To the Editor: Type I interferons (IFNs) are crucial in protecting against severe coronavirus disease 2019 (COVID-19), and a high percentage of patients with life-threatening COVID-19 either carry loss-of-function variants in the genes for type I IFNs or neutralizing autoantibodies (aAbs) against type I IFNs. 1, 2 This is in agreement with observations that the IFN response is important in limiting the early viremic phase of the disease, as well as for the subsequent resolution of inflammation. 3 Removal of aAbs through plasmapheresis has been suggested as a targeted treatment in severe COVID-19 with concomitant type I IFN aAbs. 1, 4

Autoimmune polyendocrine syndrome type 1 (APS1) is characterized by neutralizing aAbs to type I IFNs. 5 As a proof-of-concept, we present the case of a child with APS1 and aAbs to type I IFN who developed life-threatening COVID-19 and responded rapidly to treatment with plasmapheresis, intravenous immunoglobulin (IVIg), and high-dosage corticosteroids. The patient is an 8-year-old girl with APS1, verified by homozygous AIRE [c. 1616C> T (p. Pro539Leu)] mutations, typical clinical presentation including Addison disease, hypoparathyroidism, and vitiligo. She carried aAbs characteristic for APS1, among them high-titer aAbs against IFN-v and IL-22 (Fig 1, C). The patient presented with a cough, fever, and a positive PCR result for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Her clinical condition deteriorated, leading to transfer to the intensive care unit where she was put on a ventilator on day 7 from the onset of symptoms. Because the patient had high concentrations of aAbs to type I IFN before infection, we hypothesized that removal of these aAbs might improve her severe clinical manifestation of COVID-19. Therefore, daily plasmapheresis, followed by IVIg, was applied for 5 consecutive days (days 7-11). After 4 days on the ventilator, the patient could be extubated on day 10, and on day 22, the patient was discharged in good condition without any sequelae (Fig 1, A).