Anti-IL15RA monoclonal antibody, clone fCjpKN8B5

Interleukin-15 (IL-15) is a putative myokine hypothesized to induce an oxidative skeletal muscle phenotype. The specific IL-15 receptor alpha subunit (IL-15R alpha) has also been implicated in specifying this contractile phenotype. The purposes of this study were to determine the muscle-specific effects of IL-15R alpha functional deficiency on skeletal muscle isometric contractile properties, fatigue characteristics, spontaneous cage activity, and circulating IL-15 levels in male and female mice. Muscle creatine kinase (MCK)-driven IL-15R alpha knockout mice (mIl15ra(fl/fl)/Cre(+)) were generated using the Cre-loxP system. We tested the hypothesis that IL-15R alpha functional deficiency in skeletal muscle would increase resistance to contraction-induced fatigue, cage activity, and circulating IL-15 levels. There was a significant effect of genotype on the fatigue curves obtained in extensor digitorum longus (EDL) muscles from female mIl15ra(fl/fl)/Cre(+) mice, such that force output was greater during the repeated contraction protocol compared with mIl15ra(fl/fl)/Cre(+) control mice. Muscles from female mIl15ra(fl/fl)/Cre(+) mice also had a twofold greater amount of the mitochondrial genome-specific COXII gene compared with muscles from mIl15ra(fl/fl)/Cre(+) control mice, indicating a greater mitochondrial density in these skeletal muscles. There was a significant effect of genotype on the twitch: tetanus ratio in EDL and soleus muscles from mIl15ra(fl/fl)/Cre(+) mice, such that the ratio was lower in these muscles compared with mIl15ra(fl/fl)/Cre(+) control mice, indicating a pro-oxidative shift in muscle phenotype. However, spontaneous cage activity was not different and IL-15 protein levels were lower in male and female mIl15ra(fl/fl)/Cre(+) mice compared with control. Collectively, these data support a direct effect of muscle IL-15R alpha deficiency in altering contractile properties and fatigue characteristics in skeletal muscles.

Purpose: Immunotherapy with IL2, GM-CSF, and an antidisialoganglioside (GD2) antibody significantly increases event-free survival in children with high-risk neuroblastoma. However, therapy failure in one third of these patients and IL2-related toxicities pose a major challenge. We compared the immunoadjuvant effects of IL15 with those of IL2 for enhancing antibody-dependent cell-mediated cytotoxicity (ADCC) in neuroblastoma. Experimental Design: We tested ADCC against neuroblastoma patient-derived xenografts (PDX) in vitro and in vivo and examined the functional and migratory properties of NK cells activated with IL2 and IL15. Results: In cell culture, IL15-activated NK cells induced higher ADCC against two GD(+) neuroblastoma PDXs than did IL2-activated NK cells (P < 0.001). This effect was dose-dependent (P < 0.001) and was maintained across several effector-to-tumor ratios. As compared with IL2, IL15 also improved chemotaxis of NK cells, leading to higher numbers of tumorsphere-infiltrating NK cells in vitro (P = 0.002). In an orthotopic PDX model, animals receiving chemoimmunotherapy with an anti-GD2 antibody, GM-CSF, and a soluble IL15/IL15Ra complex had greater tumor regression than did those receiving chemotherapy alone (P = 0.012) or combined with anti-GD2 antibody and GM-CSF with (P = 0.016) or without IL2 (P = 0.035). This was most likely due to lower numbers of immature tumor-infiltrating NK cells (DX5(+)CD27(+)) after IL15/IL15Ra administration (P = 0.029) and transcriptional upregulation of Gzmd. Conclusions: The substitution of IL15 for IL2 leads to significant tumor regression in vitro and in vivo and supports clinical testing of IL15 for immunotherapy in pediatric neuroblastoma.