Subcutaneous Immunoglobulin Substitutions in Previously Untreated (PUPs) and Treated Patients (PTPs) Result in Rapid Improvement of Total and Serum IgG Levels - a Novel Substitution Protocol for PUPs.
Authors: Königs Christoph , Dunsch Dominik , Linde Richard , Klingebiel Thomas , Kreuz Wolfhart 
Published: October 2019

Abstract
In primary immunodeficiencies the substitution of human immunoglobulins (Ig) is a major therapeutic concept. In Germany, Ig substitutions relied on various Ig formulations for intravenous (iv) substitutions. From December 2002 Ig preparations for subcutaneous (sc) home treatment were licensed in Germany.
In the Frankfurt cohort several PID PTPs decided to switch from intravenous therapy (ivIg) in our outpatient clinic to subcutaneous infusions (scIg) at home. For PUPs current protocols suggest an iv loading dose prior to scIg or daily scIg infusions for one week. In a Pediatric cohort, daily infusions seem not feasible, therefore a novel approach was developed to rapidly achieve sufficient IgG levels sparing an iv loading dose and daily infusions. In a longitudinal analysis, immune parameters were monitored for PTPs changed to scIg and PUPs starting on scIg primarily.
In a prospective study we report about 12 patients at the age of 14 to 58 years that have been switched to or were started on scIg. These are pediatric as well as adult patients. Their conditions include IgG2-IgA deficiencies, IgG3 deficiency, CVID, hypo- and agammaglobulinemia. Trough levels of total IgG, IgG subclasses, markers of infection and white blood cell counts were monitored under ivIg for at least one year prior to changing to scIg for PTPs retrospectively. Identical parameters have been monitored for 3 to 16 months since the start of scIg prospectively. Monitoring also included the history of any infections, general well-being and the body weight. For all patients the monthly scIg dose was identical to the respective ivIg dose at the time of switching therapy (200-400mg/kg bw). For PUPs a protocol of infusions on every other day was established changing to weekly intervals when sufficient IgG levels were achieved.
The scIg infusions were well tolerated by all patients besides initial local swelling and slight pain on the following day. Before starting home therapy, patients were trained for a period of 4 weeks and were able to safely perform infusions. For PTPs, after switching to scIg the IgG trough levels increased. Also serum IgG subclasses increased and reached physiological levels in all subclasses. Patients that did not have a sufficient amount of IgG of any subclasses under ivIg reached normal levels after scIg was initiated within a maximum of 6 weeks (average of 3,5 weeks). We saw a tendency to a decrease in the frequency of infections. For PUPs, patients with subclass deficiencies reached normal IgG levels in total and in the respective subclasses after 2 to 3 infusions. A PUP with CVID needed 4 infusions (1 week) to achieve sufficient levels to change to weekly infusions. In summary at the Frankfurt immunodeficiency outpatient clinic switching from ivIg to self-administered scIg was well tolerated. In all PTPs higher IgG trough levels were reached with the same amount of substituted IgG. Patients with subclass deficiencies under ivIg reached physiological levels after changing to scIg. For PUPs a novel protocol was established with infusions on every second day for one week to achieve sufficient IgG levels without iv loading dose. In comparison to established protocols, this novel approach spares daily visits and infusions. Additionally this prevents injections into still painful tissues, which is highly relevant especially for the treatment and adherence of pediatric patients.