Refractoriness can occur after repeated PLT transfusions because of alloimmunization to HLA class I antigens on transfused PLTs and generation of anti-HLA antibodies that bind to the foreign PLTs and initiate their destruction. Such refractoriness can be overcome by provision of HLA-matched PLTs from HLA typed donors. However, since the procedure is both expensive and time-consuming, an alternative approach is to deplete PLTs of HLA class I molecules by a brief treatment with citric acid, on ice at low pH. This is shown to be feasible without damaging PLT function