Melissa M. Herbst-Kralovetz

Organotypic 3D cell culture models: using the rotating wall vessel to study host–pathogen interactions

Appropriately simulating the three-dimensional (3D) environment in which tissues normally develop and function is crucial for engineering in vitro models that can be used for the meaningful dissection of host–pathogen interactions. This Review highlights how the rotating wall vessel bioreactor has been used to establish 3D hierarchical models that range in complexity from a single cell type to multicellular co-culture models that recapitulate the 3D architecture of tissues observed in vivo. The application of these models to the study of infectious diseases is discussed.

Norwalk virus-like particles as vaccines

Noroviruses (NoV) cause the great majority of epidemic nonbacterial gastroenteritis in humans. Expression of the capsid protein in recombinant systems, including insect and plant cells, yields assembly of virus-like particles (VLPs) that mimic the antigenic structure of authentic virions, and are relatively acid- and heat-stable. Norwalk virus (NV), the prototype NoV, has been studied extensively, and Norwalk virus-like particles (NVLPs) produced in insect cells and plants are immunogenic in mice and humans when delivered orally, stimulating the production of systemic and mucosal anti-NV antibodies. NVLPs are also highly immunogenic when delivered intranasally, provoking antibodies at levels similar to orally delivered VLP at much lower doses. Oral and nasal delivery of NVLPs efficiently produces antibodies at distal mucosal sites, which suggests that NVLPs could be used to deliver heterologous peptide antigens by production of genetic fusion chimeric capsid proteins. Examination of norovirus VLP surface structures and receptor binding motifs facilitates identification of potential sites for insertion of foreign peptides that will minimally affect the efficiency of VLP assembly and receptor binding. Thus, there is strong potential to use norovirus VLPs as vaccine-delivery vehicles.

Bacteria in the Vaginal Microbiome Alter the Innate Immune Response and Barrier Properties of the Human Vaginal Epithelia in a Species-Specific Manner

BACKGROUND Bacterial vaginosis increases the susceptibility to sexually transmitted infections and negatively affects womens reproductive health. METHODS To investigate host-vaginal microbiota interactions and the impact on immune barrier function, we colonized 3-dimensional (3-D) human vaginal epithelial cells with 2 predominant species of vaginal microbiota (Lactobacillus iners and Lactobacillus crispatus) or 2 prevalent bacteria associated with bacterial vaginosis (Atopobium vaginae and Prevotella bivia). RESULTS Colonization of 3-D vaginal epithelial cell aggregates with vaginal microbiota was observed with direct attachment to host cell surface with no cytotoxicity. A. vaginae infection yielded increased expression membrane-associated mucins and evoked a robust proinflammatory, immune response in 3-D vaginal epithelial cells (ie, expression of CCL20, hBD-2, interleukin 1β, interleukin 6, interleukin 8, and tumor necrosis factor α) that can negatively affect barrier function. However, P. bivia and L. crispatus did not significantly upregulate pattern-recognition receptor-signaling, mucin expression, antimicrobial peptides/defensins, or proinflammatory cytokines in 3-D vaginal epithelial cell aggregates. Notably, L. iners induced pattern-recognition receptor-signaling activity, but no change was observed in mucin expression or secretion of interleukin 6 and interleukin 8. CONCLUSIONS We identified unique species-specific immune signatures from vaginal epithelial cells elicited by colonization with commensal and bacterial vaginosis-associated bacteria. A. vaginae elicited a signature that is consistent with significant disruption of immune barrier properties, potentially resulting in enhanced susceptibility to sexually transmitted infections during bacterial vaginosis.

Intranasal delivery of Norwalk virus-like particles formulated in an in-situ gelling, dry powder vaccine

The development of a vaccine to prevent norovirus infections has been focused on immunization at a mucosal surface, but has been limited by the low immunogenicity of self-assembling Norwalk virus-like particles (NV VLPs) delivered enterically or at nasal surfaces. Nasal immunization, which offers the advantage of ease of immunization, faces obstacles imposed by the normal process of mucociliary clearance, which limits residence time of applied antigens. Herein, we describe the use of a dry powder formulation (GelVac) of an inert in situ gelling polysaccharide (GelSite) extracted from Aloe vera for nasal delivery of NV VLP antigen. Powder formulations, with or without NV VLP antigen, were similar in structure in dry form or when rehydrated in simulated nasal fluids. Immunogenicity of the dry powder VLP formulation was compared to equivalent antigen/adjuvant liquid formulations in animals. For the GelVac powder, we observed superior NV-specific serum and mucosal (aerodigestive and reproductive tracts) antibody responses relative to liquid formulations. Incorporation of the TLR7 agonist gardiquimod in dry powder formulations did not enhance antibody responses, although its inclusion in liquid formulations did enhance VLP immunogenicity irrespective of the presence or absence of GelSite. We interpret these data as showing that GelSite-based dry powder formulations (1) stabilize the immunogenic structural properties of VLPs and (2) induce systemic and mucosal antibody titers which are equal or greater than those achieved by VLPs plus adjuvant in a liquid formulation. We conclude that in situ gelation of the GelVac dry powder formulation at nasal mucosal surfaces delays mucociliary clearance and thereby prolongs VLP antigen exposure to immune effector sites.

Development and Characterization of a Three-Dimensional Organotypic Human Vaginal Epithelial Cell Model

Abstract We have developed an in vitro human vaginal epithelial cell (EC) model using the innovative rotating wall vessel (RWV) bioreactor technology that recapitulates in vivo structural and functional properties, including a stratified squamous epithelium with microvilli, tight junctions, microfolds, and mucus. This three-dimensional (3-D) vaginal model provides a platform for high-throughput toxicity testing of candidate microbicides targeted to combat sexually transmitted infections, effectively complementing and extending existing testing systems such as surgical explants or animal models. Vaginal ECs were grown on porous, collagen-coated microcarrier beads in a rotating, low fluid-shear environment; use of RWV bioreactor technology generated 3-D vaginal EC aggregates. Immunofluorescence and scanning and transmission electron microscopy confirmed differentiation and polarization of the 3-D EC aggregates among multiple cell layers and identified ultrastructural features important for nutrient absorption, cell-cell interactions, and pathogen defense. After treatment with a variety of toll-like receptor (TLR) agonists, cytokine production was quantified by cytometric bead array, confirming that TLRs 2, 3, 5, and 6 were expressed and functional. The 3-D vaginal aggregates were more resistant to nonoxynol-9 (N-9), a contraceptive and previous microbicide candidate, when compared to two-dimensional monolayers of the same cell line. A dose-dependent production of tumor necrosis factor-related apoptosis-inducing ligand and interleukin-1 receptor antagonist, biomarkers of cervicovaginal inflammation, correlated to microbicide toxicity in the 3-D model following N-9 treatment. These results indicate that this 3-D vaginal model could be used as a complementary tool for screening microbicide compounds for safety and efficacy, thus improving success in clinical trials.

A nonreplicating subunit vaccine protects mice against lethal Ebola virus challenge

Ebola hemorrhagic fever is an acute and often deadly disease caused by Ebola virus (EBOV). The possible intentional use of this virus against human populations has led to design of vaccines that could be incorporated into a national stockpile for biological threat reduction. We have evaluated the immunogenicity and efficacy of an EBOV vaccine candidate in which the viral surface glycoprotein is biomanufactured as a fusion to a monoclonal antibody that recognizes an epitope in glycoprotein, resulting in the production of Ebola immune complexes (EICs). Although antigen–antibody immune complexes are known to be efficiently processed and presented to immune effector cells, we found that codelivery of the EIC with Toll-like receptor agonists elicited a more robust antibody response in mice than did EIC alone. Among the compounds tested, polyinosinic:polycytidylic acid (PIC, a Toll-like receptor 3 agonist) was highly effective as an adjuvant agent. After vaccinating mice with EIC plus PIC, 80% of the animals were protected against a lethal challenge with live EBOV (30,000 LD50 of mouse adapted virus). Surviving animals showed a mixed Th1/Th2 response to the antigen, suggesting this may be important for protection. Survival after vaccination with EIC plus PIC was statistically equivalent to that achieved with an alternative viral vector vaccine candidate reported in the literature. Because nonreplicating subunit vaccines offer the possibility of formulation for cost-effective, long-term storage in biothreat reduction repositories, EIC is an attractive option for public health defense measures.

Antimicrobial peptides in the female reproductive tract: a critical component of the mucosal immune barrier with physiological and clinical implications

BACKGROUND At the interface of the external environment and the mucosal surface of the female reproductive tract (FRT) lies a first-line defense against pathogen invasion that includes antimicrobial peptides (AMP). Comprised of a unique class of multifunctional, amphipathic molecules, AMP employ a wide range of functions to limit microbial invasion and replication within host cells as well as independently modulate the immune system, dampen inflammation and maintain tissue homeostasis. The role of AMP in barrier defense at the level of the skin and gut has received much attention as of late. Given the far reaching implications for womens health, maternal and fetal morbidity and mortality, and sexually transmissible and polymicrobial diseases, we herein review the distribution and function of key AMP throughout the female reproductive mucosa and assess their role as an essential immunological barrier to microbial invasion throughout the reproductive cycle of a womans lifetime. METHODS A comprehensive search in PubMed/Medline was conducted related to AMP general structure, function, signaling, expression, distribution and barrier function of AMP in the FRT, hormone regulation of AMP, the microbiome of the FRT, and AMP in relation to implantation, pregnancy, fertility, pelvic inflammatory disease, complications of pregnancy and assisted reproductive technology. RESULTS AMP are amphipathic peptides that target microbes for destruction and have been conserved throughout all living organisms. In the FRT, several major classes of AMP are expressed constitutively and others are inducible at the mucosal epithelium and by immune cells. AMP expression is also under the influence of sex hormones, varying throughout the menstrual cycle, and dependent on the vaginal microbiome. AMP can prevent infection with sexually transmissible and opportunistic pathogens of the female reproductive tissues, although emerging understanding of vaginal dysbiosis suggests induction of a unique AMP profile with increased susceptibility to these pathogens. During pregnancy, AMP are key immune effectors of the fetal membranes and placenta and are dysregulated in states of intrauterine infection and other complications of pregnancy. CONCLUSIONS At the level of the FRT, AMP serve to inhibit infection by sexually and vertically transmissible as well as by opportunistic bacteria, fungi, viruses, and protozoa and must do so throughout the hormone flux of menses and pregnancy. Guarding the exclusive site of reproduction, AMP modulate the vaginal microbiome of the lower FRT to aid in preventing ascending microbes into the upper FRT. Evolving in parallel with, and in response to, pathogenic insults, AMP are relatively immune to the resistance mechanisms employed by rapidly evolving pathogens and play a key role in barrier function and host defense throughout the FRT.

An Intranasally Delivered Toll-Like Receptor 7 Agonist Elicits Robust Systemic and Mucosal Responses to Norwalk Virus-Like Particles

ABSTRACT Norwalk virus (NV) is an enteric pathogen from the genus Norovirus and a major cause of nonbacterial gastroenteritis in humans. NV virus-like particles (VLPs) are known to elicit systemic and mucosal immune responses when delivered nasally; however, the correlates of immune protection are unknown, and codelivery with a safe and immunogenic mucosal adjuvant may enhance protective anti-NV immune responses. Resiquimod (R848), an imidazoquinoline-based Toll-like receptor 7 and/or 8 (TLR7/8) agonist, is being evaluated as an adjuvant in FDA-approved clinical vaccine trials. As such, we evaluated the adjuvant activity of two imidazoquinoline-based TLR7 and TLR7/8 agonists when codelivered intranasally with plant-derived NV VLPs. We also compared the activity of these agonists to the gold standard mucosal adjuvant, cholera toxin (CT). Our results indicate that codelivery with the TLR7 agonist, gardiquimod (GARD), induces NV VLP-specific serum IgG and IgG isotype responses and mucosal IgA responses in the gastrointestinal, respiratory, and reproductive tracts that are superior to those induced by R848 and comparable to those induced by the mucosal adjuvant CT. This study supports the continued investigation of GARD as a mucosal adjuvant for NV VLPs and possible use for other VLP-based vaccines for which immune responses at distal mucosal sites (e.g., respiratory and reproductive tracts) are desired.

Intranasal Vaccination with Murabutide Enhances Humoral and Mucosal Immune Responses to a Virus-Like Particle Vaccine

Murabutide (MB) is a synthetic immunomodulator recognized by the nucleotide-binding oligomerization domain-containing protein 2 (NOD2) receptor on mammalian cells. MB has previously been approved for testing in multiple human clinical trials to determine its value as an antiviral therapeutic, and as an adjuvant for injected vaccines. We have found a new use for this immunomodulator; it functions as a mucosal adjuvant that enhances immunogenicity of virus-like particles (VLP) administered intranasally. MB enhanced Norwalk virus (NV) VLP-specific IgG systemically and IgA production at distal mucosal sites following intranasal (IN) vaccination. A dose escalation study identified 100 µg as the optimal MB dosage in mice, based on the magnitude of VLP-specific IgG, IgG1, IgG2a and IgA production in serum and VLP-specific IgA production at distal mucosal sites. IN vaccination using VLP with MB was compared to IN delivery VLP with cholera toxin (CT) or gardiquimod (GARD) and to parenteral VLP delivery with alum; the MB groups were equivalent to CT and GARD and superior to alum in inducing mucosal immune responses and stimulated equivalent systemic VLP-specific antibodies. These data support the further testing of MB as a potent mucosal adjuvant for inducing robust and durable antibody responses to non-replicating subunit vaccines.

Menopause and the vaginal microbiome

For over a century it has been well documented that bacteria in the vagina maintain vaginal homeostasis, and that an imbalance or dysbiosis may be associated with poor reproductive and gynecologic health outcomes. Vaginal microbiota are of particular significance to postmenopausal women and may have a profound effect on vulvovaginal atrophy, vaginal dryness, sexual health and overall quality of life. As molecular-based techniques have evolved, our understanding of the diversity and complexity of this bacterial community has expanded. The objective of this review is to compare the changes that have been identified in the vaginal microbiota of menopausal women, outline alterations in the microbiome associated with specific menopausal symptoms, and define how hormone replacement therapy impacts the vaginal microbiome and menopausal symptoms; it concludes by considering the potential of probiotics to reinstate vaginal homeostasis following menopause. This review details the studies that support the role of Lactobacillus species in maintaining vaginal homeostasis and how the vaginal microbiome structure in postmenopausal women changes with decreasing levels of circulating estrogen. In addition, the associated transformations in the microanatomical features of the vaginal epithelium that can lead to vaginal symptoms associated with menopause are described. Furthermore, hormone replacement therapy directly influences the dominance of Lactobacillus in the microbiota and can resolve vaginal symptoms. Oral and vaginal probiotics hold great promise and initial studies complement the findings of previous research efforts concerning menopause and the vaginal microbiome; however, additional trials are required to determine the efficacy of bacterial therapeutics to modulate or restore vaginal homeostasis.