Gene Therapy-Gene Therapy

Many diseases, such as genetic disorders and tumors, have a close causal relationship with genetic abnormalities in the human body. The idea of introducing normal gene sequences into patients for gene level therapy has been proposed even before DNA recombination technology. Edward Tatum and Joshua Lederberg proposed the use of viruses as gene transfer vectors in the early 1960s. It was not until 1990 that gene therapy was successfully attempted to treat adenosine deaminase deficiency.

So far, there have been over a hundred reported gene therapy options. More than 300 patients have received this new treatment method. The target of gene therapy is no longer limited to genetic diseases, but has been expanded to various diseases such as tumors and infectious diseases. Its development is quite rapid and its prospects are very promising. Chinese scholars have also done some work in using gene therapy to treat hemophilia. At present, we have accumulated certain experience and lessons, and have some operational procedures and treatment options to follow. But there are still many aspects of this new treatment that need to be continuously improved and enhanced.

1.The concept and strategy of gene therapy

Gene therapy is a treatment method that uses normal or wild type genes to correct or replace pathogenic genes. In this treatment method, the target genes are introduced into the target cells, and they either integrate with the host cell chromosome to become part of the host genetic material, or are located outside the chromosome without integration, but can be expressed in the cell to treat the disease.

At present, the concept of gene therapy has been greatly expanded. Any disease treatment method that adopts molecular biology methods and principles and is carried out at the nucleic acid level can be called gene therapy. With a deeper understanding of the nature of diseases and the continuous emergence of new molecular biology methods, gene therapy has made significant progress. According to the different methods used, gene therapy strategies can be roughly divided into the following categories:

Gene replacement: Gene replacement is the process of replacing the pathogenic gene in a diseased cell with a normal gene in situ, allowing the DNA inside the cell to fully return to its normal state. This treatment method is the most ideal, but it is currently difficult to achieve due to technical reasons.

　　Gene correction:Gene repair refers to correcting the mutated base sequence of a disease causing gene while preserving the normal part. This gene therapy method can ultimately achieve complete recovery of pathogenic genes, with high operational requirements and certain difficulties in practice.

　　Gene augmentation(Also known as gene supplementation):Introducing the target gene into diseased cells or other cells, the expression product of the target gene can modify the function of defective cells or enhance certain existing functions. In this treatment method, defective genes still exist inside the cells, and currently gene therapy mostly uses this approach. If the gene of tissue type plasminogen activator is introduced into endothelial cells and expressed, it can prevent the formation of blood tests induced by percutaneous coronary angioplasty.

　　Gene inactivation:The use of antisense technology can specifically block gene expression characteristics and inhibit the expression of some harmful genes, achieving the goal of treating diseases. Using antisense RNA, nucleases, or peptide nucleic acids to inhibit the expression of certain oncogenes, suppress tumor cell proliferation, and induce tumor cell differentiation. This technology can also block the expression of drug resistance genes in tumor cells, increasing the effectiveness of chemotherapy.

　　Immune adjustment:Introducing genes of antibodies, antigens, or cytokines into the body of a patient to alter their immune status and achieve the goal of preventing and treating diseases. If interleukin-2 is introduced into the body of tumor patients to increase the level of IL-2 and activate the anti-tumor activity of the immune system, the goal of preventing and treating tumor recurrence can be achieved.

Other: Increase the sensitivity of tumor cells to radiotherapy or chemotherapy: Reduce the damage of chemotherapy drugs to normal cells by administering precursor drugs. If the herpes simplex virus thymidine kinase gene is introduced into tumor cells and then non-toxic GCV drugs are given to patients, only cells containing the HSV-TK gene can convert CGV into toxic drugs. Therefore, tumor cells are killed without affecting normal cells.

In short, there are many strategies for gene therapy, and each method has its own advantages and disadvantages in practice. And gene therapy itself is not limited to the treatment of genetic diseases, it has now been extended to tumors, viral diseases, and so on. Gene therapy can be used for the treatment and prevention of diseases. It should be pointed out that gene therapy is not omnipotent and cannot replace existing treatment methods. As a new method, there are still some areas that need further improvement. In practice, it should be combined with each other, complement each other's strengths and weaknesses, in order to achieve better therapeutic effects.

2.The basic procedure of gene therapy

(I) Selection and preparation of target genes　

The primary issue in gene therapy is selecting the target genes for treating diseases. For genetic diseases, as long as it has been studied that the occurrence of a certain disease is caused by an abnormality in a certain gene, its wild-type gene can be used for gene therapy, such as ADA gene therapy for ADA deficiency diseases. But under current conditions, this alone is not enough. The genes that can be used for gene therapy need to meet the following requirements: only a small amount of expression in the body can significantly improve symptoms; Overexpression of this gene will not cause harm to the body. Obviously, some hormone genes, such as insulin gene related to blood glucose concentration, cannot be used for gene therapy of diabetes at present. In antiviral and pathogen gene therapy. The selected target gene should play an important role in the life history of viruses and pathogens, and the sequence should be specific, such as the HBeAg or X gene targeting HBV.

Tumor patients often have immune deficiencies, and immune factor genes can be transferred into the human body. There are often multiple abnormal forms of genes in tumor cells, and antisense technology can be used to block activated oncogenes or transfer wild-type tumor suppressor genes into cells to inhibit tumor growth. The targeted oncogene or tumor suppressor gene should have a clear correlation with the occurrence and development of the tumor. After determining the target gene, prepare the target gene. The positively expressed genes can be cDNA (complementary DNA) or genomic DNA fragments. It can be obtained using traditional methods, or new technologies such as polymerase chain reaction PCR can be used for in vitro amplification. Partial antisense genes can also be obtained using this method, but in most cases, they are synthesized artificially.

(II)Gene transport

There are currently multiple ways of gene transport, and the basic principle is to transport exogenous genes into cells. There are two main types of vectors that have been used: viral vectors and non viral vectors. Virus vector: Viruses have some unique properties, such as being able to infect specific cells and being difficult to degrade within cells;

RNA viruses can integrate into chromosomes and at a higher genetic level. Therefore, viral vectors are excellent gene transport carriers. The viruses currently used as vectors include retroviruses, adenoviruses, and adeno-associated viruses. Herpes virus and hepatitis virus, etc. When retroviruses are used as vectors, several modifications are required:

(1) Transform natural wild-type RNA pre viruses into DNA vectors and insert relevant exogenous genes for transfer. The basic principle is to replace the coding genes of the virus with marker genes and exogenous genes, as shown in Figure 1.

(2) Prepare auxiliary cells to provide the lost function of the carrier DNA, as shown in Figure 2.

(3) Importing vector DNA into auxiliary to generate viral vectors. As shown in Figure 3.

(4) Virus vectors infect target cells, and exogenous genes are expressed inside the cells, as shown in Figure 4.

next item: The Current Status and Prospects of Gene Therapy

About Sunma

Product Center

Technical Data

News Center

Gene Therapy-Gene Therapy

Gene Therapy-Gene Therapy