Status of Gene Therapy in the United States

As provided in the document, ''Application of Current Statutory Authorities to Human Somatic Cell Therapy Products and Gene Therapy Products,'' human gene therapy is defined as a medical intervention based on the administration of genetic material in order to modify or manipulate the expression of a gene product or to alter the biological properties of living cells. Cells may be modified ex vivo for subsequent administration or altered in vivo by gene therapy products given directly to the subject. Examples that fall under this definition include, but are not limited to, autologous bone marrow stem cells modified with a viral vector, intramuscular injection of a plasmid DNA vector, and direct injection of a viral vector for treatment of hemophilia. Since submission of the first human gene therapy IND in 1989, 317 human gene therapy INDs have been submitted to CBER for review (through September 2002). The review of gene therapy INDs was the responsibility of the Office of Therapeutics Research and Review until September 30, 2002. Effective October 1, 2002, the review of gene therapy INDs is coordinated through the newly created Office of Cellular, Tissues, and Gene Therapies within CBER.

Currently, there are 197 active gene therapy INDs at CBER (Fig. 1). Although more than one-half of the INDs submitted have involved ex vivo modification of cells using gene therapy vectors, since 1995 the number of INDs involving direct administration of gene therapy vectors has been increasing. Currently, almost 48% of all INDs use direct vector administration. Overall, almost 90% of INDs submitted have involved expression or replacement of a gene with therapeutic intent and comprise indications as broad as cancer, HIV, cystic fibro-

Figure 1 Schematic of currently active INDs showing the types and number of vectors being used in U.S. gene therapy clinical trials.

sis, hemophilia, peripheral and arterial vascular disease, arthritis, and many rare diseases (i.e., x-linked SCID, Fanconi anemia). In approximately 26% of the INDs, nonviral plasmid vectors were used for gene delivery. Of the viral vector systems used, more than one-half of the INDs submitted have used retroviral vectors, about one-quarter adenoviral vectors, and a small number have used adeno-associated, herpes and vaccina viral vector systems.

For the area of gene therapy, CBER has applied a unique regulatory approach that has included an element of public process that is not typically used to regulate other products at the FDA. The goal of this public interaction has been to increase the community's understanding of the CBER review process and requirements, to allow deliberation of ethical and social issues that surround the area of gene therapy, to receive input into CBER gene therapy policy development, and to provide accurate information to the public about the progress of gene therapy clinical trials. Much of this process has been facilitated by the National Institutes of Health (NIH) Office of Biotechnology Activities (OBA), through quarterly meetings of the Recombinant DNA Advisory Committee (RAC). The FDA also convenes its Biological Response Modifiers Advisory Committee to discuss relevant issues regarding the safe use of gene therapy products and conduct of clinical trails. In addition, the FDA routinely takes part in forums with industry, trade groups, academia, and the public in order to foster public understanding in the area of gene therapy, which is essential for continued progress of the field.

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