Nurse like cells promote differentiation of CLL cells via Galectin-1 dependent mechanisms

CROCCI D; CAÑONES C; TOSCANO M; MORANDE P; BORGE M; BEZARES RF; SANCHEZ AVALOS JC; NARBAITZ M; GAMBERALE R; RABINOVITCH G; GIORDANO M

Workshop; XIII International Workshop on CLL; 2009

Accumulation of neoplastic cells in CLL is conditioned by a variety of signals delivered by accompanying cells in lymphoid tissues, which provide an appropriate niche for differentiation and survival. We examined the relevance of galectin-1 (Gal-1), a glycan-binding protein with immunoregulatory activity, within the CLL microenvironment. In vitro exposure to Gal-1 (1-10 M) promoted the differentiation of CLL cells in a saccharide-dependent manner by up-regulating the expression of CD86 and CD25, and favoring the release of IL-10 (n= 6, P<0.01). Of note, Gal-1 did not alter these parameters when added to tonsillar normal B lymphocytes although it markedly bound to these cells. As Gal-1 could affect leukemic cells by acting in an autocrine fashion or could be secreted by cells present in the CLL microenvironment, we further examined these posibilities. By flow cytometry analysis, we found no considerable expression of Gal-1 in freshly isolated CLL cells. However, we found high expression of Gal-1 in  nurse-like cells (NLC) differentiated from CD14+ peripheral leukocytes by co-cultured with CLL cells for two weeks. Both confocal microscopy and immunoblot analysis revealed selective expression of Gal-1 in NLC but not in leukemic cells. Remarkably, silencing of Gal-1 in NLC using siRNA-mediated strategies significantly reduced the expression of co-stimulatory molecules in CLL cells and the release of IL-10 to supernatants (P<0.05). In addition, using quantitative real-time RT-PCR analysis we found markedly reduced levels of the chemokine CCL3 but not CCL4 in leukemic cells co-cultured for 48 h with Gal-1-interfered NLC (P<0.05) and considerable reduction of the cytokine BAFF but not APRIL in NLCs (P<0.05). To determine whether Gal-1 is produced by cells surrounding leukemic lymphocytes in vivo, we analyzed bone marrow samples from CLL patients by immunohistochemistry and found high expression of Gal-1 in CD68+ myeloid cells. Collectively, these results indicate that accompanying myeloid cells deliver differentiation signals to CCL cells via Gal-1-dependent mechanisms, suggesting that manipulation of Gal-1 expression in NLC or signaling in CLL may influence CLL survival, a critical effect with profound implications in the design of novel anti-leukemic therapies.