Various phases are involved in the development of gene therapy product and its approval. The first stage for the development of the product is known as the pre-IND stage followed by the three investigational phases (phaseI-III) during which the data produced helps in getting a license for the product. After getting the license, in the post licensing phase (phaseIV), post marketing studies are conducted. The FDA is involved in reviewing all the phases of IND.

Phase-I is conducted to monitor and assess the product safety in a given population of patients. It enables assessment of the mechanism of action, structure-activity relationship and metabolic as well as the pharmacologic behaviour of the drugs in human. Effectivity of the drug and the associated side effects can also be established with the change in dose. Generally 10-40 study subjects are administered with the drug in the phase-I gene therapy study. The scientific design of phase-II studies depend on the amount of information accumulated with respect to the pharmacokinetics as well as the pharmacological effects of the drug.