Distinct gene expression signatures comparing latent tuberculosis infection with different routes of Bacillus Calmette-Guérin vaccination.

Tuberculosis remains an international health threat partly because of limited protection from pulmonary tuberculosis provided by standard intradermal vaccination with Bacillus of Calmette and Guérin (BCG); this may reflect the inability of intradermal vaccination to optimally induce pulmonary immunity. In contrast, respiratory Mycobacterium tuberculosis infection usually results in the immune-mediated bacillary containment of latent tuberculosis infection (LTBI). Here we present RNA-Seq-based assessments of systemic and pulmonary immune cells from LTBI participants and recipients of intradermal and oral BCG. LTBI individuals uniquely display ongoing immune activation and robust CD4 T cell recall responses in blood and lung. Intradermal BCG is associated with robust systemic immunity but only limited pulmonary immunity. Conversely, oral BCG induces limited systemic immunity but distinct pulmonary responses including enhanced inflammasome activation potentially associated with mucosal-associated invariant T cells. Further, IL-9 is identified as a component of systemic immunity in LTBI and intradermal BCG, and pulmonary immunity following oral BCG.

Phase 1 Open-Label Dose Escalation Trial for the Development of a Human Bacillus Calmette-Guérin Challenge Model for Assessment of Tuberculosis Immunity In Vivo.

BACKGROUND: A controlled human infection model for assessing tuberculosis (TB) immunity can accelerate new vaccine development. METHODS: In this phase 1 dose escalation trial, 92 healthy adults received a single intradermal injection of 2 × 106 to 16 × 106 colony-forming units of Bacillus Calmette-Guérin (BCG). The primary endpoints were safety and BCG shedding as measured by quantitative polymerase chain reaction, colony-forming unit plating, and MGIT BACTEC culture. RESULTS: Doses up to 8 × 106 were safe, and there was evidence for increased BCG shedding with dose escalation. The MGIT time-to-positivity assay was the most consistent and precise measure of shedding. Power analyses indicated that 10% differences in MGIT time to positivity (area under the curve) could be detected in small cohorts (n = 30). Potential biomarkers of mycobacterial immunity were identified that correlated with shedding. Transcriptomic analysis uncovered dose- and time-dependent effects of BCG challenge and identified a putative transcriptional TB protective signature. Furthermore, we identified immunologic and transcriptomal differences that could represent an immune component underlying the observed higher rate of TB disease incidence in males. CONCLUSIONS: The safety, reactogenicity, and immunogenicity profiles indicate that this BCG human challenge model is feasible for assessing in vivo TB immunity and could facilitate the vaccine development process. CLINICAL TRIALS REGISTRATION: NCT01868464 (ClinicalTrials.gov).

Identification of immunodominant T cell epitopes induced by natural Zika virus infection.

Zika virus (ZIKV) is a flavivirus primarily transmitted by Aedes species mosquitoes, first discovered in Africa in 1947, that disseminated through Southeast Asia and the Pacific Islands in the 2000s. The first ZIKV infections in the Americas were identified in 2014, and infections exploded through populations in Brazil and other countries in 2015/16. ZIKV infection during pregnancy can cause severe brain and eye defects in offspring, and infection in adults has been associated with higher risks of Guillain-Barré syndrome. We initiated a study to describe the natural history of Zika (the disease) and the immune response to infection, for which some results have been reported. In this paper, we identify ZIKV-specific CD4+ and CD8+ T cell epitopes that induce responses during infection. Two screening approaches were utilized: an untargeted approach with overlapping peptide arrays spanning the entire viral genome, and a targeted approach utilizing peptides predicted to bind human MHC molecules. Immunoinformatic tools were used to identify conserved MHC class I supertype binders and promiscuous class II binding peptide clusters predicted to bind 9 common class II alleles. T cell responses were evaluated in overnight IFN-γ ELISPOT assays. We found that MHC supertype binding predictions outperformed the bulk overlapping peptide approach. Diverse CD4+ T cell responses were observed in most ZIKV-infected participants, while responses to CD8+ T cell epitopes were more limited. Most individuals developed a robust T cell response against epitopes restricted to a single MHC class I supertype and only a single or few CD8+ T cell epitopes overall, suggesting a strong immunodominance phenomenon. Noteworthy is that many epitopes were commonly immunodominant across persons expressing the same class I supertype. Nearly all of the identified epitopes are unique to ZIKV and are not present in Dengue viruses. Collectively, we identified 31 immunogenic peptides restricted by the 6 major class I supertypes and 27 promiscuous class II epitopes. These sequences are highly relevant for design of T cell-targeted ZIKV vaccines and monitoring T cell responses to Zika virus infection and vaccination.

Impact of BCG vaccination on the repertoire of human γδ T cell receptors.

Introduction: Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) infection is a serious threat to human health. Vaccination with BCG prevents the development of the most severe forms of TB disease in infants and was recently shown to prevent Mtb infection in previously uninfected adolescents. γδ T cells play a major role in host defense at mucosal sites and are known to respond robustly to mycobacterial infection. However, our understanding of the effects of BCG vaccination on γδ T cell responses is incomplete. Methods: In this study we performed γδ T cell receptor (TCR) repertoire sequencing of samples provided pre- and post-BCG vaccination from 10 individuals to identify specific receptors and TCR clones that are induced by BCG. Results: Overall, there was no change in the diversity of γTCR or δTCR clonotypes in post- vs pre-BCG samples. Furthermore, the frequencies of TCR variable and joining region genes were minimally modulated by BCG vaccination at either the γTCR or δTCR loci. However, the γTCR and δTCR repertoires of individuals were highly dynamic; a median of ~1% of γTCR and ~6% of δTCR in the repertoire were found to significantly expand or contract in post- vs pre-BCG comparisons (FDR-q < 0.05). While many of the clonotypes whose frequency changed after BCG vaccination were not shared among multiple individuals in the cohort, several shared (i.e., "public") clonotypes were identified with a consistent increase or decrease in frequency across more than one individual; the degree of sharing of these clonotypes was significantly greater than the minimal sharing that would be expected among γTCR and δTCR repertoires. An in vitro analysis of Mtb antigen-reactive γδ T cells identified clonotypes that were similar or identical to the single-chain γTCRs and δTCRs that changed consistently after BCG vaccination; pairings of γTCRs and δTCRs that increased after BCG vaccination were significantly over-represented among the Mtb-reactive γδ T cells (p = 1.2e-6). Discussion: These findings generate hypotheses about specific γδTCR clonotypes that may expand in response to BCG vaccination and may recognize Mtb antigens. Future studies are required to validate and characterize these clonotypes, with an aim to better understand the role of γδ T cells in Mtb immunity.

Safety and immunogenicity of a thermostable ID93 + GLA-SE tuberculosis vaccine candidate in healthy adults.

Adjuvant-containing subunit vaccines represent a promising approach for protection against tuberculosis (TB), but current candidates require refrigerated storage. Here we present results from a randomized, double-blinded Phase 1 clinical trial (NCT03722472) evaluating the safety, tolerability, and immunogenicity of a thermostable lyophilized single-vial presentation of the ID93 + GLA-SE vaccine candidate compared to the non-thermostable two-vial vaccine presentation in healthy adults. Participants were monitored for primary, secondary, and exploratory endpoints following intramuscular administration of two vaccine doses 56 days apart. Primary endpoints included local and systemic reactogenicity and adverse events. Secondary endpoints included antigen-specific antibody (IgG) and cellular immune responses (cytokine-producing peripheral blood mononuclear cells and T cells). Both vaccine presentations are safe and well tolerated and elicit robust antigen-specific serum antibody and Th1-type cellular immune responses. Compared to the non-thermostable presentation, the thermostable vaccine formulation generates greater serum antibody responses (p < 0.05) and more antibody-secreting cells (p < 0.05). In this work, we show the thermostable ID93 + GLA-SE vaccine candidate is safe and immunogenic in healthy adults.

Corrigendum: The Vacc-SeqQC project: Benchmarking RNA-Seq for clinical vaccine studies.

[This corrects the article DOI: 10.3389/fimmu.2022.1093242.].

The Vacc-SeqQC project: Benchmarking RNA-Seq for clinical vaccine studies.

Introduction: Over the last decade, the field of systems vaccinology has emerged, in which high throughput transcriptomics and other omics assays are used to probe changes of the innate and adaptive immune system in response to vaccination. The goal of this study was to benchmark key technical and analytical parameters of RNA sequencing (RNA-seq) in the context of a multi-site, double-blind randomized vaccine clinical trial. Methods: We collected longitudinal peripheral blood mononuclear cell (PBMC) samples from 10 subjects before and after vaccination with a live attenuated Francisella tularensis vaccine and performed RNA-Seq at two different sites using aliquots from the same sample to generate two replicate datasets (5 time points for 50 samples each). We evaluated the impact of (i) filtering lowly-expressed genes, (ii) using external RNA controls, (iii) fold change and false discovery rate (FDR) filtering, (iv) read length, and (v) sequencing depth on differential expressed genes (DEGs) concordance between replicate datasets. Using synthetic mRNA spike-ins, we developed a method for empirically establishing minimal read-count thresholds for maintaining fold change accuracy on a per-experiment basis. We defined a reference PBMC transcriptome by pooling sequence data and established the impact of sequencing depth and gene filtering on transcriptome representation. Lastly, we modeled statistical power to detect DEGs for a range of sample sizes, effect sizes, and sequencing depths. Results and Discussion: Our results showed that (i) filtering lowly-expressed genes is recommended to improve fold-change accuracy and inter-site agreement, if possible guided by mRNA spike-ins (ii) read length did not have a major impact on DEG detection, (iii) applying fold-change cutoffs for DEG detection reduced inter-set agreement and should be used with caution, if at all, (iv) reduction in sequencing depth had a minimal impact on statistical power but reduced the identifiable fraction of the PBMC transcriptome, (v) after sample size, effect size (i.e. the magnitude of fold change) was the most important driver of statistical power to detect DEG. The results from this study provide RNA sequencing benchmarks and guidelines for planning future similar vaccine studies.

Induction of mycobacterial protective immunity by sublingual BCG vaccination.

Tuberculosis (TB) remains a tremendous global health problem, with 1/4 of the world's population infected and causing > 1 million deaths annually. Intradermal Bacillus Calmette-Guérin (BCG) vaccine given during infancy protects against severe forms of acute disease but does not prevent chronic infection or development of pulmonary TB. TB vaccine mucosal targeting potentially could induce mucosal resident immune cells with increased protective capacity against pulmonary infection and disease. Sublingual (SL) administration of vaccines may be an optimal mucosal delivery platform based on the high absorptive capacity of this mucosal surface, the extensive lymphoid tissue, and published preclinical studies demonstrating efficacy of SL vaccination against other pathogens. To this end, we performed preliminary testing of sublingual TB vaccines. Vaccination of mice with SL BCG elicited potent mycobacteria-specific T cell responses which persisted 16 weeks post-immunization. The magnitudes of the T cell responses were similarly induced after sublingual, intranasal, and subcutaneous BCG vaccination. Interestingly, serum mycobacteria-specific antibody responses and systemic recovery of BCG post-vaccination were lower after SL BCG compared with systemic BCG immunization. However, more importantly, SL BCG vaccinated mice were significantly protected against an aerosolized virulent M. tuberculosis challenge (P < 0.0001 compared to unvaccinated mice). Furthermore, this protection was long-lived, persisting for 16 weeks with >1 log CFU reduction compared with naïve challenged mice in both lungs and spleens (P < 0.0001 and P < 0.0028, respectively). These exciting results provide strong support for further studies exploring the mechanisms of protective immunity induced by sublingual BCG vaccination.

A Subset of Mycobacteria-Specific CD4+ IFN-γ+ T Cell Expressing Naive Phenotype Confers Protection against Tuberculosis Infection in the Lung.

Failure of the most recent tuberculosis (TB) vaccine trial to boost bacillus Calmette-Guérin-mediated anti-TB immunity despite the induction of Th1-specific central memory cell and effector memory cell responses highlights the importance of identifying optimal T cell targets for protective vaccines. In this study, we describe a novel, Mycobacterium tuberculosis-specific IFN-γ+CD4+ T cell population expressing surface markers characteristic of naive-like memory T cells (TNLM), which were induced in both human (CD45RA+CCR7+CD27+CD95-) and murine (CD62L+CD44-Sca-1+CD122-) systems in response to mycobacteria. In bacillus Calmette-Guérin-vaccinated subjects and those with latent TB infection, TNLM were marked by the production of IFN-γ but not TNF-α and identified by the absence of CD95 expression and increased surface expression CCR7, CD27, the activation markers T-bet, CD69, and the survival marker CD74. Increased tetramer-positive TNLM frequencies were noted in the lung and spleen of ESAT-61-20-specific TCR transgenic mice at 2 wk postinfection with M. tuberculosis and progressively decreased at later time points, a pattern not seen with TNF-α+CD4+ T cells expressing naive cell surface markers. Importantly, adoptive transfer of highly purified TNLM alone, from vaccinated ESAT-61-20-specific TCR transgenic mice, conferred equivalent protection against M. tuberculosis infection in the lungs of Rag-/- mice when compared with total memory populations (central and effector memory cells). Thus, TNLM may represent a memory T cell population that, if optimally targeted, may significantly improve future TB vaccine responses.

Preliminary aggregate safety and immunogenicity results from three trials of a purified inactivated Zika virus vaccine candidate: phase 1, randomised, double-blind, placebo-controlled clinical trials.

BACKGROUND: A safe, effective, and rapidly scalable vaccine against Zika virus infection is needed. We developed a purified formalin-inactivated Zika virus vaccine (ZPIV) candidate that showed protection in mice and non-human primates against viraemia after Zika virus challenge. Here we present the preliminary results in human beings. METHODS: We did three phase 1, placebo-controlled, double-blind trials of ZPIV with aluminium hydroxide adjuvant. In all three studies, healthy adults were randomly assigned by a computer-generated list to receive 5 µg ZPIV or saline placebo, in a ratio of 4:1 at Walter Reed Army Institute of Research, Silver Spring, MD, USA, or of 5:1 at Saint Louis University, Saint Louis, MO, USA, and Beth Israel Deaconess Medical Center, Boston, MA, USA. Vaccinations were given intramuscularly on days 1 and 29. The primary objective was safety and immunogenicity of the ZPIV candidate. We recorded adverse events and Zika virus envelope microneutralisation titres up to day 57. These trials are registered at ClinicalTrials.gov, numbers NCT02963909, NCT02952833, and NCT02937233. FINDINGS: We enrolled 68 participants between Nov 7, 2016, and Jan 25, 2017. One was excluded and 67 participants received two injections of Zika vaccine (n=55) or placebo (n=12). The vaccine caused only mild to moderate adverse events. The most frequent local effects were pain (n=40 [60%]) or tenderness (n=32 [47%]) at the injection site, and the most frequent systemic reactogenic events were fatigue (29 [43%]), headache (26 [39%]), and malaise (15 [22%]). By day 57, 52 (92%) of vaccine recipients had seroconverted (microneutralisation titre ≥1:10), with peak geometric mean titres seen at day 43 and exceeding protective thresholds seen in animal studies. INTERPRETATION: The ZPIV candidate was well tolerated and elicited robust neutralising antibody titres in healthy adults. FUNDING: Departments of the Army and Defense and National Institute of Allergy and Infectious Diseases.

Pilot studies of a human BCG challenge model.

Despite the great effort to develop an effective vaccine against tuberculosis (TB) there is currently no reliable and safe human challenge model that can be used for in vivo evaluation of new TB vaccine candidates and/or elucidation of the mechanisms of TB protective immunity. In this study, five volunteers were challenged with BCG intradermally (ID). Swab specimens were collected at multiple time points from the vaccination site pre- and post-vaccination to quantitate mycobacterial shedding as a surrogate of in vivo mycobacterial immunity. We compared the performance of the TaqMan qPCR assay against colony-forming unit cultures on 7H10 agar plates, and time to positivity (TTP) of mycobacterial growth indicator tubes (MGIT) in order to evaluate the reproducibility and sensitivity in measuring BCG burden in swab specimens. BCG was detected in swab specimens from all five volunteers by at least one method, and no single method was superior in terms of sensitivity and reproducibility. A comparison of all three methods showed significant correlations by Spearman's rank test between 7H10 agar plating and qPCR (R = 0.601, P = 0.00072), MGIT culture TTP and 7H10 agar plating (R = 0.412, P = 0.029) as well as MGIT culture TTP and qPCR (R = -0.708, P = 0.00003). However, the three methods were somewhat different with regard to early versus late detection of BCG shedding post-challenge. This ID BCG challenge model has unique potential to further explore correlations between reactogenicity and immune mechanisms involved in protection against mycobacterial infections, and could therefore become a reliable tool in the evaluation process of new TB vaccination strategies.

Comparisons of the Humoral and Cellular Immune Responses Induced by Live Attenuated Influenza Vaccine and Inactivated Influenza Vaccine in Adults.

Both live attenuated influenza vaccines (LAIV) and inactivated influenza vaccines (IIV) induce protective immunity against influenza. There is evidence that LAIV induces superior protection in children, whereas IIV may induce superior protection in adults. The immune mechanisms responsible for these differences have not been identified. We previously compared LAIV and IIV in young children of 6 to 36 months of age, and we demonstrated that while both induced similar hemagglutination inhibition (HAI) antibody responses, only LAIV induced significant increases in T cell responses. In the present study, 37 healthy adult subjects of 18 to 49 years of age were randomized to receive seasonal influenza vaccination with LAIV or IIV. Influenza virus-specific HAI, T cell, and secretory IgA (sIgA) responses were studied pre- and postvaccination. In contrast to the responses seen in young children, LAIV induced only minimal increases in serum HAI responses in adults, which were significantly lower than the responses induced by IIV. Both LAIV and IIV similarly induced only transient T cell responses to replication-competent whole virus in adults. In contrast, influenza virus-specific sIgA responses were induced more strongly by LAIV than by IIV. Our previous studies suggest that LAIV may be more protective than IIV in young children not previously exposed to influenza virus or influenza vaccines due to increased vaccine-induced T cell and/or sIgA responses. Our current work suggests that in adults with extensive and partially cross-reactive preexisting influenza immunity, LAIV boosting of sIgA responses to hemagglutinin (HA) and non-HA antigenic targets expressed by circulating influenza virus strains may be an important additional mechanism of vaccine-induced immunity.

Safety and Immunogenicity of the Recombinant BCG Vaccine AERAS-422 in Healthy BCG-naïve Adults: A Randomized, Active-controlled, First-in-human Phase 1 Trial.

BACKGROUND: We report a first-in-human trial evaluating safety and immunogenicity of a recombinant BCG, AERAS-422, over-expressing TB antigens Ag85A, Ag85B, and Rv3407 and expressing mutant perfringolysin. METHODS: This was a randomized, double-blind, dose-escalation trial in HIV-negative, healthy adult, BCG-naïve volunteers, negative for prior exposure to Mtb, at one US clinical site. Volunteers were randomized 2:1 at each dose level to receive a single intradermal dose of AERAS-422 (>10(5)-<10(6)CFU=low dose, ≥10(6)-<10(7)CFU=high dose) or non-recombinant Tice BCG (1-8×10(5)CFU). Randomization used an independently prepared randomly generated sequence of treatment assignments. The primary and secondary outcomes were safety and immunogenicity, respectively, assessed in all participants through 182days post-vaccination. ClinicalTrials.gov registration number: NCT01340820. FINDINGS: Between Nov 2010 and Aug 2011, 24 volunteers were enrolled (AERAS-422 high dose, n=8; AERAS-422 low dose, n=8; Tice BCG, n=8); all were included in the safety and immunogenicity analyses. All 24 subjects had at least one adverse event, primarily expected local reactions. High dose AERAS-422 vaccination induced Ag85A- and Ag85B-specific lymphoproliferative responses and marked anti-mycobacterial activity in a whole blood bactericidal activity culture assay (WBA), but was associated with varicella zoster virus (VZV) reactivation in two vaccinees. These volunteers displayed high BCG-specific IFN-γ responses pre- and post-vaccination possibly predisposing them to autocrine/paracrine negative regulation of immune control of latent VZV. A systems biology transcriptomal approach identified positive correlations between post-vaccination T cell expression modules and WBA, and negative correlations between post-vaccination monocyte expression modules and WBA. The expression of one key macrophage marker (F4/80) was constitutively elevated in the two volunteers with zoster. INTERPRETATION: The unexpected development of VZV in two of eight healthy adult vaccine recipients resulted in discontinuation of AERAS-422 vaccine development. Immunological and transcriptomal data identified correlations with the development of TB immunity and VZV that require further investigation. FUNDING: Aeras, FDA, Bill and Melinda Gates Foundation.

Mycobacterium-Specific γ9δ2 T Cells Mediate Both Pathogen-Inhibitory and CD40 Ligand-Dependent Antigen Presentation Effects Important for Tuberculosis Immunity.

Numerous pathogens, including Mycobacterium tuberculosis, can activate human γ9δ2 T cells to proliferate and express effector mechanisms. γ9δ2 T cells can directly inhibit the growth of intracellular mycobacteria and may also act as antigen-presenting cells (APC). Despite evidence for γδ T cells having the capacity to function as APC, the mechanisms involved and importance of these effects on overall tuberculosis (TB) immunity are unknown. We prepared M. tuberculosis-specific γ9δ2 T cell lines to study their direct protective effects and APC functions for M. tuberculosis-specific αß T cells. The direct inhibitory effects on intracellular mycobacteria were measured, and the enhancing effects on proliferative and effector responses of αß T cells assessed. Furthermore, the importance of cell-to-cell contact and soluble products for γ9δ2 T cell effector responses and APC functions were investigated. We demonstrate, in addition to direct inhibitory effects on intracellular mycobacteria, the following: (i) γ9δ2 T cells enhance the expansion of M. tuberculosis-specific αß T cells and increase the ability of αß T cells to inhibit intracellular mycobacteria; (ii) although soluble mediators are critical for the direct inhibitory effects of γ9δ2 T cells, their APC functions do not require soluble mediators; (iii) the APC functions of γ9δ2 T cells involve cell-to-cell contact that is dependent on CD40-CD40 ligand (CD40L) interactions; and (iv) fully activated CD4(+) αß T cells and γ9δ2 T cells provide similar immune enhancing/APC functions for M. tuberculosis-specific T cells. These effector and helper effects of γ9δ2 T cells further indicate that these T cells should be considered important new targets for new TB vaccines.

Functional Heterogeneity and Antimycobacterial Effects of Mouse Mucosal-Associated Invariant T Cells Specific for Riboflavin Metabolites.

Mucosal-associated invariant T (MAIT) cells have a semi-invariant TCR Vα-chain, and their optimal development is dependent upon commensal flora and expression of the nonpolymorphic MHC class I-like molecule MR1. MAIT cells are activated in an MR1-restricted manner by diverse strains of bacteria and yeast, suggesting a widely shared Ag. Recently, human and mouse MR1 were found to bind bacterial riboflavin metabolites (ribityllumazine [RL] Ags) capable of activating MAIT cells. In this study, we used MR1/RL tetramers to study MR1 dependency, subset heterogeneity, and protective effector functions important for tuberculosis immunity. Although tetramer(+) cells were detected in both MR1(+/+) and MR1(-/-) TCR Vα19i-transgenic (Tg) mice, MR1 expression resulted in significantly increased tetramer(+) cells coexpressing TCR Vß6/8, NK1.1, CD44, and CD69 that displayed more robust in vitro responses to IL-12 plus IL-18 and RL Ag, indicating that MR1 is necessary for the optimal development of the classic murine MAIT cell memory/effector subset. In addition, tetramer(+) MAIT cells expressing CD4, CD8, or neither developing in MR1(+/+) Vα19i-Tg mice had disparate cytokine profiles in response to RL Ag. Therefore, murine MAIT cells are considerably more heterogeneous than previously thought. Most notably, after mycobacterial pulmonary infection, heterogeneous subsets of tetramer(+) Vα19i-Tg MAIT cells expressing CXCR3 and α4ß1 were recruited into the lungs and afforded early protection. In addition, Vα19iCα(-/-)MR(+/+) mice were significantly better protected than were Vα19iCα(-/-)MR1(-/-), wild-type, and MR1(-/-) non-Tg mice. Overall, we demonstrate considerable functional diversity of MAIT cell responses, as well as that MR1-restricted MAIT cells are important for tuberculosis protective immunity.

Investigations of TB vaccine-induced mucosal protection in mice.

A better understanding of mucosal immunity is required to develop more protective vaccines against Mycobacterium tuberculosis. We developed a murine aerosol challenge model to investigate responses capable of protecting against mucosal infection. Mice received vaccinations intranasally with CpG-adjuvanted antigen 85B (Ag85B/CpG) and/or Bacillus Calmette-Guerin (BCG). Protection against aerosol challenge with a recombinant GFP-expressing BCG was assessed. Mucosal prime/boost vaccinations with Ag85B/CpG and BCG were protective, but did not prevent lung infection indicating more efficacious mucosal vaccines are needed. Our novel finding that protection correlated with increased airway dendritic cells early post-challenge could help guide the development of enhanced mucosal vaccines.

Dipterinyl calcium pentahydrate inhibits intracellular mycobacterial growth in human monocytes via the C-C chemokine MIP-1ß and nitric oxide.

Tuberculosis remains one of the top three leading causes of morbidity and mortality worldwide, complicated by the emergence of drug-resistant Mycobacterium tuberculosis strains and high rates of HIV coinfection. It is important to develop new antimycobacterial drugs and immunomodulatory therapeutics and compounds that enhance antituberculous immunity. Dipterinyl calcium pentahydrate (DCP), a calcium-complexed pterin compound, has previously been shown to inhibit human breast cancer cells and hepatitis B virus (HBV). DCP inhibitory effects were attributed to induction of apoptosis and/or increased production of interleukin 12 (IL-12) and granulocyte-macrophage colony-stimulating factor (GM-CSF). In this study, we tested the ability of DCP to mediate inhibition of intracellular mycobacteria within human monocytes. DCP treatment of infected monocytes resulted in a significant reduction in viability of intracellular but not extracellular Mycobacterium bovis BCG. The antimicrobial activity of DCP was comparable to that of pyrazinamide (PZA), one of the first-line antituberculosis drugs currently used. DCP potentiated monocyte antimycobacterial activity by induction of the cysteine-cysteine (C-C) chemokine macrophage inflammatory protein 1ß (MIP-1ß) and inducible nitric oxide synthase 2. Addition of human anti-MIP-1ß neutralizing antibody or a specific inhibitor of the l-arginase-nitric oxide pathway (N(G)-monomethyl l-arginine [l-NMMA] monoacetate) reversed the inhibitory effects of DCP on intracellular mycobacterial growth. These findings indicate that DCP induced mycobacterial killing via MIP-1ß- and nitric oxide-dependent effects. Hence, DCP acts as an immunoregulatory compound enhancing the antimycobacterial activity of human monocytes.

Granzyme A produced by γ(9)δ(2) T cells induces human macrophages to inhibit growth of an intracellular pathogen.

Human γ(9)δ(2) T cells potently inhibit pathogenic microbes, including intracellular mycobacteria, but the key inhibitory mechanism(s) involved have not been identified. We report a novel mechanism involving the inhibition of intracellular mycobacteria by soluble granzyme A. γ(9)δ(2) T cells produced soluble factors that could pass through 0.45 µm membranes and inhibit intracellular mycobacteria in human monocytes cultured below transwell inserts. Neutralization of TNF-α in co-cultures of infected monocytes and γ(9)δ(2) T cells prevented inhibition, suggesting that TNF-α was the critical inhibitory factor produced by γ(9)δ(2) T cells. However, only siRNA- mediated knockdown of TNF-α in infected monocytes, but not in γ(9)δ(2) T cells, prevented mycobacterial growth inhibition. Investigations of other soluble factors produced by γ(9)δ(2) T cells identified a highly significant correlation between the levels of granzyme A produced and intracellular mycobacterial growth inhibition. Furthermore, purified granzyme A alone induced inhibition of intracellular mycobacteria, while knockdown of granzyme A in γ(9)δ(2) T cell clones blocked their inhibitory effects. The inhibitory mechanism was independent of autophagy, apoptosis, nitric oxide production, type I interferons, Fas/FasL and perforin. These results demonstrate a novel microbial defense mechanism involving granzyme A-mediated triggering of TNF-α production by monocytes leading to intracellular mycobacterial growth suppression. This pathway may provide a protective mechanism relevant for the development of new vaccines and/or immunotherapies for macrophage-resident chronic microbial infections.

Polyclonal mucosa-associated invariant T cells have unique innate functions in bacterial infection.

Mucosa-associated invariant T (MAIT) cells are a unique population of αß T cells in mammals that reside preferentially in mucosal tissues and express an invariant Vα paired with limited Vß T-cell receptor (TCR) chains. Furthermore, MAIT cell development is dependent upon the expression of the evolutionarily conserved major histocompatibility complex (MHC) class Ib molecule MR1. Using in vitro assays, recent studies have shown that mouse and human MAIT cells are activated by antigen-presenting cells (APCs) infected with diverse microbes, including numerous bacterial strains and yeasts, but not viral pathogens. However, whether MAIT cells play an important, and perhaps unique, role in controlling microbial infection has remained unclear. To probe MAIT cell function, we show here that purified polyclonal MAIT cells potently inhibit intracellular bacterial growth of Mycobacterium bovis BCG in macrophages (MΦ) in coculture assays, and this inhibitory activity was dependent upon MAIT cell selection by MR1, secretion of gamma interferon (IFN-γ), and an innate interleukin 12 (IL-12) signal from infected MΦ. Surprisingly, however, the cognate recognition of MR1 by MAIT cells on the infected MΦ was found to play only a minor role in MAIT cell effector function. We also report that MAIT cell-deficient mice had higher bacterial loads at early times after infection compared to wild-type (WT) mice, demonstrating that MAIT cells play a unique role among innate lymphocytes in protective immunity against bacterial infection.

A recombinant adenovirus expressing immunodominant TB antigens can significantly enhance BCG-induced human immunity.

BACKGROUND: Despite the availability of Bacille Calmette Guérin (BCG) vaccines, Mycobacterium tuberculosis currently infects billions of people and millions die annually from tuberculosis (TB) disease. New TB vaccines are urgently needed. METHODS: We studied the ability of AERAS-402, a recombinant, replication-deficient adenovirus type 35 expressing the protective M. tuberculosis antigens Ag85A, Ag85B, and TB10.4, to boost BCG immunity in an area of low TB endemicity. RESULTS: In volunteers primed with BCG 3 or 6 months prior to AERAS-402 boosting, significant CD4(+) and CD8(+) T cell responses were induced. Ag85-specific responses were more strongly boosted than TB10.4-specific responses. Frequencies of TB-specific CD8(+) T cells reached>50 fold higher than pre-AERAS boosting levels, remarkably higher than reported in any previous human TB vaccine trial. Multiparameter flow cytometric assays demonstrated that AERAS-402-boosted CD4(+) and CD8(+) T cells were multifunctional, producing multiple cytokines and other immune effector molecules. Furthermore, boosted T cells displayed lymphoproliferative capacity, and tetramer analyses confirmed that antigen-specific CD8(+) T cells were induced. BCG and AERAS-402 vaccinations given 3 and 6 months apart appeared equivalent. CONCLUSIONS: Our results indicate that AERAS-402 is a promising TB vaccine candidate that can significantly enhance both CD4(+) and CD8(+) TB-specific T cell responses after BCG priming. ClinicalTrials.gov Identifier: NCT01378312.