The impact of maternal infection with Mycobacterium tuberculosis on the infant response to bacille Calmette-Guérin immunization

Maternal pertussis immunization and the blunting of routine vaccine effectiveness: a meta-analysis and modeling study

A key goal of pertussis control is to protect infants too young to be vaccinated, the age group most vulnerable to this highly contagious respiratory infection. In the last decade, maternal immunization has been deployed in many countries, successfully reducing pertussis in this age group. Because of immunological blunting, however, this strategy may erode the effectiveness of primary vaccination at later ages. Here, we systematically reviewed the literature on the relative risk (RR) of pertussis after primary immunization of infants born to vaccinated vs. unvaccinated mothers. The four studies identified had ≤6 years of follow-up and large statistical uncertainty (meta-analysis weighted mean RR: 0.71, 95% CI: 0.38-1.32). To interpret this evidence, we designed a new mathematical model with explicit blunting mechanisms and evaluated maternal immunization's short- and long-term impact on pertussis transmission dynamics. We show that transient dynamics can mask blunting for at least a decade after rolling out maternal immunization. Hence, the current epidemiological evidence may be insufficient to rule out modest reductions in the effectiveness of primary vaccination. Irrespective of this potential collateral cost, we predict that maternal immunization will remain effective at protecting unvaccinated newborns, supporting current public health recommendations.

Immune Responses Following BCG Immunization of Infants in Uganda and United Kingdom Are Similar for Purified Protein Derivative but Differ for Secretory Proteins of Mycobacterium tuberculosis

Introduction: The immunogenicity of BCG vaccination in infants differs between populations. We hypothesized that prenatal exposure to mycobacterial antigens might explain the differences in immune responses to BCG seen in other studies of infants in Africa and the United Kingdom (UK) and we explored this in birth cohorts in Uganda and the UK. Materials and Methods: Blood samples were obtained from BCG-immunized infants of mothers with (n = 110) and without (n = 121) latent Mycobacterium tuberculosis infection (LTBI) in Uganda and BCG-immunized infants of mothers without LTBI (n = 25) in the UK at 10 and 52 weeks after birth. Cytokine and chemokine responses to PPD were measured to assess responses to BCG immunization, and to ESAT6/CFP10 to assess exposure to or infection with M. tuberculosis or non-tuberculous mycobacteria (NTM) in 6-day whole blood culture supernatants by a 17-plex Luminex assay. Median responses were compared between Ugandan infants (together, and separated by maternal LTBI status) and UK infants. Results: The IFN-γ response to BCG vaccination was similar between Ugandan and UK infants at 10 and 52 weeks. At week 52, TNF production was marginally higher in Ugandan infants, but after adjusting for multiple comparisons this difference was not significant. At weeks 10 and 52, stimulation of blood with ESAT6/CFP10 produced significantly higher IFN-γ, TNF, IL-12p40, IL-1α, IL-1β, IL-1Ra, IP-10, MIP-1α, MIP-1β, and GM-CSF in Ugandan compared to UK infants. Stimulation of blood with ESAT6/CFP10 produced significantly higher amounts of IL-8 (p = 0.0001), IL-10 (p = 0.0022), and IL-13 (p = 0.0020) in the UK than in Ugandan infants of mothers without LTBI at week 10, but not at week 52. Conclusions: Immune responses to mycobacterial antigens following BCG immunization are similar for PPD, but differ for ESAT6/CFP10, between infants in Uganda and the UK. Neither maternal LTBI nor infant exposure to or infection with mycobacteria impacts the response to BCG. The observed global differences in immune response to BCG immunization are likely to be due to other causes.

The role of antibodies in Bacille Calmette Guérin-mediated immune responses and protection against tuberculosis in humans: A systematic review

BACKGROUND

The mechanisms underlying Bacille Calmette-Guérin (BCG) vaccine's protective effects against tuberculosis (TB) are incompletely understood but are proposed to involve a predominantly cell-mediated process. However, there is increasing evidence for the involvement of antibodies in the control of Mycobacteria tuberculosis and in the immune response to BCG.

METHODS

We did a systematic review of studies investigating anti-BCG antibodies in individuals with active or latent TB, and in the response to BCG vaccination.

RESULTS

Of 1417 articles screened, 70 were relevant, comprising 52 investigating anti-BCG antibodies in TB and 18 investigating the anti-BCG antibody response to BCG-vaccination. Individuals with active TB have higher levels of anti-BCG antibodies compared with individuals with latent TB or healthy individuals. Antibodies to BCG are present after BCG vaccination. There is some evidence for the in utero transfer of maternal anti-BCG antibodies to infants.

CONCLUSIONS

BCG vaccination induces a humoral response. Antibodies targeted against BCG and its antigens may play a role in protection against active TB.

Maternal Latent Mycobacterium tuberculosis Does Not Affect the Infant Immune Response Following BCG at Birth: An Observational Longitudinal Study in Uganda

Background: BCG has low efficacy in tropical countries. We hypothesized that maternal latent Mycobacterium tuberculosis (M.tb) infection (LTBI) results in fetal tolerance to mycobacterial antigens and impaired responses to BCG immunization.

Methods: We enrolled 132 LTBI-positive and 150 LTBI-negative mothers and their babies in Entebbe, Uganda. Infants were BCG-immunized at birth. Cord blood and samples at weeks 1, 4, 6, 10, 14, 24, and 52 were analyzed for cytokine/chemokine responses to M.tb antigens by Luminex 17-plex assay in 6-day whole blood cultures and antibody responses by ELISA. Of the 17 Luminex analytes, seven (IL-2, IL-5, IL-10, IL-13, IL-17A, TNF, and IFN-γ) were included in the main analysis as they were considered most likely to represent T cell responses. Immune sensitization was defined as a detectable cord blood cytokine response to PPD for any of the seven cytokines. Patterns of cytokine and antibody responses were compared between infants of mothers with and without LTBI using linear mixed models adjusting for confounders.

Results: Most infants (73%) were sensitized in utero to M.tb antigens, with no overall difference seen between infants born to mothers with or without LTBI. Patterns of post-BCG cytokine and antibody responses to mycobacterial antigens were similar between the two infant groups.

Conclusions: Our data do not support the hypothesis that maternal LTBI results in an impaired response to BCG immunization, in Ugandan infants. BCG vaccination at or shortly after birth is likely to be beneficial to all infants, irrespective of maternal LTBI status.

BCG as a Case Study for Precision Vaccine Development: Lessons From Vaccine Heterogeneity, Trained Immunity, and Immune Ontogeny

Vaccines have been traditionally developed with the presumption that they exert identical immunogenicity regardless of target population and that they provide protection solely against their target pathogen. However, it is increasingly appreciated that vaccines can have off-target effects and that vaccine immunogenicity can vary substantially with demographic factors such as age and sex. Bacille Calmette-Guérin (BCG), the live attenuated Mycobacterium bovis vaccine against tuberculosis (TB), represents a key example of these concepts. BCG vaccines are manufactured under different conditions across the globe generating divergent formulations. Epidemiologic studies have linked early life immunization with certain BCG formulations to an unanticipated reduction (∼50%) in all-cause mortality, especially in low birthweight males, greatly exceeding that attributable to TB prevention. This mortality benefit has been related to prevention of sepsis and respiratory infections suggesting that BCG induces "heterologous" protection against unrelated pathogens. Proposed mechanisms for heterologous protection include vaccine-induced immunometabolic shifts, epigenetic reprogramming of innate cell populations, and modulation of hematopoietic stem cell progenitors resulting in altered responses to subsequent stimuli, a phenomenon termed "trained immunity." In addition to genetic differences, licensed BCG formulations differ markedly in content of viable mycobacteria key for innate immune activation, potentially contributing to differences in the ability of these diverse formulations to induce TB-specific and heterologous protection. BCG immunomodulatory properties have also sparked interest in its potential use to prevent or alleviate autoimmune and inflammatory diseases, including type 1 diabetes mellitus and multiple sclerosis. BCG can also serve as a model: nanoparticle vaccine formulations incorporating Toll-like receptor 8 agonists can mimic some of BCG's innate immune activation, suggesting that aspects of BCG's effects can be induced with non-replicating stimuli. Overall, BCG represents a paradigm for precision vaccinology, lessons from which will help inform next generation vaccines.

Early BCG-Denmark and Neonatal Mortality Among Infants Weighing <2500 g: A Randomized Controlled Trial

Background

BCG vaccine may reduce overall mortality by increasing resistance to nontuberculosis infections. In 2 randomized trials in Guinea-Bissau of early BCG-Denmark (Statens Serum Institut) given to low-weight (LW) neonates (<2500 g at inclusion) to reduce infant mortality rates, we observed a very beneficial effect in the neonatal period. We therefore conducted the present trial to test whether early BCG-Denmark reduces neonatal mortality by 45%. We also conducted a meta-analysis of the 3 BCG-Denmark trials.

Methods

In 2008–2013, we randomized LW neonates to “early BCG-Denmark” (intervention group; n = 2083) or “control” (local policy for LW and no BCG-Denmark; n = 2089) at discharge from the maternity ward or at first contact with the health center. The infants were randomized (1:1) without blinding in blocks of 24. Data was analyzed in Cox hazards models providing mortality rate ratios (MRRs). We had prespecified an analysis censoring follow-up at oral poliovirus vaccine campaigns.

Results

Early administration of BCG-Denmark was associated with a nonsignificant reduction in neonatal mortality rate (MRR, 0.70; 95% confidence interval [CI], .47–1.04) and a 34% reduction (0.66; .44–1.00) when censoring for oral poliovirus vaccine campaigns. There was no reduction in mortality rate for noninfectious diseases, but a 43% reduction in infectious disease mortality rate (MRR, 0.57; 95% CI, .35–.93). A meta-analysis of 3 BCG trials showed that early BCG-Denmark reduced mortality by 38% (MRR, 0.62; 95% CI, .46–.83) within the neonatal period and 16% (0.84; .71–1.00) by age 12 months.

Conclusion

Early administration of BCG-Denmark in LW infants is associated with major reductions in mortality rate. It is important that all LW infants receive early BCG in areas with high neonatal mortality rates.

Clinical Trials Registration

NCT00625482.

Neonatal BCG Vaccination Influences Cytokine Responses to Toll-like Receptor Ligands and Heterologous Antigens

Background

BCG vaccination is associated with a reduction in all-cause infant mortality in high-mortality settings. The underlying mechanisms remain uncertain, but long-term modulation of the innate immune response (trained immunity) may be involved.

Methods

Whole-blood specimens, collected 7 days after randomization from 212 neonates enrolled in a randomized trial of neonatal BCG vaccination, were stimulated with killed pathogens and Toll-like receptor (TLR) ligands to interrogate cytokine responses.

Results

BCG-vaccinated infants had increased production of interleukin 6 (IL-6) in unstimulated samples and decreased production of interleukin 1 receptor antagonist, IL-6, and IL-10 and the chemokines macrophage inflammatory protein 1α (MIP-1α), MIP-1β, and monocyte chemoattractant protein 1 (MCP-1) following stimulation with peptidoglycan (TLR2) and R848 (TLR7/8). BCG-vaccinated infants also had decreased MCP-1 responses following stimulation with heterologous pathogens. Sex and maternal BCG vaccination status interacted with neonatal BCG vaccination.

Conclusions

Neonatal BCG vaccination influences cytokine responses to TLR ligands and heterologous pathogens. This effect is characterized by decreased antiinflammatory cytokine and chemokine responses in the context of higher levels of IL-6 in unstimulated samples. This supports the hypothesis that BCG vaccination modulates the innate immune system. Further research is warranted to determine whether there is an association between these findings and the beneficial nonspecific (heterologous) effects of BCG vaccine on all-cause mortality.

What Have We Learnt about BCG Vaccination in the Last 20 Years?

A number of new tuberculosis (TB) vaccines have been or are entering clinical trials, which include genetically modified mycobacteria, mycobacterial antigens delivered by viral vectors, or mycobacterial antigens in adjuvant. Some of these vaccines aim to replace the existing BCG vaccine but others will be given as a boosting vaccine following BCG vaccination given soon after birth. It is clear that the existing BCG vaccines provide incomplete and variable protection against pulmonary TB. This review will discuss what we have learnt over the last 20 years about how the BCG vaccine induces specific and non-specific immunity, what factors influence the immune responses induced by BCG, and progress toward identifying correlates of immunity against TB from BCG vaccination studies. There is still a lot to learn about the BCG vaccine and the insights gained can help the development of more protective vaccines.

Tuberculosis vaccines - perspectives from the NIH/NIAID Mycobacteria vaccine testing program

The development of novel vaccine candidates against infections with Mycobacterium tuberculosis has highlighted our limited understanding of immune mechanisms required to kill M. tuberculosis. The induction of a Th1 immunity is vital, but new studies are required to identify other mechanisms that may be necessary. Novel vaccines formulations that invoke effector cells such as innate lymphoid cells may provide an environment that promote effector mechanisms including T cell and B cell mediated immunity. Identifying pathways associated with killing this highly successful infectious agent has become critical to achieving the goal of reducing the global tuberculosis burden.

Maternal BCG scar is associated with increased infant proinflammatory immune responses

Introduction

Prenatal exposures such as infections and immunisation may influence infant responses. We had an opportunity to undertake an analysis of innate responses in infants within the context of a study investigating the effects of maternal mycobacterial exposures and infection on BCG vaccine-induced responses in Ugandan infants.

Material and methods

Maternal and cord blood samples from 29 mother-infant pairs were stimulated with innate stimuli for 24 h and cytokines and chemokines in supernatants were measured using the Luminex® assay. The associations between maternal latent Mycobacterium tuberculosis infection (LTBI), maternal BCG scar (adjusted for each other’s effect) and infant responses were examined using linear regression. Principal Component Analysis (PCA) was used to assess patterns of cytokine and chemokine responses. Gene expression profiles for pathways associated with maternal LTBI and with maternal BCG scar were examined using samples collected at one (n = 42) and six (n = 51) weeks after BCG immunisation using microarray.

Results

Maternal LTBI was positively associated with infant IP-10 responses with an adjusted geometric mean ratio (aGMR) [95% confidence interval (CI)] of 5.10 [1.21, 21.48]. Maternal BCG scar showed strong and consistent associations with IFN-γ (aGMR 2.69 [1.15, 6.17]), IL-12p70 (1.95 [1.10, 3.55]), IL-10 (1.82 [1.07, 3.09]), VEGF (3.55 [1.07, 11.48]) and IP-10 (6.76 [1.17, 38.02]). Further assessment of the associations using PCA showed no differences for maternal LTBI, but maternal BCG scar was associated with higher scores for principal component (PC) 1 (median level of scores: 1.44 in scar-positive versus −0.94 in scar-negative, p = 0.020) in the infants. PC1 represented a controlled proinflammatory response. Interferon and inflammation response pathways were up-regulated in infants of mothers with LTBI at six weeks, and in infants of mothers with a BCG scar at one and six weeks after BCG immunisation.

Conclusions

Maternal BCG scar had a stronger association with infant responses than maternal LTBI, with an increased proinflammatory immune profile.

Nonspecific effect of BCG vaccination at birth on early childhood infections: a randomized, clinical multicenter trial

BACKGROUND

Childhood infections are common and Bacillus Calmette-Guérin (BCG) vaccination at birth may prevent these via nonspecific effects.

METHODS

A randomized, clinical multicenter trial. All women planning to give birth (n = 16,521) at the three study sites were invited during the recruitment period. Participating children were randomized to receive BCG within 7 d of birth or to a no intervention control group. Parent-reported infections (events) were collected using telephone interviews at 3 and 13 mo. Data collectors were blinded to allocation.

RESULTS

The analyses included 4,224/4,262 (99%) and 4,192/4,262 (98%) children at 3 and 13 mo. From 0 to 3 mo, there were 291 events in the BCG group vs. 336 events in the control group, incidence rate ratio (IRR) = 0.87 (95% confidence interval (CI): 0.72 to 1.05). In this age group, the IRR was 0.62 (95% CI: 0.39 to 0.98) if the mother was BCG vaccinated. From 3 to 13 mo, there were 7,028 vs. 6,791 events, IRR = 1.02 (95% CI: 0.97 to 1.07).

CONCLUSION

This study did not find a nonspecific public health benefit of BCG on parent-reported infections. BCG may have reduced the incidence of infections in children of BCG-vaccinated mothers during the first 3 mo.

Biological challenges to effective vaccines in the developing world

The reason for holding a meeting to discuss biological challenges to vaccines is simple: not all vaccines work equally well in all settings. This special issue reviews the performance of vaccines in challenging environments, summarizes current thinking on the reasons why vaccines underperform and considers what approaches are necessary to understand the heterogeneity in responses and to improve vaccine immunogenicity and efficacy.