In line with this notion, IL-15 has been ranked first among the agents with an elevated potential for the treatment of multiple neoplasms,2 and is currently being evaluated in several Phase I clinical trials enrolling patients with advanced solid tumors such as renal cell carcinoma and melanoma.3 2,6-Dimethoxybenzoic acid Several preclinical studies have revealed a specific mode of action for IL-15 in vivo, which has been named trans-presentation. signal transducing components. In addition, the IL-2 and IL-15 receptors each use a private ? chain (IL-2R? or IL-15R?), which confers cytokine specificity by preferentially enhancing ligand binding affinity. Although displaying similar effects in vitro, IL-2 and IL-15 exert distinct and often competing effects in the course of adaptive immune responses. Indeed, unlike IL-2, IL-15 does not promote activation-induced cell death (AICD) among CD8+ effector cells, and does not seem to exert an important influence on immunosuppressive regulatory T cells (Tregs). However, IL-15 is crucial not only for the development of natural killer (NK) cells and the survival of memory T lymphocytes, but also for initiating T-cell activation. IL-15 therefore plays a major role in anticancer immunosurveillance. In line with this notion, IL-15 has been ranked first among the agents with an elevated potential for the treatment of multiple neoplasms,2 and is currently being evaluated in several Phase 2,6-Dimethoxybenzoic acid I clinical trials enrolling patients with advanced solid tumors such as renal cell carcinoma and melanoma.3 Several 2,6-Dimethoxybenzoic acid preclinical studies have revealed a specific mode of action for IL-15 in vivo, which has been named trans-presentation. In the course of trans-presentation, IL-15R? expressed at the surface of IL-15-secreting cells (including dendritic cells, macrophages and epithelial SCKL cells), presents IL-15 in trans to IL-15-sensitive cells (such as NK cells or memory CD8+ T lymphocytes) that bear IL-15R?/? dimers. A soluble form of IL-15R? has also been described to result from the proteolytic cleavage of membrane-anchored IL-15R? by metalloproteases.4 Multiple studies have shown that the soluble IL-15/IL-15R? complex exerts more consistent immunostimulatory effects (in the context of trans-activation) than soluble IL-15. Based on these premises, we have previously engineered a fusion protein called RLI, linking the sushi domain of human IL-15R? to human IL-15. As a single molecule, RLI exerted improved biological activities in vitro5 and in vivo, both as a promoter of the development of lymphoid cells and as an adjuvant to immune responses against murine and human cancers.6 To further capitalize on the antitumor activity of RLI, we sought to develop RLI-based immunocytokines (ICKs) by fusing RLI to antibodies targeting tumor-associated antigens. The rationale of ICKs is to specifically direct to the tumor site both the effector activities of tumor-specific antibodies and the cytokine-dependent immunostimulatory signal that is required for the generation of cytotoxic cellular immunity (Fig.?1). An additional advantage of this approach is that reduced concentrations of cytokines are needed to achieve a biological effect in the tumor environment, resulting in minimal systemic toxicity.7 Among the most advanced ICKs, IL-2-based fusion proteins have shown promising results in Phase II clinical trials, yet were associated with adverse effects resembling those observed with recombinant IL-2.7 Based on preclinical studies, IL-15 is considered to have an improved safety profile and immunostimulatory activity over IL-2. In this context, we have developed the first RLI-based ICK targeting the GD2 disialoganglioside (Fig.?1),8 a validated tumor-associated antigen ranked 12th among all promising targets for the prevention or treatment 2,6-Dimethoxybenzoic acid of cancer.9 GD2 is a sialic acid-bearing glycosphingolipid expressed on several tumors of neuroectodermal origin, including melanoma, glioma, neuroblastoma, and small cell lung carcinoma, but only to minimal levels by the peripheral nervous system and the cerebellum.10 Open in a separate window Figure?1. Development of a RLI-based immunocytokine targeting the tumor-associated 2,6-Dimethoxybenzoic acid antigen GD2. The C-terminus of the heavy chain of an anti-GD2 antibody was fused to the N-terminus of RLI. The purified anti-GD2-RLI immunocytokine not only efficiently bound GD2 and the interleukin (IL)-15 receptor ?/? dimer, but also conserved both the cytotoxic effector functions of the antibody and the biological activity of the cytokine. Such an RLI-based immunocytokine targeting GD2 has a higher therapeutic activity in vivo than RLI and anti-GD2, whether they be employed as standalone interventions or combined. ADCC, antibody-dependent cell-mediated cytotoxicity; CDC, complement-dependent cytotoxicity. By flow cytometry, we demonstrated the specific binding of our ICK to GD2+ EL4 cells as well.