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Tumor-specific gene delivery using recombinant vaccinia virus in a rabbit model of liver metastases
M F Gnant1, L A Noll, K R Irvine
1Surgery Branch, Division of Clinical Sciences, National Cancer Institute, Bethesda, MD, USA.
Background:
Several approaches to gene therapy for cancer have yielded promising results in rodent models. The translation of these results to the clinical realm has been delayed by the lack of tumor models in large animals. We investigated the pattern of transgene (i. e., foreign or introduced gene) expression and virus vector elimination after systemic gene delivery using a thymidine kinase-negative vaccinia virus in a rabbit model of disseminated liver metastases.
Methods:
VX-2 rabbit carcinoma cells were maintained by serial transplantation in the thigh muscles of New Zealand White rabbits, and disseminated liver metastases were established by direct injection of tumor cells into the portal vein of the animals. Different doses of a recombinant thymidine kinase-negative vaccinia virus vector encoding the firefly luciferase reporter gene (i.e., transgene) were injected into tumor-bearing rabbits. Transgene activity in tumors and other organs was measured at multiple time points thereafter. The pattern of development of antibodies against the vaccinia virus vector was also examined. Two-tailed Student's paired t test was used for comparisons of transgene activity.
Results:
Transgene expression was increased in tumors by at least 16-fold in comparison with expression in other tissues by day 4 after vector injection (all P<. 001) and was maintained for approximately 1 week, providing evidence of tumor-specific gene delivery in this model. Rapid elimination of the circulating vector by the host immune system was observed. Anti-vector antibodies were detectable in serum as early as day 6 and were maintained for more than 3 months.
Conclusions:
Tumor-specific gene delivery is possible after systemic injection of a thymidine kinase-negative vaccinia virus vector in a model of rabbit liver metastases. Although the period of transgene expression appears limited because of a rapid immune response, the therapeutic window might be sufficient for an enzyme/prodrug gene therapy approach in clinical application.
Insights
Gene therapy in large animals is challenging. This study shows tumor-specific gene delivery using a vaccinia virus vector in rabbits, with expression lasting about a week before an immune response limits it.
Area of Science:
- Oncology
- Gene Therapy
- Virology
Background:
- Gene therapy for cancer shows promise in rodents but lacks large animal models.
- Translating gene therapy to clinical use requires effective large animal tumor models.
Purpose of the Study:
- To investigate transgene expression and virus vector elimination after systemic gene delivery.
- To evaluate a thymidine kinase-negative vaccinia virus vector in a rabbit model of liver metastases.
Main Methods:
- VX-2 rabbit carcinoma cells were used to create liver metastases in New Zealand White rabbits.
- Recombinant thymidine kinase-negative vaccinia virus encoding luciferase was injected systemically.
- Transgene activity, antibody response, and vector elimination were monitored over time.
Main Results:
- Transgene expression in tumors was 16-fold higher than in other tissues by day 4 (P<.001).
- Tumor-specific gene delivery was observed, with expression maintained for approximately one week.
- Rapid elimination of the circulating vector occurred, with anti-vector antibodies detected by day 6.
Conclusions:
- Systemic injection of a thymidine kinase-negative vaccinia virus vector enables tumor-specific gene delivery in a rabbit liver metastasis model.
- The immune response limits transgene expression duration, but the therapeutic window may suffice for enzyme/prodrug gene therapy.