Small vessels, big trouble in the kidneys and beyond: hematopoietic stem cell transplantation–associated thrombotic microangiopathy

Experimental glomerular endothelial injury in vivo

The microvascular endothelium of the kidney glomerulus is injured in Shiga-like toxigenic bacterial infection, genetic or acquired loss of complement regulatory protein function, and allo-immune responses of solid-organ or bone marrow transplantation. Existing models of diseases with glomerular endothelial cell (EC) injury, collectively grouped as thrombotic microangiopathies, are problematic, impeding investigation of the mechanisms of microvascular defense and repair. To develop a model of glomerular endothelial injury in the mouse, we conjugated the M. oreades lectin to the cytotoxin, saporin, (LS) to selectively injure the glomerular endothelium. Injury of the microvasculature was evaluated by light, immunofluorescence, and electron microscopy, and by quantitative RT-PCR of cell-type specific transcripts. Renal function was evaluated by quantitation of serum creatinine. The toxin conjugate induced apoptosis of microvascular ECs in vitro, and subtle histologic features of thrombotic microangiopathy in vivo that were enhanced by co-injection of 50 μg/kg LPS. Among LS/LPS-treated animals, loss of glomerular EC staining correlated with decreased expression of EC-specific transcripts, and impaired kidney function. Selective injury of the glomerular microvasculature with LS toxin conjugate and LPS elicits histologic features of thrombotic microangiopathy and acute kidney failure.

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.

Pulmonary hypertension after hematopoietic stem cell transplantation

Pulmonary hypertension (PH) is a potentially fatal complication of hematopoietic stem cell transplantation (HSCT). Given its nonspecific clinical presentation, it is likely that this clinical entity is underdiagnosed after HSCT. Data describing the incidence, risk factors, and etiology of PH in HSCT recipients are minimal. Physicians caring for HSCT recipients should be aware of this severe post-transplant complication because timely diagnosis and treatment may allow improved clinical outcomes. We summarize the pathophysiology, clinical presentation, diagnosis, and management of PH in HSCT recipients.

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.

Advances in the treatment of acute graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (HSCT) has been widely used for the treatment of hematologic malignant and non-malignant hematologic diseases and other diseases. However, acute graft-versus-host disease (GVHD) is a life-threatening complication of allogeneic transplantation. Acute GVHD may occur in 30% of transplant recipients, which is a syndrome of erythematous skin eruption, cholestatic liver disease and intestinal dysfunction, resulting from the activation of donor T lymphocytes by host antigen-presenting cells, resulting in an immune-mediated inflammatory response. Recent scientific advances in the understanding of the pathogenesis involved in the development of acute GVHD and clinical investigation have provided more effective therapeutic strategies for acute GVHD. This review focuses on major scientific and clinical advances in the treatment of acute GVHD.

Advances in critical care of the pediatric hematopoietic stem cell transplant patient

Hematopoietic stem cell transplant (SCT) remains a curative option for a variety of malignant and non-malignant disorders in children. Following transplant a proportion of SCT recipients become critically ill and need intensive care. Critical illness may occur in the setting of transplant complications such as graft versus host disease (GVHD), idiopathic pneumonia syndrome (IPS), veno-occlusive disease (VOD) and transplant associated thrombotic microangiopathy (TA-TMA). Hence, familiarity with recent advances in the transplant process and complications is crucial for the intensivist. This article will highlight common complications encountered in the critically ill SCT recipient.

Tacrolimus-associated thrombotic microangiopathy in a lung transplant recipient

A 25-year-old woman with a history of bilateral lung transplant secondary to cystic fibrosis presented with non-specific abdominal complaints and was found to have acute kidney injury, thrombocytopaenia and laboratory findings consistent with a microangiopathic haemolytic anaemia. Her thrombotic microangiopathy (TMA) was attributed to tacrolimus, which was discontinued and replaced with cyclosporine with resolution of her TMA and no subsequent complications. This is the fifth reported case of TMA associated with tacrolimus use in a lung transplant patient, and the third to be successfully managed with cyclosporine substitution. Clinicians must be aware of this uncommon, but likely under-reported complication of tacrolimus therapy in lung transplant recipients. Cyclosporine replacement may be used as a successful therapy to treat tacrolimus-associated TMA without increasing the risk of acute rejection that may be associated with other treatment strategies.

Kidney complications of hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) exposes a patient's kidneys to a unique combination of challenges, including high-dose radiation, anemia, chemotherapeutic agents, graft-versus-host disease, opportunistic infections, attenuated and altered immunologic responses, fluid and electrolyte imbalances, and extensive courses of antimicrobial agents. Since the inception of HSCT in the 1950s, there has been increasing interest in defining, determining, and managing the kidney complications that accompany this procedure. In this article, we review the common causes of acute kidney injury and chronic kidney disease that occur with HSCT, including HSCT-associated thrombotic microangiopathy, a distinct cause of chronic kidney disease with a multifactorial cause previously known as bone marrow transplant nephropathy or radiation nephropathy. Additionally, we review other kidney complications, including calcineurin inhibitor nephrotoxicity and chronic graft-versus-host disease-associated glomerulonephritis, that develop post-HSCT. Critically, due to its grave prognosis, it is important to identify HSCT-associated thrombotic microangiopathy early, as well as distinguish it from the other causes of chronic kidney disease.

Concise review: acute graft-versus-host disease: immunobiology, prevention, and treatment

Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic stem cell transplant (AHSCT) associated with significant morbidity and mortality. This review focuses on the pathophysiology, clinical features, prevention, and treatment of acute GVHD. Specifically, we explain how new discoveries in immunology have expanded our understanding of GVHD, in which tissue damage from chemotherapy or radiation results in cytokine release, which activates T cells, resulting in proliferation and differentiation, trafficking to target organs, and tissue destruction and inflammation. Insights into the mechanisms of this disease relate directly to the development of preventive strategies and therapies, such as immunosuppression, T-cell depletion, calcineurin inhibitors, CCR5 antagonists, gut decontamination, extracorporeal photopheresis, and more. We also discuss how GVHD affects the gut, liver, and skin, as well as diagnosis, grading, and scoring. We end by examining future directions of treatment, including new immunomodulators and biomarkers. Understanding the immunobiology of GVHD and developing effective preventions and treatments are critical to the continuing success of AHSCT.

Pulmonary arterial hypertension in pediatric patients with hematopoietic stem cell transplant-associated thrombotic microangiopathy

Pulmonary arterial hypertension (PAH) is rarely included in the differential diagnosis of cardiorespiratory failure after pediatric hematopoietic stem cell transplant (HSCT) as the clinical presentation is nonspecific and may mimic other etiologies. The pathogenesis of PAH in HSCT is poorly understood and the diagnosis requires a high degree of suspicion. We describe 5 children diagnosed with PAH after allogeneic HSCT. All 5 patients had prolonged clinical signs of transplantation-associated thrombotic microangiopathy (TA-TMA) when they presented with hypoxemic respiratory failure and evidence of PAH. Four of the 5 patients had echocardiographic evidence of PAH, and 1 patient was diagnosed with PAH only on autopsy. PAH was diagnosed a median of 76 days (range, 56-101 days) after a diagnosis of TA-TMA. Despite aggressive medical management, including inhaled nitric oxide, 4 of the 5 patients died. One patient recovered from PAH after 11 months of sildenafil therapy. Three of the 4 deceased patients had an autopsy performed, demonstrating severe pulmonary vascular disease consistent with TA-TMA and severe PAH. We conclude that TA-TMA can be associated with significant pulmonary vascular injury presenting as hypoxemic respiratory failure with PAH after HSCT. Pediatric patients with unexplained hypoxemia after HSCT should be evaluated for both transplantation complications, TA-TMA and PAH, accordingly.

Thrombosis in stem cell transplantation

Hemostatic changes and thrombotic events are frequent in patients undergoing stem cell transplantation. Arterial and venous thromboses are major causes of morbidity and mortality. Thrombotic complications can be classified into four groups including: catheter-related thrombosis, venous thromboembolic (VTE) events, sinusoidal obstructive syndrome (SOS)/veno-occlusive disease, and transplant-associated thrombotic microangiopathy (TAM). The incidence of catheter-related thrombosis is 8-20% in patients undergoing autologous hematopoietic stem cell transplantation (HSCT), and the incidence is low in syngeneic and allogeneic transplant patients. Venous duplex Doppler ultrasound, venogram, and computed tomography scan are required to visualize the venous thrombus. The treatment should be aimed at the prevention of pulmonary embolism, the avoidance of thrombus extension, and the preservation of catheter patency. Patients undergoing HSCT may have risk factors for VTE including underlying malignancy, traumatic brain injury, prolonged hospitalization, administration of conditioning regimens, and central venous catheters. Important risk factors are presence of history of VTE and graft-versus-host disease. One-year incidence of symptomatic VTE is 3.7%. SOS, also known as veno-occlusive disease, is a serious liver disease, seen in approximately 50-60% of HSCT patients. The mortality rate from the severe form of SOS is 84.3% and majority of the patients have multi-organ failure. The frequency is quite low after autologous transplantation. Risk factors for SOS include pre-existing hepatic damage, previous high-dose chemotherapy and abdominal irradiation, female gender and donor-recipient human leukocyte antigen disparity. Cyclophosphamide and busulphan are the most common agents with the highest incidence and fatal SOS. Histopathologic features of SOS include dilatation of sinusoids, necrosis of perivenular hepatocytes, and obstruction of small intrahepatic central venules by microthrombi and fibrin deposition. Signs of SOS usually occur within first 30 days after HSCT including hyperbilirubinemia, hepatomegaly, ascites, and weight gain. Symptoms of liver failure, including encephalopathy, coagulopathy, and renal failure will appear in severe form. A hepatic venous pressure gradient above 10 mmHg is highly specific for SOS. Early use of defibrotide has been shown to be effective in the treatment of high-risk SOS. TAM is a distinct, infrequent, and significant life-threatening complication of HSCT. TAM is seen in the range of 0·5-76% and was reported to be 10-25% in patients undergoing allogeneic HSCT with a mortality rate around 50%. It can also be seen after autologous HSCT and mainly affects the glomerular capillaries. There has been no standard therapy for TAM. Few case series reported good response to rituximab and high-dose corticosteroids were used with limited success. Trials with complement inhibitors such as eculizumab are currently underway.

Onco-nephrology: AKI in the cancer patient

AKI is common in patients with cancer, and it causes interruptions in therapy and increased hospital length of stay, cost, and mortality. Although cancer patients are susceptible to all of the usual causes of AKI in patients without cancer, there are a number of AKI syndromes that occur more frequently or are unique to this patient population. AKI also confers substantially increased risk of short-term death, and the ability to reverse AKI portends a better outcome in some cancers, such as multiple myeloma. Several trends in oncology, including increased survival, better supportive care, older patients who have received multiple chemotherapy regimens, and new therapeutic options, are driving an increase in the numbers of cancer patients who develop AKI. As a result, nephrologists should be increasingly familiar with the diagnosis, management, and treatment of AKI in this setting. Here, we summarize recent data on epidemiology of AKI in cancer patients, describe the most common AKI syndromes in this population, and highlight emerging areas in the growing field of onconephrology.

Why does my patient have thrombocytopenia?

Thrombocytopenia, usually defined as a platelet count of less than 150,000/μL, is a common reason for a hematology consult in both the inpatient and outpatient setting. In most patients, the cause of the thrombocytopenia can be identified and treated. This article reviews the clinical approach to the patient with thrombocytopenia, the mechanisms that underlie it, and the laboratory tests available to investigate it. A practical approach to the investigation and management of thrombocytopenia in the clinical settings commonly encountered by the hematology consultant is then described.

Does early initiation of therapeutic plasma exchange improve outcome in pediatric stem cell transplant-associated thrombotic microangiopathy?

BACKGROUND

The use of therapeutic plasma exchange (TPE) in hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA) is controversial because the exact mechanism of injury in TA-TMA is not yet understood.

STUDY DESIGN AND METHODS

The study objective was to retrospectively review the outcome of children receiving TPE for TA-TMA at our institution. We hypothesized that patients initiating TPE earlier in their disease course would receive a greater benefit than those starting later, regardless of the therapeutic mechanism.

RESULTS

We identified 10 consecutive pediatric patients with TA-TMA treated with TPE. Nine of these patients showed normalization of the laboratory variables associated with microangiopathy during their TPE course, but only five patients recovered renal function and survived TA-TMA. The five survivors started TPE a median of 17 days (range, 4-25 days) after TA-TMA diagnosis while the five patients who died started TPE a median of 32 days (range, 17-73 days) after TA-TMA was diagnosed. Three of the five survivors had multiorgan failure at TA-TMA diagnosis and completely recovered with early institution of TPE. These three survivors were able to discontinue renal replacement therapy, and all achieved a normal posttreatment creatinine. The five patients with later institution of TPE progressed to end-stage renal disease and all died. There were no serious TPE-related complications in either group.

CONCLUSION

This is the first report evaluating TPE response in regard to procedure initiation time after TA-TMA diagnosis. Our data suggests that early initiation of TPE might be beneficial even in patients with multiorgan failure due to TA-TMA.

Cystatin C-estimated glomerular filtration rate in pediatric autologous hematopoietic stem cell transplantation

Formal evaluation of kidney function is essential to determine chemotherapy dosing based on established treatment protocols in children undergoing autologous stem cell transplantation. Cystatin C has been widely studied as a marker of the glomerular filtration rate (GFR), although data regarding its use in stem cell transplantation are limited. We evaluated the performance of cystatin C-based equations and determined their sensitivity to detect a nuclear GFR of <100 mL/min/1.73 m(2) in children undergoing autologous transplantation. We performed a retrospective cohort analysis in 16 children undergoing 26 transplantations using a modified Bland-Altman analysis to account for repeated measures. Cystatin C-based equations published by Hoek, Le Bricon, Rule, Filler, Zappitelli, Larsson, and Schwartz (the New Chronic Kidney Disease in Children formula, New CKiD formula) were evaluated and compared to the creatinine-based modified Schwartz equation. We found that cystatin C-based equations demonstrated improved sensitivity to detect a nuclear GFR of <100 mL/min/1.73 m(2) compared to the creatinine-based modified Schwartz equation, which significantly overestimated GFR. Most cystatin C-based equations, however, tended to underestimate the nuclear GFR. The New CKiD formula, combining cystatin C and creatinine, offered a sensitivity of 100% and a specificity of 95% for detecting a nuclear GFR <100 mL/min/1.73 m(2). Institutions using cystatin C-based GFR estimation should be aware of the specific prediction formula and GFR measurement techniques available at their center, as each method's performance can vary considerably. As more research becomes available, this easily measured marker should become a valuable component of GFR estimation, providing cost savings (a nuclear GFR is 5.5 times more costly than a cystatin C) and reducing radiation exposure.