Hypogammaglobulinemia after Rituximab Treatment in an Italian Real-Life Cohort of Iim

ABSTRACT

Background. Rituximab (RTX) is a chimeric monoclonal antibody that binds the CD20 molecule on the surface of B cells and leads to B cell depletion. RTX is recommended by the European League Against Rheumatism (EULAR) as off-label in patients affected by idiopathic inflammatory myopathies (IIM). The real-world experience has shown that hypogammaglobulinemia occurring early after anti-CD20 treatment can be multifactorial (active disease, effect of other drugs) and usually transient, with a minimal increase in the risk of infections. The present study aimed to analyse the differences in the rate of RTX-associated hypogammaglobulinemia in a cohort of IIM patients in clinical practice, as well as the onset of major infections and its correlation with hypogammaglobulinemia. Methods. Patients followed at Rheumatology Unit of Siena University Hospital from January 2020 to September 2021 were retrospectively enrolled. Inclusion criteria were as follows fulfilment of disease-specific classification criteria 2017 EULAR criteria and /or Peter and Bohan criteria for dermatomyositis (DM) and polymyositis (PM), positivity of anti-synthetase antibody and typical clinical features for anti-synthetase syndrome (ASS) and the measurement of serum Ig levels at the time of RTX administration (maximum 2 weeks before) (T0) and 6 (T1) to 12 (T2) months later, consistently with previous studies. Ig serum levels, measured by standard nephelometry (normal ranges IgG 700-1600 mg/dL, IgM 40-240 mg/dL, IgA 70-400 mg/dL) were assessed as part of routine clinical care. Hypogammaglobulinemia was defined as moderate (serum IgG <600 mg/dL) and severe (IgG <400 mg/dL), as previously reported. Results. Seven patients (mean+/-SD, 57.3+/-19.7 years;7 female) were enrolled. Three of them had diagnosis of DM, three ASS and one PM. Two patients showed MDA5-positivity, two JO1-positivity, one TIF1-gamma-positivity, one PL7-positivity and the other one PM/Scl-positivity. All patients had at least two organs involved, and 4 out of 7 (57%) suffered from interstitial lung disease. Before starting RTX treatment, three and four patients underwent at least one and two synthetic immunosuppressants. All patients underwent low dosage of corticosteroids, and four patients underwent concomitant synthetic immunosuppressants (2 hydroxychloroquine and 2 MTX). IgG concentrations were statically lower at T2 compared to those at baseline (p=0.0391). None of them showed severe hypogammaglobulinemia. Similarly, IgM concentration significantly decreased at T2 compared to those at baseline (p=0.0078). Two patients showed major infections and two patients had paucisymptomatic COVID-19 (one of them had twice). Corticosteroids dosages were inversely correlated with IgG T2 concentrations (p=0.040, r=-0.919). Conclusion. Hypogammaglobulinemia following RTX is uncommon in IIM and is more likely in patients with high glucocorticoids, immunosuppressants and CYC exposure. IgG monitoring at least 6 months after RTX treatment may be useful in stratifying patients to identify those who require closer monitoring. These results shine a spotlight for increased awareness of the role of immunoglobulin measurement before maintenance doses of RTX.