Transcriptional and Immune Parameters of Response to Belimumab

The investigators propose to perform RNA-sequencing of the whole blood initially, in a cohort of 80 SLE patients who will receive belimumab as part of standard clinical practice, in order to assess intra-patient longitudinal (baseline, 1, 3 and 6 months) transcriptome changes and examine whether treatment can ameliorate the activity/flare, severity and major organ disease gene signatures. The investigators will also obtain preliminary information on molecular signatures predicting clinical responses and the impact of belimumab on gene signatures of host defense against viral and bacterial (including mycobacterial) pathogens. Using modules of cell type-specific genes and co-expression gene networks, The investigators will deconvolute our data to define pertinent molecular alterations in specific immune cell types. Results will be validated and functionally characterized by single-cell mass cytometry (performed at the aforementioned time points), which enables investigation of the cell identity (including subsets of B-cells and myeloid cells of particular relevance to the disease) and activation status at protein level (e.g. phosphorylation) through next-generation, high-dimensional flow cytometry. Through a focused analysis followed by targeted gene expression and function studies in purified monocytes, the investigators will determine whether belimumab can restore \"SLE-primed\" monocytes thus, alleviating their inflammatory and pro-atherogenic phenotype and enhancing their bactericidal activity. Collectively, these studies will provide novel mechanistic insights on the beneficial efficacy/toxicity ratio of belimumab therapy in SLE.