Archive for ‘Gene therapy’

October 14, 2011

Researchers demonstrate that iPS stem cells may be used for gene therapy

Gene therapy sounds good, in principle, as a means of treating diseases that result from genetic defects. But there have been at least two major practical problems in making use of gene therapy in the clinic. First, it’s very important for the safety of the procedure to make changes only to the defective gene (or even just the critical part of the gene) and no other portion of the DNA. Second, there needs to be an effective way to deliver the therapy, in whatever form it takes, to exactly the right tissues in the body that are affected by the defective gene.

Solving these two problems simultaneously is especially difficult. There are a variety of techniques for modifying DNA in specific ways, using a number of specialized enzymes. But these techniques are actually usable only in a test tube. Simply setting the enzymes loose in a patient’s body doesn’t work. The usual way to get around this is by preparing the appropriate modified DNA segments and incorporating them into “vectors”, such as some sort of virus, and introducing the vector into a patient’s body, in the hope that it will reach the right tissues to deliver the DNA, without causing any other problems. That hasn’t worked very well, so far, despite a large number of attempts.

What about taking some cells from the patient, modifying their DNA in vitro and then putting them back in the body? The problem there is being able to produce enough cells with good DNA, either before or after reintroduction to the patient’s body, to make a significant difference. Most human cells just don’t reproduce very prolifically outside the body, or even inside for that matter.

At this point you should be thinking, “stem cells!” They are specialized to reproduce quickly, when needed. Up until now, there have been practical problems here, too. Adult stem cells capable of differentiating into the specific type of cell needed in a given tissue may be difficult or impossible to find in useful quantities. And embryonic stem cells, well, even any other problems aside, there’s the problem of avoiding rejection by the patient’s immune system.

The potential solution: induced pluripotent stem cells (iPSCs), made from any convenient cell type of the actual patient. It’s only been five years since iPSCs were first produced. Various practical problems have arisen along the way since then. Some have been mostly overcome; some haven’t. But progress seems to be occurring steadily – including very recently. The application to gene therapy involves making appropriate corrections to the DNA, producing a sufficient number of differentiated cells of the required type from the “fixed” iPSCs, and finally reintroducing them into the patient.

Alpha 1-antitrypsin deficiency is a genetic disorder caused by a point mutation that results in inadequate production of the alpha 1-antitrypsin (A1AT) enzyme in liver cells. The disease affects functioning of the lungs, as well as the liver. Research just published has shown that gene therapy to correct the mutation, applied to iPSCs, is successful at treating the condition in a mouse model.

Researchers demonstrate that iPS stem cells may be used for gene therapy

Researchers from the University of Cambridge, directed by Ludovic Vallier and David Lomas, and from the Sanger Institute, coordinated by Allan Bradley, began by sampling patients’ skin cells, which were then cultured in vitro for “differentiation” before applying the properties of the pluripotent stem cells: this is the “iPS cells” stage. Through genetic engineering, scientists were then able to correct the mutation responsible for the disease. They then engaged the now “healthy” stem cells in the maturation process, leading them to differentiate to liver cells.

Scientists from the Institut Pasteur and Inserm, led by H-l-ne Strick-Marchand in the mixed Institut Pasteur/Inserm Innate Immunity unit (directed by James Di Santo), then tested new human hepatic cells thus produced on an animal model afflicted with liver failure. Their research showed that the cells were entirely functional and suited to integration in existing tissue and that they may contribute to liver regeneration in the mice treated.

Further reading:

Liver-disease mutation corrected in human stem cells

Spell-Checked Stem Cells Show Promise Against Liver Disease

Targeted gene correction of α1-antitrypsin deficiency in induced pluripotent stem cells

September 20, 2011

Gene Therapy May Thwart HIV

In another recent test case, gene therapy has scored an additional small, but significant, success. (See Gene therapy kills breast cancer stem cells, boosts chemotherapy.)

It has been widely reported that during the past year a German man with an HIV infection was apparently fully cleared of the infection after receiving blood transfusions, in therapy for an unrelated case of leukemia, from a donor who had a particular genetic mutation affecting immune system cells. Upon investigation, the nature of the mutation was determined. It has now been functionally reproduced and used in experimental trials with other HIV patients.

The mutation affected the CCR5 receptor of T cells, which is used by HIV to infect the cells and compromise the immune system. 15 experimental subjects had T cells removed and treated with a zinc finger nuclease to disable their CCR5 receptor gene. The cells were then reintroduced in the subjects. In some cases, modified cells persisted for up to 6 months. In one case, the subject stopped taking antiretroviral drugs. HIV returned at first, but it eventually dropped to undetectable levels.

Although this is a very preliminary result, and certainly not yet an effective therapy, it seems to show that researchers are on the right track.

Gene Therapy May Thwart HIV – ScienceNOW

This past year, a Berlin man, Timothy Brown, became world famous as the first—and thus far only—person to apparently have been cured of his HIV infection. Brown’s HIV disappeared after he developed leukemia and doctors gave him repeated blood transfusions from a donor who harbored a mutated version of a receptor the virus uses to enter cells. Now, researchers report promising results from two small gene-therapy studies that mimic this strategy, hinting that the field may be moving closer to a cure that works for the masses.

At the Interscience Conference on Antimicrobial Agents and Chemotherapy in Chicago, Illinois, this weekend, researchers reported preliminary results from tests of a novel treatment in 15 HIV-infected people designed to free them from the need to take antiretroviral drugs

Further reading:

Double whammy gene therapy clears HIV from body

Preliminary Results of Trial Using Gene Therapy Against HIV Show Potential

September 15, 2011

Gene therapy kills breast cancer stem cells, boosts chemotherapy

Gene therapy has had a somewhat tortuous history – as well as some fairly recent successes. The key issue is being able to deliver appropriate genes to exactly the cells where they are needed.

The way this therapy works is somewhat complicated. The agent is targeted to cells, such as cancer cells, that overexpress a gene called claudin4, which encodes a cell membrane protein. Cancer therapies such as chemotherapy and radiation therapy work by causing apoptosis (programmed cell death). But some types of cancer overexpress genes for certain members of the Bcl-2 family of proteins, which inhibit apoptosis. Another protein, BIK counteracts the effects of these Bcl-2 proteins, but it falls short if they are overexpressed. However, BIKDD is a mutant form of BIK that is better at the same task. The experimental therapy delivers BIKDD genes to targeted cancer cells, and pre-clinical tests show that it improves the anti-cancer activity of the lapatinib chemotherapy drug.

Gene therapy kills breast cancer stem cells, boosts chemotherapy

Gene therapy delivered directly to a particularly stubborn type of breast cancer cell causes the cells to self-destruct, lowers chance of recurrence and helps increase the effectiveness of some types of chemotherapy, researchers at The University of Texas MD Anderson Cancer Center reported in the Sept. 13 edition of Cancer Cell.

In cellular and mouse studies, scientists found the gene mutation BikDD significantly reduced treatment-resistant breast-cancer initiating cells (BCICs), also known as breast cancer stem cells, by blocking the activity of three proteins in the Bcl-2 family. This genetic approach increased the benefits of lapatinib, one of the most common chemotherapy drugs for breast cancer.

Further reading:

BikDD Eliminates Breast Cancer Initiating Cells and Synergizes with Lapatinib for Breast Cancer Treatment