Adjuvant-dependent impact of inactivated SARS-CoV-2 vaccines during heterologous infection by a SARS-related coronavirus

Whole virus-based inactivated SARS-CoV-2 vaccines adjuvanted with aluminum hydroxide have been critical to the COVID-19 pandemic response. Although these vaccines are protective against homologous coronavirus infection, the emergence of novel variants and the presence of large zoonotic reservoirs harboring novel heterologous coronaviruses provide significant opportunities for vaccine breakthrough, which raises the risk of adverse outcomes like vaccine-associated enhanced respiratory disease. Here, we use a female mouse model of coronavirus disease to evaluate inactivated vaccine performance against either homologous challenge with SARS-CoV-2 or heterologous challenge with a bat-derived coronavirus that represents a potential emerging disease threat. We show that inactivated SARS-CoV-2 vaccines adjuvanted with aluminum hydroxide can cause enhanced respiratory disease during heterologous infection, while use of an alternative adjuvant does not drive disease and promotes heterologous viral clearance. In this work, we highlight the impact of adjuvant selection on inactivated vaccine safety and efficacy against heterologous coronavirus infection.

Host Genetic Variation Impacts SARS-CoV-2 Vaccination Response in the Diversity Outbred Mouse Population

The COVID-19 pandemic led to the rapid and worldwide development of highly effective vaccines against SARS-CoV-2. However, there is significant individual-to-individual variation in vaccine efficacy due to factors including viral variants, host age, immune status, environmental and host genetic factors. Understanding those determinants driving this variation may inform the development of more broadly protective vaccine strategies. While host genetic factors are known to impact vaccine efficacy for respiratory pathogens such as influenza and tuberculosis, the impact of host genetic variation on vaccine efficacy against COVID-19 is not well understood. To model the impact of host genetic variation on SARS-CoV-2 vaccine efficacy, while controlling for the impact of non-genetic factors, we used the Diversity Outbred (DO) mouse model. We found that DO mice immunized against SARS-CoV-2 exhibited high levels of variation in vaccine-induced neutralizing antibody responses. While the majority of the vaccinated mice were protected from virus-induced disease, similar to human populations, we observed vaccine breakthrough in a subset of mice. Importantly, we found that this variation in neutralizing antibody, virus-induced disease, and viral titer is heritable, indicating that the DO serves as a useful model system for studying the contribution of genetic variation of both vaccines and disease outcomes.

Interferon regulatory factor 7 modulates virus clearance and immune responses to alphavirus encephalomyelitis

IMPORTANCE

Viral encephalomyelitis outcome is dependent on host responses to neuronal infection. Interferon (IFN) is an important component of the innate response, and IFN regulatory factor (IRF) 7 is an inducible transcription factor for the synthesis of IFN-α. IRF7-deficient mice develop fatal paralysis after CNS infection with Sindbis virus, while wild-type mice recover. Irf7 -/- mice produce low levels of IFN-α but high levels of IFN-β with induction of IFN-stimulated genes, so the reason for this difference is not understood. The current study shows that Irf7 -/- mice developed inflammation earlier but failed to clear virus from motor neuron-rich regions of the brainstem and spinal cord. Levels of IFN-γ and virus-specific antibody were comparable, indicating that IRF7 deficiency does not impair expression of these known viral clearance factors. Therefore, IRF7 is either necessary for the neuronal response to currently identified mediators of clearance or enables the production of additional antiviral factor(s) needed for clearance.

Pharmacokinetic Considerations for Optimizing Inhaled Spray-Dried Pyrazinoic Acid Formulations

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a leading cause of death with 1.6 million deaths worldwide reported in 2021. Oral pyrazinamide (PZA) is an integral part of anti-TB regimens, but its prolonged use has the potential to drive the development of PZA-resistant Mtb. PZA is converted to the active moiety pyrazinoic acid (POA) by the Mtb pyrazinamidase encoded by pncA, and mutations in pncA are associated with the majority of PZA resistance. Conventional oral and parenteral therapies may result in subtherapeutic exposure in the lung; hence, direct pulmonary administration of POA may provide an approach to rescue PZA efficacy for treating pncA-mutant PZA-resistant Mtb. The objectives of the current study were to (i) develop novel dry powder POA formulations, (ii) assess their feasibility for pulmonary delivery using physicochemical characterization, (iii) evaluate their pharmacokinetics (PK) in the guinea pig model, and (iv) develop a mechanism-based pharmacokinetic model (MBM) using in vivo PK data to select a formulation providing adequate exposure in epithelial lining fluid (ELF) and lung tissue. We developed three POA formulations for pulmonary delivery and characterized their PK in plasma, ELF, and lung tissue following passive inhalation in guinea pigs. Additionally, the PK of POA following oral, intravenous, and intratracheal administration was characterized in guinea pigs. The MBM was used to simultaneously model PK data following administration of POA and its formulations via the different routes. The MBM described POA PK well in plasma, ELF, and lung tissue. Physicochemical analyses and MBM predictions suggested that POA maltodextrin was the best among the three formulations and an excellent candidate for further development as it has: (i) the highest ELF-to-plasma exposure ratio (203) and lung tissue-to-plasma exposure ratio (30.4) compared with POA maltodextrin and leucine (75.7/16.2) and POA leucine salt (64.2/19.3) and (ii) the highest concentration in ELF (CmaxELF: 171 nM) within 15.5 min, correlating with a fast transfer into ELF after pulmonary administration (KPM: 22.6 1/h). The data from the guinea pig allowed scaling, using the MBM to a human dose of POA maltodextrin powder demonstrating the potential feasibility of an inhaled product.

Core mitochondrial genes are down-regulated during SARS-CoV-2 infection of rodent and human hosts

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral proteins bind to host mitochondrial proteins, likely inhibiting oxidative phosphorylation (OXPHOS) and stimulating glycolysis. We analyzed mitochondrial gene expression in nasopharyngeal and autopsy tissues from patients with coronavirus disease 2019 (COVID-19). In nasopharyngeal samples with declining viral titers, the virus blocked the transcription of a subset of nuclear DNA (nDNA)-encoded mitochondrial OXPHOS genes, induced the expression of microRNA 2392, activated HIF-1α to induce glycolysis, and activated host immune defenses including the integrated stress response. In autopsy tissues from patients with COVID-19, SARS-CoV-2 was no longer present, and mitochondrial gene transcription had recovered in the lungs. However, nDNA mitochondrial gene expression remained suppressed in autopsy tissue from the heart and, to a lesser extent, kidney, and liver, whereas mitochondrial DNA transcription was induced and host-immune defense pathways were activated. During early SARS-CoV-2 infection of hamsters with peak lung viral load, mitochondrial gene expression in the lung was minimally perturbed but was down-regulated in the cerebellum and up-regulated in the striatum even though no SARS-CoV-2 was detected in the brain. During the mid-phase SARS-CoV-2 infection of mice, mitochondrial gene expression was starting to recover in mouse lungs. These data suggest that when the viral titer first peaks, there is a systemic host response followed by viral suppression of mitochondrial gene transcription and induction of glycolysis leading to the deployment of antiviral immune defenses. Even when the virus was cleared and lung mitochondrial function had recovered, mitochondrial function in the heart, kidney, liver, and lymph nodes remained impaired, potentially leading to severe COVID-19 pathology.

Effect of Viral Strain and Host Age on Clinical Disease and Viral Replication in Immunocompetent Mouse Models of Chikungunya Encephalomyelitis

The alphavirus chikungunya virus (CHIKV) represents a reemerging public health threat as mosquito vectors spread and viruses acquire advantageous mutations. Although primarily arthritogenic in nature, CHIKV can produce neurological disease with long-lasting sequelae that are difficult to study in humans. We therefore evaluated immunocompetent mouse strains/stocks for their susceptibility to intracranial infection with three different CHIKV strains, the East/Central/South African (ECSA) lineage strain SL15649 and Asian lineage strains AF15561 and SM2013. In CD-1 mice, neurovirulence was age- and CHIKV strain-specific, with SM2013 inducing less severe disease than SL15649 and AF15561. In 4-6-week-old C57BL/6J mice, SL15649 induced more severe disease and increased viral brain and spinal cord titers compared to Asian lineage strains, further indicating that neurological disease severity is CHIKV-strain-dependent. Proinflammatory cytokine gene expression and CD4+ T cell infiltration in the brain were also increased with SL15649 infection, suggesting that like other encephalitic alphaviruses and with CHIKV-induced arthritis, the immune response contributes to CHIKV-induced neurological disease. Finally, this study helps overcome a current barrier in the alphavirus field by identifying both 4-6-week-old CD-1 and C57BL/6J mice as immunocompetent, neurodevelopmentally appropriate mouse models that can be used to examine CHIKV neuropathogenesis and immunopathogenesis following direct brain infection.

Fc-mediated pan-sarbecovirus protection after alphavirus vector vaccination

Group 2B β-coronaviruses (sarbecoviruses) have caused regional and global epidemics in modern history. Here, we evaluate the mechanisms of cross-sarbecovirus protective immunity, currently less clear yet important for pan-sarbecovirus vaccine development, using a panel of alphavirus-vectored vaccines covering bat to human strains. While vaccination does not prevent virus replication, it protects against lethal heterologous disease outcomes in both severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and clade 2 bat sarbecovirus challenge models. The spike vaccines tested primarily elicit a highly S1-specific homologous neutralizing antibody response with no detectable cross-virus neutralization. Rather, non-neutralizing antibody functions, mechanistically linked to FcgR4 and spike S2, mediate cross-protection in wild-type mice. Protection is lost in FcR knockout mice, further supporting a model for non-neutralizing, protective antibodies. These data highlight the importance of FcR-mediated cross-protective immune responses in universal pan-sarbecovirus vaccine designs.

Pharmacokinetic considerations for optimizing inhaled spray-dried pyrazinoic acid formulations

Tuberculosis (TB), caused by Mycobacterium tuberculosis ( Mtb ), remains a leading cause of death with 1.6 million deaths worldwide reported in 2021. Oral pyrazinamide (PZA) is an integral part of anti-TB regimens, but its prolonged use has the potential to drive development of PZA resistant Mtb . PZA is converted to the active moiety pyrazinoic acid (POA) by the Mtb pyrazinamidase encoded by pncA , and mutations in pncA are associated with the majority of PZA resistance. Conventional oral and parenteral therapies may result in subtherapeutic exposure in the lung, hence direct pulmonary administration of POA may provide an approach to rescue PZA efficacy for treating pncA- mutant PZA-resistant Mtb . The objectives of the current study were to i) develop novel dry powder POA formulations ii) assess their feasibility for pulmonary delivery using physicochemical characterization, iii) evaluate their pharmacokinetics (PK) in the guinea pig model and iv) develop a mechanism based pharmacokinetic model (MBM) using in vivo PK data to select a formulation providing adequate exposure in epithelial lining fluid (ELF) and lung tissue. We developed three POA formulations for pulmonary delivery and characterized their PK in plasma, ELF, and lung tissue following passive inhalation in guinea pigs. Additionally, the PK of POA following oral, intravenous and intratracheal administration was characterized in guinea pigs. The MBM was used to simultaneously model PK data following administration of POA and its formulations via the different routes. The MBM described POA PK well in plasma, ELF and lung tissue. Physicochemical analyses and MBM predictions suggested that POA maltodextrin was the best among the three formulations and an excellent candidate for further development as it has: (i) the highest ELF-to-plasma exposure ratio (203) and lung tissue-to-plasma exposure ratio (30.4) compared with POA maltodextrin and leucine (75.7/16.2) and POA leucine salt (64.2/19.3); (ii) the highest concentration in ELF ( Cmac ELF : 171 nM) within 15.5 minutes, correlating with a fast transfer into ELF after pulmonary administration ( k PM : 22.6 1/h). The data from the guinea pig allowed scaling, using the MBM to a human dose of POA maltodextrin powder demonstrating the potential feasibility of an inhaled product.

Table of Contents TOC/Abstract Graphic

Human ACE2 expression, a major tropism determinant for SARS-CoV-2, is regulated by upstream and intragenic elements

Angiotensin-converting enzyme 2 (ACE2), part of the renin-angiotensin system (RAS), serves as an entry point for SARS-CoV-2, leading to viral proliferation in permissive cell types. Using mouse lines in which the Ace2 locus has been humanized by syntenic replacement, we show that regulation of basal and interferon induced ACE2 expression, relative expression levels of different ACE2 transcripts, and sexual dimorphism in ACE2 expression are unique to each species, differ between tissues, and are determined by both intragenic and upstream promoter elements. Our results indicate that the higher levels of expression of ACE2 observed in the lungs of mice relative to humans may reflect the fact that the mouse promoter drives expression of ACE2 in populous airway club cells while the human promoter drives expression in alveolar type 2 (AT2) cells. In contrast to transgenic mice in which human ACE2 is expressed in ciliated cells under the control of the human FOXJ1 promoter, mice expressing ACE2 in club cells under the control of the endogenous Ace2 promoter show a robust immune response after infection with SARS-CoV-2, leading to rapid clearance of the virus. This supports a model in which differential expression of ACE2 determines which cell types in the lung are infected, and this in turn modulates the host response and outcome of COVID-19.

Fc mediated pan-sarbecovirus protection after alphavirus vector vaccination

Two group 2B β-coronaviruses (sarbecoviruses) have caused regional and global epidemics in modern history. The mechanisms of cross protection driven by the sarbecovirus spike, a dominant immunogen, are less clear yet critically important for pan-sarbecovirus vaccine development. We evaluated the mechanisms of cross-sarbecovirus protective immunity using a panel of alphavirus-vectored vaccines covering bat to human strains. While vaccination did not prevent virus replication, it protected against lethal heterologous disease outcomes in both SARS-CoV-2 and clade 2 bat sarbecovirus HKU3-SRBD challenge models. The spike vaccines tested primarily elicited a highly S1-specific homologous neutralizing antibody response with no detectable cross-virus neutralization. We found non-neutralizing antibody functions that mediated cross protection in wild-type mice were mechanistically linked to FcgR4 and spike S2-binding antibodies. Protection was lost in FcR knockout mice, further supporting a model for non-neutralizing, protective antibodies. These data highlight the importance of FcR-mediated cross-protective immune responses in universal pan-sarbecovirus vaccine designs.

A Multitrait Locus Regulates Sarbecovirus Pathogenesis

Infectious diseases have shaped the human population genetic structure, and genetic variation influences the susceptibility to many viral diseases. However, a variety of challenges have made the implementation of traditional human Genome-wide Association Studies (GWAS) approaches to study these infectious outcomes challenging. In contrast, mouse models of infectious diseases provide an experimental control and precision, which facilitates analyses and mechanistic studies of the role of genetic variation on infection. Here we use a genetic mapping cross between two distinct Collaborative Cross mouse strains with respect to SARS-CoV disease outcomes. We find several loci control differential disease outcome for a variety of traits in the context of SARS-CoV infection. Importantly, we identify a locus on mouse Chromosome 9 that shows conserved synteny with a human GWAS locus for SARS-CoV-2 severe disease. We follow-up and confirm a role for this locus, and identify two candidate genes, CCR9 and CXCR6 that both play a key role in regulating the severity of SARS-CoV, SARS-CoV-2 and a distantly related bat sarbecovirus disease outcomes. As such we provide a template for using experimental mouse crosses to identify and characterize multitrait loci that regulate pathogenic infectious outcomes across species.

An inactivated SARS-CoV-2 vaccine causes enhanced type 2 inflammation in mice during coronavirus challenge

Inactivated vaccines administered with the adjuvant aluminum hydroxide (Alum) are currently the most widely used COVID-19 vaccines in the world and have been critical to responding to the SARS-CoV-2 pandemic. Although these vaccines are efficacious against homologous virus infection in healthy young adults, the emergence of novel SARS-CoV-2 variants has resulted in significant vaccine breakthrough. Pre-clinical studies with inactivated SARS-CoV-1 and MERS-CoV vaccines have reported enhanced immunopathology upon breakthrough infection, characterized by pulmonary eosinophilia and upregulation of type 2 cytokines. These previous reports therefore raise the concern that inactivated COVID-19 vaccines may cause enhanced immunopathology upon vaccine breakthrough. To investigate this possibility, we vaccinated female BALB/c mice with inactivated SARS-CoV-2 (iCoV2) prior to coronavirus challenge. Although iCoV2 protected mice from severe clinical disease and pulmonary pathology upon homologous challenge with pathogenic SARS-CoV-2, we observed increased pulmonary pathology and pulmonary eosinophilia upon challenge in mice vaccinated with iCoV2 and Alum (iCoV2 + Alum) compared to mice vaccinated with iCoV2 alone. Furthermore, to model vaccine breakthrough upon heterologous coronavirus infection, we challenged iCoV2-vaccinated mice with a zoonotic SARS-like coronavirus (SHC014). Upon SHC014 challenge, iCoV2 + Alum vaccination failed to control virus replication and caused enhanced pulmonary pathology, pulmonary eosinophilia and upregulation of pulmonary type 2 cytokines. Ongoing studies are investigating the mechanism of iCoV2-related immunopathology, including the role of specific iCoV2 antigens.

Supported by grants from NIH (K01 OD026529, U19 AI100625, U19 AI109680, and MSTP T32 GM008719), Infectious Disease Drug Discovery Program (ID3), Rapidly Emerging Antiviral Drug Development Initiative (READDI), NCTraCS and Emerging Challenges in Biomedical Research COVID Pilot Award, SOM Junior Investigator Development Award, Department of Pathology and Laboratory Medicine.

Neurological chikungunya virus infection induces corpus callosum degeneration associated with resident immune cell activation and peripheral immune cell infiltration

Chikungunya virus (CHIKV) is an Old World alphavirus that typically induces arthralgia and rash. However, CHIKV is also capable of infecting the central nervous system (CNS), resulting in encephalitis, myelitis, and peripheral neuropathy. Patients who survive acute infection typically have long lasting neurological effects. To date, an immunocompetent small animal model that recapitulates CHIKV CNS disease has not been established. To develop a mouse model of CNS CHIKV infection, we intracranially inoculated 4–6 week old C57BL/6J mice with 1 of 3 clinical CHIKV isolates: Asian lineage strains SM2013 and AF15561, and ECSA lineage strain SL15649. CHIKV CNS disease is most commonly reported in regions where ECSA lineage strains circulate; in agreement with observations in humans, SL15649 was associated with more severe neurological disease, while SM2013 induced minimal to no disease, and AF15561 induced an intermediate clinical phenotype. At 7dpi when mice demonstrated signs of CNS disease but infectious virus was cleared from the brain, significant corpus callosum degeneration was observed in mice infected with SL15649, and to a lesser extent AF15561. Recruited CD4+ T cells and B cells were significantly elevated in the corpus callosum of mice infected with SL15649 compared to mice infected with SM2013. SL1549 infected mice also had significant micro- and astrogliosis in this area. At 3dpi, prior to neurological signs, the corpus callosum in SL1549 infected mice did not show significant degeneration but did have an influx of peripheral immune cells and increased gliosis. These results suggest that the CNS manifestations of CHIKV are associated with corpus callosum degeneration driven by both peripheral and CNS resident immune cells.

Supported by the following grants: K01 OD026529 (VKB) T32AI0075151 (ACK) AAI Careers in Immunology Fellowship (VKB, ACK) UNC SOM Junior Investigator Development Award (VKB) UNC Department of Pathology and Laboratory Medicine (VKB)

Preclinical coronavirus studies and pathology: Challenges of the high-containment laboratory

The COVID-19 pandemic has highlighted the critical role that animal models play in elucidating the pathogenesis of emerging diseases and rapidly analyzing potential medical countermeasures. Relevant pathologic outcomes are paramount in evaluating preclinical models and therapeutic outcomes and require careful advance planning. While there are numerous guidelines for attaining high-quality pathology specimens in routine animal studies, preclinical studies using coronaviruses are often conducted under biosafety level-3 (BSL3) conditions, which pose unique challenges and technical limitations. In such settings, rather than foregoing pathologic outcomes because of the inherent constraints of high-containment laboratory protocols, modifications can be made to conventional best practices of specimen collection. Particularly for those unfamiliar with working in a high-containment laboratory, the authors describe the logistics of conducting such work, focusing on animal experiments in BSL3 conditions. To promote scientific rigor and reproducibility and maximize the value of animal use, the authors provide specific points to be considered before, during, and following a high-containment animal study. The authors provide procedural modifications for attaining good quality pathologic assessment of the mouse lung, central nervous system, and blood specimens under high-containment conditions while being conscientious to maximize animal use for other concurrent assays.

TARGETED DOWN REGULATION OF CORE MITOCHONDRIAL GENES DURING SARS-COV-2 INFECTION

Defects in mitochondrial oxidative phosphorylation (OXPHOS) have been reported in COVID-19 patients, but the timing and organs affected vary among reports. Here, we reveal the dynamics of COVID-19 through transcription profiles in nasopharyngeal and autopsy samples from patients and infected rodent models. While mitochondrial bioenergetics is repressed in the viral nasopharyngeal portal of entry, it is up regulated in autopsy lung tissues from deceased patients. In most disease stages and organs, discrete OXPHOS functions are blocked by the virus, and this is countered by the host broadly up regulating unblocked OXPHOS functions. No such rebound is seen in autopsy heart, results in severe repression of genes across all OXPHOS modules. Hence, targeted enhancement of mitochondrial gene expression may mitigate the pathogenesis of COVID-19.

Mouse Models for the Study of SARS-CoV-2 Infection

Mice are an invaluable resource for studying virus-induced disease. They are a small, genetically modifiable animal for which a large arsenal of genetic and immunologic tools is available for evaluation of pathogenesis and potential vaccines and therapeutics. SARS-CoV-2, the betacoronavirus responsible for the COVID-19 pandemic, does not naturally replicate in wild-type mice, due to structural differences between human and mouse ACE2, the primary receptor for SARS-CoV-2 entry into cells. However, several mouse strains have been developed that allow for SARS-CoV-2 replication and clinical disease. Two broad strategies have primarily been deployed for developing mouse strains susceptible to COVID-19-like disease: adding in the human ACE2 gene and adapting the virus to the mouse ACE2 receptor. Both approaches result in mice that develop several of the clinical and pathologic hallmarks of COVID-19, including acute respiratory distress syndrome and acute lung injury. In this review, we describe key acute pulmonary and extrapulmonary pathologic changes seen in COVID-19 patients that mouse models of SARS-CoV-2 infection ideally replicate, the essential development of mouse models for the study of Severe Acute Respiratory Syndrome and Middle Eastern Respiratory Syndrome and the basis of many of the models of COVID-19, and key clinical and pathologic features of currently available mouse models of SARS-CoV-2 infection.

Novel virus-like nanoparticle vaccine effectively protects animal model from SARS-CoV-2 infection

The key to battling the COVID-19 pandemic and its potential aftermath is to develop a variety of vaccines that are efficacious and safe, elicit lasting immunity, and cover a range of SARS-CoV-2 variants. Recombinant viral receptor-binding domains (RBDs) are safe vaccine candidates but often have limited efficacy due to the lack of virus-like immunogen display pattern. Here we have developed a novel virus-like nanoparticle (VLP) vaccine that displays 120 copies of SARS-CoV-2 RBD on its surface. This VLP-RBD vaccine mimics virus-based vaccines in immunogen display, which boosts its efficacy, while maintaining the safety of protein-based subunit vaccines. Compared to the RBD vaccine, the VLP-RBD vaccine induced five times more neutralizing antibodies in mice that efficiently blocked SARS-CoV-2 from attaching to its host receptor and potently neutralized the cell entry of variant SARS-CoV-2 strains, SARS-CoV-1, and SARS-CoV-1-related bat coronavirus. These neutralizing immune responses induced by the VLP-RBD vaccine did not wane during the two-month study period. Furthermore, the VLP-RBD vaccine effectively protected mice from SARS-CoV-2 challenge, dramatically reducing the development of clinical signs and pathological changes in immunized mice. The VLP-RBD vaccine provides one potentially effective solution to controlling the spread of SARS-CoV-2.

Robust Anti-SARS-CoV-2 Humoral and Cellular Immunity through cGAMP-loaded Microparticle Adjuvanted Subunit Vaccination

In less than one year, the COVID-19 pandemic has infected over 95 million people with greater than two million deaths globally. Vaccines against the SARS-CoV-2 virus offer the best chance at curbing the severity and spread of COVID-19. While initial COVID-19 vaccine candidates have demonstrated great promise and efficacy, it is unknown how broad and durable those responses will be. Furthermore, eliciting strong antiviral immune responses will prove critical against future emerging strains. Previously, we demonstrated that cyclic-AMP-GMP (cGAMP) encapsulated within acetalated dextran microparticles (MPs) adjuvants influenza subunit antigens to strongly protect against influenza viral challenge when used as an intramuscular vaccination in a mouse and ferret model. Based on these studies, we hypothesized that vaccination with the stabilized spike protein of SARS-CoV-2 (S2P) and cGAMP MPs would lead to protective anti-SARS-CoV-2 immune responses. We demonstrate that S2P vaccination with cGAMP MPs lead to increased total anti-SARS-CoV-2 IgG with a strong Th1 skewed IgG2c antibody response compared to other clinically relevant adjuvants. Vaccination using cGAMP MPs also increased the frequency of activated Th1 antigen-specific T cell responses compared to controls and other vaccine adjuvants, as determined by IL-2 and INFg ELISPOTs. Finally, vaccination using cGAMP MPs lead to comparable SARS-CoV-2 neutralizing antibody production and protection against mouse adapted SARS-CoV-2 infection. These studies demonstrate that vaccination with S2P and cGAMP MPs lead to a protective humoral response and improved antigen-specific T cell responses compared to other clinically relevant adjuvants.

Immunopathogenesis of alphaviruses

Alphaviruses, members of the enveloped, positive-sense, single-stranded RNA Togaviridae family, represent a reemerging public health threat as mosquito vectors expand into new geographic territories. The Old World alphaviruses, which include chikungunya virus, Ross River virus, and Sindbis virus, tend to cause a clinical syndrome characterized by fever, rash, and arthritis, whereas the New World alphaviruses, which consist of Venezuelan equine encephalitis virus, eastern equine encephalitis virus, and western equine encephalitis virus, induce encephalomyelitis. Following recovery from the acute phase of infection, many patients are left with debilitating persistent joint and neurological complications that can last for years. Clues from human cases and studies using animal models strongly suggest that much of the disease and pathology induced by alphavirus infection, particularly atypical and chronic manifestations, is mediated by the immune system rather than directly by the virus. This review discusses the current understanding of the immunopathogenesis of the arthritogenic and neurotropic alphaviruses accumulated through both natural infection of humans and experimental infection of animals, particularly mice. As treatment following alphavirus infection is currently limited to supportive care, understanding the contribution of the immune system to the disease process is critical to developing safe and effective therapies.

Association of persistent wild-type measles virus RNA with long-term humoral immunity in rhesus macaques

Recovery from measles results in life-long protective immunity. To understand induction of long-term immunity, rhesus macaques were studied for 6 months after infection with wild-type measles virus (MeV). Infection caused viremia and rash, with clearance of infectious virus by day 14. MeV RNA persisted in PBMCs for 30-90 days and in lymphoid tissue for 6 months most often in B cells but was rarely detected in BM. Antibody with neutralizing activity and binding specificity for MeV nucleocapsid (N), hemagglutinin (H), and fusion proteins appeared with the rash and avidity matured over 3-4 months. Lymph nodes had increasing numbers of MeV-specific antibody-secreting cells (ASCs) and germinal centers with late hyalinization. ASCs appeared in circulation with the rash and continued to appear along with peripheral T follicular helper cells for the study duration. ASCs in lymph nodes and PBMCs produced antibody against both H and N, with more H-specific ASCs in BM. During days 14-21, 20- to 100-fold more total ASCs than MeV-specific ASCs appeared in circulation, suggesting mobilization of preexisting ASCs. Therefore, persistence of MeV RNA in lymphoid tissue was accompanied by continued germinal center formation, ASC production, avidity maturation, and accumulation of H-specific ASCs in BM to sustain neutralizing antibody and protective immunity.

Interferon-Gamma Modulation of the Local T Cell Response to Alphavirus Encephalomyelitis

Infection of mice with Sindbis virus (SINV) provides a model for examining the role of the immune response to alphavirus infection of the central nervous system (CNS). Interferon-gamma (IFN-γ) is an important component of this response, and we show that SINV-infected differentiated neurons respond to IFN-γ in vitro by induction of antiviral genes and suppression of virus replication. To determine the in vivo effects of IFN-γ on SINV clearance and T cell responses, C57BL/6 mice lacking IFN-γ or IFN-γ receptor-1 were compared to wild-type (WT) mice after intracranial SINV infection. In WT mice, IFN-γ was first produced in the CNS by natural killer cells and then by CD4+ and CD8+ T cells. Mice with impaired IFN-γ signaling initiated clearance of viral RNA earlier than WT mice associated with CNS entry of more granzyme B-producing CD8+ T cells. However, these mice established fewer CD8+ tissue-resident memory T (TRM) cells and were more likely to experience reactivation of viral RNA synthesis late after infection. Therefore, IFN-γ suppresses the local development of granzyme B-expressing CD8+ T cells and slows viral RNA clearance but promotes CD8+ TRM cell establishment.

Effectiveness of Various Floor Contamination Control Methods in Reducing Environmental Organic Load and Maintaining Colony Health in Rodent Facilities

Floor contamination control practices in rodent housing facilities commonly include disposable shoe covers despite the lack of evidence for their usefulness in bioexclusion. Contamination control flooring mats are advertised as an economical and environmentally-responsible alternative to shoe covers, yet little is published regarding their efficacy in preventing the transfer of organic material and the introduction of infectious agents into facilities. We evaluated 4 floor contamination control strategies-shoe covers (ShCv), contamination control flooring (CCF), using both products concurrently (ShCv+CCF) compared with using neither-in preventing bacterial transfer and reducing organic load on facility floors and maintaining murine colony health status. According to PCR assay and culture analysis, ShCv provided the greatest reduction in bacte- rial numbers. Either ShCv, CCF, or ShCv+CCF significantly decreased ATP levels within the facility compared with those at facility entrances, with ShCv+CCF yielding the greatest reduction; however, even when neither ShCv nor CCF was used, intrafacility floor ATP levels were about half those at entrances. According to PCR analyses, no murine parasitic, viral, and bacterial pathogens excluded at the institution were detected in any floor, exhaust air dust, or sentinel samples at any time or location, regardless of the floor contamination control method in use. These findings show that floor contamination control methods help to reduce the organic load in rodent IVC facilities but do not enhance protection from environmental contamination due to murine pathogens.

Critical Size Limit of Biodegradable Nanoparticles for Enhanced Lymph Node Trafficking and Paracortex Penetration

Lymph node (LN) targeting through interstitial drainage of nanoparticles (NPs) is an attractive strategy to stimulate a potent immune response, as LNs are the primary site for lymphocyte priming by antigen presenting cells (APCs) and triggering of an adaptive immune response. NP size has been shown to influence the efficiency of LN-targeting and retention after subcutaneous injection. For clinical translation, biodegradable NPs are preferred as carrier for vaccine delivery. However, the selective "size gate" for effective LN-drainage, particularly the kinetics of LN trafficking, is less well defined. This is partly due to the challenge in generating size-controlled NPs from biodegradable polymers in the sub-100-nm range. Here, we report the preparation of three sets of poly(lactic-co-glycolic)-b-poly(ethylene-glycol) (PLGA-b-PEG) NPs with number average diameters of 20-, 40-, and 100-nm and narrow size distributions using flash nanoprecipitation. Using NPs labeled with a near-infrared dye, we showed that 20-nm NPs drain rapidly across proximal and distal LNs following subcutaneous inoculation in mice and are retained in LNs more effectively than NPs with a number average diameter of 40-nm. The drainage of 100-nm NPs was negligible. Furthermore, the 20-nm NPs showed the highest degree of penetration around the paracortex region and had enhanced access to dendritic cells in the LNs. Together, these data confirmed that small, size-controlled PLGA-b-PEG NPs at the lower threshold of about 30-nm are most effective for LN trafficking, retention, and APC uptake after s.c. administration. This report could inform the design of LN-targeted NP carrier for the delivery of therapeutic or prophylactic vaccines.

Interferon regulatory factors 3 and 7 have distinct roles in the pathogenesis of alphavirus encephalomyelitis

Interferon (IFN) regulatory factors (IRFs) are important determinants of the innate response to infection. We evaluated the role(s) of combined and individual IRF deficiencies in the outcome of infection of C57BL/6 mice with Sindbis virus, an alphavirus that infects neurons and causes encephalomyelitis. The brain and spinal cord levels of Irf7, but not Irf3 mRNAs, were increased after infection. IRF3/5/7-/- and IRF3/7-/- mice died within 3-4 days with uncontrolled virus replication, similar to IFNα receptor-deficient mice, while all wild-type (WT) mice recovered. IRF3-/- and IRF7-/- mice had brain levels of IFNα that were lower, but brain and spinal cord levels of IFNβ and IFN-stimulated gene mRNAs that were similar to or higher than WT mice without detectable serum IFN or increases in Ifna or Ifnb mRNAs in the lymph nodes, indicating that the differences in outcome were not due to deficiencies in the central nervous system (CNS) type I IFN response. IRF3-/- mice developed persistent neurological deficits and had more spinal cord inflammation and higher CNS levels of Il1b and Ifnγ mRNAs than WT mice, but all mice survived. IRF7-/- mice died 5-8 days after infection with rapidly progressive paralysis and differed from both WT and IRF3-/- mice in the induction of higher CNS levels of IFNβ, tumour necrosis factor (TNF) α and Cxcl13 mRNA, delayed virus clearance and more extensive cell death. Therefore, fatal disease in IRF7-/- mice is likely due to immune-mediated neurotoxicity associated with failure to regulate the production of inflammatory cytokines such as TNFα in the CNS.

Death and gastrointestinal bleeding complicate encephalomyelitis in mice with delayed appearance of CNS IgM after intranasal alphavirus infection

Central nervous system (CNS) infection of C57BL/6 mice with the TE strain of Sindbis virus (SINV) provides a valuable animal model for studying the pathogenesis of alphavirus encephalomyelitis. While SINV TE inoculated intracranially causes little mortality, 20-30 % of mice inoculated intranasally (IN) died 8 to 11 days after infection, the period during which immune cells typically infiltrate the brain and clear infectious virus. To examine the mechanism behind the mortality, mice infected IN with SINV TE were monitored for evidence of neurological disease, and those with signs of severe disease (moribund) were sacrificed and tissues collected. Mice showing the usual mild signs of encephalomyelitis were concurrently sacrificed to serve as time-matched controls (sick). Sixty-eight per cent of the moribund mice, but none of the sick mice, showed upper gastrointestinal bleeding due to gastric ulceration. Clinical disease and gastrointestinal pathology could not be attributed to direct viral infection of tissues outside of the CNS, and brain pathology and inflammation were comparable in sick and moribund mice. However, more SINV antigen was present in the brains of moribund mice, and clearance of infectious virus from the CNS was delayed compared to sick mice. Lower levels of SINV-specific IgM and fewer B220⁺ B cells were present in the brains of moribund mice compared to sick mice, despite similar levels of antiviral IgM and IgG in serum. These findings highlight the importance of the local antibody response in determining the outcome of viral encephalomyelitis and offer a model system for understanding individual variation in this response.

Glutamine antagonist-mediated immune suppression decreases pathology but delays virus clearance in mice during nonfatal alphavirus encephalomyelitis

Infection of weanling C57BL/6 mice with the TE strain of Sindbis virus (SINV) causes nonfatal encephalomyelitis associated with hippocampal-based memory impairment that is partially prevented by treatment with 6-diazo-5-oxo-l-norleucine (DON), a glutamine antagonist (Potter et al., J Neurovirol 21:159, 2015). To determine the mechanism(s) of protection, lymph node and central nervous system (CNS) tissues from SINV-infected mice treated daily for 1 week with low (0.3mg/kg) or high (0.6mg/kg) dose DON were examined. DON treatment suppressed lymphocyte proliferation in cervical lymph nodes resulting in reduced CNS immune cell infiltration, inflammation, and cell death compared to untreated SINV-infected mice. Production of SINV-specific antibody and interferon-gamma were also impaired by DON treatment with a delay in virus clearance. Cessation of treatment allowed activation of the antiviral immune response and viral clearance, but revived CNS pathology, demonstrating the ability of the immune response to mediate both CNS damage and virus clearance.

Interferon gamma modulation of disease manifestation and the local antibody response to alphavirus encephalomyelitis

Infection of mice with Sindbis virus (SINV) produces encephalomyelitis and provides a model for examination of the central nervous system (CNS) immune response to alphavirus infection. Clearance of infectious virus is accomplished through a cooperative effort between SINV-specific antibody and IFN-γ, but the regulatory interactions are poorly understood. To determine the effects of IFN-γ on clinical disease and the antiviral immune response, C57BL/6 mice lacking IFN-γ (Ifng-/-) or IFN-γ receptor (Ifngr1-/-) were studied in comparison to WT mice. Maximum production of Ifng mRNA and IFN-γ protein in the CNS of WT and Ifngr1-/- mice occurred 5-7 days after infection, with higher levels of IFN-γ in Ifngr1-/- mice. Onset of clinical disease was earlier in mice with impaired IFN-γ signalling, although Ifngr1-/- mice recovered more rapidly. Ifng-/- and Ifngr1-/- mice maintained body weight better than WT mice, associated with better food intake and lower brain levels of inflammatory cytokines. Clearance of infectious virus from the spinal cords was slower, and CNS, but not serum, levels of SINV-specific IgM, IgG2a and IgG2b were lower in Ifngr1-/- and Ifng-/- mice compared to WT mice. Decreased CNS antiviral antibody was associated with lower expression of mRNAs for B-cell attracting chemokines CXCL9, CXCL10 and CXCL13 and fewer B cells in the CNS. Therefore, IFN-γ signalling increases levels of CNS pro-inflammatory cytokines, leading to clinical disease, but synergistically clears virus with SINV-specific antibody at least in part by increasing chemokine production important for infiltration of antibody-secreting B cells into the CNS.

Ectoparasite Burden, Clinical Disease, and Immune Responses throughout Fur Mite (Myocoptes musculinus) Infestation in C57BL/6 and Rag1(-/-) Mice

Immunocompetent weanling mice infested with Myocoptes musculinus harbor high mite loads, yet burdens decrease with age. The development of immunity to the parasite may explain this observation. In this study, we followed M. musculinus burdens in Rag1(-/-) mice and immunocompetent C57BL/6 controls from 4 to 36 wk of age and compared the clinical signs and body weights of noninfested and infested mice of both strains over time. In addition, histopathology of skin lesions and expression of cytokines and transcription factors associated with Th1- and Th2-type immune responses were assessed. Myocoptes burdens decreased and remained low in B6 mice over time, whereas Rag1(-/-) mice showed an initial decrease in burdens after 4 wk of age followed by an increase from 24 to 36 wk. In addition, Rag1(-/-) mice had higher burdens than B6 mice over time. Both strains of infested mice exhibited clinical signs of fur mite infestation-including alopecia, poor weight gain, mite-associated debris, and pruritus-and clinical signs positively correlated with the severity of the Myocoptes burden. Histopathology of skin from both strains of infested mice showed decreased lesion severity with age, likely a result of declining mite populations. Finally, compared with noninfested controls, infested B6 mice had increased expression of markers associated with the Th2-type immune response, which increased in magnitude with increasing age and duration of infestation. These results suggest that development of adaptive immunity plays a role in control of fur mite populations and that heavier infestations may result in more severe clinical signs and skin lesions.

Guidance Regarding Sample Collection and Refinement of Fecal Flotation Exam for the Isolation of Aspiculuris tetraptera

Aspiculuris tetraptera continues to be a problem in rodent vivaria, in part due to difficulties in parasite detection. Although PCR testing is highly sensitive, it is expensive and does not always provide immediate results. Consequently, many institutions rely on passive fecal flotation as a quick inhouse exam for diagnosing A. tetraptera infections. To increase the sensitivity of this test, we examined multiple parameters to determine the optimal test protocol. A 30-min soaking period prior to fecal flotation for 15 min allowed fecal pellets to soften and facilitated efficient egg isolation. We also evaluated the effect of time of day, sample size, age, sex, and housing status on egg isolation. No evidence of cyclical egg shedding was found, and although larger fecal sample sizes did not result in more eggs isolated, their use reduced the incidence of false-negative exams. The most eggs were isolated from 8- and 12-wk-old mice, and as mice aged, the number of eggs isolated declined. Overall, neither sex nor housing status influenced the number of eggs isolated. Finally, examination of multiple diagnostic tests (fecal flotation exam, direct examination of cecal and colonic contents, and fecal PCR) revealed that no single test was definitive, thus indicating that multiple tests might be required to successfully screen mice with low pinworm burdens. These findings provide guidance regarding sample selection, collection, and processing to efficiently detect A. tetraptera.

Bone Disease in the Common Marmoset: Radiographic and Histological Findings

The common marmoset (Callithrix jacchus) is a New World primate that is used in biomedical research due to its small size and relative ease of handling compared with larger primates. Although bone disease in common marmosets is well recognized, there are very few detailed descriptions in the literature that cover the range of lesions seen in these animals. For all animals used to model human disease, it is important to be aware of background lesions that may affect the interpretation of study findings. This retrospective study details bone diseases encountered in marmoset breeding colonies at 2 different institutions. Affected marmosets at Johns Hopkins University had lesions compatible with diagnoses of rickets, fibrous osteodystrophy and osteopenia. Affected marmosets at the Wisconsin National Primate Research Center exhibited severe lesions of osteoclastic bone resorption and remodeling that had an unusual distribution and were not easily categorized into a known disease entity. The purpose of this report is to document these naturally occurring skeletal lesions of common marmosets and suggest an approach to evaluating skeletal disease in prospective studies of these animals that will allow the most accurate diagnoses.

Interleukin 10 modulation of pathogenic Th17 cells during fatal alphavirus encephalomyelitis

Mosquito-borne alphaviruses are important causes of epidemic encephalomyelitis. Neuronal cell death during fatal alphavirus encephalomyelitis is immune-mediated; however, the types of cells involved and their regulation have not been determined. We show that the virus-induced inflammatory response was accompanied by production of the regulatory cytokine IL-10, and in the absence of IL-10, paralytic disease occurred earlier and mice died faster. To determine the reason for accelerated disease in the absence of IL-10, immune responses in the CNS of IL-10(-/-) and wild-type (WT) mice were compared. There were no differences in the amounts of brain inflammation or peak virus replication; however, IL-10(-/-) animals had accelerated and increased infiltration of CD4(+)IL-17A(+) and CD4(+)IL-17A(+)IFNγ(+) cells compared with WT animals. Th17 cells infiltrating the brain demonstrated a pathogenic phenotype with the expression of the transcription factor, Tbet, and the production of granzyme B, IL-22, and GM-CSF, with greater production of GM-CSF in IL-10(-/-) mice. Therefore, in fatal alphavirus encephalomyelitis, pathogenic Th17 cells enter the CNS at the onset of neurologic disease and, in the absence of IL-10, appear earlier, develop into Th1/Th17 cells more often, and have greater production of GM-CSF. This study demonstrates a role for pathogenic Th17 cells in fatal viral encephalitis.

Complete protection against aflatoxin B(1)-induced liver cancer with a triterpenoid: DNA adduct dosimetry, molecular signature, and genotoxicity threshold

In experimental animals and humans, aflatoxin B1 (AFB1) is a potent hepatic toxin and carcinogen. The synthetic oleanane triterpenoid 1-[2-cyano-3-,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole (CDDO-Im), a powerful activator of Keap1-Nrf2 signaling, protects against AFB1-induced toxicity and preneoplastic lesion formation (GST-P-positive foci). This study assessed and mechanistically characterized the chemoprotective efficacy of CDDO-Im against AFB1-induced hepatocellular carcinoma (HCC). A lifetime cancer bioassay was undertaken in F344 rats dosed with AFB1 (200 μg/kg rat/day) for four weeks and receiving either vehicle or CDDO-Im (three times weekly), one week before and throughout the exposure period. Weekly, 24-hour urine samples were collected for analysis of AFB1 metabolites. In a subset of rats, livers were analyzed for GST-P foci. The comparative response of a toxicogenomic RNA expression signature for AFB1 was examined. CDDO-Im completely protected (0/20) against AFB1-induced liver cancer compared with a 96% incidence (22/23) observed in the AFB1 group. With CDDO-Im treatment, integrated level of urinary AFB1-N(7)-guanine was significantly reduced (66%) and aflatoxin-N-acetylcysteine, a detoxication product, was consistently elevated (300%) after the first AFB1 dose. In AFB1-treated rats, the hepatic burden of GST-P-positive foci increased substantially (0%-13.8%) over the four weeks, but was largely absent with CDDO-Im intervention. The toxicogenomic RNA expression signature characteristic of AFB1 was absent in the AFB1 + CDDO-Im-treated rats. The remarkable efficacy of CDDO-Im as an anticarcinogen is established even in the face of a significant aflatoxin adduct burden. Consequently, the absence of cancer requires a concept of a threshold for DNA damage for cancer development.

Serum albumin and body weight as biomarkers for the antemortem identification of bone and gastrointestinal disease in the common marmoset

The increasing use of the common marmoset (Callithrix jacchus) in research makes it important to diagnose spontaneous disease that may confound experimental studies. Bone disease and gastrointestinal disease are two major causes of morbidity and mortality in captive marmosets, but currently no effective antemortem tests are available to identify affected animals prior to the terminal stage of disease. In this study we propose that bone disease and gastrointestinal disease are associated disease entities in marmosets and aim to establish the efficacy of several economical antemortem tests in identifying and predicting disease. Tissues from marmosets were examined to define affected animals and unaffected controls. Complete blood count, serum chemistry values, body weight, quantitative radiographs, and tissue-specific biochemical markers were evaluated as candidate biomarkers for disease. Bone and gastrointestinal disease were associated, with marmosets being over seven times more likely to have either concurrent bone and gastrointestinal disease or neither disease as opposed to lesions in only one organ system. When used in tandem, serum albumin <3.5 g/dL and body weight <325 g identified 100% of the marmosets affected with concurrent bone and gastrointestinal disease. Progressive body weight loss of 0.05% of peak body weight per day predicted which marmosets would develop disease prior to the terminal stage. Bone tissue-specific tests, such as quantitative analysis of radiographs and serum parathyroid hormone levels, were effective for distinguishing between marmosets with bone disease and those without. These results provide an avenue for making informed decisions regarding the removal of affected marmosets from studies in a timely manner, preserving the integrity of research results.

Genetic Factors in Outcome After Traumatic Brain Injury

It is becoming increasingly clear that genetic factors modify outcome after traumatic brain injury (TBI). The best known example of this is the association between the apolipoprotein E4 allele (APOE epsilon4) and poorer outcomes. However, our knowledge of the many other genes that might influence outcome is still in its infancy. This article will review the basic principles underlying recent advances in genetics, and then describe the current state of knowledge regarding the impact of genetic factors on TBI outcome. We conclude that although genetic advances have implications for prognosis, their biggest contribution will be to elucidate the pathophysiology of TBI, potentially leading to new treatments.