Agenda

We live in a time, where translational, applied, “useful” research is in a very high demand. Without arguing against the values of that, I am, in this talk, strongly advocating curiosity-driven research. Out of curiosity, I chose the Chelonid herpesvirus 5 (ChHV5) as my study object, starting at a time, where this virus was not even known by its present name. However, it was suspected to exist by Veterinarians and marine biologists as its DNA was strongly associated to “fibropapillomatosis” (FP), i.e. tumors on the skin and in various mucosae of marine turtles. Meanwhile, the virus has been fully sequenced and many of its biological properties have been described, although the Koch’s postulates, proving that ChHV5 is actually the agent of FP, have not yet been fulfilled. Throughout my talk, I will try to convince you that ChHV5 is a very ancient virus and that, as an exception to the rule, it relies heavily on tumor formation to be transmitted in order to survive in nature. I also wish to instill a longing within my audience and curiosity that makes them go to fulfill their dreams.

The market for cytomegalovirus (CMV) therapeutics is primarily driven by infections in patients undergoing either solid organ transplantation (SOT) or hematopoietic stem cell transplantation (HSCT). Current treatment opportunities including Valcyte and Letermovir/PREVYMIS are associated with either significant side effects or limited efficacy. Novel safe and efficient drugs targeting CMV infections are therefore a high priority.

We have developed a novel intervention strategy building upon the development of a highly efficient biopharmaceutical targeting CMV infections through targeting of the CMV-encoded receptor US28. This broad-spectrum chemokine receptor binds and scavenges multiple CC- and CX3C-chemokines. It signals with high constitutive activity and internalizes ligand-independently. The biopharmaceutical developed in our group is a fusion toxin protein (FTP) between a modified CX3CL1 and a trimmed pseudomonas exotoxin A. The FTP selectively binds to and kills CMV infected cells via high affinity interaction with US28 that is only expressed in virus-infected cels. It shows superior efficacy and potency over ganciclovir in vitro as well as in an in vivo model for human CMV infection.

Since US28 is also expressed during latency, this targeting mechanism allows the opportunity to target and kill the latently infected cells, including latently infected CD34+ progenitor cells. The unique ability to kill both lytic and latently infected cells allows for unprecedented opportunities for medicinal treatment of CMV infected transplant recipients, including the opportunity to treat organs and cells ex vivo before transplantation as well as systemic treatment of patients undergong transplantation.

Marek’s disease is a deadly disease primarily affecting chickens that has a significant impact on the poultry industry. Virtually all chickens worldwide have been vaccinated against Marek’s disease alphaherpesvirus (MDV) since the 1970’s. MDV is strictly cell-associated in cell culture and during replication in chickens. However, when MDV reaches the feather follicle epithelial (FFE) cells in the skin, fully infectious cell-free virus (CFV) is produced and it is believed this form of virus is required for chicken to chicken transmission. This is like human varicella zoster virus in which the virus has evolved to complete its replicative cycle in epithelial skin cells where it is shed into the environment. The strict cell-associated nature of MDV in cell culture and cell-free nature in the skin makes it a terrific model to study viral genes important for cell-to-cell spread (CCS) and complete viral assembly in the natural hosts. With these unique characteristics and the ease with which to study MDV in chickens, we fortuitously identified two herpesviral proteins, previously thought to have limited importance in during replication, to be absolutely essential for interindividual spread of MDV from chicken to chicken. Without utilizing the natural herpesvirus-host model system, the great importance for these genes in the grand scheme of the herpesvirus lifecycle would have been difficult to identify.  With this work, we identified the Herpesviridae conserved herpesvirus protein kinase (CHPK) and the Alphaherpesvirinae conserved glycoprotein C are both required, individually, for interindividual spread of MDV. This talk with summarize the history of these findings and our current research into understanding the roles each essential protein plays during natural infection.

In lytic infection, Epstein-Barr virus must manipulate many cellular processes in order to avoid host antiviral responses, ensure cell survival and provide an optimum environment for virion production. However, the viral proteins and mechanisms involved in these roles are incompletely understood. The functions of many host and viral proteins and antiviral responses are regulated by SUMOylation.  We screened a library of EBV proteins for those that affect SUMOylation of cellular proteins, identifying a few that upregulate SUMOylation and one that degrades SUMOylated proteins. Among these, the EBV SM protein, known to function in viral mRNA export, was found to induce SUMOylation and this activity was conserved in homologues in HSV-1 (ICP27/UL54) and CMV (UL69). All three homologues were subsequently shown to be SUMO E3 ligases; the first SUMO ligases reported for these three viruses. We have also used affinity purification- mass spectroscopy to identify host proteins targeted by specific EBV proteins. An exciting finding was that EBV BORF2 (the ribonucleotide reductase large subunit) bound the cellular cytosine deaminase APOBEC3B (A3B) and relocalized it from the replicating EBV genomes in the nucleus into the cytoplasm. Other APOBEC family members are known to restrict infection of HIV and some other viruses by mutating their replicating genomes. We showed that loss of BORF2 led to A3B-dependent hypermutation of EBV genomes and reduced infectivity, implicating A3B as a restriction factor for EBV and possibly other herpesviruses.  Accordingly, the BORF2 homologue in Kaposi’s sarcoma associated herpesvirus (ORF61) also bound and relocalized A3B, suggesting that this mechanism of disabling A3B to protect viral genome integrity is conserved in γ-herpesviruses.  Replicating α and β herpesvirus genomes are also expected to be susceptible to A3B mutation and their mechanisms of A3B neutralization are being investigated.