GENETICALLY-ENGINEERED DEGLYCOSYLATION OF THE VARIABLE DOMAIN INCREASES THE AFFINITY OF AN ANTI-CD33 MONOCLONAL-ANTIBODY

M195 is a murine monoclonal antibody that binds to the CD33 antigen an d is being tested for the treatment of myeloid leukemia. Surprisingly, a complementarity determining region (CDR)-grafted, humanized M195 an tibody displayed a several-fold higher binding affinity for the CD33 a ntigen than the original murine antibody. Here we show the the increas e in binding affinity resulted from eliminating an N-linked glycosylat ion site at residue 73 in the heavy chain variable region in the cours e of humanization. Re-introducing the glycosylation site in the humani zed antibody reduces its binding affinity to that of the murine antibo dy, while removing the glycosylation site from the murine M195 variabl e domain increases its affinity. The removal of variable region carboh ydrates may provide a method for increasing the affinity of certain mo noclonal antibodies with diagnostic and therapeutic potential.