Human bodies, such as tumors and hereditary diseases, are often closely related to genetic abnormalities. The idea of introducing normal gene sequence into patients for gene level therapy was put forward long before DNA recombination technology. Edward Tatum and joshua lederberg put forward the idea of using virus as gene transfer vector in 1960s, but it was not until 1990 that gene therapy was successfully used to treat adenosine deaminase deficiency. Up to now, 100 gene therapy schemes have been reported. More than 300 patients have received this new treatment. The object of gene therapy is no longer limited to genetic diseases, but has been extended to many diseases such as tumors and infectious diseases. Its development is quite rapid and its prospects are very promising. Scholars in China have also done some work in treating hemophilia with gene therapy. At present, we have accumulated some experiences and lessons, and have some operational procedures to follow and alternative treatment methods. However, there are still many aspects to be improved and perfected in this new treatment.

Concept and strategy of gene therapy;

Gene therapy is a therapeutic method to correct or replace pathogenic genes with normal or wild-type genes. In this treatment method, the target genes are introduced into the target cells, and they are either integrated with the chromosomes of the host cells to become a part of the host genetic material, or they are located outside the chromosomes without integration with the chromosomes, but they can all be expressed in the cells, thus playing a role in treating diseases.

At present, the concept of gene therapy has been greatly expanded, and any disease treatment method at the nucleic acid level by using the methods and principles of molecular biology can be called gene therapy. With the deepening understanding of the nature of diseases and the emergence of new molecular biological methods, gene therapy has made great progress. According to the different methods adopted, the strategies of gene therapy can be roughly divided into the following categories:

1. gene replacement: gene replacement is to replace the pathogenic gene in the diseased cell with the normal gene in situ, so that the DNA in the cell can be completely restored to normal state. This treatment is the most ideal, but it is still difficult to achieve due to technical reasons.

2. Gene modification: Gene modification refers to modifying the mutated base sequence of the disease-causing gene while retaining the normal part. In the end, this gene therapy can completely restore the pathogenic gene, which requires high operation and is difficult to practice.

3. Gene modification, also known as gene addition, is to introduce the target gene into diseased cells or other cells, and the expression product of the target gene can modify the function of defective cells or strengthen some original functions. In this treatment method, the defective gene still exists in the cell, and this method is commonly used in gene therapy at present. For example, after the gene of tissue plasminogen activator is introduced into vascular endothelial cells and expressed, the formation of blood test induced by percutaneous coronary angioplasty can be prevented.

4. Gene inactivation: Antisense technology can specifically block gene expression characteristics and inhibit the expression of some harmful genes, thus achieving the purpose of treating diseases. For example, antisense RNA, ribozyme or peptide nucleic acid can inhibit the expression of some oncogenes, inhibit the proliferation of tumor cells and induce the differentiation of tumor cells. This technique can also block the expression of drug-resistant genes in tumor cells and increase the effect of chemotherapy.

5. Immunoregulation: The gene of antibody, antigen or cytokine is introduced into the patient's body to change the patient's immune state and achieve the purpose of preventing and treating diseases. For example, the introduction of interleukin -2 into tumor patients can improve the level of IL-2 in patients and activate the anti-tumor activity of immune system in vivo, thus achieving the purpose of preventing tumor recurrence.

6. Others: increase the sensitivity of tumor cells to radiotherapy or chemotherapy: reduce the damage of chemotherapy drugs to normal cells by giving prodrug. For example, herpes simplex virus thymidine kinase gene is introduced into tumor cells, and then non-toxic GCV drugs are given to patients, because only cells containing HSV-TK gene can convert CGV into toxic drugs. Therefore, tumor cells are killed without affecting normal cells.

In a word, there are many strategies of gene therapy, and different methods have their own advantages and disadvantages in practice. Gene therapy itself is not limited to the treatment of genetic diseases, but has now been extended to tumors, viral diseases and so on. Gene therapy can be used to treat and prevent diseases. It should be pointed out that gene therapy is not a panacea, nor can it replace the existing treatment methods. As a new method, there are still some places that need to be further improved. In practice, we should combine each other and learn from each other's strengths to achieve better therapeutic effects.