Humoral Responses to Rv1733c, Rv0081, Rv1735c, and Rv1737c DosR Regulon-Encoded Proteins of Mycobacterium tuberculosis in Individuals with Latent Tuberculosis Infection

Mucosal and systemic antigen-specific antibody responses correlate with protection against active tuberculosis in nonhuman primates

BACKGROUND

Increasing evidence supports that antibodies can protect against active tuberculosis (TB) but knowledge of potentially protective antigens, especially in the airways, is limited. The main objective of this study was to identify antigen-specific airway and systemic immunoglobulin isotype responses associated with the outcome of controlled latent Mycobacterium tuberculosis (Mtb) infection (LTBI) versus uncontrolled infection (TB) in nonhuman primates.

METHODS

In a case-control design, using non-parametric group comparisons with false discovery rate adjustments, we assessed antibodies in 57 cynomolgus macaques which, following low-dose airway Mtb infection, developed either LTBI or TB. We investigated airway and systemic IgG, IgA, and IgM responses in paired bronchoalveolar lavage and plasma samples prior to, two-, and 5-6-months post Mtb infection using an antigen-unbiased approach with Mtb glycan and proteome-wide microarrays.

FINDINGS

Macaques that developed LTBI (n = 36) had significantly increased airway and plasma IgA reactivities to specific arabinomannan (AM) motifs prior to Mtb infection compared to those that developed TB (n = 21; p < 0.01, q < 0.05). Furthermore, LTBI macaques had higher plasma IgG reactivity to protein MTB32A (Rv0125) early post Mtb infection (p < 0.05) and increasing airway IgG responses to some proteins over time.

INTERPRETATION

Our results support a protective role of pre-existing mucosal (lung) and systemic IgA to specific Mtb glycan motifs, suggesting that prior exposure to nontuberculous mycobacteria could be protective against TB. They further suggest that IgG to Mtb proteins early post infection could provide an additional protective mechanism. These findings could inform TB vaccine development strategies.

FUNDING

NIH/NIAID AI117927, AI146329, and AI127173 to JMA.

Peptide microarray-based identification of dormancy-associated Mycobacterium tuberculosis antigens inducing immune responses among latent tuberculosis infection individuals in Thailand

Multi-stage tuberculosis (TB) vaccines composed of active- and dormancy-associated antigens are promising to trigger the immune protection against all TB stages. However, scientists are still in quest of the suitable vaccine candidates. In this study, we identified the potential targets for this vaccine in a high TB burden country, Thailand. Peptide microarray was applied to gauge IgA and IgG antibodies specific to 16,730 linear epitopes of 52 dormancy-associated Mycobacterium tuberculosis (M. tb) proteins in three study groups: active tuberculosis (ATB), latent tuberculosis infection (LTBI) and endemic healthy control (EHC). Preferential IgA recognition against epitopes of dormancy-associated proteins was identified in LTBI group. Validation of these findings revealed that LTBI subjects exhibited the greater levels of Rv2659c- and Rv1738-specific IgA than those of household contacts, but less than did ATB subjects. Frequencies of IFNγ-producing CD4⁺ and CD8⁺ T cells induced by proteins Rv2659c and Rv1738 were higher in LTBI than ATB individuals. The results indicated that LTBI group in a high TB burden country demonstrated cell-mediated immune response to proteins Rv2659c and Rv1738 stronger than those of ATB. These immune responses likely contribute to natural protection against dormant M. tb and might be potential targets for a multi-stage TB vaccine.

Alteration of Endocrine Hormones and Antibody Responses in Different Spectrum of Tuberculosis Disease

Effective control of Mycobacterium tuberculosis (Mtb) infection is mediated by multifaceted factors that involve both the endocrine and immune system. Profiling hormones and antibodies in different stages of TB provides insight in the pathogenesis of the disease. In this study, we profiled endocrine hormones (dehydroepiandrosterone (DHEA), cortisol, testosterone, estradiol, growth hormone and leptins) and Mtb strain H37RV lipoarabinomannan (LAM)-specific antibody levels in plasma samples, collected from pulmonary TB (PTB) patients, TB lymphadenitis (TBLN) patients and latently infected (QFT-positive) or uninfected (QFT-negative) apparently healthy individuals using ELISA. Plasma levels of leptin and DHEA were significantly low in PTB and TBLN patients compared to healthy controls (P<0.0001 and P=0.02, respectively), whereas these levels significantly increased following anti-TB treatment (P=0.002 and P=0.0001, respectively) among TB patients. The levels of estradiol and testosterone significantly improved following anti-TB treatment (P=0.03 and P=0.0003, respectively), whereas cortisol and growth hormones declined significantly (P <0.05). Similarly, LAM-specific IgG, IgM and IgA were significantly higher in PTB patients compared to other groups, whereas levels of IgG1 subtype were significantly higher among LTBI groups compared to both TB patients and QFT-negative individuals (P<0.0001). Overall, we observed significantly variable levels of endocrine hormones as well as immunoglobulins across the spectrum of TB illness and such profiling has a significant contribution in selection of effective biomarkers that have roles in TB treatment monitoring or diagnostics. Although this study did not show a functional association between hormones and antibodies, alterations in the levels of these biomarkers suggest the key roles these markers play in TB pathogenesis.

Revisiting tuberculosis screening: An insight to complementary diagnosis and prospective molecular approaches for the recognition of the dormant TB infection in human and cattle hosts

Tuberculosis (TB) is defined as a chronic infection in both human and cattle hosts and many subclinical cases remain undetected. After the pathogen is inhaled by a host, phagocyted bacilli can persist inside macrophages surviving intracellularly. Hosts develop granulomatous lesions in the lungs or lymph nodes, limiting infection. However, bacilli become persister cells. Immunological diagnosis of TB is performed basically by routine tuberculin skin test (TST), and in some cases, by ancillary interferon-gamma release assay (IGRA). The concept of human latent TB infection (LTBI) by M. tuberculosis is recognized in cohorts without symptoms by routine clinical diagnostic tests, and nowadays IGRA tests are used to confirm LTBI with either active or latent specific antigens of M. tuberculosis. On the other hand, dormant infection in cattle by M. bovis has not been described by TST or IGRA testing as complications occur by cross-reactive immune responses to homolog antigens of environmental mycobacteria or a false-negative test by anergic states of a wained bovine immunity, evidencing the need for deciphering more specific biomarkers by new-generation platforms of analysis for detection of M. bovis dormant infection. The study and description of bovine latent TB infection (boLTBI) would permit the recognition of hidden animal infection with an increase in the sensitivity of routine tests for an accurate estimation of infected dairy cattle. Evidence of immunological and experimental analysis of LTBI should be taken into account to improve the study and the description of the still neglected boLTBI.

The knowns and unknowns of latent Mycobacterium tuberculosis infection

Humans have been infected with Mycobacterium tuberculosis (Mtb) for thousands of years. While tuberculosis (TB), one of the deadliest infectious diseases, is caused by uncontrolled Mtb infection, over 90% of presumed infected individuals remain asymptomatic and contain Mtb in a latent TB infection (LTBI) without ever developing disease, and some may clear the infection. A small number of heavily Mtb-exposed individuals appear to resist developing traditional LTBI. Because Mtb has mechanisms for intracellular survival and immune evasion, successful control involves all of the arms of the immune system. Here, we focus on immune responses to Mtb in humans and nonhuman primates and discuss new concepts and outline major knowledge gaps in our understanding of LTBI, ranging from the earliest events of exposure and infection to success or failure of Mtb control.

Mycobacterium tuberculosis infection is associated with increased B cell responses to unrelated pathogens

Antigens from Mycobacterium tuberculosis (M.tb), have been shown to stimulate human B cell responses to unrelated recall antigens in vitro. However, it is not known whether natural M.tb infection or whether vaccination with, Mycobacterium bovis BCG, has a similar effect. This study investigated the effects of M.tb infection and BCG vaccination on B cell responses to heterologous pathogen recall antigens. Antibodies against several bacterial and viral pathogens were quantified by ELISA in 68 uninfected controls, 62 individuals with latent TB infection (LTBI) and 107 active pulmonary TB (APTB) cases, and 24 recently BCG-vaccinated adolescents and naive controls. Antibody avidity was investigated using surface plasmon resonance and B cell ELISPOTs were used to measure plasmablast and memory B cell responses (MBC) in APTB cases and healthy donor controls. APTB was associated with higher levels of antibodies to respiratory syncytial virus and measles virus, compared to uninfected controls. BCG vaccination did not alter levels of antibodies against heterologous pathogens. Tetanus toxoid (TT)-specific antibody avidity was increased in APTB cases in comparison to uninfected individuals and the ratio of TT-specific plasmablasts to MBCs in the APTB cases was 7:1. M.tb infection is associated with increased antibody responses to heterologous pathogens in human subjects.

Career development for infection and immunity research in Uganda: a decade of experience from the Makerere University - Uganda Virus Research Institute research and training programme

Background: The Makerere University/Uganda Virus Research Institute (UVRI) Centre of Excellence for Infection & Immunity Research and Training (MUII) is a collaborative programme supporting excellence in Infection and Immunity (I&I) research in Uganda. Set up in 2008, MUII aims to produce internationally competitive Ugandan and East African I&I research leaders, and develop human and infrastructural resources to support research and training excellence. We undertook an internal evaluation of MUII’s achievements, challenges and lessons learned between 08-2008 and 12-2019, to inform programmes seeking to build Africa’s health research expertise.

Methods: Quantitative data were abstracted from programme annual reports. Qualitative data were obtained in 03-04/2019: a cross-sectional evaluation was undertaken among a purposefully selected representative sample of 27 trainees and two programme staff. Qualitative data was analysed according to pre-determined themes of achievements, challenges, lessons learned and recommendations for improvement.

Results: By 12-2019, MUII had supported 68 fellowships at master’s-level and above (50% female: 23 Masters, 27 PhD, 15 post-doctoral, three group-leaders) and over 1,000 internships. Fellows reported career advancement, mentorship by experts, and improved research skills and outputs. Fellows have published over 300 papers, secured grants worth over £20m, established over 40 international collaborations, and taken on research and academic leadership positions in the country. Key lessons were: i) Efficient administration provides a conducive environment for high quality research; ii) Institutions need supportive policies for procurement, including provisions for purchases of specific biological research reagents from international manufacturers; iii) Strong international and multi-disciplinary collaboration provides a critical mass of expertise to mentor researchers in development; and iv) Mentorship catalyses young scientists to progress from graduate trainees to productive academic researchers, relevant to society’s most pressing health challenges.

Conclusions: Sustainable academic productivity can be achieved through efficient operational support, global collaboration and mentorship to provide solutions to Africa’s health challenges.

Career development for infection and immunity research in Uganda: a decade of experience from the Makerere University – Uganda Virus Research Institute research and training programme

Background: The Makerere University/Uganda Virus Research Institute (UVRI) Centre of Excellence for Infection & Immunity Research and Training (MUII) is a collaborative programme supporting excellence in Infection and Immunity (I&I) research in Uganda. Set up in 2008, MUII aims to produce internationally competitive Ugandan and East African I&I research leaders, and develop human and infrastructural resources to support research and training excellence. We undertook an internal evaluation of MUII’s achievements, challenges and lessons learned between August 2008 and December 2019, to inform programmes seeking to build Africa’s health research expertise. Methods: Quantitative data were abstracted from programme annual reports. Qualitative data were obtained in March and April 2019: a cross-sectional evaluation was undertaken among a purposefully selected representative sample of 27 trainees and two programme staff. Qualitative data was analysed according to pre-determined themes of achievements, challenges, lessons learned and recommendations for improvement. Results: By December 2019, MUII had supported 68 fellowships at master’s-level and above (50% female: 23 Masters, 27 PhD, 15 post-doctoral, three group-leader fellows) and over 1,000 internships. Fellows reported career advancement, mentorship by experts, and improved research skills and outputs. Fellows have published over 300 papers, secured grants worth over £20m, established over 40 international collaborations, and taken on research and academic leadership positions in the country. Key lessons for success include the following: efficient administration provides an enabling environment; institutions need supportive policies for procurement, including provisions for purchases of specific biological research reagents from international manufacturers; strong international, multi-disciplinary collaboration provides a critical mass of expertise to mentor researchers in development; and mentorship catalyses young scientists to progress from graduate trainees to productive academic researchers, relevant to society’s most pressing health challenges. Conclusions: Sustainable academic productivity can be achieved through efficient operational support, global collaboration and mentorship to provide solutions to Africa’s health challenges.

Maternal Latent Mycobacterium tuberculosis Does Not Affect the Infant Immune Response Following BCG at Birth: An Observational Longitudinal Study in Uganda

Background: BCG has low efficacy in tropical countries. We hypothesized that maternal latent Mycobacterium tuberculosis (M.tb) infection (LTBI) results in fetal tolerance to mycobacterial antigens and impaired responses to BCG immunization.

Methods: We enrolled 132 LTBI-positive and 150 LTBI-negative mothers and their babies in Entebbe, Uganda. Infants were BCG-immunized at birth. Cord blood and samples at weeks 1, 4, 6, 10, 14, 24, and 52 were analyzed for cytokine/chemokine responses to M.tb antigens by Luminex 17-plex assay in 6-day whole blood cultures and antibody responses by ELISA. Of the 17 Luminex analytes, seven (IL-2, IL-5, IL-10, IL-13, IL-17A, TNF, and IFN-γ) were included in the main analysis as they were considered most likely to represent T cell responses. Immune sensitization was defined as a detectable cord blood cytokine response to PPD for any of the seven cytokines. Patterns of cytokine and antibody responses were compared between infants of mothers with and without LTBI using linear mixed models adjusting for confounders.

Results: Most infants (73%) were sensitized in utero to M.tb antigens, with no overall difference seen between infants born to mothers with or without LTBI. Patterns of post-BCG cytokine and antibody responses to mycobacterial antigens were similar between the two infant groups.

Conclusions: Our data do not support the hypothesis that maternal LTBI results in an impaired response to BCG immunization, in Ugandan infants. BCG vaccination at or shortly after birth is likely to be beneficial to all infants, irrespective of maternal LTBI status.

Two-Hit in vitro T-Cell Stimulation Detects Mycobacterium tuberculosis Infection in QuantiFERON Negative Tuberculosis Patients and Healthy Contacts From Ghana

IFN-γ release assays [e.g., QuantiFERON (QFT)] are widely used for diagnosis of Mycobacterium tuberculosis (Mtb) infection. T-cell responses against QFT antigens ESAT6 and CFP10 are highly Mtb specific but previous studies indicated suboptimal assay sensitivity. Especially for potentially infected healthy contacts (HCs) of tuberculosis patients, alternative antigen usage and more sensitive tests may contribute to improved detection of latent Mtb infection. In a pilot case-control study of tuberculosis patients (n = 22) and HCs (n = 20) from Ghana, we performed multifaceted in vitro assays to identify optimal assay conditions. This included a two-hit stimulation assay, which is based on initial and second re-stimulation with the same antigen on d6 and intracellular IFN-γ analysis, to compare T-cell responses against ESAT6/CFP10 (E6/C10) and selected latency antigens (i.e. Rv2628, Rv1733, Rv2031, Rv3407) of Mtb. Considerable subgroups of tuberculosis patients (64%) and HCs (75%) had negative or indeterminate QFT results partially accompanied by moderate PHA induced responses and high IFN-γ background values. Intracellular IFN-γ analysis of E6/C10 specific CD4⁺ T-cell subpopulations and evaluation of responder frequencies had only moderate effects on assay sensitivity. However, two-hit in vitro stimulation significantly enhanced E6/C10 specific IFN-γ positive T-cell proportions especially in QFT non-responders, and in both study groups. Mtb latency antigen-specific T cells against Rv1733 and Rv2628 were especially detected in HCs after two-hit stimulation and T-cell responses against Rv2628 were highly capable to discriminate tuberculosis patients and HCs. Two-hit in vitro stimulation may improve moderate sensitivity of short term IFN-γ based assays, like QFT, to detect Mtb infection. Latency stage-specific antigens added significantly to detection of Mtb infection in HCs and tuberculosis patients with negative QFT test results.

Characterising antibody avidity in individuals of varied Mycobacterium tuberculosis infection status using surface plasmon resonance

There is increasing evidence supporting a role for antibodies in protection against tuberculosis (TB), with functional antibodies being described in the latent state of TB infection. Antibody avidity is an important determinant of antibody-mediated protection. This study characterised the avidity of antibodies against Ag85A, an immunodominant Mycobacterium tuberculosis (M.tb) antigen and constituent of several anti-TB vaccine candidates, in individuals of varied M.tb infection status. Avidity of Ag85A specific antibodies was measured in 30 uninfected controls, 34 individuals with latent TB infection (LTBI) and 75 active pulmonary TB (APTB) cases, employing the more commonly used chaotrope-based dissociation assays, and surface plasmon resonance (SPR). Chaotrope-based assays indicated that APTB was associated with a higher antibody avidity index compared to uninfected controls [adjusted geometric mean ratio (GMR): 1.641, 95% confidence interval (CI): 1.153, 2.337, p = 0.006, q = 0.018] and to individuals with LTBI [adjusted GMR: 1.604, 95% CI: 1.282, 2.006, p < 0.001, q <0.001]. SPR assays showed that APTB was associated with slower dissociation rates, an indication of higher avidity, compared to uninfected controls (adjusted GMR: 0.796, 95% CI: 0.681, 0.932, p = 0.004, q = 0.012) and there was also weak evidence of more avid antibodies in the LTBI compared to the uninfected controls (adjusted GMR: 0.871, 95% CI: 0.763, 0.994, p = 0.041, q = 0.123). We found no statistically significant differences in anti-Ag85A antibody avidity between the APTB and LTBI groups. This study shows that antibodies of increased avidity are generated against a principle vaccine antigen in M.tb infected individuals. It would be important to determine whether TB vaccines are able to elicit a similar response. Additionally, more research is needed to determine whether antibody avidity is important in protection against infection and disease.

Use of QuantiFERON®-TB Gold in-tube culture supernatants for measurement of antibody responses

QuantiFERON®-TB Gold in-tube (QFT-GIT) supernatants may be important samples for use in assessment of anti-tuberculosis (TB) antibodies when only limited volumes of blood can be collected and when a combination of antibody and cytokine measurements are required. These analytes, when used together, may also have the potential to differentiate active pulmonary TB (APTB) from latent TB infection (LTBI). However, few studies have explored the use of QFT-GIT supernatants for investigations of antibody responses. This study determined the correlation and agreement between anti-CFP-10 and anti-ESAT-6 antibody concentrations in QFT-GIT nil supernatant and serum pairs from 68 TB household contacts. We also explored the ability of Mycobacterium tuberculosis (M.tb) specific antibodies, or ratios of antibody to interferon gamma (IFN-γ) in QFT-GIT supernatants, to differentiate 97 APTB cases from 58 individuals with LTBI. Sputum smear microscopy was used to define APTB, whereas the QFT-GIT and tuberculin skin test were used to define LTBI. There were strong and statistically significant correlations between anti-CFP-10 and anti-ESAT-6 antibodies in unstimulated QFT-GIT supernatants and sera (r = 0.89; p<0.0001 for both), and no significant differences in antibody concentration between them. Anti-CFP-10 & anti-ESAT-6 antibodies differentiated APTB from LTBI with sensitivities of 88.7% & 71.1% and specificities of 41.4% & 51.7% respectively. Anti-CFP-10 antibody/M.tb specific IFN-γ and anti-ESAT-6 antibody/M.tb specific IFN-γ ratios had sensitivities of 48.5% & 54.6% and specificities of 89.7% and 75.9% respectively. We conclude that QFT-GIT nil supernatants may be used in the place of sera when measuring antibody responses, reducing blood volumes needed for such investigations. Antibodies in QFT-GIT nil supernatants on their own discriminate APTB from LTBI with high sensitivity but have poor specificity, whereas the reverse is true when antibodies are used in combination with M.tb specific cytokines. Further antibody and antibody/cytokine combinations need to be explored to achieve better diagnostic accuracy.

Mycobacterium tuberculosis Latent Antigen Rv2029c from the Multistage DNA Vaccine A39 Drives TH1 Responses via TLR-mediated Macrophage Activation

Targeting of Mycobacterium tuberculosis (MTB) latent antigens comprises a crucial strategy for the development of alternative tuberculosis (TB) vaccine(s) that protects against TB reactivation. Here, we generated a multistage DNA vaccine, A39, containing the early antigens Ag85A and Rv3425 as well as the latency-associated protein Rv2029c, which conferred protective immunity in a pre-exposure mouse model. Moreover, administration of the A39 vaccination after MTB exposure inhibited reactivation and resulted in significantly lower bacterial loads in the lungs and spleen of mice, compared to those in the control population. Subsequently, we investigated the effect of Rv2029c on innate immunity and characterized the molecular details of the interaction of this protein with the host via iTRAQ proteomic and biochemical assay analyses. Rv2029c activated macrophages, triggered the production of pro-inflammatory cytokines, and promoted toll-like receptor/mitogen-activated protein kinase (TLR/MAPK)-dependent macrophage apoptosis. Furthermore, Rv2029c treatment enhanced the ability of Mycobacterium bovis Bacillus Calmette-Guérin (BCG)-infected macrophages to present antigens to CD4⁺ T cells in vitro, which correlated with an increase in MHC-II expression. Lastly, Rv2029c-treated macrophages activated T cells, effectively polarized CD4⁺ and CD8⁺ T cells to secrete IFN-γ and IL-2, and specifically expanded a population of CD44^highCD62L^lowCD4⁺/CD8⁺ effector/memory cells, indicating that Rv2029c, as a specific recall antigen, contributes to Th1 polarization in T cell immunity. These results suggest that Rv2029c and A39 comprise promising targets for the development of next-generation clinical TB therapeutic vaccines.