Project 6 - Evaluation of Protective CMV Vaccines in Rhesus Macaques

The 35 year quest for a vaccine that confers protective efficacy against congenital infection with human cytomegalovirus (HCMV) remains unmet. Complexities in HCMV natural history, incompletely defined correlates of immune protection, and financial and logistical factors in designing sufficiently powered clinical trials all contribute to the absence of a licensed prophylactic HCMV vaccine. There is now increased recognition from studies in both humans and rhesus macaques (RM) that (1) the mechanism of HCMV and rhesus CMV (RhCMV) entry into cells, such as endothelial and epithelial cells, is distinct from the mechanism of fibroblast entry, and (2) seroimmune individuals develop neutralizing antibodies (NAb) against the viral proteins mediating epithelial/endothelial cell tropism. Recent findings have shown that a pentameric virion complex formed by the glycoproteins gH, gL, UL128, UL130 and UL131A (UL128C) is required for HCMV entry into epithelial/endothelial cells (Epi/EC) and is the target of potent NAb in HCMV-seropositive individuals. Using bacterial artificial chromosome (BAC)  technology, we have generated a modified vaccinia Ankara virus (MVA) that stably coexpresses all five rhesus CMV (RhCMV) proteins homologous to HCMV UL128C, termed MVA-RhUL128C. All eight RhCMV-naïve rhesus macaques (RM) vaccinated with MVA-RhUL128C developed NAb that blocked infection of monkey kidney epithelial cells (MKE) and rhesus fibroblasts. NAb titers induced by MVARhUL128C measured on both cell types at two to six weeks postvaccination were comparable to levels observed in naturally infected RM. In contrast, MVA expressing a subset of RhUL128C proteins or RhgB glycoprotein only minimally stimulated NAb that inhibited infection of MKE. In addition, following subcutaneous RhCMV challenge at eight weeks postvaccination, animals vaccinated with MVA-RhUL128C showed reduced plasma viral loads. These results indicate that MVA expressing the RhUL128C induces NAb inhibiting RhCMV entry into both Epi/EC and fibroblasts and limits RhCMV replication in RM. This novel approach is the first step in developing a prophylactic HCMV vaccine designed to interfere with virus entry into major cell types permissive for viral replication, a required property of an effective vaccine.
Felix Wussow, Ph.D.
Post-doctoral Fellow, Division of Translational Vaccine Research

Flavia Chiupessi, Ph.D.
Post-doctoral Fellow, Division of Translational Vaccine Research
Peter A Barry, Ph.D.
Vice Chair for Research, Department of Pathology and Laboratory Medicine, UC Davis
Principal Investigator of the UC Davis consortium site