HLA class I depletion by citric acid, and irradiation of apheresis platelets for transfusion of refractory patients

Background Patients can form antibodies to foreign human leukocyte antigen (HLA) Class I antigens after exposure to allogeneic cells. These anti‐HLA class I antibodies can bind transfused platelets (PLTs) and mediate their destruction, thus leading to PLT refractoriness. Patients with PLT refractoriness need HLA‐matched PLTs, which require expensive HLA typing of donors, antibody analyses of patient sera and/or crossmatching. An alternative approach is to reduce PLT HLA Class I expression using a brief incubation in citric acid on ice at low pH. Methods and Materials Apheresis PLT concentrates were depleted of HLA Class I complexes by 5 minutes incubation in ice‐cold citric acid, at pH 3.0. Surface expression of HLA Class I complexes, CD62P, CD63, phosphatidylserine, and complement factor C3c was analyzed by flow cytometry. PLT functionality was tested by thromboelastography (TEG). Results Acid treatment reduced the expression of HLA Class I complexes by 71% and potential for C3c binding by 11.5‐fold compared to untreated PLTs. Acid‐treated PLTs were significantly more activated than untreated PLTs, but irrespective of this increase in steady‐state activation, CD62P and CD63 were strongly upregulated on both acid‐treated and untreated PLTs after stimulation with thrombin receptor agonist peptide. Acid treatment did not induce apoptosis over time. X‐ray irradiation did not significantly influence the expression of HLA Class I complexes, CD62P, CD63, and TEG variables on acid treated PLTs. Conclusion The relatively simple acid stripping method can be used with irradiated apheresis PLTs and may prevent transfusion‐associated HLA sensitization and overcome PLT refractoriness