Peptide nanovaccine conjugated via a retro-Diels–Alder reaction linker for overcoming the obstacle in lymph node penetration and eliciting robust cellular immunity†

Nanoparticles have been regarded as a promising vaccine adjuvant due to their innate immune potentiation and enhanced antigen transport. However, the inefficient infiltration into the lymph node (LN) paracortex of nanoparticles caused by subcapsular sinus (SCS) obstruction is the main challenge in further improvement of nanovaccine immune efficacy. Herein, we propose to overcome paracortex penetration by using nanovaccine to spontaneously and continuously release antigens after retention in the SCS. In detail, we utilized a spontaneous retro-Diels–Alder (r-D–A) reaction linker to connect poly{(2-methyl-2-oxazoline)₈₀-co-[(2-butyl-2-oxazoline)₁₅-r-(2-thioethyl-2-oxazoline)₈]} (PMBOxSH) and peptides for the peptide nanovaccine construction. The r-D–A reaction linker can spontaneously break over time, allowing the nanovaccine to release free antigens and adjuvants upon reaching the LN, thereby facilitating the entry of released antigens and adjuvants into the interior of the LNs. We showed that the efficacy of the peptide nanovaccine constructed using this dynamic linker could be significantly improved, thus greatly enhancing the tumor inhibition efficacy in the B16-OVA model. This dynamic-covalent-chemistry-based vaccine strategy may inspire designing more efficient therapeutic vaccines, especially those that require eliciting high-amount T cell responses.