ENGRAFTMENT OF HUMAN CHRONIC LYMPHOCYTIC-LEUKEMIA CELLS IN SCID MICE - IN-VIVO AND IN-VITRO STUDIES

Chronic Lymphocytic leukemia (CLL) is a heterogeneous disease of the e lderly which can present in one of three stages; benign, intermediate or advanced. The molecular events governing the progression of CLL are poorly understood. In order to develop model systems for predicting t he aggressiveness of leukemic clones in CLL, in vivo transplantation o f SCID mice with CLL cells, and the in vitro growth of CLL cells on mo use and human stromal layers, were investigated, Bone marrow or periph eral blood cells from 40 patients at different stages of CLL were tran splanted into 172 immune-deficient SCID mice. Thirty-five percent of S CID mice injected with CLL cells were positive for the presence of hum an DNA by Southern blot or PCR analysis. The most frequently involved sites were the spleen, lung, kidney and bone marrow, at levels corresp onding from 0.1 to 10% human DNA. Thrice-weekly intraperitoneal inject ions of IL-2, atone or in combination with IL-7, did not increase the level of human cell engraftment. SCID mice developed endogenous thymic lymphomas at an incidence of 10-33%, a rate that was not increased by CLL cell transplantation. In vitro, CLL cells were able to proliferat e for 9 weeks on human stromal layers supplemented with CM (conditione d media from a culture of the human bladder carcinoma cell line 5637), but failed to thrive on the murine stromal cell line MTE cultured eit her in CM or autologous serum. FAGS analysis revealed that 81% of prol iferating cells on human stromal layers carried the CD5 cell surface m arker, identifying them as CLL cells. Previously EBV-negative CLL cell s became EBV-positive after 9 to 12 weeks in culture. The results of t his study provide a firm foundation for the development of in vivo and in vitro model systems for the study of human CLL.