Polymeric Nucleic Acid Delivery for Immunoengineering

Purpose: Nucleic acids can be used to engineer the immune system, but their clinical use requires better specificity and intracellular delivery efficiency. Viral vectors have manufacturing, cargo-capacity, safety, and immunological drawbacks; therefore, polymers are being developed as non-viral delivery vehicles whose chemical and physical properties can be tuned to improve efficacy.

Hypothesis: As a review, this paper does not test a single formal hypothesis. Its central premise is: if polymers are formulated with nucleic acids — DNA, mRNA, siRNA, shRNA, or immunostimulatory nucleic acids — then they can enhance delivery to immune cells and enable prophylactic vaccines, therapeutic immunomodulation, gene overexpression/knockdown, and innate immune activation.

Aims: Describe polymers as a non-viral method for delivering nucleic acids for immunoengineering. - Review major nucleic acid cargo types and the intracellular barriers they face. - Discuss polymer classes and design features, including cationic complexation, degradable linkages, and targeting modifications. - Summarize immune cell targets and recent applications in prophylactic vaccines and therapeutic immunoengineering.

Delivery system: Platform: Polymer-based nucleic acid delivery vehicles. - Cationic polymers: Poly(L-lysine) (PLL), polyethylenimine (PEI), poly(beta-amino ester)s (PBAEs), PAMAM dendrimers, chitosan. These electrostatically complex negatively charged nucleic acids into nanoparticles, often approximately 50–200 nm. - Hydrophobic/encapsulating polymers: PLGA, PLA, poly(ortho ester)s (POEs); nucleic acids are physically entrapped, sometimes with polyamines to improve encapsulation and delivery. - Modifications: Degradable linkages (e.g., disulfide-containing PAMAM, bioreducible PBAEs), T-cell-specific ligands, mannose, folate. - Payloads: Plasmid DNA, mRNA, siRNA, shRNA, CpG oligodeoxynucleotides, poly(I:C), cyclic dinucleotides (CDNs), immunostimulatory RNA. - Formulations: Nanocomplexes, micro/nanoparticles, microneedle patches, hydrogels, intertwining DNA-RNA nanocapsules (iDR-NCs).

Approach: Narrative literature review covering preclinical in vitro, ex vivo, and in vivo studies. - Immune targets: Antigen-presenting cells (APCs), especially dendritic cells, macrophages, B cells, T cells, myocytes, and tumor cells. - Disease contexts: Infectious disease/HIV, cancer/melanoma, ovarian cancer, breast tumor, murine adenocarcinoma. - Model systems summarized: Mouse skin immunization, tumor challenge models, immunocompetent mouse melanoma model, APC maturation and T-cell activation assays. - Design rigor: No systematic review, meta-analysis, or primary group structure is provided; evidence is synthesized from cited primary studies.

Key methods: The review summarizes methods used in the cited primary studies rather than presenting new methods: - Nanocomplex/nanoparticle formation and characterization. - Cellular uptake and APC internalization. - APC maturation markers and cytokine secretion. - Antigen presentation and antibody responses. - CD4⁺ and CD8⁺ T-cell activation. - RNAi-mediated knockdown of immunosuppressive genes (e.g., PD-L1, STAT3, SOCS1). - In vivo tumor growth, survival, and vaccination challenge outcomes.

Key results: No primary quantitative results are reported; the review summarizes qualitative outcomes from cited studies: - CDN/PBAE nanoparticles promoted APC uptake and significantly reduced tumor growth after intratumoral injection in an immunocompetent mouse melanoma model. - CDN-loaded hydrogels extended CDN release, slowed tumor growth, and drastically improved survival. - iDR-NCs co-delivering CpG ODN, STAT3 shRNA, and antigen trafficked to draining lymph nodes, increased APC maturation, and reduced tumor burden after vaccination. - PD-L1 siRNA/folate-PEI knockdown sensitized ovarian cancer cells to T-cell-mediated killing. - SOCS1 siRNA + ovalbumin in PLGA nanoparticles improved dendritic cell internalization and ovalbumin-specific T-cell activation. - DNA/mannose polymer microneedles elicited a strong antibody response; DNA/poly(I:C)/PBAE microneedles generated strong CD4 and CD8 responses against an HIV antigen. - TNF-α plasmid nanocomplexes and IL-12 plasmid polyphosphazene slowed tumor growth in breast and adenocarcinoma models, respectively.

Interpretation: The authors conclude that polymeric nucleic acid delivery can overexpress or knock down specific genes, act as adjuvants or danger signals, and genetically modify immune cells. Cationic polymers facilitate cellular entry via electrostatic nanocomplexes, while hydrophobic polymers physically entrap nucleic acids. APCs are common targets, and these technologies may lead to new, effective immunoengineering strategies.

Limitations: This is a narrative review, not a systematic review or meta-analysis; no quantitative synthesis or risk-of-bias assessment is provided. - Most cited strategies remain preclinical; clinical translation is limited. - Non-viral transfection efficiency in APCs is generally much lower than viral methods. - Ex vivo dendritic cell manipulation is labor-intensive, costly, and challenging for broad patient application. - DNA vaccines tend to have poor immunogenicity; RNA is chemically unstable; PLGA encapsulation can suffer from poor nucleic acid stability and low encapsulation efficiency without added materials. - Chitosan has poor water solubility at neutral pH and moderate transfection efficacy; PEI is toxic; PAMAM dendrimers face a trade-off between low-molecular-weight efficacy and high-molecular-weight toxicity. - The review is from 2018, so it predates later advances in mRNA vaccines, CRISPR delivery, and newer polymeric systems.