Final answer:
The FDA can halt gene therapy development at the submission of an IND, during clinical trials, or after the therapy is marketed, ensuring patient safety and that high standards for effectiveness and safety are maintained.
Step-by-step explanation:
The FDA can halt the development or use of gene therapy at multiple stages: a) on submission of an IND (Investigational New Drug) application, b) during clinical trials, or c) after manufacturing and marketing of the approved therapy. The FDA can issue a “clinical hold" if any problems are identified prior to or during clinical trials to ensure patient safety and to address any issues related to the therapy's effectiveness and safety. Moreover, cases of adverse outcomes during or after trials, such as the infamous Gelsinger case or the development of leukemia in SCID patients, can prompt the FDA to temporarily stop clinical trials for further investigation and reassessment of the risk-benefit balance of the therapy.