Gene expression in Galectin-3 KO vs. WT CD8 T cells

The goal of this study was to examine differences in gene expression of tumor specific CD8 T cells in an in vivo tumor mouse model after inhibition of galectin-3 protein expression by genetic knockout. Galectin-3 is thought to modulate CD8 T cell response by cross-linking cell surface glycoproteins Galectin-3 is a 31 kD carbohydrate-binding lectin that is over-expressed by many human malignancies. It also modulates T cell responses through a diverse array of mechanisms including induction of apoptosis, TCR cross linking in CD8+ T cells, and T cell receptor (TCR) down regulation in CD4+ T cells. We found that patients responding to a granulocyte-macrophage colony-stimulating factor (GM-CSF) secreting allogeneic pancreatic tumor vaccine developed post immunization antibody responses to galectin-3 on a proteomic screen. We used the HER-2/neu (neu-N) transgenic mouse model to study galectin-3 binding on adoptively transferred high avidity neu-specific CD8+ T cells derived from TCR transgenic mice. Here, we show that galectin-3 binds preferentially to activated antigen-committed CD8+ T cells only in the tumor microenvironment (TME). Galectin-3 deficient mice exhibit improved CD8+ T cell effector function and increased expression of several inflammatory genes when compared with wild type (WT) mice. We also show that galectin-3 binds to LAG-3, and LAG-3 expression is necessary for galectin-3 mediated suppression of CD8+ T cells in vitro. Lastly, galectin-3 deficient mice have significantly elevated levels of circulating plasmacytoid dendritic cells (pDCs), which are superior to conventional dendritic cells (cDCs) in activating CD8+ T cells. Binding of galectin-3 to cell-surface glycoproteins on immune cells suppresses a pro-inflammatory immune response. Thus, inhibiting galectin-3 in conjunction with CD8+ T cell directed immunotherapies should enhance the tumor specific immune response.