Recombinant human IgG molecules lacking Fc gamma receptor I binding and monocyte triggering activities

Subclasses of human IgG have a range of activity levels with different effe ctor systems but each triggers at least one mechanism of cell destruction. We are aiming to engineer nondestructive human IgG constant regions for the rapeutic applications where depletion of cells bearing the target antigen i s undesirable. The attributes required ave a lack of killing via Fc gamma r eceptors (R) and complement but retention of neonatal FcR binding to mainta in placental transport and the prolonged half-life of IgG. Eight variants o f human IgG constant regions were made with anti-RhD and CD52 specificities . The mutations, in one or two key regions of the CH2 domain, were restrict ed to incorporation of motifs from other subclasses to minimize potential i mmunogenicity. IgG2 residues at positions 233-236, substituted into IgG1 an d IgG4, reduced binding to Fc gamma RI by 10(4)-fold and eliminated the hum an monocyte response to antibody-sensitized red blood cells, resulting in a ntibodies which blocked the functions of active antibodies. If glycine 236, which is deleted in IgG2, was restored to the IgG1 and IgG4 mutants, low l evels of activity were observed. Introduction of the IgG4 residues at posit ions 327, 330 and 331 of IgG1 and IgG2 had no effect on Fc gamma RI binding but caused a small decrease in monocyte triggering.