Introduction: The widespread clinical use of cancer gene therapy has been prevented by the inability to deliver high levels of local transgene expression while limiting the systemic host response. Our lab has developed an ex vivo technique to transduce microvascular free flaps with a recombinant adenoviral vector which expresses the anti-tumor cytokine IL-12. Using this approach, we are able to target treatment specifically to the required area without eliciting the known toxic effects associated with systemic administration of IL-12.

Methods: Superficial inferior epigastric flaps were dissected in male Fischer rats and perfused with Ad.IL-12 following division of the pedicle. After a one hour incubation period, the flap was flushed with saline to remove unincorporated virions and a microvascular re-anastomosis performed. 1x10^6 beta-hCG secreting MADB-106 tumor cells were injected into the underlying muscle. Tumor growth was monitered directly with calipers and indirectly by rising levels of beta-hCG. Serum levels of pro-inflammatory cytokines (IL-6/TNF-á) and liver enzymes (AST/ALT) were measured to assess systemic inflammation. Distal organs were graded histologically for any evidence of toxicity.

Results: IL-12 expression from the flap and peri-flap tissue was confirmed by ELISA. The rate of tumor growth in the IL-12 treated group was markedly suppressed compared to the control group and the difference in tumor volume was statistically significant after day 15 (p<0.05). Liver enzymes and pro-inflammatory cytokines were not significantly elevated in treated versus control groups. Histological evaluation of liver, lung and spleen revealed no evidence of inflammation.

Conclusion: Using genetically modified microvascular free flaps we were able to deliver the therapeutic protein IL-12 directly into the local environment of a tumor and suppress its growth without eliciting the toxic systemic effects associated with this cytokine. This technique could provide valuable adjuvant treatment after oncologic surgery for soft tissue cancers. The ex vivo transduced flap would serve not only to correct the resulting defect but also to supply a therapeutic agent to the resected tumor bed.