Hybrid herpes simplex virus/Epstein-Barr virus amplicon viral vectors confer enhanced transgene expression in primary human tumors and human bone marrow-derived mesenchymal stem cells.

Background: Herpes simplex virus type-1 (HSV-1) amplicon vectors are attractive tools for gene transfer because of their large DNA insert capacity, their broad host range of vector transduction and a minimal immune response as a result of the absence of helper viruses during viral packaging. However, the transient gene expression remains a challenge for the translation of HSV-1 amplicon based therapeutic strategies to a clinical setting. Although oriP/EBV nuclear antigen (EBNA)-1 elements of Epstein-Barr virus (EBV) have been successfully employed to achieve prolonged transgene expression, little is known about the stability of the EBNA-1 elements in the context of HSV-1 amplicon viral vectors.

Methods: We have generated HSV/EBV hybrid vectors expressing the mutant EBNA-1 gene with the luciferase reporter gene bicistronically to enable monitoring of EBNA-1 expression in real-time, both in vitro and in vivo.

Results: The results obtained showed that the HSV/EBV hybrid vectors could mediate high levels of transgene expression (ranging from approximately two-fold to nine-fold) in primary human tumor cells and human bone marrow-derived mesenchymal stem cells compared to the control vector. Prolonged transgene expression could also be observed in primary patient-derived human hepatocellular carcinoma xenografts and in the mouse brain parenchyma up to a period of 17 and 365 days, respectively.

Conclusions: Taken together, we have demonstrated that these hybrid vectors could be promising tools as carriers of therapeutic genes in mesenchymal stem cells or even provide an alternative non-integrating platform for the generation of induced pluripotent stem cells.