Efficacy, Safety, Tolerability, and Serum IgG Trough Levels of Hyaluronidase-Facilitated Subcutaneous Immunoglobulin 10% in US Pediatric Patients with Primary Immunodeficiency Diseases

Purpose: To investigate the efficacy, safety, tolerability, and serum IgG trough levels of hyaluronidase-facilitated subcutaneous immunoglobulin (fSCIG) 10% in US pediatric patients with primary immunodeficiency diseases (PIDDs). Methods: This phase 3, open-label, prospective study (NCT03277313) was conducted at 17 US centers. Eligible patients aged 2 to < 16 years had PIDDs and had received immunoglobulin G (IgG) at a consistent dose for ≥ 3 months before screening. Participants received fSCIG 10% via dose ramp-up for up to 6 weeks (Epoch 1), then every 3–4 weeks for ≤ 3 years (Epoch 2). The primary endpoint was the rate of acute serious bacterial infections (ASBIs). Results: Data were provided by 44 participants for Epoch 1 (mean ± SD age: 9.0 ± 3.6 years) and 43 (97.7%) for Epoch 2; 34 (77.3%) completed the study. Two ASBIs (both bacterial pneumonia) were reported in one participant with specific antibody deficiency. The mean rate of ASBIs was 0.04 events/participant-year (99% upper confidence interval limit: 0.20), significantly lower than the regulatory-defined threshold of 1.0 (p < 0.001). The mean rate of all infections was 3.12 events/participant-year. Stable mean serum IgG trough levels were maintained during Epoch 2 (10.4, 9.2, and 9.2 g/L at Months 0, 6, and 12, respectively). Most related treatment-emergent adverse events were mild or moderate in severity. No participant developed anti-recombinant human hyaluronidase neutralizing antibodies; 1/44 participants (2.3%) developed binding antibodies. Conclusion: fSCIG 10% effectively prevented ASBIs in pediatric patients with PIDDs, with a favorable safety profile consistent with previous clinical studies.