Recent developments in retroviral gene delivery systems

Since the first gene therapy clinical trial carried out by Rosenberg et al. in 1990 fit, recombinant retroviral vectors are still the most popular gene delivery tools for gene therapy purposes. According to the databases of the Jour nal of Gene Medicine [101] 35% of gene therapy protocols employ retroviruses, other vectors such as adenoviral vectors are used in 27%, pox viral vectors in 6%, adeno-associated viral vectors in 2% and herpes simplex based vectors in 0.5% of clinical trials. It has become clear that the early retroviral vectors based on simple retroviruses (e.g., murine leukaemia viruses (MLV) are characterised by relatively low viral titre, low transduction efficiency and difficulties in in vivo administration. On the other hand, lentiviral vectors (complex retroviruses) can be grown to a high titre, can stably transduce non-dividing cells and can effectively deliver genes to human progenitor cells (CD34+). This article aims to summarise the first year of the 21st century's developments in the retroviral gene delivery system.