Comparison of Antibody Concentrations and Protective Activity of Respiratory Syncytial Virus Immune Globulin and Conventional Immune Globulin

Relative to conventional immune globulins (IG, 13 lots), IGs prepared from donors with high activity by microneutralization assay to respiratory syncytial virus (RSVIG, 8 lots) had significantly higher neutralizing antibodies to 6 RSV strains (mean enrichment, 5.2-fold; range, 2.6- to 10.0-fold). In contrast, IgG antibody concentrations to whole RSV, fusion protein, or glycoproteins of A and B strains were similar in RSVIG and IG. Treatment of cotton rats with RSVIG at 0.5 g/kg 24 h before RSV challenge reduced RSV by 99% in the lungs (P < .001). RSVIG at 5.0 g/kg reduced RSV by 99% in the nose. IG at 5.0 g/kg had efficacy similar to that of RSVIG at 0.5 g/kg. Serum plaque-reduction neutralization titers of 1/390 resulted in 99% reduction of lung RSV and titers of 1/3500 resulted in 99% reduction in nose RSV. Relative to IG, RSVIG is enriched selectively in RSV neutralizing antibodies and has approximately 10 times greater protective activity in cotton rats.