The effectiveness of BCG vaccination in preventing Mycobacterium tuberculosis infection and disease in Greenland.

BACKGROUND: The BCG vaccine's ability to prevent Mycobacterium tuberculosis infection (MTI) remains highly debated. In Greenland, BCG vaccination was introduced in 1955, but was temporarily discontinued (1991-1996) due to nationwide policy changes. The study aimed to use the transient stop in BCG vaccination to evaluate the effect of vaccination on MTI prevalence and TB incidence. METHODS: MTI study: A cross-sectional study (2012), comprising East Greenlanders born during 1982-2006, evaluated the effect of BCG vaccination on MTI prevalence; a positive interferon γ release assay defined an MTI case. Associations were estimated using logistic regression. TB study: a cohort study covering the same birth cohorts with follow-up until 2012 evaluated the vaccine's effect on TB incidence. A personal identifier allowed for follow-up in the TB notification system. Associations were estimated using Cox regression. RESULTS: MTI study: Included 953 participants; 81% were BCG-vaccinated; 29% had MTI, 23% among vaccinated and 57% among non-vaccinated. BCG vaccination reduced the odds of MTI, OR 0.52 (95% CI 0.32 to 0.85), p=0.01. Vaccine effectiveness against MTI was 20%. TB study: Included 1697 participants followed for 21,148 person-years. 6% were notified with TB, 4% among vaccinated and 11% among non-vaccinated. BCG vaccination reduced the risk of TB, HR 0.50 (95% CI 0.26 to 0.95), p=0.03, yielding a vaccine effectiveness of 50%. CONCLUSIONS: BCG vaccination was effective in reducing both MTI and TB disease among children and young adults in a TB high-endemic setting in Greenland.

Subunit vaccine H56/CAF01 induces a population of circulating CD4 T cells that traffic into the Mycobacterium tuberculosis-infected lung.

The capacity of CD4 T cells to protect against Mycobacterium tuberculosis (Mtb) is governed by their ability to localize to the lung site of infection. Subunit vaccine H56/CAF01, a liposome-adjuvanted fusion protein of Mtb antigens Ag85B, ESAT-6, and Rv2660, conferred durable protection and elicited polyfunctional CD4 T cells that preferentially localized to the lung parenchyma. These lung-resident T cells had reduced KLRG1 and increased CXCR3 expression, an intermediate state of Th1 differentiation that has been associated with Mtb protection. Importantly, KLGR1- CXCR3+ cells were also enriched in the lung vasculature and peripheral circulation of vaccinated animals, but not controls. Moreover, S1P1R blockade rapidly cleared this population from the blood and adoptive transfer of T cells recovered from the vasculature of vaccinated, but not control, mice efficiently trafficked into the Mtb-infected lung parenchyma. Thus, durable immunity elicited by H56/CAF01 vaccination is associated with the maintenance of circulating CD4 T cells that selectively home to the lung parenchyma.

The effect of adjuvants on the immune response induced by a DBL4ɛ-ID4 VAR2CSA based Plasmodium falciparum vaccine against placental malaria.

A vaccine protecting women against placental malaria could be based on the sub-domains of the VAR2CSA antigen, since antibodies against the DBL4ɛ-ID4 subunit of the VAR2CSA protein can inhibit parasite binding to the placental ligand chondroitin sulphate A (CSA). Here we tested the ability of DBL4ɛ-ID4 to induce binding-inhibitory antibodies when formulated with adjuvants approved for human use. We have characterized the immune response of DBL4ɛ-ID4 in combination with Freund's complete and incomplete adjuvant and with three adjuvants currently being used in clinical trials: Montanide(®) ISA 720, Alhydrogel(®) and CAF01. Antibodies induced against DBL4ɛ-ID4 in combination with these adjuvants inhibited parasite binding to CSA from 82% to 99%. Although, different epitope recognition patterns were obtained for the different formulations, all adjuvant combinations induced strong Th1 and Th2 type responses, resulting in IgG with similar binding strength, with to the DBL4ɛ-ID4 antigen. These results demonstrate that the DBL4ɛ-ID4 antigen is highly immunogenic and that binding inhibitory antibodies are induced when formulated with any of the tested adjuvants.

Tuberculosis subunit vaccine development: on the role of interferon-gamma.

Tuberculosis (TB) remains a major global health problem and subunit vaccines for the control of the disease are presently under development. This vaccine strategy requires an in vitro correlate of protection for the identification of relevant vaccine candidate antigens and for monitoring the induction of a protective cell-mediated immune response after vaccination. New studies of experimental vaccines in the mouse model of TB support interferon-gamma as a relevant marker for the induction of a protective immune response. In contrast, searching for immunodominant antigens capable of inducing strong interferon-gamma responses in PPD positive healthy or TB infected individuals may not identify all relevant candidate antigens for inclusion in a novel TB subunit vaccine.

A novel TB vaccine; towards a strategy based on our understanding of BCG failure.

The protection afforded by the currently available tuberculosis vaccine, bacillus Calmette-Guérin (BCG) is insufficient and new vaccine strategies are urgently needed. Progress in our understanding of the immunological deficits of BCG combined with novel knowledge on genetics of mycobacteria has paved the way for promising new vaccine strategies. These include recombinant modified BCG vaccines, attenuated strains of Mycobacterium tuberculosis, and various non-live candidates such as DNA and subunit vaccines. Decisive for transforming technical progress into a novel tuberculosis (TB) vaccine strategy is the recent advance in our understanding of the failure of BCG in the third world and the interaction between this vaccine and environmental mycobacteria.

Antigen discovery and tuberculosis vaccine development in the post-genomic era.

For a number of years, a major effort has been put into the identification of candidate molecules for inclusion in a novel vaccine against tuberculosis. Various techniques have been exploited and have resulted in the identification of immunologically important antigens such as the immunodominant antigens ESAT-6 and antigen 85A/B. Today, the availability of the total nucleotide sequence of the Mycobacterium tuberculosis genome enables a post-genomic antigen discovery approach based on denotation and screening of complete protein families containing immunodominant molecules. One group of genes sharing properties with ESAT-6 constitute what has been called the esat-6 gene family. The genes have 10-35% homology to esat-6, are approximately the same size and share genomic organization. The data accumulated so far demonstrate that these molecules are immunodominant antigens strongly recognized in human TB patients and with the potential for a novel TB vaccine.

Specific acquired resistance in mice immunized with killed mycobacteria.

Past attempts to raise resistance against Mycobacterium tuberculosis using various preparations of killed mycobacteria have questioned the specificity of the generated immune response. In the present study, we have focused on the protective efficacy of experimental vaccines based on killed mycobacteria. We demonstrate that killed mycobacteria can confer high levels of protection, which can be adoptively transferred to recipient T-cell-deficient mice. Moreover, protective antigens can be found in the cell wall, membrane and cytosol of the mycobacterial cell, and hence emphasize the importance of searching for protective antigens in various compartments of the mycobacterial cell.

Diagnosis of tuberculosis based on the two specific antigens ESAT-6 and CFP10.

Tests based on tuberculin purified protein derivative (PPD) cannot distinguish between tuberculosis infection, Mycobacterium bovis BCG vaccination, or exposure to environmental mycobacteria. The present study investigated the diagnostic potential of two Mycobacterium tuberculosis-specific antigens (ESAT-6 and CFP10) in experimental animals as well as during natural infection in humans and cattle. Both antigens were frequently recognized in vivo and in vitro based on the induction of delayed-type hypersensitivity responses and the ability to induce gamma interferon production by lymphocytes, respectively. The combination of ESAT-6 and CFP10 was found to be highly sensitive and specific for both in vivo and in vitro diagnosis. In humans, the combination had a high sensitivity (73%) and a much higher specificity (93%) than PPD (7%).

Control of latent Mycobacterium tuberculosis infection is dependent on CD8 T cells.

It is estimated that one-third of the world's population is infected with Mycobacterium tuberculosis, but that only 10% of infected people break down with the disease. In the remaining 90% the infection remains clinically latent. In the present study, the immune mechanisms controlling the latent phase of tuberculosis infection were evaluated in a mouse model of latency and reactivation. Mice aerosol-infected with M. tuberculosis were treated with anti-mycobacterial drugs resulting in very low, stable bacterial numbers (<500 CFU in the spleen and lung) for 10-12 weeks followed by reactivation of the disease with increasing bacterial numbers. During latency, pathological changes in the lung had almost completely resolved and lymphocyte number and turnover were at the pre-infection level. The CD4 subset was highly active during the acute phase of infection and could be detected by intracellular staining for IFN-gamma as well as after antigen-specific stimulation with mycobacterial antigens. The CD8 subset was not involved in the acute stage of infection, but this subset was active and produced IFN-gamma during the latent phase of infection. In vivo depletion of T cell subsets supported these findings with a 6-7-fold increase in bacterial numbers in the lung following anti-CD4 treatment during the acute phase, while anti-CD8 treatment did not have an effect. The opposite was found during the latent phase where anti-CD8 treatment as well as anti-IFN-gamma treatment both resulted in a 10-fold increase in bacterial numbers in the lung, while anti-CD4 treatment induced only a modest change.

The influence of remaining live BCG organisms in vaccinated mice on the maintenance of immunity to tuberculosis.

The only available vaccine against Mycobacterium tuberculosis, the bacille Calmette-Guérin (BCG) vaccine, is at present being used as a reference for the efficacy of novel vaccines. Herein, we demonstrate that viable BCG can be detected at late time points after vaccination in C57BL/6J mice. If BCG is cleared by antibiotic treatment, the number of mycobacteria-reactive effector cells in the spleen gradually reverts to low levels and consequently immunity in this organ wanes, while resistance in the lung remains stable. The implications for comparing BCG vaccination with experimental vaccines including non-replicating vaccines are discussed.