Isolated follicular lymphoma cells are resistant to apoptosis and can be grown in vitro in the CD40/stromal cell system

Low-grade follicular non-Hodgkin's lymphomas are characterized by the presence of a t(14;18) chromosomal translocation that results in deregulation of the B-cell lymphoma (Bcl-2) gene. Studies in cell lines and transgenic animal models have suggested that this results in the suppression of apoptotic cell death in germinal centers. B lymphocytes from normal germinal centers and lymph nodes infiltrated by follicular lymphoma were isolated by immunomagnetic depletion of cells bearing CD4, CD8, or slgD for study in vitro. Follicular lymphoma cells expressing Bcl-2 protein were shown to resist apoptosis after isolation, and could be induced to proliferate in a culture system previously described for the growth of normal B lymphocytes. By the use of a mouse fibroblast monolayer transfected with the CDw32 Fc receptor to present CD40 monoclonal antibody in the presence of interleukin-4, prolonged culture was possible. Karyotypic analysis of cultured lymphoma cells showed the t(14;18) translocation, with clonal identity confirmed by polymerase chain reaction amplification of the breakpoints and direct sequence analysis. These findings support the hypothesis that resistance to apoptosis is an influence on the initiation of follicular lymphoma, and provide a novel means of studying in vitro the intercellular reactions that may be important in progression of the disease.