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RS1-00186-1: Developing an Effective Stem Cell Gene Therapy to Treat Human Disease

Recommendation: Not recommended for funding

Public Abstract (provided by applicant)

The human body functions because there are specific proteins (enzymes) that perform all the work (chemical reactions) necessary to allow mechanical movement, eating, reproducing and eliminating wastes. Enzymes are produced by specific genes. Each person can have slightly different enzymes produced by slightly different genes. Sometimes these changes provide advantages, sometimes these changes cause dis-advantages. Essentially all diseases can be linked to the interference of one or more enzymes in regard to performing its chemical reaction. Human medicine has been based on drugs, which are chemicals that affect the activity of enzymes. By increasing or decreasing the activity of enzymes, drugs can reduce and (sometimes) eliminate the deleterious effects of diseases. A potential problem with many drugs is that they commonly are associated with unwanted side-effects and their potency can be reduced by acclimation of the body’s response to that particular drug.

With the advances in understanding the human body, it is now possible to cure diseases by altering the expression of genes to affect the activity of specific enzymes. The advantages of “gene therapy” are specificity to the established target, long-term duration of treatment and reduced chances of side-effects. While gene therapy has been proposed as a method to treat many human diseases having devastating effects, there are limited examples of successful outcomes. We are now at a cross-roads in our knowledge of being able to learn how to develop successful gene therapies for treating human disease. One of the major obstacles is having the appropriate vehicle to deliver the gene therapy to the patient.

We have developed a simple method to deliver therapeutic genes to mice using stem cells that will repopulate the liver in the form of liver macrophages (i.e. Kupffer cells). Kupffer cells are immunologic cells that normally have a long lifetime, reside on the surface of liver cells and protect the body from bacteria that enter the body via the intestine. A safe drug, used to visualize arteries when irradiated with x-rays, is eaten by Kupffer cells causing them to be rapidly eliminated and replaced by new Kupffer cells which are derived from stem cells. By switching the stem cells used for replacing Kupffer cells with stem cells carrying a specific therapeutic gene, we have shown we can reduce heart disease in mice in manner that is safe, without any toxic side effects and long-term (up to a year).

The goal of this research is to further develop the Kupffer cell gene transfer technique for treating human disease. By developing an efficient means to use embryonic stem cells as the vehicle, we will be able to provide a safe, versatile, reversible and effective means to provide gene therapies for many different type of human diseases including: diabetes, infectious disease, heart disease, liver failure and metabolic deficiency diseases.

Statement of Benefit to California (provided by applicant)

During the past 20 years, scientists (many residing in California) have discovered how to identify genes, how to identify the functional role of the proteins made from these genes and how to identify if individuals have mutations in genes that affect function. In addition to providing patients with an understanding why they may have a particular disease, these advances have provided new clues that may be useful in designing a new way to treat diseases called gene therapy. Gene therapy has the potential to cure many diseases for which drugs have not been developed or have been shown to have bad side-effects.

Because of its many potential benefits, scientists have spent ~20 years designing methods to administer gene therapies that are safe and effective. So far, successful amelioration of human disease via gene therapy has been a rare occurrence.

We have developed a new method to administer gene therapy to mice. This method is safe and effective (treating mice with this gene therapy reduced heart disease in mice by 50%). We wish now to further develop this method so it can be used to treat humans. The goal of this research to develop this method and show that it is safe and effective in mice. Achieving this goal will justify it being further developed for use in humans in treating many diseases including: diabetes, heart disease, liver disease, several metabolic deficiency diseases, several forms of malignant diseases involving plasma cells, infection diseases and diseases associated with impaired immunity.

This investment by CIRM in supporting this research has the potential to provide new, safe and effective gene therapies to the citizens of California.

Review

SYNOPSIS OF PROPOSAL: Two specific aims are proposed. Aim 1 is to examine the hypothesis that genetic ablation of a gene will enhance the survival of ESC and their ability to differentiate into hematopoietic stem cells. Aim 2 is to examine the therapeutic potential of this gene transfer method. The applicant will examine how reconstitution of bone marrow and hematopoietic stem cells having genetic ablation of a gene affects cardiac repair, liver repair and protection of pancreatic β-cells under different experimental conditions.

INNOVATION AND SIGNIFICANCE: The investigator proposes to explore the ability to derive blood cells from murine embryonic stem cells for utilization in reconstitution experiments. In prior work he/she has shown that hematopoietic stem cells expressing a relevant transgene have the potential for reducing the formation of disease in a mouse model of a relevant human disease. The basic strategy used in those experiments was to transplant lethally irradiated mice with engineered hematopoietic stem cells. The investigator has also developed evidence that ablation of a gene enhances cell viability, increases cell replication and decreases apoptosis. The proposed experiments are highly innovative and yet based on prior experimental work by this investigator. Gene delivery by the method proposed in these studies would indeed have significant potential impact for the treatment of human disease.

An innovative aspect is related to understanding the mechanisms that relate to the role of a a particular gene in promoting the survival of hematopoietic stem cells. The approach would require both a gene and cell based transfer, and the optimal clinical approaches for the former (gene therapy) with regards to vector are yet to be established.

STRENGTHS OF PROPOSAL:On strength of this proposal is familiarity of the investigator with the proposed techniques. The investigator is experienced, has published extensively in this field, and has an excellent track record. He/she possesses extensive prior data indicating that cells can indeed be replaced by the proposed strategies.The work is feasible, and the preliminary data are solid for much of the work. The Principal Investigator (PI) has established good collaborations with experienced investigators having specific expertise in aspects of the proposed project. Finally, the scientific environment is strong for this work.

WEAKNESSES OF THE PROPOSAL: The initial two experiments proposed to address Aim 1 seem very predictable based on earlier studies. Since these results have already been obtained, what new will be learned? The relevant details of the proposed animal experiments are not clear. One reviewer pointed out that the overall assumption that HSCs can exert a significant, clinically relevant effect via a particular type of blood cell has inherent difficulties. The relevance of the experiments in other organ systems seems to be driven by their potential clinical importance if they were to succeed, but there is little data to support this concept at this time.

As the studies do not incorporate studies on human ES cells, one of the major points of reponsive to the RFA has not been addressed.

DISCUSSION: This proposal is not responsive to the RFA.

The following Working Group members had a conflict of interest with this application and were therefore recused from participating in review of, discussion of, and voting on the application:

• Lansing, Sherry