## 4 Nanodelivery Platform for Vaccine
### Inorganic Nanocarriers  
In addition to these natural or synthetic organic materials mentioned above, inorganic materials have also attracted attention due to their diverse and stable structures, unique optical and electrical properties, and biocompatibility. These inorganic materials with special physicochemical properties are mainly loaded with antigens through covalent bonding, electrostatic adsorption, and coupling, pioneering new modes of vaccine delivery [137] and providing a platform that can be combined with photothermal therapy [149], photodynamic therapy [59], and magnetic resonance imaging [150], among other methods. Common inorganic nanomaterials include mesoporous silica, carbonaceous materials, and metal/metal compound nanoparticles. Mesoporous silica is a porous material with ordered mesoporous molecular sieves, presenting properties that include a large specific surface area, stronger adsorption, higher biocompatibility, and lower cytotoxicity [151]. Therefore, mesoporous silica has great advantages in delivering drugs and vaccines and is one of the most stable and promising inorganic materials. Mesoporous silica nanoparticles (MSNs) are one of the more common forms. [PERSON]'s team developed a simplified and high-performance multi-antigen platform to enhance antigenic immunogenicity by using PEI in MSN vaccines. MSN-PEI vaccines containing neoantigen peptides were able to enhance DC activation and T cell responses, control tumor growth, and eradicate lung metastases [69]. To solve the problem of low efficiency of nanoparticle delivery to lymph nodes (dLN), [PERSON]'s team also skillfully coupled MSN and mesoporous silica microrods (MSRs) to make an injectable dual-scale mesoporous silica vaccine, which formed a 3D macroporous scaffold capable of recruiting rich DCs after injection and generating a greater number of antigen-specific T cells compared to a single MSN or MSR vaccine to inhibit melanoma growth, providing a new platform for DC-targeted nanovaccines [152]. In addition, MSR has been shown to encapsulate p-DNA encoding multiple antigens, especially neoantigens, directly transfecting host DCs in scaffolds, overcoming the limitations of subcutaneous and intramuscular administration of DNA vaccines, and eliciting both cellular and humoral immune responses [153]. The combination of several neoantigen peptides, a CpG oligodeoxynucleotide adjuvant, and the photosensitizer chlorin e6 in biodegradable MSN (bMSN) is another more classic example. PDT and immune reactions act simultaneously, triggering the activation of neoantigen-specific T-lymphocytes, and simultaneous imaging combined with PDT immunotherapy can be used to treat advanced cancers [59]. In addition to rod-like structures, hollow nanoparticles are preferred for vaccine delivery. [PERSON]'s team constructed a thin-shelled hollow-structured PEI-HMSN, which effectively improved the antigen loading rate as well as sustained release [154]. [PERSON]'s team encapsulated manganese oxide in hollow MSN nanoparticles (MnOx@HMSN), which released cyclic dinucleotides (CDNs); the manganese ions significantly enhanced STING activation and promoted DC activation and cross-presentation of neoantigen peptides. Vaccination with SARS-CoV-2 virus vaccine elicits a robust and long-lasting (approximately up to one year) humoral immune response [60]. However, the potential toxicity and complex modification process present in MSNs, as well as the high cost of synthesis, may be potential issues limiting the clinical translation of MSNs. The carbonaceous material graphene oxide has become a hot spot for drug or vaccine delivery due to its unique physicochemical properties. Through electrostatic, adsorption, and coupling, graphene oxide sheets can achieve high multilayered antigen loading while preferring the folded state in APCs [155]. [PERSON]'s team designed a highly modular, biodegradable PEGylated reduced graphene oxide nanosheet (RGO-PEG), with a diameter of around 20-30 nm, which can rapidly produce neoantigen vaccines.