Clinicaltrials.gov lists 23 clinical trials of hemophilia B gene therapies (active and interrupted), of which most candidate drugs are AAV-based therapies, with the exception of a study involving lentiviral delivery of the F9 gene to autologous hematopoietic and mesenchymal stem cells (NCT03961243; see Table 1). Here, F9 is linked to hemophilia B.