HEM platelet transfusions in HLA alloimmunized patients with platelet refractoriness. Matching at the epitope level occurs by characterizing short sequences of amino acids from linearly consecutive (left; triplet) or discontinuous and spatially close (right; eplet) amino acid residues of the HLA molecules. HEM platelets are expected to not be targeted by pathogenic donor-specific anti-HLA alloantibodies and consequently to not undergo antibody-mediated phagocytic internalization, allowing platelet counts to increase posttransfusion.