Karin M. Ekström

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles ("MISEV") guidelines for the field in 2014. We now update these "MISEV2014" guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points.

BACKGROUND: Exosomes are 30-100 nm membrane vesicles of endocytic origin produced by numerous cells. They can mediate diverse biological functions, including antigen presentation. Exosomes have recently been shown to contain functional RNA, which can be delivered to other cells. Exosomes may thus mediate biological functions either by surface-to-surface interactions with cells, or by the delivery of functional RNA to cells. Our aim was therefore to determine the presence of RNA in exosomes from human saliva, plasma and breast milk and whether these exosomes can be taken up by macrophages. METHOD: Exosomes were purified from human saliva, plasma and breast milk using ultracentrifugation and filtration steps. Exosomes were detected by electron microscopy and examined by flow cytometry. Flow cytometry was performed by capturing the exosomes on anti-MHC class II coated beads, and further stain with anti-CD9, anti-CD63 or anti-CD81. Breast milk exosomes were further analysed for the presence of Hsc70, CD81 and calnexin by Western blot. Total RNA was detected with a Bioanalyzer and mRNA was identified by the synthesis of cDNA using an oligo (dT) primer and analysed with a Bioanalyzer. The uptake of PKH67-labelled saliva and breast milk exosomes by macrophages was examined by measuring fluorescence using flow cytometry and fluorescence microscopy. RESULTS: RNA was detected in exosomes from all three body fluids. A portion of the detected RNA in plasma exosomes was characterised as mRNA. Our result extends the characterisation of exosomes in healthy humans and confirms the presence of RNA in human saliva and plasma exosomes and reports for the first time the presence of RNA in breast milk exosomes. Our results also show that the saliva and breast milk exosomes can be taken up by human macrophages. CONCLUSIONS: Exosomes in saliva, plasma and breast milk all contain RNA, confirming previous findings that exosomes from several sources contain RNA. Furthermore, exosomes are readily taken up by macrophages, supporting the notion that exosomal RNA can be shuttled between cells.

A substantial excess risk of lymphomas and nonmelanoma skin cancer has been demonstrated following organ transplantation. Large sample size and long follow-up time may, however, allow more accurate risk estimates and detailed understanding of long-term cancer risk. The objective of the study was to assess the risk of cancer following organ transplantation. A nationwide cohort study comprising 5931 patients who underwent transplantation of kidney, liver or other organs during 1970-1997 in Sweden was conducted. Complete follow-up was accomplished through linkage to nationwide databases. We used comparisons with the entire Swedish population to calculate standardised incidence ratios (SIRs), and Poisson regression for multivariate internal analyses of relative risks (RRs) with 95% confidence intervals (CI). Overall, we observed 692 incident first cancers vs 171 expected (SIR 4.0; 95% CI 3.7-4.4). We confirmed marked excesses of nonmelanoma skin cancer (SIR 56.2; 95% CI 49.8-63.2), lip cancer (SIR 53.3; 95% CI 38.0-72.5) and of non-Hodgkin's lymphoma (NHL) (SIR 6.0; 95% CI 4.4-8.0). Compared with patients who underwent kidney transplantation, those who received other organs were at substantially higher risk of NHL (RR 8.4; 95% CI 4.3-16). Besides, we found, significantly, about 20-fold excess risk of cancer of the vulva and vagina, 10-fold of anal cancer, and five-fold of oral cavity and kidney cancer, as well as two- to four-fold excesses of cancer in the oesophagus, stomach, large bowel, urinary bladder, lung and thyroid gland. In conclusion, organ transplantation entails a persistent, about four-fold increased overall cancer risk. The complex pattern of excess risk at many sites challenges current understanding of oncogenic infections that might become activated by immunologic alterations.