Willis Gareth R, Kourembanas Stella, Mitsialis S Alex
Division of Newborn Medicine, Department of Medicine, Boston Children's Hospital, Boston, MA, United States.
Department of Pediatrics, Harvard Medical School, Boston, MA, United States.
Front Cardiovasc Med. 2017 Oct 9;4:63. doi: 10.3389/fcvm.2017.00063. eCollection 2017.
Exosomes are defined as submicron (30-150 nm), lipid bilayer-enclosed extracellular vesicles (EVs), specifically generated by the late endosomal compartment through fusion of multivesicular bodies with the plasma membrane. Produced by almost all cells, exosomes were originally considered to represent just a mechanism for jettisoning unwanted cellular moieties. Although this may be a major function in most cells, evolution has recruited the endosomal membrane-sorting pathway to duties beyond mere garbage disposal, one of the most notable examples being its cooption by retroviruses for the generation of Trojan virions. It is, therefore, tempting to speculate that certain cell types have evolved an exosome subclass active in intracellular communication. We term this EV subclass "signalosomes" and define them as exosomes that are produced by the "signaling" cells upon specific physiological or environmental cues and harbor cargo capable of modulating the programming of recipient cells. Our recent studies have established that signalosomes released by mesenchymal stem/stromal cells (MSCs) represent the main vector of MSC immunomodulation and therapeutic action in animal models of lung disease. The efficacy of MSC-exosome treatments in a number of preclinical models of cardiovascular and pulmonary disease supports the promise of application of exosome-based therapeutics across a wide range of pathologies within the near future. However, the full realization of exosome therapeutic potential has been hampered by the absence of standardization in EV isolation, and procedures for purification of signalosomes from the main exosome population. This is mainly due to immature methodologies for exosome isolation and characterization and our incomplete understanding of the specific characteristics and molecular composition of signalosomes. In addition, difficulties in defining metrics for potency of exosome preparations and the challenges of industrial scale-up and good manufacturing practice compliance have complicated smooth and timely transition to clinical development. In this manuscript, we focus on cell culture conditions, exosome harvesting, dosage, and exosome potency, providing some empirical guidance and perspectives on the challenges in bringing exosome-based therapies to clinic.
外泌体被定义为亚微米级（30 - 150纳米）、由脂质双层包裹的细胞外囊泡（EVs），其由晚期内体区室通过多囊泡体与质膜融合而特异性产生。外泌体几乎由所有细胞产生，最初被认为仅仅是一种抛弃不需要的细胞成分的机制。尽管这可能是大多数细胞中的主要功能，但进化已将内体膜分选途径用于除了简单垃圾处理之外的职责，最显著的例子之一是逆转录病毒利用它来产生特洛伊病毒粒子。因此，很容易推测某些细胞类型已经进化出一种在细胞内通讯中起作用的外泌体亚类。我们将这种EV亚类称为“信号体”，并将它们定义为由“信号”细胞在特定生理或环境线索下产生的外泌体，其携带的货物能够调节受体细胞的编程。我们最近的研究已经证实，间充质干/基质细胞（MSCs）释放的信号体代表了MSC在肺部疾病动物模型中的免疫调节和治疗作用的主要载体。MSC外泌体治疗在许多心血管和肺部疾病的临床前模型中的疗效支持了在不久的将来基于外泌体的治疗方法在广泛的病理情况下应用的前景。然而，外泌体治疗潜力的充分实现受到了EV分离缺乏标准化以及从主要外泌体群体中纯化信号体的程序的阻碍。这主要是由于外泌体分离和表征的方法不成熟以及我们对信号体的特定特征和分子组成的不完全理解。此外，定义外泌体制剂效力指标的困难以及工业规模扩大和良好生产规范合规性的挑战使得向临床开发的顺利和及时过渡变得复杂。在本手稿中，我们关注细胞培养条件、外泌体收获、剂量和外泌体效力，为将基于外泌体的疗法带入临床所面临的挑战提供一些经验指导和观点。
