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Meeting Reports 2002
SLE: Targets for New Therapeutics Conference Summary
January 10-12, 2002 (historical)
I. Executive Summary
The National Institute of Arthritis and Musculoskeletal and Skin Diseases cosponsored a meeting on "SLE:Targets for New Therapeutics" with the S.L.E. Foundation, Inc., the Lupus Research Institute, the National Institute of Allergy and Infectious Diseases, the National Institute of Diabetes and Digestive and Kidney Diseases, and the NIH Office of Research on Women's Health. The meeting, held January 10-12, brought together world leaders in the contemporary biology of systemic lupus erythematosus (SLE, lupus) to focus on specific targets that may be amenable to treatment interventions. The planning committee included representatives from the cosponsoring organizations. Drs. Jane Salmon (Hospital for Special Surgery and Weill Medical College of Cornell University, New York) and David Wofsy (University of California at San Francisco and San Francisco VA Medical Center) chaired the meeting.
The major short term goal of this conference was to facilitate the exchange and integration of scientific information among scientists working in fairly disparate areas related to SLE, while the long term goal was to identify promising new strategies for clinical intervention.
To meet these goals, the conference was focused around five areas:
- Extrinsic and Intrinsic Triggers of Autoimmunity
- Predisposing Factors
- Immunoregulatory Mechanisms
- Mediators of Tissue Injury
- Novel Therapies
These five areas were addressed as formal sessions with presentations by invited speakers (see below). In addition there were two poster sessions in which 92 posters were presented. There were also two evening sessions. On the first evening, there were 5 concurrent workshops where a total of 35 of the submitted abstracts were presented for discussion. On the second evening there was a plenary session entitled "Drug Trials and Tribulations", aimed at identifying the obstacles to clinical research in lupus and finding their solutions. In this special session a panel of investigators, from government agencies, academia, and the biotechnology industry, and a lupus patient were asked to discuss what does and does not work in constructing drug trials for patients with SLE. Audience members were invited to participate. Overall, the concept of multiple organ system involvement, small numbers of patients, the non-concordance of disease activity measures, and the lack of suitable instruments to measure responses to treatment were identified.
II. Meeting Summary
Session I: Extrinsic and Intrinsic Triggers of Autoimmunity (Chair: Dr. David Pisetsky)
SLE is a prototypic autoimmune disease that arises in a genetically susceptible host under the influence of extrinsic and intrinsic factors. The nature of these triggers has been extensively studied with the goal of understanding disease pathogenesis as well as developing new strategies for prevention and treatment. Among extrinsic factors, infection has the potential to trigger autoimmunity by non-specifically increasing immune system activity as well as inducing specific autoantibody responses through cross-reactivity or molecular mimicry. Dr. Pisetsky presented an analysis of the anti-DNA response in which bacterial DNA may play a unique triggering role. While DNA has usually been considered inert, DNA from bacteria has potent adjuvant activities which, in concert with shared structural epitopes on the DNA backbone, may allow induction of a cross-reactive anti-DNA response. Dr. Judith James, in an analysis of the immune response to snRNP proteins, demonstrated that patients with SLE manifest an increase in the frequency of antibodies to the Epstein-Barr virus (EBV). Because of cross-reactivity of EBV proteins and snRNP proteins, these findings suggest that an aberrant response to EBV may lead to the generation of an autoantibody response which subsequently diversifies by epitope spreading.
In another perspective on the role of extrinsic factors in disease pathogenesis, Dr. Westley Reeves discussed the pristane model of SLE. In this model, which can be induced in normal mice by treatment with the mineral oil pristane, autoantibodies arise in a pattern similar to SLE under the influence of various cytokines. As suggested by analysis of cell populations in the treated mice, induction of disease may follow prolonged non-specific immune stimulation which culminates in the generation of dendritic cells. These cells may be an abundant source of cytokines and contribute to disease by their ability to present self antigen. Dr. Ann Marshak-Rothstein described another role of self antigen in a transgenic rheumatoid factor (RF) model. In mice with a RF transgene, immune complexes containing nucleosomal antigens may trigger B cells by a mechanism that ultimately involves the Toll-like receptor 9, with the RF on the surface providing a means of uptake and access to the receptor. Since the Toll-like receptor 9 mediates the response to bacterial DNA, it may represent a critical step in disease pathogenesis, whether triggered by foreign or self DNA.
Other factors that are intrinsic to the host may also influence a propensity for autoreactivity. As discussed by Dr. Michael Lockshin, female sex can be an important determinant of autoimmunity although the magnitude of this effect varies by disease. In SLE, the effect is large and approximates a 5-8 fold increase in females to males. In other diseases, the effect is much less. The explanation for the range of this effect is not clear but points to the variety of immune system changes that may have sex determination and operate variously depending on the presence of other susceptibility factors. These considerations suggest that the analysis of disease susceptibility would benefit by expanded information on the differences between sexes in immune system regulation. By understanding the critical changes in immune regulation conferred by sex (including hormonal influences), it may be possible to develop specific approaches for their interdiction as a novel form of immunomodulation.
Session II-Predisposing Factors: Genetics of SLE (Chair: Dr. Brian Kotzin)
Considerable evidence indicates that the development of SLE has a strong genetic basis. Studies in patients and animal models have emphasized that lupus is a complex genetic trait with contributions from major histocompatibility complex (MHC) and multiple non-MHC genes. This session on the genetics of SLE was divided into two sections depending on whether studies were done in mouse models of lupus or in humans.
In the session on animal models, Dr. Kotzin focused on the (NZB x NZW)F1 model of lupus and particularly on one NZB locus (named Nba2) mapped to mouse distal chromosome 1. He described the development of lupus traits and contribution to lupus nephritis in mice congenic for this locus. Expression profiling using oligonucleotide microarrays showed differential expression of an interferon-inducible gene (Ifi202), and additional studies suggested that this gene influenced the development of lupus by interfering with lymphocyte apoptosis. Dr. Edward Wakeland presented follow-up studies on the closely related NZM mouse model of lupus. He provided new insight into the gene underlying the susceptibility locus, Sle1b, which has been mapped to the same region on distal chromosome 1, but is inherited from the NZW strain. The results of positional cloning studies, sequence analysis, and expression profiling suggested that the etiologic gene for Sle1b lies within the CD2 complex. This complex includes a variety of genes, such as Ly9, Ly108, CD84, and CD48, involved in the activation and signaling of B lymphocytes. Dr. Mark Walport discussed the important associations between hereditary deficiency of complement and the development of SLE. He presented data that supported a role for the complement system in the clearance of cellular debris. Additional data illustrated the importance of background genes in mice (and presumably humans) in determining the lupus phenotype associated with complement deficiency. Results of genetic studies in mice demonstrated that the development of autoantibodies to the endogenous retroviral antigen, gp70, was linked to a locus on murine chromosome 13 that controlled the level of expression of gp70 antigen. This finding emphasizes the potential importance of autoantigen levels in determining autoimmune responses in lupus.
Dr. Timothy Behrens presented studies examining the contribution of HLA alleles and haplotypes to human SLE. Using a dense map of polymorphic microsatellites across the HLA, Dr. Behrens and his colleagues identified three distinct risk haplotypes that encompassed the HLA class II region in 334 SLE families. By visualizing ancestral recombinants, two of these haplotypes could be narrowed to a ~400 kb region, supporting the hypothesis that particular DRB1 and DQB1 alleles are strong risk factors for human SLE. In other work, Dr. Behrens explored the potential utility of gene expression microarrays of peripheral blood mononuclear cells in patients with SLE and normal controls. This approach has identified a large number of genes important for immunity and inflammation that are dysregulated in the blood cells of SLE patients. Dr. Lindsey Criswell reviewed the genetic mapping studies in SLE that have been presented to date. She emphasized the elements of genetic complexity that contribute to the difficulty of confirming reports of linkage and association. In order to illustrate these concepts, Dr. Criswell also presented preliminary data examining the possible association of angiotensin converting enzyme (ACE) polymorphisms with human SLE and lupus nephritis. Dr. John Harley also reviewed the genetic linkage studies in SLE done to date. He emphasized the strong evidence of linkage for a number of different loci, especially when genetic heterogeneity due to ethnic variation is considered. Dr. Harley also emphasized that clinical variation in lupus appears to have a genetic basis, and presented data showing that this clinical variation could be used to advantage in linkage studies by making the families being analyzed more homogeneous. Dr. Betty Tsao concluded the session on genetic susceptibility in SLE by presenting data that confirmed significant linkage to 1q23 and 16q12 in their cohort of 109 multiethnic nuclear families containing 135 SLE-affected sibpairs. Overall, these and other data to date provide support for linkage at 6p11-21, 1q22-23, 1q41-42, 2q35-37, 4p15.2-16, and 6q12-13 in the susceptibility to SLE. In addition, evidence was presented supporting an interaction between SLE-susceptibility genes at 1q23 and 16q12 that may impact susceptibility. Their strategy to facilitate the identification of susceptibility genes within loci of confirmed significant linkage is to minimize disease heterogeneity by stratifying families on SLE subphenotypes.
Session III: Immunoregulatory Mechanisms (Chair: Dr. Katherine Siminovitch)
The session on Immunoregulatory Mechanisms began with a presentation on the use of "tolerizing" synthetic peptides as possible therapeutic reagents in SLE by Dr. Bevra Hahn. The peptide described represents a consensus sequence present in the variable regions of murine anti-DNA antibodies and its repeated injection in lupus-prone mice appears to evoke a tolerogenic immune response associated with disease amelioration. Mechanisms underlying the loss of T-cell tolerance and development of polyclonal activation in SLE were then addressed by Dr. Joseph Craft. Dr. Craft has studied lupus-prone mice carrying a specific T-cell antigen receptor (TCR) transgene with respect to their T-cell responses to low affinity TCR peptide ligands. His data reveal T-cell activation to be increased in the lupus relative to control animals and suggest that an intrinsically (genetically) heightened response to self antigens represents an important factor driving the polyclonal T-cell activation characteristic of spontaneous lupus. The next two presentations dealt with roles of the SHP-1 tyrosine phosphatase and selected Jak/Stat proteins in modulating lymphocyte activation. In the discussion by Dr. Katherine Simnovitch, the capacity of SHP-1 to suppress B- and T-cell antigen receptor-triggered lymphocyte activation was demonstrated and described in relation to the systemic autoimmune phenotype found in SHP-1-deficient motheaten mice. The inhibitory properties of SHP-1 were shown to reflect the capacity of SHP-1 to interact with and dephosphorylate the antigen receptors, comodulatory accessory proteins, such as CD22, and a wide range of cytosolic effectors involved in antigen receptor signaling (such as the Lyn kinase and phosphatidylinositol-3-kinase). Dr. John O'Shea then described the variable clinical phenotypes associated with deficiency of Janus Kinase 3 and emphasized the complexity of the roles this kinase plays in modulating T-cell function. In addition he showed data identifying a novel IFN-g-driven autocrine loop in T cells wherein IFN-g triggers Stat 4-mediated induction of the T-bet transcription factor and thereby promotes further IFN-g production and T helper 1 cell responses.
A discussion of the molecules regulating B-cell homeostasis was then initiated by Dr. Jane Gross who described the physiological roles for two newly-identified members of the TNF receptor family, TACI and BMCA and their ligands, BLyS and APRIL. Blockade of these receptors by TACI-Ig treatment or overexpression was shown to be associated with an arrest in development of mature follicular and marginal zone B-2 cells. Similarly B-cell development is blocked at the immature transitional T1 stage in BLyS-deficient mice. Importantly, TACI-Ig treatment was found to suppress the development of pathogenic antibodies to collagen and inhibit disease progression in an animal model of rheumatoid arthritis. Thus the neutralization of BLyS may prove of therapeutic value in the suppression of autoimmune diseases. In the final talk, Dr. Peter Lipsky also emphasized the important role of "overly active" germinal centres as a source of autoantibody-producing B cells in SLE. His data indicated the numbers of circulating B cells with a germinal centre phenotype and circulating plasmablasts to be markedly increased in patients with active SLE. Importantly, these abnormalities were no longer detected in patients treated with a monoclonal antibody to CD40 ligand (CD154) that blocks germinal centre reactions. This finding is consistent with the conclusion that CD40/CD154 interactions modulate B-cell overactivity and autoantibody production in SLE and suggest that the blockade of such interactions reduce the B-cell abnormalities and potentially the clinical manifestations of SLE. Together, the data presented in this session identified a number of novel molecular interactions which regulate B and T-cell activation and which may serve as targets for therapeutic intervention in SLE.
Session IV: Mediators of Tissue Injury (Chair: Dr. Jane Salmon)
Autoantibodies, complement, leukocytes and thrombosis contribute to target organ damage. This session dealt with novel ways in which these mediators cause tissue injury and new approaches to intervene in these pathways to prevent damage. For example, anti-cardiolipin antibodies are associated with thrombosis and pregnancy loss in the anti-phospholipid syndrome. Dr. Salmon provided data that showed that anti-cardiolipin antibodies activate complement to mediate this phenotype in a murine model. That inhibitors of complement activation prevent disease suggests that complement might be a target for treatment in patients with the anti-phospholipid syndrome. Another family of pathogenic antibodies, those that recognize double-stranded DNA, is a major contributor to renal disease. Dr. Betty Diamond presented evidence that anti-DNA reactive antibodies also recognize human NMDA (N-methyl-D-aspartate) receptor subunits NR2a and NR2b and this cross-reactivity mediates apoptotic death of neurons in vivo and in vitro. She showed that lupus antibodies cross-react with DNA and NMDA receptors, gain access to cerebrospinal fluid, and may mediate non-thrombotic and non-vasculitic abnormalities of the central nervous system. Thus, a new target for preventing CNS disease was revealed.
Leukocytes and their products are important as mediators of organ injury in immune complex disease. Dr. Mark Ginsberg, in his discussion of leukocyte migration and alpha-4 integrins, described strategies to modulate leukocyte trafficking through blockade of the intracellular interactions between the cytoplasmic domains of integrins and intracellular cytoskeletal elements. It has become increasingly clear that coagulation augments inflammation. Dr. Charles Esmon discussed the basis for the interactions between the coagulation and inflammation pathways and the role of natural coagulation inhibitors, such as activated protein C, in modulating inflammatory responses. Dr. Jose-Carlos Guiterrez-Ramos presented evidence for two new genes that regulate T effector cells (TIM-3 and ICOS) and suggested that these proteins also could be targets for treatment of SLE as modulators of T helper cell activation and TH1 responses.
Session V - Novel Therapies (Chair: Dr. David Wofsy)
The session devoted to novel therapies began with an acknowledgment of the happy problem that there are so many promising new therapeutic strategies that they could not all be covered in a single session. Some of these strategies are directed at T-cell targets (e.g., CD3, CD4, CD28, CD40L), some against B-cell targets (e.g, CD20, CD22, B7, TACI), some against cytokines (e.g., interferon-g, interleukin 10), and some against complement (CR1, C5). Other therapeutic strategies are designed to restore regulatory cells and/or to reprogram the immune system (e.g., high-dose immunoablative therapy or autologous stem-cell transplantation).
After Dr. James Balow opened the session with an update on our understanding of current therapies, examples of several novel strategies were discussed in detail. Dr. David Daikh presented new findings indicating that lupus nephritis can be reversed in murine models by an induction regimen consisting of CTLA4Ig in combination with a single dose of cyclophosphamide; thereafter, the benefit can be maintained by CTLA4Ig alone. Dr. Robert Eisenberg reviewed the scientific rationale for several B-cell directed therapies and described the early phase I experience with anti-CD20 therapy. Dr. Richard Quigg presented evidence from murine models indicating that complement inhibitors, such as anti-C5 or recombinant soluble complement receptor 1, can retard lupus nephritis. Anti-C5 is already in the early stages of clinical investigation in people with membranous nephritis, rheumatoid arthritis, and SLE. Dr. Michelle Petri described a growing experience using high-dose immunoablative therapy with cyclophosphamide in people with severe SLE. Among 14 patients treated thus far at Johns Hopkins University, the complete response rate is 43%. Dr. Ann Traynor concluded the session with an update on autologous stem-cell transplantation for SLE. Fifteen patients have received this treatment at Northwestern University over the past 5 years. The complete response rate at 18 months was 70%; at three years, 80% of the subjects did not require immunosuppression. Based on these encouraging findings, an NIH-sponsored phase III trial will be initiated soon.