Primary Human Naive B Cells.

Primary naive B cells were obtained from fresh buffy coats provided by the Institute for Transfusion Medicine and Gene Therapy, ITG Freiburg. Peripheral blood mononuclear cells were separated by Ficoll gradient centrifugation of whole blood and negatively selected using EasySep Human Naive B Cell Isolation kit (StemCell). Prior to the experiments, primary naive B cells were controlled for purity and rested overnight. The study was approved by the Institutional Review Board of the University of Freiburg (ethical vote nos. 507/16 and 336/16). Additional details can be found in SI Appendix, Methods.