Leveraging Antibody, B Cell and Fc Receptor Interactions to Understand Heterogeneous Immune Responses in Tuberculosis

Evaluation of serological assays for the diagnosis of childhood tuberculosis disease: a study protocol

BACKGROUND

Tuberculosis (TB) poses a major public health challenge, particularly in children. A substantial proportion of children with TB disease remain undetected and unconfirmed. Therefore, there is an urgent need for a highly sensitive point-of-care test. This study aims to assess the performance of serological assays based on various antigen targets and antibody properties in distinguishing children (0-18 years) with TB disease (1) from healthy TB-exposed children, (2) children with non-TB lower respiratory tract infections, and (3) from children with TB infection.

METHODS

The study will use biobanked plasma samples collected from three prospective multicentric diagnostic observational studies: the Childhood TB in Switzerland (CITRUS) study, the Pediatric TB Research Network in Spain (pTBred), and the Procalcitonin guidance to reduce antibiotic treatment of lower respiratory tract infections in children and adolescents (ProPAED) study. Included are children diagnosed with TB disease or infection, healthy TB-exposed children, and sick children with non-TB lower respiratory tract infection. Serological multiplex assays will be performed to identify M. tuberculosis antigen-specific antibody features, including isotypes, subclasses, Fc receptor (FcR) binding, and IgG glycosylation.

DISCUSSION

The findings from this study will help to design serological assays for diagnosing TB disease in children. Importantly, those assays could easily be developed as low-cost point-of-care tests, thereby offering a potential solution for resource-constrained settings.

CLINICALTRIALS

GOV IDENTIFIER

NCT03044509.

Microbiome Alteration in Lung Tissues of Tuberculosis Patients Revealed by Metagenomic Next-Generation Sequencing and Immune-Related Transcriptional Profile Identified by Transcriptome Sequencing

This study explored alterations in the respiratory microbiome and transcriptome after Mycobacterium tuberculosis infection in tuberculosis (TB) patients. Metagenomic next-generation sequencing (mNGS) was adopted to reveal the microbiome in lung tissues from 110 TB and 25 nontuberculous (NonTB) patients. Transcriptome sequencing was performed in TB tissues (n = 3), tissues adjacent to TB (ParaTB, n = 3), and NonTB tissues (n = 3) to analyze differentially expressed genes (DEGs) and functional pathways. The microbial β diversity (p = 0.01325) in TB patients differed from that in the NonTB group, with 17 microbial species distinctively distributed. Eighty-three co-up-regulated DEGs were identified in the TB versus NonTB and the TB versus ParaTB comparison groups, and six were associated with immune response to Mtb. These DEGs were significantly enriched in the signaling pathways such as immune response, NF-κB, and B cell receptor. Data in the lung tissue microbiome and transcriptome in TB patients offer a sufficient understanding of the pathogenesis of TB.

Pathogenicity and virulence of Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis, an infectious disease with one of the highest morbidity and mortality rates worldwide. Leveraging its highly evolved repertoire of non-protein and protein virulence factors, Mtb invades through the airway, subverts host immunity, establishes its survival niche, and ultimately escapes in the setting of active disease to initiate another round of infection in a naive host. In this review, we will provide a concise synopsis of the infectious life cycle of Mtb and its clinical and epidemiologic significance. We will also take stock of its virulence factors and pathogenic mechanisms that modulate host immunity and facilitate its spread. Developing a greater understanding of the interface between Mtb virulence factors and host defences will enable progress toward improved vaccines and therapeutics to prevent and treat tuberculosis.

Non-clinical evaluation of local and systemic immunity induced by different vaccination strategies of the candidate tuberculosis vaccine M72/AS01

A new efficacious tuberculosis vaccine targeting adolescents/adults represents an urgent medical need. The M72/AS01E vaccine candidate protected half of the latently-infected adults against progression to pulmonary tuberculosis in a Phase IIb trial (NCT01755598). We report that three immunizations of mice, two weeks apart, with AS01-adjuvanted M72 induced polyfunctional, Th1-cytokine-expressing M72-specific CD4+/CD8+ T cells in blood and lungs, with the highest frequencies in lungs. Antigen-dose reductions across the three vaccinations skewed pulmonary CD4+ T-cell profiles towards IL-17 expression. In blood, reducing antigen and adjuvant doses of only the third injection (to 1/5th or 1/25th of those of the first injections) did not significantly alter CD4+ T-cell/antibody responses; applying a 10-week delay for the fractional third dose enhanced antibody titers. Delaying a full-dose booster enhanced systemic CD4+ T-cell and antibody responses. Cross-reactivity with PPE and non-PPE proteins was assessed, as Mycobacterium tuberculosis (Mtb) virulence factors and evasion mechanisms are often associated with PE/PPE proteins, to which Mtb39a (contained in M72) belongs. In silico/in vivo analyses revealed that M72/AS01 induced cross-reactive systemic CD4+ T-cell responses to epitopes in a non-vaccine antigen (putative latency-associated Mtb protein PPE24/Rv1753c). These preclinical data describing novel mechanisms of M72/AS01-induced immunity could guide future clinical development of the vaccine.

Antibody glycosylation correlates with disease progression in SIV-Mycobacterium tuberculosis coinfected cynomolgus macaques

Objectives

Tuberculosis (TB) remains a substantial cause of morbidity and mortality among people living with human immunodeficiency virus (HIV) worldwide. However, the immunological mechanisms associated with the enhanced susceptibility among HIV-positive individuals remain largely unknown.

Methods

Here, we used a simian immunodeficiency virus (SIV)/TB-coinfection Mauritian cynomolgus macaque (MCM) model to examine humoral responses from the plasma of SIV-negative (n = 8) and SIV-positive (n = 7) MCM 8-week postinfection with Mycobacterium tuberculosis (Mtb).

Results

Antibody responses to Mtb were impaired during SIV coinfection. Elevated inflammatory bulk IgG antibody glycosylation patterns were observed in coinfected macaques early at 8-week post-Mtb infection, including increased agalactosylation (G0) and reduced di-galactosylation (G2), which correlated with endpoint Mtb bacterial burden and gross pathology scores, as well as the time-to-necropsy.

Conclusion

These studies suggest that humoral immunity may contribute to control of TB disease and support growing literature that highlights antibody Fc glycosylation as a biomarker of TB disease progression.

Vaccine development against tuberculosis before and after Covid-19

Coronavirus disease (Covid-19) has not only shaped awareness of the impact of infectious diseases on global health. It has also provided instructive lessons for better prevention strategies against new and current infectious diseases of major importance. Tuberculosis (TB) is a major current health threat caused by Mycobacterium tuberculosis (Mtb) which has claimed more lives than any other pathogen over the last few centuries. Hence, better intervention measures, notably novel vaccines, are urgently needed to accomplish the goal of the World Health Organization to end TB by 2030. This article describes how the research and development of TB vaccines can benefit from recent developments in the Covid-19 vaccine pipeline from research to clinical development and outlines how the field of TB research can pursue its own approaches. It begins with a brief discussion of major vaccine platforms in general terms followed by a short description of the most widely applied Covid-19 vaccines. Next, different vaccination regimes and particular hurdles for TB vaccine research and development are described. This specifically considers the complex immune mechanisms underlying protection and pathology in TB which involve innate as well as acquired immune mechanisms and strongly depend on fine tuning the response. A brief description of the TB vaccine candidates that have entered clinical trials follows. Finally, it discusses how experiences from Covid-19 vaccine research, development, and rollout can and have been applied to the TB vaccine pipeline, emphasizing similarities and dissimilarities.

Airway T cells are a correlate of i.v. Bacille Calmette-Guerin-mediated protection against tuberculosis in rhesus macaques

Bacille Calmette-Guerin (BCG), the only approved Mycobacterium tuberculosis (Mtb) vaccine, provides limited durable protection when administered intradermally. However, recent work revealed that intravenous (i.v.) BCG administration yielded greater protection in macaques. Here, we perform a dose-ranging study of i.v. BCG vaccination in macaques to generate a range of immune responses and define correlates of protection. Seventeen of 34 macaques had no detectable infection after Mtb challenge. Multivariate analysis incorporating longitudinal cellular and humoral immune parameters uncovered an extensive and highly coordinated immune response from the bronchoalveolar lavage (BAL). A minimal signature predicting protection contained four BAL immune features, of which three remained significant after dose correction: frequency of CD4 T cells producing TNF with interferon γ (IFNγ), frequency of those producing TNF with IL-17, and the number of NK cells. Blood immune features were less predictive of protection. We conclude that CD4 T cell immunity and NK cells in the airway correlate with protection following i.v. BCG.

Immune cell interactions in tuberculosis

Despite having been identified as the organism that causes tuberculosis in 1882, Mycobacterium tuberculosis has managed to still evade our understanding of the protective immune response against it, defying the development of an effective vaccine. Technology and novel experimental models have revealed much new knowledge, particularly with respect to the heterogeneity of the bacillus and the host response. This review focuses on certain immunological elements that have recently yielded exciting data and highlights the importance of taking a holistic approach to understanding the interaction of M. tuberculosis with the many host cells that contribute to the development of protective immunity.

B21 DNA vaccine expressing ag85b, rv2029c, and rv1738 confers a robust therapeutic effect against latent Mycobacterium tuberculosis infection

Latent tuberculosis infection (LTBI) treatment is known to accelerate the decline in TB incidence, especially in high-risk populations. Mycobacterium tuberculosis (M. tb) expression profiles differ at different growth periods, and vaccines protective and therapeutic effects may increase when they include antigenic compositions from different periods. To develop a post-exposure vaccine that targets LTBI, we constructed four therapeutic DNA vaccines (A39, B37, B31, and B21) using different combinations of antigens from the proliferation phase (Ag85A, Ag85B), PE/PPE family (Rv3425), and latent phase (Rv2029c, Rv1813c, Rv1738). We compared the immunogenicity of the four DNA vaccines in C57BL/6j mice. The B21 vaccine stimulated the strongest cellular immune responses, namely Th1/Th17 and CD8⁺ cytotoxic T lymphocyte responses. It also induced the generation of strengthened effector memory and central memory T cells. In latently infected mice, the B21 vaccine significantly reduced bacterial loads in the spleens and lungs and decreased lung pathology. In conclusion, the B21 DNA vaccine can enhance T cell responses and control the reactivation of LTBI.

Modulation of TDM-induced granuloma pathology by human lactoferrin: a persistent effect in mice

Lactoferrin (LTF), an iron binding protein, is known to exhibit immune modulatory effects on pulmonary pathology during insult-induced models of primary Mycobacterium tuberculosis (Mtb) infection. The effects of LTF correlate with modulation of the immune related development of the pathology, and altering of the histological nature of the physically compact and dense lung granuloma in mice. Specifically, a recombinant human version of LTF limits immediate progression of granulomatous severity following administration of the Mtb cell wall mycolic acid, trehalose 6,6'-dimycolate (TDM), in part through reduced pro-inflammatory responses known to control these events. This current study investigates a limited course of LTF to modulate not only initiation, but also maintenance and resolution of pathology post development of the granulomatous response in mice. Comparison is made to a fusion of LTF with the Fc domain of IgG2 (FcLTF), which is known to extend LTF half-life in circulation. TDM induced granulomas were examined at extended times post insult (day 7 and 14). Both LTF and the novel FcLTF exerted sustained effects on lung granuloma pathology. Reduction of pulmonary pro-inflammatory cytokines TNF-α and IL-1β occurred, correlating with reduced pathology. Increase in IL-6, known to regulate granuloma maintenance, was also seen with the LTFs. The FcLTF demonstrated greater impact than the recombinant LTF, and was superior in limiting damage to pulmonary tissues while limiting residual inflammatory cytokine production.