Quantifying peripheral blood antigen-specific memory B cells as a new biomarker in patients with PLA2R-associated membranous nephropathy

Quantifying peripheral blood antigen-specific memory B cells as a new biomarker in patients with PLA2R-associated membranous nephropathy Primary membranous nephropathy (PMN) is the most common cause of nephrotic syndrome in nondiabetic adults. The dominant autoantigen, phospholipase A2 receptor (PLA2R), is associated with 70~80% of clinical cases. B-cell depletion therapies such as Rituximab have now become the first-line treatment option for PMN. Although effective, Rituximab (alone or combined with Calcineurin inhibitors) has an overall failure rate of 30- 35%, raising controversies on the ideal dosage and best treatment protocol. Monitoring circulating CD20+ B-cell recovery is instrumental in guiding Rituximab therapy; however, it provides little value in predicting the treatment outcome. None of the current diagnostic tests, including measuring proteinuria, serum creatinine, glomerular filtration rate, and antibody titers by ELISA test, nor kidney biopsy, can predict a patient’s response to immunosuppressive therapies and disease progression. We developed a flow cytometry-based assay that detects and quantifies circulating PLA2R antigen-specific memory B cells (PLA2R-MBCs), the precursor of anti- PLA2R autoantibody production, in PMN patients. We applied the test to 94 human subjects, including a retrospective longitudinal study of 19 patients with PLA2R-MN followed over 2 to 12 years. We observed that the levels of circulating PLA2R-MBCs are associated with the disease status and could provide crucial immunological information not captured by the PLA2R-Ab ELISA and other biomarker tests, which could help to 1) assess patient response to immunosuppressive therapies for optimal dosages and courses for the best treatment outcome, and 2) monitor the earliest sign of disease relapse for early treatment intervention to preserve kidney functions. Building upon these promising initial clinical observations, we propose to develop the assay into a test kit for future extensive cohort studies. We envision the test will enable nephrologists for the first time to customize treatments for individual patients to achieve the best treatment outcome with minimal side effects, significantly reducing the social and financial burden on the US healthcare system and driving down the Medicare spending for this group of patients.