Subclinical atypical haemolytic uremic syndrome relapse following discontinuation of eculizumab

Complement gene variant effect on relapse of complement-mediated thrombotic microangiopathy after eculizumab cessation

Eculizumab is effective for complement-mediated thrombotic microangiopathy (CM-TMA), also known as atypical hemolytic uremic syndrome. Although lifelong therapy had been suggested, discontinuation does not universally lead to relapse. Comprehensive data evaluating risk factors for recurrence following discontinuation are limited. Our aim was to systematically review available literature assessing the role of complement genetic variants in this setting. Reports on CM-TMA and eculizumab withdrawal published before 1 January 2021, were included. Key reasons for patient exclusion were no follow-up after drug withdrawal and patients lacking complement genetic testing. Two-hundred eighty patients from 40 publications were included. Median age was 28 years, and 25 patients had a known history of renal transplant. Complement genetic variants were identified in 60%, most commonly in CFH (n = 59) and MCP/CD46 (n = 38). Of patients with a complement gene variant, 51.3% had ≥1 likely pathogenic/pathogenic variant whereas the remaining had variants of uncertain significance (VUS). Overall relapse rate after therapy discontinuation was 29.6%. Relapse rate was highest among patients with CFH variants and MCP/CD46 variants in canonical splice regions. VUS (P < .001) and likely pathogenic/pathogenic variants (P < .001) were associated with increased relapse. Presence of a renal allograft (P = .009); decreasing age (P = .029); and detection of variants in CFH (P < .001), MCP/CD46 (P < .001), or C3 (P < .001) were all independently associated with relapse after eculizumab discontinuation. Eculizumab discontinuation is appropriate in specific patients with CM-TMA. Caution should be exerted when attempting such a strategy in patients with high risk of recurrence, including a subgroup of patients with MCP/CD46 variants.

An Ex Vivo Test of Complement Activation on Endothelium for Individualized Eculizumab Therapy in Hemolytic Uremic Syndrome

RATIONALE & OBJECTIVE

Although primary atypical hemolytic uremic syndrome (aHUS) is associated with abnormalities in complement genes and antibodies to complement factor H, the role of complement in secondary aHUS remains debatable. We evaluated the usefulness of an ex vivo test to: (1) detect complement activation within the endothelium in primary and secondary aHUS, (2) differentiate active disease from remission, (3) monitor the effectiveness of eculizumab therapy, and (4) identify relapses during eculizumab dosage tapering and after discontinuation of treatment.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

121 patients with primary aHUS and 28 with secondary aHUS. Serum samples were collected during acute episodes, following remission, and during eculizumab treatment and were assessed using a serum-induced ex vivo C5b-9 endothelial deposition test.

RESULTS

Serum-induced C5b-9 deposition on cultured microvascular endothelium was quantified by calculating the endothelial area covered by C5b-9 staining; values were expressed as percentage of C5b-9 deposits induced by a serum pool from healthy controls. Testing with adenosine diphosphate-activated endothelium demonstrated elevated C5b-9 deposits for all untreated patients with aHUS independent of disease activity, while testing with unstimulated endothelium demonstrated deposits only in active disease. Similar findings were observed in secondary aHUS. Serum-induced C5b-9 deposits on activated and unstimulated endothelium normalized during eculizumab treatment. 96% (22/23) of patients receiving eculizumab at extended 3- or 4-week dosing intervals demonstrated normal C5b-9 deposits on activated endothelium, despite most patients having CH50Eq (serum complement activity) > 20 UEq/mL, indicating that adequate complement control was achieved even with incomplete blockade of circulating C5. During eculizumab dosage tapering or after treatment discontinuation, all patients experiencing relapses versus only 6% (1/17) of those in stable remission had elevated C5b-9 deposits on unstimulated endothelium.

LIMITATIONS

The C5b-9 endothelial deposition test can be performed in only specialized laboratories. Findings on eculizumab dosage tapering need to be confirmed with longitudinal monitoring of C5b-9 deposition.

CONCLUSIONS

The C5b-9 endothelial deposition assay may represent an advance in our ability to monitor aHUS activity and individualize therapy.