Relationship between IgG titers and opsonocytophagocytic activity of anti-pneumococcal antibodies after immunization with the 7-valent conjugate vaccine in allogeneic stem cell transplant.

The European Group for Blood and Marrow Transplantation has recently run a prospective, randomized trial comparing an early (3 months) vs a late (9 months) immunization program after allo-SCT with three doses of the conjugate 7-valent pneumococcal vaccine. This trial has shown that the response rate assessed 1 month after the third dose of conjugate vaccine was not inferior after an early vaccination vs a late vaccination. Part of the responder cohort of these patients (n=28) were chosen to assess the functionality of the anti-pneumococcal antibodies through an opsonophagocytic assay, 1 month after the third dose of conjugate vaccine. We have assessed the relationship between IgG titers measured by the pneumococcal ELISA and functional titers measured by opsonophagocytic assay of anti-pneumococcal antibodies. We found a significant correlation between titers for both assays, and conclude that the response to PCV7 after SCT induces functional antibodies.