Clinical Trials FAQs

ASGCT offers a curated, searchable database of ongoing and recruiting clinical trials in the United States. Check out the ASGCT Clinical Trials Finder to search trials. Still have more questions? Learn about topics like informed consent and the safety and importance of clinical trials for gene and cell therapy.

Frequently Asked Questions

What is a clinical trial?

A clinical trial is a research study that seeks to determine if a treatment is safe and effective. Clinical trials are regulated by the federal government. Participants must be informed, both verbally and in writing, about the risks and benefits of participation in a clinical trial. The written document is called an Informed Consent Document. Participation in clinical trials is voluntary, you may withdraw from the study at any time before, during, or after the treatment is received. 

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What is Informed Consent?

Before patients can be enrolled in clinical research, investigators are ethically and legally required to seek the patient's agreement in regards to the research procedures, risks, potential benefits, and other relevant information. Patients can decide whether to participate in research, and this is called informed consent.

In general, the informed consent process involves both written and oral components. The written Informed Consent Document provides the basic details of the study-how it will be conducted, what it involves, by whom, the risks, potential benefits, alternatives to participation, right to withdraw, whether the patient will receive payment for participation, and other key information.

It is equally important that patients have an opportunity to meet with researchers and discuss the study in person. Once a patient has met with the researchers, had their questions answered, and decided that they would like to participate in the study, they should they sign the Informed Consent Document. Signing the Informed Consent Document verifies that the patient's questions have been answered, that they agree to participate in the research, and their participation is voluntary. Many patients take the informed consent document home to read and share with family members before deciding to participate in clinical research. If a patient has additional questions, researchers are expected to make themselves available to discuss the concerns.

Voluntary participation is a cornerstone of ethical research. Therefore, when doctors are also researchers they should ensure that every patient is treated without prejudice whether they decide not to participate in a research study at all, or choose to withdraw from the study at a later time. This is an important point for patients to understand: signing an informed consent document does not require them to continue in the study if they change their mind. Also, if a patient decides to stop participation the researchers must ensure their medical needs are met and facilitate their further care.

The Informed Consent Document is developed by the individuals conducting the research and it must follow explicit government regulations for the protection of human subjects. In particular, the Informed Consent Document must be approved by an Institutional Review Board (IRB), a committee with the legal authority to protect the rights and welfare of research subjects. The IRB has the authority to require changes in the consent document if it believes that the information is incomplete or too complicated. After the IRB is satisfied that the Informed Consent Document is accurate, they approve the document.

Further Reading about Informed Consent

The US Department of Health and Human Services, Office of Human Research Protections has a series of Frequently Asked Questions about Informed Consent on their website. This includes questions that parents have regarding informed consent for children participating in clinical research and participation of those with diminished capacity to provide consent:

The National Cancer Institute also maintains information about informed consent:

The American Cancer Society, a non-governmental organization, also provides information about informed consent on their website:

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Are clinical trials safe?

When considering a clinical trial, the risk and benefit will relate to the phase of the trial. For example, in early studies (Phase I), the proper dose is being studied so some patients may receive a dose that will not be effective while others could receive a dose that has side effects. At later phase studies, more patients have been treated with the product so there is generally more data regarding safety. The Informed Consent Document provided to all study participants should indicate what phase the patient will be part of, whether the study is likely to provide benefit, and a summary of known side effects from animal studies and/or prior human studies.

As with any drugs or treatments, there is some risk involved. Clinical trials evaluate the severity of predicted and unpredicted side effects. Predicted side effects are ones that were seen in animal studies. A known side effect does not necessarily mean a drug will not be FDA approved, if the potential benefit outweighs the side effects. For example, a drug that caused temporary hair loss may still be given FDA approval if it is an effective cancer treatment. In this case, the Informed Consent Document is required to state that temporary hair loss is an expected side effect of the drug.

Unfortunately, a drug can affect animals differently than humans. Therefore, unpredicted side effects can occur in man that were never detected in animals. A major goal of clinical trials is to detect unpredicted side effects before the treatment is made widely available to the public. The risk of experiencing an unpredicted side effect may be related to how commonly the side effect occurs and how many patients have already undergone treatment. All patients considering gene therapy must weigh the potential benefit with the potential side effects, both predicted and unpredicted.

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Are there any gene or cell therapy products approved by the FDA?

Yes. An increasing number of gene and cell therapies are being approved for clinical use in the United States. Treatments for cancer, inherited retinal disorders, spinal muscular atrophy, and more are either available or on their way to clinics. Other treatment products are still in the investigational stage, which means they're still being studied to assess their safety and efficacy. Gene and cell therapy products must go through the same rigorous testing that all drugs go through before being licensed by the FDA. Promising treatments that are not yet licensed are generally only available through a clinical trial.

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What are the different phases, or types, of clinical trials?

When developing a new treatment the FDA often requires a series of clinical trials before a drug is approved. These trials are done in three distinct steps, called phases.

Phase I:

The major goal is to determine a safe dose for treatment. In many Phase I trials, the initial patients receive a low dose of drug and if no major side effects are noted, the dosage is increased in subsequent patients. These studies are generally small with an average of approximately 20-40 patients. Once a potential safe dose is determined the trial will move to Phase II. 

Phase II:

A Phase II study looks to determine if the treatment is effective. These studies may include 100 or more patients. If the efficacy is encouraging, many drugs then move to a Phase III. 

Phase III:

This is the phase of the study where the new treatment is compared head-to-head with a currently accepted and FDA approved treatment. If there is no available treatment for a particular disease, some patients will receive the new treatment while other patients receive a "placebo" dug (i.e. a sugar pill). Whether the patient will get the new drug or the standard treatment will be randomized. Therefore, not all patients in a Phase III study will receive the treatment being investigated. If the Phase III study indicates the new agent has efficacy and safety that is as good as or better than the standard therapy, the FDA may grant approval. In certain cases, Phase IV studies may be performed after FDA approval to assess long-term safety.

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How can I learn more about clinical trials?

Check out the ASGCT Clinical Trials Finder to find clinical trials, or watch the Developing a Treatment video for information on the entire drug development process. Please visit How to Find a Clinical Trial to learn more. 

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What should I expect as part of a clinical trial?

Those considering clinical trials should expect to meet with a healthcare professional who will explain the purpose of the study and determine eligibility. You should be given an "informed consent" document to review. This document provides specific details about the study, the potential risk and benefits, how and when treatment will be given, and what is expected of you during the study.

Before receiving treatment, you may be asked to undergo tests to determine whether you are eligible for the study treatment. This is to make sure that you are healthy enough to participate in the study. This evaluation may include a thorough review of your medical history, a physical examination, and blood tests. Additional tests may be required. The specific tests will vary depending on the drug or therapy being studied. If you have an existing medical condition that might be made worse by the clinical trial, you may not be eligible to participate.

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What are the benefits of participating in a clinical trial?

Participating in a clinical trial is the only way to receive treatment that has not been approved by the FDA. In certain clinical trials the participant may receive free medical care or may be paid for their participation, although this is not generally the case for participants in clinical trials for gene therapy.

The potential benefits depend on the phase of the trial. Participant benefits may be unknown or low in early phase trials, but participating may provide important information that will help others who participate in future studies. Some clinical trials are performed to determine whether the treatment is as good as or better than the currently available therapy. Doctors conducting clinical trials are required to disclose both the possible risks and the potential benefits associated with the treatment. Such disclosure should be communicated both verbally and in writing through the Informed Consent Document.

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What factors should I consider in deciding about a clinical trial?

You should receive an Informed Consent Document after meeting with a healthcare provider. As this document tries to explain many aspects of the clinical trial, it can be long. Many patients bring these documents home to share with their family before deciding on participation. Before agreeing to a clinical trial, you will have an opportunity to discuss all your concerns with a healthcare provider associated with the study. A patient representative, someone not associated with the study, should also be available.

Once your questions are answered about the purpose, risks, and benefits, you should also consider whether you have the time needed to return for scheduled tests and treatments. Not all costs of the study may be covered by your insurance company. It is important that you discuss with your doctors and insurance company which, if any, costs you may be responsible for.

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Who oversees the conduct of clinical gene therapy trials?

In the US, the use of any drug or treatment is regulated by federal law. The US FDA reviews all clinical trials before patients can be treated. Federal law also requires a local review of clinical trials by a group of independent experts called the Institutional Review Board (IRB). The IRB is composed of physicians, scientists, patient advocates, and community representatives. The IRB must review and approve the clinical trial, including the informed consent document, prior to patients being treated.

Gene therapy studies have additional oversight when they are performed at centers that conduct research supported by the federal government. All such clinical trials must be submitted for federal evaluation by the National Institutes of Health. At the local level, an independent group of DNA experts, the Institutional Biosafety Committee (IBC), must review and approve the study as well.

Any and all side effects associated with treatment must be reported to the FDA, the IRB, the IBC and the NIH. Severe side effects must be reported immediately and the FDA, IBC or the IRB can stop the clinical trial if there is concern that the risk of the procedure outweighs the potential benefit.

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Why are clinical trials needed?

Before a treatment can be licensed in the US, it must pass a series of evaluations. The initial studies are performed in the laboratory and with animals to demonstrate the potential effectiveness of the treatment at a specific dose. Animal safety studies, called toxicology studies, are then conducted to determine if there are side effects when the gene therapy is administered. If a treatment passes these tests, it is then considered for further evaluation in a clinical trial. While laboratory and animal studies are helpful in predicting the potential benefit and the side effects of new treatments, the effective dose and safety can only be determined in a human clinical trial.

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Finding a Clinical Trial

Your doctor is an excellent resource to help identify clinical trials for a particular disease, but there are also a number of online resources to assist in finding clinical trials currently accepting patients.

Helpful Websites

Our list of resources helps put patients in touch with foundations and patient advocacy groups.


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