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A Tim-3 ligand, galectin-9 (Gal-9), modulates various functions of innate and adaptive immune responses. In this study, we demonstrate that Gal-9 prolongs the survival of Meth-A tumor-bearing mice in a dose- and time-dependent manner. Although Gal-9 did not prolong the survival of tumor-bearing nude mice, transfer of naive spleen cells restored a prolonged Gal-9-induced survival in nude mice, indicating possible involvement of T cell-mediated immune responses in Gal-9-mediated antitumor activity. Gal-9 administration increased the number of IFN-γ-producing Tim-3+ CD8+ T cells with enhanced granzyme B and perforin expression, although it induced CD4+ T cell apoptosis. It simultaneously increased the number of Tim-3+CD86+ mature dendritic cells (DCs) in vivo and in vitro. Coculture of CD8+ T cells with DCs from Gal-9-treated mice increased the number of IFN-γ producing cells and IFN-γ production. Depletion of Tim-3+ DCs from DCs of Gal-9-treated tumor-bearing mice decreased the number of IFN-γ-producing CD8+ T cells. Such DC activity was significantly abrogated by Tim-3-Ig, suggesting that Gal-9 potentiates CD8+ T cell-mediated antitumor immunity via Gal-9-Tim-3 interactions between DCs and CD8+ T cells.

Objective. To compare the expression of galectin 9 (Gal-9) in synovial tissue (ST) from rheumatoid arthritis (RA) patients and osteoarthritis (OA) patients and to evaluate the effects of Gal-9 on fibroblast-like synoviocytes (FLS) in these patients.Methods. The expression of Gal-9 in ST and FLS was compared using immunohistochemical techniques. Apoptotic cells in RA and OA ST samples were detected by TUNEL assay. Apoptosis of FLS was analyzed by the sub-G 1 method in vitro. The in vivo suppressive effects of Gal-9 on collagen-induced arthritis (CIA) in a mouse model were also elucidated.Results. The percentage of Gal-9-positive cells in ST samples and the amount of Gal-9 in synovial fluid samples were significantly higher in patients with RA than in patients with OA, suggesting the involvement of Gal-9 in the development of RA. Compared with the 2 wild-type Gal-9 forms, stable Gal-9, a mutant protein resistant to proteolysis, significantly induced apoptosis of FLS from RA patients. In contrast, other galectins, such as Gal-1, Gal-3, and Gal-8, did not induce apoptosis or suppress the proliferation of human RA FLS. Stable Gal-9 preferentially induced apoptosis and suppressed the proliferation of RA FLS in vitro. It also induced apoptosis of cells in RA ST implanted into SCID mice in vivo. In a mouse model of CIA, apoptotic cells were detected in the joints of stable Gal-9-treated mice, but not phosphate buffered saline-treated mice, and suppressed CIA characterized by pannus formation with inflammatory cell infiltration and bone/cartilage destruction.Conclusion. Gal-9-induced apoptosis of hyperproliferative RA FLS may play a critical role in the suppression of RA.

We previously described an inverse correlation between galectin-9 (Gal-9) expression and metastasis in patients with malignant melanoma and breast cancer. This study verified the ability of Gal-9 to inhibit lung metastasis in experimental mouse models using highly metastatic B16F10 melanoma and Colon26 colon cancer cells. B16F10 cells transfected with a secreted form of Gal-9 lost their metastatic potential. Intravenous Gal-9 administration reduced the number of metastases of both B16F10 and Colon26 cells in the lung, indicating that secreted Gal-9 suppresses metastasis. Analysis of adhesive molecule expression revealed that B16F10 cells highly express CD44, integrin alpha1, alpha 4, alpha V, and beta1, and that Colon26 cells express CD44, integrin alpha2, alpha 5, alpha V, and beta1, suggesting that Gal-9 may inhibit the adhesion of tumor cells to vascular endothelium and the extracellular matrix (ECM) by binding to such adhesive molecules. Indeed, Gal-9 suppressed the binding of hyaluronic acid to CD44 on both B16F10 and Colon26 cells, and also suppressed the binding of vascular cell adhesion molecule-1 to very late antigen-4 on B16F10 cells. Furthermore, Gal-9 inhibited the binding of tumor cells to ECM components, resulting in the suppression of tumor cell migration. The present results suggest that Gal-9 suppresses both attachment and invasion of tumor cells by inhibiting the binding of adhesive molecules on tumor cells to ligands on vascular endothelium and ECM.

Galectins constitute a family of lectins that specifically exhibit the affinity for b-galactosides and modulate various biological events. Galectin-9 is a tandem-repeat type galectin with two carbohydrate recognition domains and has recently been shown to have an anti-proliferative effect on cancer cells. We investigated the effect of recombinant protease-resistant galectin-9 (hGal9) on multiple myeloma (MM). In vitro, hGal9 inhibited the cell proliferation of five myeloma cell lines examined, including a bortezomib-resistant subcell line, with IC 50 between 75.1 and 280.0 nM, and this effect was mediated by the induction of apoptosis with the activation of caspase-8, -9, and -3. hGal9-activated Jun NH 2 -terminal kinase (JNK) and p38 MAPK signaling pathways followed by H2AX phosphorylation. Importantly, the inhibition of either JNK or p38 MAPK partly inhibited the anti-proliferative effect of hGal9, indicating the crucial role of these pathways in the anti-MM effect of hGal9. hGal9 also induced cell death in patient-derived myeloma cells, some with poor-risk factors, such as chromosomal deletion of 13q or translocation t(4;14)(p16;q32). Finally, hGal9 potently inhibited the growth of human myeloma cells xenografted in nude mice. These suggest that hGal9 is a new therapeutic target for MM that may overcome resistance to conventional chemotherapy.