Elimination of autoreactive B cells in humanized SCID mouse model of SLE

Abstract

Although the exact etiology of systemic lupus erythematosus (SLE) remains elusive, B-cell hyperactivity and production of autoantibodies directed to components of the cell nucleus are a well-established pathogenetic mechanism of the disease. Therefore, the targeted inhibition of DNA-specific B cells is a logical therapeutic approach. The complement receptor type 1 (CR1, CD35) has been shown to suppress human B-cell activation and proliferation after co-cross-linking with the BCR, and may serve as a mediator for negative signal delivery. In order to evaluate this therapeutic approach in a human-like system, we used immune-restricted SCID mice transferred with PBMCs from SLE patients. The tolerance of these humanized SCID mice to native DNA was re-established after administration of a chimeric molecule consisting of a CR1-specific mAb coupled to the decapeptide DWEYSVWLSN that mimics dsDNA. The generated protein-engineered chimera was able to co-cross-link selectively native DNA-specific BCR with the B-cell inhibitory receptor CR1, thus delivering a strong inhibitory signal.Key words: Chimeric molecules . Inhibitory B-cell receptors . SCID models of SLE IntroductionThe pathogenesis of systemic lupus erythematosus (SLE) is characterized by the formation of autoantibodies against a wide range of self-antigens. Development of this multi-system autoimmune syndrome in many severe cases leads to mortality. SLE patients develop high-titered anti-nuclear antibodies (ANA), the majority of them against double-stranded (ds) DNA. Multiple organs can be involved in human SLE (skin, lung, heart, arteries, nervous system), but kidneys being most severely affected. The pathological changes are provoked by deposition of immune complexes into renal glomeruli, followed by kidney structure damages and development of nephritis and proteinuria [1]. 3301The pathogenetic role of self-specific B cells has been attributed not only to the generation of autoreactive antibodies, but also to their antigen-presenting functions [2,3]. A number of studies have clearly documented the strong correlation between the level of these B cells and disease severity. The efficacy of B-cell depletion therapy further supports the key role of B cells in the pathology of SLE. Activity of any self-specific B cells is regulated by the interplay of multiple factors controlling B-cell proliferation and differentiation. BCR-mediated activation may be counteracted by a number of inhibitory receptors: CD32 (FcgRIIb), CD22, CD5, CD72, CD66a, ILT2, PIR-B, CD279 (PD-1), LAIR-1, as well as the complement receptor type 1 (CR1, CD35). While a reduced expression of these receptors can result in uncontrolled B-cell activation [4,5] and autoimmunity, their cross-linking inhibits B-cell activation and proliferation and may serve for targeted suppressive signal delivery [6,7].Non-specific immunosuppressive drugs are by now the most frequent therapy for autoimmune diseases, including SLE. Their effects are purely symptomatic while most of them are associated with severe side ef...

Complement Receptor Type 1 Suppresses Human B Cell Functions in SLE Patients

“…This suggests that the aberrant expression of CR1 contributes to initiation of autoimmune diseases rather than altering peripheral activation of the cells [10]. The ability of human CR1 to reduce autoimmunity has also been proven in humanized SCID mice transferred with PBMCs of lupus patients where cross-linking of the BCR and CR1 restored B cell tolerance and lowered the number of IgG anti-DNA producing plasma cells [17]. …”

Protein-engineered molecules carrying GAD65 epitopes and targeting CD35 selectively down-modulate disease-associated human B lymphocytes

“…The first chimera was constructed by coupling copies of the dsDNA‐mimicking peptide to a mouse anti‐human CD35 monoclonal antibody. Its administration to humanized SCID mice reconstituted with PBMCs from SLE patients resulted in the suppression of IgG anti‐DNA antibody‐producing plasma cell, proteinuria and glomerular deposition of human IgG immune complexes . The second chimeric molecule contained copies of the Der p 1‐derived peptide sequence (p52–71) from Dermatophagoides pteronyssinus coupled to the same anti‐human CD35 antibody.…”

“…that the human CD35 can provide a strong inhibitory signal to human B lymphocytes . We have previously shown that the binding of specific epitopes to the B cell receptors and the cross‐linking with CD35 on the surface of autoreactive cells may have a strong negative effect on them . The goal of our research is to selectively suppress anti‐GAD65 IgG antibody‐producing B lymphocytes from T1DM patients by chimeric protein molecules that contain a monoclonal antibody, specific to CD35 conjugated to peptide epitopes from GAD65.…”

The versatile functions of complement C3‐derived ligands

“…These results give evidence that human CR1 exerts an opposite effect to CR2, thus provides an additional level of regulation of humoral immunity (Figure ). The therapeutic potential of CR1 inhibition was proven in a humanized SCID model, where selective co‐cross‐linking native DNA‐specific BCR with the inhibitory CR1 suppressed B‐cell proliferation and autoantibody production . The inhibitory effect of CR1 in autoimmune patients will be detailed later.…”