Anti-Phospholipase A2 Receptor 1 and Anti-Cysteine Rich Antibodies, Domain Recognition and Rituximab Efficacy in Membranous Nephropathy: A Prospective Cohort Study.

Rationale & Objective: Proteinuria and anti-phospholipase A receptor 1 (anti-PLAR1) antibody titers are associated with primary membranous nephropathy (MN) outcomes. We evaluated the association of antibodies against the cysteine-rich (CysR) and C-type lectin 1, 7, and 8 (CTLD1, CTLD7, and CTLD8) domains of PLAR1 with MN outcomes.

Study Design: Prospective cohort study.

Setting & Participants: One-hundred-thirteen consecutive, consenting patients referred to the Nephology Unit of the Azienda-Socio-Sanitaria-Territoriale (ASST) Papa Giovanni XXIII (Bergamo, Italy) with PLAR1-related, biopsy-proven MN whose persistent nephrotic syndrome (NS) was managed conservatively for>6 months and were monitored with serial evaluations of proteinuria, autoantibodies (by enzyme-linked immunosorbent assay), and clinical outcomes.

Exposure: Rituximab.

Outcome: Complete (proteinuria<0.3g/24h) or partial (proteinuria≥0.3g/24h and<3.0g/24h with>50% reduction vs basal) NS remission.

Analytical Approach: Univariable and multivariable Cox regression analyses.

Results: All patients had anti-CysR antibodies; 62 (54.9%) were multidomain recognizers. Anti-PLAR1 and anti-CysR antibody titers were strongly correlated at baseline (P<0.001, r=0.934), 6 months (P<0.001, r=0.964), and 12 months (P<0.001, r=0.944). During a median follow-up of 37.1 (IQR, 20.3-56.9) months, 71 patients (62.8%) achieved either complete or partial remission of their NS. Lower baseline anti-PLAR1 (HR, 0.997 [95% CI, 0.996-0.999], P=0.002) and anti-CysR [HR, 0.996 [95% CI, 0.993-0.998], P=0.001) titers were associated with a higher probability of remission, along with female sex, lower proteinuria, and lower serum creatinine levels (P<0.05 for all comparisons). Anti-CTLD antibodies were not associated with outcomes. At 6 and 12 months, compared to baseline, anti-PLAR1 and anti-CysR antibody titers decreased more in patients progressing to partial or complete remission than in those without remission (P<0.05 for all comparisons).

Limitations: Observational design.

Conclusions: In PLAR1-related MN, anti-PLAR1 and anti-CysR antibodies similarly predict rituximab efficacy independent of PLAR1 domain recognition. The choice between these tests should be dictated by feasibility and costs. Evaluating anti-CTLD antibodies appears unnecessary.

Plain-language Summary: Primary membranous nephropathy (MN), a leading cause of nephrotic syndrome (NS) in adults, is an autoimmune disease caused by autoantibodies binding to the podocyte antigen phospholipase A2 receptor 1 (PLAR1). We assessed whether the effects of anti-CD20 cytolytic therapy with the monoclonal antibody rituximab are associated with detection rates and levels of anti-PLAR1 antibodies and antibodies against PLAR1 domains such as cysteine-rich (CysR), and C-type lectin 1, 7, and 8 (CTLD1, 7, and 8), in patients with PLAR1-related MN and persistent NS. The probability of rituximab-induced complete or partial NS remission was associated with baseline anti-PLAR1 and anti-CysR antibody titers, but not with anti-CTLD1, 7 and 8 antibodies or multidomain recognition. Integrated evaluation of anti-PLAR1 or anti-CysR antibodies with proteinuria and kidney function may play a role in monitoring the effects of rituximab in patients with PLAR1-related NS and MN.