Use of immunoglobulin replacement therapy in patients with secondary antibody deficiency in daily practice: a European expert Q&A-based review

IntroductionSecondary antibody deficiencies (SAD) are often a side effect of specific therapies that target B cells directly or affect the antibody response indirectly. Treatment of immunodeficiency by immunoglobulin replacement therapy (IgRT) is well established in primary antibody deficiencies, although the evidence for its use in SAD is less well established. To fill the gap and provide opinion and advice for daily practice, a group of experts met to discuss current issues and share best practical experience.Areas coveredA total of 16 questions were considered that covered use of a tailored approach, definition of severe infections, measurement of IgG levels and specific antibodies, indications for IgRT, dosage, monitoring, discontinuation of IgRT, and Covid-19.Expert opinionKey points for better management SID should include characterization of the immunological deficiency, determination of the severity and degree of impairment of antibody production, distinguish between primary and secondary deficiency, and design a tailored treatment protocol that should include dose, route, and frequency of Ig replacement. There remains the need to carry out well-designed clinical studies to develop clear guidelines for the use of IgRT in patients with SAD.