Rituximab-induced depletion of anti-PLA2R autoantibodies predicts response in membranous nephropathy

Abstract

Autoantibodies to the M-type phospholipase A(2) receptor (PLA(2)R) are sensitive and specific for idiopathic membranous nephropathy. The anti-B cell agent rituximab is a promising therapy for this disease, but biomarkers of early response to treatment currently do not exist. Here, we investigated whether levels of anti-PLA(2)R correlate with the immunological activity of membranous nephropathy, potentially exhibiting a more rapid response to treatment than clinical parameters such as proteinuria. We measured the amount of anti-PLA(2)R using Western blot immunoassay in serial serum samples from a total of 35 patients treated with rituximab for membranous nephropathy in two distinct cohorts. Pretreatment samples from 25 of 35 (71%) patients contained anti-PLA(2)R, and these autoantibodies declined or disappeared in 17 (68%) of these patients within 12 months after rituximab. Those who demonstrated this immunologic response fared better clinically: 59% and 88% attained complete or partial remission by 12 and 24 months, respectively, compared with 0% and 33% among those with persistent anti-PLA(2)R levels. Changes in antibody levels preceded changes in proteinuria. One subject who relapsed during follow-up had a concomitant return of anti-PLA(2)R. In summary, measuring anti-PLA(2)R levels by immunoassay may be a method to follow and predict response to treatment with rituximab in membranous nephropathy.

Figure 1.

Representative immunoblots demonstrate four patterns of response of IgG4 anti-PLA₂R signal at sequential time points after rituximab treatment (0 to 30 months; all patients are missing data from one or more time points). Panel A depicts the typical reduction (through 6 months) and disappearance (9 months and beyond) of anti-PLA₂R exhibited by most patients. Panel B shows a similar pattern (upper blot), but a longer exposure of the immunoblot (lower) demonstrates that the anti-PLA₂R signal persists at a very weak, subthreshold value through the final time point (arrow). Panel C is representative of the six patients in which anti-PLA₂R did not substantially decline after treatment. Panel D depicts the single patient whose anti-PLA₂R returned with relapse of his disease after having initially disappeared.

Figure 2.

The clinical response to rituximab is temporally associated with the immunologic response. Representative plots of anti-PLA₂R (gray squares) and proteinuria (black diamonds) versus time after initial rituximab treatment. Values are plotted as percent of baseline value for sake of better comparison between subjects. The four graphs correspond to the four immunoblots depicted above and to the following subjects in Table 1: A, subject 13; B, subject 6; C, subject 22; D, subject 9.

Figure 3.

Anti-PLA₂R (left box plot) declines in advance of a more gradual decline of proteinuria (right) in those patients who cleared anti-PLA₂R. Boxes represent median (line) and 25th and 75th percentiles, with whiskers to the 10th and 90th percentiles. Outliers are represented by filled circles.