Immune barriers to successful gene therapy

Immune responses to viral vectors pose one of the main obstacles to successful human gene replacement therapy, unless gene transfer vectors are applied to immune-privileged sites. Both innate and adaptive immunity work in concert against sustained gene transfer, but the functions of patients' regulatory T cells (Tregs) and tolerogenic dendritic cells (DCs) could potentially be harnessed to reduce these immune responses. Over the last few years, immunologists have gained an ever-increasing knowledge of immunoregulatory pathways, especially those that prevent or dampen adaptive immune responses. The gene therapy community is now in a position to use this expanding knowledge in basic immunology to overcome the so far nearly unsurpassable obstacles posed by the immune system to the long-term replacement of missing or faulty genes by the use of viral vectors. Here, we discuss the current challenges in overcoming immune barriers to gene therapy. In addition, we point out potential strategies that might allow circumvention of cellular or humoral immune responses against the vector or the transgene product.