Vaccine refers to biological products that are produced using various pathogenic microorganisms for inoculation. The goal of vaccination is to induce a robust immune response against a specific antigen, thus preventing the organism from getting infected. In vaccines, adjuvants have been widely employed to enhance immunity against specific antigens. An ideal adjuvant should be stable, biodegradable, and low cost, not induce system rejection and promote an immune response. Various adjuvant components have been investigated across diverse applications. Typically, adjuvants are employed to meet the following objectives: (1) to improve the effectiveness of immunization with vaccines for specific populations, such as newborns and the elderly; (2) enhance the immunogenicity of highly purified or recombinant antigens; (3) allow immunization with a smaller dose of the vaccine, reducing drug dosage. In the present review, we primarily focus on chemically synthesized compounds that can be used as built-in adjuvants. We elaborate the classification of these compounds based on the induced immune activation mechanism and summarize their application in various vaccine types.

疫苗是指利用各种病原微生物进行接种而生产的生物制品。疫苗接种的目的是诱导针对特定抗原的强烈免疫反应，从而防止有机体被感染。在疫苗中，佐剂已被广泛用于增强针对特定抗原的免疫力。理想的佐剂应该是稳定的、可生物降解的和低成本的，不会引起系统排斥和促进免疫反应。已经在不同的应用中研究了各种佐剂成分。通常，佐剂用于满足以下目标： (1) 提高针对特定人群（如新生儿和老年人）的疫苗免疫效果；(2)增强高度纯化或重组抗原的免疫原性；(3)允许用较小剂量的疫苗进行免疫，减少药物剂量。在本综述中，我们主要关注可用作内置佐剂的化学合成化合物。我们根据诱导免疫激活机制对这些化合物进行了分类，并总结了它们在各种疫苗类型中的应用。