Isoagglutinin Reduction in Human Immunoglobulin Products by Donor Screening

INTRODUCTION Hemolysis is considered a class effect and a rare adverse event that can occur following therapy with human normal immunoglobulin for intravenous administration [i.e., intravenous immunoglobulin (IVIG)]. Anti-A/B isoagglutinins (also referred to as isohemagglutinins) originating from donor plasma are present in polyvalent immunoglobulin G (IgG) products and are considered a probable risk factor for hemolysis. We hypothesized that, by excluding plasma from donors with high isoagglutinin titers, the final IVIG product would have a meaningful reduction in anti-A/B isoagglutinin titers. METHODS A method for screening donor plasma for anti-A isoagglutinins using an automated indirect agglutination test (IAT) was developed. A cut-off for donor plasma exclusion was defined. Industry-scale donor plasma pools and final IVIG product were prepared according to the manufacturing process of Privigen(®) (CSL Behring, Berne, Switzerland; human 10% liquid IVIG). Anti-A/B isoagglutinin content in pooled plasma and final IVIG product was measured by IAT, direct agglutination test, and a flow cytometry-based assay [fluorescence-activated cell sorting (FACS) anti-A]. RESULTS Screening of plasma from 705 donors identified 48 (6.8%) donors with high anti-A isoagglutinin titers in plasma (IAT agglutination score ≥2+ in a 1:200 pre-dilution). Exclusion of plasma from these donors resulted in a one-titer-step reduction of anti-A isoagglutinin in pooled plasma, confirmed by a twofold anti-A isoagglutinin concentration reduction measured by FACS anti-A (1,352 vs. 2,467 µg/g IgG). When the same screening and exclusion were applied to industrial-scale plasma pools (resulting in the exclusion of plasma from 5% of donors), anti-A isoagglutinins were reduced by one titer step in the final IVIG product. Anti-B isoagglutinins were also reduced by one titer step, as many donors with high anti-A isoagglutinins also have high anti-B. CONCLUSION Reduction of anti-A/B isoagglutinin titers in IVIG products on an industrial scale is feasible through implementation of anti-A donor screening, which may reduce the risk of hemolysis following IVIG therapy.