Accelerated progression of chronic lymphocytic leukemia in E-TCL1 mice expressing catalytically inactive RAG1

B cell chronic lymphocytic leukemia (CLL) is often preceded by a benign monoclonal or oligoclonal CD5+ B cell lymphocytosis. We have generated transgenic mice expressing a catalytically inactive, dominant-negative recombination activating gene 1 (dnRAG1 mice) in the periphery. These animals develop an early-onset indolent CD5+ B cell lymphocytosis, caused in part by a defect in secondary V(D)J rearrangements initiated to alter autoreactive B cell receptor specificity. Hypothesizing that the CD5+ B cells accumulating in dnRAG1 mice represent a CLL precursor, we crossed dnRAG1 mice with CLL-prone E-TCL1 mice to determine whether dnRAG1 expression in E-TCL1 mice accelerates the onset of CLL-like disease. We find that CD5+ B cell expansion and CLL progression occurs more rapidly and uniformly in double-transgenic mice (DTG mice) compared to E-TCL1 mice, but with similar phenotypic and leukemogenic features. To gain insight into genes or pathways responsible for CD5+ B cell accumulation in the transgenic mice, we performed comparative gene expression profiling studies using normal and CD5+ B cells isolated from wild-type and transgenic mice at either 12 weeks of age (pre-leukemia) or at CLL onset in DTG mice (using age-matched wild-type and single-transgenic mice as controls). These analyses confirm the upregulation of tolerogenic genes in CD5+ B cells and reveal a possible role for prolactin signaling in the regulation of receptor editing. This study suggests that a failure to remodel B cell antigen receptor genes in response to autoreactivity may promote the benign accumulation of CD5+ B cells, which may then be subjected to secondary genetic lesions that promote CLL progression.

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Nganga VK, Palmer VL, Naushad H, Kassmeier MD, Anderson DK, Perry GA, Schabla NM, Swanson PC