mRNA therapy is an emerging and promising approach that utilizes synthetic mRNA molecules to deliver genes encoding functional proteins or antigens to target cells, tissues, or organs. Compared to conventional gene therapy, mRNA therapy has several advantages, such as high specificity, versatility, safety, and transient expression. mRNA therapy has the potential to treat a wide range of diseases, such as infectious diseases, genetic disorders, and cancer. However, mRNA therapy also faces several challenges and opportunities for its effective and efficient delivery. mRNA molecules are inherently unstable and prone to degradation by nucleases in the extracellular and intracellular environments. mRNA molecules are also highly immunogenic and can trigger innate and adaptive immune responses, which may affect their translation efficiency and safety. Moreover, mRNA molecules have to overcome multiple biological barriers, such as cellular uptake, endosomal escape, cytoplasmic transport, and ribosomal access, to achieve high expression levels and biodistribution. Therefore, the development of suitable delivery strategies for mRNA therapy is crucial and challenging.
Nanoparticles are nanoscale particles that can encapsulate, protect, and deliver mRNA molecules to target cells. Nanoparticles can be made of various materials, such as proteins, lipids, polymers, or hybrids. Nanoparticles can enhance the stability, immunogenicity, translation efficiency, and biodistribution of mRNA by forming complexes with mRNA through electrostatic interactions, shielding mRNA from nuclease degradation and immune recognition, facilitating endosomal escape and cytoplasmic transport, and targeting specific cell types or organs.
Fig.1 Schematic representation of components of lipid nanoparticles (LNPs). (Ramachandran S, 2022.)
The protein-mRNA complex is a simple and effective delivery strategy that uses proteins such as protamine and histones to form complexes with mRNA and protect it from degradation. Protamine is a cationic protein that can bind to mRNA and form compact and stable nanoparticles with a diameter of about 100 nm. Protamine-mRNA nanoparticles can protect mRNA from nuclease degradation and enhance its translation efficiency in vitro and in vivo. Histones are another type of cationic protein that can bind to mRNA and form nanoparticles with a diameter of about 150 nm. Histone-mRNA nanoparticles can also protect mRNA from nuclease degradation and improve its expression in vitro and in vivo. Protein-mRNA complex has the advantages of low toxicity, high biocompatibility, and easy preparation. However, the protein-mRNA complex also has some limitations, such as low loading capacity, high immunogenicity, and poor endosomal escape. Therefore, the protein-mRNA complex may need further optimization and modification to achieve optimal delivery performance.
Besides nanoparticle-based delivery strategies, there are also some other delivery strategies that do not rely on any carrier materials for mRNA delivery. These include naked mRNA injection, physical delivery methods, and ex vivo loading of dendritic cells.
Naked mRNA injection is the simplest and most direct delivery strategy that involves injecting mRNA without any carrier into the muscle or skin. Naked mRNA injection can achieve high expression levels and long-term persistence of mRNA in vivo. Naked mRNA injection has been used to deliver genes encoding for therapeutic proteins such as erythropoietin, factor IX, or antibodies. However, naked mRNA injection also has some drawbacks, such as low stability, high immunogenicity, and limited biodistribution. Moreover, naked mRNA injection requires high doses and frequent administrations to achieve therapeutic effects, which may increase the cost and risk of adverse reactions.
Physical delivery methods are another type of delivery strategy that uses physical forces or devices to enhance the uptake and expression of mRNA in vivo. Physical delivery methods include electroporation, ultrasound, and microneedles. Electroporation is a technique that applies electric pulses to create transient pores in the cell membrane, allowing mRNA to enter the cytoplasm. Electroporation can increase the transfection efficiency and expression level of mRNA in vitro and in vivo. Ultrasound is a technique that uses sound waves to generate mechanical stress and cavitation, which can disrupt the cell membrane and facilitate mRNA delivery. Ultrasound can also improve the penetration and distribution of mRNA in tissues. Microneedles are tiny needles that can pierce the skin and deliver mRNA to the dermal layer, where there are abundant antigen-presenting cells. Microneedles can enhance the immunogenicity and stability of mRNA and induce a robust immune response. Physical delivery methods have the advantages of high efficiency, low toxicity, and easy operation. However, physical delivery methods also have some limitations, such as tissue damage, inflammation, and variability. Furthermore, physical delivery methods may require specialized equipment and expertise, which may limit their accessibility and scalability.
Ex vivo loading of dendritic cells is a delivery strategy that involves loading mRNA into dendritic cells outside the body and then injecting them back to induce an immune response. Dendritic cells are professional antigen-presenting cells that can activate T cells and B cells. Ex vivo loading of dendritic cells can be achieved by using various methods, such as electroporation, lipofection, or microinjection. Ex vivo loading of dendritic cells can deliver mRNA encoding for tumor-associated antigens, cytokines, or immune checkpoint inhibitors and activate anti-tumor immunity. Ex vivo loading of dendritic cells has the advantages of high specificity, low immunogenicity, and easy manipulation. However, ex vivo loading of dendritic cells also has some challenges, such as low efficiency, high cost, and limited availability. Moreover, ex vivo loading of dendritic cells may face regulatory and ethical issues as it involves the manipulation of human cells.
mRNA delivery has a wide range of biomedical applications in various fields, such as functional protein expression, vaccines, cancer immunotherapy, and genome editing.
In conclusion, mRNA delivery is an emerging and promising approach that has the potential to revolutionize the fields of gene therapy and biomedicine. mRNA delivery has shown remarkable achievements and applications in various fields, such as functional protein expression, vaccines, cancer immunotherapy, and genome editing. However, mRNA delivery also faces several challenges and limitations that need to be addressed and overcome for its clinical translation and widespread application. Therefore future research and development of mRNA delivery should focus on improving the safety, efficacy, scalability, and cost of mRNA delivery, as well as exploring novel materials and methods, multifunctional and smart delivery systems, combination and synergistic therapies, and personalized and precision medicine.
Creative Biolabs is a CRO solutions company founded and managed by a team of scientists and experts with extensive knowledge and experience in cell therapy research and development. We can customize specific mRNA delivery vectors and more suitable mRNA delivery system solutions for clients to shorten the development cycle of mRNA delivery systems.
Reference
