Twenty-five years of European Union collaboration in ANCA-associated vasculitis research

Role of complement activation in anti-neutrophil cytoplasmic antibody-associated glomerulonephritis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is an autoimmune disease characterized by necrotizing inflammation of small or medium vessels, causing ANCA associated glomerulonephritis (AAGN). AAGN is defined as pauci-immune glomerulonephritis with no or little immune deposition; hence, activation of the complement system in AAV was overlooked until recently. However, many studies in mice and humans have revealed a crucial role for complement system activation in the development of AAGN. Circulating and urinary detection of various complement components associated with AP activation, which have been broadly correlated with the clinical activity of AAGN, has been reported and may be useful for predicting renal outcome at the time of diagnosis and setting up personalized treatments. Moreover, recent investigations have suggested the possible contribution of the complement classical or lectin pathway activation in the development of AAGN. Thus, as therapeutic options targeting complement components are making rapid strides, the primary complement pathway involved in AAGN disease progression remains to be elucidated: this will directly impact the development of novel therapeutic strategies with high specificity and reduced side effects. This review summarizes and discusses the most recent evidence on the crucial roles of the complement system in the development of AAGN and possible therapeutic strategies that target complement components for disease management.

Plasma exchange and glucocorticoids to delay death or end-stage renal disease in anti-neutrophil cytoplasm antibody-associated vasculitis: PEXIVAS non-inferiority factorial RCT

BACKGROUND

Anti-neutrophil cytoplasm antibody-associated vasculitis is a multisystem, autoimmune disease that causes organ failure and death. Physical removal of pathogenic autoantibodies by plasma exchange is recommended for severe presentations, along with high-dose glucocorticoids, but glucocorticoid toxicity contributes to morbidity and mortality. The lack of a robust evidence base to guide the use of plasma exchange and glucocorticoid dosing contributes to variation in practice and suboptimal outcomes.

OBJECTIVES

We aimed to determine the clinical efficacy of plasma exchange in addition to immunosuppressive therapy and glucocorticoids with respect to death and end-stage renal disease in patients with severe anti-neutrophil cytoplasm antibody-associated vasculitis. We also aimed to determine whether or not a reduced-dose glucocorticoid regimen was non-inferior to a standard-dose regimen with respect to death and end-stage renal disease.

DESIGN

This was an international, multicentre, open-label, randomised controlled trial. Patients were randomised in a two-by-two factorial design to receive either adjunctive plasma exchange or no plasma exchange, and either a reduced or a standard glucocorticoid dosing regimen. All patients received immunosuppressive induction therapy with cyclophosphamide or rituximab.

SETTING

Ninety-five hospitals in Europe, North America, Australia/New Zealand and Japan participated.

PARTICIPANTS

Participants were aged ≥ 16 years with a diagnosis of granulomatosis with polyangiitis or microscopic polyangiitis, and either proteinase 3 anti-neutrophil cytoplasm antibody or myeloperoxidase anti-neutrophil cytoplasm antibody positivity, and a glomerular filtration rate of < 50 ml/minute/1.73 m2 or diffuse alveolar haemorrhage attributable to active anti-neutrophil cytoplasm antibody-associated vasculitis.

INTERVENTIONS

Participants received seven sessions of plasma exchange within 14 days or no plasma exchange. Oral glucocorticoids commenced with prednisolone 1 mg/kg/day and were reduced over different lengths of time to 5 mg/kg/day, such that cumulative oral glucocorticoid exposure in the first 6 months was 50% lower in patients allocated to the reduced-dose regimen than in those allocated to the standard-dose regimen. All patients received the same glucocorticoid dosing from 6 to 12 months. Subsequent dosing was at the discretion of the treating physician.

PRIMARY OUTCOME

The primary outcome was a composite of all-cause mortality and end-stage renal disease at a common close-out when the last patient had completed 10 months in the trial.

RESULTS

The study recruited 704 patients from June 2010 to September 2016. Ninety-nine patients died and 138 developed end-stage renal disease, with the primary end point occurring in 209 out of 704 (29.7%) patients: 100 out of 352 (28%) in the plasma exchange group and 109 out of 352 (31%) in the no plasma exchange group (adjusted hazard ratio 0.86, 95% confidence interval 0.65 to 1.13; p = 0.3). In the per-protocol analysis for the non-inferiority glucocorticoid comparison, the primary end point occurred in 92 out of 330 (28%) patients in the reduced-dose group and 83 out of 325 (26%) patients in the standard-dose group (partial-adjusted risk difference 0.023, 95% confidence interval 0.034 to 0.08; p = 0.5), thus meeting our non-inferiority hypothesis. Serious infections in the first year occurred in 96 out of 353 (27%) patients in the reduced-dose group and in 116 out of 351 (33%) patients in the standard-dose group. The rate of serious infections at 1 year was lower in the reduced-dose group than in the standard-dose group (incidence rate ratio 0.69, 95% confidence interval 0.52 to 0.93; p = 0.016).

CONCLUSIONS

Plasma exchange did not prolong the time to death and/or end-stage renal disease in patients with anti-neutrophil cytoplasm antibody-associated vasculitis with severe renal or pulmonary involvement. A reduced-dose glucocorticoid regimen was non-inferior to a standard-dose regimen and was associated with fewer serious infections.

FUTURE WORK

A meta-analysis examining the effects of plasma exchange on kidney outcomes in anti-neutrophil cytoplasm antibody-associated vasculitis is planned. A health-economic analysis of data collected in this study to examine the impact of both plasma exchange and reduced glucocorticoid dosing is planned to address the utility of plasma exchange for reducing early end-stage renal disease rates. Blood and tissue samples collected in the study will be examined to identify predictors of response to plasma exchange in anti-neutrophil cytoplasm in antibody-associated vasculitis. The benefits associated with reduced glucocorticoid dosing will inform future studies of newer therapies to permit further reduction in glucocorticoid exposure. Data from this study will contribute to updated management recommendations for anti-neutrophil cytoplasm antibody-associated vasculitis.

LIMITATIONS

This study had an open-label design which may have permitted observer bias; however, the nature of the end points, end-stage renal disease and death, would have minimised this risk. Despite being, to our knowledge, the largest ever trial in anti-neutrophil cytoplasm antibody-associated vasculitis, there was an insufficient sample size to assess clinically useful benefits on the separate components of the primary end-point: end-stage renal disease and death. Use of a fixed-dose plasma exchange regimen determined by consensus rather than data-driven dose ranging meant that some patients may have been underdosed, thus reducing the therapeutic impact. In particular, no biomarkers have been identified to help determine dosing in a particular patient, although this is one of the goals of the biomarker plan of this study.

TRIAL REGISTRATION

This trial is registered as ISRCTN07757494, EudraCT 2009-013220-24 and Clinicaltrials.gov NCT00987389.

FUNDING

This project was funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 26, No. 38. See the NIHR Journals Library website for further project information.

Anti-cytokine targeted therapies for ANCA-associated vasculitis

BACKGROUND

Anti-neutrophilic cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) are a group of rare auto-inflammatory diseases that affects mainly small vessels. AAV includes: granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA). Anti-cytokine targeted therapy uses biological agents capable of specifically targeting and neutralising cytokine mediators of the inflammatory response.

OBJECTIVES

To assess the benefits and harms of anti-cytokine targeted therapy for adults with AAV.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (2019, Issue 7), MEDLINE and Embase up to 16 August 2019. We also examined reference lists of articles, clinical trial registries, websites of regulatory agencies and contacted manufacturers.

SELECTION CRITERIA

Randomised controlled trials (RCTs) or controlled clinical trials of targeted anti-cytokine therapy in adults (18 years or older) with AAV compared with placebo, standard therapy or another modality and anti-cytokine therapy of different type or dose.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane.

MAIN RESULTS

We included four RCTs with a total of 440 participants (mean age 48 to 56 years). We analysed the studies in three groups: 1) mepolizumab (300 mg; three separate injections every four weeks for 52 weeks) versus placebo in participants with relapsing or refractory EGPA; 2) belimumab (10 mg/kg on days 0, 14, 28 and every 28 days thereafter until 12 months after the last participant was randomised) or etanercept (25 mg twice a week) with standard therapy (median 25 months) versus placebo with standard therapy (median 19 months) in participants with GPA/MPA; and 3) infliximab (3 mg/kg on days 1 and 14, before the response assessment on day 42) versus rituximab (0.375g/m² on days 1, 8, 15 and 22) in participants with refractory GPA for up to 12 months. None of the studies were assessed as low risk of bias in all domains: one study did not report randomisation or blinding methods clearly. Three studies were at high risk and one study was at unclear risk of bias for selective outcome reporting. One trial with 136 participants with relapsing or refractory EGPA compared mepolizumab with placebo during 52 weeks of follow-up and observed one death in the mepolizumab group (1/68, 1.5%) and none in the placebo group (0/68, 0%) (Peto odds ratio (OR) 7.39, 95% confidence interval (CI) 0.15 to 372.38; low-certainty evidence). Low-certainty evidence suggests that more participants in the mepolizumab group had ≥ 24 weeks of accrued remission over 52 weeks compared to placebo (27.9% versus 2.9%; risk ratio (RR) 9.5, 95% CI 2.30 to 39.21), and durable remission within the first 24 weeks sustained until week 52 (19.1% mepolizumab versus 1.5% placebo; RR 13.0, 95% CI 1.75 to 96.63; number needed to treat for an additional beneficial outcome (NNTB) 6, 95% Cl 4 to 13). Mepolizumab probably decreases risk of relapse (55.8% versus 82.4%; RR 0.68, 95% CI 0.53 to 0.86; NNTB 4, 95% CI 3 to 9; moderate-certainty evidence). There was low-certainty evidence regarding similar frequency of adverse events (AEs): total AEs (96.9% versus 94.1%; RR 1.03, 95% CI 0.96 to 1.11), serious AEs (17.7% versus 26.5%; RR 0.67, 95% CI 0.35 to 1.28) and withdrawals due to AEs (2.9% versus 1.5%; RR 2.00, 95% CI 0.19 to 21.54). Disease flares were not measured. Based on two trials with different follow-up periods (mean of 27 months for etanercept study; up to four years for belimumab study) including people with GPA (n = 263) and a small group of participants with MPA (n = 22) analysed together, we found low-certainty evidence suggesting that adding an active drug (etanercept or belimumab) to standard therapy does not increase or reduce mortality (3.4% versus 1.4%; Peto OR 2.45, 95% CI 0.55 to 10.97). Etanercept may have little or no effect on remission (92.3% versus 89.5%; RR 0.97, 95% CI 0.89 to 1.07), durable remission (70% versus 75.3%; RR 0.93, 95% CI 0.77 to 1.11; low-certainty evidence) and disease flares (56% versus 57.1%; RR 0.98, 95% CI 0.76 to 1.27; moderate-certainty evidence). Low-certainty evidence suggests that belimumab does not increase or reduce major relapse (1.9% versus 0%; RR 2.94, 95% CI 0.12 to 70.67) or any AE (92.5% versus 82.7%; RR 1.12, 95% CI 0.97 to 1.29). Low-certainty evidence suggests a similar frequency of serious or severe AEs (47.6% versus 47.6%; RR 1.00, 95% CI 0.80 to 1.27), but more frequent withdrawals due to AEs in the active drug group (11.2%) compared to the placebo group (4.2%), RR 2.66, 95% CI 1.07 to 6.59). One trial involving 17 participants with refractory GPA compared infliximab versus rituximab added to steroids and cytotoxic agents for 12 months. One participant died in each group (Peto OR 0.88, 95% CI, 0.05 to 15.51; 11% versus 12.5%). We have very low-certainty evidence for remission (22% versus 50%, RR 0.44, 95% Cl 0.11 to 1.81) and durable remission (11% versus 50%, RR 0.22, 95% CI 0.03 to 1.60), any severe AE (22.3% versus 12.5%; RR 1.78, 95% CI 0.2 to 16.1) and withdrawals due to AEs (0% versus 0%; RR 2.70, 95% CI 0.13 to 58.24). Disease flare/relapse and the frequency of any AE were not reported.

AUTHORS' CONCLUSIONS

We found four studies but concerns about risk of bias and small sample sizes preclude firm conclusions. We found moderate-certainty evidence that in patients with relapsing or refractory EGPA, mepolizumab compared to placebo probably decreases disease relapse and low-certainty evidence that mepolizumab may increase the probability of accruing at least 24 weeks of disease remission. There were similar frequencies of total and serious AEs in both groups, but the study was too small to reliably assess these outcomes. Mepolizumab may result in little to no difference in mortality. However, there were very few events. In participants with GPA (and a small subgroup of participants with MPA), etanercept or belimumab may increase the probability of withdrawal due to AEs and may have little to no impact on serious AEs. Etanercept may have little or no impact on durable remission and probably does not reduce disease flare.

Kinin B1 Receptor Is Important in the Pathogenesis of Myeloperoxidase-Specific ANCA GN

BACKGROUND

Myeloperoxidase-specific ANCA (MPO-ANCA) are implicated in the pathogenesis of vasculitis and GN. Kinins play a major role during acute inflammation by regulating vasodilatation and vascular permeability and by modulating adhesion and migration of leukocytes. Kinin system activation occurs in patients with ANCA vasculitis. Previous studies in animal models of GN and sclerosing kidney diseases have demonstrated protective effects of bradykinin receptor 1 (B1R) blockade via interference with myeloid cell trafficking.

METHODS

To investigate the role of B1R in a murine model of MPO-ANCA GN, we evaluated effects of B1R genetic ablation and pharmacologic blockade. We used bone marrow chimeric mice to determine the role of B1R in bone marrow-derived cells (leukocytes) versus nonbone marrow-derived cells. We elucidated mechanisms of B1R effects using in vitro assays for MPO-ANCA-induced neutrophil activation, endothelial adherence, endothelial transmigration, and neutrophil adhesion molecule surface display.

RESULTS

B1R deficiency or blockade prevented or markedly reduced ANCA-induced glomerular crescents, necrosis, and leukocyte influx in mice. B1R was not required for in vitro MPO-ANCA-induced neutrophil activation. Leukocyte B1R deficiency, but not endothelial B1R deficiency, decreased glomerular neutrophil infiltration induced by MPO-ANCA in vivo. B1R enhanced ANCA-induced neutrophil endothelial adhesion and transmigration in vitro. ANCA-activated neutrophils exhibited changes in Mac-1 and LFA-1, important regulators of neutrophil endothelial adhesion and transmigration: ANCA-activated neutrophils increased surface expression of Mac-1 and increased shedding of LFA-1, whereas B1R blockade reduced these effects.

CONCLUSIONS

The leukocyte B1R plays a critical role in the pathogenesis of MPO-ANCA-induced GN in a mouse model by modulating neutrophil-endothelial interaction. B1R blockade may have potential as a therapy for ANCA GN and vasculitis.

Complement inhibition in ANCA vasculitis

A role for the alternative complement pathway has emerged in the understanding of ANCA vasculitis pathogenesis. Current therapies of ANCA vasculitis are limited by partial efficacy and toxicity and many patients pursue a relapsing course. Improved therapies are needed. Inhibition of the alternative complement pathway component C5a is attractive due to its role in neutrophil activation and migration, and engagement of other inflammatory and thrombotic mechanisms. Two inhibitors of C5a are in clinical development for ANCA vasculitis: avacopan, an oral C5a receptor inhibitor has demonstrated efficacy, safety and steroid sparing in two Phase II trials; and IFX-1, a monoclonal antibody to C5a which is entering Phase II development. Complement inhibition has the potential to contribute to remission induction protocols achieving a higher quality of remission as well as replacing steroids. Confirmation of safety, especially infective risk, and the potential to replace steroids depends on further studies and a role in relapse prevention needs to be explored.

Malignancies in Patients with Antineutrophil Cytoplasmic Antibody-associated Vasculitis: A Population-based Cohort Study

OBJECTIVE

Patients with ANCA-associated vasculitides (AAV) exhibit higher rates of malignancy than the general population. We assessed whether the cancer risk is increased in a well-characterized population-based cohort of AAV in southern Sweden, followed for a median time of 8 years.

METHODS

With case record review, the outcomes and malignancy development in a cohort of 195 patients with AAV [granulomatosis with polyangiitis (GPA), microscopic polyangiitis, and eosinophilic GPA] diagnosed between 1997 and 2010 were assessed. The patients were followed until death or December 31, 2015. The age- and sex-standardized incidence ratios (SIR) were estimated using the Swedish population data as a reference.

RESULTS

During the observation period of about 1500 person-years, we found 60 cancers in 52 of the 195 patients. SIR (95% CI) was 2.8 (2.1-3.6) for cancers at all sites, 1.8 (1.3-2.5) for all cancers excluding squamous cell carcinoma (SCC), 12.9 (8.4-18.8) for SCC, 4.3 (1.4-10.0) for bladder cancer, and 7.0 (1.4-20.5) for pancreatic cancer. Cumulative doses of cyclophosphamide (CYC) < 10 g were not associated with higher incidence of cancers other than SCC (SIR 1.63, 95% CI 0.8-2.9).

CONCLUSION

In contrast to previous publications assessing malignancy risk in patients with AAV, we show in this population-based cohort of patients a persistent increased risk for overall malignancy, bladder cancer, and pancreatic cancer as well as a markedly increased risk for SCC. There was no increase in incidence of cancers other than SCC for those treated with < 10 g CYC.

Successful treatment outcomes in pregnant patients with ANCA-associated vasculitides: A systematic review of literature

AIM

Antineutrophil cytoplasmic antibody-associated vasculitides (AAV) are a group of small vessel vasculitis with systemic presentations and considerable morbidity and mortality. Pregnancy in these patients poses a significant therapeutic challenge. There is limited published literature regarding pregnancy in AAV.

METHODS

Two cases of successful pregnancy outcomes in patients with active AAV are described. A systematic review was conducted on the lines of the PRISMA statement for conducting systemic reviews: PubMed (inception of PubMed until 30 April 2017, English language only) and EmBase databases were searched using the following terms: 'pregnancy' AND 'ANCA associated vasculitis' OR 'granulomatosis with polyangiitis' OR 'eosinophilic granulomatosis with polyangiitis' OR 'microscopic polyangiitis' OR 'Churg-Strauss syndrome' OR 'Wegener's granulomatosis'.

RESULTS

One hundred and thirty-seven pregnancies were documented in 110 patients of AAV. Vasculitis diagnosis was made before pregnancy in 69, during pregnancy in 32 and after pregnancy in 9 patients. Mean age at the time of pregnancy was 29.3 ± 5.3 years. There were 91 term pregnancies, 28 were preterm pregnancies, 15 abortions and 3 still births; 78 had normal delivery and 26 had caesarian section.

CONCLUSION

Successful pregnancies have been reported in AAV patients.

Trimethoprim-sulfamethoxazole prophylaxis prevents severe/life-threatening infections following rituximab in antineutrophil cytoplasm antibody-associated vasculitis

Objective

We aimed to assess risk factors for the development of severe infection in patients with antineutrophil cytoplasm antibody-associated vasculitis (AAV) receiving rituximab.

Methods

192 patients with AAV were identified. Univariate and multivariate analyses were performed to identify risk factors for severe infection following rituximab. Severe infections were classified as grade ≥3 as proposed by the Common Terminology Criteria for Adverse Events V.4.0.

Results

95 severe infections were recorded in 49 (25.52%) patients, corresponding to an event rate of 26.06 per 100 person-years. The prophylactic use of trimethoprim–sulfamethoxazole was associated with a lower frequency of severe infections (HR 0.30, 95% CI 0.13 to 0.69), while older age (HR 1.03, 95% CI 1.01 to 1.05), endobronchial involvement (HR 2.21, 95% CI 1.14 to 4.26), presence of chronic obstructive pulmonary disease (HR 6.30, 95% CI 1.08 to 36.75) and previous alemtuzumab use (HR 3.97, 95% CI 1.50 to 10.54) increased the risk. When analysis was restricted to respiratory tract infections (66.3% of all infections), endobronchial involvement (HR 4.27, 95% CI 1.81 to 10.06), severe bronchiectasis (HR 6.14, 95% CI 1.18 to 31.91), higher neutrophil count (HR 1.19, 95% CI 1.06 to 1.33) and major relapse (HR 3.07, 95% CI 1.30 to 7.23) as indication for rituximab use conferred a higher risk, while refractory disease (HR 0.25, 95% CI 0.07 to 0.90) as indication had a lower frequency of severe infections.

Conclusions

We found severe infections in one quarter of patients with AAV receiving rituximab. Trimethoprim–sulfamethoxazole prophylaxis reduced the risk, while especially bronchiectasis and endobronchial involvement are risk factors for severe respiratory infections.

Vasculitis update: pathogenesis and biomarkers

Better understanding of the pathogenesis and treatment of primary systemic vasculitides (PSV) has led to the development of many potentially clinically relevant biomarkers. Genome-wide association studies have highlighted that MHC class II polymorphisms may influence the development of particular anti-neutrophil cytoplasmic antibody (ANCA) serotypes, but not the clinical phenotype of ANCA-associated vasculitis (AAV). Although ANCAs are overall poor biomarkers of disease activity, they may be useful for the prediction of flares of renal and/or pulmonary vasculitis. Moreover, patients with proteinase 3 (PR3)-AAV may respond better to rituximab than cyclophosphamide. Newer biomarkers of renal vasculitis in AAV include urinary soluble CD163, and may in the future reduce the requirement for renal biopsy. Better understanding of dysregulated neutrophil activation in AAV has led to the identification of novel biomarkers including circulating microparticles, and neutrophil extracellular traps (NETs), although their clinical utility has not yet been realised. Studies examining endothelial injury and repair responses have additionally revealed indices that may have utility as disease activity and/or prognostic biomarkers. Last, next-generation sequencing technologies are revealing monogenic forms of vasculitis, such as deficiency of adenosine deaminase type 2 (DADA2), and are profoundly influencing the approach to the diagnosis and treatment of vasculitis in the young.

Therapy and prognosis of ANCA-associated vasculitis from the clinical nephrologist's perspective

This paper reviews the recently published scientific information regarding ANCA-associated vasculitis (AAV), aiming to highlight the most important data from the clinical nephrologists' perspective. The classification, pathomechanism, recent achievements of the treatment, short-term and long-term outcomes of the disease, and the difficulties nephrologists face when taking care for patients with AAV are summarized. There has been significant progress in the understanding of the genetic and pathologic background of the disease in the last years, and results of histological studies guide us to predict long-term renal function. Findings of several multicentered trials with reasonable number of participants provide comparison of the efficacy and safety of different remission induction and maintenance therapies, and evaluate recently introduced immunosuppressive agents. Although the clinical outcome of patients with AAV has improved significantly since modern immunosuppressive drugs are available, the treatment-related complications still contribute to the morbidity and mortality. To improve the survival and quality of life of patients with AAV further, knowledge of the predictors of relapse, end-stage kidney disease, and mortality, also prevention of infections and other treatment-related adverse events are important. The eligibility for renal transplantation and the option for successful pregnancies for young women are also important factors which influence the patients' quality of life. In order to provide favorable outcome, the clinicians need to establish personalized treatment strategies to optimize the intensity and minimize the toxicity of the immunosuppressive therapy.

Therapeutic advances in the treatment of vasculitis

Considerable therapeutic advances for the treatment of vasculitis of the young have been made in the past 10 years, including the development of outcome measures that facilitate clinical trial design. Notably, these include: a recognition that some patients with Kawasaki Disease require corticosteroids as primary treatment combined with IVIG; implementation of rare disease trial design for polyarteritis nodosa to deliver the first randomised controlled trial for children; first clinical trials involving children for anti-neutrophil cytoplasmic antibody (ANCA) vasculitis; and identification of monogenic forms of vasculitis that provide an understanding of pathogenesis, thus facilitating more targeted treatment. Robust randomised controlled trials for Henoch Schönlein Purpura nephritis and Takayasu arteritis are needed; there is also an over-arching need for trials examining new agents that facilitate corticosteroid sparing, of particular importance in the paediatric population since glucocorticoid toxicity is a major concern.

Hurdles to the introduction of new therapies for immune-mediated kidney diseases

Innovative immunotherapies continue to markedly benefit many disciplines in clinical medicine but disappointingly, these benefits have not translated to the treatment of kidney diseases despite encouraging findings from preclinical models of kidney dysfunction. This lack of progress in nephrology might relate to the unique biology of the kidney. More likely, this lack of progress relates to conceptual hurdles in the application of newer therapies to renal disease. In this Review we discuss seven hurdles that must be addressed in order to appropriately assess and introduce immunologic therapies for immune-mediated kidney disease: the use of appropriate criteria to define disease categories; issues relating to the heterogeneity of kidney diseases and how this heterogeneity affects approaches to treatment; issues related to the rarity of most kidney diseases; the paucity of good animal models of human kidney disease; issues relating to trial design; problems with current approaches to the identification and use of appropriate and feasible study end points; and a lack of adequate biomarkers of intrarenal inflammation and parenchymal injury. We suggest that overcoming these hurdles, in addition to searching for better therapeutic targets, will be necessary to progress the treatment of immune-mediated kidney disease into a new age of drug therapy.