Abstract: A polypeptide which is capable of inhibiting binding of von Willebrand factor (vWF) to platelets and comprising an amino acid sequence that corresponds to the amino acid sequence of that fragment of mature von Willebrand factor subunit having its amino terminus at about Cys.sup.509 and its carboxy terminus at about Cys.sup.695, said polypeptide comprising optionally a second and/or a third domain, the second domain corresponding to the amino acid sequence of that fragment of mature vWF subunit having its amino terminus at about Thr.sup.450 and its carboxy terminus at about Tyr.sup.508, or a subfragment or combination of subfragments thereof, and a third domain corresponding to the amino acid sequence of that fragment of mature vWF subunit having its amino terminus at about Asp.sup.696 and its carboxy terminus at about Gly.sup.

Abstract: A method of inhibiting platelet transfusion refractoriness comprising administering third-party platelets to a patient whose platelet glycoprotein Ib.alpha. polypeptides expressed from the patient's DNA have been determined to have either threonine or methionine residues, or both, at amino acid residue position 145 thereof, the third-party platelets having expressed at residue position 145 of the glycoprotein Ib.alpha. polypeptide thereof amino acids that are the same as those expressed on the glycoprotein Ib.alpha. polypeptides of the patient's platelets. Also, an antibody, or a fragment thereof, in substantially pure form having as its target epitope a domain of glycoprotein Ib.alpha., the affinity of the antibody, or fragment thereof, for said epitope being dependent on the identity of the amino acid residue at position 145 of the glycoprotein.

Abstract: A method of inhibiting platelet transfusion refractoriness comprising administering third-party platelets to a patient whose platelet glycoprotein Ib.alpha. polypeptides expressed from the patient's DNA have been determined to have either threonine or methionine residues, or both, at amino acid residue position 145 thereof, said third-party platelets having expressed at residue position 145 of the glycoprotein Ib.alpha. polypeptide thereof amino acids that are the same as those expressed on the glycoprotein Ib.alpha. polypeptides of the patient's platelets. Also, an antibody, or a fragment thereof, in substantially pure form having as its target epitope a domain of glycoprotein Ib.alpha., the affinity of said antibody, or fragment thereof, for said epitope being dependent on the identity of the amino acid residue at position 145 of said glycoprotein.

Abstract: Recombinant DNA expression vectors encoding a peptide which inhibits binding of von Willebrand factor to platelet membrane glycoprotein Ib, said vector including a nucleotide sequence encoding the amino acid sequence from HIS.sup.1 to LEU.sup.610, inclusive, of the amino terminal region of platelet membrane glycoprotein Ib.alpha.