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Chronic lymphocytic leukemia (CLL) B-lymphocytes but not normal B-lymphocytes are rescued from apoptosis by contact with bone marrow stromal cells

par Lapieaux, L.;Delforfe, A.;Bron, Peter A;De Bruyn, Cécile ;Slryckmans, P.
Référence Experimental hematology, 25, 8, page (862)
Publication Publié, 1997

Article révisé par les pairs

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Résumé :

The leukemic B lymphocytes from CLL patients have a long survival in vivo although ex vivo, they rapidly die by apoptosis. To further investigate the mechanism involved in this in vivo longer survival of CLL-B lymphocytes, we studied the influence of either contact with or presence of bone marrow stromal cells (SC) established from normal subjects (N-SC) and CLL patients (CLL-SC) on leukemic and normal Blymphocyle apoptosis. 2xlOVml purified B-lymphocytes from 20 CLL patients (>95% CD19 of which 64 ±7 % coexpressed CDS) and from 11 umbilical cord blood (UCB) (89 + 2 % CD19 of which 57 + 6 % coexpressed CD5) were cultured from 48 hours in contact with SC or in culture medium alone (a-MEM + 10 % PCS). Apoptosis was analysed by flow cytometry after labelling cells, prestained with CD19-FITC, with propidium iodide or TUNEL assay. B-cells a-MEM Contact with No contact with SCM control N-SC CLL-SC N-SC CLL-SC N CLL CLL 22+3 8±2 6±2 35+10 24+10 46+8 39+11 CB 31+5 37+6 51+10 ND ND____41+12 48+12 After 48 hour incubation, leukemic and normal B-cells demonstrated respectively 22 + 3 % and 31 + 5 % (mean ±SEM) of apoptosis. Contact with N-SC and CLL-SC reduced the percentage of leukemic cells undergoing apoptosis (respectively 8 + 2 % p < 0.0003, and 6 ±2 % p < 0.008). On the contrary, N-SC and CLL-SC increased apoptosis of UCB B-lymphocytes; respectively 37 + 6 % and 51 ±10 %. Increased apoptosis of UCB B-lymphocytes plated on CLL-SC in comparison with N-SC was due to excessive production of TGF- by CLL-SC. Direct contact between leukemic cells and SC was found to be essential for inhibition of leukemic cell apoptosis: indeed, separation of leukemic cells from SC by porous membrane increased spontaneous apoptosis ans comparable results were obtained with SC conditioned medium (SCM). Experiments using anti-VLA-4 and anti-ICAM-1 blocking antibodies indicated (hat B cell adhesion to SC appears not mediated by these proteins. We observed also a reduction in bcl-2 expression in CLL-B cells during culture but contact with SC prevent the loss of bcl-2 and consequently inhibit cell death. Contaci between CLL B-lymphocytes and SC seems thus to play a major role in the accumulation and survival of B-CLL cells in die bone marrow.