Introduction to Gene Therapy 

Gene therapy involves inserting genes into a human’s cells to treat diseases. Advancing sciences in gene transfer during the 1970s and 1980s led to the first clinical trial in gene therapy in 1988. Since then, over 3000 patients have undergone gene therapy treatment. Despite many unsuccessful outcomes and significant controversy, gene therapy remains one of the most promising medical research fields for treating and curing malignant diseases.¹

Types of Gene Therapy

The two types of gene therapy include somatic gene therapy and germline gene therapy. Somatic gene therapy is used on adult cells and does not affect the offspring of the patient, and germline gene therapy targets egg and sperm cells.⁴

Methods of gene delivery: Somatic Gene Therapy  

Delivering genetic material into somatic human cells can be done through two approaches: in vivo and ex vivo. The in vivo method (Figure 1) is the delivery of genetic material directly into the target tissue. The inserted DNA will allow therapeutic genes to be expressed.¹

                                                   Figure 1. In vivo gene transfer.

The ex vivo method (Figure 2) involves transferring a therapeutic gene to cells in a culture (in vitro) and then injecting these resulting cells into the target tissue, where the cells can express the therapeutic gene.¹

                                                 Figure 2. Ex vivo gene transfer.

Methods of gene delivery: Germline Gene Therapy

There are also two methods of germline gene therapy. Before fertilization, the genetic makeup of reproductive cells can be altered. The other method involves altering the blastomere at an early developmental stage and the cells continue to divide. In both cases, the mutations are hopefully passed on to future generations. As a result of underdeveloped techniques, lack of necessary information, and increased debate and ethical issues, germline gene therapy is not currently used in humans.⁵

Diseases

Gene therapy can be used to treat genetic disorders, such as severe combined immunodeficiency, as well as some other incurable diseases.² Those diseases that are caused by only one defective gene were preliminary targets for gene therapy. Cistic fibrosis, muscular dystrophy, Alzheimer’s disease, sickle cell anemia and various types of cancer, including cancer of the lungs, ovaries, breast, head, and neck, are currently being treated using clinical trials of gene therapy.^1,3

Limitations and Risks

Currently, gene therapy can only target non-reproductive cells and the introduced treatment cannot continue to the next generation cells, resulting in a lack of long term expression. In addition, current technology does not provide for efficient gene transfer and genetically modified viruses are inefficient at transferring DNA to specific human cells. Finally, for treatment involving long-term expression, the therapeutic gene must be able to turn “on” and “off,” and this controlled gene expression remains an issue. As a result of these safety risks, multiple clinical trials have ended in death and severe complications, leading to increased doubt amongst scientists and serious public concerns.^1

Legislation regarding gene therapy is different depending on the country and state. In some areas, gene therapy can only be used to treat certain diseases, usually those that can only be cured using this method of treatment. Some countries have strict regulations on research that require committees and organizations to monitor research efforts.⁴

Ethics and morals play a major role in opinions regarding gene therapy, where germline gene therapy, which involves reproductive cells that affect future generations, proves to arouse more concern than somatic gene therapy, which only affects body cells.⁴

Future Outlook and Benefits

Despite harmful outcomes and negative outlooks, gene therapy still remains a widely researched field in medicine with potential prospects. Currently incurable diseases affecting humans can be treated using this technology, leading to an increase in gene therapy practices in the next decade. While there is still a great deal of work to be done to fully understand the strategies involved in gene therapy, there are high hopes for the future of this therapeutic intervention.¹

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