Cell-mediated immune responses in children towards secreted proteins of Mycobacterium bovis BCG

Determining reference ranges for lymphocyte proliferation responses to phytohemagglutinin and Bacillus Calmette-Guérin in Iranian children

PURPOSE

To establish reference ranges (RRs) for stimulation index of T cell proliferation triggered by phytohemagglutinin (PHA-SI) and Bacillus Calmette-Guérin (BCG-SI).

METHODS

This study investigated data from 359 healthy children and 35 patients with cellular immunodeficiency as positive controls (2010-2021). We applied a colorimetric-based method (BrdU) to measure proliferation and determine the RRs at the 2.5th and 97.5th percentiles (95% confidence intervals). A cross-validation approach was performed.

RESULTS

In healthy controls, the RRs for PHA-SI and BCG-SI ranged between 3 and 5.2 and 2.52 to 5.2, respectively. PHA-SI and BCG-SI were in Severe Combined Immunodeficiency (SCID) patients from 1.2 to 2.5 and 0 to 2, while in Mendelian susceptibility to mycobacterial diseases (MSMD) patients, 2.53 to 4.5 and 0.74 to 2.2, respectively. The thresholds' accuracy was checked for testing reference intervals with diagnostic effects.

CONCLUSION

This study establishes PHA-SI and BCG-SI reference ranges to aid in diagnosing and treating congenital immunodeficiency diseases.

Mycobacterium bovis BCG and New Vaccines for the Prevention of Tuberculosis

Tuberculosis infects millions of people worldwide and remains a leading global killer despite widespread neonatal administration of the tuberculosis vaccine, bacillus Calmette-Guérin (BCG). BCG has clear and sustained efficacy, but after 10 years, its efficacy appears to wane, at least in some populations. Fortunately, there are many new tuberculosis vaccines in development today, some in advanced stages of clinical trial testing. Here we review the epidemiological need for tuberculosis vaccination, including evolving standards for administration to at risk individuals in developing countries. We also examine proven sources of immune protection from tuberculosis, which to date have exclusively involved natural or vaccine exposure to whole cell mycobacteria. After summarizing evidence for the use and efficacy of BCG, we detail the most promising new candidate vaccines against tuberculosis. The global need for a new tuberculosis vaccine is acute and huge, but clinical trials to be completed in the coming few years are likely either to identify a new tuberculosis vaccine or to substantially reframe how we understand immune protection from this historical scourge.

The contribution of non-conventional T cells and NK cells in the mycobacterial-specific IFNγ response in Bacille Calmette-Guérin (BCG)-immunized infants

BACKGROUND

The Mycobacterium bovis Bacille Calmette-Guérin (BCG) vaccine is given to >120 million infants each year worldwide. Most studies investigating the immune response to BCG have focused on adaptive immunity. However the importance of TCR-gamma/delta (γδ) T cells and NK cells in the mycobacterial-specific immune response is of increasing interest.

METHODS

Participants in four age-groups were BCG-immunized. Ten weeks later, in vitro BCG-stimulated blood was analyzed for NK and T cell markers, and intracellular IFNgamma (IFNγ) by flow cytometry. Total functional IFNγ response was calculated using integrated median fluorescence intensity (iMFI).

RESULTS

In infants and children, CD4 and CD4-CD8- (double-negative (DN)) T cells were the main IFNγ-expressing cells representing 43-56% and 27-37% of total CD3+ IFNγ+ T cells respectively. The iMFI was higher in DN T cells compared to CD4 T cells in all age groups, with the greatest differences seen in infants immunized at birth (p=0.002) or 2 months of age (p<0.0001). When NK cells were included in the analysis, they accounted for the majority of total IFNγ-expressing cells and, together with DN Vδ2 γδ T cells, had the highest iMFI in infants immunized at birth or 2 months of age.

CONCLUSION

In addition to CD4 T cells, NK cells and DN T cells, including Vδ2 γδ T cells, are the key populations producing IFNγ in response to BCG immunization in infants and children. This suggests that innate immunity and unconventional T cells play a greater role in the mycobacterial immune response than previously recognized and should be considered in the design and assessment of novel tuberculosis vaccines.

T-cell recognition of iron-regulated culture filtrate proteins of Mycobacterium tuberculosis in tuberculosis patients and endemic normal controls

BACKGROUND

Culture filtrate proteins (CFPs) of Mycobacterium tuberculosis are potential vaccine candidates.

OBJECTIVE

The aim was to study the influence of iron levels on CFPs and assess the immuno-protective potential of defined antigenic fractions from high (8 μg Fe/mL) and low iron (0.02 μg Fe / mL) cultures of M. tuberculosis.

MATERIALS AND METHODS

The CFPs of M. tuberculosis from high (CFP-high) and low (CFP-low) iron conditions were first compared to identify iron-regulated proteins and then fractionated to obtain ten antigen pools (CF-Ags H1- H5 and L1-L5) that were used to assess the immune response of TB patients and normal healthy controls.

RESULTS

Iron limitation resulted in the up-regulation of two novel iron-regulated low-molecular-weight proteins Irp-1 (in CF-Ag L4) and Irp-2 (in CF-Ag L5) and repression of two ESAT proteins (identified with monoclonal antibody HYB 76.8). The median stimulation indices (SIs) against most of the CF-Ags were high in pulmonary TB patients. The CF-Ags L1 and L2 showed statistically significant SI (P values of 0.0027 and 0.0029 respectively); the % case recognition was high with these antigens as well as with L4 ( P = 0.0275). IFN-γ in response to these CF-Ags was significantly high in the endemic normals; maximal expression was seen with CF-Ag L5 (median value of 233 pg mL -1 ) that was higher than the corresponding H5 (140 pg mL -1 ) and H3 and L3 (205 and 206 pg mL -1 respectively).

CONCLUSIONS

CF-Ags L5, H3 and L3 showed immuno-protective potential in this geographical location.

Interferon-gamma Low producer genotype +874 overrepresented in Bacillus Calmette-Guerin nonresponding children

BACKGROUND

There are limited reports on the influence of the immune regulatory genotypes on the efficacy of Bacillus Calmette-Guerin (BCG) in man. This study was designed to evaluate the influence of the cytokine genotype interferon (IFN)-gamma +874T/A on T cell in vitro assays in BCG nonresponders (negative to either in vivo or in vitro test with purified protein derivative or both).

METHODS

Ninety healthy children who were without any clinical evidence of the disease, 45 with a BCG-scar and the remaining 45 without scar were assessed for in vitro T cell responses. CD4+ and CD8+ cell counts were measured by flow cytometry. r32kDaBCG (Ag85A-BCG) protein was used to stimulate T cells and IFN-gamma cytokine concentration in the cultures were measured by enzyme-linked immunosorbent assay. Polymorphism in IFN-gamma (+874T/A) region was detected by amplification refractory mutation system-polymerase chain reaction.

RESULTS

T cell subsets were within the normal range in all subjects. Children with TT genotype showed significantly higher antigen-induced IFN-gamma (P < 0.001) as compared with those with AT/AA genotype. The highest values were observed in children with TT genotype combined with positive antigen-specific peripheral blood mononuclear cells proliferation. Seventy-five percent of the vaccinated children with TT genotype showed high amounts of stimulated IFN-gamma compared with 66% of scar negative and 16% of scar positive but with AA genotype.

CONCLUSIONS

IFN-gamma (+874T/A) polymorphism seemed to be a strong and independent predictor for clinical outcome of both scar-positive and scar-negative children. These results may help in planning future vaccination strategies. The ability to mount in vitro lymphoproliferation did not distinguish the success or failure of BCG vaccination nor predict susceptibility to the disease.

Age-related waning of in vitro Interferon-gamma levels against r32kDaBCG in BCG vaccinated children

Background

Mycobacterium bovis BCG vaccine has displayed inconsistent efficacy in different trials conducted in various geographical regions. Nevertheless, it significantly reduces the risk of severe childhood tuberculosis and continues to be used to prevent tuberculosis in many countries. Many studies revealed that efficacy of vaccine wanes with age. Most of the studies were based on in vivo and in vitro responses to tuberculin. With the advent of newer tests such as in vitro interferon-γ assays and identification of potent immunogenic mycobacterial proteins there is a need to corroborate the observations. This study aims at ascertaining the need for a booster at a later age as indicated by in vitro release of IFN-γ while evaluating Ag85A as an antigen.

Methods

Ninety healthy children who were without any clinical evidence of the disease, 45 with a BCG-scar and the remaining 45 without scar and 25 with tuberculosis were included in the study. The incidence of TB was analyzed in 216 children attending a DOTS clinic during 1996–2005. CD3+, CD4+ and CD8+ cell counts were measured by Flow cytometry. r32kDaBCG (Ag85A-BCG) protein was used to stimulate T cells in in vitro T cell responses and interferon-γ (IFN-γ) cytokine levels in the supernatants were measured by ELISA.

Results

High incidence of TB was observed in age group 13–14 years followed by children in the age group 10–12 years (Chi-square 242.22; p < 0.000). T cell subsets were within the normal range in all subjects. 79% of vaccinated children showed positive proliferative responses with a mean SI value of 4.98 ± 1.99 while only 39% of the unvaccinated and 58% of the tuberculosis children showed positive responses with mean values of 2.9 ± 1.6 (p < 0.001) and 2.9 ± 1.7(p < 0.057), respectively. The stimulation indices in vaccinated children decreased in the older children concurring with an increase in the incidence of TB.

Conclusion

Significantly high levels of in vitro IFN-γ demonstrated in BCG vaccinated children in our study substantiate the observation that BCG is effective in children, but the effect may wane with age. The immunity could be boosted using modified r32kDa (Ag85A) of BCG.

A boy undergoing maintenance hemodialysis who developed mediastinal lymph node tuberculosis

The incidence of tuberculosis (TBC) in patients undergoing maintenance hemodialysis is reported to be higher than that in the general population. We report an 8-year-old boy receiving such treatment for chronic renal failure who developed mediastinal lymph node TBC. He showed only intermittent fever, recurring every 2 weeks, with no other symptoms suggesting TBC. Although staining and culture of pharyngeal swab and gastric juice specimens failed to provide evidence of TBC, a lymph node biopsy specimen disclosed typical pathologic findings of tuberculoma, including caseating granulomas. Antituberculous therapy with isoniazid (INH), rifampicin, pyrazinamide, and ethambutol was given for 12 months, resulting in complete resolution of the TBC, with no subsequent recurrence. To our knowledge, mediastinal lymph node localization of TBC is relatively rare, in a patient on maintenance hemodialysis, especially in a child.