Michael Robek PhD
Associate Professor of Pathology; Director of Graduate Studies
Virus-host interactions; viral immunology; hepatitis viruses; interferon
Many viruses establish chronic infections that persist for the lifetime of their hosts. Some of these viruses, including HIV, HBV, and HCV, are associated with a large degree of worldwide mortality. Current therapies for these infections are only moderately effective and are often limited by a number of variables. Therefore, new therapies for these diseases are needed. Our laboratory studies the host-pathogen interactions related to HBV infection. HBV infection leads to millions of deaths each year from liver diseases such as cirrhosis and hepatocellular carcinoma. We are investigating the relationships between HBV and cellular and immunological regulatory pathways, as these might be exploited therapeutically to block virus replication. These studies have the potential to expand the repertoire of antiviral drugs beyond those currently in use, and therefore significantly impact public health.
Extensive Research Description
Our laboratory studies the cellular and immunological regulatory pathways that control virus replication. First, we are investigating the relationships between HBV and cellular regulatory pathways, as these may be exploited pharmacologically to block virus replication. Second, we are characterizing the ability of novel antiviral and immunomodulatory cytokines to inhibit HBV replication and prevent liver damage. Third, we are studying new methodologies for therapeutic vaccination to boost the immune response to HBV in people who are chronically infected. These studies not only make important contributions to our understanding of fundamental questions relating to viral pathogenesis, but may also identify new potential approaches to prevent and treat disease.
Antiviral activity of type III interferon. We previously had found that a new family of IFN-related cytokines (IL-28, IL-29, also known as IFN-lambda or type III interferon) non-cytopathically inhibits HBV and hepatitis C virus (HCV) in cell culture models of virus replication (Robek et al., 2005). To understand this activity in more detail,we are further defining the antiviral response generated by this cytokine family. First, we found that IFN-lambda functions cooperatively with IFN-alpha and IFN-gamma to inhibit HCV replication. These findings provided new insight into the co-regulation of a critical innate immune response by structurally distinct cytokine families, and indicated that combinations of IFN-lambda with other cytokines could be clinically beneficial for HCV therapy (Pagliaccetti et al., 2008). Second,we characterized the sensitivity of IFN-lambda to neutralization by viral immunomodulatory proteins. Orthopoxviruses such as vaccinia and variola virus are highly resistant to IFN-alpha because they encode well-characterized proteins that inhibit IFN activity. Our results demonstrated differential sensitivity of IFN-lambda to multiple distinct evasion mechanisms employed by a single virus, and indicated that IFN-lambda might be useful as a therapy for poxvirus infection (Bandi, Pagliaccetti, and Robek, 2009). Finally, we elucidated the mechanism and in vivo antiviral activity of IFN-lambda against HBV. Our results demonstrated that the IFN-alpha and IFN-lambda anti-HBV responses operate through a single molecular mechanism, but that sensitivity to serum proteases may limit IFN-lambda activity to local, rather than systemic, effects. These results extended the idea that the type I and type III IFN families play tissue-specific roles in antiviral immunity (Pagliaccetti et al., 2010)
Ubiquitin-proteasome activity in HBV replication. Protein ubiquitination and proteasome-mediated degradation are critical regulators of many cellular processes, but the role of this regulatory mechanism in virus replication has been understudied. We have focused our attention on how this pathway regulates HBV replication. First, we demonstrated the ability of the IFN-induced proteasome catalytic subunits to shape the HBV-specific CD8 T cell response, and thus potentially influence the progression of infection from acute to chronic disease. These studies also identified a potential key role for IFN in regulating the adaptive immune response to HBV through alterations in viral antigen processing (Robek et al., 2007). Second, we studied the role of ubiquitin in HBV replication and release. While ubiquitin plays an important role in the release of many viruses, the requirement for direct ubiquitin conjugation to viral structural proteins is less well understood. We demonstrated that although ubiquitin regulates the HBV replication cycle, these mechanisms function independently of direct lysine ubiquitination of the viral core protein (Garcia et al., 2009). Finally,we examined the effect of proteasome inhibition on HBV replication in vivo using HBV transgenic mice, and found that pharmacological manipulation of the ubiquitin-proteasome pathway represents a possible new alternative therapeutic approach for the treatment of chronic HBV infection (Bandi et al. 2010).
Therapeutic immunization for chronic HBV. In those individuals who become acutely infected with HBV but ultimately clear the virus, a relatively strong, multi-specific T cell response to HBV is generated. However, in those that become chronically infected, the T cell response is much weaker in magnitude, and is directed toward fewer viral antigens. One promising new approach for treating chronic hepatitis B is by therapeutic vaccination to induce an immune response that is capable of controlling the virus. Unfortunately however, although the current HBV vaccine is very effective at preventing infection, it does not eliminate the virus in those people who are already infected. We have been working toward the long-term goal of developing a new therapeutic vaccine vector for chronicHBV based on recombinant vesicular stomatitis virus (VSV). We found that a VSV vector expressing the HBV surface glycoprotein induces strong CD8 T cell responses in immunized mice, and that these immune responses are protective in mouse models of virus challenge (Cobleigh et al., 2010). We are now working to determine whether the immune response generated by this vaccine can control ongoing HBV replication.