15.10
Gene Therapy
Gene therapy is a technique where a gene is inserted into a person’s cells to prevent or treat a serious disease. The added gene may be a healthy vers…
Gene therapy is the introduction of a gene into a patient’s cells to treat or prevent a disease caused by a mutated gene.
The introduced gene may be a functional copy of the mutated gene, or it may be a different gene that helps counter the effects of the mutation.
The therapeutic gene can be delivered directly into the patient’s body through in vivo therapy.
Alternatively, ex vivo therapy involves removing cells from the patient, genetically modifying them in the laboratory, and then transplanting them back into the patient.
The therapeutic gene is delivered using a vector. This vector is most commonly a genetically modified virus that enters the target cell and delivers the therapeutic gene for expression.
Some vectors integrate the therapeutic gene into the cell’s genome, allowing long-term expression of the introduced gene.
Other vectors keep the therapeutic gene outside the chromosomes as episomal DNA, which can remain active without integrating into the genome.
The vectors also contain promoter regions that enable transcription of the introduced gene into messenger RNA.
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Q1: What is the main purpose of gene therapy?
Gene therapy inserts a healthy gene into a patient's cells to prevent or treat serious diseases. The inserted gene may replace a mutated gene or counteract the effects of a faulty one. For example, in severe combined immunodeficiency (SCID), a functioning copy of the adenosine deaminase gene can be inserted, allowing patients' cells to produce the missing enzyme and potentially curing the disease.
Q2: How are genes delivered into patient cells during gene therapy?
Genes are delivered using vectors, typically modified viruses engineered to enter cells without causing disease. The vector carries the gene to the cell nucleus, where it may integrate into the genome or remain outside the chromosome. The vector also contains a promoter region enabling the gene to be transcribed into messenger RNA and translated into therapeutic protein.
Q3: What is the difference between in vivo and ex vivo gene therapy?
In vivo gene therapy delivers genes directly into a patient's body through injection into specific tissues or the bloodstream. Ex vivo gene therapy removes cells from the patient, inserts the gene into those cells outside the body, and then transplants the modified cells back. Both approaches aim to introduce therapeutic genes, but differ in where the genetic modification occurs.
Q4: Why do some gene therapy vectors integrate into the genome while others don't?
Different vector types have different integration capabilities. Retroviral vectors randomly insert genes into the patient's genome, providing stable, long-term expression of the inserted gene. Adenoviral vectors do not integrate into the host genome and produce only transient expression. The choice depends on whether permanent or temporary gene expression is therapeutically desired.
Q5: What are the main risks associated with gene therapy?
Gene therapy carries significant risks because the integration and activity of inserted genes cannot be fully controlled. Early clinical trials for SCID resulted in some patients developing cancer, leading to trial halts. However, for serious diseases with no other effective treatment options, the potential benefits can outweigh the risks, and the technology continues to improve.
Q6: Which diseases have shown successful outcomes with gene therapy?
Gene therapy has demonstrated success in treating severe combined immunodeficiency (SCID), certain types of inherited blindness, and treatment-resistant B-cell leukemia. In SCID cases, inserting a functional adenosine deaminase gene has cured the disease in some patients. These successes demonstrate the therapeutic potential of gene therapy for previously untreatable genetic disorders.
Q7: How does the inserted gene produce a therapeutic effect in patient cells?
After the vector delivers the gene to the cell nucleus, the promoter region enables transcription into messenger RNA. The cell's own machinery then translates this mRNA into functional protein. This protein product, such as adenosine deaminase, provides the therapeutic treatment by restoring the missing or defective protein function in the patient's cells.