A HUMAN MONOCLONAL-ANTIBODY SPECIFIC FOR THE LEUCINE-33 (P1(A1), HPA-1A) FORM OF PLATELET GLYCOPROTEIN IIIA FROM A V-GENE PHAGE DISPLAY LIBRARY

IgG alloantibodies to polymorphic platelet glycoproteins (GPs) are kno wn to be responsible for severe thrombocytopenia in the neonate and af ter transfusion. Platelet GPIIIa can have either a leucine or a prolin e at residue 33, The most immunogenic platelet alloantigen in thromboc ytopenia is the leucine 33 form of GPIIIa. Here, we have generated hum an monoclonal antibody fragments that are specific for the leucine and not the proline form of GPIIIa and can inhibit the binding of polyclo nal human IgG alloantibodies to GPIIIa leucine 33 on platelets. The an tibody fragments were selected from a library of single chain Fv fragm ents displayed on the surface of filamentous phage. The VH gene repert oire was derived from the peripheral blood lymphocytes of an alloimmun ized individual and recombined with a VL gene repertoire from a nonimm une source. Antibodies such as these, which are able to distinguish be tween two variant forms of a native antigen and which have been unobta inable by conventional hybridoma technology, have both diagnostic and potential therapeutic applications. (C) 1996 by The American Society o f Hematology.