Recombinant HBHA boosting effect on BCG-induced immunity against Mycobacterium tuberculosis infection

Abstract

Heterologous prime-boost regimens are effective strategies to promote long-term memory and strong cellular Th1 responses to Mycobacterium tuberculosis, when BCG is used in the priming step. Subcutaneous or intranasal boosting of BCG-vaccinated newborn mice with native heparin-binding haemagglutinin (nHBHA) significantly enhances protection against M. tuberculosis. However, nHBHA is characterized by a complex methylation pattern in its C-terminal domain, which is important for protective immunogenicity in primary vaccination. In this study we addressed the question whether boosting with recombinant, non-methylated HBHA (rHBHA) produced in Escherichia coli may enhance protection of BCG-primed newborn mice. We found that while subcutaneous rHBHA boosting enhanced protection of BCG-primed mice against intranasal M. tuberculosis infection both in spleen and lungs, enhanced protection against aerosol infection was only seen in the spleen (0.72 logs; P < 0.05) but not in the lungs. Thus, in BCG-primed mice the methylation of the C-terminal domain of HBHA is dispensable for the induction of enhanced protection in the lungs against intranasal but not aerosol infection, whereas it enhances protection in the spleen in both challenge models. This report thus provides evidence that rHBHA may be considered as a booster vaccine against disseminated tuberculosis.

Figure 1

Spleen cell cytokine profile of BCG-vaccinated mice with or without rHBHA boost after M. tuberculosis infection. Eight weeks after i.n. (A) or aerosol (B) challenge spleen cells from control mice (white bars), BCG-vaccinated mice (black bars), or BCG-vaccinated/rHBHA-boosted mice (gray bars) were cultured in the presence of medium only, ConA (2.5 μg/mL), or rHBHA (5 μg/mL). Levels of cytokines were measured after 72 h culture in the supernatants by using the OptEIA kit (BD Biosciences). Values are expressed in pg/mL and represent media ± SEM of samples tested in duplicates from each group of mice. The data was considered statistically significant when P < 0.05 (*), P < 0.001 (**), and P < 0.0001 (***).

Figure 2

Lung cell cytokine profile of BCG-vaccinated mice with or without rHBHA boost after M. tuberculosis infection. Eight weeks after i.n. (A) or aerosol (B) challenge lung cells from control mice (white bars), BCG-vaccinated mice (black bars), or BCG-vaccinated/rHBHA-boosted mice (gray bars) were cultured in the presence of medium only, ConA (2.5 μg/mL), or rHBHA (5 μg/mL). Levels of cytokines were measured after 72 h culture in the supernatants by using the OptEIA kit (BD Biosciences). Values are expressed in pg/mL and represent media ± SEM of samples tested in duplicates from each group of mice. Statistically significant data: P < 0.05 (*), P < 0.001 (**), and P < 0.0001 (***).