Transformation of mature mouse B cells into malignant plasma cells in vitro via introduction of defined genetic elements.

An experimental system where defined alterations in gene function or gene expression levels in primary B cells would result in the development of transformed plasma cells in vitro would be useful in order to facilitate studies of the underlying molecular mechanisms of plasma cell malignancies. Here, such a system is described in which primary murine B cells rapidly become transformed into surface CD138+ , IgM-/low , CD19- IgM-secreting plasma cells as a result of expression of the transcription factors IRF4 and MYC together with simultaneous expression of BMI1, mutated p53 or silencing of p19Arf , and suppression of intrinsic apoptosis through expression of BCLXL. Analysis of gene expression patterns revealed that this combination of transforming genes resulted in expression of a number of genes previously associated with terminally differentiated B cells (plasma cells) and myeloma cells, whereas many genes associated with mature B cells and B-cell lymphomas were not expressed. Upon transplantation, the transformed cells preferentially localized to the bone marrow, presenting features of a plasma cell malignancy of the IgM isotype. The present findings may also be applicable in the development of novel methods for production of monoclonal antibodies.