HspX‐mediated protection against tuberculosis depends on its chaperoning of a mycobacterial molecule

Abstract

New approaches consisting of ‘multistage' vaccines against (TB) are emerging that combine early antigenic proteins with latency-associated antigens. In this study, HspX was tested for its potential to elicit both short- and long-term protective immune responses. HspX is a logical component in vaccine strategies targeting protective immune responses against primary infection, as well as against reactivation of latent infection, because as previously shown, it is produced during latency, and as our studies show, it elicits protection within 30 days of infection. Recent studies have shown that the current TB vaccine, bacilli Calmette-Guerin (BCG), does not induce strong interferon-γ T-cell responses to latency-associated antigens like HspX, which may be in part why BCG fails to protect against reactivation disease. We therefore tested HspX protein alone as a prophylactic vaccine and as a boost to BCG vaccination, and found that HspX purified from M. tuberculosis cell lysates protected mice against aerosol challenge and improved the protective efficacy of BCG when used as a booster vaccine. Native HspX was highly immunogenic and protective, in a dose-dependent manner, in both short- and long-term infection models. Based on these promising findings, HspX was produced as a recombinant protein in E. coli, as this would enable facile purification; however, recombinant HspX (rHspX) alone consistently failed to protect against aerosol challenge. Incubation of rHspX with mycobacterial cell lysate and re-purification following incubation restored the capacity of the protein to confer protection. These data suggest the possibility that the native form may chaperone an immunogenic and protective antigen that is mycobacteria-specific.

Virulence of Mycobacterium tuberculosis after Acquisition of Isoniazid Resistance: Individual Nature of katG Mutants and the Possible Role of AhpC

“…Clinical and laboratory strains of Mtb were cultured in Proskauer-Beck (PB) media to prepare the infectivity stocks as previously described [27]. Bacterial stocks were stored in PB media with 20% glycerol at -80°C until used for the mouse infection study.…”

IgA Response to ESAT‐6/CFP‐10 and Rv2031 Antigens Varies in Patients With Culture‐Confirmed Pulmonary Tuberculosis, Healthy Mycobacterium tuberculosis–Infected and Non‐Infected Individuals in a Tuberculosis Endemic Setting, Ethiopia

“…The expression of the gene coding for the 16 kDa antigen is tightly regulated by the DosR transcriptional regulator [24], which would reduce cross-reactivity with antigens from NTM. The 16 kDa has been found to be highly immunogenic and recommended as one of the component antigens in vaccine strategies targeting protective immune responses against primary TB infection, as well as against reactivation of latent infection [25]. This antigen has been used as part of the commercially available TB diagnostic kit, 'pathozyme TB complex plus', together with the 38 kDa antigen [26].…”

Heat Shock Proteins: Stimulators of Innate and Acquired Immunity

“…This study indicated that native but not recombinant HSP16 (when administered with the adjuvant dioctadecylammonium bromide) could elicit protection in a mouse model of TB, and in addition, it had the capacity to boost an existing BCG vaccination. Although HSP16 has not previously been linked with an ability to chaperone antigenic material and deliver it to the immune system, this study does suggest that native mycobacterial HSPs could exploit this pathway for other mycobacterial components [15, 109]. …”

“…Induction of a potentially protective phenotype has also been shown by a DNA vaccine construct that expresses mycobacterial HSP70 fused to the secreted mycobacterial protein MPT51: these studies demonstrated that linkage to the 27 kDa C terminus substrate binding domain of HSP70 was apparently sufficient to induce the protective immune response as no protection was observed using the 44 kDa N-terminal nucleotide binding domain [108]. An investigation into the immunogenicity of native and recombinant mycobacterial HSP16 (HSPx) was recently published [109]. This study indicated that native but not recombinant HSP16 (when administered with the adjuvant dioctadecylammonium bromide) could elicit protection in a mouse model of TB, and in addition, it had the capacity to boost an existing BCG vaccination.…”