429. Adenoviral-Mediated Interleukin-15 Receptor-α Gene Therapy of Murine Breast Cancer
Authors: Brian J. Morrison, Yutaka Tagaya, Jason C. Steel, Poonam Mannan, Thomas A. Waldmann, John C. Morris, Yoshio Sakai
Journal: Molecular Therapy (2006)

Background: Interleukin-15 (IL-15) is a critical cytokine involved in the activation, proliferation and survival of natural killer (NK) and CD8+ T cells. The high-affinity IL-15 receptor (IL-15Rα) expressed on monocytes and dendritric cells supplies IL-15 in trans to NK and T cells. Tumor cells engineered to express IL-15Rα may enhance the immune response to tumor. We studied the antitumor activity of adenoviral-mediated transfer of the murine IL-15Rα gene in a mouse breast cancer model.Methods: An E1–, E3– adenovirus expressing the murine IL-15Rα (Ad.mIL-15Rα) under the control of the CMV promoter and a control vector expressing no transgene (Ad.null) were generated. The expression of mIL-15Rα was examined in murine TS/A mammary carcinoma cells after infection with Ad.mIL-15Rα. The ability of Ad.mIL-15Rα to enhance NK cytolytic killing of transfected TS/A cells in the presence and absence of IL-15 was examined. TS/A cells infected ex vivo (MOI 30) with Ad.mIL-15Rα or Ad.null were subcutaneously (s.c.) injected (5 × 105) into groups of BALB/c mice. The mice were monitored for tumor growth. To study the effect of Ad.mIL-15Rα on pre-established tumors, mice with 150 mm3 TS/A tumors were intratumorally injected with 3 × 109 pfu of Ad.mIL-15Rα or Ad.null, and the tumor growth monitored. To investigate the mechanism of action, depletion of specific immune cell populations was carried out using anti-asialo- GM1, anti-CD4 and anti-CD8 antibodies.Results: Infection of TS/A cells with Ad.mIL-15Rα at an MOI 30 resulted in 60% of the cells expressing IL-15Rα as detected by flow cytometry. The addition of IL-15 enhanced NK cell killing by 2-fold at low NK cell:target cell ratios (1:1). No enhancement by IL-15 was seen at high ratios (10:1). On day 24 mean tumor volumes of mice injected with TS/A cells infected with Ad.mIL-15Rα were 256.2 ±37.1 mm3 compared to 1054.1 ±154.3 mm3 for mice injected with TS/A cells transduced with Ad.null (p <0.05) and 1225.8 ±123.2 mm3 for the untreated tumors (p <0.05). In animals with established tumors, Ad.mIL-15Rα reduced tumor size as measured on day 21 (265.3 ±37.1 mm3) compared to tumors injected with Ad.null (746.1±157.2 mm3) or PBS (799.2 ±121.0 mm3) (p <0.05). Depletion of NK cells abolished the effectiveness of Ad.mIL-15Rα; depletion of CD8+ T cells reduced the treatment effectiveness, whereas depletion of CD4+ T cells had no effect. Immunohistochemical staining of tumors injected with Ad.mIL-15Rα showed extensive infiltration of NK and CD8+ T cells compared to tumors treated with Ad.null, or untreated TS/A tumors.Conclusion: Adenoviral-mediated transfer of the mIL-15Rα gene into tumor demonstrated antitumor activity in the TS/A syngeneic breast cancer model. The effect appears to be mediated by the action of NK cells and CD8+ T cells. IL-15Rα gene transfer represents a cytokine receptor-mediated immunotherapy approach to activate the innate and adaptive immune systems against cancer. Background: Interleukin-15 (IL-15) is a critical cytokine involved in the activation, proliferation and survival of natural killer (NK) and CD8+ T cells. The high-affinity IL-15 receptor (IL-15Rα) expressed on monocytes and dendritric cells supplies IL-15 in trans to NK and T cells. Tumor cells engineered to express IL-15Rα may enhance the immune response to tumor. We studied the antitumor activity of adenoviral-mediated transfer of the murine IL-15Rα gene in a mouse breast cancer model. Methods: An E1–, E3– adenovirus expressing the murine IL-15Rα (Ad.mIL-15Rα) under the control of the CMV promoter and a control vector expressing no transgene (Ad.null) were generated. The expression of mIL-15Rα was examined in murine TS/A mammary carcinoma cells after infection with Ad.mIL-15Rα. The ability of Ad.mIL-15Rα to enhance NK cytolytic killing of transfected TS/A cells in the presence and absence of IL-15 was examined. TS/A cells infected ex vivo (MOI 30) with Ad.mIL-15Rα or Ad.null were subcutaneously (s.c.) injected (5 × 105) into groups of BALB/c mice. The mice were monitored for tumor growth. To study the effect of Ad.mIL-15Rα on pre-established tumors, mice with 150 mm3 TS/A tumors were intratumorally injected with 3 × 109 pfu of Ad.mIL-15Rα or Ad.null, and the tumor growth monitored. To investigate the mechanism of action, depletion of specific immune cell populations was carried out using anti-asialo- GM1, anti-CD4 and anti-CD8 antibodies. Results: Infection of TS/A cells with Ad.mIL-15Rα at an MOI 30 resulted in 60% of the cells expressing IL-15Rα as detected by flow cytometry. The addition of IL-15 enhanced NK cell killing by 2-fold at low NK cell:target cell ratios (1:1). No enhancement by IL-15 was seen at high ratios (10:1). On day 24 mean tumor volumes of mice injected with TS/A cells infected with Ad.mIL-15Rα were 256.2 ±37.1 mm3 compared to 1054.1 ±154.3 mm3 for mice injected with TS/A cells transduced with Ad.null (p <0.05) and 1225.8 ±123.2 mm3 for the untreated tumors (p <0.05). In animals with established tumors, Ad.mIL-15Rα reduced tumor size as measured on day 21 (265.3 ±37.1 mm3) compared to tumors injected with Ad.null (746.1±157.2 mm3) or PBS (799.2 ±121.0 mm3) (p <0.05). Depletion of NK cells abolished the effectiveness of Ad.mIL-15Rα; depletion of CD8+ T cells reduced the treatment effectiveness, whereas depletion of CD4+ T cells had no effect. Immunohistochemical staining of tumors injected with Ad.mIL-15Rα showed extensive infiltration of NK and CD8+ T cells compared to tumors treated with Ad.null, or untreated TS/A tumors. Conclusion: Adenoviral-mediated transfer of the mIL-15Rα gene into tumor demonstrated antitumor activity in the TS/A syngeneic breast cancer model. The effect appears to be mediated by the action of NK cells and CD8+ T cells. IL-15Rα gene transfer represents a cytokine receptor-mediated immunotherapy approach to activate the innate and adaptive immune systems against cancer.