Results. Rituximab was well tolerated in this patient population, with most experiencing no significant adverse effects. Only 3 serious adverse events, which were thought to be unrelated to rituximab administration, were noted. A majority of patients (11 of 17) had profound B cell depletion (to <5 CD19؉ B cells/ l). In these patients, the SLAM score was significantly improved at 2 and 3 months compared with baseline (P ‫؍‬ 0.0016 and P ‫؍‬ 0.0022, respectively, by paired t-test). This improvement persisted for 12 months, despite the absence of a significant change in anti-doublestranded DNA antibody and complement levels. Six patients developed human antichimeric antibodies (HACAs) at a level >100 ng/ml. These HACA titers were associated with African American ancestry, higher baseline SLAM scores, reduced B cell depletion, and lower levels of rituximab at 2 months after initial infusion.Conclusion. Rituximab therapy appears to be safe for the treatment of SLE and holds significant therapeutic promise, at least for the majority of patients experiencing profound B cell depletion. Based on these results, controlled trials of rituximab appear to be warranted.

Objective. B lymphocyte depletion has recently emerged as a promising approach to the treatment of systemic lupus erythematosus (SLE). As part of a phase I/II dose-ranging trial of rituximab in the treatment of SLE, we evaluated the fate of discrete B cell subsets in the setting of selective depletion by anti-CD20 monoclonal antibody and during the B cell recovery phase.Methods. B cell depletion and phenotype were examined by flow cytometry of peripheral blood mononuclear cells for CD19, CD20, CD27, IgD, and CD38 expression. Changes in autoreactive B lymphocytes and plasma cells were assessed by determination of serum autoantibody levels (anti-double-stranded DNA and VH4.34) and by direct monitoring of a unique autoreactive B cell population bearing surface antibodies whose heavy chain is encoded by the VH4.34 gene segment.Results. Compared with normal controls, SLE patients displayed several abnormalities in peripheral B cell homeostasis at baseline, including naive lymphopenia, expansion of a CD27؊,IgD؊ (double negative) population, and expansion of circulating plasmablasts. Remarkably, these abnormalities resolved after effective B cell depletion with rituximab and immune reconstitution. The frequency of autoreactive VH4.34 memory B cells also decreased 1 year posttreatment, despite the presence of low levels of residual memory B cells at the point of maximal B cell depletion and persistently elevated serum autoantibody titers in most patients.Conclusion. This study is the first to show evidence that in SLE, specific B cell depletion therapy with rituximab dramatically improves abnormalities in B cell homeostasis and tolerance that are characteristic of this disease. The persistence of elevated autoantibody titers may reflect the presence of low levels of residual autoreactive memory B cells and/or long-lived autoreactive plasma cells.

Objective. Despite wide use of the anti-CD20 monoclonal antibody rituximab in the treatment of B cell lymphomas, the mechanism by which it causes B cell depletion remains a subject of controversy. As part of an ongoing phase I/II trial of rituximab in the treatment of systemic lupus erythematosus (SLE), we sought to determine whether the effectiveness of B cell depletion was influenced by polymorphisms of Fc receptors (FcR) on effector cells.Methods. During rituximab treatment of 12 SLE patients, B cell depletion was monitored as a function of the serum rituximab level and Fc␥RIIa and Fc␥RIIIa genotypes at baseline and at 1 month and 2 months after treatment. FcR genotypes were determined by polymerase chain reaction. Serum levels of rituximab were measured by enzyme-linked immunosorbent assay (ELISA). B lymphocyte percentages were assessed by flow cytometry.Results. B cell depletion was highly variable in this patient cohort, with B cell percentages at the 1-2-month posttreatment nadir ranging from undetectable (<0.1 cell/ l) to 16% (ϳ30 cells/ l) of the total peripheral blood lymphocytes. At 2 months posttreatment, B cell percentages were highly correlated with both the serum rituximab level and the Fc␥RIIIa genotype (R 2 ‫؍‬ 0.75, P ‫؍‬ 0.002). The Fc␥RIIIa genotype was a significant independent predictor of the efficacy of B cell depletion (P ‫؍‬ 0.019). Conclusion. These results highlight the potential variability of B cell depletion by rituximab in the treatment of autoimmune disease and indicate that Fc receptors are an important determinant of that variability. The findings further suggest the importance of antibody-dependent cell-mediated cytotoxicity and/or apoptosis induction via Fc␥RIIIa-expressing effector cells in the mechanism of B cell depletion by this widely used monoclonal antibody.Rituximab is a chimeric mouse-human monoclonal antibody against the B cell-specific antigen CD20, a cell surface protein believed to function in B cell cycle initiation and differentiation (1-3). CD20 is first expressed in the early pre-B cell stage, and it remains present until terminal differentiation into plasma cells. The CD20 antigen represents an ideal target for immunotherapy of B cell lymphomas and, more recently, B cell-mediated autoimmune diseases due to its high and relatively sustained expression on malignant and normal B cells (4). Rituximab can effectively deplete B cells for several months and, as such, represents an effective treatment of B cell lymphoma (5).Several potential mechanisms have been proposed as mediators of the effects of rituximab (6). Thus, in vitro studies have demonstrated that rituximab bound to CD20ϩ cells induces complement-dependent cytotoxicity (CDC) and, in the presence of effector cells, antibody-dependent cell-mediated cytotoxicity (ADCC) (5). Additionally, rituximab can induce B cell apoptosis when crosslinked by Fc␥ receptor (Fc␥R)-bearing cells (7). The relative importance of antibody-mediated apoptosis, CDC, and ADCC in the depletion of B cells by rituximab remains to be...

Polyclonal rATG induces complement-independent apoptosis of naive, activated, and plasma B cells. This effect appears to involve the caspase- and cathepsin-mediated apoptosis pathways.

Unmethylated CpG DNA activation of naive CD27 ؊ B cells has been reported to require B-cell-receptor (BCR) cross-linking. We describe a culture system using CpG DNA with sequential steps for T-cell-independent activation of naive CD19 ؉ CD27 ؊ human peripheral blood B cells that induces efficient CD138 ؉ plasma-cell differentiation. CD27 ؉ and CD27 ؊ B cells were cultured in a 3-step system: (1)

Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used for the treatment of inflammatory diseases and target cyclooxygenases 1 and 2 (Cox-1, Cox-2) that are responsible for PG production. Newer Cox-2-selective drugs have been heavily prescribed to quench inflammation. Little is known about whether or not these drugs influence human B lymphocytes and their ability to produce Ab. We report herein that activated human B cells not only highly express Cox-2 and produce PGs, but that the NSAID indomethacin and Cox-2-selective drugs profoundly inhibit the ability of human B cells to produce IgG and IgM in vitro. Human blood B cells highly express Cox-2 mRNA and protein and produce PGs after activation with CD40L, pansorbin, or CD40L plus BCR engagement. Cox-2 is also highly expressed by human tonsil B cells, as shown by immunohistochemistry. Cox-inhibiting drugs modestly affect purified B cell proliferation but profoundly reduce Ab production. The ability of whole blood to produce IgM and IgG following stimulation is also strongly inhibited. In support that Cox-2 plays a seminal role in B lymphocyte Ab production, Cox-2 knockout mice have 64% less IgM and 35% less IgG than normal littermate controls. These findings support that NSAIDs and the new Cox-2-selective drugs have an unsuspected target, the B cell, and attenuate Ab production in humans. Use of NSAIDs may therefore influence autoantibody production in autoimmune diseases and may dampen humoral immunity in response to antigenic challenge/vaccination.

Gamma/delta T cell lymphomas (gamma/delta TCL) represent rare, often aggressive types of T cell malignancy that are clinically and pathologically diverse. Most gamma/delta TCL occur as a hepatosplenic or subcutaneous type. To date, analysis of the T cell receptor delta (TCRS) gene repertoire of hepatosplenic gamma/delta TCL (gamma/delta HSTCL) and subcutaneous panniculitis-like gamma/delta TCL (gamma/delta SPTCL) has been reported only in a limited number of cases. In this study we analyzed 11 gamma/delta HSTCL and 4 gamma/delta SPTCL by polymerase chain reaction and immunostaining to determine their usage of the Vdelta subtypes (Vdelta1-6). It is noteworthy that 10 of 11 gamma/delta HSTCL expressed the Vdelta1 gene. The remaining case also expressed T cell receptor delta (TCRS) as determined by flow cytometry and TCRdelta rearrangement in Southern blot. However, the Vdelta gene expressed by this lymphoma could not be determined, which suggests usage of an as yet unidentified Vdelta gene. In striking contrast to the gamma/delta HSTCL, all 4 gamma/delta SPTCL expressed the Vdelta2 gene. Our data demonstrate that gamma/delta HSTCL are preferentially derived from the Vdelta1 subset of gamma/delta T lymphocytes, whereas gamma/delta SPTCL are preferentially derived from the Vdelta2 subset. The pattern of Vdelta gene expression in HSTCL and SPTCL corresponds to the respective, predominant gamma/delta T cell subsets normally found in the spleen and skin. This finding suggests that gamma/delta TCL are derived from normal gamma/delta T lymphocytes which reside in the affected tissues. Furthermore, the selective, lymphoma type-specific Vdelta gene segment usage may provide a molecular tool to distinguish better among various types of gamma/delta TCL lymphoma particularly in the clinically advanced, widely disseminated cases.

Current monoclonal antibody therapies for multiple myeloma have had limited success, perhaps due to narrow target specificity. We have previously described the ability of polyclonal rabbit antithymo-cyte globulin (rATG) to induce caspase-and cathepsin-mediated apoptosis in human B and plasma cells. We now extend this observation to myeloma cells. Complement independent cell death was measured after addition of rATG (1-1000 g/mL) to cultures of myeloma cell lines or primary CD138 isolates from patient bone marrow aspirates. rATG induced significant levels of apoptosis in my-eloma cells as assayed by caspase induction , annexin V binding, subdiploid DNA fragmentation, plasma-membrane per-meability, and loss of mitochondrial-membrane potential. Addition of complement greatly augmented myeloma-cell death. Binding of rATG to individual my-eloma cell-surface proteins, primarily CD38, CD52, CD126, and CD138, was demonstrated by competitive inhibition experiments with targeted monoclonal antibod-ies. Three pathways of cell death were identified involving caspase activation, cathepsin D, and the genistein sensitive tyrosine kinase pathway. F(ab) 2 fragments of rATG had reduced proapoptotic activity, which was restored by coincuba-tion with Fc fragments, and anti-CD32 or anti-CD64 antibodies. We conclude that rATG is an effective agent for in vitro induction of apoptosis in multiple myeloma, and that exploratory clinical trials may be warranted. (Blood. 2006;107:2895-2903)