A cytokine was identified that stimulated the proliferation of T lymphocytes, and a complementary DNA clone encoding this new T cell growth factor was isolated. The cytokine, designated interleukin-15 (IL-15), is produced by a wide variety of cells and tissues and shares many biological properties with IL-2. Monoclonal antibodies to the beta chain of the IL-2 receptor inhibited the biological activity of IL-15, and IL-15 competed for binding with IL-2, indicating that IL-15 uses components of the IL-2 receptor.

We have recently cloned a novel cytokine, IL‐15, with shared bioactivities but no sequence homology with IL‐2. We found high affinity IL‐15 binding to many cell types, including cells of non‐lymphoid origin. Analysis of IL‐15 interaction with subunits of the IL‐2 receptor (IL‐2R) revealed that the alpha subunit was not involved in IL‐15 binding. We demonstrated directly in cells transfected with IL‐2R subunits that both the beta and gamma chains are required for IL‐15 binding and signaling. Hence, IL‐15, like IL‐2, IL‐4 and IL‐7, utilizes the common IL‐2R gamma subunit found to be defective in X‐linked severe combined immunodeficiency in humans. IL‐15 is the only cytokine other than IL‐2 that has also been shown to share the beta signaling subunit of IL‐2R. The differential ability of some cells to bind and respond to IL‐2 and IL‐15 implies the existence of an additional IL‐15‐specific component.

Interleukin-15 (IL-15) is a novel cytokine of the fourhelix bundle family which shares many biological activities with IL-2, probably due to its interaction with the IL-2 receptor 3 and y (IL-2RO and ye) chains.We report here the characterization and molecular cloning of a distinct murine IL-15Ra chain. IL-15Ra alone displays an affinity of binding for IL-15 equivalent to that of the heterotrimeric IL-2R for IL-2. A biologically functional heteromeric IL-15 receptor complex capable of mediating IL-15 responses was generated through reconstruction experiments in a murine myeloid cell line. IL-l5Rca is structurally similar to IL-2Ra; together they define a new cytokine receptor family. The distribution of IL-15 and IL15Ra mRNA suggests that IL-15 may have biological activities distinct from IL-2.

Two receptors for the proinflammatory cytokine interleukin 1 (IL-1) have been cloned and characterized biochemically. While it has been well established that the type I (80-kDa) IL There are two known receptors for IL-1, which differ in both size and tissue distribution (2-4). The ligand-binding portions of the two receptors are similar, but whereas the cytoplasmic region of the type I (-80-kDa) receptor contains -215 amino acids, that of the type II (=60-kDa) receptor is only 29 amino acids long. It is well established that the type I receptor is capable of mediating biological responses (5, 6). In studies reported elsewhere, it has also been clearly shown that the type I and type II receptors are not subunits of a multimeric receptor complex but instead bind IL-1 independently of one another (7). This raises the possibility that each receptor might couple to different signal transduction pathways. In the studies reported here, however, we have been unable to find any evidence that the type II receptor signals at all.

Antibody-drug conjugates (ADC) have emerged as potent antitumor drugs that provide increased efficacy, specificity, and tolerability over chemotherapy for the treatment of cancer. ADCs generated by targeting cysteines and lysines on the antibody have shown efficacy, but these products are heterogeneous, and instability may limit their dosing. Here, a novel technology is described that enables site-specific conjugation of toxins to antibodies using chemistry to produce homogeneous, potent, and highly stable conjugates. We have developed a cell-based mammalian expression system capable of site-specific integration of a non-natural amino acid containing an azide moiety. The azide group enables click cycloaddition chemistry that generates a stable heterocyclic triazole linkage. Antibodies to Her2/neu were expressed to contain N6-((2-azidoethoxy)carbonyl)-l-lysine at four different positions. Each site allowed over 95% conjugation efficacy with the toxins auristatin F or a pyrrolobenzodiazepine (PBD) dimer to generate ADCs with a drug to antibody ratio of >1.9. The ADCs were potent and specific in in vitro cytotoxicity assays. An anti Her2/neu conjugate demonstrated stability in vivo and a PBD containing ADC showed potent efficacy in a mouse tumor xenograph model. This technology was extended to generate fully functional ADCs with four toxins per antibody. The high stability of the azide-alkyne linkage, combined with the site-specific nature of the expression system, provides a means for the generation of ADCs with optimized pharmacokinetic, biological, and biophysical properties.