Human leukocyte antigen-DQ8 transgenic mice: a model to examine the toxicity of aerosolized staphylococcal enterotoxin B.

Staphylococcal enterotoxins (SEs) belong to a large group of bacterial exotoxins that cause severe immunopathologies, especially when delivered as an aerosol. SEs elicit the release of lethal amounts of cytokines by binding to major histocompatibility complex (MHC) class II and cross-linking susceptible T-cell receptors. Efforts to develop effective therapeutic strategies to protect against SEs delivered as an aerosol have been hampered by the lack of small animal models that consistently emulate human responses to these toxins. Here, we report that human leukocyte antigen-DQ8 (HLA-DQ8) transgenic (Tg) mice, but not littermate controls, succumbed to lethal shock induced by SEB aerosols without potentiation. Substantial amounts of perivascular edema and inflammatory infiltrates were noted in the lungs of Tg mice, similar to the pathology observed in nonhuman primates exposed by aerosol to SEB. Furthermore, the observed pathologies and lethal shock correlated with an upsurge in proinflammatory cytokine mRNA gene expression in the lungs and spleens, as well as with marked increases in the levels of proinflammatory circulating cytokines in the Tg mice. Unlike the case for littermate controls, telemetric evaluation showed significant hypothermia in Tg mice exposed to lethal doses of SEB. Taken together, these results show that this murine model will allow for the examination of therapeutics and vaccines developed specifically against SEB aerosol exposure and possibly other bacterial superantigens in the context of human MHC class II receptors.

Ebola virus-like particles protect from lethal Ebola virus infection.

The filovirus Ebola causes hemorrhagic fever with 70-80% human mortality. High case-fatality rates, as well as known aerosol infectivity, make Ebola virus a potential global health threat and possible biological warfare agent. Development of an effective vaccine for use in natural outbreaks, response to biological attack, and protection of laboratory workers is a higher national priority than ever before. Coexpression of the Ebola virus glycoprotein (GP) and matrix protein (VP40) in mammalian cells results in spontaneous production and release of virus-like particles (VLPs) that resemble the distinctively filamentous infectious virions. VLPs have been tested and found efficacious as vaccines for several viruses, including papillomavirus, HIV, parvovirus, and rotavirus. Herein, we report that Ebola VLPs (eVLPs) were immunogenic in vitro as eVLPs matured and activated mouse bone marrow-derived dendritic cells, assessed by increases in cell-surface markers CD40, CD80, CD86, and MHC class I and II and secretion of IL-6, IL-10, macrophage inflammatory protein (MIP)-1alpha, and tumor necrosis factor alpha by the dendritic cells. Further, vaccinating mice with eVLPs activated CD4+ and CD8+ T cells, as well as CD19+ B cells. After vaccination with eVLPs, mice developed high titers of Ebola virus-specific antibodies, including neutralizing antibodies. Importantly, mice vaccinated with eVLPs were 100% protected from an otherwise lethal Ebola virus inoculation. Together, our data suggest that eVLPs represent a promising vaccine candidate for protection against Ebola virus infections and a much needed tool to examine the genesis and nature of immune responses to Ebola virus.

Mutational effects on protein folding stability and antigenicity: the case of streptococcal pyrogenic exotoxin A.

The influence of mutationally induced changes in protein folding on development of effective neutralizing antibodies during vaccination remains largely unexplored. In this study, we probed how mutational substitutions of streptococcal pyrogenic exotoxin A (SPEA), a model bacterial superantigen, affect native conformational stability and antigenicity. Stability changes for the toxin variants were determined using circular dichroism and fluorescence measurements, and scanning calorimetry. Self-association was assayed by dynamic light scattering. Inactivated SPEA proteins containing particular combinations of mutations elicited antibodies in HLA-DQ8 transgenic mice that neutralized SPEA superantigenicity in vitro, and protected animals from lethal toxin challenge. However, a highly destabilized cysteine-free mutant of SPEA did not provide effective immunity, nor did an irreversibly denatured version of an otherwise effective mutant protein. These results suggest that protein conformation plays a significant role in generating effective neutralizing antibodies to this toxin, and may be an important factor to consider in vaccine design.

Lethal shock induced by streptococcal pyrogenic exotoxin A in mice transgenic for human leukocyte antigen-DQ8 and human CD4 receptors: implications for development of vaccines and therapeutics.

Streptococcal and staphylococcal infections result in significant human morbidity and mortality. This study used a transgenic murine model expressing human major histocompatibility complex (MHC) class II and human CD4 in which, without additional toxic sensitization, human-like responses to the bacterial superantigen (SAg) streptococcal pyrogenic exotoxin A (SpeA) could be simulated, as determined by studying multiple biologic effects of the SAgs in vivo. Expression of human leukocyte antigen (HLA)-DQ8 rendered the mice susceptible to SpeA-induced lethal shock that was accompanied by massive cytokine production and marked elevation of serum alanine and aspartate aminotransferase levels. Of importance, this model enabled examination of the efficacy of an engineered non-SAg vaccine candidate against SpeA in the context of HLA. This report is thought to be the first of a lethal shock triggered in mice by bacterial SAgs without prior sensitization and examination of a vaccine against streptococcal SAg in the context of human MHC receptors.

Humanlike immune response of human leukocyte antigen-DR3 transgenic mice to staphylococcal enterotoxins: a novel model for superantigen vaccines.

This study examined the biologic responses of transgenic mice expressing human leukocyte antigen (HLA)-DR3 and human CD4 molecules, in the absence of murine major histocompatibility complex (MHC) class II molecules (Ab(0)), to staphylococcal enterotoxins (SEs) and evaluated protective immunity of a nonsuperantigen form of SEB against wild-type holotoxin. HLA-DR3 transgenic mice responded to several log lower concentrations of SEs and secreted higher levels of proinflammatory cytokines than did wild-type mice. Vaccination of transgenic mice with a nonsuperantigenic form of SEB induced high levels of neutralizing anti-SEB antibodies, which protected the mice from a surge in proinflammatory cytokine secretion after SEB challenge. The humanlike responses of the transgenic mice to SEs support the hypothesis that these mice represent an appropriate model to examine vaccines and therapeutics against SEs. This is thought to be the first report of examination of a vaccine against SEB in the context of human MHC class II receptors.