Exosome may be the next generation of promising cell-free vaccines

Figures & data

Table 1. Advantages and disadvantages of exosome isolation methods.

Methods	Advantages	Disadvantages
Ultracentrifugation	① Low cost ② Large number of samples can be extracted at once	① Impurities ② Time-consuming ③ Expensive equipment ④ Low recovery and purity ⑤ Poor reproducibility ⑥ Damage to exosome
Density gradient centrifugation	① High purity	① Cumbersome operation ② Time-consuming ③ Require preliminary preparation
Ultrafiltration	① Simple and quick ② Cheap equipment and chemicals	① Pressure may deform or rupture exosome ② Pore clogging ③ Contamination
SEC	① High yield and purity ② Stability of exosomes in structure and biological activity	① Cannot distinguish the same size vesicles of exosomes ② Special columns and packings required
Polymer precipitation	① High yield ② Large-scale isolation of exosomes is possible	① Low Purity
Immunoaffinity capture	① High purity ② High specificity	① Only the positive labeled exosome subtypes are included ② High cost ③ Require time for antigen-antibody binding
Microfluidic	① High-throughput ② High specificity ③ High purity and recovery	① High cost and complex ② Low yield

Figure 1. The common exosome characterization techniques.

ELISA, enzyme-linked immunosorbent analysis; PCR, polymerase chain reaction; NGS, next-generation sequencing; SEM, scanning electron microscope; TEM, transmission electron microscope; cryo-EM, cryo-electron microscope; AFM, atomic force microscope; NTA, nanoparticle tracking analysis; DLS, dynamic light scatterin; TRPS, tunable resistive pulse sensing; WB, western blot; FTIR, fourier-transform infrared spectroscopy; ddPCR, droplet digital PCR.

Table 2. Advantages and disadvantages of vaccine types.

Vaccine types	Advantages	Disadvantages
Inactivated vaccine	① Mature technology ② Relatively simple to construct ③ Inactive ingredient	① Booster immunization is needed
Adenoviral vector vaccine	① Mass production ② Multiple epitopes can be induced simultaneously ③ Strong immunogenicity	① Relatively complex to construct ② Pre-existing anti-adenovirus immune responses with potential adverse events
DNA vaccine	① Vectors can be constructed to encode different antigens in a single vaccine ② Mass production, low cost, high stability of production and storage ③ No active ingredients, no risk of vaccine-triggering disease	① Weak immune response ② Delivery agent is required to reach the nucleus
RNA vaccine	① Rapid development ② Novel mRNA sequences can be quickly assembled into existing vaccine formulations ③ No risk of integration with host cell genes ④ No active ingredients, no risk of vaccine-triggering disease	① High cost ② Lipid nanoparticles must be stored at ultra-low temperature ③ Prone to severe and rare allergic reactions
Recombinant protein vaccine	① Mature technology ② Mass production ③ No active ingredients ④ Relatively stable	① Adjuvants required ② Elicit weak immune response ③ Only protein fragments are expressed, not all proteins ④ Screening for the best combination of antigens take time
EV-based Vaccine	① Self-presenting antigen ② Crossing the blood-brain barrier ③ High absorptivity	① Mass production is difficult ② Immune response to disease need to be further explored

Figure 2. The mechanism of action of tumor-derived exosomes and immune cell-derived exosomes on tumor cells.

(a) TEXs is modified to enrich tumor antigens, microRNAs, and immunostimulatory molecules on TEXs to enhance tumor cell death or to be killed by immune cells. (b) TEX is presented to CD8⁺ T cells by DC, ultimately leading to tumor cell death through cytotoxicity. (c) TEX activates the B cell response to produce antibodies, which eventually causes the tumor cells are phagocytosed by macrophages. (d) TEX-loaded DCs with activate macrophages, which participate in cytotoxicity by releasing TNF. (e) DCexo induces NK cell function and NK cell-derived exosome presents cytotoxic effects via perforin and FasL. (f) CTL cell-derived exosomes cause tumor cell death through TCR-MHC/antigen interactions.

Data availability statement

Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.