1. ¹The Children's Hospital of Philadelphia, Department of Pediatrics, Hematology Division, Philadelphia, Pennsylvania, USA
2. ²University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA

Correspondence: Valder R Arruda, University of Pennsylvania School of Medicine, The Children's Hospital of Philadelphia, 302F Abramson Research Center, 34th Street and Civic Center Boulevard, Philadelphia, PA 19104. E-mail: arruda@email.chop.edu

Received 15 April 2009; Accepted 15 June 2009; Published online 7 July 2009.

Abstract

The success of gene therapy strategies to cure disease relies on the control of unwanted immune responses to transgene products, genetically modified cells and/or to the vector. Effective treatment of an established immune response is much harder to achieve than prevention of a response before it has had a chance to develop. However, preventive strategies are not always effective in avoiding immune responses, thus the use of drugs to induce immunosuppression (IS) is required. The growing discovery of novel drugs provides a conceptual shift from using generalized, moderately intensive immunosuppressive regimens towards a refined approach to attain the optimal balance of naive cells, effector cells, memory cells, and regulatory cells, harnessing the natural tolerance mechanisms of the body. We review several strategies based on transient IS coupled with gene therapy for sustained immune tolerance induction to the therapeutic transgene.