title: A clinical and biological perspective of human myeloid-derived suppressor cells in cancer.
abstract: Considering the large number of studies focused on myeloid-derived suppressor cells (MDSCs) to date, only a handful of well-defined relationships in human cancer have been established. The difficulty of assessing the impact of MDSCs in human cancer is partly due to the relatively small number of studies performed in humans. This is compounded in the literature by a common lack of clear indication of which species is being referred to for each characteristic described. These aspects may result in inappropriate extrapolation of animal studies to those in the human setting. This is especially the case for studies focused on investigating therapies which can be used to target MDSCs or those aimed at understanding their mechanism. Here, we attempt to rectify this by reviewing only studies on MDSC performed in humans. We survey studies which explore (1) whether MDSC levels are altered in cancer patients and if this is correlated with patient survival, (2) the so far identified mechanisms employed by MDSC to exert immune suppression, and (3) whether therapeutic agents can be used to target MDSCs by either altering their level, influencing their differentiation or inhibiting their suppressive function. Despite the fact that these studies clearly show that MDSCs are important in human cancer, the clinical employment of agents intended to target them has not yet been accomplished. We identify factors which have contributed to this and propose steps which may facilitate the translation of these therapies to the clinic in future.
authors.affiliation: Second Department of Internal Medicine, University Hospital Tübingen, Waldhörnlestr. 22, 72072, Tübingen, Germany. christopher.shipp@uni-tuebingen.de.
authors.forename: Christopher
authors.initials: C
authors.lastname: Shipp
authors.affiliation: Second Department of Internal Medicine, University Hospital Tübingen, Waldhörnlestr. 22, 72072, Tübingen, Germany.
authors.forename: Lisa
authors.initials: L
authors.lastname: Speigl
authors.affiliation: Second Department of Internal Medicine, University Hospital Tübingen, Waldhörnlestr. 22, 72072, Tübingen, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: Janssen
authors.affiliation: Second Department of Internal Medicine, University Hospital Tübingen, Waldhörnlestr. 22, 72072, Tübingen, Germany.|Department of Dermatology, University Hospital Tübingen, Liebermeisterstr. 24, 72076, Tübingen, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Martens
authors.affiliation: Second Department of Internal Medicine, University Hospital Tübingen, Waldhörnlestr. 22, 72072, Tübingen, Germany. graham.pawelec@uni-tuebingen.de.|School of Science and Technology, College of Arts and Science, Nottingham Trent University, Burton St, Nottingham, NG1 4BU, UK. graham.pawelec@uni-tuebingen.de.
authors.forename: Graham
authors.initials: G
authors.lastname: Pawelec
mesh_terms: D006801:Humans; D007107:Immune System / Q000473:pathology; D007165:Immunosuppression Therapy; D008954:Models, Biological; D058990:Molecular Targeted Therapy; D000072737:Myeloid-Derived Suppressor Cells / Q000473:pathology*; D009369:Neoplasms / Q000378:metabolism* / Q000473:pathology*
keywords: Clinical; Human; MDSCs; Mechanism; Suppression; Targeting