Neoadjuvant interleukin-12 immunogene therapy protects against cancer recurrence after liver resection in an animal model

Abstract

Objective: To evaluate the neoadjuvant use of a herpes simplex viral (HSV) amplicon vector expressing the murine interleukin-12 (IL-12) gene.

Summary background data: Surgery is the most effective therapy for hepatic malignancy. Recurrences, which are common, most often occur in the remnant liver and are due partly to growth of residual microscopic disease in the setting of postoperative host cellular immune dysfunction. The authors hypothesized that engineering tumors to secrete IL-12 in vivo would elicit an immune response directed at residual tumor and would reduce the incidence of recurrence after resection.

Methods: Solitary hepatomas were established in Buffalo rat livers and directly injected with 106 particles of HSV carrying the gene for IL-12, lacZ (beta-galactosidase) or with saline. One week after injection, the animals were challenged with an intraportal injection of 106 tumor cells, with subsequent resection of the hepatic lobe containing the previously established macroscopic tumor nodule, recreating the clinical scenario of residual microscopic cancer.

Results: Hepatoma cells transfected with HSV-IL-12 produced high levels of IL-12 in vitro and in vivo. A significant local immune response developed, as evidenced by a progressive increase in the number of CD4(+) and CD8(+) lymphocytes in the tumor. Treatment of established hepatomas with HSV-IL-12 protected against growth of microscopic residual cancer after hepatic resection. Sixty-four percent of the animals treated with HSV-IL-12 had zero or one tumors compared with 30% of HSVlac-treated and 24% of saline-treated animals.

Conclusions: This neoadjuvant immune strategy may prove useful in reducing the incidence of cancer recurrence after hepatic resection.

Figures

Figure 1. Experimental protocol, beginning with tumor implantation into the liver.

Figure 2. (A) Photograph illustrating a typical subcapsular tumor nodule 1 week after implantation. (B) Photomicrograph of tumor injected with HSVlac, fixed and stained for β-galactosidase expression. Low-power view (×10), 48 hours after direct injection. (C) Higher-power view (×20) of B.

Figure 3. Time course of in vivo interleukin-12 (IL-12) expression after tumor injection. Tumors injected with saline or HSVlac had no detectable levels of IL-12. (Inset) In vitro IL-12 expression in irradiated hepatoma cells over time.

Figure 4. (A) Number of hepatic tumors after pretreatment with HSV–IL-12, HSVlac, or saline, partial hepatectomy, and tumor cell challenge. The graph represents the combined results of three separate experiments. *P = .05 vs. HSVlac, P = .03 vs. saline. (B) Proportion of animals in each treatment group in which zero, one, or more than one hepatic tumors developed. The graph represents the combined results of three separate experiments. *P = .05 vs. HSVlac, P = .02 vs. saline.

Figure 5. Representative sections of tumor stained for CD4(+) and CD8(+) cell populations at 1 and 5 days after injection with HSV–IL-12. The positively stained cells appear light brown.