Impact of prior Dengue immunity on Zika vaccine protection in rhesus macaques and mice

Pre-existing immunity to flaviviruses can influence the outcome of subsequent flavivirus infections. Therefore, it is critical to determine whether baseline DENV immunity may influence subsequent ZIKV infection and the protective efficacy of ZIKV vaccines. In this study, we investigated the impact of pre-existing DENV immunity induced by vaccination on ZIKV infection and the protective efficacy of an inactivated ZIKV vaccine. Rhesus macaques and mice inoculated with a live attenuated DENV vaccine developed neutralizing antibodies (NAbs) to multiple DENV serotypes but no cross-reactive NAbs responses to ZIKV. Animals with baseline DENV NAbs did not exhibit enhanced ZIKV infection and showed no overall reduction in ZIKV vaccine protection. Moreover, passive transfer of purified DENV-specific IgG from convalescent human donors did not augment ZIKV infection in STAT2 -/- and BALB/c mice. In summary, these results suggest that baseline DENV immunity induced by vaccination does not significantly enhance ZIKV infection or impair the protective efficacy of candidate ZIKV vaccines in these models. These data can help inform immunization strategies in regions of the world with multiple circulating pathogenic flaviviruses.

Antibody-mediated protection against SHIV challenge includes systemic clearance of distal virus

HIV-1-specific broadly neutralizing antibodies (bNAbs) can protect rhesus monkeys against simian-human immunodeficiency virus (SHIV) challenge. However, the site of antibody interception of virus and the mechanism of antibody-mediated protection remain unclear. We administered a fully protective dose of the bNAb PGT121 to rhesus monkeys and challenged them intravaginally with SHIV-SF162P3. In PGT121-treated animals, we detected low levels of viral RNA and viral DNA in distal tissues for seven days following challenge. Viral RNA-positive tissues showed transcriptomic changes indicative of innate immune activation, and cells from these tissues initiated infection after adoptive transfer into naïve hosts. These data demonstrate that bNAb-mediated protection against a mucosal virus challenge can involve clearance of infectious virus in distal tissues.

Rapid Inflammasome Activation following Mucosal SIV Infection of Rhesus Monkeys

The earliest events following mucosal HIV-1 infection, prior to measurable viremia, remain poorly understood. Here, by detailed necropsy studies, we show that the virus can rapidly disseminate following mucosal SIV infection of rhesus monkeys and trigger components of the inflammasome, both at the site of inoculation and at early sites of distal virus spread. By 24 hr following inoculation, a proinflammatory signature that lacked antiviral restriction factors was observed in viral RNA-positive tissues. The early innate response included expression of NLRX1, which inhibits antiviral responses, and activation of the TGF-β pathway, which negatively regulates adaptive immune responses. These data suggest a model in which the virus triggers specific host mechanisms that suppress the generation of antiviral innate and adaptive immune responses in the first few days of infection, thus facilitating its own replication. These findings have important implications for the development of vaccines and other strategies to prevent infection.

Adenovirus 5 vaccination elicits IL-27, which impairs CD4 and CD8 T cell functionality (VAC12P.1113)

In pre-clinical studies Ad26 has shown increased protective efficacy compared to Ad5. We hypothesize this is due, in part, to differences in phenotype and function of the elicited CD4 and CD8 T cell responses. Thus, our goal is to elucidate the phenotypic differences of the CD4 and CD8 T cell repertoire following Ad5 or Ad26 vaccination and the underlying mechanism. B6 mice vaccinated with Ad5 upregulate PD1 and Tim3 (p<0.01) expression on both CD4 and CD8 T cells 10 days post-immunization. On day 60, high PD1 and low CD226 expression (P<0.01) was observed following only Ad5 immunization. Ad5, but not Ad26, induced a population of regulatory CD4 T cells that co-produce IFN-γ and IL-10 (p<0.01). In Ad5 vaccinated non-human primates we also observed elevated expression of PD-1 and production of IL-10 (p<0.01), and less IL-2 expression by CD4 T cells. Mouse DCs stimulated in vitro with Ad5 showed a four-fold increase on Il27 mRNA compared to Ad26 stimulated cells. Immunization of IL-27ra KO mice with Ad5 resulted in downregulation of IL-10 (p<0.01), and up-regulation of IL-2 and CD226 (p<0.01) by CD4 T cells compared to WT. CD8 T cells from KO mice exhibited increased TNF-α and IL-2 polyfunctionality (p<0.01). These data demonstrate that Ad5 vaccination induces greater IL-27 production that drives inhibitory molecule expression and dysfunctional cytokine secretion by CD4 and CD8 T cells. These data suggest a mechanistic explanation for one reason why Ad5 is a suboptimal vector.

Temporal regulation of adenovirus vector-elicited antibody responses by CD4 T cells (VAC4P.1111)

BACKGROUND: Recombinant adenovirus (Ad) vectors have recently garnered interest as vaccine platforms to elicit robust antibody (Ab) responses. In this study we seek to determine the timing of CD4 T cell help for the induction of these Ab responses. METHODS: B6 mice were immunized intramuscularly with 1010 vp of Ad serotype 26 expressing SIVmac239 Env. Anti-CD4 Ab (GK1.5) was used to deplete CD4 T cells. Serum Env-specific IgG was quantified by ELISA. Statistical analysis was performed by Mann-Whitney U test. RESULTS: Depletion of CD4 T cells at immunization completely abolished SIV Env-specific Ab responses at day 30 post-immunization. Surprisingly, by day 60 post-immunization Env-specific IgG responses spontaneously developed in these mice, and by day 90 these responses were of equal titer to those in control mice (Endpoint titer of 18225 for untreated vs. 12150 for anti-CD4 treated mice; P=0.9). Delayed Ab responses coincided temporally with the recovery of CD4 T cells following anti-CD4 Ab treatment. Recovery of CD4 T cells was necessary for this phenomenon, as repeated administration of anti-CD4 Ab blocked the development of Env-specific Ab responses long term. CONCLUSION: These data demonstrate that CD4 T cells actively promote the development of Ad vector-elicited Ab responses even when CD4 T cells are absent at the time of immunization. These data have potential implications for the utility of Ad vectors in immunocompromised individuals, such as AIDS patients.

LCMV-specific CD4 T cells induce immunopathology and impair immune protection following chronic LCMV infection (VIR1P.1132)

CD4 T cells promote memory immune responses, but it is unclear whether vaccine-induced CD4 T cells contribute to immune protection. We interrogated if virus-specific CD4 T cells would protect mice against infection with chronic lymphocytic choriomeningitis virus (LCMV). Immunization with vaccines that induced CD4 T cell responses resulted in mortality following infection with persistent strains of LCMV. Immunopathology was associated with high levels of virus-specific CD4 T cells, generalized inflammation and collapse of adaptive immunity. Interestingly, virus-specific CD8 T cells or antibodies abrogated these lethal effects of CD4 T cell vaccines. Our data demonstrate the importance of tightly regulating CD4 T cell responses following vaccination, and suggest that CD4 T cells in the absence of effective antiviral immune responses could induce lethal immunopathology.

Aberrant differentiation and exhaustion of adenovirus vaccine-elicited CD8 T cells primed in the absence of CD4 T cells (VAC3P.940)

Replication-incompetent recombinant adenovirus (Ad) vectors have garnered considerable interest as candidate vaccine platforms for an array of diseases. However, the efficacy of such vaccines in settings of impaired CD4 T cell function remains poorly understood. We demonstrate that monoclonal antibody-mediated depletion of CD4 T cells prior to Ad immunization of C57BL/6 mice impaired expansion of responding CD8 T cells and led to aberrant differentiation and exhaustion. The absence of CD4 T cells resulted in a failure of antigen-specific CD8 T cells to differentiate into KLRG1hiCD127lo effector cells. This phenotypic defect corresponded to reduced ex vivo cytotoxicity and decreased expression of IFN-γ and TNF-α. Strikingly, CD8 T cells primed in the absence of CD4 T cells expressed elevated levels of the inhibitory molecules PD-1, LAG-3, and Tim-3. Consistent with this, these cells were identified as exhausted using gene expression profiling and gene set enrichment analysis. Blockade of PD-1 signaling by administration of anti-PDL-1 antibody at the time of immunization rescued expansion of antigen-specific CD8 T cells primed in the absence of CD4 T cells. This treatment also rescued differentiation into KLRG1hiCD127lo effector cells, and corrected defects in expression of IFN-γ and TNF-α. Collectively, these data suggest a novel mechanism of CD4 T cell help whereby CD4 T cells prevent the exhaustion of vaccine-elicited CD8 T cells by modulating PD-1 signaling during priming.

Ad5 but not Ad26 induces an IFN-γ+IL-10+ CD4+ T cell population following immunization (VAC12P.1023)

Adenovirus-based vaccines have arisen as an attractive method to elicit robust cellular and humoral immune responses. Multiple vector serotypes have been developed, but the CD4+ regulatory T cell responses generated by these vectors have not previously been compared. We therefore, compared the functionality of antigen-specific CD4+ regulatory T cells induced following Ad5 or Ad26 immunization. C57BL/6 mice were immunized intramuscularly with 1010vp of Ad5-SIVgag or Ad26-SIVgag. Spleen cells were harvest at day 10, and SIVgag-specific CD4+ regulatory T cell responses were evaluated. Immunization with 1010vp of Ad5-SIVgag induced a population of IL-10+ producing cells that comprised 30% of gag-specific IFN-γ+ CD4+ T cells. In contrast, the number of CD4+ T cells that co-produced IFN-γ and IL-10 was 8 times lower following Ad26 immunization. These cells were T-bet+ and FoxP3-. In addition, Ad5 immunization induced a substantially larger fraction of IL-10+ cells that co-express PD-1 than Ad26 immunization. Moreover, a larger fraction of IFN-γ+ CD4+ T cells were Tim-3+ following Ad5 versus Ad26 immunization. We also observed increasing frequency of IFN-γ+IL-10+ CD4+ T cells with increasing doses of Ad5. These data suggest that Ad5 vectors, but not Ad26 vectors, induce a large population of CD4+ T cells that co-produce IFN-γ and IL-10, an immunosuppressive cytokine that may potentially limit vaccine efficacy.

Vaccine induced immunopathology mediated by memory CD4 T cells following chronic viral infection (VIR7P.1054)

CD4 T cells are important for promoting functional adaptive immune responses following viral infections, but the specific contribution of vaccine-elicited CD4 T cell responses to immune protection remains unclear. We interrogated whether selective induction of virus-specific CD4 T cell responses by vaccination, in the absence of other adaptive immune responses, would improve immune protection against a chronic lymphocytic choriomeningitis virus (LCMV) challenge in mice. Surprisingly, we observed that immunization of mice with a vaccine that induced predominantly CD4 T cell responses resulted in severe immunopathology and mortality following chronic LCMV clone 13 challenge. Vaccinated mice exhibited impaired adaptive responses, severe inflammation, accelerated destruction of lymphoid tissues, and fulminant mortality as compared with naïve mice following challenge. This immunopathology was caused by uncontrolled antigen-driven stimulation of memory CD4 T cells that resulted in cytokine storm and widespread inflammation. The adverse effects of vaccination were abrogated by co-immunization with vaccines that generated CD8 T cell responses, adoptive transfer of virus-specific CD8 T cells, or passive immunization with virus-specific immunoglobulins. Altogether, these data raise important concerns for vaccines that predominantly elicit CD4 T cell responses.

CD4 T cells control the induction, magnitude, and phenotype of the primary CD8 T cell response following adenovirus vector immunization (P4465)

Despite the widespread use of replication-incompetent recombinant Adenovirus (Ad) vectors as candidate vaccine platforms for the elicitation of CD8 T cell responses, the mechanism by which these vectors elicit a CD8 T cell response remains poorly understood. Our data demonstrate that the induction of a primary CD8 T cell response by Ad immunization is dependent on CD4 T cell help. CD4 and MHC class II knockout mice had substantial defects in the primary CD8 T cell response following Ad vaccination. Furthermore, The CD8 T cell response generated in the absence of CD4 T cells exhibited a less effector-like phenotype, as assessed by surface staining, cytokine production, and expression of transcription factors. The unhelped CD8 T cell population also exhibited increased apoptosis and increased PD-1 expression. Intriguingly, longitudinal removal of the CD4 T cell population by monoclonal antibody depletion demonstrated that CD4 T cell help is required for at least eight days post-immunization to facilitate normal expansion and effector differentiation of the responding CD8 T cell population. Collectively, these data suggest that CD4 T cell help is needed not only at the time of initial antigen exposure but also during the first week of induction of CD8 T cell responses. Future experiments will aim to identify the mechanism(s) by which CD4 T cell help is provided in this system.

Bradykinin inducible receptor is essential to lipopolysaccharide-induced acute lung injury in mice

Lipopolysaccharides from gram-negative bacteria are amongst the most common causative agents of acute lung injury, which is characterized by an inflammatory response, with cellular infiltration and the release of mediators/cytokines. There is evidence that bradykinin plays a role in lung inflammation in asthma but in other types of lung inflammation its role is less clear. In the present study we evaluated the role of the bradykinin B1 receptor in acute lung injury caused by lipopolysaccharide inhalation and the mechanisms behind bradykinin actions participating in the inflammatory response. We found that in C57Bl/6 mice, the bradykinin B1 receptor expression was up-regulated 24h after lipopolysaccharide inhalation. At this time, the number of cells and protein concentration were significantly increased in the bronchoalveolar lavage fluid and the mice developed airway hyperreactivity to methacholine. In addition, there was an increased expression of tumor necrosis factor-alpha, interleukin-1 beta and interferon-gamma and chemokines (monocytes chemotactic protein-1 and KC) in the bronchoalveolar lavage fluid and in the lung tissue. We then treated the mice with a bradykinin B1 receptor antagonist, R-954 (Ac-Orn-[Oic2, alpha-MePhe5, D-betaNal7, Ile8]desArg9-bradykinin), 30 min after lipopolysaccharide administration. We observed that this treatment prevented the airway hyperreactivity as well as the increased cellular infiltration and protein content in the bronchoalveolar lavage fluid. Moreover, R-954 inhibited the expression of cytokines/chemokines. These results implicate bradykinin, acting through B1 receptor, in the development of acute lung injury caused by lipopolysaccharide inhalation.

Enhancement of Th1 lung immunity induced by recombinant Mycobacterium bovis Bacillus Calmette-Guerin attenuates airway allergic disease

Mycobacterium bovis Bacillus Calmette-Guerin (BCG) has been shown to down-regulate experimental allergic asthma, a finding that reinforced the hygiene hypothesis. We have previously found that recombinant BCG (rBCG) strain that express the genetically detoxified S1 subunit of pertussis toxin (rBCG-S1PT) exerts an adjuvant effect that enhances Th1 responses against BCG proteins. Here we investigated the effect of this rBCG-S1PT on the classical ovalbumin-induced mouse model of allergic lung disease. We found that rBCG-S1PT was more effective than wild-type BCG in preventing Th2-mediated allergic immune responses. The inhibition of allergic lung disease was not associated with increased concentration of suppressive cytokines or with an increased number of pulmonary regulatory T cells but was positively correlated with the increase in IFN-gamma-producing T cells and T-bet expression in the lung. In addition, an IL-12-dependent mechanism appeared to be important to the inhibition of lung allergic disease. The inhibition of allergic inflammation was found to be restricted to the lung because when allergen challenge was given by the intraperitoneal route, rBCG-S1PT administration failed to inhibit peritoneal allergic inflammation and type 2 cytokine production. Our work offers a nonclassical interpretation for the hygiene hypothesis indicating that attenuation of lung allergy by rBCG could be due to the enhancement of local lung Th1 immunity induced by rBCG-S1PT. Moreover, it highlights the possible use of rBCG strains as multipurpose immunomodulators by inducing specific immunity against microbial products while protecting against allergic asthma.

Toll-like receptor 4 agonists adsorbed to aluminium hydroxide adjuvant attenuate ovalbumin-specific allergic airway disease: role of MyD88 adaptor molecule and interleukin-12/interferon-gamma axis

BACKGROUND

Epidemiological and experimental data suggest that bacterial lipopolysaccharides (LPS) can either protect from or exacerbate allergic asthma. Lipopolysaccharides trigger immune responses through toll-like receptor 4 (TLR4) that in turn activates two major signalling pathways via either MyD88 or TRIF adaptor proteins. The LPS is a pro-Type 1 T helper cells (Th1) adjuvant while aluminium hydroxide (alum) is a strong Type 2 T helper cells (Th2) adjuvant, but the effect of the mixing of both adjuvants on the development of lung allergy has not been investigated.

OBJECTIVE

We determined whether natural (LPS) or synthetic (ER-803022) TLR4 agonists adsorbed onto alum adjuvant affect allergen sensitization and development of airway allergic disease. To dissect LPS-induced molecular pathways, we used TLR4-, MyD88-, TRIF-, or IL-12/IFN-gamma-deficient mice.

METHODS

Mice were sensitized with subcutaneous injections of ovalbumin (OVA) with or without TLR4 agonists co-adsorbed onto alum and challenged with intranasally with OVA. The development of allergic lung disease was evaluated 24 h after last OVA challenge.

RESULTS

Sensitization with OVA plus LPS co-adsorbed onto alum impaired in dose-dependent manner OVA-induced Th2-mediated allergic responses such as airway eosinophilia, type-2 cytokines secretion, airway hyper-reactivity, mucus hyper production and serum levels of IgE or IgG1 anaphylactic antibodies. Although the levels of IgG2a, Th1-affiliated isotype increased, investigation into the lung-specific effects revealed that LPS did not induce a Th1 pattern of inflammation. Lipopolysaccharides impaired the development of Th2 immunity, signaling via TLR4 and MyD88 molecules and via the IL-12/IFN-gamma axis, but not through TRIF pathway. Moreover, the synthetic TLR4 agonists that proved to have a less systemic inflammatory response than LPS also protected against allergic asthma development.

CONCLUSION

Toll-like receptor 4 agonists co-adsorbed with allergen onto alum down-modulate allergic lung disease and prevent the development of polarized T cell-mediated airway inflammation.

Anti-inflammatory effects of Lafoensia pacari and ellagic acid in a murine model of asthma

We have shown that the ethanolic extract of Lafoensia pacari inhibits eosinophilic inflammation induced by Toxocara canis infection, and that ellagic acid is the secondary metabolite responsible for the anti-eosinophilic activity seen in a model of beta-glucan peritonitis. In the present study, we investigated the preventive and curative effects of L. pacari extract and ellagic acid on allergic lung inflammation using a murine model of ovalbumin-induced asthma. In bronchoalveolar lavage fluid, preventive (22-day) treatment with L. pacari (200 mg/kg) and ellagic acid (10 mg/kg) inhibited neutrophil counts (by 75% and 57%) and eosinophil counts (by 78% and 68%). L. pacari reduced IL-4 and IL-13 levels (by 67% and 73%), whereas ellagic acid reduced IL-4, IL-5 and IL-13 (by 67%, 88% and 85%). To investigate curative anti-inflammatory effects, we treated mice daily with ellagic acid (0.1, 1, or 10 mg/kg), also treating selected mice with L. pacari (200 mg/kg) from day 18 to day 22. The highest ellagic acid dose reduced neutrophil and eosinophil numbers (by 59% and 82%), inhibited IL-4, IL-5, and IL-13 (by 62%, 61%, and 49%). Neither L. pacari nor ellagic acid suppressed ovalbumin-induced airway hyperresponsiveness or cysteinyl leukotriene synthesis in lung homogenates. In mice treated with ellagic acid (10 mg/kg) or L. pacari (200 mg/kg) at 10 min after the second ovalbumin challenge, eosinophil numbers were 53% and 69% lower, respectively. Cytokine levels were unaffected by this treatment. L. pacari and ellagic acid are effective eosinophilic inflammation suppressors, suggesting a potential for treating allergies.