Carrier-free mRNA vaccine induces robust immunity against SARS-CoV-2 in mice and non-human primates without systemic reactogenicity.

Carrier-free naked mRNA vaccines may reduce the reactogenicity associated with delivery carriers; however, their effectiveness against infectious diseases has been suboptimal. To boost efficacy, we targeted the skin layer rich in antigen-presenting cells (APCs) and utilized a jet injector. The jet injection efficiently introduced naked mRNA into skin cells, including APCs in mice. Further analyses indicated that APCs, after taking up antigen mRNA in the skin, migrated to the lymph nodes (LNs) for antigen presentation. Additionally, the jet injection provoked localized lymphocyte infiltration in the skin, serving as a physical adjuvant for vaccination. Without a delivery carrier, our approach confined mRNA distribution to the injection site, preventing systemic mRNA leakage and associated systemic proinflammatory reactions. In mouse vaccination, the naked mRNA jet injection elicited robust antigen-specific antibody production over 6 months, along with germinal center formation in LNs and the induction of both CD4- and CD8-positive T cells. By targeting the SARS-CoV-2 spike protein, this approach provided protection against viral challenge. Furthermore, our approach generated neutralizing antibodies against SARS-CoV-2 in non-human primates at levels comparable to those observed in mice. In conclusion, our approach offers a safe and effective option for mRNA vaccines targeting infectious diseases.

Comb-structured mRNA vaccine tethered with short double-stranded RNA adjuvants maximizes cellular immunity for cancer treatment.

Integrating antigen-encoding mRNA (Messenger RNA) and immunostimulatory adjuvant into a single formulation is a promising approach to potentiating the efficacy of mRNA vaccines. Here, we developed a scheme based on RNA engineering to integrate adjuvancy directly into antigen-encoding mRNA strands without hampering the ability to express antigen proteins. Short double-stranded RNA (dsRNA) was designed to target retinoic acid-inducible gene-I (RIG-I), an innate immune receptor, for effective cancer vaccination and then tethered onto the mRNA strand via hybridization. Tuning the dsRNA structure and microenvironment by changing its length and sequence enabled the determination of the structure of dsRNA-tethered mRNA efficiently stimulating RIG-I. Eventually, the formulation loaded with dsRNA-tethered mRNA of the optimal structure effectively activated mouse and human dendritic cells and drove them to secrete a broad spectrum of proinflammatory cytokines without increasing the secretion of anti-inflammatory cytokines. Notably, the immunostimulating intensity was tunable by modulating the number of dsRNA along the mRNA strand, which prevents excessive immunostimulation. Versatility in the applicable formulation is a practical advantage of the dsRNA-tethered mRNA. Its formulation with three existing systems, i.e., anionic lipoplex, ionizable lipid-based lipid nanoparticles, and polyplex micelles, induced appreciable cellular immunity in the mice model. Of particular interest, dsRNA-tethered mRNA encoding ovalbumin (OVA) formulated in anionic lipoplex used in clinical trials exerted a significant therapeutic effect in the mouse lymphoma (E.G7-OVA) model. In conclusion, the system developed here provides a simple and robust platform to supply the desired intensity of immunostimulation in various formulations of mRNA cancer vaccines.

Enzymatically Transformable Polymersome-Based Nanotherapeutics to Eliminate Minimal Relapsable Cancer.

Prevention of metastatic and local-regional recurrence of cancer after surgery remains difficult. Targeting postsurgical premetastatic niche and microresiduals presents an excellent prospective opportunity but is often challenged by poor therapeutic delivery into minimal residual tumors. Here, an enzymatically transformable polymer-based nanotherapeutic approach is presented that exploits matrix metalloproteinase (MMP) overactivation in tumor-associated tissues to guide the codelivery of colchicine (microtubule-disrupting and anti-inflammatory agent) and marimastat (MMP inhibitor). The dePEGylation of polymersomes catalyzed by MMPs not only exposes the guanidine moiety to improve tissue/cell-targeting/retention to increase bioavailability, but also differentially releases marimastat and colchicine to engage their extracellular (MMPs) and intracellular (microtubules) targets of action, respectively. In primary tumors/overt metastases, the vasculature-specific targeting of nanotherapeutics can function synchronously with the enhanced permeability and retention effect to deter malignant progression of metastatic breast cancer. After the surgical removal of large primary tumors, nanotherapeutic agents are localized in the premetastatic niche and at the site of the postsurgical wound, disrupting the premetastatic microenvironment and eliminating microresiduals, which radically reduces metastatic and local-regional recurrence. The findings suggest that nanotherapeutics can safely widen the therapeutic window to resuscitate colchicine and MMP inhibitors for other inflammatory disorders.

Co-encapsulation of Cas9 mRNA and guide RNA in polyplex micelles enables genome editing in mouse brain.

Genome editing using CRISPR/Cas9 has attracted considerable attention for the treatment of genetic disorders and viral infections. Co-delivery of Cas9 mRNA and single guide (sg)RNA is a promising strategy to efficiently edit the genome of various cell types, including non-dividing cells, with minimal safety concerns. However, co-delivery of two RNA species with significantly different sizes, such as Cas9 mRNA (4.5 kb) and sgRNA (0.1 kb), is still challenging, especially in vivo. Here, we addressed this issue by using a PEGylated polyplex micelle (PM) condensing the RNA in its core. PM loading sgRNA alone released sgRNA at minimal dilution in buffer, while PM loading Cas9 mRNA alone was stable even at higher dilutions. Interestingly, co-encapsulating sgRNA with Cas9 mRNA in a single PM prevented sgRNA release upon dilution, which led to the enhanced tolerability of sgRNA against enzymatic degradation. Subsequently, PM with co-encapsulated RNA widely induced genome editing in parenchymal cells in the mouse brain, including neurons, astrocytes, and microglia, following intraparenchymal injection, at higher efficiency than that by co-delivery of PMs loaded with either Cas9 mRNA or sgRNA separately. To the best of our knowledge, this is the first report demonstrating the utility of RNA-based delivery of CRISPR/Cas9 in inducing genome editing in the brain parenchymal cells. Furthermore, the efficiency of genome editing using PMs was higher than using a non-PEGylated polyplex, due to the enhanced diffusion of PMs in the brain tissue. The results reported herein demonstrate the potential of using PMs to co-encapsulate Cas9 mRNA and sgRNA for in vivo genome editing.

Targeting nanoparticles to the brain by exploiting the blood-brain barrier impermeability to selectively label the brain endothelium.

Current strategies to direct therapy-loaded nanoparticles to the brain rely on functionalizing nanoparticles with ligands which bind target proteins associated with the blood-brain barrier (BBB). However, such strategies have significant brain-specificity limitations, as target proteins are not exclusively expressed at the brain microvasculature. Therefore, novel strategies which exploit alternative characteristics of the BBB are required to overcome nonspecific nanoparticle targeting to the periphery, thereby increasing drug efficacy and reducing detrimental peripheral side effects. Here, we present a simple, yet counterintuitive, brain-targeting strategy which exploits the higher impermeability of the BBB to selectively label the brain endothelium. This is achieved by harnessing the lower endocytic rate of brain endothelial cells (a key feature of the high BBB impermeability) to promote selective retention of free, unconjugated protein-binding ligands on the surface of brain endothelial cells compared to peripheral endothelial cells. Nanoparticles capable of efficiently binding to the displayed ligands (i.e., labeled endothelium) are consequently targeted specifically to the brain microvasculature with minimal "off-target" accumulation in peripheral organs. This approach therefore revolutionizes brain-targeting strategies by implementing a two-step targeting method which exploits the physiology of the BBB to generate the required brain specificity for nanoparticle delivery, paving the way to overcome targeting limitations and achieve clinical translation of neurological therapies. In addition, this work demonstrates that protein targets for brain delivery may be identified based not on differential tissue expression, but on differential endocytic rates between the brain and periphery.

Transient stealth coating of liver sinusoidal wall by anchoring two-armed PEG for retargeting nanomedicines.

A major critical issue in systemically administered nanomedicines is nonspecific clearance by the liver sinusoidal endothelium, causing a substantial decrease in the delivery efficiency of nanomedicines into the target tissues. Here, we addressed this issue by in situ stealth coating of liver sinusoids using linear or two-armed poly(ethylene glycol) (PEG)-conjugated oligo(l-lysine) (OligoLys). PEG-OligoLys selectively attached to liver sinusoids for PEG coating, leaving the endothelium of other tissues uncoated and, thus, accessible to the nanomedicines. Furthermore, OligoLys having a two-armed PEG configuration was ultimately cleared from sinusoidal walls to the bile, while OligoLys with linear PEG persisted in the sinusoidal walls, possibly causing prolonged disturbance of liver physiological functions. Such transient and selective stealth coating of liver sinusoids by two-arm-PEG-OligoLys was effective in preventing the sinusoidal clearance of nonviral and viral gene vectors, representatives of synthetic and nature-derived nanomedicines, respectively, thereby boosting their gene transfection efficiency in the target tissues.

Dual-Sensitive Nanomicelles Enhancing Systemic Delivery of Therapeutically Active Antibodies Specifically into the Brain.

Delivering therapeutic antibodies into the brain across the blood-brain barrier at a therapeutic level is a promising while challenging approach in the treatment of neurological disorders. Here, we present a polymeric nanomicelle (PM) system capable of delivering therapeutically effective levels of 3D6 antibody fragments (3D6-Fab) into the brain parenchyma for inhibiting Aß aggregation. PM assembly was achieved by charge-converting 3D6-Fab through pH-sensitive citraconylation to allow complexation with reductive-sensitive cationic polymers. Brain targeting was achieved by functionalizing the PM surface with glucose molecules to allow interaction with recycling glucose transporter (Glut)-1 proteins. Consequently, 41-fold enhanced 3D6-Fab accumulation in the brain was achieved by using the PM system compared to free 3D6-Fab. Furthermore, therapeutic benefits were obtained by successfully inhibiting Aß1-42 aggregation in Alzheimer's disease mice systemically treated with 3D6-Fab-loaded glucosylated PM. Hence, this nanocarrier system represents a promising method for effectively delivering functional antibody agents into the brain and treating neurological diseases.

Single-Stranded DNA-Packaged Polyplex Micelle as Adeno-Associated-Virus-Inspired Compact Vector to Systemically Target Stroma-Rich Pancreatic Cancer.

Despite the rigidity of double-stranded DNA (dsDNA), its packaging is used to construct nonviral gene carriers due to its availability and the importance of its double-helix to elicit transcription. However, there is an increasing demand for more compact-sized carriers to facilitate tissue penetration, which may be easily fulfilled by using the more flexible single-stranded DNA (ssDNA) as an alternative template. Inspired by the adeno-associated virus (AAV) as a prime example of a transcriptionally active ssDNA system, we considered a methodology that can capture unpaired ssDNA within the polyplex micelle system (PM), an assembly of DNA and poly(ethylene glycol)-b-poly(l-lysine) (PEG-PLys). A micellar assembly retaining unpaired ssDNA was prepared by unpairing linearized pDNA with heat and performing polyion complexation on site with PEG-PLys. The PM thus formed had a compact and spherical shape, which was distinguishable from the rod-shaped PM formed from dsDNA, and still retained its ability to activate gene expression. Furthermore, we demonstrated that its capacity to encapsulate DNA was much higher than AAV, thereby potentially allowing the delivery of a larger variety of protein-encoding DNA. These features permit the ssDNA-loaded PM to easily penetrate the size-restricting stromal barrier after systemic application. Further, they can elicit gene expression in tumor cell nests of an intractable pancreatic cancer mouse model to achieve antitumor effects through suicide gene therapy. Thus, single-stranded DNA-packaged PM is appealing as a potential gene vector to tackle intractable diseases, particularly those with target delivery issues due to size-restriction barriers.

Precise tuning of disulphide crosslinking in mRNA polyplex micelles for optimising extracellular and intracellular nuclease tolerability.

The major issues in messenger (m)RNA delivery are rapid mRNA degradation in the extracellular and intracellular spaces, which decreases the efficiency and duration for protein expression from mRNA. Stabilization of mRNA carriers using environment-responsive crosslinkings has promises to overcome these issues. Herein, we fine-tuned the structure of disulphide crosslinkings, which are selectively cleaved in the intracellular reductive environment, using the mRNA-loaded polyplex micelles (PMs) prepared from poly(ethylene glycol)-poly(L-lysine) (PEG-PLys) block copolymers, particularly by focussing on cationic charge density after the crosslinking. Primary amino groups in PLys segment were partially thiolated in two ways: One is to introduce 3-mercaptopropionyl (MP) groups via amide linkage, resulting in the decreased cationic charge density [PEG-PLys(MP)], and the other is the conversion of amino groups to 1-amidine-3-mercaptopropyl (AMP) groups with preserving cationic charge density [PEG-PLys(AMP)]. Compared to non-crosslinked and PEG-PLys(MP) PMs, PEG-PLys(AMP) PM attained tighter mRNA packaging in the PM core, thereby improving mRNA nuclease tolerability in serum and intracellular spaces, and providing enhanced protein expression in cultured cells at the optimal crosslinking density. These findings highlight the importance of cationic charge preservation in installing crosslinking moieties, providing a rationale for mRNA carrier design in the molecular level.

Effect of shear stress on structure and function of polyplex micelles from poly(ethylene glycol)-poly(l-lysine) block copolymers as systemic gene delivery carrier.

Structural stability of polyplex micelles (PMs), prepared from plasmid DNA (pDNA) and poly(ethylene glycol)-b-poly(l-lysine) block catiomer (PEG-PLys), was evaluated in terms of their resistance against shear stress. When exposed to shear stress at magnitudes typically present in the blood stream, structural deterioration was observed in PMs owing to the partial removal of PEG-PLys strands. Eventually, impaired PEG coverage of the polyplex core led to accelerated degradation by nucleases, implying that structural deterioration by shear stress in blood stream may be a major cause of rapid clearance of PMs from blood circulation. To address this issue, introduction of disulfide crosslinking into the PM core was shown to be an efficient strategy, which successfully mitigated unfavorable effects of shear stress. Furthermore, improved in vivo blood retention profile and subsequently enhanced antitumor efficacy in systemic treatment of pancreatic adenocarcinoma were confirmed for the crosslinked PMs loaded with pDNA encoding an anti-angiogenic protein, suggesting that high stability under the shear stress during blood circulation may be a critical factor in systemically applicable gene delivery systems.

Poly(ethylene glycol) Crowding as Critical Factor To Determine pDNA Packaging Scheme into Polyplex Micelles for Enhanced Gene Expression.

A critical role of polyethylene glycol (PEG) crowding in the packaging of plasmid DNA (pDNA) into polyplex micelles (PMs) was investigated using a series of PEG-b-poly(l-lysine) (PEG-PLys) block copolymers with varying molecular weights of both PEG and PLys segments. Rod-shaped PMs preferentially formed when the tethered PEG chains covering pDNA in a precondensed state were dense enough to overlap one another (reduced tethering density (RTD) > 1), whereas globular PMs were obtained when they were not overlapped (RTD < 1). These results submitted a scheme that steric repulsive effect of PEG regulated packaging pathways of pDNA either through folding into rod-shape or collapsing into globular depending on whether the PEG chains are overlapped or not. The rod-shaped PMs gave significantly higher gene expression efficacies in a cell-free system compared to the globular PMs, demonstrating the practical relevance of regulating packaging structure of pDNA for developing efficient gene delivery systems.

Polyplex micelle installing intracellular self-processing functionalities without free catiomers for safe and efficient systemic gene therapy through tumor vasculature targeting.

Both efficiency and safety profiles are crucial for promotion of gene delivery systems towards practical applications. A promising template system was previously developed based on block catiomer of poly(ethylene glycol) (PEG)-b-poly{N'-[N-(2-aminoethyl)-2-aminoehtyl]aspartamide}-cholesteryl [PEG-PAsp(DET)-cholesteryl] with strategies of ligand conjugation at the α-terminus for specific affinity to the targeted cells and cholesteryl conjugation at the ω-terminus for structural stabilization to obtain systemic retention. Aiming for advocating this formulation towards practical applications, in the current study, the binding profile of this polymer to plasmid DNA (pDNA) was carefully studied to address an issue of toxicity origin. Quantification of free polymer composition confirmed that the toxicity mainly results from unbound polymer and polyplex micelle itself has negligible toxicity. This evaluation allowed for identifying an optimal condition to prepare safe polyplex micelles for systemic application that possess maximal polymer-binding but exclude free polymers. The identified polyplex micelles then faced a drawback of limited transfection efficiency due to the absence of free polymer, which is an acknowledged tendency found in various synthetic gene carriers. Thus, series of functional components was strategically compiled to improve the transfection efficiency such as attachment of cyclic (Arg-Gly-Asp) (cRGD) peptide as a ligand onto the polyplex micelles to facilitate cellular uptake, use of endosome membrane disruptive catiomer of PAsp(DET) for facilitating endosome escape along with use of the conjugated cholesteryl group to amplify the effect of PAsp(DET) on membrane disruption, so as to obtain efficient transfection. The mechanistic investigation respecting the appreciated pH dependent protonation behavior of PAsp(DET) permitted to depict an intriguing scenario how the block catiomers manage to escape from the endosome entrapment in response to the pH gradient. Subsequent systemic application to the pancreatic tumor demonstrated a capability of vascular targeting mediated by the cRGD ligand, which was directly confirmed based on in situ confocal laser scanning microscopy observation. Encouraging this result, the vascular targeting to transfect a secretable anti-angiogenic gene was attempted to treat the intractable pancreatic tumor with anticipation that the strategy could circumvent the intrinsic physiological barriers derived from hypovascular and fibrotic characters. The obtained therapeutic efficiency demonstrates promising utilities of the proposed formulation as a safe systemic gene delivery carrier in practical use.

Rod-to-Globule Transition of pDNA/PEG-Poly(l-Lysine) Polyplex Micelles Induced by a Collapsed Balance Between DNA Rigidity and PEG Crowdedness.

The role of poly(ethylene-glycol) (PEG) in rod-shaped polyplex micelle structures, having a characteristic core of folded plasmid DNA (pDNA) and a shell of tethered PEG chains, is investigated using PEG-detachable polyplex micelles. Rod shapes undergo change to compacted globule shapes by removal of PEG from polyplex micelles prepared from block copolymer with acid-labile linkage between PEG and poly(l-lysine) (PLys) through exposure to acidic milieu. This structural change supports the previous investigation on the rod shapes that PEG shell prevents the DNA structure from being globule shaped as the most favored structure in minimizing surface area. Noteworthy, despite the PEG is continuously depleted, the structural change does not occur in gradual shortening manner but the rod shapes keep their length unchanged and abruptly transform into globule shapes. Analysis of PEG density reveals the transition occurred when tethered PEG of rod shapes has decreased to a critical crowdedness, i.e., discontacted with neighboring PEG, which eventually illuminates another contribution, rigidity of DNA packaged as bundle in the rod shapes, in addition to the steric repulsion of PEG, in sustaining rod shapes. This investigation affirms significant role of PEG and also DNA rigidity as bundle in the formation of rod-shaped structures enduring the quest of compaction of charge-neutralized DNA in the polyplex micelles.

Toroidal Packaging of pDNA into Block Ionomer Micelles Exerting Promoted in Vivo Gene Expression.

Selectively spooling single plasmid DNA (pDNA), as a giant polyelectrolyte, into a nanosized toroidal structure or folding it into a rod-like structure has been accomplished by polyion complexation with block catiomers to form polymeric micelles in varying NaCl concentrations. The interactive potency between the pDNA and block catiomers was determined to play a critical role in defining the ultimate structure of the pDNA; the formation of toroidal or rod-like structures was achieved by complexation in 600 or 0 mM NaCl solutions, respectively. Compared with the rod-like structure, the toroidal structure possessed superior biological functions capable not only of elevating in vitro transcription but also of elevating in vivo gene transduction efficiency. This demonstrated the great utility of the toroidal pDNA packaging as a distinct structured gene carrier. Furthermore, the fact that the NaCl concentration at which the toroidal structure was specifically formed corresponds to seawater stimulates interest in this ordered nanostructure as a possible inherent structure for DNA.

A tadpole-shaped gene carrier with distinct phase segregation in a ternary polymeric micelle.

A distinct tadpole-shaped nanostructure characterized by a spherical head and an extended shaft was identified in a single plasmid DNA (pDNA)-based polymeric micelle. The tadpole-shaped structure was constructed by adding anionic chondroitin sulfate (CS) to the rod-shaped polyplex micelle containing a single pDNA molecule packaged by the PEG-polycation block copolymer through their electrostatic self-assembly. The complex consequently developed a novel structure composed of segregated domains of the CS-rich inflated head and CS-poor folded DNA tail. Hence, this tadpole structure can be regarded as evidence that distinct phase segregation occurred in a single polymeric micelle containing pDNA.

Optimized rod length of polyplex micelles for maximizing transfection efficiency and their performance in systemic gene therapy against stroma-rich pancreatic tumors.

Poly(ethylene glycol) (PEG) modification onto a gene delivery carrier for systemic application results in a trade-off between prolonged blood circulation and promoted transfection because high PEG shielding is advantageous in prolonging blood retention, while it is disadvantageous with regard to obtaining efficient transfection owing to hampered cellular uptake. To tackle this challenging issue, the present investigation focused on the structure of polyplex micelles (PMs) obtained from PEG-poly(l-lysine) (PEG-PLys) block copolymers characterized as rod-shaped structures to seek the most appreciable formulation. Comprehensive investigations conducted with particular focus on stability, PEG crowdedness, and rod length, controlled by varying PLys segment length, clarified the effect of these structural features, with particular emphasis on rod length as a critical parameter in promoting cellular uptake. PMs with rod length regulated below the critical threshold length of 200 nm fully exploited the benefits of cross-linking and the cyclic RGD ligand, consequently, exhibiting remarkable transfection efficiency comparable with that of ExGen 500 and Lipofectamine(®) LTX with PLUS™ even though PMs were PEG shielded. The identified PMs exhibited significant antitumor efficacy in systemic treatment of pancreatic adenocarcinoma, whereas PMs with rod length above 200 nm exhibited negligible antitumor efficacy despite a superior blood circulation property, thereby highlighting the significance of controlling the rod length of PMs to promote gene transduction.

Targeted gene delivery by polyplex micelles with crowded PEG palisade and cRGD moiety for systemic treatment of pancreatic tumors.

Adequate retention in systemic circulation is the preliminary requirement for systemic gene delivery to afford high bioavailability into the targeted site. Polyplex micelle formulated through self-assembly of oppositely-charged poly(ethylene glycol) (PEG)-polycation block copolymer and plasmid DNA has gained tempting perspective upon its advantageous core-shell architecture, where outer hydrophilic PEG shell offers superior stealth behaviors. Aiming to promote these potential characters toward systemic applications, we strategically introduced hydrophobic cholesteryl moiety at the ω-terminus of block copolymer, anticipating to promote not only the stability of polyplex structure but also the tethered PEG crowdedness. Moreover, Mw of PEG in the PEGylated polyplex micelle was elongated up to 20 kDa for expecting further enhancement in PEG crowdedness. Furthermore, cyclic RGD peptide as ligand molecule to integrin receptors was installed at the distal end of PEG in order for facilitating targeted delivery to the tumor site as well as promoting cellular uptake and intracellular trafficking behaviors. Thus constructed cRGD conjugated polyplex micelle with the elevated PEG shielding was challenged to a modeled intractable pancreatic cancer in mice, achieving potent tumor growth suppression by efficient gene expression of antiangiogenic protein (sFlt-1) at the tumor site.

Homo-catiomer integration into PEGylated polyplex micelle from block-catiomer for systemic anti-angiogenic gene therapy for fibrotic pancreatic tumors.

Homo-poly{N'-[N-(2-aminoethyl)-2-aminoehtyl]aspartamide} [PAsp(DET), H] was attempted to integrate into poly (ethylene glycol) (PEG)-b-PAsp(DET)] (B) formulated polyplex micelle with the aim of enhancing cell transfection efficiency for PEGylated polyplex micelle via H integration. In vitro evaluations verified H integration of potent stimulation in enhancing cell-transfecting activity of PEGylated polyplex micelles via promoted cellular uptake and facilitated endosome escape. In vivo anti-angiogenic tumor suppression evaluations validated the feasibility of H integration in promoting gene transfection to the affected cells via systemic administration, where loaded anti-angiogenic gene remarkably expressed in the tumor site, thereby imparting significant inhibitory effect on the growth of vascular endothelial cells, ultimately leading to potent tumor growth suppression. These results demonstrated potency of H integration for enhanced transfection activity and potential usage in systemic applications, which could have important implications on the strategic use of H integration in the non-viral gene carrier design.

Enhanced gene expression promoted by the quantized folding of pDNA within polyplex micelles.

Selective packaging of plasmid DNA (pDNA) into folded rod or collapsed sphere structures in polyplex micelles was demonstrated by modulating the PLys segment length of poly(ethylene glycol)-block- poly(L-lysine) (PEG-PLys) block catiomers used for micelle formation. The two basic packaging structures correlated well to the integrity of double-stranded DNA contained within the micelles. Rod structures formed by the quantized folding mechanism, which results in dissociation of double-stranded DNA only at each fold. Collapsed sphere structures formed by substantial random disruption of the double-stranded DNA structure. Analysis of gene expression in a cell-free transcription/translation system, cultured cells and also skeletal muscle of mice showed that micelles containing pDNA packaged by quantized folding exhibited higher gene expression than naked pDNA and micelles containing collapsed pDNA. These results indicate that controlled packaging of pDNA into an appropriate structure is critical for achieving effective gene expression. Improved gene transfection and expression resulting from the quantized folding of pDNA within polyplex micelles is promising for application in therapeutic gene delivery systems.