Treating IgA Nephropathy: Looking at the Future Without Forgetting the Past

IgA nephropathy (IgAN) is an inflammatory glomerular disease caused by the production of galactose-deficient IgA1 (Gd-IgA1), which induces the formation of autoantibodies and IgA immune complexes (IgAICs) that are ultimately deposited in the mesangium. This event triggers mesangial cell proliferation, cytokine release and complement activation, and both glomerular and interstitial damage, eventually leading to kidney function decline. Persisting proteinuria is the most relevant marker of disease progression. Systemic corticosteroids (CSs), a powerful anti-inflammatory approach, have shown kidney protective effects in early trials involving patients with IgAN at risk of progression with persistent proteinuria. However, later studies raised concerns regarding severe adverse events associated with high doses of methylprednisolone and questioned the long-term benefits. As a result, the KDIGO 2021 guidelines recommended limiting CS therapy to selected patients who accepted the high risk of adverse events. The treatment landscape shifted when reduced doses of methylprednisolone, combined with Pneumocystis pneumonia prophylaxis, demonstrated similar kidney protection compared to full methylprednisolone doses with fewer adverse events. An innovative approach involves a targeted budesonide formulation acting on Peyer's patches, the main site of Gd-IgA1 production. This treatment showed benefits comparable to systemic CSs, with valuable limitations of adverse events. Several new drugs targeting key pathogenetic events of IgAN are under investigation, with promising results published in recent months. These new therapies target B cell activation (and subsequent Gd-IgA1 production), the complement cascade triggered by IgAIC deposition and the endothelin system, a key amplifier of kidney damage that contributes to the chronicity of IgAN.