In vitro induction of human germinal center B cells.

During antibody responses, germinal centers (GCs) act as a key site for somatic hypermutation (SHM) and affinity maturation of B cells. However, their lymphoid tissue localization has made experimental manipulation of human germinal center B (GCB) cells difficult. Here, we describe a simple in vitro method, modeling T cell-derived signaling, that converts human naive B cells into BCL6+ induced GCB-like (iGCB) cells. Through side-by-side proteomic and transcriptional single-cell analysis of iGCB and human tonsil GCB cells, we show that iGCB cells recapitulate the surface marker, transcription factor, DNA repair, and glycosylation signatures that define human GCB cells and display ongoing activation-induced cytidine deaminase (AID)-dependent SHM. iGCB cells can be generated from naive B cells and from unswitched memory/circulating marginal zone cells but not class-switched memory B cells. Using this system, we define signals critical for human GCB formation and identify interventions that block their induction, providing a simple and manipulable model of human GCB cell biology.