Humanization and epitope mapping of neutralizing anti-human fas ligand monoclonal antibodies: Structural insights into Fas/Fas ligand interaction

Fas ligand (L)/CD95L, a proapoptotic member of the TNF family, is a potenti al target for clinical intervention in various diseases. In the present stu dy, we generated a humanized anti-human FasL mAb and characterized the epit opes of neutralizing mAbs by extensive alanine-scanning mutagenesis of huma n FasL. The predicted molecular model of FasL trimer revealed that the mAbs recognize largely overlapped conformational epitopes that are composed of two clusters, one around the outer tip-forming D-E loop and another near th e top of FasL. Both of these sites on FasL are critically involved in the d irect interaction with the corresponding receptor, Fas. These results sugge st that the mAbs efficiently neutralize FasL cytotoxicity by masking both o f these FasL/Fas contact sites.