Humanization of 60.3, an anti-CD18 antibody; importance of the L2 loop

Abstract

Monoclonal antibody 60.3 binds to the CD18 component of the β2 integrin family of adhesion molecules. 60.3 has potential clinical application in blocking the neutrophilmediated organ damage which occurs following a myocardial infarct or hemorrhagic shock. Analysis of the nucleotide and deduced amino acid sequences of murine 60.3 shows that the light chain contains no amino acid substitutions relative to the closest germline sequence, while the heavy chain is heavily substituted. We report here the humanization of 60.3. The humanized antibody binds to CD18-bearing cells with ˜4-fold less affinity than the murine or chimeric antibody. We have shown that modification of amino acid L50 in the L2 loop of the humanized antibody results in loss of binding, while modification of a structural determinant (H71) for the H2 loop has no effect.