Factors affecting immunogenicity of BCG in infants, a study in Malawi, The Gambia and the UK

Background

BCG immunogenicity in infants differs between populations and these differences have been attributed to various factors. In this study, the influence of geographical location, season of birth, timing of vaccination, micronutrient status (zinc) and inflammatory status (C-reactive protein, CRP) were assessed.

Methods

Immunogenicity was assessed by cytokine signature in culture supernatants from diluted whole blood samples stimulated with M. tuberculosis PPD, using a multiplex bead assay. Results were correlated with the plasma zinc and CRP concentrations at the time of sampling, and with interview and household data. BCG vaccinated infants were recruited in Malawi, The Gambia and the UK.

Results

In Malawi, infants vaccinated within the first week after birth showed lower production of most cytokines measured than those vaccinated later. The number of cytokines showing significant differences between Malawian and Gambian infants decreased after adjusting for season of birth. In Malawi, a proportion of infants had zinc deficiency and elevated plasma CRP (>10 mg/L), but neither zinc deficiency nor high CRP was associated with production of any of the cytokines measured.

Conclusions

The cytokine/chemokine signatures observed in response to M. tuberculosis PPD in infants at 3 months post BCG vaccination were affected by geographical location, season of birth, and timing of vaccination but not associated with the concentration of plasma zinc or inflammatory status. These factors should be considered in future trials of new TB vaccines.

Soluble ecto-5'-nucleotidase (5'-NT), alkaline phosphatase, and adenosine deaminase (ADA1) activities in neonatal blood favor elevated extracellular adenosine

Extracellular adenosine, a key regulator of physiology and immune cell function that is found at elevated levels in neonatal blood, is generated by phosphohydrolysis of adenine nucleotides released from cells and catabolized by deamination to inosine. Generation of adenosine monophosphate (AMP) in blood is driven by cell-associated enzymes, whereas conversion of AMP to adenosine is largely mediated by soluble enzymes. The identities of the enzymes responsible for these activities in whole blood of neonates have been defined in this study and contrasted to adult blood. We demonstrate that soluble 5′-nucleotidase (5′-NT) and alkaline phosphatase (AP) mediate conversion of AMP to adenosine, whereas soluble adenosine deaminase (ADA) catabolizes adenosine to inosine. Newborn blood plasma demonstrates substantially higher adenosine-generating 5′-NT and AP activity and lower adenosine-metabolizing ADA activity than adult plasma. In addition to a role in soluble purine metabolism, abundant AP expressed on the surface of circulating neonatal neutrophils is the dominant AMPase on these cells. Plasma samples from infant observational cohorts reveal a relative plasma ADA deficiency at birth, followed by a gradual maturation of plasma ADA through infancy. The robust adenosine-generating capacity of neonates appears functionally relevant because supplementation with AMP inhibited whereas selective pharmacologic inhibition of 5′-NT enhanced Toll-like receptor-mediated TNF-α production in neonatal whole blood. Overall, we have characterized previously unrecognized age-dependent expression patterns of plasma purine-metabolizing enzymes that result in elevated plasma concentrations of anti-inflammatory adenosine in newborns. Targeted manipulation of purine-metabolizing enzymes may benefit this vulnerable population.

Optimisation of a functional mycobacterial growth-inhibition assay to improve its suitability for infant TB vaccine studies

The development of vaccines against tuberculosis continues to be hindered by the lack of correlates of protection. Immunity to Mycobacterium tuberculosis (M.tb) infection relies predominantly on cell mediated response, which is routinely measured using a read-out of host cytokine profiles. However, to date none of the cytokine profiles have been found to predict protection. A number of functional in vitro approaches that measure growth of mycobacteria pre- and post-vaccination as a potential functional surrogate marker for vaccine take have been developed. The use of a reporter-gene tagged BCG-lux assay measuring the viability of mycobacteria in whole blood samples has previously been described by our group to assess vaccine immunogenicity. Since only very small blood samples are usually available in paediatric studies, we now report a modification of the BCG-lux assay to reduce the volume required and make it more field-friendly. Our results show that a 2-fold reduction in blood volume made no significant difference to bacterial growth ratios, used as the main read-out. These results confirm the suitability of the BCG-lux assay for functional studies of vaccine immunogenicity and immunopathogenesis in young children and could play a role in late-phase TB vaccine trials of novel candidates.

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A 2-fold reduction in blood volume can now be used in a functional BCG-lux assay.

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This growth-restriction assay is a useful tool for vaccine assessment.

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Reduction in blood volumes will aid its use in trials of TB vaccines in infants.

Vitamin D in early childhood and the effect on immunity to Mycobacterium tuberculosis

A potential role for vitamin D as a therapeutic immunomodulator in tuberculosis (TB) has been recognised for over 150 years, but has only recently returned to the centre of the research arena due to the increasing awareness of the global vitamin D deficiency epidemic. As early as birth a child is often deficient in vitamin D, which may not only affect their bone metabolism but also modulate their immune function, contributing to the increased susceptibility to many infections seen early in life. Recent studies have begun to explain the mechanisms by which vitamin D affects immunity. Antimicrobial peptides are induced in conjunction with stimulation of innate pattern recognition receptors enhancing immunity to particular infections. In contrast the role of vitamin D within the adaptive immune response appears to be more regulatory in function, perhaps as a mechanism to reduce unwanted inflammation. In this paper we focus on the effect of vitamin D on immunity to TB. Where much of the attention has been paid by past reviews to the role of vitamin D in adult TB patients, this paper, where possible, focuses on research in paediatric populations.

Immunological impact of an additional early measles vaccine in Gambian children: responses to a boost at 3 years

BACKGROUND

Measles vaccine in early infancy followed by a dose at 9 months of age protects against measles and enhances child survival through non-specific effects. Little is known of immune responses in the short or long term after booster doses.

METHODS

Infants were randomized to receive measles vaccine at 9 months of age (group 1) or 4 and 9 months of age (group 2). Both groups received a boost at 36 months of age. T-cell effector and memory responses using IFN-γ ELIspot and cytokine assays and antibody titres using a haemagglutination-inhibition assay were compared at various times.

RESULTS

Vaccination at 4 months of age elicited antibody and CD4 T-cell mediated immune responses .Two weeks after vaccination at 9 months of age group 2 had much higher antibody titres than group1 infants; cell-mediated effector responses were similar. At 36 months of age group 2 antibody titres exceeded protective levels but were 4-fold lower than group 1; effector and cytokine responses were similar. Re-vaccination resulted in similar rapid and high antibody titres in both groups (median 512); cellular immunity changed little. At 48 months of age group 2 antibody concentrations remained well above protective levels though 2-fold lower than group 1; T-cell memory was readily detectable and similar in both groups.

CONCLUSIONS

An additional early measles vaccine given to children at 4 months of age induced a predominant CD4 T-cell response at 9 months and rapid development of high antibody concentrations after booster doses. However, antibody decayed faster in these children than in the group given primary vaccination at 9 months of age. Cellular responses after 9 months were generally insignificantly different.

Age-dependent maturation of Toll-like receptor-mediated cytokine responses in Gambian infants

The global burden of neonatal and infant mortality due to infection is staggering, particularly in resource-poor settings. Early childhood vaccination is one of the major interventions that can reduce this burden, but there are specific limitations to inducing effective immunity in early life, including impaired neonatal leukocyte production of Th1-polarizing cytokines to many stimuli. Characterizing the ontogeny of Toll-like receptor (TLR)-mediated innate immune responses in infants may shed light on susceptibility to infection in this vulnerable age group, and provide insights into TLR agonists as candidate adjuvants for improved neonatal vaccines. As little is known about the leukocyte responses of infants in resource-poor settings, we characterized production of Th1-, Th2-, and anti-inflammatory-cytokines in response to agonists of TLRs 1-9 in whole blood from 120 Gambian infants ranging from newborns (cord blood) to 12 months of age. Most of the TLR agonists induced TNFα, IL-1β, IL-6, and IL-10 in cord blood. The greatest TNFα responses were observed for TLR4, -5, and -8 agonists, the highest being the thiazoloquinoline CLO75 (TLR7/8) that also uniquely induced cord blood IFNγ production. For most agonists, TLR-mediated TNFα and IFNγ responses increased from birth to 1 month of age. TLR8 agonists also induced the greatest production of the Th1-polarizing cytokines TNFα and IFNγ throughout the first year of life, although the relative responses to the single TLR8 agonist and the combined TLR7/8 agonist changed with age. In contrast, IL-1β, IL-6, and IL-10 responses to most agonists were robust at birth and remained stable through 12 months of age. These observations provide fresh insights into the ontogeny of innate immunity in African children, and may inform development of age-specific adjuvanted vaccine formulations important for global health.

The tuberculin skin test (TST) is affected by recent BCG vaccination but not by exposure to non-tuberculosis mycobacteria (NTM) during early life

The tuberculin skin test (TST) is widely used in TB clinics to aid Mycobacterium tuberculosis (M.tb) diagnosis, but the definition and the significance of a positive test in very young children is still unclear. This study compared the TST in Gambian children at 4½ months of age who either received BCG vaccination at birth (Group 1) or were BCG naïve (Group 2) in order to examine the role of BCG vaccination and/or exposure to environmental mycobacteria in TST reactivity at this age. Nearly half of the BCG vaccinated children had a positive TST (≥5 mm) whereas all the BCG naïve children were non-reactive, confirming that recent BCG vaccination affects TST reactivity. The BCG naïve children demonstrated in vitro PPD responses in peripheral blood in the absence of TST reactivity, supporting exposure to and priming by environmental mycobacterial antigens. Group 2 were then vaccinated at 4½ months of age and a repeat TST was performed at 20–28 months of age. Positive reactivity (≥5 mm) was evident in 11.1% and 12.5% infants from Group 1 and Group 2 respectively suggesting that the timing of BCG vaccination had little effect by this age. We further assessed for immune correlates in peripheral blood at 4½ months of age. Mycobacterial specific IFNγ responses were greater in TST responders than in non-responders, although the size of induration did not correlate with IFNγ. However the IFNγ: IL-10 ratio positively correlated with TST induration suggesting that the relationship between PPD induced IFNγ and IL-10 in the peripheral blood may be important in controlling TST reactivity. Collectively these data provide further insights into how the TST is regulated in early life, and how a positive response might be interpreted.

The challenge of assessing infant vaccine responses in resource-poor settings

Newborns and infants are highly susceptible to infectious diseases, resulting in high mortality and morbidity, particularly in resource-poor settings. Many vaccines require several booster doses, resulting in an extensive vaccine schedule, and yet there is still inadequate protection from some of these diseases. This is partly due to the immaturity of the neonate and infant immune system. Little is known about the specific modifications to immunological assessment protocols in early life but increasing knowledge of infant immunology has helped provide better recommendations for assessing these responses. Since most new vaccines will eventually be deployed in low-income settings such as Africa, the logistics and resources of assessing immunity in such settings also need to be understood. In this article, we will review immunity to vaccines in early life, discuss the many challenges associated with assessing immunogenicity and provide practical tips.

The effect of placental malaria infection on cord blood and maternal immunoregulatory responses at birth

Placental malaria (PM), a frequent infection of pregnancy, provides an ideal opportunity to investigate the impact on immune development of exposure of the foetal immune system to foreign Ag. We investigated the effect of PM on the regulatory phenotype and function of cord blood cells from healthy Gambian newborns and peripheral blood cells from their mothers, and analyzed for effects on the balance between regulatory and effector responses. Using the gold standard for classifying PM we further distinguished between resolved infection and acute or chronic PM active at the time of delivery. We show that exposure to malarial Ag in utero results in the expansion of malaria-specific FOXP3(+) Treg and more generalized FOXP3(+) CD4(+) Treg in chronic and resolved PM, alongside increased Th1 pro-inflammatory responses (IFN-gamma, TNF-alpha, IFN-gamma:IL-10) in resolved PM infection only. These observations demonstrate a clear effect of exposure to malarial Ag in foetal life on the immune environment at birth, with a regulatory response dominating in the newborns with ongoing chronic PM, while those with resolved infection produce both regulatory and inflammatory responses. The findings might explain some of the adverse effects on the health of babies born to women with PM.

FOXP3 gene expression in a tuberculosis case contact study

Regulatory T lymphocytes (T(regs)) that express FOXP3 are involved in the beneficial attenuation of immunopathology, but are also implicated in down-regulation of protective responses to infection. Their role in tuberculosis (TB) is unknown. We classified 1272 healthy TB contacts according to their tuberculin skin test (TST) and interferon (IFN)-gamma enzyme-linked immunospot (ELISPOT) results and 128 TB cases, and studied the expression of FOXP3 and interleukin (IL)-10 in blood samples. Compared to the uninfected contact group (TST(-), ELISPOT(-)), we observed higher levels of FOXP3 mRNA in blood from TB patients (< 0.001), but IL-10 expression was slightly lower (P = 0.04). In contrast, FOXP3 expression levels were significantly lower (P = 0.001) in the recently infected contacts (TST(+), ELISPOT(+)) but there was no difference for IL-10 (P = 0.74). We hypothesize that during early/subclinical TB, most of which will become latent, FOXP3(+) T(regs) may be sequestered in the lungs, but when TB becomes progressive, FOXP3 reappears at increased levels in the periphery. While these findings do not reveal the role, beneficial or harmful, of T(regs) in TB, they emphasize the probable importance of these cells.

Genetic modification of sheep by nuclear transfer with gene-targeted somatic cells

For many years the lack of germline competent embryonic stem cell lines in livestock meant that the targeted modification of endogenous genes was not possible in these species. The demonstration that livestock could be cloned by nuclear transfer from cultured somatic cells has now provided an alternative route to accomplish gene targeting. This chapter describes protocols for culturing primary sheep fibroblasts, introducing and selecting targeted modifications into them and then using these modified cells in nuclear transfer experiments.

Proliferative lifespan is conserved after nuclear transfer

Cultured primary cells exhibit a finite proliferative lifespan, termed the Hayflick limit. Cloning by nuclear transfer can reverse this cellular ageing process and can be accomplished with cultured cells nearing senescence. Here we describe nuclear transfer experiments in which donor cell lines at different ages and with different proliferative capacities were used to clone foetuses and animals from which new primary cell lines were generated. The rederived lines had the same proliferative capacity and rate of telomere shortening as the donor cell lines, suggesting that these are innate, genetically determined, properties that are conserved by nuclear transfer.

Gene targeting in primary fetal fibroblasts from sheep and pig

Nuclear transfer offers a new cell-based route for introducing precise genetic modifications in a range of animal species. However, significant challenges, such as establishment of somatic gene targeting techniques, must be overcome before the technology can be applied routinely. In this report, we describe targeted deletion at the GGTA1 (alpha 1,3-galactosyl transferase) and PrP (prion protein) loci in primary fibroblasts from livestock. We place particular emphasis on the growth characteristics of the primary cell cultures, since these are key to determining success.

Deletion of the alpha(1,3)galactosyl transferase (GGTA1) gene and the prion protein (PrP) gene in sheep

Nuclear transfer offers a cell-based route for producing precise genetic modifications in a range of animal species. Using sheep, we report reproducible targeted gene deletion at two independent loci in fetal fibro-blasts. Vital regions were deleted from the alpha(1,3)galactosyl transferase (GGTA1) gene, which may account for the hyperacute rejection of xenografted organs, and from the prion protein (PrP) gene, which is directly associated with spongiform encephalopathies in humans and animals. Reconstructed embryos were prepared using cultures of targeted or nontargeted donor cells. Eight pregnancies were maintained to term and four PrP-/+ lambs were born. Although three of these perished soon after birth, one survived for 12 days. These data show that lambs carrying targeted gene deletions can be generated by nuclear transfer.

Gene targeting in livestock: a preview

Until recently genetically modified livestock could only be generated by pronuclear injection. The discovery that animals can be cloned by nuclear transfer from cultured somatic cells means that it will now be possible to achieve gene targeting in these species. We discuss current developments in NT, the prospects and technical challenges for introducing targeted changes into the germline by this route, and the types of application for which this new technology will be used.

TGF-beta1 binding protein-like modules of fibrillin-1 and -2 mediate integrin-dependent cell adhesion

Human fibrillin, a major component of the extracellular matrix, exists as two highly homologous forms (fibrillin-1 and -2). Several modules of fibrillin are homologous to TGF-beta1 binding protein. Two of these modules, D25 (the 25th module of fibrillin-1 and -2 D segment) and D12 (the 12th module of fibrillin-2 D segment) contain the cell adhesion motif arginyl-glycyl-aspartyl (RGD). The ability of RGD to mediate adhesion to D25-1 and D12-2 was investigated using bacterially expressed fusion proteins. Human skin fibroblasts and murine L-cells were used in microassays of cell attachment and cell spreading on fibrillin fusion-protein substrata. Dose-dependent experiments and competitive inhibition by soluble RGD-containing peptides demonstrated that D25-1 and D12-2 mediate RGD-dependent cell adhesion. These results provide evidence for a cell adhesion function of fibrillin-2. Inhibition with anti-integrin antibodies showed that alpha(v) and beta3 integrins mediate adhesion to D25-1, while alpha3, alpha(v) and beta1 are involved in adhesion to D12-2. Binding of different receptors may elicit distinct cell signalling supporting the hypothesis that fibrillin-1 and fibrillin-2 have distinct roles.

BCR-ABL accelerates C2-ceramide-induced apoptosis

In patients with chronic myeloid leukemia (CML), the neoplastic (BCR-ABL+) progenitor cells are characterized by an increased proliferative activity. Whether these cells are also resistant to apoptosis and if so, under what conditions remains controversial. We now show that highly purified populations of very primitive neoplastic progenitor cells obtained directly from CML patients survive and proliferate in vitro for several weeks in the absence of any added growth factors (except insulin). In contrast, purified primary normal progenitors maintained under the same conditions die rapidly. Nevertheless, both primary CML cells and BCR-ABL+ BAF3 cells show the same dose-dependent sensitivity to TNF-alpha or ceramide-induced apoptosis as their respective normal counterparts. In fact, time course studies demonstrated an even faster onset of apoptosis in ceramide-treated BCR-ABL+ BAF3 cells as compared to normal controls. BCR-ABL+ cells treated with ceramide also showed a rapid and sequential increase in the tyrosine phosphorylation of p210(BCR-ABL), p46-56SHC and p120Cbl. These findings suggest growth factor deprivation and treatment with TNF-alpha or ceramide trigger different initial events both of which can lead to apoptosis in factor-dependent hematopoietic cells. However, in the first case, activation of apoptosis is blocked by the basal activity of p210(BCR-ABL), whereas in the second, the presence of p210(BCR-ABL) appears to accelerate the onset of apoptosis by a mechanism that may involve an activation of its kinase function.