Even though gene therapy has worked well in animal models (mice and dogs), its success is yet to be replicated in patients of haemophilia. The practical problem of delivering the therapeutic genes at the appropriate site that efficiently produce clinical benefits without any toxic side effects has yet to materialise. Gene therapy must avoid altering the DNA of germ line cells (sperm or ova) to avoid the potential of transferring unknown effects to a patient’s child. In a liver-directed gene therapy clinical trial, the gene therapy product was directly infused to patients’ livers as that is thought to more efficiently produce clotting factor from a given amount of gene product. One haemophilia B patient did achieve about 10% of normal Factor IX activity but the level fell within a month due to an immune response to the modified cells. Current work is going on to attenuate the immune responses so that long-lasting effect can be achieved.
As yet gene therapy remains a promising treatment modality for the future.