LONG-TERM SURVIVAL AND PROLIFERATION OF PRECURSOR-B ACUTE LYMPHOBLASTIC-LEUKEMIA CELLS ON HUMAN BONE-MARROW STROMA

Leukemic cells frequently persist in the bone marrow of patients treat ed for acute lymphoblastic leukemia (ALL), and may regrow to produce r elapse. We have used a long-term co-culture system to analyze the inte raction of ALL blasts with components of the marrow microenvironment. Blast cells from 10 cases of precursor-B ALL were cultured on allogene ic human bone marrow stromal layers at 37 degrees C in microtiter well s, and replated when stroma showed evidence of deterioration. Leukemic cells from seven of 10 cases showed evidence of survival and prolifer ation beyond 30 days in culture, while in three cases there was a prog ressive decline in the number of viable leukemic cells by 7-21 days. T wo cases continued to proliferate for 149 to 332+ days, while five und erwent senescence after 34-52 days. In the two cases with long-term pr oliferation, the leukemic identity of the cells was confirmed by immun ophenotyping, cytogenetics, and demonstration of clonal immunoglobulin gene rearrangements. Evidence of selection of leukemic subclones was seen in two cases, with immunophenotypic evidence of loss of CD10 and CD34 antigens, and acquisition of CD20 and surface mu chain. The leuke mic cells in these cases grew either in clumps attached to the surface of the stroma, or as 'cobblestone areas' beneath the stromal cells. S urvival and growth of two evaluable cases was dependent on the continu ing presence of stromal cells in the culture system. In one case, dire ct contact with stroma was shown to be necessary to maintain viability , while blast cells from the other case survived equally well when sep arated from the stroma by a 0.4-micron pore size microporous membrane. These results indicate that leukemic cells from the majority of cases of precursor-B ALL are able to persist and undergo proliferation in v itro in the presence of normal marrow stroma. This process appears dep endent on either direct cell-cell contact, or on diffusible factors de rived from the stroma. The availability of ALL cells capable of indefi nite proliferation under these conditions will allow further analysis of the mechanisms mediating leukemic cell proliferation.