Gene delivery is the introduction of exogenous genes into cells for biomedical purposes, such as gene therapy, vaccination, and regenerative medicine. It can be done by viral or non-viral methods. Viral methods use viruses as vectors, while non-viral methods use physical, chemical, or biological means. Viral methods are efficient, specific, and long-lasting, but they are also immunogenic, toxic, mutagenic, and limited in capacity. Non-viral methods are low in immunogenicity, toxicity, and mutagenesis, but they are also low in efficiency, specificity, and duration. The choice of gene delivery cargo depends on the application and the outcome. Common types of gene delivery cargoes are mRNA and DNA. mRNA and DNA have different characteristics and challenges for gene delivery. For example, mRNA is more stable, transient, immunogenic, and non-integrative than DNA. Therefore, mRNA and DNA delivery require different strategies and optimization.
Non-viral gene delivery methods are based on physical, chemical, or biological means to deliver genes into cells without using viral vectors. Non-viral gene delivery methods have the advantages of low immunogenicity, low toxicity, easy modification, and large cargo capacity, but they also have the disadvantages of low efficiency, low specificity, and transient expression. Non-viral gene delivery methods can be classified into three main categories: microinjection, electroporation, and nanocarrier delivery.
Microinjection is a physical method that uses a micropipette to inject genes directly into the cytoplasm, or nucleus, of a cell. Microinjection is highly efficient and precise, but it is also labor-intensive, time-consuming, and limited by the number and size of cells that can be injected. Microinjection is mainly used for delivering genes into single cells or small groups of cells, such as oocytes, embryos, or stem cells. Microinjection can deliver both mRNA and DNA, but it requires different injection parameters and techniques. For example, mRNA injection requires higher injection pressure and a shorter injection time than DNA injection, and DNA injection requires the use of a piezo-electric device to facilitate nuclear entry.
Electroporation is a physical method that uses electric pulses to create transient pores in the cell membrane, allowing genes to enter the cell. Electroporation is relatively efficient and scalable, but it is also potentially damaging and stressful to the cells. Electroporation can deliver both mRNA and DNA, but it requires different electric parameters and buffers. For example, mRNA electroporation requires a lower voltage and longer pulse duration than DNA electroporation, and mRNA electroporation requires the use of a hypertonic buffer to prevent mRNA degradation.
Nanocarrier delivery is a chemical or biological method that uses nanoparticles to encapsulate and protect genes and to facilitate their cellular uptake and endosomal escape. Nanocarrier delivery is versatile and biocompatible, but it is also complex and challenging to design and optimize. Nanocarrier delivery can deliver both mRNA and DNA, but it requires different nanomaterials and functionalization. For example, mRNA nanocarrier delivery requires the use of cationic or pH-sensitive nanomaterials to enhance mRNA stability and endosomal escape, and DNA nanocarrier delivery requires the incorporation of targeting ligands or stimuli-responsive moieties to improve DNA specificity and expression.
mRNA and DNA are two common types of gene delivery cargoes that have different characteristics and challenges for non-viral gene delivery methods. mRNA and DNA delivery can be compared and contrasted in terms of stability, expression duration, immunogenicity, and integration risk.
Stability refers to the resistance of the gene delivery cargo to degradation by nucleases and other factors in the extracellular and intracellular environment. Stability is important for gene delivery efficiency and expression level. mRNA and DNA have different stability profiles for non-viral gene delivery methods. mRNA is more stable than DNA in the extracellular environments, as it is less susceptible to degradation by serum nucleases and pH changes. However, mRNA is less stable than DNA in the intracellular environment, as it is more susceptible to degradation by cytoplasmic nucleases and endosomes. Therefore, mRNA delivery requires more protection and enhancement of stability than DNA delivery. For example, mRNA delivery can use modified nucleotides, such as pseudouridine and 5-methylcytosine, to increase mRNA stability and reduce immunogenicity. mRNA delivery can also use cationic or pH-sensitive nanocarriers, such as liposomes, polymers, or peptides, to protect mRNA from degradation and facilitate endosomal escape.
Expression duration refers to the length of time that the delivered gene is expressed in the target cells. Expression duration is important for gene delivery outcome and safety. mRNA and DNA have different expression duration profiles for non-viral gene delivery methods. mRNA is more transient than DNA, as it has a shorter half-life and does not integrate into the host genome. mRNA expression typically lasts from hours to days, depending on the mRNA stability, degradation rate, and translation efficiency. DNA is more persistent than mRNA, as it has a longer half-life and can integrate into the host genome. DNA expression can last from days to weeks, or even longer, depending on the DNA stability, integration rate, and transcription efficiency. Therefore, mRNA delivery requires more control and enhancement of expression duration than DNA delivery. For example, mRNA delivery can use self-amplifying mRNA, which encodes a viral replicase that can produce multiple copies of mRNA in the cytoplasm, to increase mRNA expression duration and level. mRNA delivery can also use inducible promoters, such as tetracycline-responsive or heat-shock promoters, to regulate mRNA expression according to external stimuli.
Immunogenicity refers to the ability of the gene delivery cargo to elicit an immune response in the host. Immunogenicity is important for gene delivery safety and efficacy. mRNA and DNA have different immunogenicity profiles for non-viral gene delivery methods. mRNA is more immunogenic than DNA, as it can activate both the innate and adaptive immune systems. mRNA can trigger the innate immune system by binding to pattern recognition receptors, such as toll-like receptors and retinoic acid-inducible gene I, and induce the production of pro-inflammatory cytokines, such as interferons and interleukins. mRNA can also trigger the adaptive immune system by presenting the encoded antigens to the major histocompatibility complex class I and II molecules and activating the cytotoxic T cells and the B cells. DNA is less immunogenic than mRNA, as it can mainly activate the innate immune system. DNA can trigger the innate immune system by binding to cytosolic DNA sensors, such as cyclic GMP-AMP synthase and stimulators of interferon genes and induce the production of type I interferons. DNA can also trigger the adaptive immune system by presenting the encoded antigens to the major histocompatibility complex class II molecules, but not to the class I molecules and activate the helper T cells and the B cells. Therefore, mRNA delivery requires more prevention and reduction of immunogenicity than DNA delivery. For example, mRNA delivery can use modified nucleotides, such as pseudouridine and 5-methylcytosine, to decrease mRNA immunogenicity and increase mRNA translation. mRNA delivery can also use immunomodulatory agents, such as anti-inflammatory drugs or cytokines, to suppress the immune response and enhance the gene delivery outcome.
Integration risk refers to the possibility of the gene delivery cargo to integrate into the host genome and cause unwanted effects, such as insertional mutagenesis, gene silencing, or oncogenesis. Integration risk is important for gene delivery safety and ethics. mRNA and DNA have different integration risk profiles for non-viral gene delivery methods. mRNA is non-integrative, as it does not enter the nucleus and does not have the enzymes or the sequences to integrate into the host genome. mRNA delivery does not pose any integration risk, and it is considered safe and ethical gene delivery method. DNA is integrative, as it can enter the nucleus and integrate into the host genome by non-homologous end joining or homologous recombination. DNA delivery poses a high integration risk, and it can cause serious and irreversible effects on the host cells and the organism. Therefore, DNA delivery requires more control and prevention of integration risk than mRNA delivery. For example, DNA delivery can use episomal vectors, such as plasmids or minicircles, to avoid integration into the host genome and maintain extrachromosomal expression. DNA delivery can also use site-specific integration systems, such as zinc finger nucleases, transcription activator-like effector nucleases, or clustered regularly interspaced short palindromic repeats, to target the integration into safe and specific genomic loci.
Non-viral gene delivery methods have great potential for mRNA and DNA delivery, as they offer low immunogenicity, low toxicity, easy modification, and large cargo capacity, but they also face challenges such as low efficiency, low specificity, and transient expression. mRNA and DNA delivery have different characteristics and challenges for non-viral gene delivery methods, such as stability, expression duration, immunogenicity, and integration risk. mRNA delivery requires more protection and enhancement of stability and expression duration and more prevention and reduction of immunogenicity than DNA delivery. In addition, DNA delivery requires more control and prevention of integration risk than mRNA delivery. mRNA and DNA delivery have different applications and prospects for non-viral gene delivery methods, such as vaccination, gene editing, and tissue engineering. mRNA delivery is more suitable for applications that require transient and high expression, such as vaccination and gene editing, while DNA delivery is more suitable for applications that require persistent and low expression, such as tissue engineering and gene therapy.
