Advances in understanding of the innate immune response to human norovirus infection using organoid models

Norovirus is the leading cause of epidemic and endemic acute gastroenteritis worldwide and the most frequent cause of foodborne illness in the United States. There is no specific treatment for norovirus infections and therapeutic interventions are based on alleviating symptoms and limiting viral transmission. The immune response to norovirus is not completely understood and mechanistic studies have been hindered by lack of a robust cell culture system. In recent years, the human intestinal enteroid/human intestinal organoid system (HIE/HIO) has enabled successful human norovirus replication. Cells derived from HIE have also successfully been subjected to genetic manipulation using viral vectors as well as CRISPR/Cas9 technology, thereby allowing studies to identify antiviral signaling pathways important in controlling norovirus infection. RNA sequencing using HIE cells has been used to investigate the transcriptional landscape during norovirus infection and to identify antiviral genes important in infection. Other cell culture platforms such as the microfluidics-based gut-on-chip technology in combination with the HIE/HIO system also have the potential to address fundamental questions on innate immunity to human norovirus. In this review, we highlight the recent advances in understanding the innate immune response to human norovirus infections in the HIE system, including the application of advanced molecular technologies that have become available in recent years such as the CRISPR/Cas9 and RNA sequencing, as well as the potential application of single cell transcriptomics, viral proteomics, and gut-on-a-chip technology to further elucidate innate immunity to norovirus.

Influenza Virus Infects and Depletes Activated Adaptive Immune Responders

Influenza infections cause several million cases of severe respiratory illness, hospitalizations, and hundreds of thousands of deaths globally. Secondary infections are a leading cause of influenza's high morbidity and mortality, and significantly factored into the severity of the 1918, 1968, and 2009 pandemics. Furthermore, there is an increased incidence of other respiratory infections even in vaccinated individuals during influenza season. Putative mechanisms responsible for vaccine failures against influenza as well as other respiratory infections during influenza season are investigated. Peripheral blood mononuclear cells (PBMCs) are used from influenza vaccinated individuals to assess antigen-specific responses to influenza, measles, and varicella. The observations made in humans to a mouse model to unravel the mechanism is confirmed and extended. Infection with influenza virus suppresses an ongoing adaptive response to vaccination against influenza as well as other respiratory pathogens, i.e., Adenovirus and Streptococcus pneumoniae by preferentially infecting and killing activated lymphocytes which express elevated levels of sialic acid receptors. These findings propose a new mechanism for the high incidence of secondary respiratory infections due to bacteria and other viruses as well as vaccine failures to influenza and other respiratory pathogens even in immune individuals due to influenza viral infections.

Novel approaches for studying cell-mediated immune responses to influenza vaccination in humans

Vaccination is the most cost-effective public health intervention strategy in the prevention of the spread of infectious diseases. Unfortunately, each year, a substantial proportion of individuals do not respond or respond poorly to vaccination due to age, nutrition, pre-existing medical conditions, vaccine mismatch, or other unknown reasons. To investigate this further, we propose studying the mechanisms and molecular signatures associated with immunogenicity and the efficacy of influenza vaccination in different populations.

The priming environment, induced by the innate immune system is crucial for initiating and fine-tuning antigen-specific adaptive immune responses. Comprehensive antibody panels have been developed to identify the new paradigms in the innate priming environment, focusing on NK, innate lymphoid cells and γδ T cells by flow cytometry in PBMC from vaccine recipients. The specific functions of these cells are then analyzed using single cell sorting and high-throughput transcriptomic and proteomics analysis. To further probe the adaptive response, we have successfully developed receptor binding site mutant HA (H1, H3, B) and HA stem (group 1 and 2) probes that are conjugated to fluorochromes to enumerate and characterize HA-specific B cells. M2e antigen probes are under development. Combining cell sorting, single cell molecular analyses, and the Illumina MiSeq system, paired heavy and light chains of B cell receptors (BCR) from isolated antigen specific B cells are sequenced to dissect antibody diversity.

Through these novel approaches, we aim to identify and characterize critical host factors that can be exploited to develop as novel adjuvants and strategies for more effective influenza vaccines.

Nasal delivery of H5N1 avian influenza vaccine formulated with GenJet™ or in vivo-jetPEI® induces enhanced serological, cellular and protective immune responses

Avian influenza virus infection is a serious public health threat and preventive vaccination is the most cost-effective public health intervention strategy. Unfortunately, currently available unadjuvanted avian influenza vaccines are poorly immunogenic and alternative vaccine formulations and delivery strategies are in urgent need to reduce the high risk of avian influenza pandemics. Cationic polymers have been widely used as vectors for gene delivery in vitro and in vivo. In this study, we formulated H5N1 influenza vaccines with GenJet™ or in vivo-jetPEI^®, and showed that these formulations significantly enhanced the immunogenicity of H5N1 vaccines and conferred protective immunity in a mouse model. Detailed analyses of adaptive immune responses revealed that both formulations induced mixed T_H1/T_H2 antigen-specific CD4 T-cell responses, antigen-specific cytotoxic CD8 T-cell and memory B-cell responses. Our findings suggest that cationic polymers merit future development as potential adjuvants for mucosal delivery of poorly immunogenic vaccines.

Not just showboating: Shp1 may keep B cells afloat during gammaherpesvirus infection

Gammaherpesviruses (GHVs) are ubiquitous pathogens that establish lifelong infections. Importantly, GHVs manipulate B cell differentiation to establish latency, and are associated with several types of B cell lymphomas. Specifically, GHV infection stimulates an abnormal germinal center expansion, and germinal center B cells are thought to be the target of malignant transformation. Thus, defining host factors that affect the germinal center response during GHV infection may offer insights into the biology of viral latency and lymphomagenesis. Shp1 is a tyrosine phosphatase that acts as a negative regulator of immune cell activation, including B cells. Therefore, we hypothesized that Shp1 opposes GHV-driven germinal center expansion. Surprisingly, our studies utilizing a mouse model of B cell-specific Shp1 deficiency have discovered that Shp1 may be required to sustain the abnormal germinal center expansion characteristic of GHV infection.

In mice with B cell-specific Shp1 deficiency we observed a significant reduction in germinal center B cells along with decreased viral loads during early stages of chronic GHV infection. Further evidence suggests that total loss of Shp1 in B cells disrupts the delicate balance of proliferation and apoptosis during germinal center expansion, resulting in an increased level of apoptosis. Based on these data, we hypothesize that Shp1 prevents hyper-activation, and subsequent cell death, of germinal center B cells during GHV infection. Ongoing studies are examining the mechanism by which Shp1 mediates B cell survival.

Gammaherpesvirus targets peritoneal B-1 B cells for long-term latency

Gammaherpesviruses establish life-long infection in most adults and are associated with the development of B cell lymphomas. While the interaction between gammaherpesviruses and splenic B cells has been explored, very little is known about gammaherpesvirus infection of B-1 B cells, innate-like B cells that primarily reside in body cavities. This study demonstrates that B-1 B cells harbor the highest frequency of latently infected cells in the peritoneum throughout chronic infection, highlighting a previously unappreciated feature of gammaherpesvirus biology.

ATM facilitates mouse gammaherpesvirus reactivation from myeloid cells during chronic infection

Gammaherpesviruses are cancer-associated pathogens that establish life-long infection in most adults. Insufficiency of Ataxia-Telangiectasia mutated (ATM) kinase leads to a poor control of chronic gammaherpesvirus infection via an unknown mechanism that likely involves a suboptimal antiviral response. In contrast to the phenotype in the intact host, ATM facilitates gammaherpesvirus reactivation and replication in vitro. We hypothesized that ATM mediates both pro- and antiviral activities to regulate chronic gammaherpesvirus infection in an immunocompetent host. To test the proposed proviral activity of ATM in vivo, we generated mice with ATM deficiency limited to myeloid cells. Myeloid-specific ATM deficiency attenuated gammaherpesvirus infection during the establishment of viral latency. The results of our study uncover a proviral role of ATM in the context of gammaherpesvirus infection in vivo and support a model where ATM combines pro- and antiviral functions to facilitate both gammaherpesvirus-specific T cell immune response and viral reactivation in vivo.

Mouse gammaherpesvirus-68 infection acts as a rheostat to set the level of type I interferon signaling in primary macrophages

Type I interferon (IFN) is a critical antiviral response of the host. We found that Interferon Regulatory Factor 3 (IRF-3) was responsible for induction of type I IFN following mouse gammaherpesvirus-68 (MHV68) infection of primary macrophages. Intriguingly, type I IFN signaling was maintained throughout the entire MHV68 replication cycle, in spite of several known viral IFN antagonists. However, MHV68-infected primary macrophages displayed attenuated responses to exogenous type I IFN, suggesting that MHV68 controls the level of type I IFN signaling that is allowed to occur during replication. Type I IFN receptor and IRF-3 were necessary to attenuate transcription of MHV68 RTA, an immediate early gene critical for replication. Furthermore, higher constitutive activity of RTA promoters was observed in the absence of type I IFN signaling. Our study suggests that MHV68 has preserved the ability to sense type I IFN status of the host in order to limit lytic replication.