HUMAN BONE-MARROW STROMAL CELLS PREVENT APOPTOSIS AND SUPPORT THE SURVIVAL OF CHRONIC LYMPHOCYTIC-LEUKEMIA CELLS IN-VITRO

Leukaemic cells from most cases of B-chronic lymphocytic leukaemia die rapidly by apoptosis in vitro unless they are cultured in the presenc e of interleukin-4 or interferon alpha or gamma. We now report prolong ed survival of purified CLL cells cultured on bone marrow (BM) derived stromal cells in the absence of exogenous growth factors. In 10 cases of CLL examined 0-61% (mean 14.7%) of the cells were viable after 10 d culture in medium alone, whereas in the presence of BM stromal cells 10-102% (mean 47.0%) of cells were recovered alive (P < 0.005) in 7/1 0 cases of CLL, cells remained viable after 30 d of culture in BM stro mal cells with cell recovery of 12-65%. These long-term cultured CLL c ells were Epstein Barr virus negative, shown by the failure to detect the ENBA-2 and BZLF1 genes of EBV by PCR analysis. Identity between da y 0 and day 30 CLL cells was demonstrated by sequence analysis of thei r clonal IgH CDR3 region. Adherence of CLL cells to BM stromal cell la yers was critical for their protection from apoptosis. Separation of C LL cells from stroma by 0.45 mu m culture filters resulted in loss of the protective effect of the stromal cells. Stromal cells were also ab le to protect CLL cells from hydrocortisone-induced apoptotic cell dea th. Our findings provide an in vitro system that can tie used to analy se the growth requirements of CLL cells and their chemosensitivity in an in vitro environment that mimics the in vivo milieu.