Thrombotic microangiopathy after allogeneic hematopoietic stem cell transplantation: an autopsy study

Neurological involvement in hematopoietic stem cell transplantation-associated thrombotic microangiopathy

Transplantation-associated thrombotic microangiopathy (TA-TMA) is a well-recognized serious complication of hematopoietic stem cell transplantation (HSCT). The understanding of TA-TMA pathophysiology has expanded in recent years. Dysregulation of the complement system is thought to cause endothelial injury and, consequently, microvascular thrombosis and tissue damage. TA-TMA can affect multiple organs, and each organ exhibits specific features of injury. Central nervous system (CNS) manifestations of TA-TMA include posterior reversible encephalopathy syndrome, seizures, and encephalopathy. The development of neurological dysfunction is associated with a significantly lower overall survival in patients with TA-TMA. However, there are currently no established histopathological or radiological criteria for the diagnosis of CNS TMA. Patients who receive total body irradiation (TBI), calcineurin inhibitors (CNI), and severe acute and chronic graft-versus-host disease (GVHD) are at a high risk of experiencing neurological complications related to TA-TMA and should be considered for directed TA-TMA therapy. However, the incidence and clinical manifestations of TA-TMA neurotoxicity remain unclear. Studies specifically examining the involvement of CNS in TMA syndromes are limited. In this review, we discuss clinical manifestations and imaging abnormalities in patients with nervous system involvement in TA-TMA. We summarize the mechanisms underlying TA-TMA and its neurological complications, including endothelial injury, evidence of complement activation, and treatment options for TA-TMA.

Late transplant-associated thrombotic microangiopathy verified in bone marrow biopsy specimens is associated with chronic GVHD and viral infections

OBJECTIVES

To describe late transplant-associated thrombotic microangiopathy (TA-TMA) as chronic endothelial complication in bone marrow (BM) after allogeneic hematopoietic stem cell transplantation (HSCT).

METHODS

BM specimens along with conventional diagnostic parameters were assessed in 14 single-institutional patients with late TA-TMA (more than 100 days after HCST), including 11 late with history of early TA-TMA, 10 with early TA-TMA (within 100 days), and 12 non TA-TMA patients. Three non-HSCT patients served as control. The time points of BM biopsy were +1086, +798, +396, and +363 days after HSCT, respectively.

RESULTS

Late TA-TMA patients showed an increase of CD34+ and von Willebrand Factor (VWF)+ microvascular endothelial cells with atypical VWF+ conglomerates forming thickened VWF+ plaque sinus in the BM compared to patients without late TA-TMA and non-HSCT. Severe chronic (p = .002), steroid-refractory GVHD (p = .007) and reactivation of HHV6 (p = .002), EBV (p = .003), and adenovirus (p = .005) were pronounced in late TA-TMA. Overall and relapse-free survival were shorter in late TA-TMA than in patients without late TA-TMA (5-year OS and RFS: 78.6% vs. 90.2%, 71.4% vs. 86.4%, respectively).

CONCLUSION

Chronic allo-immune microangiopathy in BM associated with chronic, steroid-refractory GVHD and/or viral infections are key findings of late, high-risk TA-TMA, which deserves clinical attention.

Kidney Injury in Children after Hematopoietic Stem Cell Transplant

Hematopoietic cell transplant (HCT), used for treatment of many malignant and non-malignant pediatric diseases, is associated with serious complications, limiting this therapy’s benefit. Acute kidney injury (AKI), seen often after HCT, can occur at different stages of the transplant process and contributes to morbidity and mortality after HCT. The etiology of AKI is often multifactorial, including kidney hypoperfusion, nephrotoxicity from immunosuppressive and antimicrobial agents, and other transplant-related complications such as transplant-associated thrombotic microangiopathy and sinusoidal obstructive syndrome. Early recognition of AKI is crucial to prevent further AKI and associated complications. Initial management includes identifying the etiology of AKI, preventing further kidney hypoperfusion, adjusting nephrotoxic medications, and preventing fluid overload. Some patients will require further support with kidney replacement therapy to manage fluid overload and AKI. Biomarkers of AKI, such as neutrophil gelatinase-associated lipocalin can aid in detecting AKI before a rise in serum creatinine, allowing earlier intervention. Long-term kidney dysfunction is also prominent in this population. Therefore, long-term follow-up and monitoring of renal function (glomerular filtration rate, microalbuminuria) is required along with management of hypertension, which can contribute to chronic kidney disease.

Histopathologically TMA-like distribution of multiple organ thromboses following the initial dose of the BNT162b2 mRNA vaccine (Comirnaty, Pfizer/BioNTech): an autopsy case report

Background

Coronavirus disease 2019 (COVID-19) has spread worldwide. Vaccination is now recommended as one of the effective countermeasures to control the pandemic or prevent the worsening of symptoms. However, its adverse effects have been attracting attention. Here, we report an autopsy case of multiple thromboses after receiving the first dose of the BNT162b2 mRNA vaccine (Comirnaty, Pfizer/BioNTech) in an elderly woman.

Case presentation

A 72-year-old woman with a history of diffuse large B-cell lymphoma in the stomach and hyperthyroidism received the first dose of the BNT162b2 mRNA vaccine and died 2 days later. The autopsy revealed multiple microthrombi in the heart, brain, liver, kidneys, and adrenal glands. The thrombi were CD61 and CD42b positive and were located in the blood vessels primarily in the pericardial aspect of the myocardium and subcapsular region of the adrenal glands; their diameters were approximately 5–40 μm. Macroscopically, a characteristic myocardial haemorrhage was observed, and the histopathology of the characteristic thrombus distribution, which differed from that of haemolytic uraemic syndrome and disseminated intravascular coagulation, suggested that the underlying pathophysiology may have been similar to that of thrombotic microangiopathy (TMA).

Conclusion

This is the first report on a post-mortem case of multiple thromboses after the BNT162b2 mRNA vaccine. The component thrombus and characteristic distribution of the thrombi were similar to those of TMA, which differs completely from haemolytic uraemic syndrome or disseminated intravascular coagulation, after vaccination. Although rare, it is important to consider that fatal adverse reactions may occur after vaccination and that it is vital to conduct careful follow-up.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12959-022-00418-7.

Cerebral vascular injury in transplant-associated thrombotic microangiopathy

Transplant-associated thrombotic microangiopathy (TA-TMA) and atypical hemolytic uremic syndrome (aHUS) are complement-mediated TMAs. The central nervous system (CNS) is the most common extrarenal organ affected by aHUS, and, despite mechanistic overlap between aHUS and TA-TMA, CNS involvement is rarely reported in TA-TMA, suggesting that CNS involvement in TA-TMA may be underdiagnosed and that these patients may benefit from complement blockers. In addition, there are no widely used histologic or radiologic criteria for the diagnosis of TMA in the brain. Thirteen recipients of pediatric hematopoietic cell transplants (HCTs) who had TA-TMA and who underwent autopsy were studied. Seven of 13 brains had vascular injury, and 2 had severe vascular injury. Neurologic symptoms correlated with severe vascular injury. Classic TMA histology was present and most often observed in the cerebellum, brainstem, and cerebral white matter. Abnormalities in similar anatomic regions were seen on imaging. Brain imaging findings related to TMA included hemorrhages, siderosis, and posterior reversible encephalopathy syndrome. We then studied 100 consecutive HCT recipients to identify differences in neurologic complications between patients with and those without TA-TMA. Patients with TA-TMA were significantly more likely to have a clinical concern for seizure, have an electroencephalogram performed, and develop altered mental status. In summary, our study confirms that TA-TMA involves the brains of recipients of HCT and is associated with an increased incidence of neurologic symptoms. Based on these findings, we propose that patients with low- or moderate-risk TA-TMA who develop neurologic complications should be considered for TA-TMA-directed therapy.

Upregulation of HIF-1α contributes to complement activation in transplantation-associated thrombotic microangiopathy

Transplantation-associated thrombotic microangiopathy (TA-TMA) is a severe complication of haematopoietic stem cell transplantation (HSCT). Complement activation is involved in the development of TA-TMA. However, the underlying mechanism is unclear. Therefore, 21 samples of TA-TMA and 1:1 matched controls were measured for hypoxia-inducible factor-1α (HIF-1α) and complement protein. The mechanism was investigated both in vitro and in vivo. In this study, we found that levels of HIF-1α were significantly higher in TA-TMA patients than that in non-TA-TMA controls. Upregulation of HIF-1α induced an increase in membrane-bound complement C3 and dysfunction of human umbilical vein endothelial cells (HUVECs) in vitro. Increasing HIF-1α in vivo led to C3 and C5b-9 deposition in the glomerular endothelial capillary complex, thrombocytopenia, anaemia, and increased serum lactate dehydrogenase (LDH) levels in wild-type (WT) but not in C3^-/- mice subjected to HSCT. High platelet aggregation in peripheral blood and CD41-positive microthrombi in the kidney were also found in dimethyloxallyl glycine (DMOG)-treated mice, recapitulating the TA-TMA phenotype seen in patients. Comprehensive analysis, including DNA array, luciferase reporter assay, chromatin immunoprecipitation (ChIP)-seq, and quantitative polymerase chain reaction (PCR), revealed that HIF-1α interacted with the promoter of complement factor H (CFH) to inhibit its transcription. Decreased CFH led to complement activation in endothelial cells.

Diffuse alveolar hemorrhage: An underreported complication of transplant associated thrombotic microangiopathy

Hematopoietic stem cell transplantation-associated thrombotic microangiopathy (TA-TMA) and diffuse alveolar hemorrhage (DAH) are well recognized post-transplant complications that carry a high risk of mortality; however, the risk of DAH complicating the course of transplant patients with TA-TMA is not well understood. We conducted a ten-year retrospective study at our institution to determine the incidence of DAH in a cohort of pediatric patients with TA-TMA and described their presentation and outcomes. Additionally, autopsy slides, when available, were reviewed to assess for histological evidence of microvascular injury and alveolar hemorrhages. A total of 58 pediatric patients with TA-TMA were identified. Of these, 14 (24%) had DAH. Majority of DAH cases occurred within a week of TA-TMA diagnosis (n = 8, 57%, range 0-698 days). Mortality was 100% for patients with DAH and TA-TMA. Infections were found to be a significant risk factor for DAH in TA-TMA. Autopsy was performed in 11 of the 14 patients, and pulmonary slides were available for review in ten cases. 70% cases had pathological evidence of microvascular injury, concerning for pulmonary TA-TMA. We conclude that DAH is a potentially fatal complication in patients with TA-TMA and may be a result of pulmonary microangiopathy.

Treatment outcome and efficacy of therapeutic plasma exchange for transplant-associated thrombotic microangiopathy in a large real-world cohort study

The efficacy and outcome of therapeutic plasma exchange (TPE) for transplant-associated thrombotic microangiopathy (TA-TMA) remain controversial. We therefore sought to evaluate the outcome and efficacy of TPE in patients with TA-TMA and to identify TA-TMA patients who would benefit from TPE management. Eighty-two patients with TA-TMA were treated with TPE. We reported a response rate of 52% and overall survival rates of 20% and 15% at 100 days and 1 year after TA-TMA, respectively, in TPE-treated patients, with a significantly lower survival in gastrointestinal (GI) bleeding patients (5% vs. 41% in non-GI bleeding patients, P = 0.003). Multivariate analysis revealed that patients with GI bleeding, grade III-IV aGVHD, severe anemia, and a lower cumulative volume of TPE were less likely to respond to TPE. GI bleeding, a lower initial volume of TPE, and elevated total bilirubin were independently associated with 100-day mortality. The leading causes of death were infection, active TA-TMA, and MODS. The results of this large cohort of real-world practice indicate that the efficacy and outcome of TPE for TA-TMA patients without GI bleeding are encouraging, and a higher volume of TPE is warranted to achieve favorable outcomes.

Recent Advances of Acute Kidney Injury in Hematopoietic Cell Transplantation

Acute kidney injury (AKI) is a common complication of allogeneic hematopoietic cell transplantation (allo-HCT) and is associated with non-relapse mortality (NRM) and quality of life (QOL). Multiple factors may contribute to AKI during allo-HCT and are often present at the same time making it difficult to determine the cause of AKI in each patient. Nephrotoxic drugs, infections, thrombotic microangiopathy (TMA), and sinusoidal obstruction syndrome (SOS) are well described causes of AKI during allo-HCT. Acute graft-versus-host disease (aGVHD) is a major complication of allo-HCT that mainly targets the intestines, liver, and skin. However, recent studies suggest aGVHD may also attack the kidney and contribute to AKI following allo-HCT. For example, severe aGVHD is associated with AKI, suggesting a link between the two. In addition, animal models have shown donor immune cell infiltration and increased expression of inflammatory cytokines in recipient kidneys after allo-HCT. Therefore, aGVHD may also target the kidney and contribute to AKI following allo-HCT. Herein, we describe the etiology, diagnosis, risk factors, pathophysiology, prevention, and treatment of renal injury after allo-HCT. In addition, we highlight emerging evidence that aGVHD may contribute to the development of AKI after allo-HCT.

Kidney Disease Following Hematopoietic Stem Cell Transplantation

Hematopoietic stem cell transplantation (SCT) provides a curative option for the treatment of several malignancies. Its growing use is associated with an increased burden of kidney disease. Acute kidney injury is usually seen within the first 100 days of transplantation and has an incidence ranging between 12 and 73%, with the highest rate in myeloablative allogeneic SCT. A large subset of patients after SCT develop chronic kidney disease. They can be broadly classified into thrombotic microangiopathy, nephrotic syndrome, and calcineurin toxicity. Dialysis requirement after SCT is associated with mortality exceeding 80%. Given the higher morbidity and mortality related to development kidney disease, nephrologists need to be aware of the various causes and best treatment options.

Infection in Patients with Suspected Thrombotic Microangiopathy Based on Clinical Presentation

BACKGROUND AND OBJECTIVES

In contrast to shigatoxin-associated Escherichia coli (STEC) causing hemolytic uremic syndrome, STEC-unrelated infections associated with thrombotic microangiopathy are less characterized.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Our retrospective study in a four-hospital institution of 530 consecutive patients with adjudicated thrombotic microangiopathies during the 2009-2016 period studied STEC-unrelated infections' epidemiology and major outcomes (death, acute dialysis, and major cardiovascular events).

RESULTS

STEC-unrelated infection was present in 145 of 530 (27%) patients, thrombotic microangiopathies without infection were present in 350 of 530 (66%) patients, and STEC causing hemolytic and uremic syndrome was present in 35 of 530 (7%) patients. They (versus thrombotic microangiopathy without infection) were associated with age >60 years (36% versus 18%), men (53% versus 27%), altered consciousness (32% versus 11%), mean BP <65 mm Hg (21% versus 4%), lower hemoglobin and platelet count, and AKI (72% versus 49%). They were associated with more than one pathogen in 36 of 145 (25%) patients (either isolated [14%] or combined [86%] to other causes of thrombotic microangiopathy); however, no significant clinical or biologic differences were noted between the two groups. They were more frequently due to bacteria (enterobacteria [41%], Staphylococcus aureus [11%], and Streptococcus pneumonia [3%]) than viruses (Epstein-Barr [20%], cytomegalovirus [18%], influenza [3%], hepatitis C [1%], HIV [1%], and rotavirus [1%]). STEC-unrelated infections were independent risk factors for in-hospital death (odds ratio, 2.22; 95% confidence interval, 1.18 to 4.29), major cardiovascular event (odds ratio, 3.43; 95% confidence interval, 1.82 to 6.69), and acute dialysis (odds ratio, 3.48; 95% confidence interval, 1.78 to 7.03). Bacteria (versus other pathogens), and among bacteria, enterobacteria, presence of more than one bacteria, and E. coli without shigatoxin were risk factors for acute dialysis.

CONCLUSIONS

Infections are frequent thrombotic microangiopathy triggers or causes, and they are mostly unrelated to STEC. Infections convey a higher risk of death and major complications. The most frequent pathogens were enterobacteria, S. aureus, Epstein-Barr virus, and cytomegalovirus.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2021_09_07_CJN17511120.mp3.

A prognostic model (BATAP) with external validation for patients with transplant-associated thrombotic microangiopathy

Transplant-associated thrombotic microangiopathy (TA-TMA) is a potentially life-threatening complication following allogeneic hematopoietic stem cell transplantation (allo-HSCT). Information on markers for early prognostication remains limited, and no predictive tools for TA-TMA are available. We attempt to develop and validate a prognostic model for TA-TMA. A total of 507 patients who developed TA-TMA following allo-HSCT were retrospectively identified and separated into a derivation cohort and a validation cohort according to the time of transplantation to perform external temporal validation. Patient age (OR 2.371, 95% CI 1.264-4.445), anemia (OR 2.836, 95% CI 1.566-5.138), severe thrombocytopenia (OR 3.871, 95% CI 2.156-6.950), elevated total bilirubin (OR 2.716, 95% CI 1.489-4.955) and proteinuria (OR 2.289, 95% CI 1.257-4.168) were identified as independent prognostic factors for the 6-month outcome of TA-TMA. A risk score model termed BATAP (Bilirubin, Age, Thrombocytopenia, Anemia, Proteinuria) was then constructed according to the regression coefficients. The validated c-statistics were 0.816 (95% CI 0.766-0.867) and 0.756 (95% CI 0.696-0.817) in the internal and external validation, respectively. Calibration plots indicated that the model-predicted probabilities correlated well with the actual observed frequencies. This predictive model may facilitate the prognostication of TA-TMA and contribute to the early identification of high-risk patients.

Endothelial dysfunction and vascular complications after allogeneic hematopoietic cell transplantation: an expert analysis

Allogeneic hematopoietic cell transplantation (alloHCT) is the standard of care for many diseases. However, survivors often present with serious complications resulting from acute and chronic toxicities and it is crucial to increase consciousness from treating physicians. We performed a comprehensive review of the literature and critically examined recent available data, mostly using the PubMed and Medline search engines for original articles published over the last decade. Better understanding of many alloHCT-related disorders has shown that endothelial injury and vascular damage plays a critical role. The most widely studied endothelial injury syndromes (EIS) are veno-occlusive disease/sinusoidal obstruction syndrome (SOS/VOD), graft-versus-host-disease (GVHD), and transplant-associated thrombotic microangiopathy (TA-TMA). TA-TMA, frequently underdiagnosed, needs to be clarified using certain criteria and, as a life-threatening condition, requires immediate and intensive treatment. The first-in-class complement inhibitor eculizumab has significantly improved outcomes in both the pediatric and adult population. Cardiovascular (CV) events are the second major cause of morbidity and mortality of alloHCT survivors, after GVHD. Long-term monitoring and management of CV risk is expected to also incorporate patient stratification with CV risk prediction models, early markers of vascular dysfunction or procoagulant activity, subclinical target organ damage, arterial stiffness, and subclinical atherosclerosis.

Thrombotic microangiopathy increases the risk of chronic kidney disease but not overall mortality in long-term transplant survivors

Thrombotic microangiopathy (TMA) after allogeneic hematopoietic cell transplant (HCT) is associated with acute kidney injury (AKI) and increased mortality. The impact of TMA on chronic kidney disease (CKD) and long-term mortality among HCT survivors has not been fully examined. To assess the risk of CKD and mortality in HCT survivors with and without history of TMA, we conducted a retrospective cohort study among adult allogeneic HCT recipients who survived to at least 1 year post-transplantation. We examined the association between the history of TMA within 1 year and the onset of CKD longitudinally for 5 years with generalized estimating equation (GEE) while adjusting for other key confounders. CKD was defined as an estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m² using the CKD-EPI formula with outpatient creatinine values collected during the annual long-term follow-up unit follow-up visits. Kaplan Meier curves landmarked at 1 year were used for survival analyses. Among 2091 adult patients who underwent allogeneic HCT, we identified 1151 patients who survived at least 1 year and had available long-term follow-up data. Among them, 57 patients developed TMA within 1 year and 1094 did not have TMA. There was no pretransplantation baseline difference in eGFR between groups. After adjusting for confounders, history of TMA was associated with an odds ratio of 2.83 (95% confidence interval 1.33-6.03) for CKD development over 5 years after transplantation. The conditional 5-year survival was 78% in the TMA survivors and 80% in the non-TMA survivors (log rank P = .122). HCT survivors with a history of TMA had increased risk of CKD development. Although TMA was associated with high risk of mortality within 1 year after transplantation, long-term survival was comparable with non-TMA survivors. Future therapeutic interventions should focus on not only short-term mortality outcomes, but also short- and long-term kidney outcomes for HCT patients with TMA.

A pragmatic multi-institutional approach to understanding transplant-associated thrombotic microangiopathy after stem cell transplant

Transplant-associated thrombotic microangiopathy (TA-TMA) is a severe complication of hematopoietic stem cell transplantation (HSCT). A single-center prospective screening study has shown that the incidence of TA-TMA is much higher than prior retrospective studies that did not systematically screen. These data have not been replicated in a multicenter study. Our objective was to determine the incidence and risk factors for TA-TMA and compare outcomes of pediatric HSCT patients with and without TA-TMA. Patients were prospectively screened for TA-TMA at participating centers using a simple to implement and inexpensive strategy from the start of the preparative regimen through day +100. TA-TMA was diagnosed if ≥4 of 7 laboratory/clinical markers diagnostic for TA-TMA were present concurrently or if tissue histology showed TA-TMA. A total of 614 patients (359 males; 58%) received prospective TA-TMA screening at 13 pediatric centers. TA-TMA was diagnosed in 98 patients (16%) at a median of 22 days (interquartile range, 14-44) posttransplant. Patients with TA-TMA had significantly increased bloodstream infections (38% [37/98] vs 21% [107/51], P ≤ .001), mean total hospitalization days (68; 95% confidence interval [CI], 63-74 vs 43; 95% CI, 41-45; P ≤ .001), and number of days spent in the intensive care unit (10.1; 95% CI, 6.4-14; vs 1.6; 95% CI, 1.1-2.2; P ≤ .001) in the first 100 days after HSCT compared with patients without TA-TMA. Overall survival was significantly higher in patients without TA-TMA (93%; 490/516) compared with patients with TA-TMA (78%; 76/98) (P ≤ .001). These data support the need for systematic screening for TA-TMA and demonstrate the feasibility and efficacy of an easy to implement strategy to do so.

A critical role of the Gas6-Mer axis in endothelial dysfunction contributing to TA-TMA associated with GVHD

Endothelial dysfunction in the early phases of hematopoietic stem cell transplantation (HSCT) contributes to a common pathology between transplant-associated thrombotic microangiopathy (TA-TMA) and graft-versus-host disease (GVHD), which are serious complications of HSCT. Growth arrest-specific (Gas) 6 structurally belongs to the family of plasma vitamin K-dependent proteins working as a cofactor for activated protein C, and has growth factor-like properties through its interaction with receptor tyrosine kinases of the TAM family: Tyro3, Axl, and Mer. Serum Gas6 levels were significantly increased in HSCT patients with grade II to IV acute GVHD (aGVHD), and Gas6 and Mer expression levels were upregulated in aGVHD lesions of the large intestine and skin. The increased serum Gas6 levels were also correlated with elevated lactate dehydrogenase, d-dimer, and plasmin inhibitor complex values in HSCT patients with aGVHD. In human umbilical vein endothelial cells (ECs), exogenous Gas6 or the exposure of sera isolated from patients with grade III aGVHD to ECs induced the downregulation of thrombomodulin and the upregulation of PAI-1, as well as the upregulation of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, which were inhibited by UNC2250, a selective Mer tyrosine kinase inhibitor. In mouse HSCT models, we observed hepatic GVHD with hepatocellular apoptosis, necrosis, and fibrosis, as well as TA-TMA, which is characterized pathologically by thrombosis formation in the microvasculature of the liver and kidney. Of note, intravenous administration of UNC2250 markedly suppressed GVHD and TA-TMA in these mouse HSCT models. Our findings suggest that the Gas6-Mer axis is a promising target for TA-TMA after GVHD.

Incidence, Risk Factors for and Outcomes of Transplant-Associated Thrombotic Microangiopathy

Transplant-associated thrombotic microangiopathy (TA-TMA) is a complication of allogeneic transplantation (allo-HCT). The incidence and risk factors associated with TA-TMA are not well known. A retrospective analysis from the Center for International Blood and Marrow Transplant Research (CIBMTR) was conducted including patients receiving allo-HCT between 2008 and 2016, with the primary objective of evaluating the incidence of TA-TMA. Secondary objectives included identification of risk factors associated with TA-TMA, and the impact of TA-TMA on overall survival and the need for renal replacement therapy (RRT). Among 23,665 allo-HCT recipients, the 3-year cumulative incidence of TA-TMA was 3%. Variables independently-associated with increased incidence of TA-TMA included female sex, prior autologous transplant, primary disease (acute lymphoblastic leukaemia and severe aplastic anaemia), donor type (mismatched or unrelated donor), conditioning intensity (myeloablative), GVHD prophylaxis (sirolimus + calcineurin inhibitor), pre-transplant kidney dysfunction and acute GVHD (time-varying effect). TA-TMA was associated with higher mortality (HR = 3·1, 95% Confidence Interval [CI] = 2·8-16·3) and RRT requirement (HR = 7·1, 95% CI = 5·7-311·6). This study provides epidemiologic data on TA-TMA and its impact on transplant outcomes. Increased awareness of the risk factors will enable providers to be vigilant of this uncommon but serious transplant complication. The results will also provide benchmarking for future study designs and comparisons.

The alternative complement pathway activation product Ba as a marker for transplant-associated thrombotic microangiopathy

BACKGROUND

Transplant-associated thrombotic microangiopathy (TA-TMA) occurs after hematopoietic stem cell transplantation (HSCT) and is characterized by microvascular thrombosis and end-organ injury particularly of the kidneys. TA-TMA is challenging to diagnose and treat, which can lead to long-term complications and death in patients with severe disease. Studies have shown that genetic abnormalities of the alternative complement pathway (AP) are associated with TA-TMA. We hypothesized that patients with TA-TMA may generate elevated levels of the AP activation product, Ba, compared with HSCT patients without TA-TMA.

PROCEDURE

We longitudinally measured plasma levels of complement activation products C3a, Ba, and C5a in 14 HSCT patients: 7 with TA-TMA and 7 without TA-TMA. We assessed renal function by calculating estimated glomerular filtration rate (eGFR) and correlated the extent of AP activation with renal dysfunction in both patient populations.

RESULTS

The median days from HSCT to study enrollment were 154 (39-237) in the TA-TMA group and 84 (39-253) in the HSCT group without TA-TMA. Median Ba levels (ng/mL) at enrollment were 1096.9 (826.5-1562.0) in the TA-TMA group and 725.7 (494.7-818.9) in the HSCT group without TA-TMA (P = 0.007). Over the study duration, Ba levels inversely correlated with eGFR. There were no differences in C3a, C5a, or sC5b9 levels between the two populations at any measured interval.

CONCLUSIONS

We conclude in this preliminary study that Ba protein may serve as a marker for TA-TMA, and furthermore, that components generated in the early phase of AP activation may be involved in the pathogenesis of renal endothelial injury in TA-TMA.

Acute kidney injury in the patient with cancer

Dramatic advances in the care of patients with cancer have led to significant improvement in outcomes and survival. However, renal manifestations of the underlying cancer as well as the effects of anti-neoplastic therapies leave patients with significant morbidity and chronic kidney disease risks. The most common renal manifestations associated with cancer include acute kidney injury (AKI) in the setting of multiple myeloma, tumor lysis syndrome, post-hematopoietic stem cell therapy, and AKI associated with chemotherapy. Knowledge of specific risk factors, modification of risk and careful attention to rapid AKI diagnosis are critical for improving outcomes.

Complement-mediated thrombotic microangiopathy as a link between endothelial damage and steroid-refractory GVHD

Transplant-associated thrombotic microangiopathy (TA-TMA), a complication of hematopoietic cell transplant (HCT), is associated with significant morbidity and mortality. The pathophysiology and overlap of TA-TMA with other posttransplant complications such as graft-versus-host disease (GVHD) is poorly understood. We retrospectively identified cases of TA-TMA among patients with grade 3/4 gastrointestinal (GI) GVHD, reviewed intestinal biopsy specimens, and performed correlative testing of biomarkers associated with TA-TMA. TA-TMA was more common in patients with steroid-refractory GVHD compared with steroid-responsive GVHD (79.3% vs 42.1%; P = .001). Among patients surviving 100 days post-HCT, 1-year survival from day 100 was significantly better for patients who had not developed TA-TMA in the first 100 days (69.5% vs 36.7%; P < .001). Only 1 of 7 proposed TA-TMA histology criteria (mucosal hemorrhage) differed significantly based on GVHD steroid response. In multivariable modeling, steroid-refractory GVHD was a risk factor for development of TA-TMA (hazard ratio, 3.09; 95% confidence interval, 1.68-5.67; P < .001). There were no differences in complement activation at GVHD onset; however, 2 to 6 weeks later, patients with TA-TMA had higher levels of BBPlus and C5b-9, markers of alternative and terminal pathway activation (BBPlus: median, 600 vs 209.3 ng/mL; P = .0045) (C5b-9: median, 425.9 vs 258.4 ng/mL; P = .029). TA-TMA is associated with poor overall survival (OS) following HCT and may be detected early by histologic findings and may be differentiated from GVHD by measurement of alternative and terminal complement pathway activation. It is unknown whether treatment of TA-TMA will improve survival in steroid-refractory GVHD.

Distribution of Transplantation-Associated Thrombotic Microangiopathy (TA-TMA) and Comparison between Renal TA-TMA and Intestinal TA-TMA: Autopsy Study

Transplantation-associated thrombotic microangiopathy (TA-TMA) is an important complication of hematopoietic stem cell transplantation. To date, information regarding the organs that are affected by TA-TMA as confirmed histologically remains limited; the clinicopathologic differences between renal TA-TMA and intestinal TA-TMA have not been examined despite being the well-known and commonly affected sites of TA-TMA. We therefore examined 165 autopsied patients after hematopoietic stem cell transplantation and compared the clinicopathologic factors of renal and intestinal TA-TMA. It was clear that 38 (23%) of our patients had TA-TMA. In the TA-TMA cases, the kidney (61%) and intestine (53%) were commonly affected, and the ileum and right colon were vulnerable. Other organs that we found to be affected by TA-TMA included the stomach (8%), gallbladder (5%), and oral cavity, pharynx, esophagus, liver, heart, urinary bladder, and ureter (all at 3%), and symptoms thought to be caused by TA-TMA of these organs were not observed in any patient. Histologically, TA-TMA only affected the arteriole, or small arteries, regardless of the organ, and the veins or larger arteries were not affected at all. In the kidney, the glomerular capillary was also affected, and mesangiolysis and double contours of the basement membranes were often in evidence. The histologic overlap of renal and intestinal TA-TMA was rare (13%), and the patients in the intestinal TA-TMA group exhibited more frequency of a history of intestinal acute graft-versus-host disease (GVHD) during the clinical course compared with that of the renal TA-TMA group (80% versus 22%, P = .0016). Although TA-TMA can affect many other organs, the frequency of these ancillary events was low, and the clinical effect may have been small. Our results suggest that in comparison to renal TA-TMA, intestinal GVHD could be more closely associated with intestinal TA-TMA as a risk factor.

Emerging Concepts in Hematopoietic Stem Cell Transplantation-Associated Renal Thrombotic Microangiopathy and Prospects for New Treatments

Thrombotic microangiopathy associated with hematopoietic stem cell transplantation (HSCT-TMA) is a well-recognized complication of HSCT that has a high risk for death. Even in patients who survive, HSCT-TMA is associated with long-term morbidity and chronic organ injury. HSCT-TMA is a multisystem disease that often affects the kidneys. Renal manifestations of HSCT-TMA include reduced glomerular filtration rate, proteinuria, and hypertension. Understanding of the pathophysiology of HSCT-TMA has expanded in the last decade. Endothelial injury plays a major role. Recent studies also suggest involvement of complement activation. HSCT-TMA has also been considered by some to be an endothelial variant of graft-versus-host disease. Understanding the pathophysiology of HSCT-TMA and its association with activation of the complement system may aid in developing novel therapeutic options. In this review, we summarize current knowledge focusing on epidemiology and prognosis, evidence of complement activation, and endothelial injury; the possible link to graft-versus-host disease; and treatment options for HSCT-TMA.

Brain microvascular endothelial cells exhibit lower activation of the alternative complement pathway than glomerular microvascular endothelial cells

Atypical hemolytic uremic syndrome (aHUS) and bone marrow transplantation-associated thrombotic microangiopathy (TA-TMA) are associated with excessive activation of the alternative complement pathway (AP) and with severe renal, but rarely cerebral, microvascular damage. Here, we compared AP activation and regulation in human glomerular and brain microvascular endothelial cells (GMVECs and BMVECs, respectively) unstimulated or stimulated by the proinflammatory cytokine, tumor necrosis factor (TNF). Compared with GMVECs and under both experimental conditions, BMVECs had increased gene expression of the AP-related genes C3, CFB, and C5 and decreased expression of CFD This was associated with increased expression in BMVECs (relative to GMVECs) of the genes for surface and soluble regulatory molecules (CD46, THBD, CD55, CFI, and CFH) suppressing formation of the AP C3 and C5 convertases. Of note, unlike GMVECs, BMVECs generated extremely low levels of C3a and C5a and displayed decreased activation of the AP (as measured by a lower percentage of Ba generation than GMVECs). Moreover, BMVECs exhibited increased function of CD141, mediating activation of the natural anticoagulant protein C, compared with GMVECs. We also found that the C3a receptor (C3aR) is present on both cell types and that TNF greatly increases C3AR1 expression in GMVECs, but only slightly in BMVECs. Higher AP activation and C3a generation in GMVECs than in BMVECs, coupled with an increase in C3aR production in TNF-stimulated GMVECs, provides a possible explanation for the predominance of renal damage, and the absence of cerebral injury, in individuals with episodes of aHUS and TA-TMA.

Plasma levels of complement activation fragments C3b and sC5b-9 significantly increased in patients with thrombotic microangiopathy after allogeneic stem cell transplantation

Transplantation-associated thrombotic microangiopathy (TA-TMA) is an uncommon but severe complication in patients undergoing allogeneic stem cell transplantation (allo-SCT). However, the mechanism is unclear. From 2011 to 2014, 20 patients with TA-TMA, 20 patients without, and 54 patients with various other complications, including veno occlusive disease (VOD), graft-versus-host disease (GVHD), and infection, were recruited in the study. Plasma vWF antigen (vWFAg), vWF activity (vWFAc), and ADAMTS13 activity were determined in these patients by ELISAs and FRETS-vWF73 assay, respectively. Plasma C3b, sC5b-9, and CH50 were also determined by ELISAs. Plasma levels of C3b were significantly increased in patients with either TA-TMA (p < 0.0001) or GVHD (p < 0.01). Plasma sC5b-9 and CH50 levels in patients with TA-TMA were also significantly increased (p < 0.001). Plasma ADAMTS13 activity was lower in patients with VOD, but normal with other complications. Both plasma vWFAg and vWFAc levels were not elevated in patients with TA-TMA or VOD compared with those of other groups. Complement activation likely via an alternative pathway (increased C3b, sC5b-9, and CH50) may play a role in the pathogenesis of TA-TMA. ADAMTS13 activity is reduced in VOD, but the ADAMTS13/vWF axis appears to be unaffected in patients with TA-TMA.

A Complete Histologic Approach to Gastrointestinal Biopsy From Hematopoietic Stem Cell Transplant Patients With Evidence of Transplant-Associated Gastrointestinal Thrombotic Microangiopathy

CONTEXT

- Transplant-associated thrombotic microangiopathy is a serious complication of hematopoietic stem cell transplant that may progress to multi-organ dysfunction. Transplant-associated thrombotic microangiopathy may involve the intestinal vasculature (intestinal transplant-associated thrombotic microangiopathy [iTMA]), causing patients to experience debilitating symptoms of ischemic colitis, including disproportionately severe abdominal pain and gastrointestinal bleeding, requiring heavy narcotic use and frequent transfusion support. Pathophysiology remains poorly investigated but may include endothelial damage mediated by inflammatory markers and the complement system. Endoscopy of hematopoietic stem cell transplant patients often produces biopsy samples, in which mucosal lamina propria capillaries are sufficient for an evaluation of iTMA features.

OBJECTIVE

- To provide a detailed review of histologic features of iTMA.

DATA SOURCES

- We conducted a systematic review of studies assessing histologic features of iTMA. Studies were identified by PubMed search and included a cohort study performed by our group.

CONCLUSIONS

- The histologic hallmark of iTMA is endothelial cell injury that leads to hemorrhage and thrombosis of the capillaries. Histologic features include endothelial cell swelling, endothelial cell separation, perivascular mucosal hemorrhage, intraluminal schistocytes, intraluminal fibrin, intraluminal microthrombi, loss of glands, and total denudation of mucosa. Identification of features consistent with iTMA has immediate implications for clinical management that could potentially improve outcome and survival.

Guidelines on the Use of Therapeutic Apheresis in Clinical Practice-Evidence-Based Approach from the Writing Committee of the American Society for Apheresis: The Seventh Special Issue

The American Society for Apheresis (ASFA) Journal of Clinical Apheresis (JCA) Special Issue Writing Committee is charged with reviewing, updating, and categorizing indications for the evidence-based use of therapeutic apheresis in human disease. Since the 2007 JCA Special Issue (Fourth Edition), the Committee has incorporated systematic review and evidence-based approaches in the grading and categorization of apheresis indications. This Seventh Edition of the JCA Special Issue continues to maintain this methodology and rigor to make recommendations on the use of apheresis in a wide variety of diseases/conditions. The JCA Seventh Edition, like its predecessor, has consistently applied the category and grading system definitions in the fact sheets. The general layout and concept of a fact sheet that was used since the fourth edition has largely been maintained in this edition. Each fact sheet succinctly summarizes the evidence for the use of therapeutic apheresis in a specific disease entity. The Seventh Edition discusses 87 fact sheets (14 new fact sheets since the Sixth Edition) for therapeutic apheresis diseases and medical conditions, with 179 indications, which are separately graded and categorized within the listed fact sheets. Several diseases that are Category IV which have been described in detail in previous editions and do not have significant new evidence since the last publication are summarized in a separate table. The Seventh Edition of the JCA Special Issue serves as a key resource that guides the utilization of therapeutic apheresis in the treatment of human disease. J. Clin. Apheresis 31:149-162, 2016. © 2016 Wiley Periodicals, Inc.

Hematopoietic cell transplantation-associated thrombotic microangiopathy: a review of pathophysiology, diagnosis, and treatment

Transplant-associated thrombotic microangiopathy (TA-TMA) is a multifactorial disorder caused by systemic vascular endothelial injury that can be triggered by several mechanisms during the transplant process. Thrombotic microangiopathy may affect multiple systems and occurs in ~30% of patients undergoing hematopoietic stem cell transplantation. A subgroup of patients with thrombotic microangiopathy develop TA-TMA, and the other may develop other thrombotic microangiopathic disorders such as thrombotic thrombocytopenic purpura, a condition with similar finding but different pathophysiology involving ADAMTS-13. The mortality rates in patients who develop severe TA-TMA are in excess of 80%. Recent investigations show that complement system activation in patients with TA-TMA is a very poor prognostic sign and implicates complement dysregulation as a key pathway in the pathogenesis of TA-TMA and its disease phenotype. The original diagnostic criteria for TA-TMA included hematologic and renal injury markers, which are limited in their ability to detect only advanced disease, and therefore may result in delayed TA-TMA diagnosis in transplant patients. A recent set of diagnostic criteria added markers of complement activation, proteinuria, and hypertension, with predicted improved detection of early TA-TMA. Supportive care that includes elimination of potentially toxic agents such as calcineurin inhibitors and sirolimus, adequate antimicrobial treatment, and maintaining adequate renal functions using renal replacement therapy may be sufficient for treatment of mild-to-moderate TA-TMA. Plasma exchange, which is a potentially curative therapy in thrombotic thrombocytopenic purpura, has no proven efficacy in TA-TMA. Blocking the complement system with eculizumab is currently the most effective treatment to circumvent the poor outcome in patients with severe TA-TMA.

Renal dysfunction following bone marrow transplantation

Acute kidney injury and long-term renal dysfunction are common problems following bone morrow transplantation (BMT) and highly related to mortality. The frequency and risk of renal dysfunction are directly related to the method of BMT, with myeloablative allogeneic BMT being associated to the highest risk followed by non-myeloablative allogeneic and myeloablative autologous BMT. The type of BMT is, thus, more important than co-factors such as advanced age, comorbidities, or high baseline serum creatinine. The causes for renal failure are multiple and include chemotherapy and high-dose radiation with fluid loss by diarrhea or vomiting, sepsis or nephrotoxic drugs such as calcineurin inhibitors and antimicrobials. Additionally, there are BMT-specific reasons for renal dysfunction including marrow infusion toxicity, hepatic veno-occlusive disease, thrombotic microangiopathy (TMA) and graft versus host disease (GvHD). Once the kidney has been damaged, the therapy depends on the underlying disease. Particularly in cases of TMA and GvHD, immunosuppressive therapy is essential. In TMA, plasma exchange therapy or eculizumab should be additionally considered if the complement system is affected. Hence, patients with these causes should preferably be referred to tertiary centers to allow early diagnosis and appropriate treatment.

Renal pathology in hematopoietic cell transplant recipients: a contemporary biopsy, nephrectomy, and autopsy series

Renal injury in hematopoietic cell transplant recipients may be related to a combination of factors including chemotherapy, radiation, infection, immunosuppressive agents, ischemia, and graft-versus-host disease, and can involve glomerular, tubulointerstitial, and vascular structures. We reviewed renal pathology from 67 patients at a single institution (2009-2014), including 14 patients with biopsy for clinical dysfunction, 6 patients with surgical kidney resection for other causes, and 47 autopsy patients. Kidney specimens frequently contained multiple histopathologic abnormalities. Thrombotic microangiopathy, membranous nephropathy, minimal change disease, and focal segmental glomerulosclerosis were the most common glomerular findings. Pathologies not previously reported in the hematopoietic cell transplant setting included collapsing glomerulopathy, antiglomerular basement membrane disease, fibrillary glomerulonephritis, and in the case of two surgical resections distinctive cellular segmental glomerular lesions that defied classification. Kidney specimens frequently demonstrated acute tubular injury, interstitial fibrosis, arteriolar hyaline, and arteriosclerosis. Other kidney findings at autopsy included leukemia and amyloid (both recurrent), diabetic nephropathy, bacterial infection, fungal invasion, and silver deposition along glomerular and tubular basement membranes. Also in the autopsy cohort, C4d immunohistochemistry demonstrated unexpected membranous nephropathy in two patients, yet C4d also colocalized with arteriolar hyaline. This retrospective hematopoietic cell transplant cohort illustrates multifaceted renal injury in patients with renal dysfunction, as well as in patients without clinically recognized kidney injury.

New approaches in the diagnosis, pathophysiology, and treatment of pediatric hematopoietic stem cell transplantation-associated thrombotic microangiopathy

Hematopoietic stem cell transplantation (HSCT)-associated thrombotic microangiopathy (TA-TMA) is an understudied complication of HSCT that significantly affects transplant-related morbidity and mortality. Over the past several decades, the cause of TA-TMA has remained unknown, limiting treatment options to non-specific therapies adapted from other diseases. Recent prospective studies dedicated to the study of TA-TMA have provided new insights into the pathogenesis of, and genetic susceptibility to TA-TMA, raising awareness of this important transplant complication and allowing for the identification of potentially novel therapeutic targets. Specifically, many patients with TA-TMA develop multi-organ tissue injury through endothelial damage mediated by the activation of the complement pathway, leading to rational therapeutic strategies including complement blockade. This new knowledge has the potential to favorably influence clinical practice and change the standard of care for how patients with TA-TMA are managed. In this review, we summarize novel approaches to the recognition and management of TA-TMA, using case examples to illustrate key clinical points that hopefully lead to improved short and long-term outcomes for these complex HSCT patients, who remain at significant risk for treatment-related morbidity and mortality.

Hematopoietic Stem Cell Transplant-Associated Thrombotic Microangiopathy

Hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA) is a fatal, multifactorial disorder, which may present with thrombocytopenia, hemolysis, acute renal failure, mental status changes and involvement of other organs. The pathogenesis of TA-TMA is complex and includes multiple risk factors such as certain conditioning regimens, calcineurin inhibitors (CNIs), graft-versus-host disease (GVHD), human leukocyte antigen mismatch, and opportunistic infections. The end result of these insults is endothelial injury in the kidney and other organs. Recent studies also indicate a role of complement activation in tissue damage. The lack of sensitive and specific diagnostic tests for TA-TMA often results in delayed diagnosis. Biopsy is not always possible for diagnosis because of the risk of complications such as bleeding. Recently, an emerging role of renal-centered screening approach has been demonstrated, which utilize the monitoring of blood pressure, urine protein, serum lactate dehydrogenase and hemogram for early detection. Therapeutic options are limited, and plasma exchange plays a minor role. Withdrawal of offending agent such as CNIs and the use of rituximab can be effective in some patients. However, the current treatment strategy is suboptimal and associated with high mortality rate. Recently, eculizumab has been utilized in a few patients with good outcomes. Patients, who develop TA-TMA, are also at an increased risk of GVHD, infection, renal, cardiovascular, and other complications, which can contribute to high mortality. Better understanding of molecular pathogenesis, improvement in posttransplant management, leading to early diagnosis, and management of TA-TMA are required to improve outcomes of this fatal entity.

Thrombotic microangiopathy associated with proteasome inhibitors

The ubiquitin proteasome pathway plays a key role in cell cycle, function and survival. Bortezomib (BTZ) and Carfilzomib (CFZ) are the first two inhibitors of the proteasome pathway, indicated in treatment of patients with multiple myeloma. In the past few years, there have been few case reports that have highlighted the association between proteasome inhibitors (BTZ and CFZ) with acute kidney injury (AKI). In most of these case reports and initial trials, the underlying mechanism of AKI has been unclear. In this article, we discuss the association and pathogenesis of proteasome inhibitors-associated AKI. We also report the first case of CFZ-associated AKI with kidney biopsy evidence of thrombotic microangiopathy and the presence of microangiopathic hemolytic anemia.

Thrombotic microangiopathy, cancer, and cancer drugs

Thrombotic microangiopathy (TMA) is a complication that can develop directly from certain malignancies, but more often results from anticancer therapy. Currently, the incidence of cancer drug-induced TMA during the last few decades is >15%, primarily due to the introduction of anti-vascular endothelial growth factor (VEGF) agents. It is important for clinicians to understand the potential causes of cancer drug-induced TMA to facilitate successful diagnosis and treatment. In general, cancer drug-induced TMA can be classified into 2 types. Type I cancer drug-induced TMA includes chemotherapy regimens (ie, mitomycin C) that can potentially promote long-term kidney injury, as well as increased morbidity and mortality. Type II cancer drug-induced TMA includes anti-VEGF agents that are not typically associated with cumulative dose-dependent cell damage. In addition, functional recovery of kidney function often occurs after drug interruption, assuming a type I agent was not given prior to or during therapy. There are no randomized controlled trials to provide physician guidance in the management of TMA. However, previously accumulated information and research suggest that endothelial cell damage has an underlying immunologic basis. Based on this, the emerging trend includes the use of immunosuppressive agents if a refractory or relapsing clinical course that does not respond to plasmapheresis and steroids is observed.

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.

Renal pathology associated with hematopoietic stem cell transplantation

The kidney is subject to a large variety of injurious factors before, during, and after hematopoietic stem cell transplantation (HCT), leading to a high incidence of acute kidney injury in the peritransplant period. Chronic kidney disease is estimated to impact 15% to 20% of HCT recipients. Although renal biopsies may be deferred in the setting of thrombotic microangiopathy, acute self-limited impairment, or slowly progressive functional decline, in many patients renal biopsy yields important diagnostic insight to guide treatment. Light microscopic, immunofluorescence, and ultrastructural analysis often reveals a number of concurrent abnormalities in glomeruli, tubules, interstitium, and vessels. Meta-analysis of the literature reveals that membranous nephropathy is the most commonly reported glomerular lesion in the setting of HCT, followed by minimal change disease. Autopsy and biopsy studies show that clinical criteria lack sensitivity and specificity for renal acute and chronic thrombotic microangiopathy. Viral infection and other causes of interstitial nephritis and tubular injury are important findings in HCT renal biopsies, which in many instances may not be clinically suspected. Given the complexity and variability of HCT protocols, clinicopathologic correlation is needed.

Risk factors for thrombotic microangiopathy in allogeneic hematopoietic stem cell recipients receiving GVHD prophylaxis with tacrolimus plus MTX or sirolimus

Transplantation-associated thrombotic microangiopathy (TA-TMA) is a feared complication of allogeneic hematopoietic SCT (HSCT) owing to its high mortality rate. The use of calcineurin inhibitors or sirolimus (SIR) for GVHD prophylaxis has been suggested as a potential risk factor. However, the impact of tacrolimus (TAC) and SIR combinations on the increased risk of TA-TMA is currently not well defined. We retrospectively analyzed the incidence of TA-TMA in 102 allogeneic HSCT recipients who consecutively received TAC plus SIR (TAC/SIR) (n=68) or plus MTX (TAC/MTX)±ATG (n=34) for GVHD prophylaxis. No significant differences were observed in the incidence of TA-TMA between patients receiving TAC/SIR vs TAC/MTX±ATG (7.4% vs 8.8%, P=0.8). Only grade III-IV acute GVHD, previous HSCT and serum levels of TAC >25 ng/mL were associated with a greater risk of TA-TMA. Patients developing TA-TMA have significantly poorer survival (P<0.001); however, TA-TMA ceased to be an independent prognostic factor when it was included in a multivariate model. In conclusion, the combination of TAC/SIR does not appear to pose a higher risk of TA-TMA. By contrast, we identified three different risk groups for developing TA-TMA.