LYMPHOPROLIFERATIVE DISORDERS IN AN IL-7 TRANSGENIC MOUSE LINE

A high incidence of severe lymphoproliferative disease was observed in a newly generated strain of mice carrying murine IL-7 as a transgene under the control of the Ealpha (MHC class II) promoter. An analysis o f the cells from lesions in these mice shows the selective expansion o f cells at an early stage of B cell development and, more interestingl y, expansion of cells phenotypically identical to the recently reporte d bipotent (B/macrophage) stem cell populations described in midgestat ion embryonic liver. Such cells can be propagated (and remain dependen t upon) bone marrow feeder cell lines obtained from IL-7 transgenic mi ce. A molecular analysis of fresh and cultured cells reveals that the lesions are oligoclonal, or in rare cases monoclonal, and include clon es of cells with unrearranged Ig heavy chain loci. These data suggest that IL-7 acts at multiple stages of B cell development. Furthermore c ell lines derived from IL-7 transgenic mice may provide a novel source of rare factor-dependent bipotent stem cells.