B cells and immunological tolerance

A perspective on B-cell-targeting therapy for SLE

In recent years, large controlled trials have tested several new agents for systemic lupus erythematosus (SLE). Unfortunately, none of these trials has met its primary outcome. This does not mean progress has not been made. In fact, a great deal has been learned about doing clinical trials in lupus and about the biological and clinical effects of the drugs being tested. Many of these drugs were designed to target B cells directly, e.g., rituximab, belimumab, epratuzumab, and transmembrane activator and calcium modulator and cyclophilin ligand interactor-immunoglobulin (TACI-Ig). The enthusiasm for targeting B cells derives from substantial evidence showing the critical role of B cells in murine models of SLE, as well promising results from multiple open trials with rituximab, a chimeric anti-CD20 monoclonal antibody that specifically depletes B cells (Martin and Chan in Immunity 20(5):517-527, 2004; Sobel et al. in J Exp Med 173:1441-1449, 1991; Silverman and Weisman in Arthritis Rheum 48:1484-1492, 2003; Silverman in Arthritis Rheum 52(4):1342, 2005; Shlomchik et al. in Nat Rev Immunol 1:147-153, 2001; Looney et al. in Arthritis Rheum 50:2580-2589, 2004; Lu et al. in Arthritis Rheum 61(4):482-487, 2009; Saito et al. in Lupus 12(10):798-800, 2003; van Vollenhoven et al. in Scand J Rheumatol 33(6):423-427, 2004; Sfikakis et al. Arthritis Rheum 52(2):501-513, 2005). Why have the controlled trials of B-cell-targeting therapies failed to demonstrate efficacy? Were there flaws in design or execution of these trials? Or, were promising animal studies and open trials misleading, as so often happens? This perspective discusses the current state of B-cell-targeting therapies for human lupus and the future development of these therapies.

Insights into the heterogeneity of human B cells: diverse functions, roles in autoimmunity, and use as therapeutic targets

B cells are critical players in the orchestration of properly regulated immune responses, providing protection against infectious agents without inflicting autoinflammatory damage. A balanced B cell compartment is also essential to create protective immunity in response to vaccines. This difficult compromise is achieved through the finely regulated participation of multiple B cell populations with different antibody-dependent and independent functions. Both types of functions allow B cells to powerfully modulate other components of the innate and adaptive immune system. For the most part, however, the necessary division of labor among different B cell populations is poorly understood. B cell dysfunction has been implicated in multiple autoimmune conditions. The physiological importance and complexity of B cell functions has been brought to the fore in recent years by the success of rituximab-based B cell depletion therapy (BCDT) in multiple autoimmune diseases including rheumatoid arthritis (RA) and multiple sclerosis (MS) which are conventionally viewed as T-cell mediated conditions. Given the widespread utilization of BCDT in malignant and autoimmune diseases and the key role of B cells in both protective immunity and pathogenic autoimmunity, a better understanding of B cell functions is of the essence and a focus of the research in our division. We are investigating these issues through a variety of approaches, including the study of the phenotype and function of human B cell populations in health, their perturbation in autoimmune disease states, the effects of targeted biologic therapies, and the study of relevant murine models.