Gene expression profiles of peripheral blood mononuclear cells (PBMC) from children with active idiopathic nephrotic syndrome (INS) and healthy controls (HC) [RTXrel_vs_RTXrem]

An autoimmune B cell origin for childhood idiopathic nephrotic syndrome (INS) is predicted based on the efficacy of rituximab (RTX) at maintaining long-term remission from proteinuria. Knowledge regarding the nature of the culprit B cell response is very limited. In particular, no transcriptomics work has been performed to evaluate the B cell response in INS. Here, we performed single-cell RNA-sequencing (scRNAseq) on B cells isolated from peripheral blood mononuclear cells (PBMC) collected from four children with INS during the B cell recovery phase of a previous RTX treamtent while in remission or relapse (paired relapse-remisison samples). We show that the post-RTX B cell landscape is overwhelmingly antigen-inexperienced with minimal transcriptomic differences between relapse and remission. However, post-RTX relapses were associated with an early resurgence of an extrafollicular B cell population expressing genes associated with marginal zone B cells (MZB1, CD24, IGHM, CD1C, TNFRSF13B, GPR183). Together, our study provides evidence for an extrafollicular origin for humoral immunity in active INS. PBMC were isolated from the blood of four children with INS during the B cell recovery phase of previous RTX treatments during relapse and remission. Live B cells were sorted by fluorescence-activated cell sorting (FACS) and analyzed by single-cell RNA-sequencing (scRNAseq).