Potential of bovine herpesvirus 4 as a gene delivery vector

A cloning system was developed for construction of BHV-4 recombinants and recombinant virus BHV-4EGFPDeltaTK containing an enhanced green fluorescent protein (EGFP) gene was constructed. The host range of BHV-4EGFPDeltaTK was characterized in vitro. When cell lines from various species and tissues were infected, most of the non-bovine cell lines exhibited neither cytopathic effect (CPE) nor supported viral replication, but EGFP expression was clearly observed. Next, embryonic stem cells were infected and induced to either non-specific or neural differentiation to determine whether they could survive and differentiate after BHV-4EGFPDeltaTK infection. Embryonic stem cells were infected successfully, as indicated by EGFP expression prior to differentiation, and EGFP expression could be detected in many differentiated cells. No CPE was noted. Therefore, BHV-4EGFPDeltaTK infection caused neither cell death nor interfered with non-specific or neural differentiation of embryonic stem cells. Finally, to assess the capability of BHV-4EGFPDeltaTK to infect post-mitotic neurons, cultures from brains of 2-weeks old mice were infected. No death of neuronal cells due to infection was observed and EGFP expression persisted for at least 15 days. Several biological characteristics of BHV-4 demonstrated previously make it a good candidate for a gene delivery vector. These include: little or no pathogenicity, unlikely oncogenicity, ability to establish persistent infection, and capability of herpesviruses to accommodate large amounts of foreign genetic material. These findings add the ability to infect several cell types coming from different animal species, usually without CPE, lack of interference with differentiation, and ability to maintain transgene expression in both undifferentiated and differentiated cells.