Human leukocyte antigen G (HLA-G) is a non-classical major histocompatibility complex (MHC) class I molecule that, through interaction with its receptors, exerts important tolerogenic functions. Its main physiological expression occurs in placenta where it seems to participate in the maternal tolerance toward the fetus. HLA-G has been studied as a marker of pregnancy complications such as abortion or pre-eclapmsia. Although HLA-G is not expressed in most adult tissues, its ectopic expression has been observed in some diseases such as viral infections, autoimmune disorders, and especially cancer. HLA-G neo-expression in cancer is associated with the capability of tumor cells to evade the immune control. In this review, we will summarize HLA-G biology and how it participates in these physiopathological processes. Special attention will be paid to its role as a diagnostic tool and also as a therapeutic target.

Context .—Malignant melanoma is an aggressive tumor that produces exosomes, which contain microRNAs (miRNAs) that could be of utility in following tumoral cell dysregulation. MicroR-125b is a miRNA whose down-regulation seems to be implicated in melanoma progression. Objective .—To analyze miR-125b levels in serum, and in exosomes obtained from serum, from patients with advanced melanoma. Design .—Serum samples were obtained from 21 patients with advanced melanoma, from 16 disease-free patients with melanoma, and from 19 healthy volunteers. Exosomes were isolated from serum by precipitation, and miR-16 and miR-125b levels were quantified by real-time polymerase chain reaction. Results .—MicroR-16, but not miR-125b, was detected in all samples, and miR-16 levels were significantly higher in serum than they were in exosomes. MicroR-16 expression levels did not differ significantly between the 2 groups (patients with melanoma and healthy donors). There was a significant relationship between miR-125b and miR-16 levels in exosomes. Additionally, miR-125b levels in exosomes were significantly lower in patients with melanoma compared with disease-free patients with melanoma and healthy controls. Conclusions .—Exosomes can provide a suitable material to measure circulating miRNA in melanoma, and miR-16 can be used as an endogenous normalizer. Lower levels of miR-125b in exosomes obtained from serum are associated with advanced melanoma disease, probably reflecting the tumoral cell dysregulation.

Background: Exosomes are nanovesicles released by cells that can be detected in blood. Exosomes contain several molecules, such as cytokines that have potential utility as disease biomarkers. The aim of the present work is to compare six different commercial kits suitable for the clinical laboratory in relation to the efficiency and purity of exosome isolation, and their effect in subsequent cytokines analysis. Methods: Serum exosomes were obtained from 10 volunteers using six commercial kits: exoEasy, ExoQuick, Exo-spin, ME kit, ExoQuick Plus and Exo-Flow. Exosome concentrations and size distributions were quantified by nanoparticle tracking analysis. Exosome markers CD63, CD9 and TSG101 were determined by Western blot. ApoB and albumin were measured using nephelometry. S100A9, CXCL5 and CXCL12 were measured using a Luminex assay. Results: The concentration of particles obtained between different kits varied by a factor of 100. There was no correlation in particle concentrations extracted between different kits, except between ExoQuick and Exo-Flow. The highest exosome purity was achieved with ExoQuick Plus and exoEasy, while the lowest were achieved with ME and ExoQuick. Albumin was present in all exosome extracts analyzed and ApoB in all except those extracted with Exo-Flow and ME. Cytokine detection varied depending on the purification kit used and there was no correlation in cytokine concentrations between samples obtained with different kits. Conclusions: Both the sample and the type of commercial kit used affect the efficiency and purity of exosome isolation. In addition, the exosome purification method deeply affects the capability to detect and quantify cytokines.

Human leukocyte antigen-G (HLA-G) is a low polymorphic nonclassical HLA-I molecule restrictively expressed and with suppressive functions. HLA-G gene products are quite complex, with seven HLA-G isoforms, four membrane bound, and other three soluble isoforms that can suffer different posttranslational modifications or even complex formations. In addition, HLA-G has been described included in exosomes. In this review we will focus on HLA-G biochemistry with special emphasis to the mechanisms that regulate its expression and how the protein modifications affect the quantification in biological fluids.