Effect of Immunosuppressive Therapy on the Occurrence of Atypical Hemolytic Uremic Syndrome in Renal Transplant Recipients

Atypical Hemolytic-Uremic Syndrome: Genetic Basis, Clinical Manifestations, and a Multidisciplinary Approach to Management

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy (TMA) defined by the triad of hemolytic anemia, thrombocytopenia, and acute kidney injury. Microthrombi develop in the glomerular capillaries secondary to endothelial damage and exert shear stress on red blood cells, consume platelets, and contribute to renal dysfunction and failure. Per current understanding of pathophysiology, HUS is classified into infectious, secondary, and atypical disease. The most common etiology is infectious sequelae of Shiga toxin-producing Escherichia coli (STEC); other causative organisms include shigella and salmonella. Secondary HUS arises from cancer, chemotherapy, solid organ and hematopoietic stem cell transplant, pregnancy, or autoimmune disorders. Primary atypical hemolytic-uremic syndrome (aHUS) is associated with genetic mutations in complement and complement regulatory proteins. Under physiologic conditions, complement regulators keep the alternative complement system continuously active at low levels. In times of inflammation, mutations in complement-related proteins lead to uncontrolled complement activity. The hyperactive inflammatory state leads to glomerular endothelial damage, activation of the coagulation cascade, and TMA findings. Atypical hemolytic-uremic syndrome is a rare disorder with a prevalence of 2.21 to 9.4 per million people aged 20 years or younger; children between the ages of 0 and 4 are most affected. Multidisciplinary health care is necessary for timely management of its extra-renal manifestations. These include vascular disease of the heart, brain, and skin, pulmonary hypertension and hemorrhage, and pregnancy complications. Adequate screening is required to monitor for sequelae. First-line treatment is the monoclonal antibody eculizumab, but several organ systems may require specialized interventions and coordination of care with sub-specialists.

Interventions for atypical haemolytic uraemic syndrome

BACKGROUND

Atypical haemolytic uraemic syndrome (aHUS) is a rare disorder characterised by thrombocytopenia, microangiopathic haemolytic anaemia, and acute kidney injury. The condition is primarily caused by inherited or acquired dysregulation of complement regulatory proteins with ~40% of those affected aged < 18 years. Historically, kidney failure and death were common outcomes, however, improved understanding of the condition has led to discovery of novel therapies.

OBJECTIVES

To evaluate the benefits and harms of interventions for aHUS.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies for randomised controlled studies (RCTs) up to 3 September 2020 using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov. MEDLINE(OVID) 1946 to 27 July 2020 and EMBASE (OVID) 1974 to 27 July 2020 were searched for non-RCTs.

SELECTION CRITERIA

All randomised and non-randomised clinical trials comparing an intervention with placebo, an intervention with supportive therapy, or two or more interventions for aHUS were included. Given the rare nature of the condition in question, prospective single-arm studies of any intervention for aHUS were also included.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted pre-specified data from eligible studies and evaluated risk of bias using a newly developed tool based on existing Cochrane criteria. As statistical meta-analysis was not appropriate, qualitative analysis of data was then performed.

MAIN RESULTS

We included five single-arm studies, all of which evaluated terminal complement inhibition for the treatment of aHUS. Four studies evaluated the short-acting C5 inhibitor eculizumab and one study evaluated the longer-acting C5 inhibitor ravulizumab. All included studies within the review were of non-randomised, single-arm design. Thus, risk of bias is high, and it is challenging to draw firm conclusions from this low-quality evidence. One hundred patients were included within three primary studies evaluating eculizumab, with further data reported from 37 patients in a secondary study. Fifty-eight patients were included in the ravulizumab study. After 26 weeks of eculizumab therapy there were no deaths and a 70% reduction in the number of patients requiring dialysis. Complete thrombotic microangiopathic (TMA) response was observed in 60% of patients at 26 weeks and 65% at two years. After 26 weeks of ravulizumab therapy four patients had died (7%) and complete TMA response was observed in 54% of patients. Substantial improvements were seen in estimated glomerular filtration rate and health-related quality of life in both eculizumab and ravulizumab studies. Serious adverse events occurred in 42% of patients, and meningococcal infection occurred in two patients, both treated with eculizumab.

AUTHORS' CONCLUSIONS

When compared with historical data, terminal complement inhibition appears to offer favourable outcomes in patients with aHUS, based upon very low-quality evidence drawn from five single-arm studies. It is unlikely that an RCT will be conducted in aHUS and therefore careful consideration of future single-arm data as well as longer term follow-up data will be required to better understand treatment duration, adverse outcomes and risk of disease recurrence associated with terminal complement inhibition.