Engineered Extracellular Vesicles as a New Class of Nanomedicine

Abstract

Extracellular vesicles (EVs) are secreted from biological cells and contain many molecules with diagnostic values or therapeutic functions. There has been great interest in academic and industrial communities to utilize EVs as tools for diagnosis or therapeutics. In addition, EVs can also serve as delivery vehicles for therapeutic molecules. An indicator of the enormous interest in EVs is the large number of review articles published on EVs, with the focus ranging from their biology to their applications. An emerging trend in EV research is to produce and utilize "engineered EVs", which are essentially the enhanced version of EVs. EV engineering can be conducted by cell culture condition control, genetic engineering, or chemical engineering. Given their nanometer-scale sizes and therapeutic potentials, engineered EVs are an emerging class of nanomedicines. So far, an overwhelming majority of the research on engineered EVs is preclinical studies; there are only a very small number of reported clinical trials. This Review focuses on engineered EVs, with a more specific focus being their applications in therapeutics. The various approaches to producing engineered EVs and their applications in various diseases are reviewed. Furthermore, in vivo imaging of EVs, the mechanistic understandings, and the clinical translation aspects are discussed. The discussion is primarily on preclinical studies while briefly mentioning the clinical trials. With continued interdisciplinary research efforts from biologists, pharmacists, physicians, bioengineers, and chemical engineers, engineered EVs could become a powerful solution for many major diseases such as neurological, immunological, and cardiovascular diseases.

Figure 1

Biogenesis and identification of exosomes. Reproduced with permission from ref (2). Copyright 2024 The American Association for the Advancement of Science.

Figure 2

Schematic illustration of the various methods of modifying the content and structure of EVs, for enhanced and integrated and new functions.

Figure 3

Multifunctional EVs, composed of MSC-derived exosomes incorporating curcumin-loaded SPIONs, for PD treatment. Reproduced with permission from ref (60). Copyright 2024 American Chemical Society.

Figure 4

Metabolic tagging of EVs. Reproduced with permission from ref (66). Copyright 2024 Springer Nature.

Figure 5

Overview of two different general approaches for encapsulating EVs into a hydrogel. (A) EVs and polymers are mixed, after which a cross-linker and/or an external trigger (e.g., heat, UV light) starts the gelation process. (B) Polymers, cross-linker and EVs are added simultaneously in a dual chamber syringe to achieve in situ gelation at the target site. Reproduced with permission from ref (74). Copyright 2024 Elsevier.

Figure 6

Schematic diagram of developing EV-GlucB reporter for in vivo multimodal imaging of EVs. (A) Membrane-bound Gluc (GlucB) or Gluc (control) and the secreted form of humanized bacterial biotin ligase (sshBirA) were delivered via lentivectors to HEK 293T cells for stable expression. (B) Upon expression and EV production by the cells, the sshBirA tags the BAP sequence of GlucB with a single biotin moiety at a specific lysine residue, which is then displayed on the cell surface as well as on the EV surface. EVs were isolated from conditioned medium of cells and injected intravenously (iv) via tail or retro-orbital veins into nude mice for bioluminescence and fluorescence-mediated tomography (FMT) imaging. For bioluminescence imaging, coelentrazine, a Gluc substrate, was iv-administered immediately prior to imaging. For FMT imaging, isolated EVs were conjugated with streptavidin-Alexa680 prior to administration into nude mice. (C) EVs derived from cells synthesizing naturally secreted Gluc were used as controls as Gluc is not present in the EVs. Abbreviations: BAP, biotin acceptor peptide; CMV, cytomegalovirus; GFP, green fluorescent protein; hBirA, humanized biotin ligase; hGluc, humanized Gaussia luciferase; IRES, internal ribosome entry site; SA, streptavidin; ss, signal peptide; TM, transmembrane domain of platelet-derived growth factor receptor. Reproduced with permission from ref (92). Copyright 2024 American Chemical Society.