Single-cell mass cytometry and transcriptomic profiling of circulating immune cells identifies an expansion of CD25hi switched memory B cells in Osteoarthritis
Osteoarthritis (OA) is a chronic, debilitating disease with no available disease-modifying drugs with end-stage surgery being the only treatment option. Biomarker identification in blood specimens of OA patients has hitherto been limited to serum proteins and bulk transcriptomics and epigenomic feature identification. We sought to capitalize on high resolution, single-cell techniques of mass cytometry by time-of-flight (cyTOF) and sc-RNA-seq to identify OA-associated features in the immune cells of the patients' peripheral blood. Comparison of healthy donors and OA patients' peripheral blood mononuclear cells (PBMC) revealed that frequencies of specific subpopulations of B cells, monocytes, CD4+ and CD8+T cells were distinctly perturbed in OA. While many immune subtypes were depleted, a CD25hiCD27+IgD- switched memory B cell population was identified to be significantly expanded in OA blood. Sc-RNA seq revealed a dysfunction of IL2/Stat3 and Notch signaling in the switched memory B cells expanded in OA. Upon profiling peripheral blood of patients with degenerative meniscal tears (DMT), a population known to be at enhanced risk for OA, we observed a similar expansion of CD25hiCD27+IgD- switched memory B cells suggesting that it can be a biomarker of early and late OA. Unsupervised clustering utilizing immune cell correlates stratified the profiled OA patients into three distinct subsets. Development of such single cell platforms can be a powerful clinical tool for OA prognosis as well as precision therapeutics. Overall design: PBMC samples from OA patients and healthy donors (3 samples pooled as 1 replicate, n = 2/group) were enriched for B-cells and profiled using scRNAseq. 3 samples each were pooled to obtain 2 single cell cDNA libraries per group.