HUMANIZATION OF 60.3, AN ANTI-CD18 ANTIBODY - IMPORTANCE OF THE L2 LOOP

Monoclonal antibody 60.3 binds to the CD18 component of the beta 2 int egrin family of adhesion molecules. 60.3 has potential clinical applic ation in blocking the neutrophil-mediated organ damage which occurs fo llowing a myocardial infarct or hemorrhagic shock. Analysis of the nuc leotide and deduced amino acid sequences of murine 60.3 shows that the light chain contains no amino acid substitutions relative to the clos est germline sequence, while the heavy chain is heavily substituted. W e report here the humanization of 60.3. The humanized antibody binds t o CD18-bearing cells,vith similar to 4-fold less affinity than the mur ine or chimeric antibody. We have shown that modification of amino aci d L50 in the L2 loop of the humanized antibody results in loss of bind ing, while modification of a structural determinant (H71) for the H2 l oop has no effect.