Despite the promise of RNA interference (RNAi) and its potential, e.g. for use in cancer therapy, several technical obstacles must first be overcome. The major hurdle of RNAi-based therapeutics is to deliver nucleic acids across the cell’s plasma membrane. This study demonstrates that exosome vesicles derived from humans can deliver short interfering RNA (siRNA) to human mononuclear blood cells. Exosomes are nano-sized vesicles of endocytic origin that are involved in cell-to-cell communication, i.e. antigen presentation, tolerance development and shuttle RNA (mainly mRNA and microRNA). Having tested different strategies, an optimized method (electroporation) was used to introduce siRNA into human exosomes of various origins. Plasma exosomes (exosomes from peripheral blood) were used as gene delivery vector (GDV) to transport exogenous siRNA to human blood cells. The vesicles effectively delivered the administered siRNA into monocytes and lymphocytes, causing selective gene silencing of mitogen-activated protein kinase 1. These data suggest that human exosomes can be used as a GDV to provide cells with heterologous nucleic acids such as therapeutic siRNAs.

Key Points Healthy human BM is enriched for PC lacking CD19 that express a prosurvival and distinctly mature phenotype. CD19− PC resist mobilization into blood during immune responses after vaccination as well as B-cell depletion with rituximab.

The posttranslational modification of proteins has the potential to generate neoepitopes that may subsequently trigger immune responses. The carbamylation of lysine residues to form homocitrulline may be a key mechanism triggering inflammatory responses. We evaluated the role of carbamylation in triggering immune responses and report a new role for this process in the induction of arthritis. Immunization of mice with homocitrulline-containing peptides induced chemotaxis, T cell activation, and Ab production. The mice also developed erosive arthritis following intra-articular injection of peptides derived from homocitrulline and citrulline. Adoptive transfer of T and B cells from homocitrulline-immunized mice into normal recipients induced arthritis, whereas systemic injection of homocitrulline-specific Abs or intra-articular injection of homocitrulline-Ab/citrulline-peptide mixture did not. Thus, the T cell response to homocitrulline-derived peptides, as well as the subsequent production of anti-homocitrulline Abs, is critical for the induction of autoimmune reactions against citrulline-derived peptides and provides a novel mechanism for the pathogenesis of arthritis.

SummaryWe demonstrate that humans have a phenotypically and functionally distinct subset of B lymphocytes that express the interleukin (IL)-2 receptor (IL-2R) a-chain, cluster of differentiation (CD) 25. We found that one-third of the circulating CD20 + B cells expressed CD25 and, using

RHO family proteins are important for the function of inflammatory cells. They are modified with a 20-carbon geranylgeranyl lipid in a process catalyzed by protein geranylgeranyltransferase type I (GGTase-I). Geranylgeranylation is viewed as essential for the membrane targeting and activity of RHO proteins. Consequently, inhibiting GGTase-I to interfere with RHO protein activity has been proposed as a strategy to treat inflammatory disorders. However, here we show that mice lacking GGTase-I in macrophages develop severe joint inflammation resembling erosive rheumatoid arthritis. The disease was initiated by the GGTase-I-deficient macrophages and was transplantable and reversible in bone marrow transplantation experiments. The cells accumulated high levels of active GTP-bound RAC1, CDC42, and RHOA, and RAC1 remained associated with the plasma membrane. Moreover, GGTase-I deficiency activated p38 and NF-κB and increased the production of proinflammatory cytokines. The results challenge the view that geranylgeranylation is essential for the activity and localization of RHO family proteins and suggest that reduced geranylgeranylation in macrophages can initiate erosive arthritis.