Novel use of Siltuximab in a patient with VEXAS Syndrome.

VEXAS syndrome (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) is an increasingly recognized disorder that occurs due to somatic mutations of a ubiquitin-activating enzyme encoded by ubiquitin-like modifier activating enzyme 1 gene, UBA1. Clinical findings associated with VEXAS syndrome include recurrent fevers, polychondritis, periorbital edema, pleural effusions, myocarditis and/or pericarditis, hepatosplenomegaly, myelodysplastic syndrome, cytopenias, inflammatory arthritis, neutrophilic dermatosis, and deep venous thrombosis. Novel renal manifestations like interstitial nephritis are infrequent, and to our knowledge, acute renal failure due to C3 glomerulonephritis (C3GN) has not yet been reported. Overwhelming systemic inflammation can result in morbid end-organ damage and death. While there is no formal guideline or established protocol for its management, treatment of VEXAS syndrome with tocilizumab, an interleukin-6 (IL-6)-directed therapy, has been described in the literature. Here, we report a case of a 71-year-old male patient presenting with C3GN as an initial manifestation of VEXAS syndrome and explore the rationale for our approach to treatment with IL-6 blockade. Our patient was initially treated with two inpatient doses of tocilizumab with successful transition to siltuximab in the outpatient setting. He continues to benefit from ongoing siltuximab treatment for more than one year to date without any safety issues or relapse of VEXAS syndrome.

Glomerular injury induced by vinyl carbamate in A/J inbred mice: a novel model of membranoproliferative glomerulonephritis.

Ethyl carbamate (EC) is a process contaminant found in fermented foods and alcoholic beverages. Metabolic conversion of ethyl carbamate generates vinyl carbamate (VC), a carcinogenic metabolite. EC, as a Group 2A probable human carcinogen, and the more potent VC, are known to cause tumors in rodents. However, their effects on the kidney are unknown and were explored here. Female A/J inbred mice received an intraperitoneal injection of vehicle or VC. Beginning 5 weeks after VC injection, mice showed signs of moribund state. Mouse necropsies revealed renal glomerular injury that histopathologically recapitulated human membranoproliferative glomerulonephritis (MPGN), as evidenced by light microscopy, immunostaining for immunoglobulins and complements, and electron microscopy. To determine the molecular pathomechanisms, a post-hoc analysis was performed on a publicly available RNA-Seq transcriptome of kidneys from control rats and rats treated with fermented wine containing high concentrations of EC. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses of the differentially expressed genes revealed that the complement and coagulation cascades were a top predicted biological process involved. Furthermore, pathway-based data integration and visualization revealed that key regulators of complement activation were altered by high EC treatment. Among these, complement factors (CF) D and H, critical positive and negative regulators of the alternative pathway, respectively, were most affected, with CFD induced by 3.49-fold and CFH repressed by 5.9-fold, underscoring a hyperactive alternative pathway. Consistently, exposure of primary glomerular endothelial cells to EC or VC resulted in induction of CFD and repression of CFH, accompanied by increased fixation of C3 and C5b9. This effect seems to be mediated by Ras, one of the top genes that interact with both EC and VC, as identified by analyzing the chemical-gene/protein interactions database. Indeed, EC or VC-elicited complement activation was associated with activation of Ras signaling, but was abolished by the Ras inhibitor farnesyl thiosalicylic acid. Collectively, our findings suggest that VC, a metabolite of EC, induces glomerular injury in mice akin to human MPGN, possibly via perturbing the expression of complement regulators, resulting in an effect that favors activation of the alternative complement pathway.

Truncated Complement Factor H Y402 Gene Therapy Cures C3 Glomerulonephritis.

Patients with both age-related macular degeneration (AMD) and C3 glomerulonephritis (C3G) are challenged by the absence of effective therapies to reverse and eliminate their disease burden. Capitalizing on complement dysregulation as both a significant risk factor for AMD and the known pathophysiology of C3G, we investigated the potential for adeno-associated virus (AAV) delivery of complement factor H (CFH) to rescue C3G in a Cfh-/- mouse model of C3G. While past efforts to treat C3G using exogenous human CFH resulted in limited success before immune rejection led to a foreign protein response, our findings demonstrate the capacity for long-term AAV-mediated delivery of truncated CFH (tCFH) to restore inhibition of the alternative pathway of complement and ultimately reverse C3G without immune rejection. Comparing results from the administration of several tCFH vectors also revealed significant differences in their relative efficiency and efficacy. These discoveries pave the way for subsequent development of AAV-mediated tCFH replacement therapy for patients with C3G, while simultaneously demonstrating proof of concept for a parallel AAV-mediated tCFH gene augmentation therapy for patients with AMD.

Clinical characteristics and outcomes of immune-complex membranoproliferative glomerulonephritis and C3 glomerulopathy in Japanese children.

BACKGROUND: Membranoproliferative glomerulonephritis (MPGN) can be divided into immune-complex MPGN (IC-MPGN) and C3 glomerulopathy (C3G), which includes dense deposit disease (DDD) and C3 glomerulonephritis (C3GN). These conditions result from abnormalities in different complement pathways and may lead to different prognoses. However, there are limited studies describing the respective clinical courses. METHODS: In this study, Japanese pediatric patients diagnosed with MPGN based on kidney biopsies conducted between February 2002 and December 2022 were reclassified as having IC-MPGN or C3G (DDD or C3GN). We retrospectively analyzed the clinical characteristics and outcomes of these patients. RESULTS: Out of 25 patients with MPGN, three (12.0%) were diagnosed with DDD, 20 (80.0%) with C3GN, and two (8.0%) with IC-MPGN. There were 13 (65.0%) patients and one (33.3%) patient in remission after treatment for C3GN and DDD, respectively, and no patients with IC-MPGN achieved remission. The median follow-up period was 5.3 (2.5-8.9) years, and none of the patients in either group progressed to an estimated glomerular filtration rate < 15 ml/min/1.73 m2. Patients with C3GN presenting mild to moderate proteinuria (n = 8) received a renin-angiotensin system inhibitor (RAS-I) alone, and these patients exhibited a significant decrease in the urinary protein creatinine ratio and a notable increase in serum C3 levels at the last follow-up. CONCLUSIONS: Most patients with MPGN were diagnosed with C3GN. The remission rate for C3GN was high, and no patients developed kidney failure during the approximately 5-year follow-up. Additionally, patients with C3GN with mild to moderate proteinuria had good outcomes with RAS-I alone, but continued vigilance is necessary to determine long-term prognosis.

Apolipoprotein E is enriched in dense deposits and is a marker for dense deposit disease in C3 glomerulopathy.

C3 glomerulopathy (C3G) is a rare disease resulting from dysregulation of the alternative pathway of complement. C3G includes C3 glomerulonephritis (C3GN) and dense deposit disease (DDD), both of which are characterized by bright glomerular C3 staining on immunofluorescence studies. However, on electron microscopy (EM), DDD is characterized by dense osmiophilic mesangial and intramembranous deposits along the glomerular basement membranes (GBM), while the deposits of C3GN are not dense. Why the deposits appear dense in DDD and not in C3GN is not known. We performed laser microdissection (LCM) of glomeruli followed by mass spectrometry (MS) in 12 cases each of DDD, C3GN, and pretransplant kidney control biopsies. LCM/MS showed marked accumulation of complement proteins C3, C5, C6, C7, C8, C9 and complement regulating proteins CFHR5, CFHR1, and CFH in C3GN and DDD compared to controls. C3, CFH and CFHR proteins were comparable in C3GN and DDD. Yet, there were significant differences. First, there was a six-to-nine-fold increase of C5-9 in DDD compared to C3GN. Secondly, an unexpected finding was a nine-fold increase in apolipoprotein E (ApoE) in DDD compared to C3GN. Most importantly, immunohistochemical and confocal staining for ApoE mirrored the dense deposit staining in the GBM in DDD but not in C3GN or control cases. Validation studies using 31 C3G cases confirmed the diagnosis of C3GN and DDD in 80.6 % based on ApoE staining. Overall, there is a higher burden of terminal complement pathway proteins in DDD compared to C3GN. Thus, our study shows that dense deposits in DDD are enriched with ApoE compared to C3GN and control cases. Hence, ApoE staining may be used as an adjunct to EM for the diagnosis of DDD and might be valuable when EM is not available.

Anti-factor H antibody-positive C3 glomerulonephritis secondary to poststreptococcal acute glomerulonephritis with diabetic nephropathy.

Poststreptococcal acute kidney glomerulonephritis (PSAGN) has been seen in adults in recent years, especially in patients with type 2 diabetes mellitus, and the renal prognosis has not always been good. There have been cases of PSAGN in which complete remission was not achieved and hematuria and proteinuria persisted, leading to end-stage renal disease. Previous reports showed that the patients subjected to PSAGN have an underlying defect in regulating the alternative pathway of complement, and they identified that antibodies to the C3 convertase, C3 nephritic factors (C3NeF), are involved. C3NeF stabilizes C3 convertase, sustains C3 activation, and causes C3 glomerulonephritis (C3GN). On the other hand, factor H is a glycoprotein that suppresses the overactivation of the alternative pathway by decaying the C3 convertase. Anti-factor H (aFH) antibodies interfere with factor H and cause the same activation of the alternative pathway as C3NeF. However, a limited number of reports describe the clinical course of C3GN with aFH antibodies. We encountered a 49-year-old Japanese man with type 2 diabetes mellitus. He was referred to our hospital because of his elevated serum creatinine, proteinuria, hematuria, and developed edema on both legs. He was diagnosed as PSAGN at the first kidney biopsy, and his renal function improved and edema and hematuria disappeared, but proteinuria persisted after 5 months. He was diagnosed as C3GN at the second kidney biopsy. In our case, no C3NeF was detected. However, a high titer of aFH antibodies was detected in stored serum from the initial presentation, providing a unified diagnosis of aFH antibody-positive C3GN secondary to PSAGN. He progressed to end-stage renal disease (ESRD) and hemodialysis was started. The persistence of high levels of aFH autoantibodies may have caused C3GN secondary to PSAGN due to activating the alternative complement pathway, which eventually worsened the nephropathy and led to ESRD.

Morphological and etiological analyses of C3 and non-C3 glomerulonephritis in primary membranoproliferative glomerulonephritis using periodic acid-methenamine silver stain electron microscopy: a retrospective multicentered study.

This study elucidated the etiology of C3 glomerulonephritis (C3GN) and non-C3GN with primary membranoproliferative glomerulonephritis (MPGN) using transmission electron microscopy (TEM) and periodic acid-methenamine silver stain (PAM-EM). Thirty-one primary MPGN cases were analyzed by TEM and PAM-EM to distinguish among MPGN I, MPGN II, MPGN III Burkholder subtype (MPGN IIIB), and Anders and Strife subtype (MPGN IIIA/S). Each case was also classified into C3GN or non-C3GN according to the standard C3GN definition using immunostaining. Four cases of MPGN II met C3 glomerulopathy; whereas, four cases of MPGN IIIB did not meet C3 glomerulopathy. Seven of 11 cases (64%) of MPGN I without GBM disruption and 7 of 12 cases (58%) of MPGN IIIA/S with GBM disruption met the non-C3GN criteria with significant immunoglobulins' deposition. Regardless of the C3GN or non-C3GN diagnosis, the deposits in primary MPGN I and MPGN IIIA/S exhibited ill-defined, amorphous, and foggy characteristics similar to those found in postinfectious GN but were different from immune complex (IC) deposits seen in MPGN IIIB. Not only C3GN but also non-C3GN was due to mechanisms other than IC deposition as found in postinfectious GN. Consequently, GBM disruption of MPGN IIIA/S was not due to IC deposition.

Complement gene mutations in children with C3 glomerulopathy: do they affect the response to mycophenolate mofetil?

BACKGROUND: C3 glomerulopathy (C3G) is a complement-mediated disease. Although genetic studies are not required for diagnosis, they are valuable for treatment planning and prognosis prediction. The aim of this study is to investigate the clinical phenotypes, kidney survival, and response to mycophenolate mofetil (MMF) treatment in pediatric C3G patients with and without mutations in complement-related genes. METHODS: Sixty pediatric C3G patients were included, divided into two groups based on complement-related gene mutations. Demographic and clinical-pathological findings, treatment modalities, and outcome data were compared, and Kaplan-Meier analysis was performed for kidney survival. RESULTS: Out of the 60 patients, 17 had mutations. The most common mutation was in the CFH gene (47%). The mean age at diagnosis was higher in the group with mutation (12.9 ± 3.6 vs. 11.2 ± 4.1 years, p = 0.039). While the patients without mutation most frequently presented with nephritic syndrome (44.2%), the mutation group was most likely to have asymptomatic urinary abnormalities (47.1%, p = 0.043). Serum parameters and histopathological characteristics were similar, but hypoalbuminemia was more common in patients without mutation. During 45-month follow-up,10 patients progressed to chronic kidney disease stage 5 (CKD5), with 4 having genetic mutation. The time to develop CKD5 was longer in the mutation group but not significant. MMF treatment had no effect on progression in either group. CONCLUSIONS: This study is the largest pediatric C3G study examining the relationship between genotype and phenotype. We showed that the mutation group often presented with asymptomatic urinary abnormalities, was diagnosed relatively late but was not different from the without mutation group in terms of MMF treatment response and kidney survival.

C3 glomerulopathies: dense deposit disease and C3 glomerulonephritis.

Dense deposit disease (DDD) and C3 glomerulonephritis (C3GN) are types of membranoproliferative glomerulonephritis classified as C3 glomerulopathies. These conditions are characterized by an increased number of intraglomerular cells and diffuse thickening of the glomerular capillary walls, along with the deposition of C3 and minimal or absent immunoglobulin deposits. The underlying cause of both DDD and C3Gn is an abnormal activation of the alternative complement pathway, which can result from acquired or genetic alteration. In acquired forms of DDD and C3GN, the dysregulation of the alternative pathway is commonly induced by the presence of C3 nephritic factors (C3NeFs), which are autoantibodies that stabilize C3 convertase. Both DDD and C3GN can affect individuals of any age, but DDD is primarily diagnosed in children, whereas C3GN tends to be diagnosed at a significantly higher age. The presenting features of these diseases are variable and may include proteinuria, hematuria, hypertension, or kidney failure. A common finding in these diseases is low serum C3 levels with normal serum C4 levels. Chronic deterioration of renal function is commonly observed in DDD and C3GN, often leading to end-stage renal disease (ESRD), especially in DDD. Kidney transplantation outcomes in patients with these conditions are characterized by histological recurrence, which may contribute to higher rates of allograft failure.

[Comparative characteristics of the complement system in patients with C3-glomerulopathy and atypical hemolytic uremic syndrome of chronic course who suffered an acute episode of thrombotic microangiopathy].

AIM: To compare changes in the complement system in C3-glomerulopathy (C3-GP) and atypical hemolytic uremic syndrome (aHUS) after the relief of an acute episode of thrombotic microangiopathy. MATERIALS AND METHODS: The study included 8 patients diagnosed with C3-GP and 8 with aHUS in remission. The blood levels of the complement system components were determined: C3, C4, C3a, C5a, factor H (CFH), factor B (CFB), membrane-attacking complex (MAC), antibodies to C3b (anti-C3b-AT), the level of hemolytic activity (CH50), the content of factor D (CFD) in the urine. RESULTS: C3 and CH50 levels were within the reference range in both groups, however, in the C3-GP group they were at the lower limit, and C3 level was significantly lower than in the aHUS group: 0.56 [0.44; 0.96] vs 1.37 [1.16; 2.52] (p=0.003). CFB increased level was detected in both groups, but in the C3-GP group it was significantly lower than in the aHUS group - 275.1 [222.1; 356.6] vs 438.7 [323.3; 449.3] (p=0.010). C3a, C5a and MAC levels were increased in both groups, but the maximum was in the C3-GP group, and the MAC level in the C3-GP group was 2 times higher than that in aHUS, and these differences reached statistical significance - 123 555±6686 vs 5603±1294 (p=0.036). CFH and CFD levels was increased in both groups, but their highest values was in the aHUS group. CONCLUSION: Alternative complement pathway activation signs were present in both groups of patients with complement-mediated nephropathies, regardless the stage of the disease. In C3-GP, alternative complement pathway activation was more pronounced than in aHUS after the relief of an acute episode of thrombotic microangiopathy.

Glomerular Diseases Across Lifespan: Key Differences in Diagnostic and Therapeutic Approaches.

Glomerular diseases are common causes of chronic kidney disease in childhood, adolescence, and adulthood. The epidemiology of glomerular diseases differs between different age groups, with minimal change disease being the leading cause of nephrotic syndrome in childhood, while membranous nephropathy and focal segmental glomerulosclerosis are more common in adulthood. IgA vasculitis is also more common in childhood. Moreover, there is a difference in disease severity with more children presenting with a relapsing form of nephrotic syndrome and a more acute presentation of antineutrophil cytoplasmic antibody-associated vasculitis and concomitant glomerulonephritis, as highlighted by the higher percentage of cellular crescents on kidney biopsy specimens in comparison with older patients. There is also a female preponderance in antineutrophil cytoplasmic antibody-associated vasculitis and more children present with tracheobroncholaryngeal disease. This article aims to summarize differences in the presentation of different glomerular diseases that are encountered commonly by pediatric and adult nephrologists and potential differences in the management.

[Diagnosis and treatment of glomerular diseases with a membranoproliferative glomerulonephritis (MPGN) pattern of injury]. / Diagnose und Therapie glomerulärer Erkrankungen mit einem membranoproliferativen Läsionsmuster (MPGN) ­ 2023.

Membranoproliferative glomerulonephritis (MPGN) represents a heterogeneous group of diseases. The common feature of a membranoproliferative lesion pattern in the kidney biopsy can either be idiopathic/primary or-much more frequently-have a secondary cause. The historical classification into MPGN types I to III has largely been abandoned and replaced in recent years by a pathogenesis-oriented classification. A MPGN with C1q, C3 and/or C4 deposits on light microscopy is referred to as immune complex GN (IC-GN), while a MPGN with dominant C3 deposits is referred to as C3 glomerulopathy (C3G). C3G is further divided into C3 glomerulonephritis (C3GN) and dense deposit disease (DDD). These diagnoses can only be made by a kidney biopsy. Possible causes of MPGN are chronic infections (especially hepatitis B and C, bacterial infections, infections with protozoa), autoimmune diseases (especially lupus, rheumatoid arthritis) or malignancies (especially hematological malignancies). Particularly in the case of C3G a comprehensive analysis of the complement system components is strongly recommended. Due to the low incidence and the heterogeneous clinical appearance of MPGN therapeutic decisions must be made individually; an optimal general therapy is unknown, except that supportive treatment as with other glomerular diseases should be optimized. In the case of a secondary MPGN it is generally recommended to treat the potential cause of the MPGN. If significant proteinuria persists and eGFR remains > 30 ml/min/1.73 m2, treatment with systemic steroids and mycophenolate mofetil is recommended. Other treatment options on an individual level after evaluation and discussion of the risk-benefit ratio with the patient are rituximab and eculizumab. Rapidly progressive MPGN should be treated like ANCA-associated vasculitis. The recurrence rates after kidney transplantation are very high and treatment is challenging.

Association of monoclonal gammopathy of undetermined significance and C3 glomerulopathy.

Monoclonal gammopathy of undetermined significance (MGUS) is usually an asymptomatic pre-malignant condition caused by the proliferation of clonal plasma cells. Often considered a benign condition, it has the potential to progress to malignant plasma cell or lymphoproliferative disorders. Moreover, MGUS can rarely cause glomerular disease by activating the alternative complement pathway resulting in immunoglobulin-negative C3-positive glomerulonephritis called C3 glomerulopathy. Because of its rarity, the diagnosis might not be considered by the treating physicians, leading to delayed diagnosis or misdiagnosis. Untreated C3 glomerulopathy can lead to irreversible glomerular damage and end-stage renal failure, and a high index of suspicion is essential for timely diagnosis and management. Here, we present the case of a patient with a prior diagnosis of MGUS who presented with proteinuria and microscopic haematuria and was diagnosed with C3 glomerulopathy. The patient had complete resolution of the disease after receiving treatment with a combination of dexamethasone, lenalidomide and bortezomib for the underlying MGUS.

Recurrent C3 Glomerulonephritis along with BK-Virus-Associated Nephropathy after Kidney Transplantation: A Case Report.

C3 glomerulonephritis (C3GN) is a rare cause of end-stage kidney disease and frequently recurrent in allografts following kidney transplantation (KT). Herein, we describe the case of a kidney transplant recipient who developed recurrent C3GN along with BK-virus-associated nephropathy (BKVAN) following KT. A 33-year-old man diagnosed with membranoproliferative glomerulonephritis 17 years ago underwent preemptive KT with a donor kidney from his aunt. Proteinuria gradually increased after 3 months following KT, and graft biopsy was performed 30 months after KT. Histopathological examination revealed recurrent C3GN. The dosages of triple immunosuppressive maintenance therapy agents were increased. Subsequently, serum C3 levels recovered to normal levels. However, at 33 months following KT, the BK viral load increased and graft function gradually deteriorated; a second graft biopsy was performed at 46 months following KT, which revealed BKVAN and decreased C3GN activity. The dosages of immunosuppressive agents were decreased; subsequently, BKVAN improved and graft function was maintained with normal serum C3 levels at 49 months following KT. This case indicates that C3GN is highly prone to recurrence following KT and that immunosuppressive therapy for C3GN increases the risk of BKVAN.

Immunoelectron microscopy findings in a patient with C3 glomerulonephritis.

We performed a kidney biopsy in a 36-year-old man to evaluate microscopic hematuria and proteinuria. Light microscopy showed increased mesangial matrix and partial swelling of the glomerular basement membrane (GBM), and immunofluorescence showed positive staining only for C3. Immunoelectron microscopy showed that gold particle-labeled C3 was localized in the electron-dense and moderately electron-dense deposits shown by electron microscopy in the mesangium, the thickened GBM near the paramesangium, and the thickened distal portion of the GBM but was not localized in the non-thickened GBM. Gold-labeled immunoglobulin G, κ, and λ were not seen. C3 glomerulonephritis was more evident in gold-labeled electron microscopy, which further clarified the localization of C3 deposition.

Diagnostic Problems in C3 Glomerulopathy.

BACKGROUND: C3 glomerulopathies (C3GN) are a group of rare kidney diseases associated with impaired complement regulation. The effects of this disease include the accumulation of complement C3 in the kidneys. Based on the clinical data, as well as light, fluorescence, and electron microscopy results, the diagnoses were verified. The study group consisted of biopsy specimens, which were obtained from 332 patients who were diagnosed with C3 glomerulopathy. In all cases, histopathological examinations were performed; deposits of complement C3 and C1q components, as well as the immunoglobulins IgA, IgG, and IgM, were identified using immunofluorescence. Furthermore, electron microscopy was also performed. RESULTS: The histopathological examination results presented cases of C3GN (n = 111) and dense deposit disease (DDD; n = 17). The non-classified (NC) group was the most numerous (n = 204). The lack of classification was due to the poor severity of the lesions, even on the electron microscopic examination or in the presence of intense sclerotic lesions. CONCLUSIONS: In cases of suspected C3 glomerulopathies, we believe an electron microscopy examination is necessary. This examination is beneficial in mild-to-extremely-severe cases of this glomerulopathy, where the lesions are barely discernible when using immunofluorescence microscopy.

Pembrolizumab induced-C3 glomerulonephritis and RBC cast nephropathy: a case report.

BACKGROUND: Immune checkpoint inhibitors (ICIs) are increasingly being used in the treatment of several cancers. Pembrolizumab is an anti-programmed cell death-1 (anti-PD-1) monoclonal antibody that is approved for the treatment of metastatic non-small cell lung cancer (NSCLC). Pembrolizumab-associated renal toxicity is relatively rare, even in pembrolizumab-associated glomerulonephritis. In this study, we report a rare case of pembrolizumab-induced C3 glomerulonephritis (C3GN) and RBC cast nephropathy. CASE PRESENTATION: A 68-year-old man with NSCLC was receiving treatment with pembrolizumab. After 19 cycles of pembrolizumab therapy, he presented with gross hematuria, severe lower-limb edema and oliguria. Laboratory tests revealed hypoalbuminemia, increased serum creatinine and low serum C3 level. Renal biopsy revealed a typical membranoproliferative glomerulonephritis accompanied by remarkable RBC casts in tubular cavities and tubulointerstitial infiltration of CD8-positive lymphocytes. Based on C3-only immunofluorescence deposit on glomeruli, a diagnosis of C3GN was made. Pembrolizumab was considered the cause of C3GN. Pembrolizumab was discontinued immediately, and 60 mg/day of prednisone was initiated. One dose of cyclophosphamide (400 mg, IV) was also administered. Upon treatment, his symptoms improved rapidly and serum creatinine decreased a lot. However, the patient became dialysis dependent eventually. CONCLUSION: This is the first case of C3GN with RBC cast nephropathy caused by ICIs. This rare case caused by the prolonged use of pembrolizumab further strengthens the relationship between ICIs and C3GN. Thus, periodic evaluation of urine and renal function is recommended in patients receiving pembrolizumab and other ICIs.

Utilizing therapeutic drug monitoring to optimize therapy with eculizumab and mycophenolate mofetil in a child with C3 glomerulonephritis.

BACKGROUND: C3 glomerulonephritis (C3GN) can be a devastating disease with poor response to immunosuppressive therapy. Complement inhibition with eculizumab has had equivocal results in patients with C3GN. CASE-DIAGNOSIS/TREATMENT: We report a case of a 6-year-old boy with C3GN presenting with nephrotic syndrome, severe hypertension and impaired kidney function. He did not respond to initial treatment with prednisone and mycophenolate (mofetil and sodium), and subsequent treatment with standard dosing of eculizumab. Pharmacokinetic studies identified a lack of eculizumab exposure and subsequent intensification of treatment with weekly dosing of eculizumab led to significant clinical improvement: his kidney function normalized, hypertension (weaned off 3 antihypertensive drugs), edema and proteinuria improved. Additionally, exposure to mycophenolic acid (MPA), active metabolite of mycophenolate, determined by area under the concentration-time curve of MPA was low throughout, despite significant dosing escalation. CONCLUSIONS: This case report demonstrates that individualized therapy guided by therapeutic drug monitoring might be needed in patients with nephrotic range proteinuria treated with eculizumab and mycophenolate (mofetil and sodium), an important finding that needs to be considered for further treatment trials.

A Monoclonal Antibody That Provides a Model for C3 Nephritic Factors.

Complement is a major innate defense system that protects the intravascular space from microbial invasion. Complement activation results in the assembly of C3 convertases, serine proteases that cleave complement protein C3, generating bioactive fragments C3a and C3b. The complement response is rapid and robust, largely due to a positive feedback regulatory loop mediated by alternative pathway (AP) C3 convertase. C3 nephritic factors (C3NEFs) are autoantibodies that stabilize AP convertase, resulting in uncontrolled C3 cleavage, which, in principle, can promote critical tissue injury similar to that seen in certain renal conditions. Investigations of C3NEFs are hampered by a challenging issue: each C3NEF is derived from a different donor source, and there is no method to compare one C3NEF to another. We have identified a widely available mouse anti-C3 mAb that, similar to many C3NEFs, can stabilize functional AP convertase in a form resistant to decay acceleration by multiple complement regulators. The antibody requires the presence of properdin to confer convertase stability, and hampers the activity of Salp20, a tic salivary protein that accelerates convertase dissociation by displacing properdin from the convertase complex. This mAb can serve as an urgently needed standard for the investigation of C3NEFs. This study also provides novel insights into the dynamics of AP convertase.

Eculizumab as a treatment for C3 glomerulopathy: a single-center retrospective study.

BACKGROUND: C3 Glomerulopathy (C3G) is a rare glomerular disease caused by dysregulation of the complement pathway. Based on its pathophysiology, treatment with the monoclonal antibody eculizumab targeting complement C5 may be a therapeutic option. Due to the rarity of the disease, observational data on the clinical response to eculizumab treatment is scarce. METHODS: Fourteen patients (8 female, 57%) treated for C3 glomerulopathy at the medical center of the University of Freiburg between 2013 and 2022 were included. Subjects underwent biopsy before enrollment. Histopathology, clinical data, and response to eculizumab treatment were analyzed. Key parameters to determine the primary outcome were changes of estimated glomerular filtration rate (eGFR) over time. Positive outcome was defined as > 30% increase, stable outcome as ±30%, negative outcome as decrease > 30% of eGFR. RESULTS: Eleven patients (78.8%) were treated with eculizumab, three received standard of care (SoC, 27.2%). Median follow-up time was 68 months (IQR: 45-98 months). Median eculizumab treatment duration was 10 months (IQR 5-46 months). After eculizumab treatment, five patients showed a stable outcome, six patients showed a negative outcome. Among patients receiving SoC, one patient showed a stable outcome, two patients showed a negative outcome. CONCLUSIONS: The benefit of eculizumab in chronic progressive C3 glomerulopathy is limited.