Protein A immunoadsorption treatment in hematology: an overview

Staphylococcal protein A efficiently binds immunoglobulins and circulating immune complexes (CIC) and provides an effective medium to remove immunoglobulins and CICs from plasma while sparing albumin and most coagulation proteins. Although it activates the complement system its clinical use abrogates the need for plasma expanders necessitated by plasma exchange. Despite anecdotal reports of utility in several hematologic syndromes, publications of clinical trials are available only for autoimmune thrombocytopenic purpura (AITP) and refractoriness to platelet transfusions (RFT) associated with alloimmunization. In the former situation Snyder et al. (Blood 79:2237-2245, 1992) reported on 72 patients with AITP all of whom had failed at least two previous therapies including splenectomy in 68%. Forty-six percent achieved improved platelet counts following treatment. The response was durable (8-26 mo) in all but 10%. Spleen-intact patients could not be differentiated from those who had been splenectomized. Both responders and nonresponders showed significant decreases in CIC and platelet-directed immunoglobulin (PDIG), but responders achieved near-normal levels. The beneficial response of these factors, particularly in spleen-intact patients, warrants a prospective study. In our studies at the University of Minnesota twelve patients with thrombocytopenia secondary to bone marrow failure who were refractory to platelet transfusion were treated with protein A immunoadsorption. Ten had demonstrable antiplatelet Abs (Anti-HLA, HPA, ABO). Seven of 12 demonstrated improved platelet counts and post-transfusion corrected count increments after treatment. This was associated with decreased platelet utilization and clinical bleeding. A prospective controlled clinical trial is justified.