Pneumococcal antibody levels in children with PID receiving immunoglobulin.

OBJECTIVES Clinical data are lacking on optimal levels of specific antipneumococcal antibodies (PnPsAbs) in patients with primary immunodeficiency (PID) receiving intravenous immunoglobulin (IVIG) replacement. Objectives were to conduct a prospective multicenter study providing data on total immunoglobulin G (IgG) and peak/trough levels of PnPsAbs specifically targeting the 16 most prevalent pneumococcal serotypes in IVIG-treated children with PID; to compare trough PnPsAb levels with those measured in healthy adults and the IVIG product; and to evaluate PnPsAb protection correlates with thresholds based on World Health Organization. METHODS Patients received 7 consecutive IVIG infusions. Total IgG and PnPsAb levels were determined on plasma samples obtained before and after infusion. RESULTS Twenty-two children with PID were treated with IVIG (mean weekly dose: 0.10 g/kg). The mean trough and peak levels of total IgG were 7.77 and 13.93 g/L, respectively. Trough and peak geometric mean concentrations and distribution curves differed between serotypes and showed wide dispersion (0.17-7.96 µg/mL). In patients (89%-100%), antibodies against most serotypes reached trough levels ≥ 0.2 µg/mL, a threshold considered protective against invasive pneumococcal infection. For several serotypes, trough levels reached ≥ 1.0 to 1.3 µg/mL, the level found in adults. Trough geometric mean concentrations correlated well with the PnPsAb contents of the IVIG product. CONCLUSIONS In IVIG-treated children with PID, protective PnPsAb levels for most pathogenic serotypes were obtained. A correlation was observed between PnPsAb levels in patients and in the IVIG product. This offers the potential to improve infection prevention by adapting the IVIG product and dose according to epidemiology.