Benjamin L. Laskin

Abnormalities in the alternative pathway of complement in children with hematopoietic stem cell transplant-associated thrombotic microangiopathy

Hematopoietic stem cell transplant (HSCT)-associated thrombotic microangiopathy (TMA) is a complication that occurs in 25% to 35% of HSCT recipients and shares histomorphologic similarities with hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). The hallmark of all thrombotic microangiopathies is vascular endothelial cell injury of various origins, resulting in microangiopathic hemolytic anemia, platelet consumption, fibrin deposition in the microcirculation, and tissue damage. Although significant advances have been made in understanding the pathogenesis of other thrombotic microangiopathies, post-HSCT TMA remains poorly understood. We report an analysis of the complement alternative pathway, which has recently been linked to the pathogenesis of both the Shiga toxin mediated and the atypical forms of HUS, with a focus on genetic variations in the complement Factor H (CFH) gene cluster and CFH autoantibodies in six children with post-HSCT TMA. We identified a high prevalence of deletions in CFH-related genes 3 and 1 (delCFHR3-CFHR1) and CFH autoantibodies in these patients with HSCT-TMA. Conversely, CFH autoantibodies were not detected in 18 children undergoing HSCT who did not develop TMA. Our observations suggest that complement alternative pathway dysregulation may be involved in the pathogenesis of post-HSCT TMA. These findings shed light on a novel mechanism of endothelial injury in transplant-TMA and may therefore guide the development of targeted treatment interventions.

Eculizumab Therapy in Children with Severe Hematopoietic Stem Cell Transplantation–Associated Thrombotic Microangiopathy

We recently observed that dysregulation of the complement system may be involved in the pathogenesis of hematopoietic stem cell transplantation-associated thrombotic microangiopathy (HSCT-TMA). These findings suggest that the complement inhibitor eculizumab could be a therapeutic option for this severe HSCT complication with high mortality. However, the efficacy of eculizumab in children with HSCT-TMA and its dosing requirements are not known. We treated 6 children with severe HSCT-TMA using eculizumab and adjusted the dose to achieve a therapeutic level >99 μg/mL. HSCT-TMA resolved over time in 4 of 6 children after achieving therapeutic eculizumab levels and complete complement blockade, as measured by low total hemolytic complement activity (CH50). To achieve therapeutic drug levels and a clinical response, children with HSCT-TMA required higher doses or more frequent eculizumab infusions than currently recommended for children with atypical hemolytic uremic syndrome. Two critically ill patients failed to reach therapeutic eculizumab levels, even after dose escalation, and subsequently died. Our data indicate that eculizumab may be a therapeutic option for HSCT-TMA, but HSCT patients appear to require higher medication dosing than recommended for other conditions. We also observed that a CH50 level ≤ 4 complement activity enzyme units correlated with therapeutic eculizumab levels and clinical response, and therefore CH50 may be useful to guide eculizumab dosing in HSCT patients as drug level monitoring is not readily available.

Diagnostic and risk criteria for HSCT-associated thrombotic microangiopathy: a study in children and young adults

Transplant-associated thrombotic microangiopathy (TMA) leads to generalized endothelial dysfunction that can progress to multiorgan injury, and severe cases are associated with poor outcomes after hematopoietic stem cell transplantation (HSCT). Identifying patients at highest risk for severe disease is challenging. We prospectively evaluated 100 consecutive HSCT recipients to determine the incidence of moderate and severe TMA and factors associated with poor overall outcomes. Thirty-nine subjects (39%) met previously published criteria for TMA. Subjects with TMA had a significantly higher nonrelapse mortality (43.6% vs 7.8%, P < .0001) at 1 year post-HSCT compared with those without TMA. Elevated lactate dehydrogenase, proteinuria on routine urinalysis, and hypertension were the earliest markers of TMA. Proteinuria (>30 mg/dL) and evidence of terminal complement activation (elevated sC5b-9) in the blood at the time of TMA diagnosis were associated with very poor survival (<20% at 1 year), whereas all TMA subjects without proteinuria and a normal sC5b-9 serum concentration survived (P < .01). Based on these prospective observations, we conclude that severe TMA occurred in 18% of HSCT recipients in our cohort and propose an algorithm to identify the highest-risk patients who might benefit from prompt clinical interventions.

Mortality Risk Among Children Initially Treated With Dialysis for End-Stage Kidney Disease, 1990–2010

IMPORTANCE Most children with end-stage kidney disease (ESKD) are treated with dialysis prior to transplant. It is not known whether their outcomes have changed in recent years. OBJECTIVE To determine if all-cause, cardiovascular, and infection-related mortality rates for children and adolescents beginning dialysis improved between 1990 and 2010. DESIGN, SETTING, AND PARTICIPANTS Retrospective cohort study of patients younger than 21 years initially treated with dialysis for ESKD, recorded in the United States Renal Data System between 1990 and 2010. Children with a prior kidney transplant were excluded. We used Cox proportional hazard models to estimate the hazard ratios (HRs) for mortality associated with a 5-year increment in year of ESKD treatment initiation. Primary analyses censored observation at kidney transplant. MAIN OUTCOMES AND MEASURES All-cause, cardiovascular, and infection-related mortality. RESULTS A total of 3450 children younger than 5 years and 19,951 children 5 years or older started dialysis from 1990-2010. Of those younger than 5 years, 705 died during dialysis treatment (98.8/1000 person-years); mortality rates were 112.2 and 83.4 per 1000 person-years in those initiating dialysis in 1990-1994 and 2005-2010, respectively. Of those 5 years and older at treatment initiation, 2270 died during dialysis treatment (38.6/1000 person-years). Their mortality rates were 44.6 and 25.9 per 1000 person-years in those initiating dialysis in 1990-1994 and 2005-2010, respectively. Each 5-year increment in calendar year of dialysis initiation was associated with an adjusted HR of 0.80 (95% CI, 0.75-0.85) among children younger than 5 years at initiation and an HR of 0.88 (95% CI, 0.85-0.92) among those 5 years and older. RESULTS A total of 23,401 children and adolescents who initiated ESKD treatment with dialysis at younger than 21 years between 1990 and 2010 were identified. Crude mortality rates during dialysis treatment were higher among children younger than 5 years at the start of dialysis compared with those who were 5 years and older. Mortality rates for both children and adolescents being treated for ESKD with dialysis decreased significantly between 1990 and 2010. CONCLUSIONS AND RELEVANCE In the United States, there was a substantial decrease in mortality rates over time among children and adolescents initiating ESKD treatment with dialysis between 1990 and 2010. Further research is needed to determine the specific factors responsible for this decrease.

A new paradigm: Diagnosis and management of HSCT-associated thrombotic microangiopathy as multi-system endothelial injury

Hematopoietic stem cell transplantation (HSCT)-associated thrombotic microangiopathy (TA-TMA) is now a well-recognized and potentially severe complication of HSCT that carries a high risk of death. In those who survive, TA-TMA may be associated with long-term morbidity and chronic organ injury. Recently, there have been new insights into the incidence, pathophysiology, and management of TA-TMA. Specifically, TA-TMA can manifest as a multi-system disease occurring after various triggers of small vessel endothelial injury, leading to subsequent tissue damage in different organs. While the kidney is most commonly affected, TA-TMA involving organs such as the lung, bowel, heart, and brain is now known to have specific clinical presentations. We now review the most up-to-date research on TA-TMA, focusing on the pathogenesis of endothelial injury, the diagnosis of TA-TMA affecting the kidney and other organs, and new clinical approaches to the management of this complication after HSCT.

Blood, and Not Urine, BK Viral Load Predicts Renal Outcome in Children with Hemorrhagic Cystitis following Hematopoietic Stem Cell Transplantation

BK virus is a significant cause of hemorrhagic cystitis after hematopoietic stem cell transplantation (HSCT). However, its role in nephropathy post-HSCT is less studied. We retrospectively evaluated clinical outcomes in pediatric HSCT patients with hemorrhagic cystitis. Although most of these patients had very high urine BK viral loads (viruria), patients with higher BK plasma loads (viremia) had significant renal dysfunction, a worse clinical course, and decreased survival. Patients with a peak plasma BK viral load of >10,000 copies/mL (high viremia) were more likely to need dialysis and aggressive treatment for hemorrhagic cystitis compared to patients with ≤ 10,000 copies/mL (low viremia). Conversely, most patients with low viremia had only transient elevations in creatinine, and less severe hemorrhagic cystitis that resolved with supportive therapy. Overall survival (OS) at 1 year post-HSCT was 89% in the low viremia group and 48% in the high viremia group. We conclude that the degree of BK viremia, and not viruria, may predict renal, urologic, and overall outcome in the post-HSCT population.

The genetic fingerprint of susceptibility for transplant associated thrombotic microangiopathy

Transplant-associated thrombotic microangiopathy (TA-TMA) occurs frequently after hematopoietic stem cell transplantation (HSCT) and can lead to significant morbidity and mortality. There are no data addressing individual susceptibility to TA-TMA. We performed a hypothesis-driven analysis of 17 candidate genes known to play a role in complement activation as part of a prospective study of TMA in HSCT recipients. We examined the functional significance of gene variants by using gene expression profiling. Among 77 patients undergoing genetic testing, 34 had TMA. Sixty-five percent of patients with TMA had genetic variants in at least one gene compared with 9% of patients without TMA (P < .0001). Gene variants were increased in patients of all races with TMA, but nonwhites had more variants than whites (2.5 [range, 0-7] vs 0 [range, 0-2]; P < .0001). Variants in ≥3 genes were identified only in nonwhites with TMA and were associated with high mortality (71%). RNA sequencing analysis of pretransplantation samples showed upregulation of multiple complement pathways in patients with TMA who had gene variants, including variants predicted as possibly benign by computer algorithm, compared with those without TMA and without gene variants. Our data reveal important differences in genetic susceptibility to HSCT-associated TMA based on recipient genotype. These data will allow prospective risk assessment and intervention to prevent TMA in highly susceptible transplant recipients. Our findings may explain, at least in part, racial disparities previously reported in transplant recipients and may guide treatment strategies to improve outcomes.

Early clinical indicators of transplant-associated thrombotic microangiopathy in pediatric neuroblastoma patients undergoing auto-SCT.

Patients undergoing auto-SCT for neuroblastoma present a unique population to study transplant-associated thrombotic microangiopathy (TA-TMA), due to standardized chemotherapy and later exposure to radiation and cis-retinoic acid (cis-RA). We retrospectively analyzed 20 patients after auto-SCT to evaluate early clinical indicators of TA-TMA. A total of 6 patients developing TA-TMA (30% prevalence) were compared with 14 controls. Four of six patients were diagnosed with TA-TMA by 25 days after auto-SCT. Compared with controls, TA-TMA patients had higher average systolic and diastolic blood pressure levels during high-dose chemotherapy and developed hypertension by day 13 after auto-SCT. Proteinuria was a significant marker for TA-TMA, whereas blood and platelet transfusion requirements were not. Serum creatinine did not differ between groups post transplant. However, patients with TA-TMA had a 60% decrease in renal function from baseline by nuclear glomerular filtration rate, compared with a 25% decrease in those without TA-TMA (P=0.001). There was no TA-TMA-related mortality. Significant complications included end-stage renal disease (n=1) and polyserositis (n=3). Patients with TA-TMA were unable to complete cis-RA therapy after auto-SCT. We suggest that careful attention to blood pressure and urinalysis will assist in the early diagnosis of TA-TMA, whereas serum creatinine seems to be an insensitive marker for this condition.

Renal arteriolar C4d deposition: a novel characteristic of hematopoietic stem cell transplantation-associated thrombotic microangiopathy.

Background The mechanism of kidney injury in hematopoietic stem cell transplantation (HSCT)–associated thrombotic microangiopathy (TA-TMA) is not completely understood. Renal C4d staining is a marker of classic complement activation and endothelial injury and has been described in preliminary reports of HSCT recipients with TA-TMA. Our objective was to evaluate complement in the pathogenesis of small vessel injury in children receiving HSCT. We hypothesized that kidney tissue from children with TA-TMA would more frequently show C4d deposition compared with HSCT recipients without histologic TA-TMA. Methods We reviewed kidney specimens (biopsy or autopsy) from children who had undergone HSCT at a single center. Using histologic criteria alone, subjects were divided into TA-TMA (n=8) and non–TA-TMA (control) groups (n=12). C4d staining was performed by immunohistochemistry and evaluated on arterioles, peritubular capillaries, glomeruli, and tubular basement membranes. Results Diffuse or focal renal arteriolar C4d staining was more common in subjects with histologic TA-TMA (75%) compared with controls (8%). Rare peritubular capillary C4d staining was present in 50% of TA-TMA samples and was absent in controls. Glomerular C4d staining was seen at a similar frequency in cases and controls, whereas tubular basement membrane staining was less frequently observed and only in subjects with TA-TMA. Conclusions Arteriolar C4d deposition may be a pathologic marker of TA-TMA, implicating localized complement fixation in HSCT recipients with kidney disease secondary to small vessel injury. Further studies to better characterize the preferential arteriolar C4d staining may identify a renal compartment of injury, possibly explaining the dramatic hypertension seen in TA-TMA.

BK Viremia Precedes Hemorrhagic Cystitis in Children Undergoing Allogeneic Hematopoietic Stem Cell Transplantation

BK virus is associated with hemorrhagic cystitis after hematopoietic stem cell transplantation (HSCT), although evidence supporting a causal relationship remains limited. Although BK viruria is common after HSCT, BK viremia may better predict clinically significant cystitis, similar to its predictive value for nephropathy after kidney transplantation. We hypothesized that BK viremia would precede hemorrhagic cystitis in a cohort of 88 consecutive children prospectively enrolled to originally study thrombotic microangiopathy in the first 100 days after allogeneic HSCT. Cox regression models with time-varying covariates assessed the association between different BK viremia cutoffs and the development of hemorrhagic cystitis, defined as at least macroscopic hematuria. Subjects with a peak plasma BK viral load 1 to 9999 copies/mL had an adjusted hazard ratio of 4.2 (95% confidence interval (CI), 1.3 to 13.7) for the development of hemorrhagic cystitis. Those with peak BK viremia >100,000 copies/mL had an adjusted hazard ratio of 116.8 (95% CI, 12 to 1136) for cystitis. Other independent risk factors for hemorrhagic cystitis included age >7 years and HHV-6 viremia. Neither graft-versus-host disease nor achieving engraftment increased the risk for cystitis. If therapeutic strategies are found to be effective, these observations may support screening for BK viremia after HSCT, as currently recommended for other DNA viruses.