Cancer immunotherapy using a membrane-bound interleukin-12 with B7-1 transmembrane and cytoplasmic domains

Abstract

Interleukin-12 (IL-12) has potent antitumor activity, but its clinical application is limited by severe systemic toxicity, which might be alleviated by the use of membrane-anchored IL-12. In the present study, a new membrane-bound IL-12 containing murine single-chain IL-12 and B7-1 transmembrane and cytoplasmic domains (scIL-12-B7TM) was constructed and its efficacy in cancer treatment examined and its protective antitumor mechanism investigated. Surface expression of scIL-12-B7TM on colon adenocarcinoma cells significantly inhibited the growth of subcutaneous tumors, suppressed lung metastasis, and resulted in local and systemic suppression of unmodified tumors. Intratumoral injection of an adenoviral vector encoding scIL-12-B7TM not only resulted in complete regression of a majority of local tumors, but also significantly suppressed the growth of distant, untreated tumors. Moreover, mice that had been treated with scIL-12-B7TM developed memory responses against subsequent tumor challenge. Immunohistochemical staining and in vivo depletion of lymphocyte subpopulations demonstrated that both CD8(+) T cells and CD4(+) T cells contributed to the antitumor activity of scIL-12-B7TM. Importantly, the potent antitumor activities of scIL-12-B7TM were achieved with only negligible amounts of IL-12 in the circulation. Our data demonstrate that cancer immunotherapy using membrane-bound IL-12 has the advantage of minimizing systemic IL-12 levels without compromising its antitumor efficacy.

Figure 1

Construction, expression, and bioactivity of single-chain membrane-bound IL-12 (scIL-12-B7TM). (a) Schematic diagram of scIL- 12-B7TM, which is composed of the murine immunoglobulin κ-chain signal peptide, a 9 amino acid influenza virus HA epitope, the murine single-chain IL-12, and the murine B7-1 transmembrane domain with a cytosolic tail. The single-chain IL-12 was in the p40-p35 orientation, with the two subunits separated by a flexible 18 amino acid peptide linker. (b) CT26 cells were retrovirally transduced with LNCX (left panel) or scIL-12-B7TM (right panel). Stable CT26/scIL-12-B7TM cells were stained with anti-mouse IL-12 p40/p70 mAb (solid lines) or an isotype control mAb (dashed lines) and analyzed by flow cytometry. (c) Con A-activated lymphoblasts (responder), prepared as described in the Materials and Methods, were incubated for 60 hours with mitomycin-C treated CT26/scIL-12-B7TM or CT26/LNCX cells (stimulator) at the indicated stimulator to responder ratio and proliferation was assessed by [³H]-thymidine uptake during the last 18 hours of culture. The results are the mean ± SD for triplicate wells. Con A, concanavalin A; cpm, counts per minute; HA, hemagglutinin; IL, interleukin; mAb, monoclonal antibody.

Figure 2

Antitumor activity of CT26/scIL-12-B7TM cells in BALB/c mice. (a) Groups of BALB/c mice (n = 10) were injected subcutaneously with 1 × 10⁵ CT26/LNCX, CT26/scIL-12-B7TM, or CT26/scIL-12 cells and tumor growth monitored. (b) Groups of BALB/c mice (n = 5–7) were injected intravenously with 2 × 10⁵ of the indicated tumors, then the animals were killed on day 16 and the number of lung metastases per mouse counted. (c) Groups of BALB/c mice (n = 5) were injected subcutaneously with 1 × 10⁵ CT26 cells and 1 × 10⁶ of the indicated tumor cells, and tumor growth monitored. (d) Groups of BALB/c mice (n = 10) were injected subcutaneously with 5 × 10⁶ of the indicated tumor cells in the right flank and 1 × 10⁵ CT26 cells in the left flank. Growth of CT26 in the left flank is shown. In a–c, the data are from one representative experiment of two performed. In a, c, and d, the results are the mean ± SD. In b, the metastatic foci of each mouse and the mean of each group are shown. IL, interleukin.

Figure 3

Effect of selective depletion of different lymphocyte populations on subcutaneous CT26/scIL-12-B7TM tumor growth in BALB/c mice. Groups of BALB/c mice (n = 5) were injected subcutaneously with 1 × 10⁵ CT26/scIL-12-B7TM cells on day 0 and anti-CD4 mAb and/or anti-CD8 mAb or anti-asialo GM1 antiserum was injected intraperitoneally on days −2, 0, 3, 5, 12, 19, and 26, then tumor size was monitored. Mice treated with the same dose and schedule of a monoclonal rat IgG or normal rabbit serum were included as controls. The results are the mean ± SD for the five mice. IL, interleukin; mAb, monoclonal antibody.

Figure 4

Antitumor memory responses induced by CT26/scIL-12-B7TM. Groups of BALB/c mice (n = 4–8) that had previously rejected subcutaneous tumor cells as described in Figure 2a were rechallenged (a) subcutaneously with 1 × 10⁵ CT26 tumors in the opposite flank or (b) intravenously with 2 × 10⁵ CT26 cells. Age-matched naive BALB/c mice inoculated with the same number of CT26 tumors were included as controls. In a, the results are the mean ± SD for those mice with measurable tumors. In b, the animals were killed on day 21 after intravenous inoculation of CT26 cells and the metastatic foci of each mouse and the mean of each group are shown. IL, interleukin.

Figure 5

Treatment of established CT26 tumors with adenovirus expressing scIL-12-B7TM. (a) 3T3 cells were infected with Ad/scIL-12-B7TM or Ad/scIL-12 at 100 multiplicity of infection for 48 hours, then the cells were stained with anti-mouse IL-12 p40/p70 mAb (solid lines) or an isotype control mAb (dashed lines) and analyzed by flow cytometry. (b) Groups of BALB/c mice (n = 8–12) were injected subcutaneously with 5 × 10⁵ CT26 cells, then treated with 1 × 10⁹ pfu of Ad/scIL-12-B7TM, Ad/scIL-12, or Ad/GFP on days 10 and 14 by intratumoral injection, and tumor growth was measured. (c) Groups of BALB/c mice (n = 5) were injected subcutaneously with 5 × 10⁵ CT26 cells in the right flank, and 1 × 10⁵ CT26 cells in the left flank. The right flank tumor were treated with 1 × 10⁹ pfu of Ad/scIL-12-B7TM, Ad/scIL-12, or Ad/GFP as described above, and the left flank tumor remained untreated. Tumor growth was monitored at the indicated times, and the results are presented as the mean ± SD. IL, interleukin; mAb, monoclonal antibody.

Figure 6

Immunohistochemical evaluation of CT26 tumors treated with Ad/scIL-12-B7TM. BALB/c mice with established subcutaneous CT26 tumors were treated with Ad/scIL-12-B7TM, Ad/scIL-12, or Ad/GFP as described in Figure 5. Mice were killed on day 10 after adenovirus inoculation and the tumor tissues were removed for immunohistochemical analysis. Cryostat sections were stained with (a–c) anti-CD8 (d–f) or anti-CD4 mAb and then counterstained with hematoxylin. Original magnification, ×200. IL, interleukin; mAb, monoclonal antibody.

Figure 7

Antitumor memory responses induced by Ad/scIL-12-B7TM. Groups of BALB/c mice (n = 5–6) that had been previously treated with Ad/scIL-12-B7TM or Ad/scIL-12 and eliminated the original tumors were rechallenged (a) subcutaneously with 1 × 10⁵ CT26 or (b) intravenously with 2 × 10⁵ CT26 cells. Age-matched naive BALB/c mice were included as controls. In a, the results are the mean ± SD for those mice with measurable tumors. In b, the mean and individual metastatic foci of each group are presented. IL, interleukin.

Figure 8

Systematic and local expression of IL-12. (a) 5 × 10⁴ CT26/scIL-12-B7TM or CT26/scIL-12 cells were seeded on 6-well plate and the supernatants collected 24, or 48 hours later to measure the amount of IL-12 by ELISA. The values are presented as the mean ± SD of triplicate cultures. (b) Groups of BALB/c mice (n = 5) were injected subcutaneously with 1 × 10⁷ CT26/scIL-12-B7TM, or CT26/scIL-12 cells, then serum samples were collected on the indicated days and assayed for the presence of IL-12. (c,d) Mice (n = 3–6) with established subcutaneous CT26 tumors as described in Figure 5 were injected intratumorally with 1 × 10⁹ pfu of Ad/scIL-12-B7TM, Ad/scIL-12, or Ad/GFP on day 10. (c) Tumor and (d) serum samples were collected on the indicated days and assayed for the presence of IL-12 by ELISA. The results in b–d are the mean ± SD for the indicated number of mice. ELISA, enzyme-linked immunosorbent assay; IL, interleukin.