An abnormal neutrophil subset has been identified in the PBMC fractions from lupus patients. We have proposed that these “low density granulocytes” (LDGs) play an important role in lupus pathogenesis by damaging endothelial cells and synthesizing increased levels of proinflammatory cytokines and type I interferons. To directly establish LDGs as a distinct neutrophil subset, their gene array profiles were compared to those of autologous normal density neutrophils and control neutrophils. LDGs significantly overexpress mRNA of various immunostimulatory bactericidal proteins and alarmins, relative to lupus and control neutrophils. In contrast, gene profiles of lupus normal density neutrophils do not differ from those of controls. LDGs have heightened capacity to synthesize extracellular traps (NETs) which display increased externalization of bactericidal, immunostimulatory proteins and autoantigens, including LL-37, IL-17, and double-stranded DNA (dsDNA). Through NETosis, LDGs have increased capacity to kill endothelial cells and to stimulate IFN-α synthesis by pDCs. Affected skin and kidneys from lupus patients are infiltrated by netting neutrophils, which expose LL-37 and ds-DNA. Tissue NETosis is associated with increased anti-dsDNA in sera. These results expand the potential pathogenic roles of aberrant lupus neutrophils and suggest that dysregulation of NET formation and its subsequent responses may play a prominent deleterious role.

Human mesenchymal stromal cell (MSC) lines can vary significantly in their functional characteristics, and the effectiveness of MSCbased therapeutics may be realized by finding predictive features associated with MSC function. To identify features associated with immunosuppressive capacity in MSCs, we developed a robust in vitro assay that uses principal-component analysis to integrate multidimensional flow cytometry data into a single measurement of MSC-mediated inhibition of T-cell activation. We used this assay to correlate single-cell morphological data with overall immunosuppressive capacity in a cohort of MSC lines derived from different donors and manufacturing conditions. MSC morphology after IFN-γ stimulation significantly correlated with immunosuppressive capacity and accurately predicted the immunosuppressive capacity of MSC lines in a validation cohort. IFN-γ enhanced the immunosuppressive capacity of all MSC lines, and morphology predicted the magnitude of IFN-γ-enhanced immunosuppressive activity. Together, these data identify MSC morphology as a predictive feature of MSC immunosuppressive function.H uman mesenchymal stromal cells (MSCs) can potently suppress immune responses in vitro and in animal models of human disease (1, 2), but to date MSC-based therapies have produced mixed results in clinical trials for treatment of inflammatory and autoimmune diseases (3, 4). A major challenge in the development of consistently effective MSC-based immunosuppressive therapies is that MSC lines derived from different donors and manufacturing processes (i.e., cell expansion) can possess markedly dissimilar immunosuppressive function (3,5,6). Although methods exist to assess MSC immunosuppression in vitro, they are often based on only a few measured outcomes, assay culture conditions, and donor MSC samples (5, 7-9). To improve upon these methods, we developed an experimental and analytical approach to quantify MSC-mediated immune suppression using principal-component analysis (PCA) to integrate multiple measurements of T-cell activation assessed at a range of MSC densities. This approach allowed us to determine a single value for immunosuppressive capacity for MSC lines derived from two different manufacturing processes and 13 independent donors.Another major challenge associated with MSC-based immune therapies is the lack of well-defined predictive markers to identify MSC lines with therapeutically relevant biological activities or manufacturing processes that produce more effective MSCbased products. Efforts have been made to identify MSC quality attributes associated with immunosuppression (6, 7), but the majority of clinical studies (10) rely upon the surface markers described by Dominici et al. (11). Having previously shown that morphology can predict MSC mineralization capacity (12), we hypothesized that morphological features associated with immunosuppression in MSCs could be identified and used to predict their performance in our quantitative immunosuppression assay.Using our quantitative method for as...

Suppression of the immune system after the resolution of infection or inflammation is an important process that limits immunemediated pathogenesis and autoimmunity. Several mechanisms of immune suppression have received a great deal of attention in the past three decades. These include mechanisms related to suppressive cytokines, interleukin (IL)-10 and transforming growth factor (TGF)-β, produced by regulatory cells, and mechanisms related to apoptosis mediated by death ligands, Fas ligand (FasL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), expressed by killer or cytotoxic cells. Despite many lines of evidence supporting an important role for B lymphocytes as both regulatory and killer cells in many inflammatory settings, relatively little attention has been given to understanding the biology of these cells, their relative importance or their usefulness as therapeutic targets. This review is intended to give an overview of the major mechanisms of immunosuppression used by B lymphocytes during both normal and inflammatory contexts. The more recent discoveries of expression of granzyme B, programmed death 1 ligand 2 (PD-L2) and regulatory antibody production by B cells as well as the interactions of regulatory and killer B cells with regulatory T cells, natural killer T (NKT) cells and other cell populations are discussed. In addition, new evidence on the basis of independent characterizations of regulatory and killer CD5 + B cells point toward the concept of a multipotent suppressor B cell with seemingly high therapeutic potential.

Background: Although a preponderance of pre-clinical data demonstrates the immunosuppressive potential of mesenchymal stromal cells (MSCs), significant heterogeneity and lack of critical quality attributes (CQAs) based on immunosuppressive capacity likely have contributed to inconsistent clinical outcomes. This heterogeneity exists not only between MSC lots derived from different donors, tissues and manufacturing conditions, but also within a given MSC lot in the form of functional subpopulations. We therefore explored the potential of functionally relevant morphological profiling (FRMP) to identify morphological subpopulations predictive of the immunosuppressive capacity of MSCs derived from multiple donors, manufacturers and passages. Methods: We profiled the single-cell morphological response of MSCs from different donors and passages to the functionally relevant inflammatory cytokine interferon (IFN)-g. We used the machine learning approach visual stochastic neighbor embedding (viSNE) to identify distinct morphological subpopulations that could predict suppression of activated CD4 + and CD8 + T cells in a multiplexed quantitative assay. Results: Multiple IFN-gÀstimulated subpopulations significantly correlated with the ability of MSCs to inhibit CD4 + and CD8 + T-cell activation and served as effective CQAs to predict the immunosuppressive capacity of additional manufactured MSC lots. We further characterized the emergence of morphological heterogeneity following IFN-g stimulation, which provides a strategy for identifying functional subpopulations for future single-cell characterization and enrichment techniques. Discussion: This work provides a generalizable analytical platform for assessing functional heterogeneity based on single-cell morphological responses that could be used to identify novel CQAs and inform cell manufacturing decisions.