Case Report: Tackling Complement Hyperactivation With Eculizumab in Atypical Hemolytic Uremic Syndrome Triggered by COVID-19

Abstract

Hemolytic uremic syndrome (HUS) is a rare life-threatening disease of unrestrained complement system dysregulation, microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure in genetically predisposed individuals. In this report, we describe two cases of SARS-CoV-2-associated HUS treated with eculizumab, a C5-blocking monoclonal antibody reported to be remarkably effective in the treatment of HUS. Detailed biochemical and genetic complement system analysis is reported, and the prompt clinical response after C5 pharmacological blockade is documented. Our report provides the rationale and supports the use of terminal complement pathway inhibition for the treatment of SARS-CoV-2-associated HUS.

Keywords: coronavirus disease 2019 (COVID-19); eculizumab; hemolytic uremic syndrome; severe acute respiratory syndrome coronavirus-2 (SARS-Cov-2); thrombotic microangiopathy.

FIGURE 1

Patient 1 (A) and Patient 2 (B) outcome from symptom onset to hospital discharge. Abbreviations: Thrombotic microangiopathy (TMA); Hemodialysis (HD).

FIGURE 2

Ex vivo C5b-9 deposition (A,B) and thrombus formation (C) on the cultured human microvascular endothelial cell (HMEC-1) line induced by serum of Patient 2 collected before (PRE infusion) and 10 days after (POST infusion) eculizumab treatment. (A,B). HMEC-1 resting (A) or activated with ADP (B) were incubated for 2 h with serum (diluted 1:2 with test medium, HBSS with 0.5% BSA) from the patient or with a control serum pool. At the end of incubation, the cells were washed, fixed, and stained with rabbit anti-human complement C5b-9 complex antibody followed by the FITC-conjugated secondary antibody. Fluorescence microscopy was used to view the fluorescent staining on the endothelial cell surface, and the HMEC-1 area covered by C5b-9 staining was calculated by automatic edge detection (ImageJ software) in 15 high-power fields. For each sample, the highest and lowest values were discarded, and the mean of the other 13 fields was calculated and values were expressed as the percentage of C5b-9 deposits induced by a pool of sera from 10 healthy controls run in parallel (reference 100%). Dashed lines indicate the upper and lower limit of normal range. (C) HMEC-1 were activated with ADP and exposed for 2 h to serum (diluted 1:2 with test medium, HBSS with 0.5% BSA) from the patient or with a control serum pool. Perfusion of heparinized whole blood (heparin 10 U/ml) from a healthy subject (added with the fluorescent dye mepacrine 10 µM, to label platelets) was then performed in a thermostatic flow chamber (37°C) in which one surface of the perfusion channel was a glass slide seeded with a monolayer of endothelial cells at a constant flow rate of 1,500 s⁻¹ (60 dynes/cm²). After 3-min perfusion was stopped, the slide with the endothelial cell monolayer was dehydrated and fixed in acetone for 20 min. The slides were examined under a confocal inverted laser microscope. Fifteen fields for each slide were systematically digitized along the surface, and the area covered by thrombi was quantified by ImageJ (NIH, Bethesda, MD) and expressed as pixel² per field analyzed. For each sample, the mean of 15 fields (excluding the lowest and the highest values) was calculated. Data are reported ±SE. *p < 0.0001 versus control serum pool; p < 0.0001 versus patient PRE infusion. Statistical analysis: ANOVA.