Accumulation of B1-like B cells in transgenic mice over-expressing catalytically inactive RAG1 in the periphery.

During their development, B lymphocytes undergo V(D)J recombination events and selection processes that, if successfully completed, produce mature B cells expressing a non-self-reactive B-cell receptor (BCR). Primary V(D)J rearrangements yield self-reactive B cells at high frequency, triggering attempts to remove, silence, or reprogramme them through deletion, anergy induction, or secondary V(D)J recombination (receptor editing), respectively. In principle, expressing a catalytically inactive V(D)J recombinase during a developmental stage in which V(D)J rearrangement is initiated may impair this process. To test this idea, we generated transgenic mice expressing a RAG1 active site mutant (dnRAG1 mice); RAG1 transcript was elevated in splenic, but not bone marrow, B cells in dnRAG1 mice relative to wild-type mice. The dnRAG1 mice accumulate splenic B cells with a B1-like phenotype that exhibit defects in B-cell activation, and are clonally diverse, yet repertoire restricted with a bias toward Jκ1 gene segment usage. The dnRAG1 mice show evidence of impaired B-cell development at the immature-to-mature transition, immunoglobulin deficiency, and poorer immune responses to thymus-independent antigens. Interestingly, dnRAG1 mice expressing the anti-dsDNA 3H9H56R heavy chain fail to accumulate splenic B1-like cells, yet retain peritoneal B1 cells. Instead, these mice show an expanded marginal zone compartment, but no difference is detected in the frequency of heavy chain gene replacement. Taken together, these data suggest a model in which dnRAG1 expression impairs secondary V(D)J recombination. As a result, selection and/or differentiation processes are altered in a way that promotes expansion of B1-like B cells in the spleen.

Anti-immunoglobulin E monoclonal antibody administered with immunotherapy.

Despite both efficacy and immunotolerogenic effects, many clinicians still are reluctant to use allergen-specific immunotherapy (SIT) because of the potential for acute allergic reactions. The anti-immunoglobulin E monoclonal antibody, omalizumab, is approved by the U.S. Food and Drug Administration for the treatment of moderate-to-severe allergic asthma and has proven to be a relatively safe agent. Knowledge of the distinct immunologic changes elicited by allergen SIT and omalizumab has established a rationale for investigation into their combined use for the management of allergic diseases. This review summarizes two investigative studies examining the safety and efficacy of the combination of omalizumab + allergen SIT for the treatment of allergic rhinitis. Both studies show that the combination of omalizumab and allergen SIT confer added efficacy to either treatment alone. Pretreatment of patients with omalizumab before rush allergen immunotherapy also showed added safety to rush immunotherapy with the prevention of acute allergic reactions. Results thus far provide the opportunity to develop strategies using omalizumab pretreatment to enhance the safety and efficacy of allergen-immunotherapy to treat a wide variety of allergic diseases.