Functional Properties of Human Cytomegalovirus Hyperimmunoglobulin and Standard Immunoglobulin Preparations

BACKGROUND Cytomegalovirus hyperimmunoglobulin (CMV-HIG) preparations reduce mortality after solid organ transplantation. Polyspecific intravenous immunoglobulin (IVIg) products are also used prophylactically by some centers. Since direct comparative characterizations of the preparations are scarce, it is challenging to compare different clinical studies. MATERIAL AND METHODS The functionality of 2 CMV-HIG preparations (Cytotect® CP, Cytogam®) and 2 IVIg preparations (Ig Vena®, Flebogamma®) were compared in terms of: (i) CMV-specific immunoglobulin G (IgG) antibody levels determined by enzyme-linked immunoabsorbent assay (ELISA), (ii) avidity index using a CMV IgG avidity enzyme immunoassay, (iii) immunoblot assay against CMV-specific antigens, and (iv) anti-CMV microneutralization assay. RESULTS Median CMV-specific IgG antibody concentration was similar in the 2 CMV-HIG preparations (Cytotect® CP 101.8 PEIU/ml, Cytogam® 112.5 PEIU/ml) but markedly lower in the IVIg preparations (13.5 PEIU/ml and 21.3 PEIU/ml). CMV binding avidity was virtually identical for both CMV-HIG products (~90%). Immunoblot assay showed consistently high binding of both CMV-HIG preparations against all antigenic CMV glycoproteins tested. Recognition of some CMV-specific antigens (IE1, CM2, and p65) was weaker for the 2 IVIg products. Median CMV neutralizing antibody titers were identical for both CMV-HIG preparations (1:256), and 4-fold lower (1:64) for the IVIg products. CMV IgG antibody concentration correlated with the CMV neutralization titer. CONCLUSIONS Compared to the polyspecific IVIg products tested here, CMV-HIG preparations showed higher CMV binding activity and wider recognition of tested CMV-specific glycoprotein antigens, with markedly higher neutralizing activity. There do not appear to be any relevant distinctions between the Cytotect® CP and Cytogam® CMV-HIG products in terms of functional activity.