Functional expression of thymidine kinase in human leukaemic and colorectal cells, delivered as EGFP fusion protein by herpesvirus saimiri-based vector

Vesicular Stomatitis Virus G Glycoprotein and ATRA Enhanced Bystander Killing of Chemoresistant Leukemic Cells by Herpes Simplex Virus Thymidine Kinase/Ganciclovir

Refractoriness of acute myeloid leukemia (AML) cells to chemotherapeutics represents a major clinical barrier. Suicide gene therapy for cancer has been attractive but with limited clinical efficacy. In this study, we investigated the potential application of herpes simplex virus thymidine kinase/ganciclovir (HSV-TK/GCV) based system to inhibit chemoresistant AML cells. We first generated Ara-C resistant K562 cells and doxorubicin-resistant THP-1 cells. We found that the HSV-TK/GCV anticancer system suppressed drug resistant leukemic cells in culture. Chemoresistant AML cell lines displayed similar sensitivity to HSV-TK/GCV. Moreover, HSV-TK/GCV killing of leukemic cells was augmented to a mild but significant extent by all-trans retinoic acid (ATRA) with concomitant upregulation of Connexin 43, a major component of gap junctions. Interestingly, HSV-TK/GCV killing was enhanced by expression of vesicular stomatitis virus G glycoprotein (VSV-G), a fusogenic membrane protein, which also increased leukemic cell fusion. Co-culture resistant cells expressing HSV-TK and cells stably transduced with VSV-G showed that expression of VSV-G could promote the bystander killing effect of HSV-TK/GCV. Furthermore, combination of HSV-TK/GCV with VSV-G plus ATRA produced more pronounced antileukemia effect. These results suggest that the HSV-TK/GCV system in combination with fusogenic membrane proteins and/or ATRA could provide a strategy to mitigate the chemoresistance of AML.

T-cell transformation and oncogenesis by gamma2-herpesviruses

gamma2-Herpesviruses, also termed rhadinoviruses, have long been known as animal pathogens causing lymphoproliferative diseases such as malignant catarrhal fever in cattle or T-cell lymphoma in certain Neotropical primates. The rhadinovirus prototype is Herpesvirus saimiri (HVS), a T-lymphotropic agent of squirrel monkeys (Saimiri sciureus); Herpesvirus ateles (HVA) is closely related to HVS. The first human rhadinovirus, human herpesvirus type 8 (HHV-8), was discovered a decade ago in Kaposi's sarcoma (KS) biopsies. It was found to be strongly associated with all forms of KS, as well as with multicentric Castleman's disease and primary effusion lymphoma (PEL). Since DNA of this virus is regularly found in all KS forms, and specifically in the spindle cells of KS, it was also termed KS-associated herpesvirus (KSHV). Several simian rhadinoviruses related to KSHV have been discovered in various Old World primates, though they seem only loosely associated with pathogenicity or tumor induction. In contrast, HVS and HVA cause T-cell lymphoma in numerous non-natural primate hosts; HVS strains of the subgroup C are capable of transforming human and simian T-lymphocytes to continuous growth in cell culture and can provide useful tools for T-cell immunology or gene transfer. Here, we describe their natural history, genome structure, biology, and pathogenesis in T-cell transformation and oncogenesis.

Regulated and constitutive expression of anti-inflammatory cytokines by nontransforming herpesvirus saimiri vectors

Herpesviral saimiri-(HVS) mediated expression of bovine growth hormone was one of the first applications of an episomal viral vector for gene therapy. Meanwhile, the long-term persistence of HVS vectors has been confirmed in a broad spectrum of infectable target cells in vitro and in vivo. Regulated gene expression is useful for many applications of gene therapy. Therefore, we inserted the Mifepristone-antiprogestin-inducible expression system (GeneSwitchtrade mark) into HVS viral vectors to regulate the combined expression of anti-inflammatory cytokines, IL-10 and IL-1RA. Constitutive CMV-promoter/enhancer-driven and Mifepristone-inducible cytokine expression was compared in the viral context in transduced primary human fibroblasts and rheumatoid arthritis (RA) fibroblast-like cells (RASF). Long-term persistence of vector genomes was shown for both construct types. Constitutive expression was efficient and more rapid in onset than in the inducible system, in which the selective induction of interleukin expression along with low background levels was obtained by Mifepristone concentrations that were more than 1000-fold below those required for endogenous Progesterone antagonism. Furthermore, transgene expression corresponded to vector doses. Global patterns of cytokine secretion were not significantly changed due to viral transduction, indicating a rather inert behavior of the viral vector itself. In an attempt to emulate the inflammatory cytokine-enriched environment in rheumatoid arthritic joints, the function of the vectors could be demonstrated in vitro by the successful blockade of IL-1beta-stimulated matrix-metalloproteinase (MMP)-3 expression from RASF cells. Evaluation of this system in future studies, in suitable long-term SCID models of RA or in non-human primate models, will exploit the possible in vivo benefits of nontransforming HVS vectors in gene therapy.