Antitumor treatment using interleukin- 12-secreting marrow stromal cells in an invasive glioma model

Marrow stromal cells (MSCs) have the potential to migrate toward sites of injury or disease in the central nervous system. Encouraging results have been obtained by using MSCs to deliver therapeutic molecules. However, most brain tumor animal models--unlike in actual human disease states--use cells with limited invasion properties. In the present study, C57/B16 mice were implanted with the highly invasive Ast11.9-2 glioma cell line to investigate the potential therapeutic effects of interleukin-12 (IL-12)-secreting MSCs.

MSCs were infected with adenovirus encoding murine IL-12 (AdIL12). The infection conditions were optimized by determination of cytotoxicity and IL-12 secretion after AdIL12 infection in vitro. After implanting Ast11.9-2 tumor into mouse brain, we conducted a survival experiment to compare 4 distinct treatment groups by injecting culture medium control (sham), MSCs alone, MSCs infected with control virus (MSC-adenovirus encoding green fluorescent protein), and MSCs infected with IL-12-expressing virus (MSC-AdIL12) in the peritumoral region of the brain. Tumor tissues were analyzed by hematoxylin and eosin staining. IL-12 expression was analyzed by immunohistochemistry staining. Y chromosome fluorescent in situ hybridization was used to detect injected MSCs. Cell populations of CD57 (natural killer cells), CD3 (total T cells), and 7-AAD (dead cells) in whole brain tissue were analyzed by fluorescence-activated cell sorting at days 4 and 7 after therapeutic treatment.

Serum IL-12 increased significantly at days 4 and 7 after MSC-AdIL12 implantation. IL-12-expressing cells were detected by immunohistochemistry staining and Y chromosome-positive staining cells were found in the tumor area, confirming successful IL-12 delivery. MSC-AdIL12 treatment yielded increased natural killer cell infiltration in brain tissue at day 4, leading to an expected increase in nonspecific cell death, while total T-cell counts remained unchanged. MSC-IL-12 treatment extended animal survival but did not result in a statistically significant difference in comparison to other groups. Because all animals ultimately died of the brain tumors, MSC-AdIL12 treatment did not completely arrest the invasive growth pattern of these lesions.

The results indicate that MSCs may serve as useful delivery vehicles for IL-12 and other antineoplastic agents in brain tumor therapy.