Anifrolumab, a potential treatment for ADA2 deficiency.

Adenosine deaminase 2 deficiency (DADA2) is an inborn error of immunity leading to systemic vasculitis, haematological manifestations, immune deficiency and/or autoimmunity. We report the case of a 26-year-old female with an initial diagnosis of systemic lupus erythematosus (SLE). However, atypical evolution patterns for SLE (hypogammaglobulinaemia, moderate B-cell lymphopenia, disappearance of anti-dsDNA) led to the identification of a homozygous class 5 missense variant of CECR1/ADA2, thus to a final diagnosis of DADA2. Strikingly, the patient was treated with anifrolumab (an anti-interferon alpha receptor 1 antibody) that rapidly induced clinical remission and significant corticosteroid tapering. Consistently, we show a lower type I interferon (IFN-I) score and a persistently low tumour necrosis factor α (TNFα) and IL-6 expression levels in whole blood cells of the patient during anifrolumab compared to anti-TNFα. Altogether, this case (1) illustrates the challenging diagnosis of DADA2 (SLE with hypogammaglobulinaemia) and (2) reinforces DADA2 as a disease at the border with type I interferonopathies. Besides, we report here, to our knowledge, the first description of a successful use of anifrolumab in DADA2, paving the way for further studies to validate this therapeutic approach.