The B cell: a new therapeutic target in rheumatoid arthritis and other autoimmune diseases

[Recombinant proteins or monoclonal antibodies: comparative properties and interest in systemic lupus erythematosus]

The emergence of biologic therapies, such as monoclonal antibodies or recombinant fusion proteins, have revolutionized the management of autoimmune disorders, in particular rheumatoid arthritis. These biologic agents have been engineered to deplete key cellular populations or to block cytokines or molecules involved in the activation and/or the differentiation of immune cells, such as T cells or B cells. In systemic lupus erythematosus (SLE), a monoclonal antibody directed against the B-cell activating factor of the TNF family (BAFF or BLyS), belimumab, has demonstrated its efficacy in large, randomized and placebo-controlled studies, whereas rituximab, a monoclonal antibody directed against the CD20 expressed by B cells, failed to achieve his primary endpoint in renal and non-renal SLE. Studies on the safety and the efficacy of monoclonal antibodies or recombinant fusion proteins directed against other key molecules involved in the pathogenesis of SLE are ongoing.

Modulation of molecular imprints in the antigen-experienced B cell repertoire by rituximab

OBJECTIVE

Transient B cell depletion by rituximab has recently gained more importance in the treatment of rheumatic disorders. Nevertheless, little is known about the reemerging B cells. We analyzed dynamic changes in the repopulating B cells, particularly the postswitch B cells, and studied the mutational patterns of Ig genes in antigen-experienced B cells.

METHODS

Five patients with active rheumatoid arthritis (RA) were treated with rituximab. In 3 patients, B cell receptor (BCR) gene analysis was performed before treatment and during B cell recovery using genomic DNA. In 2 patients, B cell subsets were studied during the early recovery phase using single-cell technology. For comparison, immunophenotyping of B cell subsets was performed.

RESULTS

Early B cell recovery was marked by a relatively expanded population of highly mutated B cells, which were correlated with B cells with a plasmablast phenotype on comparative immunophenotyping. Analysis of the mutational pattern in these cells revealed increased RGYW/WRCY (where R = A/G, Y = C/T, and W = A/T) hotspot targeting (44% before rituximab versus 59% after) and elevated ratios of replacement to silent mutations within the complementarity-determining regions in Ig genes (1.87 before rituximab versus 2.67 after; P < or = 0.0025).

CONCLUSION

Our findings show that rituximab leads to qualitative changes in the imprints of highly mutated, antigen-experienced BCRs, representing the result of selection, whereas molecular processes such as Ig V rearrangements are not affected by this treatment.

Rituximab Treatment of Refractory Rheumatoid Arthritis

OBJECTIVE

To review published literature using rituximab for treatment of refractory rheumatoid arthritis (RA).

DATA SOURCES

An English-language literature search was conducted using MEDLINE (1966–May 2005) and EMBASE (1980–May 2005). References of identified articles were subsequently reviewed for additional data.

DATA SYNTHESIS

Evidence suggests that B lymphocyte depletion in patients suffering from refractory RA may be a key component in the interruption of the disease pathogenesis. Successful depletion of B lymphocytes with rituximab in patients with RA has been reported in case reports, open-label pilot studies, and a randomized, double-blind, placebo-controlled trial.

CONCLUSIONS

Based on the limited published data, rituximab, when used in combination with other agents (ie, cyclophosphamide or methotrexate), appears to be a reasonable treatment option for refractory RA. However, additional controlled trials need to be conducted to further define optimal dosing, response rates, comparative long-term efficacy, and RA treatment algorithm placement of rituximab in this patient population.

Emerging biological therapies in rheumatoid arthritis

The introduction of TNFalpha inhibitors has radically changed the management of patients with refractory rheumatoid arthritis (RA) or spondyloarthropathy. However, among patients with RA unresponsive to methotrexate, only two-thirds respond to TNFalpha inhibitors. Fortunately, more than 5 years after infliximab was introduced on the market, preliminary evidence that emerging biological agents are effective is beginning to accumulate, generating new hope for patients who fail to respond to TNFalpha inhibitors. These novel biological therapies grew out of original pathophysiological hypotheses, a fact that vividly illustrates the importance of basic pathophysiological research for developing new medications. This review provides detailed information on three biological therapies whose efficacy in RA was demonstrated in recently published randomized placebo-controlled trials: a monoclonal antibody to the IL-6 receptor (MRA), CTLA4-Ig (abatacept), and a monoclonal B-cell-specific antibody to CD20 (rituximab). Good risk/benefit ratios seem to be achieved with MRA alone or with abatacept or rituximab combined with methotrexate. However, as yet, no radiographic data are available for these treatments. One of the challenges for the future is to identify ingenious combinations of biological therapies capable of improving the quality and duration of responses without exacerbating side effects.