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Background Aims: Mesenchymal stromal cells (MSCs) have powerful immunosuppressive activity. This function of MSCs is attributed to plethora of the expressed immunosuppressive factors, such as galectin-1 (Gal-1), a pleiotropic lectin with robust anti-inflammatory effect. Nevertheless, whether Gal-1 renders or contributes to the immunosuppressive effect of MSCs has not been clearly established. Therefore, this question was the focus of a complex study., Methods: MSCs were isolated from bone marrows of wild-type and Gal-1 knockout mice and their in vitro anti-proliferative and apoptosis-inducing effects on activated T cells were examined. The in vivo immunosuppressive activity was tested in murine models of type I diabetes and delayed-type hypersensitivity., Results: Both Gal-1-expressing and -deficient MSCs inhibited T-cell proliferation. Inhibition of T-cell proliferation by MSCs was mediated by nitric oxide but not PD-L1 or Gal-1. In contrast, MSC-derived Gal-1 triggered apoptosis in activated T cells that were directly coupled to MSCs, representing a low proportion of the T-cell population. Furthermore, absence of Gal-1 in MSCs did not affect their in vivo immunosuppressive effect., Conclusions: These results serve as evidence that Gal-1 does not play a role in the systemic immunosuppressive effect of MSCs. However, a local contribution of Gal-1 to modulation of T-cell response by direct cell-to-cell interaction cannot be excluded. Notably, this study serves a good model to understand how the specificity of a pleiotropic protein depends on the type and localization of the producing effector cell and its target., (Copyright © 2015 International Society for Cellular Therapy. Published by Elsevier Inc. All rights reserved.)

Secreted, extracellular galectin-1 (exGal-1) but not intracellular Gal-1 (inGal-1) has been described as a strong immunosuppressive protein due to its major activity of inducing apoptosis of activated T-cells. It has previously been reported that T-cells express Gal-1 upon activation, however its participation in T-cell functions has remained largely elusive. To determine function of Gal-1 expressed by activated T-cells we have carried out a series of experiments. We have shown that Gal-1, expressed in Gal-1-transgenic Jurkat cells or in activated T-cells, remained intracellularly indicating that Gal-1-induced T-cell death was not a result of an autocrine effect of the de novo expressed Gal-1. Rather, a particular consequence of the inGal-1 expression was that T-cells became more sensitive to exGal-1 added either as a soluble protein or bound to the surface of a Gal-1-secreting effector cell. This was also verified when the susceptibility of activated T-cells from wild type or Gal-1 knockout mice to Gal-1-induced apoptosis were compared. Murine T-cells expressing Gal-1 were more sensitive to the cytotoxicity of the exGal-1 than their Gal-1 knockout counterparts. We also conducted a study with activated T-cells from patients with systemic lupus erythematosus (SLE), a disease in which dysregulated T-cell apoptosis has been well described. SLE T-cells expressed lower amounts of Gal-1 than healthy T-cells and were less sensitive to exGal-1. These results suggested a novel role of inGal-1 in T-cells as a regulator of T-cell response to exGal-1, and its likely contribution to the mechanism in T-cell apoptosis deficiency in lupus., (Copyright © 2014 Elsevier GmbH. All rights reserved.)

One prominent immunoregulatory function of galectin-1 (Gal-1), a β-galactoside binding mammalian lectin, is induction of apoptosis in activated T-cells by a process depending on the activity of Src family tyrosine kinase, Lck. Although the requirement for Lck in Gal-1 induced T-cell death and the ability of Gal-1 to affect the membrane localization of extracellular Gal-1-binding proteins have been well documented, the consequence of the complex and related reorganization of extra- and intracellular signaling components upon Gal-1 treatment of T-cells has not yet been revealed. Therefore, we have analyzed the plasma membrane movement of Lck upon Gal-1 triggered signaling, and the significance of this event in Gal-1 induced T-cell death. Non-receptor tyrosine kinase, Lck primarily localized in the synapse of tumor cell-T-cell during 15 min of the established direct cell contact. Later, after 30 min, a lateral segregation of Lck from the cell synapse was observed. The migration of Lck to the opposite of the cell contact apparently depended on the expression and cell surface presentation of Gal-1 on the effector (tumor) cells and was accompanied by phosphorylation on the negative regulatory tyrosine residue, Tyr505. Receptor tyrosine phosphatase, CD45 played crucial role in this event since CD45 deficiency or inhibition of its phosphatase activity resulted in the failure of Lck membrane movement. Level of the Gal-1-binding glycolipid GM1 ganglioside also essentially regulated Lck localization. Segregation of Lck and Gal-1 induced apoptosis was diminished in T-cells with low GM1 expression compared to T-cells with high GM1. Our results show that spatial regulation of Lck by CD45 and GM1 ganglioside determines the outcome of apoptotic response to Gal-1 and this local regulation may occur only upon intimate effector (Gal-1 expressing) cell-T-cell attachment., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Bone marrow derived mesenchymal stromal cells (MSCs) have recently been implicated as one source of the tumor-associated stroma, which plays essential role in regulating tumor progression. In spite of the intensive research, the individual factors in MSCs controlling tumor progression have not been adequately defined. In the present study we have examined the role of galectin-1 (Gal-1), a protein highly expressed in tumors with poor prognosis, in MSCs in the course of tumor development. Co-transplantation of wild type MSCs with 4T1 mouse breast carcinoma cells enhances the incidence of palpable tumors, growth, vascularization and metastasis. It also reduces survival compared to animals treated with tumor cells alone or in combination with Gal-1 knockout MSCs. In vitro studies show that the absence of Gal-1 in MSCs does not affect the number of migrating MSCs toward the tumor cells, which is supported by the in vivo migration of intravenously injected MSCs into the tumor. Moreover, differentiation of endothelial cells into blood vessel-like structures strongly depends on the expression of Gal-1 in MSCs. Vital role of Gal-1 in MSCs has been further verified in Gal-1 knockout mice. By administering B16F10 melanoma cells into Gal-1 deficient animals, tumor growth is highly reduced compared to wild type animals. Nevertheless, co-injection of wild type but not Gal-1 deficient MSCs results in dramatic tumor growth and development.These results confirm that galectin-1 is one of the critical factors in MSCs regulating tumor progression.