Complement Biosensors Identify a Classical Pathway Stimulus in Complement-Mediated Hemolytic Uremic Syndrome

Area of Science:

• Immunology
• Hematology
• Biotechnology

Background:

• Complement-mediated hemolytic uremic syndrome (CM-HUS) is a serious thrombotic microangiopathy.
• Diagnosis often relies on identifying genetic variants or antibodies affecting complement regulation.
• Existing diagnostic methods may not fully explain all CM-HUS cases.

Purpose of the Study:

• To develop and validate novel cell-based complement biosensors for CM-HUS diagnosis.
• To investigate the role of complement pathways, particularly IgM-driven stimuli, in CM-HUS pathogenesis.
• To assess the utility of these biosensors in monitoring complement inhibitor therapies.

Main Methods:

• Engineered HEK293 cells lacking specific complement regulatory proteins (CD55, CD59, CD46) to create bioluminescent biosensors.
• Utilized a modified Ham (mHam) assay framework for ex vivo complement analysis.
• Employed specific complement pathway inhibitors to dissect pathway activation.

Main Results:

• The developed biosensors effectively diagnose CM-HUS and monitor complement blockade.
• Identified an IgM-driven classical pathway stimulus in CM-HUS patients, even during remission.
• This finding potentially explains ~50% of CM-HUS cases without alternative pathway variants.

Conclusions:

• Cell-based complement biosensors offer a sensitive diagnostic tool for CM-HUS.
• A subset of CM-HUS may result from a breakdown of IgM immunologic tolerance.
• These biosensors can aid in diagnosing CM-HUS and guiding complement inhibitor treatment.