Gene Therapy Basics Quiz

Questions and Answers

What was the purpose of the first gene therapy trial conducted by Michael Blaese in 1990?

To provide relief to patients with chronic pain.

To treat severe combined immunodeficiency (SCID) in a child. (correct)

To cure hereditary diabetes in children.

To enhance the immune system in healthy individuals.

Which gene therapy delivery mechanism allows cells to be genetically modified outside the body before reintroducing them?

Somatic cell therapy

Ex vivo (correct)

In vivo

Germ-line therapy

What is the main characteristic of germ-line gene therapy?

It only affects the patient without passing on changes.

It is the preferred method for treating acute illnesses.

It allows modifications that are transmissible and permanent. (correct)

It modifies somatic cells within a specific tissue.

Why is the ex vivo approach preferred for gene therapy targeting circulating blood cells?

The conditions can be more tightly controlled during modification. Signup and view all the answers

Which of the following correctly defines somatic cell gene therapy?

It consists of modifying tissues that do not pass changes to offspring. Signup and view all the answers

What is the main limitation of germ-line gene therapy as of now?

It has not been successfully performed in humans. Signup and view all the answers

Which of the following accurately describes the condition of patients with SCID before treatment?

They relied on living in a sterile environment to avoid infections. Signup and view all the answers

Which of the following mechanisms is NOT typically used in gene therapy?

Transplantation of whole organs Signup and view all the answers

What is the main risk associated with using viral vectors in gene therapy?

Adverse immune response Signup and view all the answers

What type of diseases can gene therapy particularly address in young children?

Severe combined immunodeficiency Signup and view all the answers

Which genetic defect prevents the formation of T-lymphocytes in SCID patients?

Defect in adenosine deaminase gene Signup and view all the answers

What can result from insertional mutagenesis during gene therapy?

Malignant neoplasia Signup and view all the answers

What is the consequence of overexpression of inserted genes in gene therapy?

Excessive protein production Signup and view all the answers

What was the primary cause of leukemia in the patients involved in the clinical trial?

Integration of retroviral DNA near an oncogene Signup and view all the answers

What structural advantage do liposomes provide for gene therapy?

Direct fusion to target cells Signup and view all the answers

Which gene therapy-associated risk involves the potential for disrupting essential genes?

Insertional inactivation Signup and view all the answers

What was identified as a serious biohazard during the gene therapy clinical trial for SCID?

Insertional mutagenesis causing leukemia Signup and view all the answers

What prompted the transient moratorium on gene therapy trials in various countries?

Health risks associated with insertional mutagenesis Signup and view all the answers

Why are viral vectors utilized in cancer treatments?

Desire for immune re-establishment Signup and view all the answers

How can mutations in the RAG1 and RAG2 genes affect SCID patients?

Prevent VDJ recombination Signup and view all the answers

What change was made in the new clinical trial for SCID-X after previous complications?

Switch to a different type of retroviral vector Signup and view all the answers

What is the primary purpose of gene augmentation therapy?

To add a normal copy of a gene to complement the mutated one. Signup and view all the answers

What is a potential consequence when viruses infect surrounding healthy tissues during gene therapy?

Reduced vector capability Signup and view all the answers

What therapeutic options remain available for parents of ADA deficiency patients?

Either gene therapy or bone marrow transplantation Signup and view all the answers

Which type of mutation is primarily targeted by gene replacement therapy?

Loss-of-function mutations. Signup and view all the answers

What advantage do adenovirus vectors have over retrovirus vectors in gene therapy?

Adenoviruses have a higher insert capacity. Signup and view all the answers

Which method utilizes antisense oligonucleotides to inhibit gene expression?

Targeted inhibition of gene expression. Signup and view all the answers

Why are lentivirus vectors particularly advantageous in gene therapy?

They can transduce non-dividing cells. Signup and view all the answers

What significant risk is associated with using retroviral vectors in gene therapy?

Insertional mutagenesis. Signup and view all the answers

What is a common challenge in using CRISPR CAS technology in clinical applications?

Potential off-target effects. Signup and view all the answers

What is the role of a foreign antigen gene in targeted killing of specific cells?

It marks disease cells for destruction. Signup and view all the answers

Which statement best describes the use of plasmid vectors in gene therapy?

They are non-viral vectors used primarily as naked DNA. Signup and view all the answers

In which scenario is pre-existing immunity to adenoviruses considered an advantage?

When enhancing the immune response against tumors. Signup and view all the answers

What is the primary purpose of gene therapy for ADA deficiency?

To replace the defective ADA gene with a normal copy Signup and view all the answers

What was a significant limitation observed in the first trial of ADA gene therapy?

Insufficient selective advantage for transduced cells Signup and view all the answers

What approach was taken in the second trial of ADA gene therapy conducted in 2002?

Only gene therapy without oral enzymatic replacement Signup and view all the answers

What condition is associated with SCID-X as discussed in the document?

Deficiency in the common γchain resulting in T-cell unresponsiveness Signup and view all the answers

What was a prerequisite for patients to be eligible for the SCID-X clinical trial?

They must have a reliable molecular diagnosis of SCID-X Signup and view all the answers

What significant finding was documented about patients in the SCID-X trial?

Mature T-cells were identified in normal peripheral blood for over 5 years Signup and view all the answers

What potential negative effect was reported in the SCID-X gene therapy study?

Development of leukemia in some patients after treatment Signup and view all the answers

What is a key factor for the effectiveness of gene therapy in SCID-X patients?

A high proliferative advantage of transduced T-cells Signup and view all the answers

Which of the following treatment options was NOT initially favored for ADA deficiency patients?

Stem cell transfusion from unrelated donors Signup and view all the answers

In the context of gene therapy for SCID-X, what does the term 'retro mutation' refer to?

A spontaneous reversion to the normal sequence in a T-cell Signup and view all the answers

What is the primary distinction between gene augmentation and gene replacement strategies in gene therapy?

Gene augmentation introduces a normal copy of a gene alongside the mutated one, while gene replacement involves replacing the mutated gene entirely with a new one. Signup and view all the answers

How does the mechanism of targeted inhibition of gene expression differ from gene augmentation therapy?

Targeted inhibition uses methods like siRNA or antisense oligonucleotides to block the expression of a pathogenic gene, whereas gene augmentation adds a functional copy of the gene. Signup and view all the answers

What role do viral vectors play in gene therapy, and what is a significant risk associated with their use?

Viral vectors are designed to deliver therapeutic genes into patient cells, but they carry a risk of insertional mutagenesis, which can disrupt essential genes. Signup and view all the answers

What advantages do adeno-associated viruses offer over retroviruses in gene therapy applications?

Adeno-associated viruses can transduce both dividing and non-dividing cells and have a lower likelihood of eliciting a strong immune response compared to retroviruses. Signup and view all the answers

How does the use of lentiviral vectors aid in targeting treatments for non-dividing cells?

Lentiviral vectors can integrate into the genome of non-dividing cells, allowing for stable gene expression necessary for addressing chronic conditions. Signup and view all the answers

Describe the main difference between in vivo and ex vivo gene therapy delivery methods.

In vivo gene therapy delivers genetic material directly into cells within a patient, while ex vivo involves removing cells, modifying them in vitro, and then reintroducing them to the patient. Signup and view all the answers

What is the key characteristic of somatic cell gene therapy compared to germ-line gene therapy?

Somatic cell gene therapy modifies non-reproductive cells, making the changes limited to the individual, while germ-line therapy would result in hereditary changes in gametes. Signup and view all the answers

Explain the significance of targeted killing of specific cells in gene therapy.

Targeted killing of specific cells aims to eliminate cells that contribute to disease while sparing healthy cells, thus reducing side effects and improving treatment efficacy. Signup and view all the answers

What challenges does gene therapy face regarding the use of viral vectors?

The use of viral vectors in gene therapy poses risks such as potential immune responses and insertional mutagenesis, which can disrupt essential genes and lead to oncogenesis. Signup and view all the answers

What are the potential long-term effects of gene therapy for patients treated for severe combined immunodeficiency (SCID)?

Long-term effects may include the sustained correction of the immune deficiency and potential risks of developing complications like leukemia from insertional mutagenesis. Signup and view all the answers

What is the primary limitation of using herpes simplex viruses as vectors in gene therapy?

Their low information capacity of only 4.0 kilobases restricts the amount of genetic information they can carry. Signup and view all the answers

Explain the reason why adverse responses to viral vectors can hinder gene therapy success.

If the immune system attacks the viral vector, the gene therapy cannot succeed as the vector is rendered ineffective. Signup and view all the answers

What impact does a mutation in the common γchain gene have on T-cell maturation?

It impairs the response to multiple cytokines, affecting the overall maturation and function of T-lymphocytes. Signup and view all the answers

Describe the role of RAG1 and RAG2 genes in T-cell development.

They are essential for VDJ recombination, which is crucial for the formation of functional T-cell receptors. Signup and view all the answers

What is insertional mutagenesis and how can it affect gene therapy outcomes?

Insertional mutagenesis occurs when a vector integrates into the host genome, potentially activating oncogenes or inactivating essential genes. Signup and view all the answers

How do liposomes facilitate gene transfer into target cells?

Liposomes fuse directly with target cells due to their lipid bilayer, releasing DNA or RNA into the cells. Signup and view all the answers

What critical challenge is associated with the overexpression of inserted genes in gene therapy?

Overexpression can lead to excessive protein production, which may be harmful to the patient. Signup and view all the answers

Identify a possible risk factor when using adenoviral vectors in gene therapy.

Adenoviral vectors may elicit a strong immune response, compromising the therapy's success. Signup and view all the answers

What are the implications of using naked DNA in gene therapy?

Naked DNA can be used for direct gene delivery but often lacks the efficiency seen with viral vectors. Signup and view all the answers

Why is gene therapy a critical option for treating severe combined immunodeficiency (SCID)?

Gene therapy offers an alternative treatment for SCID patients who have limited options for bone marrow transplants. Signup and view all the answers

Study Notes

Overview of Gene Therapy

Gene therapy began in clinical trials during the 1990s, representing an innovative method for treating monogenic disorders.
The first gene therapy approach was applied by Michael Blaese in 1990 on a child with Severe Combined Immunodeficiency (SCID).

Gene Therapy Definition

Involves modifying cells to treat or alleviate diseases through genetic modification.
Two primary delivery methods: in vivo (direct cell treatment) and ex vivo (cells modified outside the body before transplantation).

Types of Gene Therapy

Germ-line Gene Therapy: Modifies gametes or embryos; changes are heritable. No examples in humans yet.
Somatic Gene Therapy: Modifies non-germline cells; changes are not inherited, targeting specific diseases.

Mechanisms of Genetic Modification

Gene Augmentation: Addition of a normal gene to counteract a defective gene, effective in loss-of-function mutations.
Gene Replacement: Replacing the defective gene with a normal gene, often utilizing homologous recombination.
Targeted Cell Killing: Equips immune cells to attack diseased cells using genes for antigens/cytokines.
Inhibition of Gene Expression: Utilizes tools like antisense oligonucleotides to block harmful proteins from mutated genes.

Gene Transfer Process

Requires cloning the therapeutic gene and selecting a method to deliver it into the patient’s cells.
The therapeutic gene can integrate into the cell genome or exist as an episome, affecting its persistence through cell division.

Vectors in Gene Therapy

Viral Vectors: Commonly used; include retroviruses, adenoviruses, adeno-associated viruses, and herpes simplex viruses.
Non-Viral Vectors: Include liposomes and plasmids; used for targeted delivery of genetic materials.

Risks Associated with Gene Therapy

Adverse Immune Reactions: Immune response against the vector can compromise treatment success. Notable case in 1999 with a patient who died from an immune response to an adenoviral vector.
Insertional Mutagenesis: Risk of activating cancer-promoting genes or deactivating essential genes through vector integration.
Viral Infection of Healthy Tissue: Risk of unintended gene transfer to non-target cells.
Protein Overproduction: Excessive expression of inserted genes can lead to harmful effects.

Gene Therapy for SCID

SCID leads to fatal outcomes in children; traditional treatment includes bone marrow transplantation, which is limited by donor availability.
Gene therapy emerged as an alternative, especially for ADA deficiency, involving ex vivo modifications of T-cell precursors.

Notable Clinical Trials

Initial trials for ADA-deficient SCID utilized retroviral vectors to introduce a normal ADA gene, showing promise in transducing T-cells and improving patient conditions.
SCID-X trial utilized retroviral vectors to treat a different form of SCID linked to mutations in the common γchain, allowing for the development of mature T-cells from transduced precursors.

Conclusion of Trials

The importance of selective advantage for transduced cells was underscored, as initial trials involving oral enzymatic replacement alongside gene therapy impeded effective evaluation of gene therapy efficacy.
Subsequent trials focusing solely on gene therapy for SCID-X demonstrated successful outcomes with the re-establishment of mature T-cells in patients.### Gene Therapy and Long-term Effects
Correction of disease observed for over five years in patients receiving gene therapy.
Most mature T and NK cells in patients expressed the transgene, allowing for reconstitution of peripheral T-cell repertoire.
Documented negative effects include the development of leukemia in some patients after therapy.

Cases of Leukemia after Gene Therapy

French study involved ten patients; three developed leukemia within three years post-treatment.
Leukemia caused by integration of retroviral DNA next to an oncogene.
Insertional mutagenesis occurred when retroviral vector integrated near proto-oncogenes causing activation.
All three leukemia cases exploited the same genomic site adjacent to LMO-2 proto-oncogene.
One patient died, while two were treated successfully for leukemia.

Regulatory Response to Gene Therapy

Early clinical trials for Severe Combined Immunodeficiency (SCID) faced biohazard issues, leading to a worldwide moratorium on gene therapy.
Regulatory responses initiated in the USA and Europe, resulting in temporary suspensions of trials.
Moratorium began in the USA and spread to UK, France, Italy, and Germany.
Therapy allowed to continue subsequently on a case-by-case basis due to lack of alternative treatments for patients with severe conditions.

Advances and Approval of Gene Therapy

Studies focused on understanding insertional mutagenesis linked to specific viral vectors.
New clinical trials for SCID-X resumed with modifications in retroviral vector types to improve safety.
Clinical trials for ADA deficiency showed no adverse side effects, leading to positive conclusions on the safety and efficacy of gene therapy for these patients.
In 2016, gene therapy for ADA deficiency received approval in Europe as a standard treatment option.
Parents can choose between bone marrow transplantation or gene therapy for their children.
Approval process for gene therapy in the US is ongoing.