Prolonged effects of short-term anti-CD20 B cell depletion therapy in murine systemic lupus erythematosus.

Systemic lupus erythematosis (SLE) is a complex autoimmune disease involving multiple organ systems. The immunological events triggering the onset of clinical manifestations are not been fully defined, but a central role for B cells in the pathogenesis of this disease has been established by work performed in multiple laboratories using both mice and humans (1–3). Given the strong evidence supporting an abnormal B cell compartment in SLE, B cell depletion therapy (BCDT) is being investigated as a potential treatment strategy. Several open-label studies, including our own, demonstrate that B cell depletion provides significant clinical benefit in SLE (4, 5). Our studies show that clinical improvement precedes the decline of conventional serum autoantibody, strongly supporting the notion of antibody-independent pathogenic roles of B cells. However, there is heterogeneity in response to BCDT, as also highlighted by the recent failure of two large multi-center trials of rituximab in general lupus and lupus nephritis (6). The mechanism underlying the clinical benefit and the variation in response to BCDT are not clearly defined. Developing a murine lupus model to explore the effect of B cell depletion on the disease, variability in effects, mechanisms of benefit, and potential synergy between therapies is thus of interest. In addition to antibody production, both protective and pathogenic roles of B cells are mediated by poorly understood antibody-independent mechanisms (7). The latter are highlighted by the abrogation of disease and reduction in activated T cells in B cell deficient MRL/lpr mice (2), yet the maintenance of T cell abnormalities in mice with B cells incapable of secreting antibody (8). However, these studies do not establish the benefit of B cell depletion as a treatment in mice with an intact immune system or established disease. Autoantibody-independent B cell functions include antigen-presentation, T cell activation and polarization, and dendritic cell (DC) modulation, that may be mediated at least in part by the ability of B cells to produce cytokines (9, 10). However, the relative importance of these distinct B cell functions to the autoimmune process in SLE and the impact of B cell depletion therapy are not yet defined. Moreover, given the recent demonstration of regulatory B cell subsets that dampen harmful immune responses it is possible that B cell depletion may worsen certain autoimmune diseases depending on the relative balance of protective and pathogenic B cells (11, 12). Indeed, it has been suggested that the loss of negative regulatory B cells may contribute to exacerbation of disease in a number of murine models including collagen induced arthritis, inflammatory bowel disease, and experimental autoimmune encephalomyelitis (EAE) (13). Thus, in EAE B cell depletion therapy either exacerbated or suppressed disease depending on the timing (14). Effective reagents for depleting B cells in mice have not been available until recently, necessitating the use of human CD20 transgenic mice and anti-human CD20 for mechanistic studies in the mouse (15, 16). However, antibodies against mouse CD20 have recently become available and cause significant depletion of B cells in normal mice (17) as well as a variety of autoimmune mouse models (18–21). In this study, anti-mouse CD20 was used to determine the role of B cells in the development and maintenance of murine lupus. We find that B cell depletion therapy in NZB/NZWF1 lupus prone mice mirrors many of the clinical and immunological effects of BCD in human SLE in a number of critical aspects including B cell depletion variability, a disconnect between clinical improvement and autoantibody titers, and B cell reconstitution with an immature transitional B cell pool. This study also provides unique mechanistic insights including the significant impact of B cell depletion on the T cell compartment with decreases in T cell activation and memory T cells and the profound delay in lupus disease onset and progression even after short-term depletion. These results suggest that B cells are critical for both the initiation and maintenance of autoimmunity in SLE, and B cell depletion may favorably shift the balance of protective versus pathogenic B cell functions.