Notes From the 6th Global Arthritis Research Network (GARN) Meeting

Session 3

Saturday, May 12, 2007 (am)
B-cell biology in health and disease II
Chairs: Rachel Ettinger, Bethesda, MD, USA, and Yehuda Shoenfeld, Tal-Hashomer, Israel

Andreas Radbruch, Berlin, Germany
Long-lived autoreactive plasma cells

Session 3 on B-cell biology in health and disease was opened by Andreas Radbruch, who discussed long-lived autoreactive plasma cells. He proposed that the partial efficacy of Rituximab, which reduces levels of antibodies only by 50%, is due to the survival of mature plasma cells that do not express CD20 on their surface. Only the short-lived precursor cells are targeted by this therapy. Mature plasma cells that are kept in bone marrow or in inflamed tissue by interaction with CXCL12 (as a survival factor) produce antibodies and are not sensitive to chemoattraction by either CXCL9 or CXCL12. However, when a new antigen appears (eg, due to vaccination) in the bloodstream, mature plasma cells secreting nonspecific antibodies appear first and memory B-cells only afterward. Bone-marrow-derived plasma cells and plasmoblasts have a similar pattern of expression of proliferation genes but differ in expression of antiapoptotic and proapoptotic genes. Proliferation and apoptosis genes are up-regulated in plasma cells from systemic lupus erythematosus (SLE) patients. In the inflamed tissues in SLE there are survival factors constituting an exceptionally favorable environment for the antibody-producing long-lived plasma cells, which are also self-reacting. Andreas Radbruch proposed long-living plasma cells as a new target for the treatment of SLE.

Pierre Youinou, Brest, France
A fresh look at the B-cells in pathophysiology of systemic autoimmune diseases

Pierre Youinou from Brest, France, presented data on the genetic regulation of the expression of CD5 in B-cells. CD5 is a coreceptor expressed by all T-cells and some B-cells, namely B1b cells-a minor subset of B-cells producing polyspecific antibodies. Human CD5 is coded on 11 exons on chromosome 11. Upstream from the gene-coding sequence of the human gene is a retroviral sequence coding for viral proteins Gag, Pol, and Env, which are flanked by long terminal repeats (LTR). Since in mice and Old World monkeys there is no such sequence upstream from the gene, it has been determined that the integration of the retrovirus took place at a time interval between the divergence of New World monkeys from Old World monkeys. The transcription of CD5 starts from a new promoter coded on a retroviral sequence, but as the promoter is integrated downstream from the start codon ATG and the rest of the exon 1, a different mRNA is synthesized with a starting codon ATG on exon 3. As a consequence, a shorter truncated protein is produced. This protein lacks the membrane localization sequence. Truncated CD5 internalizes normal CD5 to the cytoplasm; thus no more CD5 is expressed on the membrane. This was suggested as central to the regulation of membrane expression of CD5 in human B lymphocytes, and, thereby, to the strength of the B-cell antigen- receptor signaling.

Ann Marshal-Rothstein, Boston, MA, USA
Non-TLR PRRs in systemic autoimmune disease

Ann Marshal-Rothstein, from Boston, Massachusetts, presented data on the immunogenicity of DNA-containing immune complexes that are mediated though high-mobility group box chromosomal protein 1 (HMGB1) and the receptor of advanced glycation end products (RAGE). AM14 receptors (AM14 B-cells) recognize immunoglobulin G2a (IgG2a) and proliferate in response to IgG2a monoclonal antibodies (mAbs), which are reactive with chromatin or DNA in a DNase-sensitive, TLR9- and MyD88-dependent way. Marshal-Rothstein showed that cell debris is a ligand causing an inflammatory response of B-cells. Oligodeoxynucleotides preincubated with supernatants from 'spent' cell cultures increase the avidity of anti-DNA antibodies for AM14 B-cells. Marshal-Rothstein showed that this is due to HMGB1 present in chromatin IC bound to the surface of AM14 FcγRIIB-/-cells. HMGB1 is a DNA-binding protein and inflammatory cytokine, which can be secreted, and works through different receptors, including RAGE. HMGB1 is needed for binding of the complex-containing DNA to B-cells that occurs at least in part through binding to the RAGE receptor. Marshal-Rothstein has shown that not only localization of TLR is important, but RAGE is required for induction of inflammatory response after stimulation of B-cells with oligodeoxynucleotides. Stimulation with HMGB1-CpG-A results in considerable association between TLR9 and RAGE. HMGB1 is important in the induction of target genes encoding type I interferon after stimulation of cells with DNA-containing immune complexes that are present in people with systemic lupus erythematosus.

Chairs: Serena Guiducci, Florence, Italy, and Alisa Koch, Ann Arbor, MI, USA.

Robert A. Eisenberg, Philadelphia, PA, USA
Biology of B-cell depletion in SLE

Robert A Eisenberg from the University of Pennsylvania discussed the open-label safety and efficacy study of an anti-CD20 antibody (Rituximab) for anti-B-cell therapy in the treatment of systemic lupus erythematosus (SLE). SLE patients show a great heterogeneity in the degree of B-cell depletion and the development of human-antichimeric antibodies (HACA), as well as the timing of B-cell return. Although B-cell depletion and disease scores seem to correlate, correlations between polymorphism in the FC gamma receptor and the amount of B-cell depletion needs further analysis. Whether phenotypic characteristics of cells (surface expression of CD38 and CD27) can predict the response to Rituximab is under investigation. Treatment with Rituximab normalizes the ratio of the amount of kappa-lambda chains of immunoglobulins. Eisenberg mentioned that two patients treated with Rituximab showed a reactivation of the polyomavirus JC virus (JCV). Another target for B-cells in SLE is Epratuzumab (anti-CD22), a humanized monoclonal antibody with modest B-cell depletion compared with Rituximab. Epratuzumab is under investigation in clinical trials.

Kyri Dunusi-Joannopoulos, Cambridge, MA, USA IL-21 blockage and a
CD20SMIP: Novel approaches to target B cells in autoimmunity

Kyri Dunusi-Joannopoulos from Wyeth Research emphasized two novel, promising compounds to target B-cells in autoimmunity. First, Dunusi-Joannopoulos focused on the blockage of Il-21/IL-21 R interactions by an IL-21R.Fc fusion protein in the lupus-prone MRL-Fas lpr mouse model, resulting in reduced proteinuria, reduced levels of circulating dsDNA autoantibodies, and fewer IgG glomerular deposits. Furthermore, in in vitro experiments IL-21R.Fc protein reduced the number of splenic T lymphocytes and the antibody production of splenic B lymphocytes. In the CIA model treatment the IL-21R.Fc protein significantly reduced disease severity. Second, Dunusi-Joannopoulos focused on a newly developed CD20-directed small-molecule immunopharmaceutical drug for targeting B-cells-humanized antibody Tru-015 SMIP-which is currently under investigation in a phase II A study.

Session 3 summarized by Astrid Jüngel and Hanna Maciejewska

6th Global Arthritis Research Network Meeting

• Introduction
• Notes From Session 1
• Notes From Session 2
• Notes From Session 3
• Notes From Session 4