Administration of Systemic or Local Interleukin-2 Enhances the Anti-tumor Effects of Interleukin-12 Gene Therapy

Abstract

Interleukin- 12 (IL- 12) is a cytokine with a wide variety of immunorerogulatory activities. These include stimulation of interferon-γ production, cytolytic activity of natural killer (NK) cells and T-cell subsets, the development of cellular immunity, and induction of maturation of Th1 cells. IL-12 also has potent anti-tumor activity in vivo. In the present study the possibility of enhanced anti-tumor activity was examined using a combination of local IL-12 by cytokine gene therapy at the tumor site, combined with systemic or local IL-2 delivery. NIH 3T3 fibroblasts transfected with the genes for both subunits of IL-12, p35 and p40, were used as the source of IL-12 therapy producing 240 HLRU/106 cells/48 hr. In the first part of the study the effect of different regimens of systemic IL-2 delivery with local IL-12 administration on the size and growth rate of subcutaneous MCA-105 murine sarcoma was examined. Local IL-12 alone reduced the sizes of tumors after 32 days from 163 to 20.8 mm2 (P < 0.002). Adding the longer-acting polyethylene-glycol-modified II-2 (PEG IL-2; 30,000 IU) for 5 days prevented the development of tumors in all treated mice compared to 1/3 mice treated with PEG IL-2 alone and 3/6 mice with IL-12, but this was a highly toxic therapy and most of the animals died. Administration of 60,000 IU of IL-2 on Days 1-5 postinoculation of tumor, delivered with IL-12 gene therapy, reduced the tumor growth rate compared to animals treated with IL-2 alone (P < 0.02) or IL-12 (0.1). After 30 days the mean tumor size was 1.2 mm2 compared to 17.8 mm2 with IL-12 alone, 85.4 mm2 with low-dose IL-2 (P < 0.05), and 46.2 mm2 in controls (P < 0.03). When IL-2 was added later, on Days 6-10, the additive effect of low-dose IL-2 with local IL-12 was less significant. Mean tumor sizes were 38.4 and 55 mm2. High-dose IL-2 abrogated the additive effect of IL-12. Tumor size was 111.4 compared to 55 mm2 with IL-12 alone. In the second part of the study the effect of local IL-2 produced by a transfected MC-38 murine colon adenocarcinoma cell line, producing IL-2 coupled with IL-12 gene therapy, was examined. Tumor cells and IL-12-producing NIH3T3 fibroblasts were injected at a ratio of 1:3 or 1:6. After 40 and 32 days, respectively, tumor sizes with the combined treatment were 8.25 and 19.6 mm2 compared to 62.5 and 134.4 mm2 with IL-12 alone or 59.8 and 133 mm2 with IL-2 alone. In conclusion, local IL-12 produced at the tumor site during cytokine gene therapy when delivered with systemic or local low-dose IL-2 causes delayed tumor growth, when they are administered at the appropriate amounts and at the right time. The initial role of sequence, timing, and means of delivery may mimic the requirement for induction of an effective natural immune response.