Mannosylated polyethylenimine-cholesterol-based nanoparticles for targeted delivery of minicircle DNA vaccine against COVID-19 to antigen-presenting cells.

DNA vaccines can be a potential solution to protect global health, triggering both humoral and cellular immune responses. DNA vaccines are valuable in preventing intracellular pathogen infections, and therefore can be explored against coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus (SARS-CoV-2). This work explored different systems based on polyethylenimine (PEI), functionalized for the first time with both cholesterol (CHOL) and mannose (MAN) to deliver parental plasmid (PP) and minicircle DNA (mcDNA) vectors encoding the receptor-binding domain (RBD) of SARS-CoV-2 to antigen-presenting cells (APCs). For comparative purposes, three different systems were evaluated: PEI, PEI-CHOL and PEI-CHOL-MAN. The systems were prepared at various nitrogen-to-phosphate group (N/P) ratios and characterized in terms of encapsulation efficiency, surface charge, size, polydispersity index (PDI), morphology, and stability over time. Moreover, in vitro transfection studies of dendritic cells (JAWS II) and human fibroblast cells were performed. Viability studies assured the biocompatibility of all nanocarriers. Confocal microscopy studies confirmed intracellular localization of systems, resulting in enhanced cellular uptake using PEI-CHOL and PEI-CHOL-MAN systems when compared with the PEI system. Regarding the RBD expression, PEI-CHOL-MAN was the system that led to the highest levels of transcripts and protein expression in JAWS II cells. Furthermore, the nanosystems significantly stimulated pro-inflammatory cytokines production and dendritic cell maturation in vitro. Overall, mannosylated systems can be considered a valuable tool in the delivery of plasmid DNA or mcDNA vaccines to APCs.