Oral Fucoidan Attenuates Lung Pathology and Clinical Signs in a Severe Influenza a Mouse Model

Fucoidans are known to be effective inhibitors of inflammation, and of virus binding and cellular entry. Undaria pinnatifida-derived fucoidan (UPF) was assessed in a severe influenza A (H1N1, PR8) infection model in mice. Initially, UPF was gavaged at 3.52 mg daily in a treatment model. Gross lung pathology (consolidation) was significantly reduced as compared to controls. UPF was then presented as a feed supplement at a rate of either nil, 3.52 mg/day or 7.04 mg/day in a prophylactic model, dosed three days before infection. A significant improvement was observed in the clinical signs of ill-health, as well as a reduction in gross lung pathology in animals treated with the higher dose, although there was no significant reduction in lung viral titres.

Abstract 2811: A translational immuno-oncology platform to model the tumor microenvironment in vitro

The tumor microenvironment (TME) is a complex network, consisting of the tumor, blood vessels, stromal and immune cells, and soluble factors. The immune system plays an important role in combating tumor growth, and multiple studies associate raised immune infiltrate with beneficial outcome. Various tractable immuno-oncology targets have been identified, both in the TME and immune cells. It is critical to test novel immuno-modulators in assays involving multiple cell types, to understand the MOA and identify biomarkers before moving into the clinic. Charles River have developed a range of primary human assays to model the TME in vitro. This platform models multiple anti-tumor immune effector pathways and has been validated with standard of care therapeutics. The assays include: T cell or NK cell-mediated tumor killing, myeloid/macrophage assays, Th1/Th17/iTreg differentiation and regulatory T cell suppression assays. Tumor killing assays were performed using an IncuCyte ZOOM and PBMC were cultured with tumor monolayers with TCR ligation. Keytruda and Yervoy raised levels of tumor cell death, indicating that they enhanced T cell killing. To further model the TME, 3D ‘spheroids’ were used to screen for either T cell mediated or ADCC-mediated NK cell killing. For ADCC, PBMC were co-cultured with tumor spheroids and killing measured by monitoring spheroid diameter in the presence of Herceptin, which potentiated NK-driven tumour killing. Myeloid/macrophage cells were differentiated from monocytes in tumor-conditioned media (TCM). TCM drove the generation of immature cells which were CD25lo, CD127lo, CD184hi, CD80lo, CD163hi, CD68lo and MHCIIlo. These cells produced IL-10 and VEGF and were suppressive in a T cell assay. Phagocytosis assays were also performed using anti-CD47 as a control. The TME is associated with increased Treg numbers and low levels of Th1 or Th17 cells. Many therapeutics aim to shift the balance away from Treg, towards Th1 or Th17 cells. Assays were therefore performed by differentiating naïve CD4+ T cells into iTreg, in the presence or absence of a USP7 inhibitor. Reduced iTreg generation, without significant alteration in Th1/17 frequency was observed. The resulting iTreg were less able to suppress T cell proliferation when compared to non-treated iTreg. Suppression assays were also performed using nTreg. As before, the USP7 inhibitor partially reversed nTreg-mediated suppression. Charles River is pleased to present an immuno-oncology platform to model the TME in human cells in vitro, enabling partners to rapidly assess the immunomodulatory capacity of their therapeutics. The 3D assays represent an important complex cell model to support translational drug discovery, sitting alongside T cell-mediated tumor killing, myeloid/macrophage assays, Th1/Th17/ iTreg differentiation and nTreg assays and helps to define the diverse aspects of micro-environmental control of immune response.

Citation Format: Louise S. Brackenbury, S. Rhiannon Jenkinson, Shilina Roman, Robert D. Nunan, Sylvie D. Hunt, Anna Willox, Neil A. Williams, Omar Aziz, Ian Waddell. A translational immuno-oncology platform to model the tumor microenvironment in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2811.

A Modular Vaccine Platform Combining Self-Assembled Peptide Cages and Immunogenic Peptides

Subunit vaccines use delivery platforms to present minimal antigenic components for immunization. The benefits of such systems include multivalency, self-adjuvanting properties, and more specific immune responses. Previously, the design, synthesis, and characterization of self-assembling peptide cages (SAGEs) have been reported. In these, de novo peptides are combined to make hubs that assemble into nanoparticles when mixed in aqueous solution. Here it is shown that SAGEs are nontoxic particles with potential as accessible synthetic peptide scaffolds for the delivery of immunogenic components. To this end, SAGEs functionalized with the model antigenic peptides tetanus toxoid632-651 and ovalbumin323-339 drive antigen-specific responses both in vitro and in vivo, eliciting both CD4+ T cell and B cell responses. Additionally, SAGEs functionalized with the antigenic peptide hemagglutinin518-526 from the influenza virus are also able to drive a CD8+ T cell response in vivo. This work demonstrates the potential of SAGEs to act as a modular scaffold for antigen delivery, capable of inducing and boosting specific and tailored immune responses.

Delayed reconstitution of B cell immunity to pneumococcus in HIV-infected Malawian children on antiretroviral therapy

OBJECTIVE

Despite CD4(+) count restoration and viral load suppression with antiretroviral therapy (ART), HIV-infected children remain at increased risk of life-threatening infections including invasive pneumococcal disease (IPD). We therefore investigated whether persistent susceptibility to IPD following ART is associated with incomplete recovery of B-cell function.

METHODS

41 HIV-infected Malawian children commencing ART were followed-up for a 1 year period during which time blood samples were collected at 0, 3, 6 and 12 months for comprehensive immunophenotyping and pneumomococcal-specific Memory B-cell Enzyme-Linked Immunospot assays. In addition, nasopharyngeal swab samples were cultured to determine pneumococcal carriage rates.

RESULTS

Normalization of major lymphocyte subsets such as CD4(+) percentages was evident following 3 months of ART. The proportions of mature naïve B cells (CD19(+) CD10(-) CD27(-) CD21(hi)) and resting memory B cells (CD19(+) CD27(+) CD21(hi)) increased and apoptosis-prone mature activated B cells (CD19(+) CD21(lo) CD10(-)) decreased markedly by 12 months. However, in the context of high nasopharyngeal pneumococcal carriage rates (83%), restoration of pneumococcal protein antigen-specific B-cell memory was more delayed.

CONCLUSIONS

These data show that, in chronically HIV-infected children receiving ART, improvement in B-cell memory profiles and function is slower than CD4(+) T-cells. This supports early initiation of ART and informs research into optimal timing of immunization with pneumococcal vaccines.

The B subunit of Escherichia coli enterotoxin helps control the in vivo growth of solid tumors expressing the Epstein-Barr virus latent membrane protein 2A

Latent membrane protein 2A (LMP2A) is expressed on almost all Epstein–Barr virus (EBV)-associated tumors and is a potential target for immunotherapeutic intervention and vaccination. However, LMP2A is not efficiently processed and presented on major histocompatibility antigens class I molecules to generate potent cytotoxic T-lymphocytes (CTL) responses capable of killing these tumors. The B subunit of Escherichia coli enterotoxin (EtxB), causes rapid internalization and processing of membrane-bound LMP2A on EBV-infected B cells, and facilitates loading of processed-LMP2A peptides onto MHC class I. This re-directed trafficking/delivery of LMP2A to the MHC class I machinery enhances recognition and killing by LMP2A-specific CTL in vitro. To test the potential of EtxB to enhance immune targeting of LMP2A expressed in solid tumors, we generated a murine tumor model (Renca-LMP2A), in which LMP2A is expressed as a transgenic neoantigen on a renal carcinoma (Renca) cell line and forms solid tumors when injected subcutaneously into BALB/c mice. The data show that in BALB/c mice which have only low levels of peripheral K^d-LMP2A-specific CD8⁺ T cells, merely a transient inhibition of tumor growth is achieved compared with naïve mice; suggesting that there is suboptimal LMP2A-specifc CTL recognition and poorly targeted tumor killing. However, importantly, treatment of these mice with EtxB led to a significant delay in the onset of tumor growth and significantly lower tumor volumes compared with similar mice that did not receive EtxB. Moreover, this remarkable effect of EtxB was achieved despite progressive reduction in tumor expression of LMP2A and MHC class I molecules. These data clearly demonstrate the potential efficacy of EtxB as a novel therapeutic agent that could render EBV-associated tumors susceptible to immune control.

A universal polysaccharide conjugated vaccine against O111 E. coli

E. coli O111 strains are responsible for outbreaks of blood diarrhea and hemolytic uremic syndrome throughout the world. Because of their phenotypic variability, the development of a vaccine against these strains which targets an antigen that is common to all of them is quite a challenge. Previous results have indicated, however, that O111 LPS is such a candidate, but its toxicity makes LPS forbidden for human use. To overcome this problem, O111 polysaccharides were conjugated either to cytochrome C or to EtxB (a recombinant B subunit of LT) as carrier proteins. The O111-cytochrome C conjugate was incorporated in silica SBA-15 nanoparticles and administered subcutaneously in rabbits, while the O111-EtxB conjugate was incorporated in Vaxcine(TM), an oil-based delivery system, and administered orally in mice. The results showed that one year post-vaccination, the conjugate incorporated in silica SBA-15 generated antibodies in rabbits able to inhibit the adhesion of all categories of O111 E. coli to epithelial cells. Importantly, mice immunized orally with the O111-EtxB conjugate in Vaxcine(TM) generated systemic and mucosal humoral responses against all categories of O111 E. coli as well as antibodies able to inhibit the toxic effect of LT in vitro. In summary, the results obtained by using 2 different approaches indicate that a vaccine that targets the O111 antigen has the potential to prevent diarrhea induced by O111 E. coli strains regardless their mechanism of virulence. They also suggest that a conjugated vaccine that uses EtxB as a carrier protein has potential to combat diarrhea induced by ETEC.

Incomplete recovery of pneumococcal CD4 T cell immunity after initiation of antiretroviral therapy in HIV-infected malawian adults

HIV-infected African adults are at a considerably increased risk of life-threatening invasive pneumococcal disease (IPD) which persists despite antiretroviral therapy (ART). Defects in naturally acquired pneumococcal-specific T-cell immunity have been identified in HIV-infected adults. We have therefore determined the extent and nature of pneumococcal antigen-specific immune recovery following ART. HIV-infected adults were followed up at 3, 6 and 12 months after initiating ART. Nasopharyngeal swabs were cultured to determine carriage rates. Pneumococcal-specific CD4 T-cell immunity was assessed by IFN-γ ELISpot, proliferation assay, CD154 expression and intracellular cytokine assay. S. pneumoniae colonization was detected in 27% (13/48) of HIV-infected patients prior to ART. The rates remained elevated after 12 months ART, 41% (16/39) (p = 0.17) and significantly higher than in HIV-uninfected individuals (HIV^neg 14%(4/29); p = 0.0147). CD4⁺ T-cell proliferative responses to pneumococcal antigens increased significantly to levels comparable with HIV-negative individuals at 12 months ART (p = 0.0799). However, recovery of the pneumococcal-specific CD154 expression was incomplete (p = 0.0015) as were IFN-γ ELISpot responses (p = 0.0040) and polyfunctional CD4⁺ T-cell responses (TNF-α, IL-2 and IFN-γ expression) (p = 0.0040) to a pneumolysin-deficient mutant strain. Impaired control of pneumococcal colonisation and incomplete restoration of pneumococcal-specific immunity may explain the persistently higher risk of IPD amongst HIV-infected adults on ART. Whether vaccination and prolonged ART can overcome this immunological defect and reduce the high levels of pneumococcal colonisation requires further evaluation.

Moraxella catarrhalis adhesin UspA1-derived recombinant fragment rD-7 induces monocyte differentiation to CD14+CD206+ phenotype

Circulating monocytes in the bloodstream typically migrate to other tissues and differentiate into tissue resident macrophages, the process being determined by the constituents of the microenvironments encountered. These may include microbes and their products. In this study, we investigated whether Moraxella catarrhalis Ubiquitous Surface Protein A1 (UspA1), known to bind to a widely expressed human cell surface receptor CEACAM1, influences monocyte differentiation as receptor engagement has been shown to have profound effects on monocytes. We used the recombinant molecules corresponding to the regions of UspA1 which either bind (rD-7; UspA1_527–665) or do not bind (r6–8; UspA1_659–863) to CEACAM1 and investigated their effects on CD206, CD80 and CD86 expression on freshly isolated human CD14+ monocytes from peripheral blood mononuclear cells (PBMC). Exposure to rD-7, but not r6–8, biased monocyte differentiation towards a CD14+CD206+ phenotype, with reduced CD80 expression. Monocytes treated with rD-7 also secreted high levels of IL-1ra and chemokine IL-8 but not IL-10 or IL-12p70. The effects of rD-7 were independent of any residual endotoxin. Unexpectedly, these effects of rD-7 were also independent of its ability to bind to CEACAM1, as monocyte pre-treatment with the anti-CEACAM antibody A0115 known to inhibit rD-7 binding to the receptor, did not affect rD-7-driven differentiation. Further, another control protein rD-7/D (a mutant form of rD-7, known not to bind to CEACAMs), also behaved as the parent molecule. Our data suggest that specific regions of M. catarrhalis adhesin UspA1 may modulate inflammation during infection through a yet unknown receptor on monocytes.

Human tonsil-derived dendritic cells are poor inducers of T cell immunity to mucosally encountered pathogens

The mucosal immune system must initiate and regulate protective immunity, while balancing this immunity with tolerance to harmless antigens and bacterial commensals. We have explored the hypothesis that mucosal dendritic cells (DC) control the balance between regulation and immunity, by studying the responses of human tonsil-derived DC to Neisseria meningitidis as a model organism. We show that tonsil DC are able to sample their antigenic environment, internalizing Nm and expressing high levels of HLA-DR and CD86. However, in comparison to monocyte-derived DC (moDC), they respond to pathogen encounter with only low level cytokine production, largely dominated by TGFβ. Functionally, tonsil DC also only stimulated low levels of antigen-specific T cell proliferation and cytokine production when compared to moDC. We therefore propose that the default role for DC in the nasopharynx is to maintain tolerance/ignorance of the large volume of harmless antigens and bacterial commensals encountered at the nasopharyngeal mucosa.

Polysaccharide-specific memory B cells generated by conjugate vaccines in humans conform to the CD27+IgG+ isotype-switched memory B Cell phenotype and require contact-dependent signals from bystander T cells activated by bacterial proteins to differentiate into plasma cells

The polysaccharides (PS) surrounding encapsulated bacteria are generally unable to activate T cells and hence do not induce B cell memory (BMEM). PS conjugate vaccines recruit CD4(+) T cells via a carrier protein, such as tetanus toxoid (TT), resulting in the induction of PS-specific BMEM. However, the requirement for T cells in the subsequent activation of the BMEM at the time of bacterial encounter is poorly understood, despite having critical implications for protection. We demonstrate that the PS-specific BMEM induced in humans by a meningococcal serogroup C PS (Men C)-TT conjugate vaccine conform to the isotype-switched (IgG(+)CD27(+)) rather than the IgM memory (IgM(+)CD27(+)) phenotype. Both Men C and TT-specific BMEM require CD4(+) T cells to differentiate into plasma cells. However, noncognate bystander T cells provide such signals to PS-specific BMEM with comparable effect to the cognate T cells available to TT-specific BMEM. The interaction between the two populations is contact-dependent and is mediated in part through CD40. Meningococci drive the differentiation of the Men C-specific BMEM through the activation of bystander T cells by bacterial proteins, although these signals are enhanced by T cell-independent innate signals. An effect of the TT-specific T cells activated by the vaccine on unrelated BMEM in vivo is also demonstrated. These data highlight that any protection conferred by PS-specific BMEM at the time of bacterial encounter will depend on the effectiveness with which bacterial proteins are able to activate bystander T cells. Priming for T cell memory against bacterial proteins through their inclusion in vaccine preparations must continue to be pursued.

Impairment of pneumococcal antigen specific isotype-switched Igg memory B-cell immunity in HIV infected Malawian adults

Pneumococcal disease is associated with a particularly high morbidity and mortality amongst adults in HIV endemic countries. Our previous findings implicating a B-cell defect in HIV-infected children from the same population led us to comprehensively characterize B-cell subsets in minimally symptomatic HIV-infected Malawian adults and investigate the isotype-switched IgG memory B-cell immune response to the pneumococcus. We show that similar to vertically acquired HIV-infected Malawian children, horizontally acquired HIV infection in these adults is associated with IgM memory B-cell (CD19(+) CD27(+) IgM(+) IgD(+)) depletion, B-cell activation and impairment of specific IgG B-cell memory to a range of pneumococcal proteins. Our data suggest that HIV infection affects both T-cell independent and T-cell dependent B-cell maturation, potentially leading to impairment of humoral responses to extracellular pathogens such as the pneumococcus, and thus leaving this population susceptible to invasive disease.

Polysaccharide-protein conjugate vaccination induces antibody production but not sustained B-cell memory in the human nasopharyngeal mucosa

Colonization of the nasopharyngeal mucosa by meningococcus and other polysaccharide (PS)-encapsulated bacteria precedes invasion. PS-conjugate vaccines induce PS-specific B-cell memory (B(MEM)) and also prevent colonization, thus blocking person-to-person transmission, generating herd protection. However, in isolation the B(MEM) are unable to sustain immunity. Furthermore, the duration of herd protection the vaccines induce appears limited. We demonstrate that, despite the persistence of PS-specific B(MEM), the population is not maintained within the nasopharynx. Although booster immunization results in the transient appearance of PS-specific B(MEM) within the mucosa, this reflects the re-circulation of systemic B(MEM) through the site rather than the generation of resident mucosal B(MEM). The induction of sustained PS-specific B(MEM) in the nasopharynx would allow the population to be activated by colonization, thus inhibiting subsequent invasion. It would also be expected to boost local mucosal immunity, thus extending herd protection. Strategies to generate PS-specific B(MEM) in the mucosa warrant further investigation.

Defective pneumococcal-specific Th1 responses in HIV-infected adults precedes a loss of control of pneumococcal colonization

BACKGROUND

African adults infected with human immunodeficiency virus (HIV) have high rates of pneumococcal colonization and invasive disease. Here we have investigated the possibility that HIV disrupts the normal balance of pneumococcal-specific helper T cell (Th) 1/Th17 immunity to colonization, resulting in a more permissive nasopharyngeal niche.

METHODS

One hundred thirty-six HIV-infected and -uninfected Malawian adults were enrolled in the study. Changes in rates and composition of nasopharyngeal pneumococcal colonization were analyzed using microarray. The underlying pneumococcal-specific Th1/Th17 responses associated with altered pneumococcal colonization were investigated using flow cytometry.

RESULTS

We find that pneumococcal carriage is only modestly increased in asymptomatic HIV-infected Malawian adults but that colonization rates rise dramatically during symptomatic disease (HIV(neg) 13%, HIV(asy) 19%, and HIV(sym) 38%). These rates remain high in subjects established on antiretroviral therapy (ART): 33% (at 6-12 months) and 52% (at 18 months), with HIV-infected individuals carrying a broader range of invasive and noninvasive serotypes compared with HIV-negative controls. The frequency of multiple serotype carriage (>1 serotype HIV(neg) 26%, HIV(asy) 30%, HIV(sym) 31%, HIV(ART) 31%) is not affected. These changes in colonization are associated with generalized CD4 T-cell depletion, impaired antigen-specific proliferation, and a defect in pneumococcal-specific T-cell interferon-γ but not interleukin 17 production.

CONCLUSIONS

These data reveal the persistently poor control of pneumococcal colonization in HIV-infected adults following immune ART-mediated reconstitution, highlighting a potential reservoir for person-to-person spread and vaccine escape. Novel approaches to control colonization either through vaccination or through improvements in the quality of immune reconstitution are required.

Naturally-acquired influenza-specific CD4+ T-cell proliferative responses are impaired in HIV-infected African adults

Background

Seasonal influenza has been associated with greater morbidity and mortality in AIDS patients. Highly-active antiretroviral therapy (HAART) has led to some reduction in influenza-related complications but the nature of naturally-acquired T-cell immunity to influenza virus in an African setting, and how this changes with immune reconstitution following HAART is unknown. We measured influenza-specific CD4⁺ T-cell immunity in unimmunized HIV-infected Malawian adults and then investigated immune reconstitution following HAART.

Methods

Peripheral blood mononuclear cells were isolated from HIV-infected and HIV-uninfected Malawian adults. CFSE proliferation and CD154 expression flow cytometry-based assays were used to measure influenza-specific CD4⁺ T-cell immunity.

Results

We found lower naturally-acquired proliferative influenza-specific CD4⁺ T-cell responses in AIDS patients that was also present in asymptomatic HIV-infected adults with relatively high CD4 counts (>350 cells/µl). Influenza-specific CD4⁺ T-cell immune reconstitution in HIV-infected patients on HAART for 12 months was poor despite a marked reduction in viral load and an increase in CD4 count. This poor immune reconstitution was characterised by a low influenza-specific proliferative CD4⁺ T-cell response and reduced proportions of CD154-expressing influenza-specific CD4⁺ T-cells in peripheral blood.

Conclusion

Our data suggest that asymptomatic HIV-infected adults may also be at risk of influenza-related complications and that HAART alone may not circumvent this risk in AIDS patients. This study highlights the need to identify possible interventions early in HIV infection to reduce the risk of influenza and to intensify influenza surveillance in these susceptible African populations.

Do multiple concurrent infections in African children cause irreversible immunological damage?

Much of the developing world, particularly sub-Saharan Africa, has high levels of morbidity and mortality associated with infectious diseases. The greatest risk of invasive disease is in the young, the malnourished and HIV-infected individuals. In many regions in Africa these vulnerable groups and the wider general population are under constant immune pressure from a range of environmental factors, under-nutrition and multiple concurrent infections from birth through to adulthood. Intermittent microbial exposure during childhood is required for the generation of naturally acquired immunity capable of protection against a range of infectious diseases in adult life. However, in the context of a resource-poor setting, the heavy burden of malarial, diarrhoeal and respiratory infections in childhood may subvert or suppress immune responses rather than protect, resulting in sub-optimal immunity. This review will explore how poor maternal health, HIV exposure, socio-economic and seasonal factors conspire to weaken childhood immune defences to disease and discuss the hypothesis that recurrent infections may drive immune dysregulation, leading to relative immune senescence and premature immunological aging.

Acquisition of pneumococci specific effector and regulatory Cd4+ T cells localising within human upper respiratory-tract mucosal lymphoid tissue

The upper respiratory tract mucosa is the location for commensal Streptococcus (S.) pneumoniae colonization and therefore represents a major site of contact between host and bacteria. The CD4⁺ T cell response to pneumococcus is increasingly recognised as an important mediator of immunity that protects against invasive disease, with data suggesting a critical role for Th17 cells in mucosal clearance. By assessing CD4 T cell proliferative responses we demonstrate age-related sequestration of Th1 and Th17 CD4⁺ T cells reactive to pneumococcal protein antigens within mucosal lymphoid tissue. CD25^hi T cell depletion and utilisation of pneumococcal specific MHCII tetramers revealed the presence of antigen specific Tregs that utilised CTLA-4 and PDL-1 surface molecules to suppress these responses. The balance between mucosal effector and regulatory CD4⁺ T cell immunity is likely to be critical to pneumococcal commensalism and the prevention of unwanted pathology associated with carriage. However, if dysregulated, such responses may render the host more susceptible to invasive pneumococcal infection and adversely affect the successful implementation of both polysaccharide-conjugate and novel protein-based pneumococcal vaccines.

The S. pneumoniae bacteria is a major cause of disease (e.g. pneumonia and meningitis) particularly affecting infants. In most cases bacteria can colonise the nose without causing harm, however colonisation is thought to be a prerequisite of disease. With increasing age colonization and disease, rates gradually decrease which is likely due to the development of immunity to the pneumococcus with age. The CD4 T cells of the immune system may contribute to the defence against bacterial colonisation by producing factors that promote pneumococcal killing. Herein, we show that CD4 T cells reactive to pneumococci are found in greater numbers at the site of colonisation and gradually increase in their levels from infancy. However, at the peak of CD4 T cell responses from late teens, we detected the presence of regulatory T cells (Tregs) which suppressed anti-pneumococci CD4 T cell activity greatly. Our finding shows that pneumococcal reactive CD4 T cells selectively populate colonisation sites and increase with age as a result of ongoing bacterial exposure throughout life, inversely correlating with colonisation and disease rates. As factors that utilise CD4 T cells become increasingly advocated as potential preventative strategies against pneumococcal carriage and disease, the observed effect of Tregs must be considered.

Deteriorating pneumococcal-specific B-cell memory in minimally symptomatic African children with HIV infection

Invasive pneumococcal disease is a leading cause of human immunodeficiency virus (HIV)-associated mortality in sub-Saharan African children. Defective T-cell-mediated immunity partially explains this high disease burden, but there is an increased risk of invasive pneumococcal disease even in the context of a relatively preserved percentage of CD4 cells. We hypothesized that impaired B-cell immunity to this pathogen further amplifies the immune defect. We report a shift in the B-cell compartment toward an apoptosis-prone phenotype evident early in HIV disease progression. We show that, although healthy HIV-uninfected and minimally symptomatic HIV-infected children have similar numbers of isotype-switched memory B cells, numbers of pneumococcal protein antigen-specific memory B cells were lower in HIV-infected than in HIV-uninfected children. Our data implicate defective naturally acquired B-cell pneumococcal immunity in invasive pneumococcal disease causation in HIV-infected children and highlight the need to study the functionality and duration of immune memory to novel pneumococcal protein vaccine candidates in order to optimize their effectiveness in this population.

Impaired CD4 T cell memory response to Streptococcus pneumoniae precedes CD4 T cell depletion in HIV-infected Malawian adults

OBJECTIVE

Invasive pneumococcal disease (IPD) is a leading cause of morbidity and mortality in HIV-infected African adults. CD4 T cell depletion may partially explain this high disease burden but those with relatively preserved T cell numbers are still at increased risk of IPD. This study evaluated the extent of pneumococcal-specific T cell memory dysfunction in asymptomatic HIV infection early on in the evolution of the disease.

METHODS

Peripheral blood mononuclear cells were isolated from asymptomatic HIV-infected and HIV-uninfected Malawian adults and stained to characterize the underlying degree of CD4 T cell immune activation, senescence and regulation. Pneumococcal-specific T cell proliferation, IFN-γ, IL-17 production and CD154 expression was assessed using flow cytometry and ELISpot.

RESULTS

We find that in asymptomatic HIV-infected Malawian adults, there is considerable immune disruption with an increase in activated and senescent CD4+CD38+PD-1+ and CD4+CD25(high)Foxp3+ Treg cells. In the context of high pneumococcal exposure and therefore immune stimulation, show a failure in pneumococcal-specific memory T cell proliferation, skewing of T cell cytokine production with preservation of interleukin-17 but decreased interferon-gamma responses, and failure of activated T cells to express the co-stimulatory molecule CD154.

CONCLUSION

Asymptomatic HIV-infected Malawian adults show early signs of pneumococcal- specific immune dysregulation with a shift in the balance of CD4 memory, T helper 17 cells and Treg. Together these data offer a mechanistic understanding of how antigen-specific T cell dysfunction occurs prior to T cell depletion and may explain the early susceptibility to IPD in those with relatively preserved CD4 T cell numbers.

Mucosal administration of the B subunit of E. coli heat-labile enterotoxin promotes the development of Foxp3-expressing regulatory T cells

Understanding the processes by which certain mucosal pathogens and their products induce regulatory T cells (Tregs) is important in determining mechanisms of pathogenicity and may point toward their use in treating immunological disorders. Accordingly, we have studied the events that follow mucosal administration of the B subunit of E. coli heat-labile enterotoxin (EtxB). EtxB modulates the response to co-administered antigens and can prevent autoimmune disease. Our data show that EtxB translocates across the nasal epithelium, modulating the expression of interleukin-10 (IL-10) and transforming growth factor-β(1) (TGF-β(1)). The modulated microenvironment drives an increase in Forkhead box P3 (Foxp3)-positive T cells, predominantly in the CD4(+)CD25(-) subset. Adoptive transfer experiments showed that enhanced Foxp3 expression was particularly evident in recently activated T cells by concomitant unrelated antigen challenge, and was both TGF-β(1) and IL-10 dependent. This ability to alter T-cell differentiation pathways following mucosal delivery explains how EtxB may modify mucosal immune environments and prevent unwanted pathologies.

Mucosal immunity in resource-limited setting: is the battle ground different?

In many developing countries, populations are under considerable pressure from high bacterial exposure on mucosal surfaces. Immune dysregulation in this setting is multifactorial and is driven by a range of environmental factors, undernutrition and coinfections such as measles, malaria and HIV. Disruption or subversion of respiratory-tract and intestinal epithelial barriers leads to increased invasion by mucosal pathogens and a high frequency of life-threatening bacterial disease. It is our opinion that a process of epithelial barrier dysfunction and immune dysregulation at these mucosal surfaces leads to the much higher rates of pneumonia, meningitis and severe sepsis seen in resource-limited countries.

T cell memory response to pneumococcal protein antigens in an area of high pneumococcal carriage and disease

BACKGROUND

Streptococcus pneumoniae is a leading cause of vaccine-preventable disease worldwide. Pneumococcal protein antigens are currently under study as components of potential vaccines that offer protection against multiple serotypes. We have therefore characterized T cell pneumococcal immunity acquired through asymptomatic carriage.

METHODS

Peripheral blood mononuclear cells from 40 healthy Gambian adults were stimulated with supernatants derived from S. pneumoniae strain (D39), 2 isogenic mutant strains lacking either pneumolysin or choline binding protein A, and recombinant pneumolysin. Immune responses were measured by cellular proliferation and by interleukin-10 (IL-10) and interferon-gamma (IFN-gamma) enzyme-linked immunosorbent spot and bioplex cytokine assays. Nasopharyngeal swabs were cultured to determine carriage rates.

RESULTS

S. pneumoniae nasopharyngeal carriage was detected in 60% of individuals. Both effector and resting (or central) CD4(+) T cell memory were frequently present to a range of pneumococcal antigens. However, the level of the effector memory response did not relate to current nasopharyngeal carriage. Pneumolysin was not immunodominant in these T cell responses but induced a distinct proinflammatory profile (high IFN-gamma, IL-12[p40], and L-17 levels and low IL-10 and IL-13 levels).

CONCLUSIONS

In this population, T cell-mediated immunological memory potentially capable of pathogen clearance and immune surveillance is common but is not associated with the absolute interruption of pneumococcal carriage. How this naturally acquired immune memory influences pneumococcal vaccine efficacy remains to be determined.

Absence of mucosal immunity in the human upper respiratory tract to the commensal bacteria Neisseria lactamica but not pathogenic Neisseria meningitidis during the peak age of nasopharyngeal carriage

The normal flora that colonizes the mucosal epithelia has evolved diverse strategies to evade, modulate, or suppress the immune system and avoid clearance. Neisseria lactamica and Neisseria meningitidis are closely related obligate inhabitants of the human upper respiratory tract. N. lactamica is a commensal but N. meningitidis is an opportunistic pathogen that occasionally causes invasive disease such as meningitis and septicemia. We demonstrate that unlike N. meningitidis, N. lactamica does not prime the development of mucosal T or B cell memory during the peak period of colonization. This cannot be explained by the induction of peripheral tolerance or regulatory CD4(+)CD25(+) T cell activity. Instead, N. lactamica mediates a B cell-dependent mitogenic proliferative response that is absent to N. meningitidis. This mitogenic response is associated with the production of T cell-independent polyclonal IgM that we propose functions by shielding colonizing N. lactamica from the adaptive immune system, maintaining immunological ignorance in the host. We conclude that, in contrast to N. meningitidis, N. lactamica maintains a commensal relationship with the host in the absence of an adaptive immune response. This may prolong the period of susceptibility to colonization by both pathogenic and nonpathogenic Neisseria species.

IgA1 antibodies specific for outer membrane protein PorA modulate the interaction between Neisseria meningitidis and the epithelium

Despite high carriage rates of Neisseria meningitidis, incidence of meningococcal disease remains low, partially due to development of natural immunity. We have previously demonstrated an inverse relationship between salivary anti-meningococcal IgA and disease incidence, but little is known about the contribution of IgA to immunity at mucosal surfaces. Here we show strong immunoreactivity by human salivary IgA against the meningococcal outer membrane porin, PorA. Monomeric anti-PorA IgA1 (humanized chimeric antibodies) but not IgG increased the association of unencapsulated serogroup B N. meningitidis (H44/76) with Chang (conjunctival) but not with either Detroit (pharyngeal) cells or with A549 (alveolar) epithelial cells. Association of encapsulated N. meningitidis was not increased. Epithelial binding of IgA was Fc fragment dependent and not inhibited by IgM. Together these data suggest the presence of a specific epithelial IgA receptor that could influence the effect of both naturally acquired and vaccine induced IgA antibodies at the epithelial surface.

Bacterial toxins as immunomodulators

Bacterial toxins are the causative agent at pathology in a variety of diseases. Although not always the primary target of these toxins, many have been shown to have potent immunomodulatory effects, for example, inducing immune responses to co-administered antigens and suppressing activation of immune cells. These abilities of bacterial toxins can be harnessed and used in a therapeutic manner, such as in vaccination or the treatment of autoimmune diseases. Furthermore, the ability of toxins to gain entry to cells can be used in novel bacterial toxin based immuno-therapies in order to deliver antigens into MHC Class I processing pathways. Whether the immunomodulatory properties of these toxins arose in order to enhance bacterial survival within hosts, to aid spread within the population or is pure serendipity, it is interesting to think that these same toxins potentially hold the key to preventing or treating human disease.

Loss of CTL function among high-avidity tumor-specific CD8+ T cells following tumor infiltration

A major problem in generating effective antitumor CTL responses is that most tumors express self-antigens to which the immune system is rendered unresponsive due to mechanisms of self-tolerance induction. CTL precursors (CTLp) expressing high-affinity T-cell receptors (TCR) are often functionally deleted from the repertoire, leaving a residual repertoire of CTLp having only low-affinity TCR. Furthermore, even when unique antigens are expressed, their presentation by dendritic cells (DC) may predispose to peripheral tolerance induction rather than the establishment of CTL responses that kill tumor cells. In this study, we examined both high-avidity (CL4) and low-avidity (CL1) CD8(+) T-cell responses to a murine renal carcinoma expressing, as a neoantigen, high and low levels of the hemagglutinin (HA) protein from influenza virus A/PR/8 H1N1 (PR8; RencaHA(high) and RencaHA(low)). Our data show that, following encounter with K(d)HA epitopes cross-presented by bone marrow-derived DC, low-avidity CL1 cells become tolerized within tumor-draining lymph nodes (TDLN), and in mice bearing either RencaHA(high) or RencaHA(low) tumors, very few form tumor-infiltrating lymphocytes (TIL). In marked contrast, high-avidity CL4 cells differentiate into effector CTL within the TDLN of mice bearing either RencaHA(high) or RencaHA(low) tumors, and although they form TIL in both tumors, they lose CTL effector function. Critically, these results show that anticancer therapies involving either adoptive transfer of high-avidity tumor-specific CTL populations or targeting of preexisting tumor antigen-specific memory CD8(+) T cells could fail due to the fact that CTL effector function is lost following tumor infiltration.

The B subunit of Escherichia coli heat-labile enterotoxin inhibits Th1 but not Th17 cell responses in established experimental autoimmune uveoretinitis

PURPOSE

To investigate the efficacy of the B subunit of Escherichia coli heat-labile enterotoxin (EtxB) in the treatment of ocular autoimmune disease. Murine experimental autoimmune uveoretinitis (EAU) is an animal model of autoimmune posterior uveitis initiated by retinal antigen-specific Th1 and Th17 CD4(+) T cells, which activate myeloid cells, inducing retinal damage. EtxB is a potent immune modulator that ameliorates other Th1-mediated autoimmune diseases, enhancing regulatory T-cell activity.

METHODS

EAU was induced in B10.RIII mice by immunization with peptide hIRBP(161-180). Disease severity was measured by clinical and histologic assessment, and functional responses of macrophages (Mphis) and T cells were assessed, both in vivo and in cocultures in vitro. EtxB was administered intranasally daily for 4 days, starting either 3 days before or 3 days after EAU induction.

RESULTS

Preimmunization treatment with EtxB protected mice from EAU, limiting both the number and the activation status of retinal infiltrating immune cells. Treatment after EAU induction did not alter the disease course, despite suppression of IFN-gamma. Although EtxB treatment of in vitro cocultures of T cells and Mphis increased IL-10 production, EtxB treatment in vivo increased the proportion and number of IL-17-producing CD4(+) cells infiltrating the eye.

CONCLUSIONS

EtxB preimmunization protects mice from EAU induction by inhibiting Th1 responses, but the resultant reduction in IFN-gamma responses by EtxB does not effect infiltration or structural damage in established EAU, where Th17 responses predominate. These data highlight the critical importance of the dynamics of T-cell phenotype and infiltration during EAU when considering immunomodulatory therapy.

Regulation of intestinal immunity: effects of the oral adjuvant Escherichia coli heat-labile enterotoxin on migrating dendritic cells

Escherichia coli heat-labile enterotoxin (Etx) is an oral adjuvant in mice. We show that this is also true for rats. To understand this adjuvant activity we examined lymph dendritic cells (DC) migrating from the intestine to mesenteric lymph nodes (MLN) in animals fed Etx. These DC can prime antigen-specific antibody responses. We show that in rats the small intestine contains 7-24 million DC and 8 x 10(5 )of these migrate to MLN each day. Surprisingly, Etx does not stimulate increased migration of lymph DC. However, oral Etx affects the activation, antigen transport and localization of migratory DC. Specifically, expression of CD25 increases on the CD172a(high) subset of lymph DC. Oral Etx also increases the number of CD172a(high) lymph DC containing co-administered ovalbumin. CD172a(high) lymph DC treated with Etx in vitro, or purified from the lymph of animals fed Etx, stimulate stronger proliferative responses from primed T cells. Etx also directs more of the CD172a(high) lymph DC into the central region of the MLN T cell areas. This change in DC localization is associated with an increase in the expression of CCR7. These data help advance our understanding of the role of DC in initiating mucosal immune responses in vivo.

Regulation of Th-1 T cell-dominated immunity to Neisseria meningitidis within the human mucosa

Neisseria meningitidis is commonly carried asymptomatically in the upper respiratory tract and only occasionally invades the bloodstream and meninges to cause disease. Naturally acquired immunity appears protective but the nature of the cellular immune response within the mucosa is uncertain. We show that following in vitro stimulation with N. meningitidis serogroup B (MenB) antigens, approximately 66% of the dividing mucosal CD4(+)CD45RO(+) memory population express the Th1-associated IL18-R while the remainder express CRTH2, a Th2-associated marker. The pro-inflammatory bias of this anti-MenB response is not evident in blood, demonstrating compartmentalization at the induction site; and occurs in the presence or absence of lipopolysacharide indicating that these responses are already fully committed. Depletion of CD25(+) cells reveals suppression of the effector CD4(+) T cell response restricted to the mucosa and most marked in children (i.e. those at greatest risk of disease). Mucosal T-regulatory cell (Treg) activity is partially overcome by blocking the human glucocorticoid-induced TNF receptor (GITR) and is not seen following stimulation with antigens from another mucosal pathogen, influenza virus. Pro-inflammatory, antimeningococcal T cell responses may limit invasive disease at the mucosa but Treg induction while reducing immunopathological damage, may also restrict the effectiveness of the protective response, particularly in children.

Protection of non-obese diabetic mice from autoimmune diabetes by Escherichia coli heat-labile enterotoxin B subunit

Autoimmune diabetes in the non-obese diabetic (NOD) mouse is associated with development of inflammation around the islets at around 4-5 weeks of age, which may be prolonged until frank diabetes begins to occur around 12 weeks of age. Although many interventions can halt disease progression if administration coincides with the beginning of the anti-beta cell response, very few are able to prevent diabetes development once insulitis is established. Here we describe a strategy which blocks cellular infiltration of islets and prevents diabetes. Intranasal treatment with the B-subunit of Escherichia coli heat labile enterotoxin (EtxB), a protein that binds GM1 ganglioside (as well as GD1b, asialo-GM1 and lactosylceramide with lower affinities), protected NOD mice from developing diabetes in a receptor-binding dependent manner. Protection was associated with a significant reduction in the number of macrophages, CD4(+) T cells, B cells, major histocompatibility complex class II(+) cells infiltrating the islets. Despite this, treated mice showed increased number of interleukin-10(+) cells in the pancreas, and a decrease in both T helper 1 (Th1) and Th2 cytokine production in the pancreatic lymph node. Disease protection was also transferred with CD4(+) splenocytes from treated mice. Taken together, these results demonstrated that EtxB is a potent immune modulator capable of blocking diabetes.

Mucosal immunity and optimizing protection with meningococcal serogroup B vaccines

Candidate Neisseria meningitidis serogroup B vaccines that are based on outer-membrane vesicles induce protective immunity in adults but provide neither crossprotection for infants nor long-lasting immunity. We suggest that this lack of vaccine efficacy is not solely because the best antigens are yet to be identified but also results from inappropriate programming of the immune response. Natural carriage of N. meningitidis and related bacteria leads to the development of protective immunity both at the mucosal surface and in the circulation. We propose that vaccine strategies that mimic this natural immunization process would better-optimize vaccine-induced protective immunity. Thus, mucosal immunization before a systemic booster vaccination could provide the solution and reduce the necessity for multiple injections to achieve immunity.

Influence of age and carriage status on salivary IgA to Neisseria meningitidis

Asymptomatic carriage of Neisseria meningitidis is common (5-35% of individuals) while the incidence of invasive meningococcal disease is fairly low (<1-5 per 100,000 per annum in Europe). Naturally acquired protective immunity may account for this difference. In this study, we investigated the relationship between anti-meningococcal salivary IgA and age and carriage. We showed that salivary IgA to a range of meningococcal antigens increased successively with age with some specificity for commonly circulating serosubtypes. In a group of 258 students 37 (14%) of whom were carriers of N. meningitidis serogroup B, higher levels of specific IgA were associated with carriage. Stratified analysis revealed a positive relationship between smoking and specific anti- N. meningitidis IgA independent of current carriage, weighted odds ratio (OR) 4.1 (95% CI 1.1-18) and OR 3.8 (95% CI 0.96-16) for reference strains B:1:P1.14 and B:4:P1.5,4 respectively. These data implicate IgA as a factor in host defence from meningococcal invasion, although the precise mechanisms remain uncertain.

The Role of Intercellular Adhesion Molecule-1/LFA-1 Interactions in the Generation of Tumor-Specific CD8+ T Cell Responses

The activation of naive CD4+ T cells requires both TCR engagement and a second costimulatory signal mediated by the interaction of CD28 with CD80/CD86 expressed on professional APC. However, the situation for naive CD8+ T cells is less clear. Although evidence indicates that induction of CD8+ T cell responses is also dependent on professional APC, the ability of some tumors, which do not express CD80/CD86, to induce CTL suggests that other pathways of costimulation exist for the activation of CD8+ T cells. We examined the ability of tumor cells expressing different levels of a tumor-specific Ag to directly prime CD8+ T cells. We demonstrate that CD8+ T cells are directly activated by tumor cells in a CD80/CD86-CD28 independent manner. In this system, costimulation requires ICAM-1/LFA-1 interaction. This results in the generation of CTL capable of inhibiting tumor growth in vivo, and maintaining long-term survival.

Parenteral Influenza Vaccination Influences Mucosal and Systemic T Cell–Mediated Immunity in Healthy Adults

We sought to determine whether palatine tonsils (PTs) harbor naturally acquired influenza-specific T cell immunity and whether routine parenteral immunization with influenza vaccine influences mucosal and systemic T cell reactivity. We demonstrate that tonsillar and peripheral blood mononuclear cells (PBMCs) proliferate strongly to influenza antigens, suggesting that naturally acquired immunity exists within both the mucosal and systemic compartments. Influenza vaccination induced significantly stronger T cell responses in both PTs and blood, in addition to increasing titers of anti-influenza antibodies in serum and saliva. More-rapid proliferative responses of PTs after vaccination were associated with a shift from a response involving both CD45RA+ and CD45RO+ T cells to an entirely CD45RO+-dependent response. Interestingly, the ratio of interferon- gamma to interleukin-5 was dramatically higher in cultures of PT T cells responding to influenza than in PBMCs. Our data indicate that parenteral influenza vaccination influences both mucosal and systemic naturally acquired T cell immunity.

The B subunit of Escherichia coli heat-labile enterotoxin induces both caspase-dependent and -independent cell death pathways in CD8+ T cells

The nontoxic B subunit of Escherichia coli heat-labile enterotoxin (EtxB) is a potent immunomodulatory molecule that acts both as an adjuvant and to stimulate immune deviation processes, resulting in the suppression of Th1-associated inflammatory responses. The ability of EtxB to alter immune reactivity is dependent on its ability to modulate immune cell function through binding to cell surface molecules, the principal receptor of which is the ubiquitous GM1-ganglioside. EtxB activates B cells and antigen-presenting cells and induces the selective apoptosis of murine CD8+ T cells. We postulated that these effects are mediated by the induction of intracellular signaling pathways following EtxB-receptor interaction. We have previously shown that CD8+ T-cell apoptosis induced by EtxB results from the activation of the transcription factor NF-kappaB and caspases. Here we report that while caspase activity is required for apoptosis, additional features of cell death are caspase independent. EtxB induces a rapid loss of mitochondrial membrane potential and cell viability that are unaffected by caspase inhibitors. In addition, our data suggest that these processes are independent of the activity of Bax and Bcl-2 but are mediated by nitric oxide synthase.

Intranasal immunisation of mice with liposomes containing recombinant meningococcal OpaB and OpaJ proteins

The opacity (Opa) proteins of Neisseria meningitidis are outer membrane proteins involved in adhesion and invasion of host epithelial cells and are therefore expected to play an important role in colonisation of the nasopharynx. The majority of meningococcal Opa proteins bind to members of the CEACAM receptor family, such as CEA. Blocking of the Opa-CEACAM interaction by mucosal anti-Opa antibodies could thus constitute an important protective mechanism for novel meningococcal vaccines. In this study we analysed the specific anti-Opa antibody responses after intranasal immunisation of mice with liposomes containing purified and native OpaB (recognising the CEA receptor) and OpaJ (no affinity for CEA) proteins. These antigens were combined with or without one of three different adjuvants, i.e. purified meningococcal LPS, monophosphoryl lipid A (MPL) or the B-subunit of Escherichia coli heat-labile enterotoxin (EtxB). After intranasal immunisation with any of these formulations, anti-Opa IgA antibodies were found in nasal lavages and in some cases anti-Opa IgA and IgG antibodies were also found in lung lavages. With OpaJ but not OpaB, significant bactericidal serum titres were obtained. Of the different adjuvants used, meningococcal LPS gave the strongest overall immune response. Non-adjuvated liposomal Opa formulations were poorly immunogenic. No differences were found between the immune response in transgenic mice expressing the CEA-receptor and non-transgenic mice, showing that the CEA-Opa interaction does not influence the antibody response.

Nasal delivery of antigen with the B subunit of Escherichia coli heat-labile enterotoxin augments antigen-specific T-cell clonal expansion and differentiation

Escherichia coli heat-labile enterotoxin has unique immunogenic and adjuvant properties when administered mucosally to mice. These properties have revealed the potential for its use in the development of mucosal vaccines, an area of increasing interest. However, the inherent toxicity mediated by the A subunit precludes its widespread use. This problem has led to attempts to dissociate toxicity from adjuvant function by use of the B subunit. The ability of the B subunit of E. coli heat-labile enterotoxin (EtxB) to enhance responses against antigens coadministered intranasally is demonstrated here with the use of the DO11.10 adoptive-transfer model, in which ovalbumin (OVA)-specific adoptively transferred T cells can be monitored directly by flow cytometry. Intranasal delivery of OVA with EtxB resulted in increased T-cell proliferative and systemic antibody responses against antigens. The increased Th2 cytokine production detected following in vitro restimulation of splenocyte and cervical lymph node (CLN) cells from the immunized mice correlated with increased OVA-specific immunoglobulin G1 antibody production. Flow cytometric analysis of T cells from mice early after immunization directly revealed the ability of EtxB to support antigen-specific clonal expansion and differentiation. Furthermore, while responses were first detected in the CLNs, they rapidly progressed to the spleen, where they were further sustained. Examination of CD69 expression on dividing cells supported the notion that activation induced by the presence of antigens is not sufficient to drive T-cell differentiation. Furthermore, a lack of CD25 expression on dividing cells suggested that EtxB-mediated T-cell clonal expansion may occur without a sustained requirement for interleukin 2.

Modulation of the Immune Response by the Cholera-like Enterotoxins

Cholera toxins and heat labile enterotoxin from E. coli differ from most soluble proteins in eliciting systemic immunity both against themselves and unrelated admixed antigens, rather than tolerance following administration to a mucosal surface. Several reports have also demonstrated preferential induction of Th2-type responses when these molecules are used as adjuvants. Conversely, these proteins and their non-toxic derivatives, including the B sub-units are also able prevent and alleviate autoimmune diseases in naïve and systemically immune hosts demonstrating wide-ranging effects on the immune system. The recent observation that amelioration of autoimmune disease is associated with the generation of regulatory T cells which inhibit pathogenic Th1 responses may also help to consolidate these two apparently contradictory outcomes of exposure to the cholera-like enterotoxins. Furthermore, the observation that EtxB is able to alleviate autoimmune disease in the absence of conjugation to autoantigen highlights its potential for use in the clinical setting where the target antigen is often unknown. Direct effects on T cells, B cells and APC have been demonstrated in vitro which have provided insights into how these molecules may elicit these diverse effects. Further investigation is required for elucidation of the mechanisms of action of adjuvanticity and tolerance induction by these molecules to realise their potential for use in vaccines and therapies for autoimmune disease in humans.

Modulation of the humoral immune response of swine and mice mediated by toxigenic Pasteurella multocida

Progressive atrophic rhinitis is an upper respiratory tract disease of pigs caused by toxigenic strains of the bacterium Pasteurella multocida. In this study the effect of P. multocida on the humoral immune response of pigs and mice was investigated. Pigs were given live intranasal challenge with either a toxigenic strain or a non-toxigenic strain of P. multocida, or were given daily intranasal instillation of a cell-free lysate of the toxigenic strain. Mice were given a live intranasal challenge of either a toxigenic or a non-toxigenic strain of P. multocida. All of the animals were immunised with ovalbumin and serum concentrations of anti-ovalbumin antibodies were quantified and compared between different treatment groups and control animals. Intranasal challenge with toxigenic P. multocida caused a significant reduction in the levels of anti-ovalbumin IgG in both species. A similar effect was seen in pigs given a cell-free extract of toxigenic P. multocida. Whilst the mechanism of this suppression is unclear, we surmise that immunomodulation of the host is an important virulence factor for toxigenic P. multocida, and could be an important function of the toxin. This immunomodulatory effect may enhance colonisation of P. multocida aiding horizontal transmission and may predispose to concurrent infection with other potential pathogens.

The B subunit of Escherichia coli heat labile enterotoxin abrogates oral tolerance, promoting predominantly Th2-type immune responses

Mucosal antigen encounter usually results in a state of systemic non-responsiveness (tolerance). This failure to mount a protective response is a major hurdle to mucosal vaccine development. Hence, the identification of safe and effective mucosal adjuvants promoting protective immunity is of critical importance. The non-toxic B subunit of Escherichia coli heat labile enterotoxin(EtxB) is a potent nasal adjuvant; however, its usefulness following oral delivery is unconfirmed. We used DO11.10 chimeric mice to assess whether EtxB could abrogate tolerance to oral OVA. We show that admixing EtxB with OVA for oral immunization abrogates oral tolerance and results in a weak anti-OVA immune response. Importantly, EtxB profoundly modulated the nature of the response to subsequent parenteral challenge, promoting IgG1 in favor of IgG2a antibodies and depressing IFN-gamma production while elevating TGF-beta secretion. The addition of EtxB promoted T cell division, as assessed by loss of staining with carboxyfluorescein diacetate succinimidyl ester. Enhanced cell division promoted by EtxB was associated with T cell differentiation (increased numbers of CD45RBlow cells) in vivo, although dividing OVA-specific T cells were CD25-. These data suggest that although EtxB is a weak oral adjuvant, it can profoundly modulate the nature of the immune response to admixed antigen.

Increased NF-kappaB DNA binding but not transcriptional activity during apoptosis induced by the COX-2-selective inhibitor NS-398 in colorectal carcinoma cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit colorectal neoplasia, an effect that is associated with their ability to induce apoptosis. Although NSAIDs have been reported to inhibit NF-κB, more recent studies show activation of NF-κB by NSAIDs. NF-κB commonly shows antiapoptotic activity and is implicated in the therapeutic resistance of cancer cells. The effects of highly COX-2-selective NSAIDs such as NS-398 on NF-κB in colorectal tumour cells have not been reported. Therefore, we addressed whether NF-κB has a role in NS-398-induced apoptosis of colorectal cancer cells. Treatment of HT-29 colorectal carcinoma cells with doses of NS-398 (50–75 μM) known to induce apoptosis had no effect on NF-κB for up to 48 h. However after 72 and 96 h NF-κB DNA-binding activity was increased by NS-398, in parallel with apoptosis induction. NS-398-treated HT-29 cells showed increased p50 homodimer binding and an induction of p50/p65 heterodimers, as demonstrated by supershift assay. However, although NS-398 increased NF-κB DNA binding it did not increase NF-κB-dependent reporter activity and inhibition of NF-κB DNA binding did not enhance NS-398-induced apoptosis. This indicates that NF-κB activated by NS-398 is transcriptionally inactive and is an encouraging result for the use of COX-2-selective NSAIDs not only in chemoprevention but also as novel therapies for colon cancer.

Evidence for Naturally Acquired T Cell-Mediated Mucosal Immunity toNeisseria meningitidis

Naturally acquired protective immunity against Neisseria meningitidis is thought to partially explain the disparity between the high levels of carriage in the human nasopharynx and the rare incidence of disease. To investigate this immunity to Neisseria meningitidis at the mucosal level, in vitro cellular responses to outer membrane vesicle preparations derived from this pathogen were examined using mononuclear cells from the palatine tonsils of adults and children. Characterization of these responses was achieved by depletion of CD45RA(+), CD45RO(+), and CD19(+) populations and outer membrane vesicles derived from isogenic mutants expressing different serosubtypes of the major outer membrane protein, porin A (PorA), no PorA and membrane preparations from a mutant with no LPS (LpxA(-)). The magnitude of cellular proliferative responses against the outer membrane vesicles were strongly associated with age and were largely T cell mediated, involving both CD45RO(+) and CD45RA(+) T cell phenotypes. Responses were not dependent on LPS but consisted of both PorA cross-specific and non-PorA-dependent responses. Cellular immunity against Neisseria meningitidis was found to be frequently associated with systemic IgG Abs but was not associated with serum bactericidal Abs. For the first time our results demonstrate an age-associated acquisition of mucosal T effector/memory cell responses to Neisseria meningitidis. This mucosal cellular immunity can be present in the absence of serum bactericidal Abs, a classical marker of protective immunity.

Selective induction of CD8+CD4- thymocyte apoptosis mediated by the B-subunit of Escherichia coli heat-labile enterotoxin

Receptor-binding by the B-subunit of Escherichia coli heat-labile enterotoxin (EtxB) induces apoptosis of peripheral CD8(+), but not CD4(+) T-cells. Given that peripheral CD8(+) and CD4(+) T cells arise from a common developmental pathway in the thymus, we investigated the effects of EtxB on different thymocyte populations. We show that the acquisition of sensitivity to EtxB-mediated cell death arises following transition of CD4(+)CD8(+) double positive cells into the CD4(-)CD8(+) pathway. Maturation of T cells into CD4(-)CD8(+) single positive cells is associated with upregulated expression of receptors for EtxB.

Protection against recurrent ocular herpes simplex virus type 1 disease after therapeutic vaccination of latently infected mice

The potential of therapeutic vaccination of animals latently infected with herpes simplex virus type 1 (HSV-1) to enhance protective immunity to the virus and thereby reduce the incidence and severity of recurrent ocular disease was assessed in a mouse model. Mice latently infected with HSV-1 were vaccinated intranasally with a mixture of HSV-1 glycoproteins and recombinant Escherichia coli heat-labile enterotoxin B subunit (rEtxB) as an adjuvant. The systemic immune response induced was characterized by high levels of virus-specific immunoglobulin G1 (IgG1) in serum and very low levels of IgG2a. Mucosal immunity was demonstrated by high levels of IgA in eye and vaginal secretions. Proliferating T cells from lymph nodes of vaccinated animals produced higher levels of interleukin-10 (IL-10) than were produced by such cells from mock-vaccinated animals. This profile suggests that vaccination of latently infected mice modulates the Th1-dominated proinflammatory response usually induced upon infection. After reactivation of latent virus by UV irradiation, vaccinated mice showed reduced viral shedding in tears as well as a reduction in the incidence of recurrent herpetic corneal epithelial disease and stromal disease compared with mock-vaccinated mice. Moreover, vaccinated mice developing recurrent ocular disease showed less severe signs and a quicker recovery rate. Spread of virus to other areas close to the eye, such as the eyelid, was also significantly reduced. Encephalitis occurred in a small percentage (11%) of mock-vaccinated mice, but vaccinated animals were completely protected from such disease. The possible immune mechanisms involved in protection against recurrent ocular herpetic disease in therapeutically vaccinated animals are discussed.

Mutant Escherichia coli heat-labile toxin B subunit that separates toxoid-mediated signaling and immunomodulatory action from trafficking and delivery functions

The homopentameric B-subunit components of Escherichia coli heat-labile enterotoxin (EtxB) and cholera toxin (CtxB) possess the capacity to enter mammalian cells and to activate cell-signaling events in leukocytes that modulate immune cell function. Both properties have been attributed to the ability of the B subunits to bind to GM1-ganglioside receptors, a ubiquitous glycosphingolipid found in the plasma membrane. Here we describe the properties of EtxB(H57S), a mutant B subunit with a His-->Ser substitution at position 57. The mutant was found to be severely defective in inducing leukocyte signaling, as shown by failure to (i) trigger caspase 3-mediated CD8(+)-T-cell apoptosis, (ii) activate nuclear translocation of NF-kappaB in Jurkat T cells, (iii) induce a potent anti-B-subunit response in mice, or (iv) serve as a mucosal adjuvant. However, its GM1 binding, cellular uptake, and delivery functions remained intact. This was further validated by the finding that EtxB(H57S) was as effective as EtxB in delivering a conjugated model class I epitope into the major histocompatibility complex class I pathway of a dendritic cell line. These observations imply that GM1 binding alone is not sufficient to trigger the signaling events responsible for the potent immunomodulatory properties of EtxB. Moreover, they demonstrate that its signaling properties play no role in EtxB uptake and trafficking. Thus, EtxB(H57S) represents a novel tool for evaluating the complex cellular interactions and signaling events occurring after receptor interaction, as well as offering an alternative means of delivering attached peptides in the absence of the potent immunomodulatory signals induced by wild-type B subunits.

Immune modulation by the cholera-like enterotoxins

The role of cholera toxin and heat-labile enterotoxin in the pathogenesis of diarrhoeal disease has been well documented for many years. In addition to these deleterious effects, a wealth of data is accumulating that suggests that these toxins and their subunits might be used to modulate immune responses in a variety of beneficial ways. In this regard, the toxins can boost immune responses to unrelated antigens, leading to the possibility of their use in the generation of improved vaccines to a variety of pathogens. Furthermore, recent evidence suggests that recombinant preparations of the nontoxic B subunits of the toxins have distinct immunomodulatory activities, with potential applications to the treatment of autoimmune and inflammatory diseases. This article reviews our current understanding of the mechanisms of immune modulation by these fascinating proteins.