Gene Therapy and SCID Trials Overview

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Questions and Answers

What key factor is being researched to improve induced pluripotent stem cells (iPSCs)?

Enhancing genetic diversity of stem cells

Using more adult stem cell samples

Eliminating the need for reprogramming

Searching for a less carcinogenic gene set (correct)

Which problem related to the cloning of human embryos was highlighted by the 2004 incident involving a South Korean group?

Fabrication of research results (correct)

Challenges in achieving successful embryo implantation

Inability to extract stem cells from embryos

Ethical implications of human cloning

Which cloning technique involves extracting the nucleus from a somatic cell and implanting it into an egg?

Therapeutic cloning (correct)

Transgenic modification

Parthenogenesis

Dolly cloning method

What was a significant outcome of Dolly the sheep's cloning?

It raised questions about aging in clones Signup and view all the answers

What challenge does transgenic modification face regarding gene insertion?

Unpredictability of insertion site Signup and view all the answers

What area of cloning research is currently considered very promising?

Therapeutic cloning for disease treatment Signup and view all the answers

Which factor is considered when searching for substitutes for cMyc in the context of iPSCs?

Mitigating mutation rates Signup and view all the answers

What common risk is associated with gene therapy in SCID trials?

Insertional mutagenesis leading to leukemia Signup and view all the answers

What is a major hurdle in gene therapy related to DNA manipulation?

Stability of the gene integration Signup and view all the answers

In the context of stem cells, what concept explains the regulation of gene expression based on the parent from which the allele is inherited?

Gene imprinting Signup and view all the answers

What distinguishes ADA-SCID trials from other SCID trials in terms of leukemia development?

ADA-SCID has not resulted in leukemia cases. Signup and view all the answers

What is a key application of hESC-derived retinal cells currently being tested?

Treating Stargardt Macular Dystrophy Signup and view all the answers

What significant setback occurred in hESC clinical trials involving retinal cells?

Development of a membrane over the eye Signup and view all the answers

Which statement best describes the Phase I clinical trial of ViaCyte beta cells?

It showed regenerative capability in animal models. Signup and view all the answers

In the context of hESC therapies, what is a concern regarding the manufacturing process?

Transmissible Spongiform Encephalopathy (TSE) Signup and view all the answers

What is an important factor for the success of directed differentiation in stem cell therapies?

Reproducible production of desired cell types with appropriate functionality Signup and view all the answers

What is the primary role of the factors Oct4, Sox2, Klf4, and cMyc in the generation of iPS cells?

They induce pluripotency in somatic cells. Signup and view all the answers

Which condition is NOT evaluated to confirm that iPS cells are true stem cells?

Stem cell cloning Signup and view all the answers

What happens when cMyc is removed from the pool of iPSC reprogramming factors?

Colonies formed are not stem-like. Signup and view all the answers

What does the term 'reprogramming efficiency' refer to in the context of iPS cells?

The percentage of somatic cells that successfully become iPS cells. Signup and view all the answers

Which of the following is a common application of human iPS cells in medicine?

Regeneration of damaged tissues and organs. Signup and view all the answers

What is the consequence of removing Sox2 factor during the iPSC generation process?

It greatly reduces stem cell colony formation. Signup and view all the answers

Which of the following pathways does cMyc aid in overriding to enhance reprogramming efficiency?

Tumor suppressor gene barrier. Signup and view all the answers

What is the significance of demonstrating cell differentiation in iPS cells?

It verifies the functionality of differentiated cells. Signup and view all the answers

Study Notes

SCID Trials

The first successful gene therapy was performed on a four-year-old girl named Ashanthi DeSilva in 1990.
Gene therapy restored the immune systems of at least 17 children with two forms (ADA-SCID and X-SCID) of Severe Combined Immunodeficiency (SCID) since 1999.
One SCID trial in 2000 resulted in patients with a functional immune system.
10 patients in one SCID trial developed leukemia due to a gene insertion near an oncogene.
No leukemia cases have been seen in trials of ADA-SCID, which does not involve a gene that may be oncogenic.

Current State of SC Therapies

The importance of stem cell therapy is recognized at many levels in the public and government.
The first approved hESC (human embryonic stem cell) clinical trial was approved in January 2009.
The first approved hESC clinical trial was for Stargardt Macular Dystrophy (SMD), an eye disease.

Current hESC Trials – US

The ACT trial is testing the safety of hESC-derived retinal cells to treat patients with Stargardt Macular Dystrophy (SMD).
A second ACT trial is testing the safety of hESC-derived retinal cells to treat patients with age-related macular degeneration.
MD trials were stopped in 2017 because a patient developed a membrane over the eye.
Phase I/II clinical trials involving retinal pigment epithelial (RPE) cells, derived from hESCs, for severe myopia were approved in February 2013.

Diabetes Trial

A Phase I clinical trial using ViaCyte beta cells from hESCs was approved in August 2014.
The diabetes trial showed the treatment to be safe and tolerable in animal models.

Scientific Concerns

Feeder cells may pose a risk of Transmissible Spongiform Encephalopathy (TSE).
There are concerns about genetic stability and Good Manufacturing Practices (GMP) in the manufacture of stem cells.
Issues with directed differentiation include:
- Reproducible production of desired cell type with appropriate functionality.

Induced Pluripotent Stem Cells (iPSC)

Kazutoshi Takahashi and Shinya Yamanaka won the Nobel Prize for their work with iPSCs.
iPSCs are somatic cells that have been reprogrammed to a pluripotent state.
iPSCs can be generated from fibroblasts.

Generation of iPSC from Fibroblasts

Researchers identified 24 candidate genes as “factors” that could potentially induce pluripotency in somatic cells.
They examined the effects of removing individual genes one at a time and identified 10 factors whose removal resulted in no stem cell formation.
They then further examined the effects of removing individual factors from the pool of 10.
- Colonies did not form when Oct4 or Klf4 were removed.
- When c-Myc was removed, colonies were not stem-like.
- Removal of Sox2 resulted in very few stem cell colonies.

Reprogramming Factors

OCT4 (O), SOX2 (S), KLF4 (K), cMYC (M) are the four key reprogramming factors for iPSCs (referred to as: OSKM).

Are iPSC TRUE Stem Cells

iPSCs express marker genes such as oct 4 and sox2.
They form embryoid bodies that can differentiate into all three germ lineages.
They can be induced to differentiate into various cell types.
They form teratomas when injected into mice.
They can contribute to a viable organism when injected into mouse embryos.

Reprogramming is Extremely Inefficient

Less than 1% of cells become iPSC cells.

Tumour Suppressor Gene Barrier

iPSC reprogramming is inefficient because of the tumour suppressor gene barrier, which is present in somatic cells and prevents them from becoming pluripotent.
The tumour suppressor genes, p16, p53, and p21, block the reprogramming process.
The gene cMyc aids in overriding the barrier by inducing senescence, which is a process of programmed cell death.

Applications of Human iPSC

iPSC’s have potential applications in disease modeling, drug discovery, and regenerative medicine.

Problems with iPSC

Researchers are searching for less carcinogenic gene sets to use in reprogramming.
Researchers are also searching for non-genetic factors that can facilitate the reprogramming process.
Researchers are also trying to develop alternatives to cMyc.
Researchers are working to increase the efficiency of iPSC production.
Researchers are also trying to decrease the mutation rates of iPSC.

Nuclear Transfer = Whole Organism Cloning

Nuclear transfer is the process of transferring the nucleus of a cell into an enucleated egg cell.

Whole Organism Cloning Projects

Dolly the sheep was cloned from the genetic material of an adult mammary gland cell in 1997.
A human embryonic clone was created in Newcastle University, UK, but survived for only a few days.
A Pyrenean ibex, an extinct form of goat, was cloned in January 2009. The clone died shortly after birth due to physical defects in its lungs.
In 2004, a South Korean group claimed to have cloned human embryos and extracted stem cells, but later retracted the claim due to fabrication of research.

Cloning

Human cloning is not a big business because there is no monetary advantage for cloning entire humans.
Pet and animal cloning are expensive and do not yield high pay.
Cloning to make tissues for diseases is a very hot area! (therapeutic cloning).

Therapeutic Cloning

Therapeutic cloning involves transferring the nucleus of a somatic cell into an enucleated egg cell.
The resulting embryo is used to generate embryonic stem cells, which can be differentiated into various tissues.

‘Manipulating’ the Genome

Genome manipulation can be used to correct mistakes in disease and understand the importance of specific genes in regeneration.

Limitations to Transgenic Modification

There is no way to control where the gene inserts, which can lead to dangerous insertion sites.
The insertion site may epigenetically modify the promoter over time.
Transgenic modification is limited to driving genes with a specific promoter.

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Description

Explore the groundbreaking advancements in gene therapy, particularly focusing on Severe Combined Immunodeficiency (SCID) trials and their outcomes. This quiz discusses the success of gene therapies, the role of stem cell therapies, and ongoing clinical trials in the United States. Evaluate your understanding of these crucial medical innovations.