Summary of Genome Engineering
Genome Engineering Explained: Concepts, Applications & Ethics
Introduction
Gene therapy is a medical approach that aims to treat or prevent disease by introducing, modifying, or replacing genetic material in a patient’s cells. This material focuses on somatic gene therapy: clinical approaches, delivery methods, successes, risks, costs, and the ethical issues around heritable (germ line) interventions.
Definition: Somatic gene therapy is the therapeutic modification of a patient’s non-reproductive cells so that the treatment affects only the treated individual and is not inherited by offspring.
Two main clinical approaches
Clinical somatic gene therapy generally follows two fundamentally different strategies: in vivo delivery and ex vivo cell modification.
In vivo approach
- The therapeutic genetic construct is delivered directly into the patient’s organ or bloodstream.
- Delivery vectors can be viral (e.g., certain adenoviruses, adeno-associated viruses) or non-viral carriers.
- Advantages:
- Can target tissues that are difficult to remove and culture.
- Suitable for treatments that require direct organ access (e.g., some retinal therapies).
- Challenges and risks:
- Efficiently transporting the therapeutic construct into target cells is difficult.
- Some viral vectors give only transient expression (useful for short-term goals like cancer immunotherapy). Other vectors integrate into the genome and can produce permanent effects but raise insertional mutagenesis risk.
- Side effects may include strong immune reactions, oncogenesis (cancer risk), and toxicity from non-viral vectors.
Ex vivo approach
- Patient cells are removed, expanded and genetically modified in the laboratory, tested for successful modification, and then reintroduced into the patient.
- Advantages:
- Allows verification of genetic change before return to patient.
- Avoids exposing the patient directly to vectors during the modification step.
- Particularly useful for blood-cell-based therapies (e.g., T cell or hematopoietic stem cell treatments).
- Limitations:
- Requires cells that can be removed, cultured, and reinfused.
- May not be applicable for many solid organs where cell harvesting and reinfusion are infeasible.
Definition: Ex vivo gene therapy is the process of modifying patient-derived cells outside the body, validating the modification, and returning the corrected cells to the patient.
Clinical progress and approved applications
- By the end of 2018, about 3,000 clinical studies on somatic gene therapy had been approved worldwide, targeting monogenic diseases, infectious diseases, cardiovascular conditions, and many cancers.
- Several gene therapy drugs have been approved and launched for different cancers; since 2015 the European Union approved nine distinct somatic gene therapy drugs.
- Two major application areas:
- Monogenic disorders (single-gene diseases): cystic fibrosis and several severe immunodeficiencies have been leading targets.
- Cancer: about two-thirds of human gene therapy trials approved in 2017 targeted tumors; immunotherapies and cell-based therapies are prominent.
Somatic therapy for monogenic diseases
- Monogenic diseases are prime candidates for somatic therapy because a single gene is responsible for the disorder.
- Example: Cystic fibrosis (CF)
- Symptoms include chronic cough, breathlessness, frequent lung infections, pancreatic malfunction, malnutrition risk, liver cirrhosis tendency, gallstones and osteoporosis.
- CF is caused by mutations in one specific gene; targeted interventions can correct or compensate for the defective gene product.
- New molecular tools have improved prospects for treating monogenic diseases.
Definition: Monogenic disease is a disorder caused primarily by mutations in a single gene.
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Gene Therapy Overview
Klíčové pojmy: Somatic gene therapy targets non-reproductive cells so effects are limited to the treated individual., Two clinical approaches: in vivo (direct delivery) and ex vivo (cells modified outside the body)., In vivo delivery risks include immune reactions, insertional mutagenesis, and vector toxicity., Ex vivo allows verification of genetic modification before reintroduction and avoids exposing patients to vectors., Monogenic diseases (e.g., cystic fibrosis) are prime candidates for somatic therapies., Historic trials showed both transient benefits and serious adverse events (e.g., vector-induced leukemia)., High costs of gene therapies drive novel payment models such as pay-for-success and pooled funds., Germ line interventions produce heritable changes and are ethically and legally restricted in many jurisdictions., Recent germ line experiments show feasibility but low efficiency and significant unintended changes., Two-thirds of 2017-approved gene therapy trials targeted cancer, reflecting intensive oncology research.