Tumour pathogenesis in multiple myeloma (MM) correlates with a high vascular index. Therefore, targeting angiogenesis is an important therapeutic tool to reduce MM progression. This study aimed to investigate the role of invariant natural killer T (iNKT) cells in angiogenesis and the mechanisms behind the stimulation by α-Galactosylceramide (α-GalCer). We have previously found that α-GalCer could increase the survival of 5T33MM mice and here we demonstrate that α-GalCer reduces the microvessel density. We performed both in vivo and in vitro angiogenic assays to confirm this observation. We found that conditioned medium of α-GalCer stimulated iNKT cells reduced neovascularization in the chick chorioallantoic membrane and in matrigel plug assays. Moreover, we observed a reduction in proliferation, migration and network formation and an induction of apoptosis upon exposure of murine endothelial cell lines to this conditioned medium. We furthermore observed that the JAK-STAT signaling pathway was highly activated in endothelial cells in response to stimulated iNKT cells, indicating the possible role of IFN-γ in the anti-angiogenic process. In conclusion, these results highlight the possibility of recruiting iNKT cells to target MM and angiogenesis. This gives a rationale for combining immunotherapy with conventional anti-tumour treatments in view of increasing their therapeutic potential.

Invariant natural killer T (iNKT) cells are a unique subset of T lymphocytes that recognize glycolipid antigens presented by the class I-like non-polymorphic histocompatibility complex (MHC) molecule, CD1d. They express both innate and adaptive immune cells’ surface receptors, but act more like cells of the innate immune system. Although iNKT cells represent a relatively small population of T lymphocytes, they can rapidly produce copious amounts of cytokines after activation which can polarize different axes of the immune response. Many glycolipid agonists have been discovered of which the marine sponge-derivative called α-Galactosylceramide (α-GalCer) is a potent ligand for iNKT cells. iNKT cells have been described by many researchers as a critical immunotherapeutic target characterized by having tumor-suppressive potential. However, their actual role in immune responses is still unclear. In addition, the need for appropriate preclinical models that mimic human diseases is important for better understanding the iNKT cell biology. This review describes the characteristics of iNKT cells and their role in immunotherapy in cancers such as multiple myeloma and how they can interact with the components of the neighbouring environment. Review Article Nur et al.; IBRR, Article no. IBRR.2013.001 45

Immunomodulators have been used in recent years to reactivate host anti-tumor immunity in several hematological malignancies. This report describes the effect of activating natural killer T (NKT) cells by α-Galactosylceramide (α-GalCer) in the 5T33MM model of multiple myeloma (MM). NKT cells are T lymphocytes, co-expressing T and NK receptors, while invariant NKT cells (iNKTs) also express a unique semi-invariant TCR α-chain. We followed iNKT numbers during the development of the disease in both 5T33MM mice and MM patients and found that their numbers dropped dramatically at the end stage of the disease, leading to a loss of total IFN-γ secretion. We furthermore observed that α-GalCer treatment significantly increased the survival of 5T33MM diseased mice. Taken together, our data demonstrate for the first time the possibility of using a preclinical murine MM model to study the effects of α-GalCer and show promising results of α-GalCer treatment in a low tumor burden setting.

Arsenate reductases (ArsCs) evolved independently as a defence mechanism against toxic arsenate. In the genome of Corynebacterium glutamicum, there are two arsenic resistance operons (ars1 and ars2) and four potential genes coding for arsenate reductases (Cg_ArsC1, Cg_ArsC2, Cg_ArsC1' and Cg_ArsC4). Using knockout mutants, in vitro reconstitution of redox pathways, arsenic measurements and enzyme kinetics, we show that a single organism has two different classes of arsenate reductases. Cg_ArsC1 and Cg_ArsC2 are single-cysteine monomeric enzymes coupled to the mycothiol/mycoredoxin redox pathway using a mycothiol transferase mechanism. In contrast, Cg_ArsC1' is a three-cysteine containing homodimer that uses a reduction mechanism linked to the thioredoxin pathway with a k(cat)/K(M) value which is 10(3) times higher than the one of Cg_ArsC1 or Cg_ArsC2. Cg_ArsC1' is constitutively expressed at low levels using its own promoter site. It reduces arsenate to arsenite that can then induce the expression of Cg_ArsC1 and Cg_ArsC2. We also solved the X-ray structures of Cg_ArsC1' and Cg_ArsC2. Both enzymes have a typical low-molecular-weight protein tyrosine phosphatases-I fold with a conserved oxyanion binding site. Moreover, Cg_ArsC1' is unique in bearing an N-terminal three-helical bundle that interacts with the active site of the other chain in the dimeric interface.