|NATIONAL INSTITUTES OF HEALTH|
|For Release: June 1997||
Contact: Elia Ben-Ari
The National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) recently awarded contracts to eight research institutions in an effort to develop gene therapy technology in the areas of skin and rheumatic diseases. "Current gene therapy techniques are not always readily applicable to skin and rheumatic diseases," says Dr. Alan Moshell, Chief of the Skin Diseases Branch at NIAMS. The NIAMS initiative was designed to tailor developments in gene therapy to the field of skin and rheumatic diseases. The outcome of the research proposed through these contracts will set the stage for pursuing further goals.
Gene therapy involves technology that introduces a new, functional gene into the patient's own cells to correct a disease-causing defect or augment disease-fighting processes. To achieve this, various technical approaches have been designed over the years through advances in the fields of molecular biology and genetics. Most commonly the functional gene, also known as the "DNA insert," is introduced into cells through the use of viruses. A virus is capable of entering a cell where it expresses its genome - its own genetic material or DNA - to produce new virus particles. Scientists can insert the new gene of interest into the virus genome in place of non- essential viral DNA regions, and use this "recombinant" virus to infect the cell, thus delivering the therapeutic gene. The virus thus serves as a vector - an agent that transmits genetic material to a cell or organism.
Although gene therapy has tremendous potential, much research and testing are still needed before it becomes a safe, effective and available method of treatment for a wide range of diseases. Application of gene therapy to rheumatic diseases and rheumatoid arthritis in particular has been limited. "The pathogenesis of these diseases is likely due to the concerted action of numerous genes with effects on the immune system as well as on the target organs," explains Dr. Susana Serrate-Sztein, Chief of the Rheumatic Diseases Branch at NIAMS. Normal function of the immune system depends on a finely tuned balance resulting from the multiple interactions of many different molecules that are part of a complex system. Potential gene therapy approaches for rheumatoid arthritis may therefore aim at modifying the immune response or the inflammatory reaction, rather than at correcting a single defective gene.
Rheumatoid arthritis is an autoimmune disease affecting more than two million people in the United States, more than 60 percent of whom are women. This chronic inflammatory disease causes pain, stiffness, swelling, and eventually loss of function in the joints. An unknown factor in the body, possibly an infectious agent, triggers an immune response that takes place in the joints. The joint lining, or synovium, becomes the site of an inflammatory reaction, where white blood cells migrate, macrophages proliferate, and cytokines are produced. (Macrophages are cells of the immune system that swallow up and destroy bacteria and other foreign cells, and cytokines are molecules that function as chemical messengers that regulate the immune response and cell growth.)
Six of the gene therapy contracts awarded by NIAMS are related to rheumatoid arthritis. At the University of Pittsburgh in Pennsylvania, Dr. Paul D. Robbins' team will create an animal model of rheumatoid arthritis and develop new viral vectors to deliver genes to the affected joints for therapeutic purposes. The researchers will produce a rabbit model of the disease by transplanting into the rabbit knee synovial cells genetically engineered to produce (or "express") various molecules known to play a role in the disease. These molecules will include interleukin-1 (IL-1), tumor necrosis factor alpha (TNF-alpha), and interleukin-6 (IL-6) - cytokines that are involved in the inflammatory response. This approach will allow the researchers to "reproduce features of rheumatoid arthritis and to dissect the cascade of events in the pathogenesis of this disease," says Dr. Sztein. Dr. Robbins' group will then use virus-based vectors to deliver genes coding for proteins such as the IL-1 receptor and TNF-alpha receptor, which inhibit the action of the very cytokines used to produce the animal model, and will test the effectiveness of this gene therapy approach on the rabbit knee model.
Another contract that revolves around the intricate network of immune system interactions in rheumatoid arthritis is the one headed by Dr. C. Garrison Fathman at Stanford University in Stanford, California . The Stanford group aims to counteract the abnormal immune response that takes place in the disease. The investigators will inhibit the actions of one subset of the T-cell population (a T cell is a type of white blood cell) that plays a key role in this abnormal immune response. They will do this by using genes encoding disease-regulating cytokines such as interleukin-4, interleukin-10, or transforming growth factor beta (TGF-beta). This is expected to "change the balance between the two T-cell populations which are involved in the immune response in rheumatoid arthritis," explains Dr. Sztein, in an attempt to stop the inflammatory process and ameliorate disease.
A critical aspect of effective gene therapy is the use of appropriate promoters (that is, special DNA sequence elements that regulate gene expression) that ensure high expression of the therapeutic gene in the target cell. Dr. Richard M. Pope and colleagues at Northwestern University in Chicago, Illinois , will focus on identifying promoters that are effective in driving gene expression in macrophages. The ultimate goal is to use these promoters to express genes that block productions of TNF-alpha, an inflammatory cytokine, in synovial tissues.
The research group led by Dr. John D. Mountz , at the University of Alabama at Birmingham , will base its gene therapy approach on Fas, a protein found on the surface of cells. When Fas is activated by certain molecules such as the "Fas ligand", it sets off a program of events within the cell leading to that cell's death (apoptosis). The body uses apoptosis to eliminate unnecessary or potentially harmful cells. Mountz and coworkers will construct viral vectors expressing either the mouse Fas or Fas ligand gene and will develop a way to target them to cell populations that are known to play a key role in rheumatoid arthritis, with the aim of inducing apoptosis in those cells. To test the potential therapeutic effect of these genes, the researchers will introduce them in Fas-deficient and Fas ligand-deficient mice, which are known to develop spontaneous arthritis, and will determine whether the constructs can reverse development of disease.
Three of the contracts have been awarded to laboratories developing new technologies for gene delivery in rheumatic or skin diseases. Dr. Raphael Hirsch , of Children's Hospital Medical Center in Cincinnati, Ohio , has developed a novel method of gene delivery known as antifection, which is short for "antibody-mediated transfection." An antibody that is targeted to a receptor present on the surface of a specific cell type is linked to a piece of DNA (that is, the therapeutic gene). Because the antibody-DNA complex enters the cell after binding to the cell receptor, this method delivers the therapeutic gene into the cell without use of a viral vector. In addition, antibodies are available that target a variety of cell receptors and cell types. Hirsch and colleagues will study various parameters, including different antibody-DNA coupling methods and an array of possible therapeutic genes and cell receptors, to identify the best cellular target for rheumatoid arthritis gene therapy in the synovium.
Another innovative delivery approach for gene therapy of rheumatoid arthritis comes from scientists at the Virginia Mason Research Center in Seattle, Washington . Their idea is to introduce in the target cell a piece of DNA (an "anti-gene" oligonucleotide) that specifically inactivates the target gene. Dr. Gerald T. Nepom and colleagues will focus on major histocompatibility (MHC) genes, which code for proteins on the cell surface that recognize and bind foreign proteins. Certain MHC genes are believed to play an as yet unknown but key role in development of rheumatoid arthritis.
The third project focusing on a new methodology for gene delivery is that directed by Dr. Blake J. Roessler of the University of Michigan in Ann Arbor . This project deals with optimizing the use of liposomes for delivery of cytokine genes to perifollicular cells (cells near the hair follicles in skin). Liposomes are bubble-like membrane structures that can fuse with the membrane that forms the outside of a cell. For that reason, liposomes have already been successfully used to deliver DNA to some cells. "The hair follicle is an anatomical break in the rather impermeable stratum corneum [the tough outer layer] of the skin," explains Dr. Moshell, and thus represents a good target region for getting genes into the skin. If successful, this technique could be applicable to gene therapy for a variety of skin and systemic diseases.
Epidermolysis bullosa simplex (EBS) is an ideal candidate for gene therapy treatment. Because of the wealth of information that scientists have recently accumulated about EBS, it is also one of the most ready for gene therapy experimentation. EB is a group of hereditary disorders that affect the skin and mucous membranes. These skin diseases are characterized by the formation of blisters that occur upon mild injury and, in some cases, even spontaneously. EB is a rare disease that can seriously alter a person's everyday life. About 50,000 people in the United States are thought to have some form of EB.
In the case of EBS, scientists have shown that people with the disease carry a defect in one of the genes encoding keratin. Keratins are the most abundant proteins in the cells of the epidermis-the outermost layer of skin and form an internal web-like network that ensures the integrity and structure of the skin. Abnormal keratins form abnormal networks, leading to skin fragility.
The project being done by Dr. Dennis R. Roop and colleagues of the Baylor College of Medicine in Houston, Texas , is "not at all far from human application if the technology works out" at each step, says Dr. Moshell. Of course, there will be safety issues to consider for humans. The researchers will develop mice that are affected by blistering disease similar to human EBS. The gene therapy approach proposed by Dr. Roop will involve the use of epidermal stem cells (cells in the epidermis from which epidermal cells derive). Targeting gene therapy to epidermal stem cells provides the best chance for a long-lasting effect of the therapy, since other epidermal cells are shorter-lived.
The researchers will introduce a normal copy of the keratin gene into epidermal stem cells in order to replace the defective gene. Then they will graft the "corrected" cells onto the skin of affected mice to confirm that this leads to formation of a normal epidermis. In this gene therapy approach the assumption is that, provided that epidermal stem cells can be corrected and put back into the patients in the blistered areas, the corrected cells will have a growth advantage over the defective ones, and will eventually repopulate the affected skin regions.
Gene therapy for human diseases continues to offer exciting opportunities for scientists and clinicians, and to inspire hope for patients. Much work is still to be done to overcome the complexity and possible pitfalls of this approach. "We will gain a lot of basic knowledge," says Dr. Sztein, "and we hope to promote interaction among the investigators," who will meet annually over the 5-year period of the contracts to share information on their progress. Through this initiative, NIAMS is supporting a systematic evaluation of the available tools and reagents and encouraging the search for new technologies and avenues of treatment for rheumatic and skin diseases.
The National Institute of Arthritis and Musculoskeletal and Skin Diseases, a component of the National Institutes of Health, leads the Federal biomedical research effort on the many forms of arthritis and diseases of the musculoskeletal system and the skin. The Institute also conducts and supports basic research on the normal structure and function of joints, muscles, bones, and skin. The Institute conducts and supports research projects, research training, clinical trials, and epidemiologic studies, and disseminates health information and research results.