Journal of Vaccine Research 2024, Vol.14, No.4, 183-195 http://medscipublisher.com/index.php/jvr 185 2.2 Enhancement of antigen presentation One of the primary roles of adjuvants in cancer vaccines is to enhance antigen presentation. This is achieved by prolonging antigen exposure to DCs and inducing their maturation, which is essential for the activation of antigen-specific T cells (Ho et al., 2018). Adjuvants such as aluminum-based nanoparticles, saponin-based adjuvants, and TLR ligands have been shown to improve the efficiency of antigen cross-presentation, a process where exogenous antigens are presented on MHC class I molecules to CD8+T cells (Ho et al., 2018; Lee and Suresh, 2022). The vaccine-site microenvironment (VSME) also plays a crucial role in antigen presentation. Studies have shown that the addition of peptide antigens to incomplete Freund's adjuvant (IFA) enhances antigen presentation pathways and induces a favorable VSME with increased dendritic cell activation and TLR adaptor protein gene expression (Meneveau et al., 2022). This suggests that the site of vaccine administration and the use of specific adjuvants can significantly impact the effectiveness of antigen presentation. 2.3 Promotion of T-cell activation Adjuvants promote T-cell activation by providing the necessary signals for T-cell priming and expansion. This is particularly important for the activation of CD8+cytotoxic T lymphocytes (CTLs), which are essential for targeting and killing tumor cells. Adjuvants such as CD80-Fc and Flt3L-Fc have been shown to enhance T-cell responses by directly stimulating T cells or by activating DCs, respectively (Thorne et al., 2020). Furthermore, the rational design of cancer vaccines often involves the use of adjuvants to balance cellular and humoral immune responses. For example, synthetic molecular agonists of pattern recognition receptors (PRRs) and adjuvant nanomaterials have been explored to optimize APC activation and T-cell priming (Li et al., 2022). The use of adjuvants in combination with other immunomodulatory agents, such as checkpoint inhibitors and cytokines, has also been shown to enhance T-cell function and memory formation, leading to more effective antitumor immunity (Hernandez and Malek, 2022). In conclusion, adjuvants play a vital role in enhancing the efficacy of cancer vaccines by modulating the immune system, enhancing antigen presentation, and promoting T-cell activation. Continued research into the mechanisms of action of adjuvants and their optimization will be crucial for the development of more effective cancer immunotherapies. 3 Types of Adjuvants Used in Cancer Vaccines 3.1 Alum-based adjuvants Alum-based adjuvants, primarily composed of aluminum salts, are among the most widely used adjuvants in vaccines. They function by creating a depot effect, which helps in the slow release of the antigen, thereby enhancing the immune response. These adjuvants are known to induce strong antibody responses but are less effective in stimulating cellular immunity, which is crucial for cancer vaccines (Del Giudice et al., 2018; Cuzzubbo et al., 2021). Despite their limitations, alum-based adjuvants are often used in combination with other adjuvants to improve their efficacy in cancer immunotherapy (Lee and Suresh, 2022). 3.2 Oil-in-water emulsions Oil-in-water emulsions, such as MF59 and AS03, are another class of adjuvants used in cancer vaccines. These emulsions enhance the immune response by promoting the recruitment and activation of antigen-presenting cells (APCs) at the site of injection. They have been shown to induce both humoral and cellular immune responses, making them suitable for cancer vaccines (Del Giudice et al., 2018; Lee and Suresh, 2022). Additionally, oil-in-water emulsions have been effective in enhancing vaccine efficacy in the elderly, who often have a waning immune response (Del Giudice et al., 2018). 3.3 Toll-like receptor (TLR) agonists TLR agonists are a promising class of adjuvants that target Toll-like receptors on immune cells to enhance the immune response. These adjuvants can stimulate both innate and adaptive immunity, making them highly
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