In-depth review of delivery carriers associated with vaccine adjuvants: current status and future perspectives

ABSTRACT

Introduction

Vaccines are powerful tools for controlling microbial infections and preventing epidemics. To enhance the immune response to antigens, effective subunit vaccines or mRNA vaccines often require the combination of adjuvants or delivery carriers. In recent years, with the rapid development of immune mechanism research and nanotechnology, various studies based on the optimization of traditional adjuvants or various novel carriers have been intensified, and the construction of vaccine adjuvant delivery systems (VADS) with both adjuvant activity and antigen delivery has become more and more important in vaccine research.

Areas covered

This paper reviews the common types of vaccine adjuvant delivery carriers, classifies the VADS according to their basic carrier types, introduces the current research status and future development trend, and emphasizes the important role of VADS in novel vaccine research.

Expert opinion

As the number of vaccine types increases, conventional aluminum adjuvants show limitations in effectively stimulating cellular immune responses, limiting their use in therapeutic vaccines for intracellular infections or tumors. In contrast, the use of conventional adjuvants as VADS to carry immunostimulatory molecules or deliver antigens can greatly enhance the immune boosting effect of classical adjuvants. A comprehensive understanding of the various delivery vehicles will further facilitate the development of vaccine adjuvant research.

KEYWORDS:

• adjuvant
• carriers
• vaccine adjuvant delivery system (VADS)
• vaccine
• nanotechnology

Article highlights

• In order to tackle challenges in vaccine research such as weak immunogenicity of antigens, instability, or the necessity for a T-cell response for disease prevention, it is crucial to focus on the development of novel adjuvants.

• Vaccine adjuvant development strategies consist of two principal types: utilizing natural or synthetic materials with adjuvant properties, and creating VADS that couple adjuvant activity with antigen delivery or protection.

• The carriers used in VADS can be grouped into three main categories based on their characteristics: inorganic salt-based, oil-water emulsions, and microparticle antigen delivery systems.

• VADS constructed from varying base vectors often display distinct immune-enhancing mechanisms. Further analysis of their overall immune enhancement principles can provide direction for the rational design of innovative adjuvants.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or material discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or mending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Author contributions

S.L. and N.S. designed and funded the study. R.Z wrote the original draft, reviewed and edited the manuscript, N.X., and S.L. participated in discussion and interpretation of the manuscript.

Data availability statement

The data that support the findings of this study are openly available in PubMed at https://pubmed.ncbi.nlm.nih.gov/.

Additional information

Funding

This work was supported by grants from the National Key Research and Development Program of China (grant no: 2021YFC2301404), the National Natural Science Foundation of China (grant no: 81991491, 82271873), CAMS Innovation Fund for Medical Sciences of China (grant no: 2019RU022), and the Fundamental Research Funds for the Central Universities (20720220004, 20720220006).