Lupus nephritis (LN) is a serious manifestation of SLE. Therapeutic studies in mouse LN models do not always predict outcomes of human therapeutic trials, raising concerns about the human relevance of these pre-clinical models. In this study we used an unbiased transcriptional network approach to define in molecular terms similarities and differences between three lupus models and human LN. Genome wide gene expression networks were generated using natural language processing and automated promoter analysis and compared across species via suboptimal graph matching. The three murine models and human LN share both common and unique features. The 20 commonly shared network nodes reflect the key pathologic processes of immune cell infiltration/activation, endothelial cell activation/injury and tissue remodeling/fibrosis, with macrophage/dendritic cell activation as a dominant cross-species shared transcriptional pathway. The unique nodes reflect differences in numbers and types of infiltrating cells and degree of remodeling between the three mouse strains. To define mononuclear phagocyte derived pathways in human LN, gene sets activated in isolated NZB/W renal mononuclear cells were compared with human LN kidney profiles. A tissue compartment specific macrophage activation pattern was seen, with NFκB1 and PPARγ as major regulatory nodes in the tubulointerstitial and glomerular networks respectively. Our study defines which pathologic processes in murine models of LN recapitulate the key transcriptional processes active in human LN and suggests that there are functional differences between mononuclear phagocytes infiltrating different renal microenvironments.

Women develop lupus more frequently than men and the reason remains incompletely understood. Evidence that men with Klinefelter’s Syndrome (XXY) develop lupus at approximately the same rate as women suggests that a second X chromosome contributes. However, since the second X is normally inactivated, how it predisposes to lupus is unclear. DNA methylation contributes to the silencing of one X chromosome in women, and CD4+ T cell DNA demethylation contributes to the development of lupus-like autoimmunity. This suggests that demethylation of genes on the inactive X may predispose women to lupus, and this hypothesis is supported by a report that CD40LG, an immune gene encoded on the X chromosome, demethylates and is overexpressed in T cells from women but not men with lupus. Overexpression of other immune genes on the inactive X may also predispose women to this disease. We therefore compared mRNA and miRNA expression profiles in experimentally demethylated T cells from women and men as well as in T cells from women and men with lupus. T cells from healthy men and women were treated with the DNA methyltransferase inhibitor 5-azacytidine, then X-linked mRNAs were surveyed with oligonucleotide arrays, and X-linked miRNA’s surveyed with PCR arrays. CD40LG, CXCR3, OGT, miR-98, let-7f-2*, miR 188-3p, miR-421 and miR-503 were among the genes overexpressed in women relative to men. MiRNA target prediction analyses identified CBL, which downregulates T cell receptor signaling and is decreased in lupus T cells, as a gene targeted by miR-188-3p and miR-98. Transfection with miR-98 and miR-188-3p suppressed CBL expression. The same mRNA and miRNA transcripts were also demethylated and overexpressed in CD4+ T cells from women relative to men with active lupus. Together these results further support a role for X chromosome demethylation in the female predisposition to lupus.

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Systemic lupus erythematosus (SLE) is a chronic autoimmune inflammatory disease affecting both adults and children. Belimumab is the only biologic approved for SLE, and the first in a class of drugs known as B-lymphocyte stimulator-specific inhibitors. The introduction of intravenous belimumab in 2011 was a major advance, being the first new therapy approved for SLE in over 50 years. As of April 2021, more than 7200 people with SLE have received belimumab in clinical studies, and it is approved in over 75 countries for the treatment of adults with SLE. A subcutaneous, self-injectable belimumab formulation was licensed in 2017 by both the US Food and Drug Administration (FDA) and European Medicines Agency (EMA). Belimumab was then approved for use in children in Europe, the USA and Japan in 2019, and China and Brazil in 2020. Recently, belimumab became the first FDA-approved drug for the treatment of adults with active lupus nephritis (LN), the most-common severe manifestation of SLE. Over the past 10 years, belimumab has established its position as a disease modifier in the SLE treatment paradigms. Robust evidence from randomised clinical studies and observational, real-world studies has demonstrated the tolerability and efficacy of belimumab for reducing disease activity and the risk of new, severe SLE flares. This enables patients to taper their glucocorticoid use, which limits damage accumulation. Significantly more patients with active LN met the criteria for renal responses and were at less risk of a renal-related event or death after receiving belimumab plus standard therapy, compared with standard therapy on top of mandatory steroid reduction. Ongoing clinical studies are evaluating belimumab’s effectiveness in various indications beyond SLE. Post-marketing and registry studies are gathering additional data on key areas such as pregnancy outcomes after belimumab exposure and belimumab co-administration with other biologics.

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