Advances in Overcoming Immune Responses following Hemophilia Gene Therapy

Both Clinical trials and pre-clinical experiments for hemophilia gene therapy showed that it is important to overcome potential immune responses against gene transfer vectors and/or transgene products to ensure the success of gene therapy. Recently various approaches have been investigated to prevent or modulate such responses. Gene transfer vectors have been specifically engineered and immunosuppressive regimens have been administered to avoid or manipulate the immune responses against the vectors. In order to prevent cytotoxic lymphocyte or antibody formation induced by transgene expression, novel approaches have been developed, including methods to manipulate antigen presentation, development of variant genes encoding less immunogenic proteins or gene transfer protocols to evade immune responses, as well as immunosuppressive strategies to target either T and/or B cell responses. Most of these successful protocols involve the induction of activated regulatory T cells to create a regulatory immune environment during tolerance induction. Recent development of these strategies to evade vector-specific immune responses and induce long-term immune tolerance specific to the transgene product will be discussed.