Tuberculosis vaccines: current status and future prospects

CHO expressed recombinant human lactoferrin as an adjuvant for BCG

Lactoferrin (LF), an iron binding protein with immune modulatory activities, has adjuvant activity to enhance vaccine efficacy. Tuberculosis (TB) is a pulmonary disease caused by the pathogen Mycobacterium tuberculosis (MTB). Progressive TB disease is clinically defined by damaging pulmonary pathology, a result of inflammation due to immune reactivity. The current vaccine for TB, an attenuated strain of Mycobacterium bovis, Bacillus Calmette Guerin (BCG), has only limited efficacy to prevent adult pulmonary TB. This study examines a Chinese hamster ovary (CHO) expressed recombinant human LF (rHLF) to boost efficacy of the BCG vaccine and delay early pathology post infectious challenge. C57BL/6 mice were immunized with BCG, or BCG admixed with either rHLF or bovine LF (bLF; internal control), or remained unvaccinated. Mice were then aerosol challenged with Erdman MTB. All vaccinated mice demonstrated decreased organ bacterial load up to 19 weeks post infection compared with non-vaccinated controls. Furthermore, mice receiving bLF or rHLF supplemented BCG vaccines showed a modest decrease in lung pathology developed over time, compared to the BCG vaccine alone. While mice vaccinated with BCG/rHLF demonstrated increased general lung inflammation at day 7, it occurred without noticeable increase in pro-inflammatory cytokines. At later times, decreased pathology in the rHLF groups correlated with decreased inflammatory cytokines. Splenic recall to BCG antigens showed BCG/rHLF vaccination increased production of IFN-γ, IL-6, and GM-CSF compared to naïve, BCG, and BCG/bLF groups. Analysis of T cell stimulating functions of bone marrow derived macrophages and dendritic cells treated with BCG/bLF or BCG/rHLF showed decreases in IL-10 production when co-cultured with sensitized CD4 and CD8 T cells, compared to those cultured with macrophages/dendritic cells treated with BCG without LF. These results indicate that addition of rHLF to the BCG vaccine can modulate development of host pathology early post infectious challenge, most likely through host immune regulation affecting hypersensitive responses.

Mechanisms of delayed anti-tuberculosis protection in the lung of parenteral BCG-vaccinated hosts: a critical role of airway luminal T cells

The immune mechanisms underlying unsatisfactory pulmonary mucosal protection by parenteral Bacillus Calmette-Guérin (BCG) immunization remain poorly understood. We found that parenteral BCG immunization failed to elicit airway luminal T cells (ALT) whereas it induced significant T cells in the lung interstitium. After Mycobacterium tuberculosis (M.tb) challenge, ALT remained missing for 10 days. The lack of ALT correlated with lack of lung protection for 14 days post-M.tb challenge. To further investigate the role of ALT, ALT were elicited in BCG-immunized animals by intranasal inoculation of M.tb culture-filtrate (CF) proteins. Installment of ALT by CF restored protection in the early phases of M.tb infection, which was linked to rapid increases in ALT, but not in lung interstitial T cells. Also, adoptive transfer of T cells to the airway lumen of BCG-immunized animals also accelerated protection. This study thus provides novel evidence that unsatisfactory lung protection by parenteral BCG immunization is due to delayed ALT recruitment after pulmonary M.tb exposure.

Long-term thermostabilization of live poxviral and adenoviral vaccine vectors at supraphysiological temperatures in carbohydrate glass

Live recombinant viral vectors based on adenoviruses and poxviruses are among the most promising platforms for development of new vaccines against diseases such as malaria, tuberculosis, and HIV-AIDS. Vaccines based on live viruses must remain infectious to be effective, so therefore need continuous refrigeration to maintain stability and viability, a requirement that can be costly and difficult, especially in developing countries. The sugars sucrose and trehalose are commonly used as stabilizing agents and cryoprotectants for biological products. Here, we have exploited the ability of these sugars to vitrify on desiccation to develop a thermostabilization technique for live viral vaccine vectors. By slowly drying vaccines suspended in solutions of these disaccharide stabilizers onto a filter-like support membrane at ambient temperature, an ultrathin glass is deposited on the fibers of the inert matrix. Immobilization of two recombinant vaccine vectors-E1/E3-deleted human adenovirus type 5 and modified vaccinia virus Ankara-in this glass on the membranes enabled complete recovery of viral titer and immunogenicity after storage at up to 45 degrees C for 6 months and even longer with minimal losses. Furthermore, the membrane carrying the stabilized vaccine can be incorporated into a holder attached to a syringe for almost simultaneous reconstitution and injection at point of use. The technology may potentially be developed for the deployment of viral vector-based biopharmaceuticals in resource-poor settings.

Dissection of regenerating T-Cell responses against tuberculosis in HIV-infected adults sensitized by Mycobacterium tuberculosis

RATIONALE

Combination antiretroviral treatment (cART) reduces the risk of tuberculosis in HIV-infected people. Therefore a novel approach to gain insight into protection against tuberculosis is to analyze the T cells that expand in people sensitized by Mycobacterium tuberculosis (MTB) during cART.

OBJECTIVES

To longitudinally analyze CD4 T-cell subsets during the first year of cART, from the time of starting cART (Day 0), in 19 HIV-infected, MTB-sensitized adults.

METHODS

Peripheral blood mononuclear cells were obtained on Day 0, Weeks 2, 4, 12, 24, 36, and 48 of cART and were stimulated with purified protein derivative (PPD) followed by flow cytometry to analyze surface markers and intracellular cytokines.

MEASUREMENTS AND MAIN RESULTS

CD4(+) T cells significantly increased during follow-up and the viral load fell to undetectable levels in each patient, indicating successful immune restoration. Central memory CD27(+)CD45RA(-) and CD27(+)CCR5(-) CD4(+) cells expanded by 12 weeks (P < 0.02) followed by naive CD27(+)CD45RA(+) cells at 36 weeks (P = 0.02). Terminally differentiated effector CD4(+)CD27(-)CCR7(-) cells decreased by 12 weeks (P = 0.02), paralleled by a proportional decline of PPD-specific CD4(+)IFN-gamma(+) cells (P = 0.02). However, the absolute numbers of PPD-specific IFN-gamma-producing cells, determined by enzyme-linked immunospot assay, increased (P = 0.02).

CONCLUSIONS

Rapid effector responses are often measured when evaluating immunity. We show that although cART is associated with an absolute increase in effector function, the proportional response decreased and the strongest correlate of increased cART-mediated immunity in this study was the central memory response.

Natural variation in immune responses to neonatal Mycobacterium bovis Bacillus Calmette-Guerin (BCG) Vaccination in a Cohort of Gambian infants

Background

There is a need for new vaccines for tuberculosis (TB) that protect against adult pulmonary disease in regions where BCG is not effective. However, BCG could remain integral to TB control programmes because neonatal BCG protects against disseminated forms of childhood TB and many new vaccines rely on BCG to prime immunity or are recombinant strains of BCG. Interferon-gamma (IFN-γ) is required for immunity to mycobacteria and used as a marker of immunity when new vaccines are tested. Although BCG is widely given to neonates IFN-γ responses to BCG in this age group are poorly described. Characterisation of IFN-γ responses to BCG is required for interpretation of vaccine immunogenicity study data where BCG is part of the vaccination strategy.

Methodology/Principal Findings

236 healthy Gambian babies were vaccinated with M. bovis BCG at birth. IFN-γ, interleukin (IL)-5 and IL-13 responses to purified protein derivative (PPD), killed Mycobacterium tuberculosis (KMTB), M. tuberculosis short term culture filtrate (STCF) and M. bovis BCG antigen 85 complex (Ag85) were measured in a whole blood assay two months after vaccination. Cytokine responses varied up to 10 log-fold within this population. The majority of infants (89–98% depending on the antigen) made IFN-γ responses and there was significant correlation between IFN-γ responses to the different mycobacterial antigens (Spearman's coefficient ranged from 0.340 to 0.675, p = 10⁻⁶–10⁻²²). IL-13 and IL-5 responses were generally low and there were more non-responders (33–75%) for these cytokines. Nonetheless, significant correlations were observed for IL-13 and IL-5 responses to different mycobacterial antigens

Conclusions/Significance

Cytokine responses to mycobacterial antigens in BCG-vaccinated infants are heterogeneous and there is significant inter-individual variation. Further studies in large populations of infants are required to identify the factors that determine variation in IFN-γ responses.

Co-infection with human immunodeficiency virus and tuberculosis in Asia

Asia has the highest numbers of tuberculosis cases (60% of the global total) and has experienced a marked rise in HIV seroprevalence (22% of the global total) in key subpopulations of these highly populous nations. Thus, co-infected patients are a challenge for practitioners and public health workers alike. The U.S.-Japan Cooperative Medical Science Program is spearheading interdisciplinary collaborations in Asia to address the many outstanding research priorities for HIV-tuberculosis co-infection. There is an urgency to this agenda for many reasons, including the frequency with which tuberculosis accounts for the death of HIV-infected persons in Asia, and the continued rise of multiple drug-resistant Mycobacterium tuberculosis. We review briefly the public health situation in Asia, highlighting research questions from US-Japan-Asian partner joint meetings, and cite salient studies to indicate trends and challenges.