subunits ID93 (Rv3619-Rv1813-Rv3620-Rv2608; Bertholet et al, 2010 ) or H56 (Ag85B-ESAT-6-Rv2660c; Aagaard et al, 2011 ) was accomplished by fusing secreted and latent antigens of M. tuberculosis . Recently, the co-existence of both actively growing and latent M. tuberculosis strains in LTBIs and patients with active TB (ATB) infections were reported ( Wang et al, 2015 , Ma et al, 2016 ). A multistage subunit designated WH121 contains fusion polypeptide comprised of antigens Rv3407, PhoY2, Ag85A, Rv2626c, and RpfB.…”

“…These antigens are expressed in different stages of TB infection. The use of WH121 in an adjuvant preparation of DMT (DDA-MPLA-TDB) reportedly provides protection against primary TB infection that is comparable to that provided by the BCG vaccine, and also enhances the protection of BCG-primed mice against the post-exposure infection ( Ma et al, 2016 ). However, adult TB is mainly caused by endogenous reactivation of LTBI ( WHO, 2015 ) and the secondary transmission route is exogenous infection ( Verver et al, 2005 ).…”

“…However, adult TB is mainly caused by endogenous reactivation of LTBI ( WHO, 2015 ) and the secondary transmission route is exogenous infection ( Verver et al, 2005 ). All the TB candidate vaccines could elicit antigen-specific Th1-type immune responses and confer significant protection against primary infection in different animal models, including mice ( Ma et al, 2016 ), monkeys ( Reed et al, 2009 , Lin et al, 2012 , Coler et al, 2013 ) and humans ( Luabeya et al, 2015 ). However, no TB vaccine devised so far can achieve sterile immunity and thus thwart the reactivation of LTBI.…”