The US FDA expects to approve 10 to 20 gene therapies a year starting in 2025.[i] 

However, for any type of new medicine to be approved, it first must be proven to be safe and effective. The FDA and federal regulators in other countries review scientific data about an investigational therapy to help decide if the potential benefits of a medicine outweigh the possible risks. These data are accumulated in preclinical and clinical trials. While preclinical research involves the treatment of animals, clinical trials evaluate the safety and effectiveness of an investigational treatment in people.

More than 800 gene therapy clinical trials are under way, and by 2020, the FDA expects to receive 200 applications per year to start other such trials.[i] 

Typically, clinical trials are classified into four progressive phases that align to the development of a therapy. Sometimes, two stages of development can be combined with the permission of federal regulators. This is why some studies are classified as Phase I/II or Phase II/III clinical trials. This is done, in part, to accelerate the development of therapies for certain diseases that are particularly serious or have an urgent need for a treatment. 

The chart below outlines the four phases of clinical development. For more detailed information, visit: the National Institutes of Health.

Phase I
  • First time a drug is administered in humans.
  • Often involves a small number of patients.
  • Designed to study how a drug interacts with the body.
  • Helps determine a safe dose.
  • Identifies adverse events.
Phase II
  • Continues to determine safety.
  • May involve a larger number of patients than Phase I.
  • Gathers initial data about effectiveness.
  • Subcategory A studies dose.
  • Subcategory B studies effectiveness.
Phase III
  • Designed to confirm effectiveness.
  • Monitors for range and severity of adverse events.
  • May involve a larger number of patients than Phase II.
  • Often labeled as "pivotal" by regulators, meaning results could be a catalyst for FDA approval.
Phase IV
  • Conducted after a drug is approved.
  • Required for only some therapies.
  • Collects additional data about risks and benefits.

Why Participate?

Participating in a clinical trial can advance medical research and help being new treatments and cures to patients faster.

Participation can also help us all learn more about a disease and ways to care for patients. Results from clinical trials provide information about the benefits and risks of a potential treatment, or ways to prevent, manage or detect a disease. The decision to volunteer for a clinical trial is important and should always be made in consultation with a physician and members of the research team.




[i] Statement from FDA on new policies to advance development of safe and effective cell and gene therapies. Jan. 15, 2019.