Lupus nephritis (LN) is among the most consequential manifestations of systemic lupus erythematosus (SLE), a chronic autoimmune disease that can affect virtually every organ system. When lupus targets the kidneys, the consequences can be severe: progressive loss of kidney function, development of chronic kidney disease (CKD), and, in a significant proportion of cases, end-stage renal disease (ESRD) requiring dialysis or transplantation. This burden falls disproportionately on young women, particularly those of African, Hispanic, and Asian descent, making lupus nephritis not only a clinical challenge but also a matter of health equity.
Over the past two decades, the International Society of Nephrology has played a pivotal role in reshaping how the global nephrology community understands, classifies, and treats lupus nephritis. From co-developing the foundational histopathological classification system to supporting landmark clinical trials and biomarker research, ISN has been at the forefront of advancing science and improving patient care. This article explores the current state of lupus nephritis — what it is, how it is classified, how it is treated, and where the field is heading.
Understanding Lupus Nephritis: The Basics
What Happens in the Kidney?
In systemic lupus erythematosus, the immune system loses its ability to distinguish between foreign invaders and the body’s own healthy tissues. It begins producing autoantibodies — immune proteins that mistakenly attack self-antigens. In lupus nephritis, immune complexes composed of autoantibodies and their target antigens accumulate in the glomeruli, the tiny filtering units of the kidney. This triggers inflammation, damages the delicate filtration structures, and, over time, leads to scarring and irreversible functional loss.
Approximately 50% of patients with SLE will develop some form of kidney involvement during the course of their disease, and up to 10–30% of those affected will progress to ESRD within 10 years if poorly managed. Early detection and accurate classification of kidney involvement are therefore critically important for guiding treatment and preserving long-term function.
Why Classification Matters
Not all cases of lupus nephritis are alike. The disease can present in many histological patterns — ranging from mild mesangial changes to severe diffuse proliferative disease — each with distinct prognostic implications and treatment requirements. Without a standardized classification framework, comparing treatment outcomes across centers and designing clinical trials would be nearly impossible.
This is where the work of the International Society of Nephrology has proven transformative.
The ISN/RPS Classification System: A Foundation for Global Practice
Origins and Development
In 2003, ISN (International Society of Nephrology) collaborated with the Renal Pathology Society (RPS) to develop the ISN/RPS classification of lupus nephritis — a standardized histopathological framework that assigns kidney biopsy findings into six distinct classes based on the location, pattern, and extent of glomerular injury. This classification system provided the nephrology and rheumatology communities with a shared language for describing renal pathology in SLE, enabling more consistent diagnosis and treatment planning across institutions and countries.
The six classes of the ISN/RPS classification are:
- Class I: Minimal mesangial lupus nephritis — immune deposits without light microscopy changes
- Class II: Mesangial proliferative lupus nephritis — mesangial hypercellularity with immune deposits
- Class III: Focal lupus nephritis — active or inactive lesions affecting less than 50% of glomeruli
- Class IV: Diffuse lupus nephritis — the most severe form, affecting 50% or more of glomeruli
- Class V: Membranous lupus nephritis — subepithelial immune deposits; may coexist with Class III or IV
- Class VI: Advanced sclerosing lupus nephritis — more than 90% globally sclerosed glomeruli without residual activity
The 2018 Revision: Refinement and Greater Precision
Building on the 2003 framework, a 2018 revision published by Bajema and colleagues in Kidney International introduced important refinements to improve diagnostic accuracy and clinical relevance. One of the most significant changes was the revision of criteria distinguishing Class III (focal) from Class IV (diffuse) disease, addressing ambiguities that had led to inconsistent classifications between pathologists.
The 2018 revision also provided clearer, more operationally precise definitions of activity and chronicity indices — two dimensions that are essential for understanding the nature of kidney injury at the time of biopsy:
- Activity indices reflect ongoing, potentially reversible inflammatory injury — such as fibrinoid necrosis, cellular crescents, and endocapillary hypercellularity. These features suggest that aggressive immunosuppressive therapy may halt or reverse damage.
- Chronicity indices capture irreversible structural damage — including interstitial fibrosis, tubular atrophy, fibrous crescents, and glomerulosclerosis. High chronicity scores indicate established scarring that is less likely to respond to therapy and correlate with poorer long-term renal outcomes.
Retrospective cohort studies published in Kidney International and the Journal of the American Society of Nephrology have substantiated the prognostic significance of these indices, demonstrating that high chronicity scores at baseline biopsy are independently associated with an increased risk of ESRD over long-term follow-up. This evidence has reinforced the importance of timely biopsy and early intervention before irreversible changes accumulate.
Landmark Clinical Trials: Transforming Treatment Paradigms
Even with the best classification system, improving outcomes in lupus nephritis ultimately depends on effective therapies. The past decade has witnessed a remarkable transformation in the LN treatment landscape, driven by rigorously designed randomized controlled trials that have expanded the therapeutic toolkit well beyond traditional immunosuppressive agents.
The Standard of Care: A Historical Overview
For decades, high-dose corticosteroids combined with cyclophosphamide represented the standard induction therapy for proliferative lupus nephritis (Class III and IV). While effective, this regimen carries a substantial burden of toxicity, including infection risk, bone loss, metabolic complications, and gonadal toxicity. Mycophenolate mofetil (MMF) emerged as a less toxic alternative for induction and became the preferred maintenance therapy based on trials comparing it favorably to azathioprine and cyclophosphamide in terms of efficacy and tolerability.
Rituximab and the LUNAR Trial
The LUNAR trial, published in Arthritis & Rheumatism in 2012 and led by Rovin and colleagues, evaluated the addition of rituximab — a chimeric anti-CD20 monoclonal antibody that depletes B cells — to standard MMF and corticosteroid induction therapy in patients with proliferative lupus nephritis. Despite strong biological rationale, the trial did not reach its primary efficacy endpoint. This outcome highlighted the inherent complexity of clinical trial design in lupus nephritis, where heterogeneous patient populations, variable background therapies, and multiple outcome definitions can obscure treatment signals. Nevertheless, LUNAR provided valuable lessons and contributed to the evolution of trial methodology in the field.
Belimumab and the BLISS-LN Trial
A significant breakthrough came with the BLISS-LN trial, whose results were published in the New England Journal of Medicine in 2020. This large multinational randomized controlled trial evaluated belimumab, a monoclonal antibody that inhibits B-lymphocyte stimulator (BLyS), added to standard therapy in patients with active lupus nephritis.
The results demonstrated that belimumab significantly reduced the risk of renal flares and improved the primary efficacy renal response rate at two years compared to placebo. This represented the first successful phase III trial of a targeted biologic agent specifically in lupus nephritis, and belimumab subsequently received regulatory approval for this indication. For the nephrology community, BLISS-LN was a landmark moment — proof that targeting the B-cell survival pathway could meaningfully change the disease course.
Voclosporin and the AURORA 1 Trial
The AURORA 1 trial, published in The Lancet in 2021, introduced voclosporin as a novel addition to the LN treatment armamentarium. Voclosporin is a next-generation calcineurin inhibitor — similar in mechanism to cyclosporine but engineered to have a more predictable pharmacokinetic profile and a lower propensity for nephrotoxicity at therapeutic doses. Calcineurin inhibitors have long been used in kidney transplantation and certain glomerular diseases, but their role in lupus nephritis had been limited by concerns about toxicity and tolerability.
The AURORA 1 trial demonstrated that voclosporin, added to background therapy of MMF and low-dose corticosteroids, achieved significantly higher rates of complete renal response at 52 weeks compared to standard therapy alone. This finding supported voclosporin’s approval for lupus nephritis and established a new multi-targeted induction regimen combining voclosporin, MMF, and low-dose steroids as a viable treatment approach.
Obinutuzumab and the NOBILITY Trial
The NOBILITY trial evaluated obinutuzumab, a type II anti-CD20 monoclonal antibody that differs from rituximab in its mechanism of B-cell depletion and is designed to achieve more complete and durable B-cell suppression. In patients with proliferative lupus nephritis receiving background MMF therapy, obinutuzumab demonstrated superior complete renal response rates at 76 weeks compared to placebo. These data suggest that more thorough B-cell depletion may translate into improved kidney outcomes and provide a rationale for further development of this agent in LN.
Summary of Key Trials
| Trial | Agent | Mechanism | Key Finding | Publication |
|---|---|---|---|---|
| LUNAR (2012) | Rituximab | Anti-CD20 (type I) | Did not meet primary endpoint; shaped trial design | Arthritis & Rheumatism |
| BLISS-LN (2020) | Belimumab | Anti-BLyS | Improved renal response and reduced flares at 2 years | New England Journal of Medicine |
| AURORA 1 (2021) | Voclosporin | Calcineurin inhibitor | Higher complete renal response at 52 weeks | The Lancet |
| NOBILITY | Obinutuzumab | Anti-CD20 (type II) | Superior complete renal response at 76 weeks | Peer-reviewed publication |
Biomarkers: Moving Toward Precision Monitoring
The Challenge of Disease Monitoring
One of the persistent challenges in managing lupus nephritis is accurately monitoring disease activity over time. Traditional tools — serum creatinine, urinary protein-to-creatinine ratio, and complement levels — are useful but imperfect. They may not capture subtle disease reactivation early enough to prevent further kidney damage, and they cannot reliably distinguish active inflammatory injury from chronic, non-treatable scarring.
This has motivated a growing body of research into urinary and serum biomarkers that more precisely reflect the biological processes driving kidney injury in lupus nephritis.
Emerging Urinary Biomarkers
The International Society of Nephrology has emphasized the need for biomarker-guided treatment monitoring in LN, recognizing that better tools for tracking disease activity could allow more timely therapeutic adjustments and ultimately protect kidney function. Among the most studied urinary biomarkers are:
- TWEAK/Fn14 axis: TWEAK (TNF-like weak inducer of apoptosis) and its receptor Fn14 are expressed in renal tubular and glomerular cells during inflammatory injury. Urinary TWEAK levels have been investigated as a marker of renal flare activity in prospective studies and may reflect active intraglomerular inflammation not always captured by standard measures.
- MCP-1 (Monocyte Chemoattractant Protein-1): This chemokine is upregulated during inflammatory renal injury and can be detected in the urine. Elevated urinary MCP-1 has been associated with active lupus nephritis and may serve as an early indicator of disease reactivation.
- ALCAM (Activated Leukocyte Cell Adhesion Molecule): Urinary ALCAM has also been investigated as a potential biomarker of renal flare and inflammatory activity, with prospective studies suggesting its utility as a complement to existing monitoring tools.
While none of these biomarkers has yet been incorporated into routine clinical practice, their continued investigation represents an important step toward individualized, precision-based management of lupus nephritis.
The Role of ISN in Shaping Clinical Trial Design
Beyond classification systems and biomarker research, the International Society of Nephrology has contributed substantively to the scientific infrastructure underlying lupus nephritis clinical trials. ISN-affiliated investigators have been involved in the development and validation of composite outcome measures used in contemporary LN trials, including the BILAG-based Composite Lupus Assessment (BICLA) and kidney-specific response criteria that define what constitutes a meaningful clinical response in lupus nephritis studies.
Robust, standardized outcome definitions are essential for generating interpretable and reproducible trial results. The complexity of lupus nephritis — with its fluctuating disease course, multiple affected organ systems, and diverse patient populations — makes this a particularly demanding scientific undertaking. The involvement of ISN in harmonizing these definitions has helped elevate the quality of evidence generated by clinical trials and facilitated the regulatory approval of new therapies.
Addressing Disparities: A Global Perspective
Lupus nephritis does not affect all populations equally. The disease is more prevalent and more severe in patients of African, Hispanic, and Asian ancestry, who carry a higher risk of progression to ESRD compared to patients of European descent — disparities that likely reflect genetic, immunological, socioeconomic, and healthcare access factors.
The ISN (International Society of Nephrology) is committed to addressing global disparities in kidney disease care. Ensuring that new therapies are evaluated in diverse patient populations, that kidney biopsy is accessible in resource-limited settings, and that treatment guidelines are applicable across different healthcare systems are priorities the International Society of Nephrology champions through its global programs and educational initiatives.
Looking Ahead: The Future of Lupus Nephritis Care
The pace of progress in lupus nephritis has accelerated considerably over the past five years. Several areas hold particular promise for the near future:
- Combination biologic regimens: Researchers are exploring combinations — such as BLyS inhibition with anti-CD20 therapy — that may provide
synergistic benefits over monotherapy approaches. - Biomarker-driven treatment algorithms: As urinary and serum biomarkers are validated, they may enable treatment decisions guided by real-time biological signals rather than waiting for clinical deterioration.
- Novel immunological targets: Research into JAK inhibitors, type I interferon pathway blockers, and plasma cell-directed therapies continues, with several agents in active clinical development for lupus nephritis.
- Patient-reported outcomes: The field is increasingly incorporating patient-reported outcome measures (PROMs) into trial design and clinical monitoring to better capture the full burden of disease.
Conclusion
Lupus nephritis remains one of the most serious and complex kidney diseases encountered in clinical practice, carrying significant risks of permanent kidney damage and a disproportionate burden on young women and underrepresented populations. Yet the scientific progress of recent years offers genuine cause for optimism. Advances in histopathological classification — anchored by the ISN/RPS framework and its 2018 revision — have given clinicians a more precise map of disease severity and prognosis. Breakthrough clinical trials have expanded the treatment landscape from a single standard regimen to a growing portfolio of targeted options, each addressing different immunological drivers of disease.
The International Society of Nephrology has been a consistent and vital force in driving these advances, from shaping classification systems and validating outcome measures to emphasizing the need for biomarker-guided monitoring and equitable global access to care. As the field continues to evolve, the work of ISN will remain central to translating scientific discovery into better, more personalized care for patients worldwide living with lupus nephritis.