Identification of Mycobacterium tuberculosis Infection in Infants and Children With Partial Discrimination Between Active Disease and Asymptomatic Infection

Flow cytometry-based method using diversity of cytokine production differentiates between Mycobacterium tuberculosis infection and disease

Authors present a pilot study of the development of innovative flow cytometry-based assay with a potential for use in tuberculosis diagnostics. Currently available tests do not provide robust discrimination between latent tuberculosis infection (TBI) and tuberculosis disease (TB). The desired application is to distinguish between the two conditions by evaluating the production of a combination of three cytokines: IL-2 (interleukin-2), IFNɣ (interferon gamma) and TNFɑ (tumor necrosis factor alpha) in CD4+ and CD8+ T cells. The study was conducted on 68 participants, divided into two arms according to age (paediatric and adults). Each arm was further split into three categories (non-infection (NI), TBI, TB) based on the immune reaction to Mycobacterium tuberculosis (M.tb) after a close contact with pulmonary TB. Each blood sample was stimulated with specific M.tb antigens present in QuantiFERON tubes (TB1 and TB2). We inferred TBI or TB based on the predominant cytokine response of the CD4+ and/or CD8+ T cells. Significant differences were detected between the NI, TBI and the TB groups in TB1 in the CD4+TNFɑ+parameter in children. Along with IL-2, TNFɑ seems to be the most promising diagnostic marker in both CD4+and CD8+ T cells. However, more detailed analyses on larger cohorts are needed to confirm the observed tendencies.

Electrochemical Detection of Single-Nucleotide Polymorphism Associated with Rifampicin Resistance in Mycobacterium tuberculosis Using Solid-Phase Primer Elongation with Ferrocene-Linked Redox-Labeled Nucleotides

Here, we report the electrochemical detection of single-point mutations using solid-phase isothermal primer elongation with redox-labeled oligonucleotides. A single-base mutation associated with resistance to rifampicin, an antibiotic commonly used for the treatment of Mycobacterium tuberculosis, was used as a model system to demonstrate a proof-of-concept of the approach. Four 5′-thiolated primers, designed to be complementary with the same fragment of the target sequence and differing only in the last base, addressing the polymorphic site, were self-assembled via chemisorption on individual gold electrodes of an array. Following hybridization with single-stranded DNA, Klenow (exo-) DNA polymerase-mediated primer extension with ferrocene-labeled 2′-deoxyribonucleoside triphosphates (dN^FcTPs) was only observed to proceed at the electrode where there was full complementarity between the surface-tethered probe and the target DNA being interrogated. We tested all four ferrocenylethynyl-linked dNTPs and optimized the ratio of labeled/natural nucleotides to achieve maximum sensitivity. Following a 20 min hybridization step, Klenow (exo-) DNA polymerase-mediated primer elongation at 37 °C for 5 min was optimal for the enzymatic incorporation of a ferrocene-labeled nucleotide, achieving unequivocal electrochemical detection of a single-point mutation in 14 samples of genomic DNA extracted from Mycobacterium tuberculosis strains. The approach is rapid, cost-effective, facile, and can be extended to multiplexed electrochemical single-point mutation genotyping.

Impact of maternal pertussis antibodies on the infants' cellular immune responses

INTRODUCTION

Maternal antibody interference of the infant's humoral immune responses raises some concern to the strategy of maternal Tdap (tetanus, diphtheria, acellular pertussis [aP]) vaccination. This study assessed the impact of maternal Tdap antibodies on the infant's pertussis-specific T lymphocyte responses following infant vaccination with an aP containing vaccine, in a term and preterm born cohort.

METHODS

Heparin samples (±0.5mL) were conveniently drawn from infants of a Belgian prospective cohort study (N=79, NCT02511327), including Tdap vaccinated (Boostrix®) and non-vaccinated women (no Tdap vaccine in the last 5 years) that delivered at term or prematurely. Sampling was performed before and one month after primary (8-12-16 weeks) and booster vaccination (13 or 15 months) with DTaP-IPV-HB-PRP~T vaccine (Hexyon®). Pertussis toxin (PT)-specific CD3 +, CD3 +CD4 + and CD3 +CD8 + lymphoblasts and their cytokine secretions were measured using a flow cytometric assay on whole blood (FASCIA) and multiplex technology (Meso Scale Discovery), respectively.

RESULTS

57% of all infants were considered PT-specific CD3 +CD4 + lymphoblasts responders after primary and booster vaccination, whereas 17% were CD3 +CD8 + lymphoblast responders. IFN-γ, IL-13, IL-17A and IL-5 cytokine secretions after primary and booster vaccination were indicative of a mixed T helper (Th) 1/Th2/Th17 cell profile. Lymphoblast and cytokine levels were comparable between term and preterm infants. Non-responders for IL-13 after booster vaccination had higher maternal PT IgG levels at birth when compared to responders.

CONCLUSIONS

Term and preterm born infants are capable of inducing Th1, Th2 and Th17 responses after aP vaccination, yet maternal vaccination modulate these responses. Evaluation of this effect in larger trials is needed.

Specific Host Signatures for the Detection of Tuberculosis Infection in Children in a Low TB Incidence Country

Diagnosis of tuberculosis (TB) in children remains challenging due to unspecific clinical presentation and low bacillary load. In low TB incidence countries, most cases are diagnosed by a contact screening strategy after exposure to an index TB case. Due to the severity of TB in young children, the priority is to determine whether a child is infected or not, whereas differential diagnosis between active TB (aTB) and latent TB constitutes a second step. In Belgium, a low TB incidence country, we prospectively included 47 children with a defined M. tuberculosis infection status (12 children with aTB, 18 with latent TB, and 17 uninfected) (exploratory cohort), and determined the optimal combinations of cytokines secreted by their peripheral blood mononuclear cells in response to a 5-days in vitro stimulation with four different mycobacterial antigens, in an attempt to classify the children according to their infectious status. Correct identification of all infected children was obtained by several combinations of two purified protein derivative (PPD)-induced cytokines (IFN-γ and either GM-CSF, MIP-1α, sCD40L or TNF-α), or by combining PPD-induced IFN-γ with culture-filtrate protein-10 (CFP-10)-induced TNF-α. Alternatively, combining CFP-10-induced TNF-α and IP-10 with heparin-binding haemagglutinin (HBHA)-induced-IFN-γ was more effective in testing recently BCG-vaccinated children or those suspected to be infected with non-tuberculous mycobacteria, providing a correct classification of 97% of the M. tuberculosis-infected children. This combination also correctly classified 98% of the children from a validation cohort comprising 40 M. tuberculosis infected children and 20 non-infected children. Further differentiation between aTB and children with latent TB was more difficult. Combining ESAT-6-induced MIP1-α and IP-10, CFP-10-induced MIG, and HBHA-induced MIG provided a correct classification of 77% of the children from the exploratory cohort but only of 57.5% of those from the validation cohort. We conclude that combining the measurement of 2–4 cytokines induced by three different mycobacterial antigens allows an excellent identification of M. tuberculosis-infected children, whereas differentiating children with aTB from those with latent TB remains far from perfect.