Direct Inoculation of DNAs and RNAs
An Overview
The gene delivery methodologies can be divided into four categories. The first one is the simple utilization of naked plasmids, such as circular, covalently closed DNA molecules, or short regulatory nucleic acids, like oligonucleotides, siRNAs, and others. They can be simply injected in vivo or added to the extracellular milieu of cultured cells. Here, this method also means the direct inoculation of DNAs and RNAs. Generally, this in vivo strategy of gene delivery can transfer the foreign gene (up to 20kb) into the skin, cardiac muscle and thymus. Furthermore, it is capable of penetrating the muscle and liver cells directly. The rest of the categories are physical methods, chemical methods, and viral vectors.
Simply Injection
Within some cell types, the process of internalization of extracellular nucleic acids is performed by efficient release into the cytosol, such as striated muscle fibers and cardiomyocytes. Naked nucleic acids (DNA, RNA, and plasmids) can be simply injected into the human skeletal muscles or the heart in vivo. Recently, this method is exploited in some clinical trials and mainly aimed at clinical gene therapies, inducing therapeutic angiogenesis in the ischemic tissues, especially for gene therapy of cardiovascular diseases.
Genetic Vaccination
Besides those cell types described above, the professional antigen-presenting cell (APC) has the striking capacity to internalize plasmid DNA present in the extracellular milieu. These cells, including dendritic cells and B lymphocytes, are very efficient at internalizing foreign antigens. They are sufficient to induce the intracellular synthesis of the proteins encoded by the plasmid, followed by their presentation as antigens to cause an immune response. According to these abilities, researchers use the strategy of genetic vaccination (or DNA vaccination) to directly inoculate DNAs and RNAs.
Figure 1. Mechanism of antigen presentation for generation of cytolytic T cells after DNA vaccination. (Srivastava, 2003)
Advantages of Direct Inoculation of DNAs and RNAs
For direct inoculation of DNAs and RNAs, the main advantage is the simplicity of production and use. This method can infect the host cells as well. Moreover, this type of delivery is safer for both recipients and the environment. The efficiency of direct inoculation of DNAs and RNAs is pretty decent, especially for the muscle cells and for the production of therapeutic proteins, such as insulin and clotting factors. In terms of genetic vaccinations, they are designed against some special diseases and improve treatment efficiency.
Disadvantages of Direct Inoculation of DNAs and RNAs
In general, injecting the DNAs and RNAs directly into the cell is not an easy process. There are several problems should be noticed. The first one is that this way cannot make DNAs and RNAs entry without creating pores in the cell surface. Secondly, it possibly engulfed or destroyed the host cells when injected. These problems indicate that direct inoculation of DNAs and RNAs has low efficiency and may just have a transitory effect. Besides that, direct inoculation of DNAs and RNAs mediated internalization only can be used in specialized cell types, such as skeletal and cardiac myocytes, and antigen-presenting cells. It is not suitable for each cell type in the host.
Reference
- Srivastava, I. K.; Liu, M. A. (2003). Gene Vaccines. Annals of Internal Medicine. 138(7): 550.
