Simultaneous antagonism of interleukin-5, granulocyte-macrophage colony-stimulating factor, and interleukin-3 stimulation of human eosinophils by targetting the common cytokine binding site of their receptors

Human interleukin-5 (IL-5), granulocyte-macrophage colony-stimulating facto r (GM-CSF), and IL-3 are eosinophilopoietic cytokines implicated in allergy in general and in the inflammation of the airways specifically as seen in asthma. All 3 cytokines function through cell surface receptors that compri se a ligand-specific alpha chain and a shared subunit (beta(c)). Although b inding of IL-5, GM-CSF, and IL-3 to their respective receptor alpha chains is the first step in receptor activation, it is the recruitment of beta(c) that allows high-affinity binding and signal transduction to proceed. Thus, beta(c) is a valid yet untested target for antiasthma drugs with the added advantage of potentially allowing antagonism of all 3 eosinophil-acting cy tokines with a single compound. We show here the first development of such an agent in the form of a monoclonal antibody (MoAb), BION-1, raised agains t the isolated membrane proximal domain of beta(c). BION-1 blocked eosinoph il production, survival, and activation stimulated by IL-5 as well as by GM -CSF and IL-3. Studies of the mechanism of this antagonism showed that BION -1 prevented the high-affinity binding of I-125-IL-5, I-125-GM-CSF, and I-1 25-IL-3 to purified human eosinophils and that it bound to the major cytoki ne binding site of beta(c). Interestingly, epitope analysis using several b eta(c) mutants showed that BION-1 interacted with residues different from t hose used by IL-5, GM-CSF, and IL-3. Furthermore, coimmunoprecipitation exp eriments showed that BION-1 prevented ligand-induced receptor dimerization and phosphorylation of beta(c), suggesting that ligand contact with beta(c) is a prerequisite for recruitment of beta(c), receptor dimerization, and c onsequent activation. These results demonstrate the feasibility of simultan eously inhibiting IL-5, GM-CSF, and IL-3 function with a single agent and t hat BION-1 represents a new tool and lead compound with which to identify a nd generate further agents for the treatment of eosinophil-dependent diseas es such as asthma. (C) 1999 by The American Society of Hematology.