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ORIGINAL RESEARCH article

Front. Neurol.

Sec. Multiple Sclerosis and Neuroimmunology

Volume 16 - 2025 | doi: 10.3389/fneur.2025.1523814

This article is part of the Research TopicLong- and Post-COVID Syndromes: Immune Mechanisms and Therapeutic StrategiesView all 7 articles

Does C1 Esterase Inhibitor Play a Role in Post COVID-19 Neurological Symptoms? A Randomized, Double-Blind, Placebo-Controlled, Crossover, Proof-of-Concept Study

Provisionally accepted
Isaac  R. MelamedIsaac R. Melamed1*Caley  BuckleyCaley Buckley2Mary  Ellen BaykoMary Ellen Bayko2Joe  Lynn WilliamsJoe Lynn Williams2Noga  Orr (Or-Geva), PhDNoga Orr (Or-Geva), PhD3
  • 1Other, Centennial, United States
  • 2IMMUNOe Research Center, Centennial, Colorado, United States
  • 3Department of Neurology and Neurological Sciences, School of Medicine, Stanford University, Stanford, California, United States

The final, formatted version of the article will be published soon.

Background: Many patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection experience neurologic changes post-infection, which has been hypothesized to be due to dysregulation in the infectious-immune axis that leads to a neuro-immune response. This immune dysfunction has been termed 'Alzheimer's of the Immune System' or AIS and there are several immune factors that may play a key role. These include, among others, complement activation due to low levels of C1-esterase inhibitor (C1-INH) and function, and a decrease in signaling of Toll-like receptor (TLR)-3. We propose that C1-INH replacement may upregulate the immune dysfunction, thereby improving neurological symptoms. Methods: In this randomized, double-blind, placebo-controlled, crossover, proof-of-concept study, adults experiencing SARS-CoV-2 post-viral fatigue syndrome for >4 weeks post-recovery from coronavirus disease 2019 (COVID-19) infection were randomized 1:1 to two arms: Arm 1 (C1-INH for 8 weeks, then placebo for 8 weeks) or to Arm 2 (placebo for 8 weeks, then C1-INH for 8 weeks). Patients were assessed for adult executive function, abnormal cognitive decline, depression (Beck Depression Inventory-II [BDI-II]), migraine, fatigue (Fatigue Severity Scale [FSS]) and pain (Shortform McGill Pain Questionnaire). Percent change in TLR signaling in response to zymosan was compared with controls at baseline, Week 8 and Week 16. Safety was assessed throughout. Results: At this interim analysis, 36 patients with SARS-CoV-2 post-viral fatigue syndrome had completed the two 8-week treatment periods. In Arm 1, trends toward improvements from baseline at Week 8 of C1-INH therapy were observed in BDI-II score (-8.7 points), mean FSS score (0.6 points), and mean McGill Pain Questionnaire score (-0.4 points). These improvements were either sustained or worsened at Week 16, following crossover to placebo. The outcomes in Arm 2 were compatible with those in Arm 1. Patients with SARS-CoV-2 post-viral fatigue syndrome had low levels of TLR-related signaling biomarkers compared with healthy controls. Conclusions: This proof-of-concept study demonstrates sustained dysregulation of the immune system after COVID-19 infection. Improvements in depression, fatigue, and pain were observed with C1-INH treatment in patients with SARS-CoV-2 post-viral fatigue syndrome, indicating C1-INH may be a potential therapeutic target.

Keywords: C1-INH, cognitive dysfunction, Complement Activation, Fatigue, Immune System, Neurological symptoms, SARS-CoV-2

Received: 06 Nov 2024; Accepted: 30 Sep 2025.

Copyright: © 2025 Melamed, Buckley, Bayko, Williams and Orr (Or-Geva), PhD. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Isaac R. Melamed, melamedi@immunoe.com

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