Prospective trial of timing of bacillus Calmette-Guérin vaccination in Canadian Cree infants

Investigating the non-specific effects of BCG vaccination on the innate immune system in Ugandan neonates: study protocol for a randomised controlled trial

Background

The potential for Bacillus Calmette-Guérin (BCG) vaccination to protect infants against non-mycobacterial disease has been suggested by a randomised controlled trial conducted in low birth-weight infants in West Africa. Trials to confirm these findings in healthy term infants, and in a non-West African setting, have not yet been carried out. In addition, a biological mechanism to explain such heterologous effects of BCG in the neonatal period has not been confirmed. This trial aims to address these issues by evaluating whether BCG non-specifically enhances the innate immune system in term Ugandan neonates, leading to increased protection from a variety of infectious diseases.

Methods

This trial will be an investigator-blinded, randomised controlled trial of 560 Ugandan neonates, comparing those receiving BCG at birth with those receiving BCG at 6 weeks of age. This design allows comparison of outcomes between BCG-vaccinated and -naïve infants until 6 weeks of age, and between early and delayed BCG-vaccinated infants from 6 weeks of age onwards. The primary outcomes of the study will be a panel of innate immune parameters. Secondary outcomes will include clinical illness measures.

Discussion

Investigation of the possible broadly protective effects of neonatal BCG immunisation, and the optimal vaccination timing to produce these effects, could have profound implications for public healthcare policy. Evidence of protection against heterologous pathogens would underscore the importance of prioritising BCG administration in a timely manner for all infants, provide advocacy against the termination of BCG’s use and support novel anti-tuberculous vaccine strategies that would safeguard such beneficial effects.

Trial registration

ISRCTN59683017: registration date: 15 January 2014

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-015-0682-5) contains supplementary material, which is available to authorized users.

The tuberculin skin test is unreliable in school children BCG-vaccinated in infancy and at low risk of tuberculosis infection

BACKGROUND

The tuberculin skin test (TST) is often used to screen for latent tuberculosis infection (LTBI) in school children, many of whom were bacille Calmette-Guérin (BCG)-vaccinated in infancy. The reliability of the TST in such children is unknown.

METHODS

TSTs performed in low-risk BCG-vaccinated and -nonvaccinated grade 1 and grade 6 First Nations (North American Indian) school children in the province of Alberta, Canada, were evaluated retrospectively. To further assess the specificity of the TST, BCG-vaccinated children with a positive TST (≥10 mm of induration) and no treatment of LTBI were administered a QuantiFERON-TB Gold In-Tube test (QFT-GIT, Cellestis International).

RESULTS

A total of 3996 children, 2063 (51.6%) BCG-vaccinated and 1933 (48.4%) BCG-nonvaccinated, were screened for LTBI. Vaccinated children were more likely than nonvaccinated children to be TST positive (5.7% vs. 0.2%, P < 0.001). Vaccinated children with a positive TST were more likely to have a recent past TST as compared with those with a negative TST (6.8% versus 2.8%, P = 0.01). Among 65 BCG-vaccinated TST-positive children who underwent a QFT-GIT, only 5 (7.7%; 95% CI: 2.5%, 17.0%) were QFT-GIT positive. A TST of ≥15 mm was more likely to be associated with a positive QFT-GIT than a TST of 10 to 14 mm, 16.0% (95% CI: 4.5%, 36.1%) versus 2.5% (95% CI: 0.1%, 13.2%), P = 0.047.

CONCLUSION

The TST is unreliable in school children, BCG-vaccinated in infancy, and who are at low risk of infection. The QFT-GIT is a useful confirmatory test for LTBI in BCG-vaccinated TST-positive school children.

Gammadelta T cells in immunity induced by Mycobacterium bovis bacillus Calmette-Guérin vaccination

Mycobacterium bovis bacillus Calmette-Guérin (BCG) vaccination is efficacious for newborns or adults with no previous exposure to environmental mycobacteria. To determine the relative contribution and the nature of gammadelta T-cell receptor-positive T cells in newborns, compared to CD4(+) T cells, in immunity induced by M. bovis BCG vaccination, 4-week-old specific-pathogen-free pigs were vaccinated with M. bovis BCG and monitored by following the gammadelta T-cell immune responses. A flow cytometry-based proliferation assay and intracellular staining for gamma interferon (IFN-gamma) were used to examine gammadelta T-cell responses. Pigs were found to mount Th1-like responses to M. bovis BCG vaccination as determined by immunoproliferation and IFN-gamma production. The gammadelta T-cell lymphoproliferation and IFN-gamma production to stimulation with mycobacterial antigens were significantly enhanced by M. bovis BCG vaccination. The relative number of proliferating gammadelta T cells after stimulating peripheral blood mononuclear cells with Mycobacterium tuberculosis H37Rv culture filtrate protein was higher than that of CD4(+) T cells at an early time point after M. bovis BCG vaccination, but CD4(+) T cells were found to be more abundant at a later time point. Although the gammadelta T-cell responses were dependent on the presence of CD4(+) T cells for the cytokine interleukin-2, the enhanced gammadelta T cells were due to the intrinsic changes of gammadelta T cells caused by M. bovis BCG vaccination rather than being due solely to help from CD4(+) T cells. Our study shows that gammadelta T cells from pigs at early ages are functionally enhanced by M. bovis BCG vaccination and suggests an important role for this T-cell subset in acquired immunity conferred by M. bovis BCG vaccination.

Neonatal and early life vaccinology

Preclinical and human vaccine studies indicate that, although neonatal immunisation does not generally lead to rapid and strong antibody responses, it may result in an efficient immunological priming, which can serve as an excellent basis for future responses. The apparent impairment of CD4 and CD8 T-cell function in early life seems to result from suboptimal antigen-presenting cells-T cell interactions, which can be overcome by use of specific adjuvants or delivery systems. Although persistence of maternal antibodies may limit infant antibody responses, induction of T-cell responses largely remain unaffected by these passively transferred antibodies. Thus, neonatal priming and early boosting with vaccine formulations optimised for sufficient early life immunogenicity and maximal safety profiles, could allow better control of the huge infectious disease burden in early life.

The tuberculin skin test in relation to immunological in vitro reactions in BCG-vaccinated healthcare workers

The aim was to study the tuberculin skin test in relation to immunological in vitro reactions in bacille Calmette-Guerin (BCG)-vaccinated healthcare workers. The present study was performed in Sweden, a country with a low incidence of tuberculosis, a high BCG vaccination efficacy and high tuberculin conversion rates. BCG-vaccinated healthcare workers (n=381) were tuberculin skin tested. From these, 11 subjects with negative tuberculin reactions (<6 mm) were matched for age and sex with 11 subjects with large positive reactions (> or = 15 mm). Lymphocyte transformation and the production of interferon-gamma (IFN-gamma) were analysed after stimulation in vitro of peripheral blood mononuclear cells with tuberculin purified protein derivative, heat-killed tubercle bacilli and a culture filtrate from tubercle bacilli. In the tuberculin-positive group the lymphocyte transformation response was 2-3 times larger, and IFN-gamma production was 7-10 times larger, than in the tuberculin-negative group (p<0.001). The present results suggest that a positive tuberculin skin test in bacille Calmette-Guerin-vaccinated subjects indicates a stronger immune response of the protective T-helper 1-type than does a negative test. In similar settings, the study supports the traditional practice of regarding the tuberculin skin test in bacille Calmette-Guerin-vaccinated subjects as an indicator of a protective immune response against tuberculosis.

Management of adverse reactions to bacille Calmette-Guérin vaccine

Published reports appear to underestimate the true rate of adverse reactions to bacille Calmette-Guérin (BCG) vaccine. At a recent national conference on tuberculosis control among aboriginal populations, lack of awareness of what constitutes an adverse reaction was considered a possible contributing factor to underreporting. The following review defines a normal BCG response and discusses the management of complications when they occur.

Vaccination in the neonatal period and early infancy

Immune maturation is responsible for a progressive increase in antibody responses that can be elicited during the first year of life, such that neonatal immunization may currently not be expected to induce strong antibody responses. In contrast, B and T cell priming can be induced very early in life, without interference of maternal immunity. Strong IL-5 and IL-13 responses in young mice, and limited IL-12 and IFN-gamma release capacity by early life APC and T cells both in young mice and infants, could contribute to the severity of infections with intracellular pathogens in early life. It calls for evaluation of novel delivery systems, adjuvants and/or prime-boost immunization strategies capable to meet the challenge of both strong neonatal immunogenicity and acceptable reactogenicity. The extent to which early life murine immunization models may be useful for preclinical evaluation of infant responses is outlined in this review.

Optimization of vaccine responses in early life: the role of delivery systems and immunomodulators

Infant immunization is a particularly important field with multiple challenges for vaccine research and development. There is, together with a high susceptibility to infections, a lower efficacy of most vaccinations in newborns and young infants, compared to those performed later in life. In the present review, the authors focus on problems arising from the attempt to vaccinate against pathogens very early in life, and on the role of selective adjuvants (i.e. antigen delivery systems or immunomodulators) that could be used to: (i) rapidly induce strong antibody responses of the appropriate isotypes; (ii) elicit sustained antibody responses extending beyond infancy; (iii) induce efficient Th1 and CTL responses in spite of the preferential Th2 polarization of early life responses; (iv) escape from maternal antibody mediated inhibition of vaccine responses; (v) show acceptable reactogenicity in early life; and (vi) allow incorporation of several vaccine antigens into a single formulation so as to reduce the number of required injections. How such objectives might be achieved by several of the vaccine formulations currently in development is illustrated by reviewing data from experimental models and clinical studies, when available.

BCG vaccination in low birth weight newborns: analysis of lymphocyte proliferation, IL-2 generation and intradermal reaction to PPD

OBJECTIVE

To study vaccinal scar formation and post-vaccinal immune response in newborns with birth weight ranging from 2000 to 2499 g vaccinated in the first week of life with intradermal bacille Calmette-Guérin (BCG) (Moreau-Rio de Janeiro strain).

METHOD

Specific immune response to PPD was assessed in 30 low birth weight newborns (mean birth weight = 2311.7 +/- 122.1 g; mean gestational age = 38.1 +/- 1.8 weeks) in comparison to 56 control infants (mean birth weight = 3198.9 +/- 267.2 g; mean gestational age = 38.5 +/- 1.2 weeks.

RESULTS

Low birth weight infants have an efficient immune response to vaccinal stimulus when compared to control infants as judged by specific in vitro lymphocyte proliferation (mean SI = 9.7 +/- 12.9 vs SI = 8.8 +/- 10.0, P = 0.72) and IL-2 production (mean SI = 3.1 +/- 3.4 vs SI = 2.6 +/- 2.0, P = 0.38). Intradermal reaction to PPD was also comparable in both groups (mean induration diameter = 9.5 +/- 5.1 mm vs 9.6 +/- 5.0 mm, P = 0.94).

CONCLUSION

These data suggest that low birth weight newborns show a good immune response to BCG, thus reinforcing the inclusion of such infants in regular vaccination programs with intradermal BCG.

The influence of BCG immunization on tuberculin reactivity in healthy Chilean women in the third trimester of pregnancy

SETTING

Tuberculin testing is an accepted method for screening pregnant women for tuberculosis. The interpretation of tuberculin reactivity in bacillus Calmette-Guerin (BCG)-immunized pregnant women is still in debate.

OBJECTIVE

Four related issues were addressed: (1) The effect of pregnancy on tuberculin reactivity; (2) the effect of age differential on tuberculin reactivity; (3) the effect of repeated immunization with BCG; and (4) the risk of developing tuberculosis during pregnancy or a 3-year post-partum period.

DESIGN

We performed tuberculin testing in 840 healthy Chilean women in the 32nd to 34th week of pregnancy; 807 had been immunized with 1 or more doses of BCG. There were 3 age groups: 177 were < or = 19 years old, 534 were 20-29 years old, and 129 were > or = 30 years old. All women in the study were followed at least 3 years post-partum.

RESULTS

Women < or = 19 years old and non-pregnant women of similar age studied in the same geographical area had a similar distribution of the size of tuberculin reactions. Over 50% of all BCG-immunized women in each group had tuberculin reactions > or = 10 mm. A differential effect of different doses of BCG was significant only in 20- to 29-year-old women. None of the women in this study developed tuberculosis during pregnancy or a 3-year post-partum observation period.

CONCLUSIONS

Healthy, BCG-immunized pregnant women may have positive tuberculin reactions without having an increased risk for tuberculosis. The incidence of tuberculosis and the BCG immunization status need to be considered in the development of policy recommendations for diagnosis and treatment of Mycobacterium tuberculosis infection in pregnant women.

Two-step tuberculin testing in staff and residents of a nursing home

This study examined the prevalence and determinants of tuberculin reactors and the booster response in 272 (97%) residents and 218 (69%) staff of an urban nursing home where a case of miliary TB was being investigated. Many subjects were foreign born (56%), and 15% had a history of BCG vaccination (34% of staff). Testing was done with 5 TU PPD-S (Connaught). Those with < 10 mm induration at 48 h were retested at 1 wk. Test sizes > 9 mm were classified positive (reactors). A questionnaire was given to collect information on risk factors for a positive test. Results showed that 28% (36% staff and 22% of residents) of subjects were reactors at the initial test, 6% at the booster test (staff and residents), and 32% at either test (40% staff and 26% residents). BCG (OR 4.8) and foreign birth (OR 1.7) were significantly associated with total reactors. The association with foreign birth was inversely related to the time since immigration. Only BCG was associated with a positive booster test (OR 6.7). Of positive tuberculin reactions in individuals with a history of BCG, 72% were attributed to the vaccine. We concluded that (1) staff as well as residents should be two-step tested when retesting is anticipated; (2) the prevalence of tuberculin reactors is highly related to the prevalence of BCG vaccinees and foreign birth; and (3) chemoprophylaxis is probably not indicated for isolated tuberculin reactors with a history of BCG.

Determinants of tuberculin sensitivity in a child population covered by mass BCG vaccination

A cross-sectional survey of 701 Indian children aged 1-15 in five northern Canadian communities showed that 82% had a documented history of BCG vaccination while only 78% had a visible scar. The prevalence of 5 mm or more induration on Mantoux testing varied from 6 to 26%. Multiple logistic regression indicated that community, age, past use of isoniazid and time since the last Mantoux test were positive predictors of sensitivity. The presence of a BCG scar and the number of past vaccinations were not significantly associated but the elapsed time since the last BCG was negatively associated with a positive reaction. Overcrowding, nutritional status and past history of household and community contact with an active case of tuberculosis were also investigated but their independent effect could not be demonstrated. Despite the presence of mass BCG vaccination in this population, tuberculin testing is still a useful tool in assessing the risk of infection.