B cells are classically considered for their unique capacity to produce antibodies. Besides this, B cells can also present antigen, costimulate T cells, and secrete cytokines. Recent studies have demonstrated that activated B cells could regulate immunity by the secretion of anti-inflammatory cytokines. Because of their capacity to inhibit immune responses, B cells became of interest as a potential vehicle for the treatment of autoimmune disorders via cell-based therapy. Different approaches have been developed to empower B cells with regulatory properties. An attractive strategy involves their genetic engineering to enforce their expression of suppressive genes. This can be achieved using retroviral vectors. However, most retroviral vectors require prior activation of the B cells for transduction, and the administration of activated B cells may lead to unpredictable outcomes in recipients, including to an enhancement of immune responses. In contrast, resting B cells are poorly immunogenic and therefore safer for the suppression of undesired immune responses in adoptive cell therapy. In this chapter, we describe an approach to generate genetically modified resting B cells with lentiviral vectors using a protocol that is rapid, simple, and neither requires nor induces activation of B cells.