[The investigation of DNA tetrahedral nanoparticles as mucosal vaccine carriers and adjuvants].

Objective: To investigate the feasibility of DNA tetrahedral framework (DNA-TH) as a carrier and adjuvant for mucosal vaccines, using streptavidin (SA) as a model antigen. Methods: DNA-TH was designed using software, integrating the adjuvant CpG sequence into its structure. After in vitro synthesis, it was conjugated with SA to form SA-DNA-TH nanoparticles. In vitro experiments: free SA and the two-dimensional structure SA-CpG (SA directly conjugated to CpG) were used as controls. The uptake efficiency of SA-DNA-TH by mouse primary macrophages and its ability to activate antigen-presenting cells (APCs) were evaluated. In vivo experiments: following submucosal oral injection, a mixture of free SA and free CpG (mixed group) was used as a control. The distribution of SA within mouse lymph nodes was observed using immunofluorescence staining. Levels of SA-specific antibodies (serum IgG, IgM; salivary sIgA) in serum and saliva were measured to assess humoral and mucosal immune responses. Results: Native polyacrylamide gel electrophoresis confirmed the successful synthesis of DNA-TH and SA-DNA-TH. In vitro experiments: SA-DNA-TH was rapidly taken up by primary macrophages. Its uptake rate (92.65%±4.43%) was significantly higher than that of the SA-CpG group (25.37%±3.56%) and the free SA group (1.80%±1.02%; both P<0.01). SA-DNA-TH also induced significantly stronger APC activation (OD value fold increase: 3.60±0.32) compared to the free SA group (1.13±0.10) and the SA-CpG group (1.21±0.02; both P<0.01). In vivo experiments: lymph node distribution analysis revealed overlapping signals of SA with subcapsular sinus macrophages (SCSMs) and dendritic cells (DCs) in the SA-DNA-TH group, whereas SA signals appeared dispersed and non-overlapping with APCs in the mixed group. Regarding immunogenicity, both serum anti-SA antibody (IgG+IgM) titers and salivary anti-SA sIgA antibody titers induced by SA-DNA-TH were significantly higher than those in the mixed group and the blank control group (both P<0.05). Conclusion: DNA-TH effectively delivers the model antigen SA to antigen-presenting cells, significantly induces the production of serum-specific antibodies, and activates mucosal immune responses. It demonstrates potential as a carrier and adjuvant for developing mucosal vaccines.