Survival and toxicity of an allogeneic cytokine-secreting fibroblast vaccine in the central nervous system

OBJECTIVE: In previous studies, we determined that C57BL/6 mice (H-2(b)) with intracerebral (i.c.) malignant glioma or melanoma treated with allogeneic fibroblasts genetically engineered to secrete interleukin (IL)-2 results in prolonged survival and a cellular antitumor response when the treatment is administered intratumorally (via i.c. injection). For this study, we evaluated the survival and toxicity of the cytokine-secreting cellular vaccine administered directly into the central nervous system in both syngeneic ((CH)-H-3 H-2(k)) and allogeneic (C57BL/6 H-2(b)) mice using bioassay and polymerase chain reaction techniques. METHODS: First, brain sections were prepared at varying time intervals (2-60 d) after i.c. injection of the IL-2-secreting fibroblasts (H-2(k)) into allogeneic and syngeneic mice, and the presence of the cells was detected by polymerase chain reaction for the neomycin gene, which was used as a selection marker for the gene transfer. As a second means of assessing survival of the IL-2-secreting cells, an in vitro bioassay technique was used. Brain sections were prepared at varying time intervals (2-60 d) after i.c. injection of the IL-2-secreting cells into allogeneic and syngeneic mice. Cells were disassociated and grown in media containing neomycin. RESULTS: A positive signal by polymerase chain reaction was no longer detectable 14 days after injection into allogeneic C57BL/6 (H-2(b)) mice. In contrast, under similar circumstances, the IL-2-secreting cellular vaccine could be detected for more than 55 days in histocompatible ((CH)-H-3) syngeneic mice (H-2(k)). Allogeneic cells could be recovered from tissue culture for only 2 to 5 days after i.c. injection of the modified cells. In contrast, syngeneic cells were recovered for up to 28 days after i.c. injection. At no time did the mice exhibit signs of neurological deficit or adverse affects on their survival (>60 d). CONCLUSION: An allogeneic cytokine-secreting cellular vaccine has a limited lifespan in the central nervous system, surviving only 14 days or less, and has no apparent adverse effects. These results indicate the advantage of using a modified allogeneic cell line as the delivery vehicle for gene therapy in the treatment of an i.c. neoplasm.