Challenges in T cell receptor gene therapy Benjamin J. Uttenthal * Ignatius Chua Emma C. Morris Hans J. Stauss Department of Immunology, Institute of Immunity, Infection and Transplantation, University College London (UCL), Royal Free Hospital, London, UK *Correspondence to: B. J. Uttenthal, Department of Immunology, Institute of Immunity, Infection and Transplantation, University College London (UCL), Royal Free Hospital, Rowland Hill Street, London NW3 2PF, UK. E-mail: b.uttenthal@ucl.ac.uk Abstract The function of T lymphocytes as orchestrators and effectors of the adaptive immune response is directed by the specificity of their T cell receptors (TCRs). By transferring into T cells the genes encoding antigen-specific receptors, the functional activity of large populations of T cells can be redirected against defined targets including virally infected or cancer cells. The potential of therapeutic T cells to traffic to sites of disease, to expand and to persist after a single treatment remains a major advantage over the currently available immunotherapies that use monoclonal antibodies. Here we review recent progress in the field of TCR gene therapy, outlining challenges to its successful implementation and the strategies being used to overcome them. We detail strategies used in the optimization of affinity and surface expression of the introduced TCR, the choice of T cell subpopulations for gene transfer, and the promotion of persistence of gene-modified T cells in vivo. We review the safety concerns surrounding the use of gene-modified T cells in patients, discussing emerging solutions to these problems, and describe the increasingly positive results from the use of gene-modified T cells in recent clinical trials of adoptive cellular immunotherapy. The increasing sophistication of measures to ensure the safety of engineered T cells is accompanied by an increasing number of clinical trials: these will be essential to guide the effective translation of cellular immunotherapy from the laboratory to the bedside. Copyright © 2012 John Wiley & Sons, Ltd. Keywords cell therapy; gene therapy; immunology; tumour targeting Introduction The potential of adoptively transferred immune cells to cure cancer was first demonstrated over 50 years ago, when leukaemia was found to be eradicated in irradiated mice receiving allogeneic but not syngeneic bone marrow transplants [1]. Much later, it became clear that the same cells that caused graft-versus-host disease (GvHD) could also mediate a graft-versus-leukaemia effect [2], with a critical role for T cells being confirmed by the finding of increased leukaemic relapse in recipients of T-cell depleted bone marrow trans- plants [3,4]. The major goal of cellular immunotherapy has subsequently been to harness the cytotoxic and other immunomodulatory capabilities of T cells to eliminate cancers or viral infections without eliciting undesired effects such as GvHD. An approach that was quickly identified involves the adoptive transfer of CD8+ T cells that are specific for antigens expressed only, or at much higher levels, in cancer or virally infected target cells. Both autologous and allogeneic T cells have been isolated, expanded in vitro in conditions that favour cells specific for a target antigen, and infused into patients successfully to treat Epstein–Barr virus (EBV) [5], cytomegalovirus (CMV) [6,7] and melanoma [8]. Essential to this strategy is the isolation of T cells with high functional avidity for the relevant antigens. The techniques of T cell receptor (TCR) gene REVIEW ARTICLE Received: 20 March 2012 Accepted: 4 May 2012 Copyright © 2012 John Wiley & Sons, Ltd. THE JOURNAL OF GENE MEDICINE J Gene Med 2012; 14: 386–399. Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/jgm.2637