The Impact of Small Extracellular Vesicles on Lymphoblast Trafficking across the Blood-Cerebrospinal Fluid Barrier In Vitro.

Ulrike Erb,Julia Hikel,Rüdiger Adam,Hiroshi Ishikawa,Christel Weiss,Philipp Nuhn,Katja Nitschke,Michael Karremann,Horst Schroten,Svenja Meyer,Thomas S Worst,Stefan Porubsky

doi:10.3390/ijms21155491

Abstract

Central nervous System (CNS) disease in pediatric acute lymphoblastic leukemia (ALL) is a major concern, but still, cellular mechanisms of CNS infiltration are elusive. The choroid plexus (CP) is a potential entry site, and, to some extent, invasion resembles CNS homing of lymphocytes during healthy state. Given exosomes may precondition target tissue, the present work aims to investigate if leukemia-derived exosomes contribute to a permissive phenotype of the blood-cerebrospinal fluid barrier (BCSFB). Leukemia-derived exosomes were isolated by ultracentrifugation from the cell lines SD-1, Nalm-6, and P12-Ichikawa (P12). Adhesion and uptake to CP epithelial cells and the significance on subsequent ALL transmigration across the barrier was studied in a human BCSFB in vitro model based on the HiBCPP cell line. The various cell lines markedly differed regarding exosome uptake to HiBCPP and biological significance. SD-1-derived exosomes associated to target cells unspecifically without detectable cellular effects. Whereas Nalm-6 and P12-derived exosomes incorporated by dynamin-dependent endocytosis, uptake in the latter could be diminished by integrin blocking. In addition, only P12-derived exosomes led to facilitated transmigration of the parental leukemia cells. In conclusion, we provide evidence that, to a varying extent, leukemia-derived exosomes may facilitate CNS invasion of ALL across the BCSFB without destruction of the barrier integrity.

Highlights

Survival of pediatric acute lymphoblastic leukemia (ALL) has dramatically improved over the last decades [1]
Extracellular vesicles released by the three leukemia cell lines SD-1 (BCP-ALL), Nalm-6 (BCP-ALL), and P12 (T-ALL) all presented with typical size of exosomes, and expressed exosomal markers including CD 63 and CD 81 (Supplementary Figure S1)
Small extracellular vesicles play a crucial role in tumor dissemination and central nervous system (CNS) infiltration may be facilitated by exosome-mediated transformation of target tissue in solid tumors, and in leukemias [5,16]

Summary

Introduction

Survival of pediatric acute lymphoblastic leukemia (ALL) has dramatically improved over the last decades [1]. Multiple mechanisms have been unraveled by which tumor-derived exosomes affect the formation of CNS metastases in numerous malignancies [12,13] These sum up, in the potential to modify tissues distant to the primary tumor site, and result in the formation of a “premetastatic niche”, facilitating circulating tumor cells to invade these tissues, and build new metastases, a mechanism that has been published in CNS infiltration by hematologic malignancies [14,15]. In this regard, Kinjyo and colleagues have recently described the impact of leukemia-derived exosomes on lymphoblast transmigration across the blood-brain barrier (BBB) in pediatric ALL. In this regard, varying microRNA expression profiles have been described in T-linage and B-cell precursor (BCP)-ALL, potentially contributing to the different clinical behavior of these ALL subtypes [17]

Methods

Results

Conclusion