From Research to Trials

Taking gene therapy from the laboratory to the clinic involves many steps. Before trying a therapy on human patients, researchers must:

• Understand the biology behind the disorder
• Develop the treatment approach
• Test its effectiveness in biological models of the disease
• Establish its safety in humans

Each of these steps requires the efforts of expert researchers and physicians, as well as funding to support the research, approval by regulatory agencies, and time to obtain and analyze results. Applying gene therapy can take a long time.

How long? Days, months, years?

Let's look at a real-life example: development of a gene therapy treatment for a disorder called Adenosine Deaminase (ADA) deficiency. In the box below, you can examine the steps needed to bring a therapy to the clinic. Milestones in developing the ADA gene therapy are boxed in blue.

Click on the "plus" icons to expand a topic, or click "expand all" to see the entire procedure.

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STEP 1: Learn about the disease
Is the disorder a good candidate for gene therapy? To find out, study the disease.

1) Get money for the project

1. Government research granting agencies
2. Private investors
3. Pharmaceutical companies

2) Get approval for the project

1. From your organization's Institutional Review Board

3) Perform clinical research

1. Diagnose and classify the disorder
   1. What are the signs and symptoms?
   2. Who gets the disorder? (Males or females? Specific ethnic groups?)
   3. At what age does the disorder appear?
   4. Clinical research on ADA deficiency began in the 1960s.
2. Examine current treatments for the disorder
   1. What treatments are available?
   2. How effective are they?
   3. What are their drawbacks?
   4. What types of new treatments are needed?
   5. 1976: Blood transfusions show limited effectiveness and potential immune system complications (graft-versus-host disease)
   6. 1987: First report of successful PEG-ADA treatment
3. Publish your results in a peer-reviewed journal

4) Perform biological research

1. Genetics
   1. Which gene(s) are involved in the disorder?
   2. What are the specific disease-causing mutations in these genes?
   3. 1974: Scientists map the ADA gene to a region on human Chromosome 20.
   4. 1986: The sequence of the ADA gene was first published.
2. Cell biology
   1. What is the normal job of the protein encoded by the gene?
   2. How do mutations in the gene affect the protein's function?
   3. How does the altered protein influence cell and tissue function?
   4. 1960s-1980s: Scientists study the ADA protein, which works as an enzyme. For ADA deficiency, the protein was identified before the gene!
3. Animal models
   1. What can you learn from animal models of the disorder?
4. Publish your results in a peer-reviewed journal

5) DECISION: Is the disorder a good candidate for gene therapy?

1. Use the criteria defined in Choosing Targets for Gene Therapy to decide
2. If you answer yes, proceed to Step 2

STEP 2: Design a gene therapy

1) Use your knowledge of the disorder to design a gene therapy

1. Which tissue do you need to target?
2. How will you deliver the gene to the tissue? Which approach is more appropriate, ex vivo or in vivo?
3. 1985 - ADA deficiency affects cells of the immune system, which are present in the blood and produced in the bone marrow. Therefore, an ex vivo approach was deemed the safest and easiest method for gene therapy. This approach involves extracting cells from the patient's bone marrow, treating them, and then putting them back into the patient.
4. How will you ensure that the gene gets into cells and starts working?
5. What can go wrong?
   1. How will you know if sonething has gone wrong?
   2. What will you do if something goes wrong?

2) Test the therapy in appropriate models of the disease

1. Test it in cells grown in the laboratory
2. Test it in appropriate animal models
3. Publish your results in a peer-reviewed journal
4. 1985 - Researchers show that a retrovirus-based approach can deliver the ADA gene into cells taken from ADA patients.
5. 1988 - Researchers show that the gene can be transferred safely and efficiently into the white blood cells of animals.

3) DECISION: Does your therapy look promising?

1. If you think your therapy will work safely in human patients, proceed to Step 3

STEP 3: Get money and approval for clinical trials

1) Get money for the trials

1. Government research granting agencies
2. Private investors
3. Pharmaceutical companies

2) Get approval for the trials

1. From your organization's Institutional Review Board

STEP 4: Phase One clinical trial

1) Establish safety and dosage limits in a small group of people (20-80)

1. Participants are usually terminally ill individuals who have not responded to other treatment.
2. Is the treatment safe?
3. At which doses is the treatment safe?
4. What are the adverse side effects, if any?
   1. How will you address these side effects?
   2. Will the benefits of the treatment outweigh the risks?
5. Publish your results in a peer-reviewed journal
6. 1989 - Researchers establish the safety of an ex vivo ADA gene therapy in human cancer patients.

2) DECISION: Does your therapy still look promising?

1. If you have established the safety and determined the dosage limits of the treatment, proceed to Step 5.

STEP 5: Phase Two clinical trial

Test the efficacy and safety in a larger group of people (100-300)

1. Can you deliver the gene effectively to target cells?
2. Do target cells express the delivered gene?
3. Do you observe health improvements in study participants?
   1. Short-term?
   2. Long-term?
4. Continue to measure side effects
5. Publish your results in a peer-reviewed journal
6. 1990 - The first clinical trial of ADA gene therapy in the United States began, using two children diagnosed with ADA deficiency. The children's immune status improved after they received the gene therapy; however, the therapy worked for only a few months and had to be repeated several times over the next two to three years. In the years following the treatment, periodic tests confirmed that the childrens reengineered cells are surviving and producing the ADA enzyme. Over the long term, however, the procedures have shown mixed success. In 2003, the researchers reported that some of the first patient's cells still expressed the delivered gene. The second patient developed an immune response to the retrovirus gene delivery system, and few of her cells still express the transferred ADA gene.
7. 1993 - In a different study, researchers performed gene therapy using the umbilical cord blood stem cells from two infants born with ADA deficiency. Both patients continue to express the transferred ADA gene in their immune cells. (For more about umbilical cord blood stem cells, see the Stem Cells in the Spotlight module.)

2) DECISION: Is your therapy effective in a larger group of people?

1. If so, proceed to Step 6

STEP 6: Phase Three clinical trial

1) Test the therapy in a large group of people (1,000-3,000)

1. Give treatment in a "double-blind" scenario. Neither the treating physicians nor the patient knows whether the treatment is authentic or a "placebo" (control). This ensures the validity of results.
2. Publish your results in a peer-reviewed journal

2) DECISION: Is your treatment successful?

1. If so, proceed to Step 7
2. 2003 - No phase three human clinical trials for ADA deficiency have yet been conducted.

STEP 7: Get FDA approval for general clinical use

1) Write proposals, fill out paperwork, answer questions and wait for approval

1. If approved, use your therapy to treat patients and proceed to Step 8

STEP 8: Phase Four clinical trial

1) Further test the efficacy and optimal use of the treatment in general use

1. Publish your results in a peer-reviewed journal

Why does gene therapy approval take so long?

It's been more than 30 years since physicians began studying ADA deficiency and more than 15 years since efforts to develop a gene therapy began in earnest. To date, no ADA gene therapy has been successful enough to become common medical practice.

Why has this process taken so long? Gene therapy techniques were just emerging when researchers began designing gene therapies for ADA deficiency. Although researchers employed the latest technologies at the time, the first therapies were far from perfect. Several major obstacles must be overcome before successful gene therapies can be developed. These obstacles are discussed in Challenges in Gene Therapy.

As we learn more about how the human body works at the molecular level, gene therapies will become more and more effective.

Supported by a Science Education Partnership Award (SEPA) [No. 1 R25 RR16291-01] from the National Center for Research Resources, a component of the National Institutes of Health, Department of Health and Human Services. The contents provided here are solely the responsibility of the authors and do not necessarily represent the official views of NCRR or NIH.