Engineering of DNA Micro- and Nanoparticles: Towards Vaccine Delivery

Abstract

Vaccines are an effective tool for preventing and controlling various diseases by inducing adaptive immunity. Nanomaterials play an important role in vaccine development. Micro- and nanocarriers can be engineered to improve the therapeutic efficacy of vaccines by (i) preventing the degradation and systemic clearance of vaccine antigens and (ii) facilitating the uptake of vaccines in antigen-presenting cells (iii) co-delivering adjuvants and antigens at desired intracellular compartments for optimal immunotherapy. However, it is important to engineer a carrier that is both effective and safe. Micro- and nanoparticles based on DNA have shown great potential for biological applications, owing to the programmable sequences, predictable interactions, versatile modification sites, and high biocompatibility of DNA strands.

This thesis aims to develop facile strategies to synthesize DNA particles for vaccine delivery by self-assembly approaches. First, a simple strategy to synthesize DNA microcapsules is reported. The cytosine-phosphate-guanosine oligodeoxynucleotides (CpG) motif is an efficient vaccine adjuvant that can effectively stimulate the immune system to secrete cytokines. By loading and crosslinking Y-shaped DNA building blocks (containing CpG motifs) into sacrificial calcium carbonate templates, monodisperse and spherical DNA capsules were obtained. These DNA microcapsules were internalized into cells efficiently, accumulated in endosomes, and induced immune cells to secrete high-level of cytokines.

Next, we developed a template-assisted and versatile approach for synthesizing a new set of multifunctional particles through the supramolecular assembly of tannic acid (TA) and DNA molecules. Uniform and stable DNA-TA particles with different morphologies could be easily synthesized by using different types of DNA strands. Intriguingly, different DNA sequences can be encoded into this DNA-TA particle for applications in immunotherapy or gene delivery. The incorporation of CpG motifs and ovalbumin into the particles allows the intracellular antigen/adjuvant co-delivery to amplify cytokines production in macrophages, through synergistic effects. In addition, green fluorescent protein (GFP)-expressing plasmid DNA could be transfected by using the DNA-TA particles in HEK293T cells.

Finally, nanometer-sized particles were engineered by exploiting the one-pot supramolecular assembly of TA, DNA, and PEG for intracellular delivery of CpG motifs. TA-DNA-PEG nanoparticles with different sizes could be fabricated by adding different molecular weight PEG chains. TA-DNA nanoparticles with tunable size were also synthesized by varying the molar ratio of TA and DNA. The obtained nanoparticles can enhance the cellular uptake of CpG oligonucleotides and consequently the production of cytokines in macrophages. Overall, the engineered DNA-based particles have potential for co-delivering nucleic acids and protein antigens in immune cells to enhance the immunological response against infectious diseases and cancer.