This prospective, open-label clinical trial (registered on clinicaltrials.gov: NCT no. 01218438) was conducted in accordance with the Declaration of Helsinki and the international standards of Good Clinical Practice. Patients were enrolled at 15 sites in the USA and Canada; informed consent was obtained from each patient prior to undergoing any study procedures.
The trial comprised four study periods: in period 1, patients received IGIV 10 % and in periods 2 to 4, they received IGSC 20 % (Supplementary material Figure S1). Period 1 was designed mainly to determine the area under the IgG concentration curve (AUC) following IV administration (AUCIV). During IGSC 20 % treatment, systemic exposure equivalent to previous IGIV 10 % treatment (as measured by the AUC of total IgG over time) was targeted. Therefore, IGSC 20 % doses were adjusted to compensate for the lower bioavailability of IgG-administered SC. The adjustment factor to calculate the IGSC 20 % dose in period 2 (145 %) was approximated from the PK data of available IGSC products [11, 12]. Next, based on the PK data collected from the first 18 patients treated with IGSC 20 % at 145 % of the IGIV 10 % dose in period 2, the IGSC 20 % dose that would (on average) provide equivalent IgG exposure as IGIV 10 % administration (“adjusted IGSC 20 % dose”) was determined to be 145 % of the IGIV 10 % dose. In period 3, patients were treated with IGSC 20 % at the “adjusted dose.” Since this adjusted dose represented the average dose-response of only 18 patients, the possibility of over- or under-dosing could not be excluded. Thus, for each patient, an individually adapted (individualized) dose of IGSC 20 % was determined by comparing the patient trough level (equivalent to the steady-state serum IgG level) attained in period 3 to the expected trough level increase calculated from the PK data of periods 1 and 2. During period 4, the patients were infused with IGSC 20 % at this dose for 40 weeks.
Patients aged 2 years and older diagnosed with PIDD involving defective antibody production and requiring IgG replacement as defined by the International Union of Immunological Societies (IUIS) Scientific Committee 2011  and by diagnostic criteria according to Conley et al.  were eligible for enrollment in the study. Inclusion criteria also required that patients had received a stable dose (IV or SC) of IgG equivalent to at least 0.3 g/kg BW/4 weeks and not higher than 1 g/kg BW/4 weeks for a minimum of 12 weeks prior to first treatment and had serum IgG trough levels >5 g/l at screening. Patients were excluded from the study if they had a history of hepatitis B or C or a positive human immunodeficiency virus test; if they had persistent abnormal alanine aminotransferase and aspartate aminotransferase values >2.5 times the upper limit of normal for the testing laboratory, creatinine clearance value <60 % of normal according to their age and gender, or severe neutropenia or protein loss at screening; or if they had been diagnosed with a malignancy, were receiving anticoagulation therapy, or had a history of thrombotic episodes. Patients were also excluded if they were receiving antibiotics, had an active infection at the time of screening, or had had an acute serious bacterial infection within 3 months prior to screening. A complete list of eligibility criteria is available in the Supplementary material.
IGSC 20 % is a liquid concentrate of functionally intact, aggregate-free IgG derived from human plasma. The production of IGSC 20 % follows the same manufacturing processes as IGI, 10 % solution (marketed under the Baxalta, now part of Shire trade-name GAMMAGARD LIQUID® in the US and Kiovig® in the EU) except for ultra/diafiltration and final formulation at 20 % (w/v) protein concentration. The manufacturing process of IGSC 20 % includes three dedicated virus inactivation and reduction steps: solvent/detergent (S/D) treatment , nanofiltration (35 nm) [15, 16], and low pH incubation with elevated temperature [17, 18]. Similar to IGI, 10 %, IGSC 20 % contains glycine as stabilizer to minimize IgG dimerization. The final IGSC 20 % product has a viscosity of 14.4 mPa/s, an osmolality of 280–292 mOsm/kg and contains trace amounts of IgA (average concentration 80 μg/ml). Each lot of IGSC 20 % is monitored for procoagulant activity using a thrombin generation assay to ensure that the final container is free of procoagulants.
Patients received IGIV 10 % at the monthly equivalent dose used prior to entering the study (required dose range 0.3-1.0 g/kg BW/4 weeks) every 3 or 4 weeks at the clinical site. IGSC 20 % was administered once a week; doses used in the respective study periods are described in the “Study design” section. IGSC 20 % was infused using an electromechanical syringe-driver pump (CME T34L, Caesarea Medical Electronics) and high-flow, 24-gauge low-resistance needles (RMS Medical Products). The needle sets used in the trial ranged from 6 to 12 mm in length at the discretion of the investigator; there was no specified needle length for infusion. Infusion rates were increased incrementally: the initial two infusions were to be started at 10 ml/h/infusion site and could be increased to a maximum of 20 ml/h/infusion site. Subsequent infusions could begin at the maximum tolerated infusion rate for the initial infusions, and as tolerated, the infusion rate was to be increased to a maximum of 60 ml/h/site. For patients with a body weight of 40 kg or above, an infusion volume of up to 60 ml was to be administered per infusion site if well tolerated. For patients with a body weight below 40 kg, it was recommended to limit infusion volume to 20 ml per site for the initial two infusions. Volumes could then be increased to a maximum of 60 ml per site as tolerated. Multiple infusion sites could be used simultaneously. Infusion sites were to be rotated to avoid any single infusion site being used repeatedly within a short time interval. Infusion of IGSC 20 % at home was possible after sufficient training of the patient/caregiver or with assistance of a healthcare professional.
Efficacy was evaluated based on the analysis of serious acute bacterial infections, all infections, and IgG levels. Serious bacterial infections, such as bacteremia/sepsis, bacterial meningitis, osteomyelitis/septic arthritis, bacterial pneumonia, and visceral abscesses caused by a recognized bacterial pathogen were diagnosed according to the Diagnostic Criteria for Serious Infection Types in the FDA Guidance for Industry, June 2008 . The primary efficacy assessment was the annualized rate of validated acute serious bacterial infections (VASBIs, defined as RVASBI = mean number of VASBI/patient/year). Efficacy was also evaluated by the annualized rate of all infections (i.e., VASBIs and all other events clinically assessed as infections), as well as the number of fever episodes (body temperature ≥ 38 °C), the number of days with fever, the number of days missed from school/work or to perform normal daily activities due to illness/infection, the number of admissions to a hospital as an in-patient, and the number of days as a stationary patient in the hospital, as well as urgent or unscheduled physician visits due to illness/infection (apart from the regular investigator/study site visits scheduled every 8–12 weeks within the study).
Safety was evaluated through clinical and laboratory assessments. Safety data were collected throughout the study. The AEs that occurred during the infusions at the site (every 8–12 weeks) were recorded by the investigator. All investigators were specifically trained on symptoms of potential AEs. All patients received an eDiary tablet to continuously record home treatments, AEs, and additional information as they occurred. The investigator provided guidance for the patient/caregiver regarding identification and documentation of local and systemic AEs, including signs of hemolysis such as fever, chills, back pain, fatigue, and dark urine. All patients were instructed to inform the investigator/site immediately in case of such an event. In addition, the patient was contacted by the investigator within 3–5 days after each infusion, either at the study site or at their home for follow-up to ensure appropriate documentation of AEs. The investigators reviewed patients’ eDiary entries at every site visit. All AEs were assessed by the investigator using comprehensive data collection systems—including the patient’s eDiary—for seriousness, severity, temporal association, and possible causal relatedness to the investigational product.
Monitoring for potential cases of hemolysis comprised routine hematology screening and hemolysis screening as recommended by the FDA Guidance for Industry (June 2008 ). If a decrease of hemoglobin ≥2 g/dl was measured during either the hematology or hemolysis screening, the assessments to monitor for potential cases of hemolysis were to be performed within 48–72 h of being informed of the hemoglobin level, unless there was a clear alternative explanation. These assessments included direct antiglobin (Coomb’s) test, plasma-free hemoglobin, reticulocyte count, lactate dehydrogenase (LDH), serum haptoglobin, and urine hemosiderin.
Determination of total serum IgG concentration was performed at a central laboratory using a validated enzyme-linked immunosorbent assay (ELISA)-based method. PK assessments were performed over a specific dosing interval: in period 1 between infusions 10 and 11, for patients aged 12 years and older; in period 2 between infusions 9 and 10, for the first 18 patients aged 12 years and older; and for all patients in period 4 between infusions 17 and 18 (Supplementary material Figure S1). In period 2 and 4, samples were collected preinfusion and on days 1, 3, 5, and 7 after IGSC 20 % administration in patients aged 12 years and older. In patients aged 2–11 years, samples to determine the AUC over a dosing interval (AUC0−τ) after IGSC 20 % administration were only drawn preinfusion and on days 3 and 7 in order to limit the number of blood draws.
Total serum IgG trough levels were assessed immediately prior to each IGIV 10 % infusion in period 1 and during IGSC 20 % treatment: prior to infusion 1, twice each in periods 2 and 3, four times during period 4, and at the end-of-study visit.
Efficacy was assessed by the mean number of VASBIs per patient per year (RVASBI). Assuming RVASBI = 0.6 and a one-sided test and a Type I error = 0.01, a sample size of 59 patients would have in excess of 85 % power to test the null hypothesis that RVASBI ≥1.0 against the alternative hypothesis RVASBI <1.0. RVASBI and 99 % upper confidence limit (CI) were calculated using a Poisson model accounting for the length of the observation periods per patient.
The AUC between adjacent infusions was calculated by the trapezoidal rule. To allow for comparisons between periods 1, 2, and 4, AUC0−τ was standardized for the infusion intervals (3 or 4 weeks vs. 1 week = AUC0−τ;h;). The bioavailability of IGSC 20 % relative to IGIV 10 % was estimated from the ratio of AUC0−τ;h in period 4 (SC treatment at an individualized dose, once per week) over AUC0−τ;h in period 1 (IV treatment every 3 or 4 weeks) standardized to 1 week.
Measures of Patient Experience
Treatment burden related to Ig therapy was evaluated with the Life Quality Index questionnaire (LQI) for the age group 2 to 12 years (observer: parent) and the age group 13 years and older (observer: patient) [20, 21]. The LQI covers four domains: treatment interference, therapy-related problems, therapy settings, and treatment costs. While data related to treatment cost LQI domain were collected, they were not included in the analysis as patients received free treatment during the study. Treatment satisfaction was surveyed in age groups from 2 to 12 years (observer: parent) and 13 years and older (observer: patient) using the Treatment Satisfaction Questionnaire for Medication (TSQM-9) . Evaluations were performed at baseline, at the end of periods 1 and 3 and during the end-of-study visit (or early termination visit). Score changes between end of period 1 and end of period 3 or end of study visit were analyzed. In both the LQI and TSQM-9, higher scores indicated higher satisfaction.