Atypical hemolytic uremic syndrome (aHUS) is a rare genetic disease that causes the formation of clots in the blood capillaries (thrombotic microangiopathy, TMA) in any organ, but with greater impact on the kidney vasculature, leading to renal failure. It is caused by a malfunction of the complement system (CS), a group of blood proteins involved in the innate immune system. In the context of aHUS, the CS is chronically and uncontrollably activated, leading to excessive formation of the C5b-9 component on the cells of the blood vessels, simultaneously promoting clot formation. The CS can also be secondarily altered for other reasons, such as transplantation.

The Ex Vivo C5b-9 deposition test is an in vitro test that detects abnormal CS activity on cultured endothelial cells. Thanks to this test, we can determine if the affected person has TMA associated with CS alterations (whether aHUS or secondary TMA) and determine the degree of disease activity.

The Translational Immunology research group, together with the Nephrology and Transplants group from VHIR, the Pediatric Nephrology service, and the Hematology service from Vall d’Hebron Hospital, have joined forces to demonstrate the utility of the test. The study sample published in Kireports included adult and pediatric patients with aHUS and also patients with TMA associated with kidney and hematopoietic stem cell transplantation.

According to the study results, the Ex Vivo C5b-9 test is a useful tool not only for detecting CS activity in patients with aHUS and transplant-associated TMA but also for monitoring the activity level. This allows for a broader spectrum of patients to benefit from the test and also to personalize the medication plan based on the disease activity level.

Currently, the test is performed at VHIR as a research trial, but efforts are being made to automate the process and, therefore, implement it at a clinical level. Research lines are also being opened in other renal pathologies where the CS might also be involved.