Cell Biol Toxicol (2010) 26:1–20 DOI 10.1007/s10565-009-9139-5 SI: GENETIC MANIPULATION OF CELLS (EIC) Using viral vectors as gene transfer tools (Cell Biology and Toxicology Special Issue: ETCS-UK 1 day meeting on genetic manipulation of cells) Joanna L. Howarth & Youn Bok Lee & James B. Uney Received: 30 June 2009 / Accepted: 24 September 2009 / Published online: 15 October 2009 # The Author(s) 2009. This article is published with open access at Springerlink.com Abstract In recent years, the development of powerful viral gene transfer techniques has greatly facilitated the study of gene function. This review summarises some of the viral delivery systems routinely used to mediate gene transfer into cell lines, primary cell cultures and in whole animal models. The systems described were originally discussed at a 1-day European Tissue Culture Society (ETCS-UK) workshop that was held at University College London on 1st April 2009. Recombinant-deficient viral vectors (viruses that are no longer able to replicate) are used to transduce dividing and post-mitotic cells, and they have been optimised to mediate regulatable, powerful, long-term and cell-specific expression. Hence, viral systems have become very widely used, especially in the field of neurobiology. This review introduces the main categories of viral vectors, focusing on their initial development and highlighting modifications and improvements made since their introduction. In partic- ular, the use of specific promoters to restrict expression, translational enhancers and regulatory elements to boost expression from a single virion and the development of regulatable systems is described. J. L. Howarth (*) : Y. B. Lee : J. B. Uney Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, University of Bristol, Whitson Street, Bristol BS1 3NY, UK e-mail: j.howarth@bristol.ac.uk Keywords Viral vectors . Gene therapy . Adenovirus . Lentivirus Gene transfer technology In 2004, the entire human genome was sequenced and over 25,000 genes were identified (Stein 2004). Some of these initially uncharacterised genes have subse- quently been identified, with many playing important roles in cellular development, maintenance and survival. Techniques that allow the study of these novel genes have therefore been instrumental in elucidating their function. Until relatively recently, gene expression could only be altered in post-mitotic neuronal cells using mouse transgenesis or microin- jection of individual neurons in culture. However, the first adenoviral and Herpes gene transfer systems were highly effective at transducing neurons and could hence be used to study gene function in whole animal systems without developmental compensatory effects (Hermens and Verhaagen 1998). Researchers were quick to see the potential of such systems and started to develop optimised vectors. An ideal gene delivery would: (1) transfer genes into both develop- ing and mature animals; (2) transduce cells with high efficiency; (3) mediate high level, long-term expres- sion; (4) cause limited cytotoxicity; (5) elicit a small/ negligible immune response in vivo; (6) incorporate sufficient lengths of DNA so that transgenes of interest can be accommodated and (7) mediate