Field trials of tuberculosis vaccines: how could we have done them better?

The effect of in vitro consecutive passages and culture medium on the genetic variations in BCG Pasteur 1173P2 vaccine

Since the introduction of the Bacillus Calmette-Guérin (BCG) vaccine, the genomes of vaccine strains have undergone variations due to repeated passages in different laboratories and vaccine production facilities. Genetic variations have been considered as one of the effective factors in the BCG variable protective efficacy. Consecutive subcultures have been shown to play an essential role in causing genetic variations in several microorganisms, including Mycobacterium bovis BCG. Therefore, the world health organization (WHO) recommendation to limit the passages of master seed lot in the BCG vaccine production should be considered. Besides, the role of other external variables such as quality of the raw ingredients of the culture media, the type of the culture medium and the cultivation methods in the vaccine production has been poorly studied. Here, the effect of passages and culture medium on genetic variations in a BCG seed lot was investigated during a year. The findings of this study revealed a total of 19 variants compared to seed lot while the passages were more than the number recommended by WHO. The first culture of seed lot in the Sauton broth and Middlebrook 7H9 media, and the last subculture in Sauton broth had the least and the most variants, respectively. The observation of the higher number of variants in the last cultures on Sauton broth and Middlebrook 7H9 in comparison to the first and the middle cultures may indicate the effect of passages on the genetic variations in BCG. Additionally, more variants in BCG grown in the Sauton broth do not necessarily represent the greater ability of this medium to cause genetic mutations. For a better conclusion, it is required to examine the medium components as independent variables.

Genomic characteristics of two most widely used BCG vaccine strains: Danish 1331 and Pasteur 1173P2

Background

Bacillus Calmette–Guérin (BCG) refers to a group of vaccine strains with unique genetic characteristics. BCG is the only available vaccine for preventing tuberculosis (TB). Genetic and biochemical variations among the BCG vaccine strains have been considered as one of the significant parameters affecting the variable protective efficacy of the vaccine against pulmonary tuberculosis. To track genetic variations, here two vaccine strains (Danish 1331 and Pasteur 1173P2) popularly used according to the BCG World Atlas were subjected to a comparative analysis against the Mycobacterium tuberculosis H37Rv, Mycobacterium bovis AF2122/97, and Mycobacterium tuberculosis variant bovis BCG str. Pasteur 1173P2 reference genomes. Besides, the presence or absence of the experimentally verified human T cell epitopes was examined.

Results

Only two variants were identified in BCG Danish 1331 that have not been reported previously in any BCG strains with the complete submitted genome yet. Furthermore, we identified a DU1-like 14,577 bp region in BCG Danish 1331; The duplication which was previously seemed to be exclusive to the BCG Pasteur. We also found that 35% of the T cell epitopes are absent from both strains, and epitope sequences are more conserved than the rest of the genome.

Conclusions

We provided a comprehensive catalog of single nucleotide polymorphisms (SNPs) and short insertions and deletions (indels) in BCG Danish 1331 and BCG Pasteur 1173P2. These findings may help determine the effect of genetic variations on the variable protective efficacy of BCG vaccine strains.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08826-9.

Genomic evidence for stability of the Bacillus Calmette-Guérin (BCG) vaccine strain (Pasteur 1173P2) from different batches in Iran

AIMS

Investigate the genetic stability of the BCG vaccine produced in Iran from different batches compared to the reference strain.

METHODS AND RESULTS

We comparatively analyzed the whole genome sequences of the vaccine batches from different years. Eleven vials of different batches from 2010, 2018, and 2019 were included. Complete genome analyses revealed no difference between the old (2010) and new (2018 and 2019) vaccine batches. Additionally, minor genetic changes include five single nucleotide polymorphisms (SNPs) and insertions/deletions (indels) were observed compared to the BCG Pasteur 1173P2 reference strain, which were shared among all batches. Besides, the batches were identical to the reference strain in terms of antibiotic resistance genes, prophage sequences, and clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated (Cas) systems.

CONCLUSIONS

High genetic stability of the BCG vaccine used in the national immunization program was confirmed, which indicates the optimal conditions in the vaccine production process.

SIGNIFICANCE AND IMPACT OF THE STUDY

Genetic differences within and between vaccine strains have been declared as one of the main parameters related to the BCG vaccine variable protective efficacy. No study has been done to investigate the genetic variations of the vaccine batches at the single-base level.

Lessons From Bacille Calmette-Guérin for SARS-CoV-2 Vaccine Candidates

Developers of severe acute respiratory syndrome coronavirus 2 vaccines should consider some of the lessons from a "new" vaccine introduced in 1921, namely bacille Calmette-Guérin.

Does the BCG vaccine have different effects on strains of tuberculosis?

Several explanations have been suggested concerning the variety in bacille Calmette-Guerin (BCG) vaccine efficacy on strains of Mycobacterium tuberculosis (Mtb). This study aimed to compare the effect of BCG vaccination history in the prevention of the occurrence of Mtb-Beijing and non-Beijing strains. In this cross-sectional study, 64 patients with pulmonary tuberculosis (TB) were recruited from the Iranian border provinces (North West and West). Isolates were subjected to restriction fragment length polymorphism (RFLP) analysis, using the insertion sequence IS6110 as a probe (IS6110 RFLP) and drug susceptibility testing using the proportion method. Samples were analyzed with Gel Compare II 6.6 and spss version 18. The mean age [standard deviation (SD)] of the patients was 54·4 (SD = 17·0). Overall, 49 cases (76·56%) had no BCG vaccination scar. The prevalence of Beijing strains was 9·38% and drug resistance proportion among the isolates was 14·1% (nine cases). There was a significant relationship between Beijing strains and tuberculosis (TB)-drug resistance in isolates (χ²  = 26·29, P < 0·001). There was also a strong association between vaccination history and Beijing strains (χ²  = 13·23, P = 0·002). Also, a statistical relationship was observed between Beijing strains and drug-resistant TB among patients with a history of vaccination (χ²  = 7·47, P = 0·002). This association was not maintained in the unvaccinated group (P = 0·102). These findings confirm the claim that the vaccine has different effects on different subspecies of tuberculosis. The cause of the high probability of drug resistance in patients with Beijing-TB and vaccination history requires further investigation with a higher sample size.

Towards new TB vaccines

Mycobacterium tuberculosis remains the leading cause of death attributed to a single infectious organism. Bacillus Calmette-Guerin (BCG), the standard vaccine against M. tuberculosis, is thought to prevent only 5% of all vaccine-preventable deaths due to tuberculosis, thus an alternative vaccine is required. One of the principal barriers to vaccine development against M. tuberculosis is the complexity of the immune response to infection, with uncertainty as to what constitutes an immunological correlate of protection. In this paper, we seek to give an overview of the immunology of M. tuberculosis infection, and by doing so, investigate possible targets of vaccine development. This encompasses the innate, adaptive, mucosal and humoral immune systems. Though MVA85A did not improve protection compared with BCG alone in a large-scale clinical trial, the correlates of protection this has revealed, in addition to promising results from candidate such as VPM1002, M72/ASO1E and H56:IC31 point to a brighter future in the field of TB vaccine development.

Tuberculosis Surveillance and Control, Puerto Rico, 1898-2015

The World Health Organization recognizes Puerto Rico as an area of low tuberculosis (TB) incidence, where TB elimination is possible by 2035. To describe the current low incidence of reported cases, provide key lessons learned, and detect areas that may affect progress, we systematically reviewed the literature about the history of TB surveillance and control in Puerto Rico and supplemented this information with additional references and epidemiologic data. We reviewed 3 periods: 1898-1946 (public health efforts before the advent of TB chemotherapy); 1947-1992 (control and surveillance after the introduction of TB chemotherapy); and 1993-2015 (expanded TB control and surveillance). Although sustained surveillance, continued care, and use of newly developed strategies occurred concomitantly with decreased incidence of reported TB cases and mortality rates, factors that may affect progress remain poorly understood and include potential delayed diagnosis and underreporting, the effects of government debt and Hurricane Maria, and poverty.

Different effects of BCG strains - A natural experiment evaluating the impact of the Danish and the Russian BCG strains on morbidity and scar formation in Guinea-Bissau

BACKGROUND

Different Bacillus Calmette-Guerin (BCG) vaccine strains may have different non-specific effects. We assessed the effect of two BCG strains (Danish and Russian) on childhood morbidity and BCG scarification in Guinea-Bissau.

METHODS

During 2011-2013, infants in the Bandim Health Project's urban study area received the Danish or Russian BCG in a natural experiment. Health center consultations were registered at point of care and scar status and size at age 4½ months. We assessed the effect of strain on consultation rates between vaccination and age 45days in Cox proportional hazards models. Scar prevalence and size were compared using binomial regression and ranksum tests.

RESULTS

Among 1206 children, 18% received Danish BCG (n=215) and 82% Russian BCG (n=991). The adjusted hazard ratio (aHR) for consultations was 0.94 (95% CI 0.60-1.46) for Danish BCG compared with Russian BCG. Girls vaccinated with Danish BCG tended to have lower consultation rates compared with girls vaccinated with Russian BCG (aHR 0.56 (0.25-1.24)), whereas the effect was opposite for boys (aHR 1.24 (0.74-2.11)), p=0.09. Children vaccinated with Danish BCG were more likely to develop a scar (97%) than children vaccinated with Russian BCG (87%), the relative risk (RR) being 1.11 (1.06-1.16). The effect was stronger in girls, and BCG scar size was larger among infants vaccinated with the Danish strain.

CONCLUSION

BCG strain influences scar prevalence and scar size, and may have sex differential effects on morbidity. BCG strains are currently used interchangeably, but BCG scarring has been linked to subsequent survival. Hence, more research into the health effects of different BCG strains is warranted. Small adjustments of BCG production could potentially lower childhood morbidity and mortality at low cost.

Contact tracing of tuberculosis: a systematic review of transmission modelling studies

The WHO recommended intervention of Directly Observed Treatment, Short-course (DOTS) appears to have been less successful than expected in reducing the burden of TB in some high prevalence settings. One strategy for enhancing DOTS is incorporating active case-finding through screening contacts of TB patients as widely used in low-prevalence settings. Predictive models that incorporate population-level effects on transmission provide one means of predicting impacts of such interventions. We aim to identify all TB transmission modelling studies addressing contact tracing and to describe and critically assess their modelling assumptions, parameter choices and relevance to policy. We searched MEDLINE, SCOPUS, COMPENDEX, Google Scholar and Web of Science databases for relevant English language publications up to February 2012. Of the 1285 studies identified, only 5 studies met our inclusion criteria of models of TB transmission dynamics in human populations designed to incorporate contact tracing as an intervention. Detailed implementation of contact processes was only present in two studies, while only one study presented a model for a high prevalence, developing world setting. Some use of relevant data for parameter estimation was made in each study however validation of the predicted impact of interventions was not attempted in any of the studies. Despite a large body of literature on TB transmission modelling, few published studies incorporate contact tracing. There is considerable scope for future analyses to make better use of data and to apply individual based models to facilitate more realistic patterns of infectious contact. Combined with a focus on high burden settings this would greatly increase the potential for models to inform the use of contract tracing as a TB control policy. Our findings highlight the potential for collaborative work between clinicians, epidemiologists and modellers to gather data required to enhance model development and validation and hence better inform future public health policy.

Perspectives for Developing New Tuberculosis Vaccines Derived from the Pathogenesis of Tuberculosis: I. Basic Principles, II. Preclinical Testing, and III. Clinical Testing

Part I. Basic Principles. TB vaccines cannot prevent establishment of the infection. They can only prevent an early pulmonary tubercle from developing into clinical disease. A more effective new vaccine should optimize both cell-mediated immunity (CMI) and delayed-type hypersensitivity (DTH) better than any existing vaccine. The rabbit is the only laboratory animal in which all aspects of the human disease can be reproduced: namely, the prevention of most primary tubercles, the arrestment of most primary tubercles, the formation of the tubercle’s solid caseous center, the liquefaction of this center, the formation of cavities and the bronchial spread of the disease. In liquefied caseum, virulent tubercle bacilli can multiply extracellularly, especially in the liquefied caseum next to the inner wall of a cavity where oxygen is plentiful. The bacilli in liquefied caseum cannot be reached by the increased number of activated macrophages produced by TB vaccines. Therefore, new TB vaccines will have little or no effect on the extracellular bacillary growth within liquefied caseum. TB vaccines can only increase the host’s ability to stop the development of new TB lesions that arise from the bronchial spread of tubercle bacilli from the cavity to other parts of the lung. Therefore, effective TB vaccines do not prevent the reactivation of latent TB. Such vaccines only control (or reduce) the number of metastatic lesions that result after the primary TB lesion was reactivated by the liquefaction process. (Note: the large number of tubercle bacilli growing extracellularly in liquefied caseum gives rise to mutations that enable antimicrobial resistance—which is a major reason why TB still exists today). Part II. Preclinical Testing. The counting of grossly visible tubercles in the lungs of rabbits after the inhalation of virulent human-type tubercle bacilli is the most pertinent preclinical method to assess the efficacy of new TB vaccines (because an effective vaccine will stop the growth of developing tubercles before while they are still microscopic in size). Unfortunately, rabbits are rarely used in preclinical vaccine trials, despite their relative ease of handling and human-like response to this infection. Mice do not generate an effective DTH response, and guinea pigs do not generate an effective CMI response. Only the rabbits and most humans can establish the proper amount of DTH and CMI that is necessary to contain this infection. Therefore, rabbits should be included in all pre-clinical testing of new TB vaccines. New drugs (and/or immunological procedures) to reduce liquefaction and cavity formation are urgently needed. A simple intradermal way to select such drugs or procedures is described herein. Part III. Clinical Testing. Vaccine trials would be much more precise if the variations in human populations (listed herein) were taken into consideration. BCG and successful new TB vaccines should always increase host resistance to TB in naive subjects. This is a basic immunological principle. The efficacies of new and old TB vaccines are often not recognized, because these variations were not identified in the populations evaluated.

Progress in Oral Vaccination against Tuberculosis in Its Main Wildlife Reservoir in Iberia, the Eurasian Wild Boar

Eurasian wild boar (Sus scrofa) is the main wildlife reservoir for tuberculosis (TB) in Iberia. This review summarizes the current knowledge on wild boar vaccination including aspects of bait design, delivery and field deployment success; wild boar response to vaccination with Bacillus Calmette-Guérin (BCG) and inactivated Mycobacterium bovis; and wild boar vaccination biosafety issues as well as prospects on future research. Oral vaccination with BCG in captive wild boar has shown to be safe with significant levels of protection against challenge with virulent M. bovis. An oral vaccination with a new heat-killed M. bovis vaccine conferred a protection similar to BCG. The study of host-pathogen interactions identified biomarkers of resistance/susceptibility to tuberculosis in wild boar such as complement component 3 (C3) and methylmalonyl coenzyme A mutase (MUT) that were used for vaccine development. Finally, specific delivery systems were developed for bait-containing vaccines to target different age groups. Ongoing research includes laboratory experiments combining live and heat-killed vaccines and the first field trial for TB control in wild boar.

Immune markers and correlates of protection for vaccine induced immune responses

Vaccines have been a major innovation in the history of mankind and still have the potential to address the challenges posed by chronic intracellular infections including tuberculosis, HIV and malaria which are leading causes of high morbidity and mortality across the world. Markers of an appropriate humoral response currently remain the best validated correlates of protective immunity after vaccination. Despite advancements in the field of immunology over the past few decades currently there are, however, no sufficiently validated immune correlates of vaccine induced protection against chronic infections in neither human nor veterinary medicine. Technological and conceptual advancements within cell-mediated immunology have led to a number of new immunological read-outs with the potential to emerge as correlates of vaccine induced protection. For T(H)1 type responses, antigen-specific production of interferon-gamma (IFN-γ) has been promoted as a quantitative marker of protective cell-mediated immune responses over the past couple of decades. More recently, however, evidence from several infections has pointed towards the quality of the immune response, measured through increased levels of antigen-specific polyfunctional T cells capable of producing a triad of relevant cytokines, as a better correlate of sustained protective immunity against this type of infections. Also the possibilities to measure antigen-specific cytotoxic T cells (CTL) during infection or in response to vaccination, through recombinant major histocompatibility complex (MHC) class I tetramers loaded with relevant peptides, has opened a new vista to include CTL responses in the evaluation of protective immune responses. Here, we review different immune markers and new candidates for correlates of a protective vaccine induced immune response against chronic infections and how successful they have been in defining the protective immunity in human and veterinary medicine.

Comparative tuberculosis (TB) prevention effectiveness in children of Bacillus Calmette-Guérin (BCG) vaccines from different sources, Kazakhstan

BACKGROUND

Except during a 1-year period when BCG vaccine was not routinely administered, annual coverage of infants with Bacillus Calmette-Guérin (BCG) in Kazakhstan since 2002 has exceeded 95%. BCG preparations from different sources (Japan, Serbia, and Russia) or none were used exclusively in comparable 7-month time-frames, September through March, in 4 successive years beginning in 2002. Our objective was to assess relative effectiveness of BCG immunization.

METHODS/FINDINGS

We compared outcomes of birth cohorts from the 4 time-frames retrospectively. Three cohorts received vaccine from one of three manufacturers exclusively, and one cohort was not vaccinated. Cohorts were followed for 3 years for notifications of clinical TB and of culture-confirmed TB, and for 21 months for TB meningitis notifications. Prevention effectiveness based on relative risk of TB incidence was calculated for each vaccinated cohort compared to the non-vaccinated cohort. Although there were differences in prevention effectiveness observed among the three BCG vaccines, all were protective. The Japanese vaccine (currently used in Kazakhstan), the Serbian vaccine, and the Russian vaccine respectively were 69%, 43%, and 22% effective with respect to clinical TB notifications, and 92%, 82%, and 51% effective with respect to culture confirmed TB. All three vaccines were >70% effective with respect to TB meningitis.

LIMITATIONS

Potential limitations included considerations that 1) the methodology used was retrospective, 2) multiple risk factors could have varied between cohorts and affected prevention effectiveness measures, 3) most cases were clinically diagnosed, and TB culture-positive case numbers and TB meningitis case numbers were sparse, and 4) small variations in reported population TB burden could have affected relative risk of exposure for cohorts.

CONCLUSIONS/SIGNIFICANCE

All three BCG vaccines evaluated were protective against TB, and prevention effectiveness varied by manufacturer. When setting national immunization policy, consideration should be given to prevention effectiveness of BCG preparations.

Immunological biomarkers of tuberculosis

Currently there are no sufficiently validated biomarkers to aid the evaluation of new tuberculosis vaccine candidates, the improvement of tuberculosis diagnostics or the development of more effective and shorter treatment regimens. To date, the detection of Mycobacterium tuberculosis or its products has not been able to adequately address these needs. Understanding the interplay between the host immune system and M. tuberculosis may provide a platform for the identification of suitable biomarkers, through both unbiased and targeted hypothesis-driven approaches. Here, we review immunological markers, their relation to M. tuberculosis infection stages and their potential use in the fight against tuberculosis.

Tuberculosis knowledge, attitudes, and beliefs in foreign-born and US-born patients with latent tuberculosis infection

Foreign-born individuals comprise the majority of patients treated for latent tuberculosis infection (LTBI) in the US. It is important to understand this population's tuberculosis-related knowledge, attitudes, and beliefs (KAB) as they may affect treatment acceptance and completion. KAB in 84 US-born and 167 foreign-born LTBI patients enrolled in a clinical trial assessing treatment completion at an urban public hospital were assessed at baseline. Demographic and substance use information was also collected.

RESULTS

Of 251 participants, 66.5% were foreign-born. While misconceptions existed among both US and foreign-born regarding transmission and contagiousness of LTBI, overall knowledge scores did not differ significantly between groups. With respect to attitudinal factors, foreign-born participants were less likely to acknowledge that they had LTBI and felt more "protected" from developing TB. Improved understanding of foreign-born patients' KAB may contribute to the reduction of barriers to treatment and improved outcomes.

Perspectives on clinical and preclinical testing of new tuberculosis vaccines

This review hopes to improve the selection of new tuberculosis (TB) vaccines by providing several perspectives on the immunization of humans, mice, guinea pigs, rabbits, and monkeys which have not usually been considered. (i) In human TB vaccine trials, the low rate of healing of Mycobacterium bovis BCG lesions (used as the control group) would distinguish individuals who might be helped by vaccination from the 95% who do not need it and would make these trials more conclusive. (ii) The rabbit immune response to Mycobacterium tuberculosis is much more effective in arresting tuberculosis than those of other laboratory animals, so pulmonary tubercle counting in rabbits should be included in all preclinical TB vaccine testing. (iii) Both delayed-type hypersensitivity (DTH) and cell-mediated immunity (CMI) are necessary to control the growth of M. tuberculosis. The testing of new TB vaccines in mice or in guinea pigs may not detect important antigens needed for human immunization. Mice respond poorly to tuberculin-like antigens that cause DTH. Guinea pigs respond poorly to antigens that cause CMI. Rabbits and humans respond well to both DTH and CMI antigens. Since monkeys are very susceptible to M. tuberculosis, they may not be as useful as rabbits for preclinical vaccine evaluation. (iv) Critical antigens (possibly ESAT-6 or CFP-10) might increase the immunity of the host to a greater extent than that produced by a natural M. tuberculosis infection and therefore would be useful in both prophylaxis and immunotherapy. Such critical antigens would increase the host's ability to neutralize key components of M. tuberculosis that enable it to survive in both laboratory animals and humans.

Oral delivery of BCG Moreau Rio de Janeiro gives equivalent protection against tuberculosis but with reduced pathology compared to parenteral BCG Danish vaccination

There is a need for an improved vaccine to better control human tuberculosis (TB), as the only currently available TB vaccine, bacillus Calmette-Guerin (BCG) delivered parenterally, offers variable levels of efficacy. Therefore, recombinant strains expressing additional antigens are being developed alongside alternative routes to parenteral delivery. There is strong evidence that BCG Moreau (RdJ) is a safe and effective vaccine in humans when given by the oral route. This study compared the efficacy of a single oral dose of wild type BCG Moreau Rio de Janeiro (RdJ), or a recombinant RdJ strain expressing Ag85B-ESAT6 fusion protein, formulated with and without lipid to enhance oral delivery, with subcutaneous BCG Danish 1331 and saline control groups in a guinea pig aerosol infection model of pulmonary tuberculosis. Protection was measured as survival at 30 weeks post-challenge and reduced bacterial load and histopathology in lungs and spleen. Results showed that a single oral dose of BCG Moreau (RdJ) or recombinant BCG Moreau (RdJ)-Ag85B-ESAT6, formulated with or without lipid, gave protection equivalent to subcutaneously delivered BCG Danish in the 30 weeks post-challenge survival study. The orally delivered vaccines gave reduced pathology scores in the lungs (three of the four formulations) and spleens (all four formulations) compared to subcutaneously delivered BCG Danish. The oral wild type BCG Moreau (RdJ) in lipid and the unformulated oral wild type BCG Moreau (RdJ) vaccine also gave statistically lower bacterial loads in the lungs and spleens, respectively, compared to subcutaneously delivered BCG Danish. This study provides further evidence to show that lipid formulation does not impair vaccine efficacy and may enhance the delivery and stability of oral vaccines intended for use in countries with poor health infrastructure. Oral delivery also avoids needles (and associated cross-infection risks) and immunisation without the need for specially trained medical professional staff.

Do antenatal parasite infections devalue childhood vaccination?

On a global basis, both potent vaccine efficacy and high vaccine coverage are necessary to control and eliminate vaccine-preventable diseases. Emerging evidence from animal and human studies suggest that neglected tropical diseases (NTDs) significantly impair response to standard childhood immunizations. A review of efficacy and effectiveness studies of vaccination among individuals with chronic parasitic infections was conducted, using PUBMED database searches and analysis of data from the authors' published and unpublished studies. Both animal models and human studies suggest that chronic trematode, nematode, and protozoan infections can result in decreased vaccine efficacy. Among pregnant women, who in developing countries are often infected with multiple parasites, soluble parasite antigens have been shown to cross the placenta and prime or tolerize fetal immune responses. As a result, antenatal infections can have a significant impact on later vaccine responses. Acquired childhood parasitic infections, most commonly malaria, can also affect subsequent immune response to vaccination. Additional data suggest that antiparasite therapy can improve the effectiveness of several human vaccines. Emerging evidence demonstrates that both antenatal and childhood parasitic infections alter levels of protective immune response to routine vaccinations. Successful antiparasite treatment may prevent immunomodulation caused by parasitic antigens during pregnancy and early childhood and may improve vaccine efficacy. Future research should highlight the varied effects that different parasites (alone and in combination) can have on human vaccine-related immunity. To optimize vaccine effectiveness in developing countries, better control of chronic NTDs may prove imperative.

Novel genome polymorphisms in BCG vaccine strains and impact on efficacy

Bacille Calmette-Guérin (BCG) is an attenuated strain of Mycobacterium bovis currently used as a vaccine against tuberculosis. Global distribution and propagation of BCG has contributed to the in vitro evolution of the vaccine strain and is thought to partially account for the different outcomes of BCG vaccine trials. Previous efforts by several molecular techniques effectively identified large sequence polymorphisms among BCG daughter strains, but lacked the resolution to identify smaller changes. In this study, we have used a NimbleGen tiling array for whole genome comparison of 13 BCG strains. Using this approach, in tandem with DNA resequencing, we have identified six novel large sequence polymorphisms including four deletions and two duplications in specific BCG strains. Moreover, we have uncovered various polymorphisms in the phoP-phoR locus. Importantly, these polymorphisms affect genes encoding established virulence factors including cell wall complex lipids, ESX secretion systems, and the PhoP-PhoR two-component system. Our study demonstrates that major virulence factors are different among BCG strains, which provide molecular mechanisms for important vaccine phenotypes including adverse effect profile, tuberculin reactivity and protective efficacy. These findings have important implications for the development of a new generation of vaccines.

Differential productions of lipid virulence factors among BCG vaccine strains and implications on BCG safety

Safety of BCG is a major concern in countries with a high burden of HIV/AIDS. Current BCG vaccine comprises of a heterogeneous group of substrains showing genotypic differences. The impact of these differences on BCG efficacy and safety remains unknown. Here we show that three BCG substrains, BCG-Japan, -Moreau, and -Glaxo, do not produce phthiocerol dimycocerosates (PDIMs) and phenolic glycolipids (PGLs), two cell wall lipids known to be important for the virulence of Mycobacterium tuberculosis and Mycobacterium bovis, suggesting that these BCG strains are more attenuated than others. We found that there is a good correlation between the ability of BCG strains to produce these two lipids and the propensity of BCG to induce complications following vaccination in children, which provides a partial explanation for the molecular mechanisms of BCG reactogenicity. Our finding has important implications for national immunization programmes particularly in HIV endemic countries. We suggest that PDIMs/PGLs analysis could offer a practical means for assessing the safety of various BCG vaccine strains currently used in the world.

Immune function in young children with previous pulmonary or miliary/meningeal tuberculosis and impact of BCG vaccination

OBJECTIVE

Children <5 years old are at increased risk of miliary/meningeal tuberculosis, but the immunologic factors that place them at risk are unknown. BCG vaccine protects against miliary/meningeal tuberculosis, but the mechanism of protection is unknown. We assessed for abnormalities in immune response associated with miliary/meningeal or pulmonary tuberculosis in young children.

PATIENTS AND METHODS

We conducted a case-control study among HIV-seronegative Brazilian children who were <5 years old. Case subjects had previous culture-confirmed or clinical miliary/meningeal tuberculosis. There were 2 sets of control subjects: those with culture-confirmed pulmonary tuberculosis and purified protein derivative-positive household contacts. All of the children had completed treatment. Peripheral blood mononuclear cells were stimulated (phytohemagglutinin, phytohemagglutinin + interleukin 12, lipopolysaccharide, lipopolysaccharide + interferon-gamma, and purified protein derivative), and cytokine responses (interleukin 1beta, interleukin-4, interleukin-6, interleukin-8, interleukin 10, interleukin 12, interferon-gamma, tumor necrosis factor-alpha, and monocyte chemoattractant protein 1) were quantified by bead-based assay. Median cytokine responses were compared by the Kruskal-Wallis test. Multivariate analysis of variance accounted for multiple comparisons.

RESULTS

There were 18 case subjects with miliary/meningeal tuberculosis, 28 pulmonary control subjects, and 29 purified protein derivative-positive control subjects. The median age was 4.2 years. There was no difference in case and control subjects by age, gender, race, BMI, or median CD4 count. Twelve (67%) of 18 case subjects, 26 (93%) of 28 pulmonary control subjects, and 28 (97%) of 29 purified protein derivative-positive subjects had received BCG vaccine. No cytokine defects were identified in case subjects with miliary/meningeal tuberculosis compared with either set of control subjects. Pulmonary control subjects had uniformly higher monocyte chemoattractant protein 1 levels than case subjects with miliary/meningeal tuberculosis and purified protein derivative-positive control subjects, both at rest and with lipopolysaccharide, lipopolysaccharide + interferon-gamma, and purified protein derivative stimulation. Pulmonary control subjects did not have a higher frequency of allele G in the -2518 monocyte chemoattractant protein 1 promoter polymorphism. Case subjects with miliary/meningeal tuberculosis who had received BCG vaccine (n = 12) had lower stimulated interleukin 8 production than children who did not receive BCG vaccine (n = 6).

CONCLUSIONS

Children with previous miliary/meningeal tuberculosis did not have a major defect in the cytokine pathways studied. Increased monocyte chemoattractant protein 1 levels were associated with pulmonary disease, occurred despite BCG vaccination, and were not associated with a polymorphism in the monocyte chemoattractant protein 1 promoter.

Childhood tuberculosis: old and new vaccines

The world is witnessing an escalation of the tuberculosis (TB) epidemic, particularly in sub-Saharan Africa and South-East Asia. The problem has been compounded by the evolution of the human immunodeficiency virus pandemic, the increase in multidrug-resistant TB and the emergence of extensively drug-resistant TB. This has led to renewed interest in vaccines aimed at preventing tuberculosis. The current Bacille Calmette-Guérin (BCG) vaccine prevents the invasive complications of childhood tuberculosis, such as meningitis and miliary disease, but provides variable protection against adult pulmonary disease. This review discusses the history of the BCG vaccine, the reasons for its variable efficacy, protective immunity and TB, and the evolution of and obstacles to development of new candidate vaccines. Several new TB vaccines have demonstrated promising results in animal models; a number have gone into phase I clinical trials in humans, and it is anticipated that phase III trials will commence by 2009. Licensing of an effective new TB vaccine by 2015 is thus a possibility.

Tuberculin reaction, BCG scar, and lower female mortality

BACKGROUND

Recent studies have suggested that bacille Calmette-Guérin (BCG) immunization may have a nonspecific beneficial effect on infant survival and that the effect may be more pronounced among girls. In a prospective birth cohort, we examine whether a positive tuberculin skin test and BCG scar in response to BCG immunization were related to better overall survival in Guinea-Bissau and, if so, whether the effect was sex-specific.

METHODS

Skin tests and BCG scarring were monitored at ages 2 months (n = 2332) and 6 months (n = 1817) in children born from March 2000 to July 2002. A tuberculosis (TB) surveillance system allowed us to exclude from the analysis children with likely TB exposure. The children were followed for survival until 18 months of age.

RESULTS

Among children with a tuberculin skin test at 2 and 6 months of age, the mortality rate ratio for skin test reactors (>1 mm) versus nonreactors (0-1 mm) was 0.54 (95% confidence interval = 0.30-0.99). Comparing children with and without a BCG scar, the ratio was 0.55 (0.31-0.96). The effect of a skin test reaction or a BCG scar seemed stronger among girls; for those with positive reaction, the mortality ratio was 0.31 (0.11-0.88) among girls and 0.84 (0.39-1.82) among boys; and for BCG scar, the results were 0.41 (0.21-0.82) and 0.88 (0.34-2.30), respectively.

CONCLUSIONS

A good response to BCG vaccination is related to lower child mortality. The effect seems most pronounced among girls. The findings may have implications for future vaccine trials and policy.

The emergence of Beijing family genotypes of Mycobacterium tuberculosis and low-level protection by bacille Calmette-Guérin (BCG) vaccines: is there a link?

The world is confronted with major tuberculosis (TB) outbreaks at a time when the protection of bacillus Calmette-Guérin (BCG) vaccine has become inconsistent and controversial. Major TB outbreaks are caused by a group of genetically similar strains of Mycobacterium tuberculosis (Mtb) strains, including the Beijing family genotypes. The Beijing family genotypes exhibit important pathogenic features such high virulence, multi-drug resistance and exogenous reinfection. These family strains have developed mechanisms that modulate/suppress immune responses by the host, such as inhibition of apoptosis of infected macrophages, diminished production of interleukin (IL)-2, interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha and elevated levels of IL-10 and IL-18. They demonstrate distinct expression of proteins, such as several species of alpha-crystallin (a known Mtb virulence factor), but decreased expression of some antigens such as heat shock protein of 65 kDa, phosphate transport subunit S and a 47-kDa protein. In addition, the Beijing family strains specifically produce a highly bioactive lipid (a polyketide synthase)-derived phenolic glycolipid. This altered expression of proteins/glycolipids may be important factors underlying the success of the Beijing family strains. The Beijing family strains are speculated to have originated from South-east Asia, where BCG vaccination has been used for more than 60 years. The hypothesis that mass BCG vaccination may have been a selective factor that favoured genotypic and phenotypic characteristic acquired by the Beijing family strains is discussed.

Bacillus Calmette-Guérin vaccination and infant mortality

When the bacillus Calmette-Guérin (BCG) vaccine was introduced in the 1920s, it was suggested that BCG occasionally had nonspecific beneficial effects on mortality beyond the specific protection against tuberculosis. Considering that BCG has since then become the most used vaccine in the world, surprisingly few studies have been undertaken into the effect of BCG on general mortality and morbidity. Recent studies suggest that BCG has beneficial nontargeted effects on general infant morbidity and mortality in low-income countries, often with the most pronounced effect among girls. These observational findings are supported by early trials in which children were randomized or alternated to BCG vaccination. Furthermore, a BCG scar and a positive tuberculin reaction are related to better survival among BCG-vaccinated children in low-income countries, especially for girls. The findings are not explained by frailty bias, in other words, that healthy children are more likely to receive BCG vaccination. A nonspecific, gender-differential effect of BCG on general infant mortality may have large implications for tuberculosis vaccine research and routine vaccination policy.

Advances in tuberculosis vaccine strategies

Tuberculosis (TB), an ancient human scourge, is a growing health problem in the developing world. Approximately two million deaths each year are caused by TB, which is the leading cause of death in HIV-infected individuals. Clearly, an improved TB vaccine is desperately needed. Heterologous prime-boost regimens probably represent the best hope for an improved vaccine regimen to prevent TB. This first generation of new vaccines might also complement drug treatment regimens and be effective against reactivation of TB from the latent state, which would significantly enhance their usefulness.

Effect of BCG vaccination on childhood tuberculous meningitis and miliary tuberculosis worldwide: a meta-analysis and assessment of cost-effectiveness

BACKGROUND

BCG vaccine has shown consistently high efficacy against childhood tuberculous meningitis and miliary tuberculosis, but variable efficacy against adult pulmonary tuberculosis and other mycobacterial diseases. We assess and compare the costs and effects of BCG as an intervention against severe childhood tuberculosis in different regions of the world.

METHODS

We calculated the number of tuberculous meningitis and miliary tuberculosis cases that have been and will be prevented in all children born in 2002, by combining estimates of the annual risk of tuberculosis infection, the proportion of infections that lead to either of these diseases in unvaccinated children, the number of children vaccinated, and BCG efficacy.

FINDINGS

We estimated that the 100.5 million BCG vaccinations given to infants in 2002 will have prevented 29,729 cases of tuberculous meningitis (5th-95th centiles, 24,063-36,192) in children during their first 5 years of life, or one case for every 3435 vaccinations (2771-4177), and 11,486 cases of miliary tuberculosis (7304-16,280), or one case for every 9314 vaccinations (6172-13,729). The numbers of cases prevented would be highest in South East Asia (46%), sub-Saharan Africa (27%), the western Pacific region (15%), and where the risk of tuberculosis infection and vaccine coverage are also highest. At US2-3 dollars per dose, BCG vaccination costs US206 dollars (150-272) per year of healthy life gained.

INTERPRETATION

BCG vaccination is a highly cost-effective intervention against severe childhood tuberculosis; it should be retained in high-incidence countries as a strategy to supplement the chemotherapy of active tuberculosis.

Vaccination technique, PPD reaction and BCG scarring in a cohort of children born in Guinea-Bissau 2000-2002

The rates of positive tuberculin skin test (TST) reactions and BCG scarring after BCG vaccination vary between studies and populations. Tuberculin reactivity and BCG scarring may be related to better child survival in low-income countries. We therefore studied determinants for TST reaction and scarring in Guinea-Bissau. In a cohort of children born in suburban Bissau from March 2000 to July 2002, we assessed a Mantoux test with Purified protein derivative (PPD) (SSI, 2 T.U.) at 2 (2689 children), 6 (N=2148) and 12 months (N=1638) of age, and BCG scar was assessed at 2 (N=2698) and 6 months (N=2225) of age. In a subgroup of the children the vaccination technique was monitored by direct observation of post-vaccination wheal and route of administration. Three different types of BCG vaccine supplied by the local Extended Programme on Immunization were used. At 6 months of age the rate of PPD reactors (>1mm) after BCG vaccination was 25% and the rate of scarring was 89%. One BCG strain was associated with fewer PPD reactors (OR=0.54 (0.31-0.91)) and BCG scars (OR=0.13 (0.05-0.37)) and larger post-vaccination wheals produced more PPD reactions (OR 1.21 (95% CI 1.02-1.43)) and BCG scars (OR 1.66 (1.24-2.21)). In the multivariable analyses of BCG-vaccinated children assessed at 6 months of age, monitoring of vaccination technique and type of BCG vaccine were important. This was not changed by control for other determinants, including sex, season, vaccination place, birthplace, ethnic group, low birth weight, place of residence, education and civil status of mother. We reason that vaccination technique and BCG strain are important for PPD reaction and scarring in response to BCG vaccination. Considering that these responses are associated with better infant survival, the importance of monitoring vaccination technique and of different BCG strains should be evaluated with respect to infant mortality.

The reinfection threshold promotes variability in tuberculosis epidemiology and vaccine efficacy

Population patterns of infection are determined largely by susceptibility to infection. Infection and vaccination induce an immune response that, typically, reduces susceptibility to subsequent infections. With a general epidemic model, we detect a 'reinfection threshold', above which reinfection is the principal type of transmission and, consequently, infection levels are much higher and vaccination fails. The model is further developed to address human tuberculosis (TB) and the impact of vaccination. The bacille Calmette-Guérin (BCG) is the only vaccine in current use against TB, and there is no consensus about its usefulness. Estimates of protection range from 0 to 80%, and this variability is aggravated by an association between low vaccine efficacy and high prevalence of the disease. We propose an explanation based on three postulates: (i) the potential for transmission varies between populations, owing to differences in socio-economic and environmental factors; (ii) exposure to mycobacteria induces an immune response that is partially protective against reinfection; and (iii) this protection is not significantly improved by BCG vaccination. These postulates combine to reproduce the observed trends, and this is attributed to a reinfection threshold intrinsic to the transmission dynamics. Finally, we demonstrate how reinfection thresholds can be manipulated by vaccination programmes, suggesting that they have a potentially powerful role in global control.

Impact of methoxymycolic acid production by Mycobacterium bovis BCG vaccines

BCG vaccines are a family of closely related daughter strains of an attenuated isolate of Mycobacterium bovis derived by in vitro passage from 1908 to 1921. During subsequent laboratory propagation of the vaccine strain until its lyophilization in 1961, BCG Pasteur underwent at least seven further genomic mutations. The impact of these mutations on the properties of the vaccine is currently unknown. One mutation, a glycine-to-aspartic acid substitution in the mmaA3 gene, occurred between 1927 and 1931 and impairs methoxymycolic acid synthesis in BCG strains obtained from the Pasteur Institute after this period. Mycolic acids of the cell wall are classified into three functional groups (alpha-, methoxy-, and ketomycolic acids), and together these lipids form a highly specialized permeability barrier around the bacterium. To explore the impact of methoxymycolic acid production by BCG strains, we complemented the functional gene of mmaA3 into BCG Denmark and tested a number of in vitro and in vivo phenotypes. Surprisingly, restoration of methoxymycolic acids alone had no effect on cell wall permeability, resistance to antibiotics, or growth in cultured macrophages and C57BL/6 mice. Our results demonstrate that the loss of methoxymycolic acid production did not apparently affect the virulence of BCG strains.

Cultivation of Mycobacterium bovis BCG in bioreactors

The Mycobacterium bovis BCG vaccine for commercial use is classically produced as surface pellicles by culture on synthetic medium. Under these conditions, reproducibility of the cultures and quality assessment are hampered by slow growth of the bacilli, the formation of bacterial aggregates and a high proportion of dead bacilli after processing and final formulation of the vaccine. Here, we established dispersed cultures of M. bovis BCG in synthetic media in small-scale bioreactors. These cultures allow recording and adjusting of culture parameters and give rise to single bacilli with a high degree of live bacteria. In the murine model, bioreactor-grown M. bovis BCG exhibited slightly stronger replication and persistence than the vaccine produced under the classical conditions. The protective efficacy against challenge with M. tuberculosis was identical for both vaccine preparations.

Naturally attenuated, orally administered Mycobacterium microti as a tuberculosis vaccine is better than subcutaneous Mycobacterium bovis BCG

Mycobacterium microti is phylogenetically closely related to Mycobacterium tuberculosis and is a member of that complex of organisms. It is a curved, acid-fast bacillus that is naturally attenuated with a narrow host range for Microtus species only. In this study, we confirm the unique susceptibility of voles to infection with M. microti and the relative resistance of mice with a significantly lower organism burden after 8 weeks of infection. In addition, histopathologic examination of lungs reveals a lack of cellular, granulomatous aggregates characteristically seen in murine M. tuberculosis infection. In the past, M. microti has been used successfully in humans as a vaccine against tuberculosis but was associated with cutaneous reactions. In an attempt to circumvent this adverse effect, we report the efficacy of aerosol and oral vaccination with M. microti. High-dose orogastric vaccination with M. microti resulted in a statistically significant improvement in protection against aerosol challenge with virulent M. tuberculosis in the murine model compared with subcutaneous M. bovis BCG Pasteur vaccination.

Beneficial impact of genome projects on tuberculosis control

The M. tuberculosis genome project is a landmark achievement in the history of TB research. The DNA sequence has provided valuable insights, along with a few surprises, into the complete genetic complement of M. tuberculosis. This information has been used to gain a better understanding of isoniazid-induced alteration in gene expression. It also has been used to construct a genealogy tree of different BCG strains, besides identifying genes that may be responsible for the human-specificity of M. tuberculosis. The impact of this project is far-reaching and in the next few years should yield innovative vaccines and therapeutic agents, besides aiding in the rapid and accurate diagnosis of TB.

BCG--different strains, different vaccines?

After nearly a century of use, BCG vaccines continue to generate controversy and confusion. Their ability to prevent tuberculosis in studies has been inconsistent. When they have been protective, no clear mechanism of action has been established. Furthermore, the existence of different BCG strains has been described since the 1940s. These strains vary according to several laboratory properties, which may or may not translate into a discernible effect on vaccination. With recent genomic comparisons, it is now clear that different BCG vaccine strains have evolved and differ from each other and from the original BCG first used in 1921. Some of these genetic alterations explain certain variations in laboratory properties of BCG. However, these mutations in BCG strains have yet to be shown to affect BCG-associated protection and/or adverse effects. Continuing research is attempting to assess the effect of these genetic alterations on properties of BCG strains, with the goals of suggesting the ideal BCG for vaccination and providing avenues for improvement on existing BCG vaccines.

Determinants of vaccine-induced resistance in animal models of pulmonary tuberculosis

A more effective vaccine will be essential if the global tuberculosis (TB) pandemic is ever to be controlled. A large number of new tuberculosis vaccines have been developed, representing the whole range of modern strategies for vaccine formulation and delivery. There is currently no alternative to testing these new vaccines in experimental animals challenged with virulent Mycobacteriurn tuberculosis in order to assess their protective efficacy. Although such testing is being carried out in several animal species (mice, guinea pigs, rabbits), all rational models include pulmonary challenge with a low dose of virulent mycobacteria. The quantitative measures for TB vaccines include increased survival, amelioration of clinical signs and symptoms (e.g. prevention of weight loss), decreased lesion size, reduction in bacillary loads in the lungs, and prevention of extrapulmonary dissemination and hematogenous reseeding of the lung. Although the ultimate objective of vaccination in humans is to prevent transmission to susceptible contacts, no such measurement is being used in animal studies of new vaccines. The validation of an immunological "correlate of protection" is urgently needed. Candidates for such a correlate include antigen-specific interferon-gamma production by T cells of the memory phenotype (CD45RB(high) or mycobacterial killing by macrophages co-cultured with immune T cells. Additional animal models must be developed for vaccines designed to prevent endogenous reactivation or exogenous reinfection, or to be used as a adjunct to chemotherapy.

A single strain of Mycobacterium bovis bacillus Calmette-Guérin (BCG) grown in two different media evokes distinct humoral immune responses in mice

Two attenuated bacillus Calmette-Guérin (BCG) preparations derived from the same Moreau strain, Copenhagen but grown in Sauton medium containing starch and bacto-peptone (onco BCG, O-BCG), or asparagine (intradermal BCG, ID-BCG), exhibited indistinguishable DNA sequences and bacterial morphology. The number of viable bacilli recovered from spleen, liver and lungs was approximately the same in mice inoculated with the vaccines and was similarly reduced (over 90%) in mice previously immunized with either BCG vaccine. The humoral immune response evoked by the vaccines was, however, distinct. Spleen cell proliferation accompanying the growth of bacilli in tissue was significantly higher in mice inoculated with O-BCG. These cells proliferated in vitro upon challenge with the corresponding BCG extract. Previous cell treatment with mAb anti-CD4 T cells abolished this effect. Anti-BCG antibodies, as assayed either in serum by ELISA or by determining the number of antibody-producing spleen cells by the spot-ELISA method, were significantly higher in mice inoculated with ID-BCG. Anti-BCG antibodies were detected in all immunoglobulin classes, but they were more prevalent in IgG with the following distribution among its isotypes: IgG1>(IgG2a = IgG2b)>IgG3. When some well-characterized Mycobacterium tuberculosis antigens were used as substitutes for BCG extracts in ELISA, although antibodies against the 65-kDa and 96-kDa proteins were detected significantly, antibodies against the 71-kDa, 38-kDa proteins and lipoarabinomannan were only barely detected or even absent. These results indicate that BCG bacilli cultured in Sauton-asparagine medium permitted the multiplication of bacilli, tending to induce a stronger humoral immune response as compared with bacilli grown in Sauton-starch/bacto-peptone-enriched medium.

Efficacies of BCG and vole bacillus (Mycobacterium microti) vaccines in preventing clinically apparent pulmonary tuberculosis in rabbits: a preliminary report

Tuberculosis (TB) kills more people in the world today than any other infectious disease, and the number of drug-resistant Mycobacterium tuberculosis isolates is increasing. Vaccines, better than most of the currently available strains of bacille Calmette-Guérin (BCG), are urgently needed to control this disease. TB in rabbits resembles human TB more closely than TB in any other common laboratory animal and a most pertinent method of assessing vaccine efficacy is Lurie's tubercle count method in this species. Vaccinated and control rabbits were infected by aerosol with virulent human-type tubercle bacilli (H37Rv). At necropsy 5 weeks thereafter, the grossly visible primary tubercles in the entire lung were counted. A decrease in the number of such tubercles is a quantitative measure of vaccine efficacy: An effective vaccine prevents microscopic tubercles from growing to grossly visible (clinically apparent) size. The Pasteur substrain of BCG and two substrains of Mycobacterium microti (the vole bacillus) reduced the number of visible primary tubercles an average of 75%, whereas three other substrains of BCG and three other substrains of vole bacilli only reduced the number an average of 40%. These initial studies indicate that Lurie's tubercle-count method in rabbits is a precise way to choose the best available tuberculosis vaccines.

Mycobacterium bovis BCG induces similar immune responses and protection by rectal and parenteral immunization routes

We compared cellular immune responses to rectal, subcutaneous, and intradermal administration of Mycobacterium bovis BCG for 5 to 20 weeks in mice, guinea pigs, and macaques. Strong lymphoproliferative responses were induced in spleen cells after in vitro stimulation with purified protein derivative in guinea pigs and macaques, whatever the route of immunization. Comparable high numbers of gamma interferon- and tumor necrosis factor alpha-producing cells were found in the spleen after rectal, subcutaneous, and intradermal immunization of mice and macaques. Similar levels of precursors of cytotoxic T lymphocytes specific for mycobacterial antigens were observed in mice for all immunization routes. In macaques, cytotoxic activity, determined only at the end of the experiment (20 weeks), was similar after rectal and intradermal immunization. Six months after immunization, rectal and subcutaneous routes induced in mice similar levels of protective immunity against challenge with a virulent Mycobacterium tuberculosis strain (H37Rv). Rectal immunization gave immune responses and protective capacity similar to those for parenteral immunization and seemed to be a promising new route of vaccination against tuberculosis; in our study, immunization via the rectal route never induced side effects associated with parenteral routes (axillary adenitis) and could also effectively reduce the risks of viral transmission associated with unsafe injections in the developing world.

Mycobacterium tuberculosis-secreted protein antigens: immunogenicity in baboons

The effective control of tuberculosis (TB) requires the development of improved vaccines. It is now well established that Mycobacterium tuberculosis-secreted antigens represent promising candidates to be included in subunit vaccine preparations. It also is accepted that studies in nonhuman primate models will be required to further develop these vaccine preparations. As a necessary step in this direction, we have assessed the immunogenicity of M. tuberculosis-secreted antigens in baboons. Animals received a total of three intramuscular injections consisting of M. tuberculosis culture filtrate proteins resuspended in an adjuvant formulation (MPL-SE) and were tested for development of specific antibody and cellular responses. All animals produced antibody and cellular proliferative responses in the absence of detectable delayed-type hypersensitivity reactions. Production of gamma-interferon following stimulation of peripheral blood lymphocytes with culture filtrate proteins was either absent or present at low levels. Results from this study show that, although M. tuberculosis-secreted protein antigens are relatively safe and immunogenic in baboons, alternative immunization approaches must be identified for the induction of T-helper type 1 responses.

Simple, practical ways to assess the protective efficacy of a new tuberculosis vaccine

There is strong evidence that tuberculin sensitivity cannot be used to evaluate the efficacy of different strains of bacille Calmette-Guérin (BCG). For identifying efficacious strains of BCG and evaluating candidates for new vaccines, the best method is a randomized trial. Simple trials in which newborns would be vaccinated with new and old vaccines in alternate years could demonstrate which vaccine was the better.