De novo thrombotic microangiopathy after kidney transplantation: clinical features, treatment, and long-term patient and graft survival

Thrombotic microangiopathy after kidney transplantation: Expanding etiologic and pathogenetic spectra

Thrombotic microangiopathy (TMA) is an uncommon but serious complication that not only affects native kidneys but also transplanted kidneys. This review is specifically focused on post-transplant TMA (PT-TMA) involving kidney transplant recipients. Its reported prevalence in the latter population varies from 0.8% to 14% with adverse impacts on both graft and patient survival. It has many causes and associations, and the list of etiologic agents and associations is growing constantly. The pathogenesis is equally varied and a variety of patho genetic pathways lead to the development of microvascular injury as the final common pathway. PT-TMA is categorized in many ways in order to facilitate its management. Ironically, more than one causes are contributory in PT-TMA and it is often difficult to pinpoint one particular cause in an individual case. Pathologically, the hallmark lesions are endothelial cell injury and intravascular thrombi affecting the microvasculature. Early diagnosis and classification of PT-TMA are imperative for optimal outcomes but are challenging for both clinicians and pathologists. The Banff classification has addressed this issue and has developed minimum diagnostic criteria for pathologic diagnosis of PT-TMA in the first phase. Management of the condition is also challenging and still largely empirical. It varies from simple maneuvers, such as plasmapheresis, drug withdrawal or modification, or dose reduction, to lifelong complement blockade, which is very expensive. A thorough understanding of the condition is imperative for an early diagnosis and quick treatment when the treatment is potentially effective. This review aims to increase the awareness of relevant stakeholders regarding this important, potentially treatable but under-recognized cause of kidney allograft dysfunction.

Unveiling the Incidence and Graft Survival Rate in Kidney Transplant Recipients With De Novo Thrombotic Microangiopathy: A Systematic Review and Meta-Analysis

De novo thrombotic microangiopathy (TMA) is a rare and challenging condition in kidney transplant recipients, with limited research on its incidence and impact on graft survival. This study conducted a systematic review and meta-analysis of 28 cohorts/single-arm studies and 46 case series/reports from database inception to June 2022. In meta-analysis, among 14,410 kidney allograft recipients, de novo TMA occurred in 3.20% [95% confidence interval (CI): 1.93-4.77], with systemic and renal-limited TMA rates of 1.38% (95% CI: 06.5-2.39) and 2.80% (95% CI: 1.27-4.91), respectively. The overall graft loss rate of de novo TMA was 33.79% (95% CI: 26.14-41.88) in meta-analysis. This study provides valuable insights into the incidence and graft outcomes of de novo TMA in kidney transplant recipients.

TMA in Kidney Transplantation

Thrombotic microangiopathy (TMA) is a rare and devastating complication of kidney transplantation, which often leads to graft failure. Posttransplant TMA (PT-TMA) may occur either de novo or as a recurrence of the disease. De novo TMA can be triggered by immunosuppressant drugs, antibody-mediated rejection, viral infections, and ischemia/reperfusion injury in patients with no evidence of the disease before transplantation. Recurrent TMA may occur in the kidney grafts of patients with a history of atypical hemolytic uremic syndrome (aHUS) in the native kidneys. Studies have shown that some patients with aHUS carry genetic abnormalities that affect genes that code for complement regulators (CFH, MCP, CFI) and components (C3 and CFB), whereas in 10% of patients (mostly children), anti-FH autoantibodies have been reported. The incidence of aHUS recurrence is determined by the underlying genetic or acquired complement abnormality. Although treatment of the causative agents is usually the first line of treatment for de novo PT-TMA, this approach might be insufficient. Plasma exchange typically resolves hematologic abnormalities but does not improve kidney function. Targeted complement inhibition is an effective treatment for recurrent TMA and may be effective in de novo PT-TMA as well, but it is necessary to establish which patients can benefit from different therapeutic options and when and how these can be applied.

Thrombotic microangiopathies after kidney transplantation in modern era: nosology based on chronology

BACKGROUND

Thrombotic microangiopathies (TMAs) are rare but can be severe in kidney transplant. recipients (KTR).

METHODS

We analysed the epidemiology of adjudicated TMA in consecutive KTR during the. 2009-2021 period.

RESULTS

TMA was found in 77/1644 (4.7%) KTR. Early TMA (n = 24/77 (31.2%); 1.5% of all KTR) occurred during the first two weeks ((median, IQR) 3 [1-8] days). Triggers included acute antibody-mediated rejection (ABMR, n = 4) and bacterial infections (n = 6). Graft survival (GS) was 100% and recurrence rate (RR) was 8%. Unexpected TMA (n = 31/77 (40.2%); 1.5/1000 patient-years) occurred anytime during follow-up (3.0 (0.5-6.2) years). Triggers included infections (EBV/CMV: n = 10; bacterial: n = 6) and chronic active ABMR (n = 5). GS was 81% and RR was 16%. Graft-failure associated TMA (n = 22/77 (28.6%); 2.2% of graft losses) occurred after 8.8 (4.9-15.5) years). Triggers included acute (n = 4) or chronic active (n = 14) ABMR, infections (viral: n = 6; bacterial: n = 5) and cancer (n = 6). 15 patients underwent transplantectomy. RR was 27%. Atypical (n = 6) and typical (n = 2) haemolytic and uremic syndrome, and isolated CNI toxicity (n = 4) were rare. Two-third of biopsies presented TMA features.

CONCLUSIONS

TMA are mostly due to ABMR and infections; causes of TMA are frequently combined. Management often is heterogenous. Our nosology based on TMA timing identifies situations with distinct incidence, causes and prognosis.

Isolated arterial mucoid intimal thickening lesion in early post-transplant kidney allograft biopsies

INTRODUCTION

Thrombotic microangiopathy (TMA) on kidney biopsy shows a variable combination of features: arterial mucoid intimal thickening, acellular closure of glomerular capillary loops, fragmented red blood cells, fibrin thrombi, and arterial fibrinoid necrosis. However, some early post-transplant kidney biopsies show only arterial mucoid intimal thickening. We aimed to elucidate the importance of this finding.

METHODS

We identified 19 biopsies showing isolated arterial mucoid intimal thickening and compared them with 22 bona fide TMA biopsies identified based on the pathological findings (excluding rejection) (2011-2020). Additionally, delayed graft function (DGF) (n = 237), and no DGF (control, n = 1314) groups were included for survival analysis.

RESULTS

Seven of 19 cases with isolated arterial mucoid intimal thickening showed peripheral blood schistocytes but no other systemic features of TMA. Eight patients underwent adjustments in maintenance immunosuppression (mainly calcineurin inhibitors). None of the cases progressed to full-blown TMA on consecutive biopsies. The overall and death-censored graft survival rates in this group were comparable to the DGF group, but significantly better than the TMA group (P = .005 and .04, respectively).

CONCLUSIONS

Isolated arterial mucoid intimal thickening in early post-transplant biopsies may be an early/mild form of TMA, probably requiring adjustment in immunosuppressive regimen. Careful exclusion of known causes of TMA, and donor-derived arterial injury are important.

Haemolytic uraemic syndrome

Haemolytic uraemic syndrome (HUS) is a heterogeneous group of diseases that result in a common pathology, thrombotic microangiopathy, which is classically characterised by the triad of non-immune microangiopathic haemolytic anaemia, thrombocytopenia, and acute kidney injury. In this Seminar, different causes of HUS are discussed, the most common being Shiga toxin-producing Escherichia coli HUS. Identifying the underlying thrombotic microangiopathy trigger can be challenging but is imperative if patients are to receive personalised disease-specific treatment. The quintessential example is complement-mediated HUS, which once carried an extremely high mortality but is now treated with anti-complement therapies with excellent long-term outcomes. Unfortunately, the high cost of anti-complement therapies all but precludes their use in low-income countries. For many other forms of HUS, targeted therapies are yet to be identified.

A Rare Case of Atypical Hemolytic Uremia Syndrome Triggered by Influenza Vaccination

Atypical hemolytic uremic syndrome (aHUS) occurs in patients with defective alternative complement pathways, making them susceptible to thrombotic microangiopathy (thrombocytopenia, intravascular hemolysis, and renal failure), and is usually triggered by infectious agents. Influenza and Streptococcus pneumonia are known triggers for aHUS. However, influenza vaccination triggering aHUS is rarely reported. We present a 30-year-old male who presented with chills, abdominal discomfort, and night sweats after receiving the influenza vaccine. The patient had thrombocytopenia, elevated creatinine, blood urea nitrogen, liver enzymes, and bilirubin with schistocytes with peripheral smear. ADAMTS13 activity was normal so the patient was diagnosed with aHUS. The patient improved with eculizumab and was ultimately found to have a mutation in CD46, which made him susceptible to aHUS. This case shows patients with dysregulated alternative complement pathways may be predisposed to develop aHUS after receiving influenza vaccination.

Rejection-associated Phenotype of De Novo Thrombotic Microangiopathy Represents a Risk for Premature Graft Loss

Supplemental Digital Content is available in the text.

Background.

Thrombotic microangiopathy (TMA) significantly affects kidney graft survival, but its pathophysiology remains poorly understood.

Methods.

In this multicenter, retrospective, case–control paired study designed to control for donor-associated risks, we assessed the recipients’ risk factors for de novo TMA development and its effects on graft survival. The study group consists of patients with TMA found in case biopsies from 2000 to 2019 (n = 93), and the control group consists of recipients of paired kidney grafts (n = 93). Graft follow-up was initiated at the time of TMA diagnosis and at the same time in the corresponding paired kidney graft.

Results.

The TMA group displayed higher peak panel-reactive antibodies, more frequent retransplantation status, and longer cold ischemia time in univariable analysis. In the multivariable regression model, longer cold ischemia times (odds ratio, 1.18; 95% confidence interval [CI], 1.01-1.39; P = 0.043) and higher peak pretransplant panel-reactive antibodies (odds ratio, 1.03; 95% CI, 1.01-1.06; P = 0.005) were found to be associated with increased risk of de novo TMA. The risk of graft failure was higher in the TMA group at 5 y (hazard ratio [HR], 3.99; 95% CI, 2.04-7.84; P < 0.0001). Concomitant rejection significantly affected graft prognosis at 5 y (HR, 6.36; 95% CI, 2.92-13.87; P < 0.001). De novo TMA associated with the active antibody-mediated rejection was associated with higher risk of graft failure at 5 y (HR, 3.43; 95% CI, 1.69-6.98; P < 0.001) compared with other TMA.

Conclusions.

Longer cold ischemia and allosensitization play a role in de novo TMA development, whereas TMA as a part of active antibody-mediated rejection was associated with the highest risk for premature graft loss.

Clinical profile and outcomes of De novo posttransplant thrombotic microangiopathy

Thrombotic microangiopathy (TMA) after kidney transplant is rather uncommon but an important reversible cause of graft loss. This retrospective study of biopsy-proven posttransplant TMA was done to identify the important etiological factors, clinical features, and outcomes of post transplant TMA in a tertiary care referral hospital in northern India. This retrospective study was conducted among all renal transplant recipients who presented with graft dysfunction between 1989 and 2015. All the cases were looked for their etiology, clinical course, treatment modalities, and renal outcomes. The study was conducted in accord with prevailing ethical principles and reviewed by our own institutional review board. Seventeen patients out of 2000 (0.008%) transplants done during the study period had posttransplant TMA, out of which all the patients had de novo TMA, and the median time of presentation after transplantation was four months. Systemic TMA was noted in only four patients. Biopsy revealed associated rejection in five patients and associated calcineurin inhibitor (CNI) toxicity in 12 patients. Patients with TMA due to CNI toxicity were managed with CNI reduction or switching to alternate CNI or mammalian target of rapamycin inhibitors. In addition, antithymocyte globulin and plasma exchange were used in rejection-associated TMA. While four out of 12 patients (33%) in CNI-related TMA developed end-stage renal disease (ESRD), all patients in rejection-associated TMA developed ESRD. The overall one-year graft survival was 47%, whereas five- and 10-year survival was 35%. There was no significant difference in graft survival between localized and systemic TMAs (P = 0.4). Posttransplant TMA should be suspected even if there are no systemic features of hemolysis and early graft biopsy and prompt action is needed. The occurrence of TMA in the setting of rejection is associated with grave prognosis.

Haematological disorders following kidney transplantation

Transplantation offers cure for some haematological cancers, end-stage organ failure, but at the cost of long-term complications. Renal transplantation is the best-known kidney replacement therapy and it can prolong end-stage renal disease patient lives for decades. However, patients after renal transplantation are at a higher risk of developing different complications connected not only with surgical procedure but also with immunosuppressive treatment, chronic kidney disease progression and rejection processes. Various blood disorders can develop in post-transplant patients ranging from relatively benign anaemia through cytopenias to therapy-related myelodysplasia and acute myeloid leukaemia (AML) and post-transplant lymphoproliferative disorders followed by a rare and fatal condition of thrombotic microangiopathy and haemophagocytic syndrome. So far literature mainly focused on the post-transplant lymphoproliferative disease. In this review, a variety of haematological problems after transplantation ranging from rare disorders such as myelodysplasia and AML to relatively common conditions such as anaemia and iron deficiency are presented with up-to-date diagnosis and management.

Atypical Hemolytic Uremic Syndrome: New Challenges in the Complement Blockage Era

Atypical hemolytic uremic syndrome (aHUS) is a rare cause of thrombotic microangiopathy (TMA), characterized by microangiopathic hemolytic anemia, consumptive thrombocytopenia, and multisystem end organ involvement, most commonly affecting the kidney. Diagnosis is clinical, after exclusion of other TMA causes. Primary aHUS arises from genetic abnormalities, resulting in uncontrolled complement activity, while a variety of clinical scenarios cause secondary aHUS, including infection, pregnancy, malignancy, autoimmune disease, and medications. They can also induce a temporary complement deregulation with an overlap between both scenarios, which can make differential diagnosis difficult. Primary aHUS can be sporadic or familial and is associated with a high rate of progression to ESRD. Many aHUS patients relapse in the native or transplanted kidneys, leading to kidney failure. The introduction of eculizumab has changed the prognosis of aHUS, by inducing hematologic remission, improving or stabilizing kidney functions, and preventing graft failure. The early institution of appropriate therapy can prevent multiorgan damage, so is essential to recognize and differentiate the TMA syndromes. Eculizumab is considered now the first-line treatment, and it is recommended lifelong therapy. However, the high cost of therapy has led to make efforts to develop precise complement functional and genetic studies that help physicians to determine the appropriate duration of eculizumab therapy. Nowadays, more studies are needed to select candidates to adjustment of therapy.

Thrombotic microangiopathy involving kidney allograft and peripheral nerves

While thrombotic microangiopathy (TMA) can commonly affect the kidney, peripheral nerve involvement has not been reported to date. A 56-year-old man, recipient of a kidney allograft, reported severe headaches, tremors, and diarrhea followed by sudden-onset right foot drop after increasing his dose of tacrolimus. He then developed acute right hand pain, numbness, and weakness. At presentation, neurological examination and electroneuromyography confirmed the presence of right worse than left, sciatic and ulnar mononeuropathies. Kidney biopsy showed evidence of a thrombotic microangiopathy. Similarly, nerve biopsy showed thrombosis of epineurial blood vessels with minimal inflammation. Herein, we demonstrated that thrombotic microangiopathy can involve the peripheral nerves, resulting in major morbidity. Distinguishing TMA from vasculitis is important because it has major treatment implications.

Clinical and pathological features of thrombotic microangiopathy influencing long-term kidney transplant outcomes

INTRODUCTION

Thrombotic microangiopathy (TMA) in post-transplant setting has heterogeneous clinical manifestations.

METHODS

We retrospectively studied data of 89 patients with post-transplant TMA, which was characterized by thrombi in at least one glomerulus and/or arteriole. Systemic TMA was defined by thrombocytopenia and microangiopathic anemia and early onset TMA, when occurred less than 90 days post transplant.

RESULTS

The cumulative incidence was 0.93%. The majority of the recipients were young (mean age 39 years), female (52%) and Caucasian (48%) with primary kidney disease of unknown etiology (37%). Early TMA occurred in 51% of the patients and systemic TMA, in 25%. Underlying precipitating factors were: infection (54%), acute rejection (34%), calcineurin inhibitor toxicity (13%) and pregnancy (3%). 18% of the patients had several triggers. Glomerular TMA was observed in 50% of the biopsies and endothelial cell activation, in 61%. The 1-year patient survival was 97% and corresponding graft survival, 66%. Allograft survival was inferior when acute antibody mediated rejection (ABMR) occurred (with 41%; without 70%, p = 0.01), however no differences were determined by hemolysis, time of onset, thrombi location or endothelial cell activation.

CONCLUSIONS

Our results suggest that post-transplant TMA is a rare but severe condition, regardless of its clinical and histological presentation, mainly when associated to ABMR.

Clinical-pathological correlations in post-transplant thrombotic microangiopathy

AIMS

Post-transplant thrombotic microangiopathy (TMA) is a rare and clinically challenging finding in renal transplant biopsies. In addition to recurrent atypical haemolytic uraemic syndrome, TMA in renal transplants is associated with various conditions, such as calcineurin inhibitor (CNI) treatment, antibody-mediated rejection (ABMR), viral infections, sepsis, pregnancy, malignancies, and surgery. The therapeutic implications of this diagnosis are considerable. In order to better understand post-transplant TMA and to identify histological or clinical differences between associated causes, we conducted a multicentre retrospective study.

METHODS AND RESULTS

Clinical parameters and transplant renal biopsy findings from 81 patients with TMA were analysed. Biopsies from 38 patients were also analysed with electron microscopy. On the basis of clinical-pathological correlation, TMA was attributed to a main aetiology, whenever possible. TMA occurred at a median of 30 days post-transplantation. Systemic features of TMA were present in only 18% of cases. Twenty-two per cent of cases were attributed to CNI and 11% to ABMR. Although other potentially contributing factors were found in 56% of patients, in most cases (63%) no clearly attributable cause of TMA was identified. Histological differences between groups were minimal. The detection of ultrastructural features that are usually associated with ABMR may help to establish ABMR as the cause of TMA.

CONCLUSIONS

Although CNI and ABMR appear to be the main contributors to post-transplant TMA, the aetiology of most cases is probably multifactorial, and TMA cannot be unequivocally attributed to a single underlying aetiology. Morphological features of TMA are not discriminating, but electron microscopy may help to identify ABMR-associated TMA.

Metastatic lung adenocarcinoma- associated thrombotic microangiopathy in a renal transplant recipient

Thrombotic microangiopathy (TMA) after renal transplantation can be a diagnostic challenge. TMA can occur with calcineurin inhibitors, allograft rejection, infection, mutations in complement regulatory proteins and autoimmunity. A 52-year-old male renal transplant recipient presented with extensive deep vein thrombosis. He developed transfusion-dependent microangiopathic haemolytic anaemia with thrombocytopenia. He did not respond calcineurin inhibitor cessation, eculizumab or plasma exchange. ADAMTS13 and complement levels were normal. Infection and autoimmune screens were negative. A diagnosis of metastatic adenocarcinoma was made on bone marrow biopsy. This represents a rare case of malignancy-associated TMA in a renal transplant recipient. Early diagnosis can facilitate the prompt initiation of chemotherapy which is the only treatment option.

De Novo Thrombotic Microangiopathy in Renal Transplant Patients

OBJECTIVES

Thrombotic microangiopathy is a form of renal capillary injury possibly associated with calcineurin inhibitor toxicity, acute humoral rejection, infections, and recurrent diseases. Here, we examined its incidence in patients diagnosed with acute and chronic active humoral rejection, polyomavirus nephropathy, acute cellular rejection, and immunoglobulin A recurrence.

MATERIALS AND METHODS

In total, 272 renal allograft recipients who met the inclusion criteria were reevaluated for presence of renal thrombotic microangiopathy. Thrombotic microangiopathy diagnosis was established by clinical, laboratory, and histologic features. C4d expression in peritubular capillaries was determined. Clinical data were collected from medical records.

RESULTS

Of 272 patients (mean age of 42.8 ± 12.7 years), only 74 patients (27.2%) had de novo thrombotic microangiopathy, which was found in 30/90 patients (33.3%) with acute humoral rejection, 9/51 (17.6%) with acute cellular rejection, 22/53 (41.5%) with chronic active humoral rejection, 10/55 (18.2%) with polyomavirus nephropathy, and 3/23 (13%) with immunoglobulin A nephropathy. Significant differences were shown between therapy type and thrombotic microangiopathy development (P = .02). Patients who received cyclosporine (38.5%) tended to show higher incidence of thrombotic microangiopathy than patients who received tacrolimus (20.7%) or sirolimus (7.7%). Patients with C4d-positive acute humoral (97.6% vs 2.4%) and chronic active humoral rejection (68.2% vs 31.8%) had greater incidence of thrombotic microangiopathy versus those who were C4d-negative. Graft loss was significantly higher in C4d-positive than in C4d-negative thrombotic microangiopathy groups (P < .001). Overall 1-, 3-, and 5-year graft survival was 94%, 85%, and 85% versus 83%, 51%, and 51% in thrombotic microangiopathy-negative versus thrombotic microangiopathy-positive patients (P < .001).

CONCLUSIONS

Acute humoral rejection and chronic active humoral rejection were the most common and therefore most important causes of de novo thrombotic microangiopathy in renal transplant patients. Its presence in the renal allograft biopsy should arouse suspicion for underlying acute or chronic active humoral rejection.

No Significant Influence of Reduced Initial Tacrolimus Dose on Risk of Underdosing and Early Graft Function in Older and Overweight Kidney Transplant Recipients

BACKGROUND

Nowadays, a reduced initial daily dose of tacrolimus (Tac) (0.1-0.15 mg/kg) is recommended for the majority of kidney transplant recipients (KTRs). The aim of the study was to analyze the safety of such a regimen, including the risk of first inadequately low Tac blood level, acute rejection (AR) occurrence, or early graft dysfunction.

METHODS

In 2011, we introduced a modified (0.1-0.15 mg/kg/d) initial Tac dosing regimen in older (>55 years) and/or overweight KTRs. To assure the safety of this protocol, we monitored the risk of inadequately low blood Tac level (<6 ng/mL) and incidence of AR or delayed graft function (DGF). The historical cohort with the higher Tac dosing regimen (0.2 mg/kg/d, n = 208) served as a control group.

RESULTS

The mean Tac daily dose in 78 KTRs (group with reduced dosing) was 0.133 (95% confidence interval [CI], 0.130-0.136) mg/kg and was significantly lower than the standard, previously prescribed dose of 0.195 (95% CI, 0.194-0.197) mg/kg. Of note, induction therapy was employed twice more often in the reduced Tac dosing group. The dose reduction resulted in a slight, nonsignificant decrease in first Tac trough level. The percentages of patients with first Tac troughs <6 ng/mL (5.1% vs 4.8%), AR (6.4% vs 5.8%), and DGF (25.6% vs 31.2%) were similar in the reduced and standard dosing groups.

CONCLUSION

The currently recommended reduction in Tac initial dosing does not increase the risk of inadequate immunosuppression and does not affect the early graft function. Regardless of Tac dose reduction, there is still a substantial risk of Tac overdosing in older or overweight KTRs.

Secondary thrombotic microangiopathy and eculizumab: A reasonable therapeutic option

Understanding the role of the complement system in the pathogenesis of atypical haemolytic uraemic syndrome and other thrombotic microangiopathies (TMA) has led to the use of anti-complement therapy with eculizumab in these diseases, in addition to its original use in patients with paroxysmal nocturnal haemoglobinuria andatypical haemolytic uraemic syndrome. Scientific evidence shows that both primary and secondary TMAs with underlying complement activation are closely related. For this reasons, control over the complement system is a therapeutic target. There are 2scenarios in which eculizumab is used in patients with TMA: primary or secondary TMA that is difficult to differentiate (including incomplete clinical presentations) and complement-mediated damage in various processes in which eculizumab proves to be efficacious. This review summarises the evidence on the role of the complement activation in the pathophysiology of secondary TMAs and the efficacy of anti-complement therapy in TMAs secondary to pregnancy, drugs, transplant, humoral rejection, systemic diseases and glomerulonephritis. Although experience is scarce, a good response to eculizumab has been reported in patients with severe secondary TMAs refractory to conventional treatment. Thus, the role of the anti-complement therapy as a new treatment option in these patients should be investigated.

Innate networking: Thrombotic microangiopathy, the activation of coagulation and complement in the sensitized kidney transplant recipient

Thrombotic microangiopathy (TMA) is a histological feature of antibody-mediated rejection and has the potential to cause problematic graft dysfunction, particularly for highly sensitized cross-match positive kidney transplant recipients. Prompt recognition of pertinent histopathological and systemic features of TMA in kidney transplantation is necessary. Underlying mechanisms of this process involve the activation of both complement and coagulation systems as a response to HLA antibody. As serine proteases, coagulation and complement cascades exhibit similar characteristics with respect to homeostatic function. Increasing evidence now exists for the interaction between these innate defenses in both activation and regulation, lending scope for intervention. Understanding the complexities of these interactions remains a challenge. This review provides an overview of the current understanding, particularly with respect to the activation of coagulation and complement by HLA antibody in the setting of highly sensitized kidney transplantation.

Which Kidney Transplant Recipients Can Benefit from the Initial Tacrolimus Dose Reduction?

Background

Observational data suggest that the fixed initial recommended tacrolimus (Tc) dosing (0.2 mg/kg/day) results in supratherapeutic drug levels in some patients during the early posttransplant period. The aim of the study was to analyze a wide panel of patient-related factors and their interactions which increase the risk for first Tc blood level > 15 ng/ml.

Materials and Methods

We performed a retrospective analysis of 488 consecutive adult kidney transplant recipients who were initially treated with triple immunosuppressive regimen containing tacrolimus twice daily. The analysis included the first assessment of Tc trough blood levels and several demographic, anthropometric, laboratory, and comedication data.

Results

The multiple logistic regression analysis showed that age > 55 years, BMI > 24.6 kg/m², blood hemoglobin concentration > 9.5 g/dl, and the presence of anti-HCV antibodies independently increased the risk for first Tc level > 15 ng/ml. The relative risk (RR) for first tacrolimus level > 15 ng/ml was 1.88 (95% CI 1.35–2.64, p < 0.001) for patients with one risk factor and 2.81 (2.02–3.89, p < 0.001) for patients with two risk factors.

Conclusions

Initial tacrolimus dose reduction should be considered in older, overweight, or obese kidney transplant recipients and in subjects with anti-HCV antibodies. Moreover, dose reduction of tacrolimus is especially important in patients with coexisting multiple risk factors.

HUS and atypical HUS

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy characterized by intravascular hemolysis, thrombocytopenia, and acute kidney failure. HUS is usually categorized as typical, caused by Shiga toxin-producing Escherichia coli (STEC) infection, as atypical HUS (aHUS), usually caused by uncontrolled complement activation, or as secondary HUS with a coexisting disease. In recent years, a general understanding of the pathogenetic mechanisms driving HUS has increased. Typical HUS (ie, STEC-HUS) follows a gastrointestinal infection with STEC, whereas aHUS is associated primarily with mutations or autoantibodies leading to dysregulated complement activation. Among the 30% to 50% of patients with HUS who have no detectable complement defect, some have either impaired diacylglycerol kinase ε (DGKε) activity, cobalamin C deficiency, or plasminogen deficiency. Some have secondary HUS with a coexisting disease or trigger such as autoimmunity, transplantation, cancer, infection, certain cytotoxic drugs, or pregnancy. The common pathogenetic features in STEC-HUS, aHUS, and secondary HUS are simultaneous damage to endothelial cells, intravascular hemolysis, and activation of platelets leading to a procoagulative state, formation of microthrombi, and tissue damage. In this review, the differences and similarities in the pathogenesis of STEC-HUS, aHUS, and secondary HUS are discussed. Common for the pathogenesis seems to be the vicious cycle of complement activation, endothelial cell damage, platelet activation, and thrombosis. This process can be stopped by therapeutic complement inhibition in most patients with aHUS, but usually not those with a DGKε mutation, and some patients with STEC-HUS or secondary HUS. Therefore, understanding the pathogenesis of the different forms of HUS may prove helpful in clinical practice.

Thrombotic microangiopathy caused by oral contraceptives in a kidney transplant recipient

Thrombotic microangiopathy (TMA) after kidney transplantation has various aetiologies, including acute antibody-mediated rejection, bacterial or viral infection and immunosuppressive drugs, particularly calcineurin inhibitors. We present the case of a 28-year-old woman who developed TMA 30 months after the transplantation of an ABO-incompatible kidney from a living unrelated donor. The patient developed a sudden onset of allograft renal dysfunction and became uremic. She was transferred to our institution from a community hospital with strongly suspected acute allograft rejection. Intensive treatments for both T- and B-cell mediated acute rejection, including steroid pulse therapy, double-filtration plasmapheresis, antithymocyte globulin (1.5 mg/kg × 14 days) and rituximab (100 mg), were initiated during haemodialysis. However, her renal allograft function did not improve. Histopathological analysis 8 days after the treatment indicated TMA, despite the absence of apparent acute T-cell- or acute antibody-mediated rejection. There were no symptoms of infectious diseases, such as intestinal haemorrhagic colitis or viral infection. We concluded that the use of oral contraceptives, which had been initiated 3 weeks before TMA onset for the treatment of irregular vaginal bleeding, was the aetiologic agent.

[A CASE OF SUCCESSFUL RECOVERY OF RENAL ALLOGRAFT FUNCTION FOLLOWING A DIAGNOSIS OF THROMBOTIC MICROANGIOPATHY CLINICALLY MADE IN THE IMMEDIATE POST-TRANSPLANT PERIOD]

A 57-year-old female patient on hemodialysis with chronic renal failure due to chronic glomerular nephritis received deceased donor kidney transplantation. Induction immunosuppressive therapy was combination of tacrolimus, mycophenolate mofetil, everolimus, prednisolone, and basiliximab. She was diagnosed with secondary thrombotic microangiopathy (TMA) by clinical findings such as hemolytic anemia, thrombocytopenia and acute kidney injury not by pathological findings on the 4th post-operative date. Plasma exchange was performed with suspension of tacrolimus. General conditions recovered, and the graft function was preserved.

Management of Thrombotic Microangiopathic Hemolytic Anemias with Therapeutic Plasma Exchange: When It Works and When It Does Not

Thrombotic microangiopathies are a heterogeneous group of inherited and acquired disorders sharing a common clinical presentation of microangiopathic hemolytic anemia, thrombocytopenia, and organ damage. These disorders have been treated with plasma exchange (TPE) based on randomized controlled trials, which found this therapy to be effective in thrombotic thrombocytopenic purpura (TTP). For the remaining disorders, low- to very low-quality evidence exists for the use of TPE. When TPE is applied, the treatment regimen used for TTP is usually applied. There is a need for further evaluation of the role of TPE in the treatment of thrombotic microangiopathies other than TTP.

De Novo Thrombotic Microangiopathy Immediately After Kidney Transplant in Patients Without Apparent Risk Factors

Thrombotic microangiopathy refers to a spectrum of conditions that share a common underlying pathologic mechanism that result in endothelial damage and microangiopathic hemolytic anemia. De novo thrombotic microangiopathy after kidney transplant is often triggered by immunosuppressive drugs, and studies most often implicate calcineurin inhibitors and/or mammalian target of rapamycin inhibitors; however, muromonab and alemtuzumab also reportedly cause thrombotic microangiopathy. In addition, thrombotic microangiopathy may be triggered by acute antibody-mediated rejection and infections like cytomegalovirus and parvovirus. Here, we present a case series of 3 patients without any apparent risk factors (eg, acute antibody-mediated rejection) who developed de novo thrombotic microangiopathy immediately following kidney transplant, but before the introduction of calcineurin inhibitors. Two of these 3 patients were successfully managed with plasma exchange, and calcineurin inhibitors were successfully introduced without the recurrence of thrombotic microangiopathy.

De novo tacrolimus-induced thrombotic microangiopathy in the early stage after renal transplantation successfully treated with conversion to everolimus

BACKGROUND

Calcineurin inhibitor (CNI)-induced thrombotic microangiopathy (TMA) is a rare complication after renal transplantation. It may be difficult to distinguish from CNI toxicity and acute antibody-mediated rejection (AMR). Its clinical presentation may vary from isolated localised forms up to catastrophic systemic presentations.

CASE

We report a case of tacrolimus-induced TMA soon after renal transplantation in an 11-year-old boy who received his second renal transplantation. His first graft was lost because of AMR. On day 12 after his second renal transplantation, his renal function started worsening and a kidney biopsy was performed, which showed histopathological signs of TMA. The diagnosis of tacrolimus-induced TMA was established after excluding AMR and other causes of de novo TMA. Genetic complement investigation disclosed two complement factor H risk polymorphisms as possible modifiers of TMA emergence. Treatment was based on replacing tacrolimus with everolimus, with a subsequent normalisation of renal function.

CONCLUSION

A prompt diagnosis of de novo TMA by early allograft biopsy is essential for the allograft outcome and genetic investigations for possible complement abnormalities are reasonable, not only for patients with a systemic aspect of their post-transplant TMA. Replacing tacrolimus with everolimus effectively controlled the TMA and stabilised renal function in our patient.

Blood disorders typically associated with renal transplantation

Renal transplantation has become one of the most common surgical procedures performed to replace a diseased kidney with a healthy kidney from a donor. It can help patients with kidney failure live decades longer. However, renal transplantation also faces a risk of developing various blood disorders. The blood disorders typically associated with renal transplantation can be divided into two main categories: (1) Common disorders including post-transplant anemia (PTA), post-transplant lymphoproliferative disorder (PTLD), post-transplant erythrocytosis (PTE), and post-transplant cytopenias (PTC, leukopenia/neutropenia, thrombocytopenia, and pancytopenia); and (2) Uncommon but serious disorders including hemophagocytic syndrome (HPS), thrombotic microangiopathy (TMA), therapy-related myelodysplasia (t-MDS), and therapy-related acute myeloid leukemia (t-AML). Although many etiological factors involve the development of post-transplant blood disorders, immunosuppressive agents, and viral infections could be the two major contributors to most blood disorders and cause hematological abnormalities and immunodeficiency by suppressing hematopoietic function of bone marrow. Hematological abnormalities and immunodeficiency will result in severe clinical outcomes in renal transplant recipients. Understanding how blood disorders develop will help cure these life-threatening complications. A potential therapeutic strategy against post-transplant blood disorders should focus on tapering immunosuppression or replacing myelotoxic immunosuppressive drugs with lower toxic alternatives, recognizing and treating promptly the etiological virus, bacteria, or protozoan, restoring both hematopoietic function of bone marrow and normal blood counts, and improving kidney graft survival.

Thrombotic microangiopathy in renal allografts: the diagnostic challenge

PURPOSE OF REVIEW

The diagnosis of thrombotic microangiopathy (TMA) is complex and often difficult. This review provides an approach to the diagnosis with emphasis on recent relevant developments.

RECENT FINDINGS

There is increasing evidence that most cases of recurrent TMA in renal allografts are secondary to mutations in genes encoding complement regulatory factors and complement components, such as factor H, factor I, membrane cofactor protein, C3, and others. Genetic work-up for these potential complement abnormalities is now available and recommended. Another important cause for recurrent TMA is the presence of autoantibodies, such as antibodies to factor H and antiphospholipid antibodies. De-novo TMA is much more common than recurrent TMA in renal allografts. De-novo TMA can be secondary to calcineurin inhibitor treatment, mammalian target of rapamycin inhibitor treatment, but frequently also to antibody-mediated rejection and less commonly to infections. Systemic signs of TMA are often absent, and the gold standard for diagnosis is the renal allograft biopsy. Unfortunately, diagnostic criteria for TMA are somewhat subjective, and the biopsy provides limited information regarding the exact underlying cause.

SUMMARY

TMA is a serious complication of renal transplantation, usually with poor outcome. However, with improving understanding of underlying pathogeneses, more effective disease-specific therapeutic interventions can be designed. Appropriate treatment depends on the correct diagnosis, which relies primarily on renal allograft biopsy. Standardization of pathologic criteria and introduction of new molecular testing methods in renal biopsy specimens hopefully will improve diagnostic accuracy.

De novo glomerular diseases after renal transplantation

Glomerular diseases developing in the kidney allograft are more often recurrences of the original disease affecting the native kidneys. However, in an undefined number of cases de novo, glomerular diseases unrelated to the original disease in the native kidneys can develop in the transplanted kidney. The clinical presentation and histologic features of de novo diseases are often similar to those features observed in patients with primary or secondary GN in the native kidneys. However, in transplanted kidneys, the glomerular, vascular, and tubulointerstitial changes are often intertwined with structural abnormalities already present at the time of transplant or caused by antibody- or cell-mediated allograft rejection, immunosuppressive drugs, or superimposed infection (most often of a viral nature). The pathophysiology of de novo glomerular diseases is quite variable. In rare cases of de novo minimal change disease, circulating factors increasing the glomerular permeability likely participate. Maladaptive hemodynamic changes and tissue fibrosis caused by calcineurin inhibitors or other factors may be involved in the pathogenesis of de novo FSGS. The exposure of cryptic podocyte antigens may favor the development of de novo membranous nephropathy. Many cases of de novo membranoproliferative GN are related to hepatitis C virus infection. Patients with Alport syndrome lacking antigenic epitopes in their glomerular basement membrane may develop antibodies against these glomerular basement membrane antigens expressed in the transplanted kidney. Infection may cause acute GN to have a heterogeneous clinical presentation and outcome. De novo pauci-immune GN in renal transplant is rare. Preexisting or acquired intolerance to glucose may, in the long term, cause diabetic nephropathy. The prognosis of de novo diseases depends on the type of GN, the severity of lesions caused by the alloimmune response, or the efficacy of immunosuppressive therapy. In most cases, the management of de novo glomerular diseases is empirical or elusive.