There are several research avenues being conducted in the lab. A few are listed below in more detail:
Immune responses to hepatitis C virus, and rational vaccine design:
Collaborators: Naglaa Shoukry and Rama Amara
Prevention of hepatitis C virus (HCV) infection remains an important public health objective even with the recent adoption of highly effective direct acting antiviral (DAA) therapies. A vaccine to prevent HCV persistence is needed to stem an emerging epidemic of infection in adolescents and young adults who inject drugs that have limited access to screening and treatment. Only twenty five percent of acute HCV infections resolve spontaneously. Resolution does, however, sharply reduce the risk of persistent infection upon re-exposure to the virus. While it has been established that memory CD4+ T helper and CD8+ cytotoxic T cell responses contribute to accelerated clearance of reinfection, recent vaccine trial to generate an equivalent T cell response failed to thwart off the rate of persistence in naïve recipients. Why HCV-specific T cell responses are sustained in some individuals and not others during both the initial primary infection and subsequent re-challenge is not known. Additionally, the role of neutralizing antibodies during infection is less clear. This gap in knowledge is particularly apparent for CD4+ T helper cells and humoral responses and could pose a formidable obstacle to development of vaccines that prevent HCV persistence. Here, we will test the central premise that memory CD4+ T cells contribute significantly to HCV reinfection outcome by promoting expansion of HCV-specific B cells and production of broadly neutralizing antibodies that contribute to viral clearance.
Unique features of this proposal are:
(i) the use of longitudinal samples from the Montreal cohort of high-risk people who inject drugs. Participants are monitored prior to, during, and after HCV infection and then subsequently followed again when they have been re-exposed to HCV a second time after resolving their primary infection.
(ii) We have assembled a team of investigators in Cairo, Egypt who will assist us with recruiting and treating subjects undergoing DAA treatment. Egypt has the highest prevalence of HCV infection in the world. In 2014, Egypt’s government has made DAA treatment affordable and 2.5 million subjects have started treatment. Understanding the immune responses in these two cohorts will provide us with valuable information to develop an efficacious vaccine regimen that would emulate the successful responses generated during a natural challenge with HCV.
Pregnancy and postpartum immune responses:
Collaborators: Christopher M. Walker, Jonathan Honegger, and Nikole Skinner
Once established, chronic infection is characterized by stable HCV replication and failure of adaptive immune responses to recover. Pregnancy is an exception to this typical profile of chronic HCV. We and others observed significant control of HCV replication in many chronically infected women after childbirth. In rare cases, persistently infected women can even spontaneously clear infection postpartum (PP). The PP period therefore appears to represent an immunologic approximation of the acute phase of infection, providing persistently infected women with a second chance at viral clearance. The molecular changes that adaptive immune cells undergo during the transition from late pregnancy to the PP period are not well understood. We have shown that PP suppression of viremia (~1-4 log decrease of viremia PP) is associated with expansion of functional HCV-specific CD4+ T cells that are usually undetectable in chronic HCV. Our more recent preliminary data shows that CD4+ T cells in women with PP viral control (termed controllers) have a combined Tfh and Th1 (Tfh1) phenotype not predominantly seen in women without PP viral control (non-controllers). The mechanisms by which CD4+ Tfh1 cells contribute to PP control of HCV are not known. We predict that multifunctional Tfh1 cells provide help to CD8+ T cells and B cells that mediate PP antiviral activity. This supposition is supported by our data showing that expansion of CD4+ T cells in controllers is associated with the emergence of new escape mutations in HCV class I epitopes, indicating recovery of exhausted CD8+ T cells and renewed immune selection pressure against the virus. We also have recent preliminary data showing more broadly neutralizing antibody (bNAb) responses in controllers which coincide with an accumulation of mutations in the front-layer of E2, the primary target for bNAb responses. We therefore proposed that control of HCV replication PP is driven by expansion of CD4+ Tfh1 T cells that promote reversal of CD8+ T cell exhaustion and development of more functional broadly neutralizing B cell responses.
Small animal model to study viral persistence:
Collaborators: Amit Kapoor and Charles M. Rice
The recent discovery of rodent analog of HCV in Norway rats, rodent hepacivirus (RHV) by our group, which can establish exclusive hepatotropic infection in rats and mice with immunological characteristics mirroring HCV infection in humans, provides a unique and indispensable model in understanding antiviral immune responses for the development of effective vaccine for HCV. Our data suggest a critical role for B cells during primary RHV infection outcome as the lack of B cells in immunocompromised mice or the early depletion of B cells in wildtype mice prevented timely clearance of virus, resulting in persistent infection. We hypothesize that an early selection and expansion of E2 glycoprotein-specific B cells is obligatory for eliciting an effector CD4+ and CD8+ T cell responses and neutralizing antibodies (NAbs) during primary RHV infection, and for the timely clearance of the virus. We propose to identify the contribution of B cells to primary RHV infection, and the longitudinal changes in antigen-specific B and T cells between resolving and persistent infections. The findings obtained from this study will serve as a requisite to design efficacious vaccination approaches that integrate the rapid induction of antigen-specific T and B cells and mitigating reinfection and viral persistence.
Hepatitis E virus pathogenesis:
Collaborators: Zongdi Feng and Christopher M. Walker
Hepatitis E virus (HEV) is an enterically transmitted RNA virus and a major cause of acute hepatitis globally. HEV infections are usually self-limited, but persistence occurs frequently in immunocompromised individuals such as solid organ transplant recipients. Persistent HEV infections can lead to progressive liver injury and cirrhosis if left untreated. However, no HEV- specific treatments are currently available. We aim to better understand the role of antibodies in HEV infection and determine if antibodies can be used to prevent or treat chronic HEV infection. HEV had been considered as a nonenveloped virus since its discovery in 1980s. However, recent studies reveal that HEV exists in two different virion forms. While the virus is shed into the feces as naked particles (nHEV), it circulates in the bloodstream as quasienveloped virions (eHEV). The eHEV particles mediate virus spread within the infected host, but they lack viral antigens on their surface and use a novel mechanism to enter the cell. We have previously shown that eHEV entry requires lysosomal degradation of the viral quasi-envelope, allowing the capsid to interact with the receptor. The lack of viral antigens on the surface also makes the circulating eHEV particles invisible to HEV-specific antibodies. However, our recent data show that HEV-specific IgG, but not IgM, effectively block eHEV-mediated spread in cell culture. Based these observations, we hypothesize that antibodies neutralize eHEV intracellularly by preventing virus uncoating in the endosome/lysosome where the viral membrane degrades. The ability of neutralizing antibodies to block eHEV-mediated spread provides the rationale for using antibodies to treat chronic HEV infection.
Progression of liver disease:
Collaborators: Manoj Thapa
Liver cirrhosis is a leading cause of mortality in the United States and the costs of treating chronic liver disease pose an enormous economic burden that is only projected to increase. Chronic hepatitis C virus (HCV) infection, alcohol liver disease (ALD) and nonalcoholic steatohepatitis (NASH) account for the majority of fibrotic and cirrhotic hepatic conditions that lead to end-stage liver disease (ESLD) cases, with chronic HCV associated with the highest incidence of liver transplantation. In fact, ESLD is the seventh leading cause of death in individuals between 25 to 64 years of age in the US. While this process can take several decades to develop, aberrant antibody production and autoimmune disorders ranging from mixed cryoglobulinemia to B cell lymphoma are among the most common extrahepatic manifestations of ESLD. The cellular immune components that contribute to fibrosis and induction of autoimmunity are not well understood. Surprisingly, we found B cells as a key mediator of fibrosis; depletion of B cells ameliorates liver fibrosis and reduces inflammatory infiltration in the liver. In addition, our preliminary systems biological analyses of hepatic B cells during liver fibrosis highlighted increased expression of genes involved in the activation of NF-kB signaling and related inflammatory genes such as the toll like receptor (TLR) pathway components, specifically MyD88, the dominant mediator of signaling following TLR activation; interferon regulatory factor 4 (IRF4), a transcription factor important in B cell activation and plasma cell development; and CCL2, a potent chemokine necessary for the recruitment of inflammatory monocytes and dendritic cells. We therefore hypothesize that induction of liver fibrosis is dependent upon the early activation and dysfunction of intrahepatic innate B cell responses. We aim to identify mechanisms by which loss of B cell tolerance induces liver fibrosis.
Gut-brain axis:
Collaborators: David S. Weiss
Recent advances suggest a correlation between gut dysbiosis and neurological diseases, however, how gut bacteria impact the brain is not clear. We have recently revealed that gut commensal bacteria can translocate directly to the brain via the vagus nerve. This translocation correlates with gut dysbiosis, gut barrier permeability, microglial activation and protein aggregation in the brain. Localization of bacteria to the brain occurs with a high-fat diet but is reversible with return to normal diet, and is also observed in murine models of Alzheimer’s, Parkinson’s, and autism. Further, high-fat diet exacerbates the bacterial load in the brain and anxiety- and depression-related behaviors in an autism model. These data reveal a commensal bacterial translocation axis to the brain with combined impacts of environmental and genetic factors. These data are paradigm-shifting and raise the surprising potential for a common link between diverse neurological diseases, with the potential to greatly improve human health.