Human FcεRIa-specific human single-chain Fv (scFv) antibody with antagonistic activity toward IgE/FcεRIα-binding

The alpha-chain of FcepsilonRI (FcepsilonRIalpha) plays a critical role in the binding of IgE to FcepsilonRI. A fully human antibody interfering with this interaction may be useful for the prevention of IgE-mediated allergic diseases. Here, we describe the successful isolation of a human single-chain Fv antibody specific to human FcepsilonRIalpha using human antibody phage display libraries. Using the non-immune phage antibody libraries constructed from peripheral blood lymphocyte cDNA from 20 healthy subjects, we isolated three phage clones (designated as FcRepsilon27, FcRepsilon51, and FcRepsilon70) through two rounds of bio-panning selection. The purified soluble scFv, FeRepsilon51, inhibited the binding of IgE to recombinant FcepsilonRIalpha, although both FcRepsilon27 and FcRepsilon70 showed fine binding specificity to FcepsilonRIalpha. Since FcRepsilon51 was determined to be a monomer by HPLC, BIAcore analysis was performed. The dissociation constant of FcRepsilon51 to FcepsilonRIalpha was estimated to be 20 nM, i.e., fortyfold lower than that of IgE binding to FcepsilonRIalpha (K-d = 0.5 nM). With these characteristics, FcRepsilon51 exhibited inhibitory activity on the release of histamine from passively sensitized human peripheral blood mononuclear cells.