Diagnostic biomarkers and improved vaccination against mycobacterial infection

Abstract: Tuberculosis (TB) remains one of the world’s most serious infectious diseases. It is estimated that a third of the world’s population is latently infected and 8 million new cases are recorded each year. Although BCG vaccination triggers protective immune responses in the neonates, it confers protection against only certain forms of childhood TB. Protection mediated by BCG, against pulmonary TB, is controversial as reported with variable efficacy ranging from 0-80%. In addition to the problems associated with the BCG vaccine, diagnosis of TB cannot be performed readily with the available tools. At present, an effective control of TB is highly dependent on the development of a new TB-vaccine as well as proper identification and treatment of individuals with active disease. Therefore, we particularly focused on identification of biomarker (s) of infection and the development of better vaccines, with special emphasis on the immune responses in the respiratory tract.In the first study, we aimed to identify immune biomarker (s) of infection for better diagnosis of TB. Mice were infected with BCG administered i.n. or i.v., and the bacterial burden in the lungs, spleen and liver was examined. We measured IL-12, IFN-?, TNF, soluble TNF receptors (sTNFR) and mycobacteria-specific antibodies in the broncho-alveolar lavage (BAL) and in serum in order to find immune correlates of infection. Results showed that sTNFR and mycobacteria-specific antibodies in BAL, but not in serum, might be useful in distinguishing active from latent infection or exposure to mycobacterial antigens.In the second study, we investigated whether we could improve the currently used BCG vaccine. For this purpose, we tested a combination of neonatal vaccination protocol using BCG and posterior boosting with the protein heparin-binding hemagglutinin adhesion (HBHA). It has been described that immunization with native (n) HBHA but not recombinant (r) HBHA conferred protection against M. tuberculosis challenge in mice.This protection was comparable to that afforded by the BCG vaccine. In order to improve the protective efficacy of the nHBHA vaccine we followed heterologous prime-boost strategy, comprising BCG vaccination at the neonatal age, followed by nHBHA boosting at the infant and adult ages. We also examined whether the rHBHA protein could boost BCG-mediated protective immunity. Cellular immune responses and protection as measured by control of bacterial growth in the lungs of the treated animals were followed. Our results showed an improved effect of BCG-priming on HBHA-immunization. The BCG/HBHA immunization protocol was more effective in induction of HBHA-specific immune responses, as well as in protection than when the animals received only BCG or HBHA alone. Importantly, our study revealed that nHBHA does not require co-administration with adjuvant provided that mice were primed with live BCG before boosting.Finally, we hypothesized that in utero sensitization of the fetal immune system with nHBHA may improve nHBHA-specific immune responses after birth. The pregnant mother was immunized with nHBHA 1 week before delivery. After birth, the offspring received two doses (week 1 and week 4) of nHBHA formulated with cholera toxin. We examined HBHA-specific recall responses and protection after challenge with a high dose of BCG. We found that immune responses were improved by priming the pregnant mother, and that this also provided better protection than when the offspring received only BCG or HBHA neonatal vaccinations.