Differential expression and biochemical activity of the immune receptor Tim-3 in healthy and malignant human myeloid cells

// Isabel Gonçalves Silva 1 , Bernhard F. Gibbs 1 , Marco Bardelli 2 , Luca Varani 2 , Vadim V. Sumbayev 1 1 School of Pharmacy, University of Kent, Anson Building, Kent, ME4 4TB, United Kingdom 2 Institute for Research in Biomedicine, Universita' della Svizzera italiana (USI) 6500 Bellinzona, Switzerland Correspondence to: Vadim V. Sumbayev, e-mail: V.Sumbayev@kent.ac.uk Bernhard F. Gibbs, e-mail: B.F.Gibbs@kent.ac.uk Luca Varani, e-mail: luca.varani@irb.usi.ch Keywords: Tim-3, acute myeloid leukaemia, myeloid cells Received: July 01, 2015      Accepted: September 04, 2015      Published: September 16, 2015 ABSTRACT The T cell immunoglobulin and mucin domain 3 (Tim-3) is a plasma membrane-associated receptor which is involved in a variety of biological responses in human immune cells. It is highly expressed in most acute myeloid leukaemia (AML) cells and therefore may serve as a possible target for AML therapy. However, its biochemical activities in primary human AML cells remain unclear. We therefore analysed the total expression and surface presence of the Tim-3 receptor in primary human AML blasts and healthy primary human leukocytes isolated from human blood. We found that Tim-3 expression was significantly higher in primary AML cells compared to primary healthy leukocytes. Tim-3 receptor molecules were distributed largely on the surface of primary AML cells, whereas in healthy leukocytes Tim-3 protein was mainly expressed intracellularly. In primary human AML blasts, both Tim-3 agonistic antibody and galectin-9 (a Tim-3 natural ligand) significantly upregulated mTOR pathway activity. This was in line with increased accumulation of hypoxia-inducible factor 1 alpha (HIF-1α) and secretion of VEGF and TNF-α. Similar results were obtained in primary human healthy leukocytes. Importantly, in both types of primary cells, Tim-3-mediated effects were compared with those induced by lipopolysaccharide (LPS) and stem cell factor (SCF). Tim-3 induced comparatively moderate responses in both AML cells and healthy leukocytes. However, Tim-3, like LPS, mediated the release of both TNF-α and VEGF, while SCF induced mostly VEGF secretion and did not upregulate TNF-α release.