Vancomycin-dependent antibodies associated with thrombocytopenia and refractoriness to platelet transfusion in patients with leukemia.

Two patients with leukemia experienced profound thrombocytopenia and refractoriness to platelet transfusion during vancomycin treatment. In one patient, withdrawal of drug and administration of platelet transfusions restored platelet counts to near normal levels (approximately 100 x 10(9)/L), however, subsequent challenge with vancomycin due to recurring infection again precipitated severe thrombocytopenia (platelets less than 10 x 10(9)/L) and life-threatening hemorrhagic symptoms. Potent vancomycin-dependent antiplatelet antibodies were detected in the serum of both patients during the refractory period using staphylococcal protein A rosette formation. Employing a monoclonal antibody-antigen capture enzyme-linked immunosorbent assay (ELISA), the patients were found to have vancomycin-dependent IgG antibodies that bound specifically to platelet glycoproteins (GP) IIb and/or IIIa. One of these antibodies failed to react with platelets deficient in GPIIb/IIIa obtained from an individual with Glanzmann's thrombasthenia. These findings provide the first major evidence for drug-dependent antibodies in association with severe thrombocytopenia and refractoriness to platelet transfusion in alloimmunized leukemia patients and, further, provide the first demonstration of vancomycin-dependent antibodies reactive with platelets.