Chronic Lymphocytic Leukemic B Cells But Not Normal B Cells Are Rescued From Apoptosis by Contact With Normal Bone Marrow Stromal Cells

Abstract

The leukemic B lymphocytes from chronic lymphocytic leukemic (CLL) patients have a long survival in vivo, although ex vivo they rapidly die by apoptosis. To further investigate the mechanism of this, we have studied the influence of bone marrow stromal cells from normal subjects on apoptosis of B-CLL cells and normal umbilical cord blood (UCB) B lymphocytes. After 48 hours of incubation in medium alone, leukemic and normal B cells showed, respectively, 22 ± 3% and 31 ± 5% of apoptosis. Cocultures with stromal cells reduced the percentage of leukemic cells undergoing apoptosis (8 ± 2%, P< .0005) and prevented the loss of bcl-2 protein expression. In contrast, stromal cells slightly increased normal B-cell apoptosis (37 ± 6%). Direct contact between leukemic cells and stromal cells was found to be essential for inhibition of leukemic cell apoptosis; indeed, separation of leukemic cells from stromal cells by microporous membrane increased spontaneous apoptosis, and comparable results were obtained with stromal cell conditioned medium. The difference in behavior observed between normal and leukemic B cells plated on stromal cells can be explained by the fact that only a few normal B cells adhere to stromal cells in comparison with B-CLL cells. B-CLL cell adhesion to stromal cells is mediated by β1 and β2 integrins acting simultaneously. Contact between B-CLL cells and bone marrow stromal cells seems to play a major role in the accumulation and survival of B-CLL cells in the bone marrow.

Intracellular IFN‐γ expression by CD3+/CD8+ cell subset in B‐CLL patients correlates with stage of the disease

“…Cell growth of normal and malignant B cells can be regulated by signals provided by soluble factors and cell interactions (12,13). B-CLL represents a neoplastic disorder of B-cell type, where changes in the cytokine network may be responsible for malignant cell accumulation.…”

“…The percentage of CD3+/CD8+/IFN-c+ cells positively and significantly correlated with lymphocyte count, TTM score and stage of the disease according to Rai et al (9) classification. In view of wellestablished role of IFN-c as anti-apoptotic factor in B-CLL (8) it seems probable that increasing IFN-c synthesis may be, among the other factors (12,13) responsible for malignant cells accumulation in the microenvironment of the bone marrow, that eventually leads to disease progression.…”

The stromal composition of malignant lymphoid aggregates in bone marrow: variations in architecture and phenotype in different B‐cell tumours

“…Following transmigration across the blood vessel wall, tumour cell interactions with ARC become dominant. It has been postulated that ARC provide important cell-to-cell signals for haematopoiesis (Lagneaux et al, 1998;Mudry et al, 2000). The close association of tumour cells to LNGFR + ARC in FL and LPL mimics the tight apposition of ARC to developing megakaryocytic and myeloid forms.…”

Enhanced outgrowth of EBV-transformed chronic lymphocytic leukemia B cells mediated by coculture with macrophage feeder cells

“…34 It is also noteworthy that coculture of B-CLL cells with "nurse-like cells," derivatives of the myelomonocytic lineage, or stromal cells prevent spontaneous apoptosis of B-CLL cells in vitro, by both cell contact and soluble mediators. [35][36][37][38] J774A.1 cells also help clear apoptotic cells in vitro. 39 In this study, recognition by scavenger receptors of oxidized phosphatidylserine may be a mechanism of apoptotic cell clearance by J774A.1 cells, and such uptake could culminate in the presentation of apoptotic antigens to B-CLL cells.…”