Abstract 3506: IL-15 or IL-15/IL-15Rα complexes activates natural killer cells and enhances anti-GD2 monoclonal antibody-mediated antibody-dependent cellular cytotoxicity in vitro and in vivo

Abstract

Abstract Antibody-dependent cellular cytotoxicity (ADCC) plays an important role in the efficacy of therapeutic anti-cancer monoclonal antibodies (mAbs). Natural killer (NK) cell is the major effector lymphocytes in mediating ADCC through Fc ≤ receptor (FcαR). Indeed, the use of cytokine such as IL2 and GM-CSF to improve the mAbs-mediated ADCC has been studied. Recently, interleukin-15 (IL-15) or IL-15/IL-15 receptor ≤ (IL-15Rβ) complexes have been shown to enhance the cytotoxicity of NK cells but their effects on ADCC mediated by NK cells have not been well-investigated. Here, we evaluated the effects of in vivo stimulation with IL-15 or IL-15/IL-15Rα complexes on the ADCC activity of NK cells mediated by anti-GD2 mAb (14G2a). Fresh DX5+ NK cells from PBS-treated mice were ineffective in inducing 14G2a-coated apoptosis of a relatively NK cell-resistant lymphoma, EL4, with 19.6% and 17.3% for EL4+14G2a compared with EL4, respectively. Upon daily injection of murine IL-15 for 3 or 5 days, a significant and persistent ADCC activity of NK cells (49.0∼50.8%, P < 0.001) was observed from day 3 to 5. In addition, a single administration of IL-15/IL-15Rα complexes on day 0 induced a peak ADCC activity at day 2 (59.8%, P < 0.001) and then slightly decreased at day 3 (37.8%, P < 0.001). Moreover, IL-15 or IL-15/IL-15Rα complexes-induced ADCC activities of NK cells could be eliminated by NKG2D blockade. FACS analysis of murine splenocytes showed that IL-15 or IL-15/IL-15Rα complexes administrations significantly increased the percentage of FcαR-positive NK cells from resting stage 75% to 85% and 92%, respectively, and also slightly enhanced the surface expression of FcαR on NK cells. Furthermore, IL-15/IL-15Rα complexes rapidly induced the expression of CD69 on FcαR-expressed NK cells from 14.5% to 92.6% at 24h, followed by returning to baseline at day 3. However, sustained IL-15 treatment maintained the expression of CD69 on FcαR-positive NK cells but the maximal expression of CD69 was only 52.5% at day 5. These results demonstrated that IL-15 and IL-15/IL-15Rα complexes exhibit different potency or time kinetics on the activation of FcαR-expressing NK cells. Based on these in vitro data, we evaluated the in vivo anti-cancer efficacy of 14G2a in syngeneic EL4 murine model in combination with timed sequential treatments of IL-15 or IL-15/IL-15Rα complexes. Both sustained IL-15 or IL-15/IL-15Rα complexes effectively and equally prolonged the survival of EL4-bearing mice compared with 14G2a only (P <0.001). In conclusion, these data show that IL-15 or IL-15/IL-15Rα complexes may enhance the therapeutic potential of anti-glycan or other therapeutic mAbs currently used clinically for patients with malignancies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3506. doi:1538-7445.AM2012-3506