mansoni schistosomes, combined with a preliminary analysis of the S. mansoni Actin 1.1 (SmAct1.1) promoter sequence (23). Expression of luciferase driven by the SmAct 1.1 promoter was only transient. The authors suggest that the loss of expression over time was probably not because of the loss of plasmid, because transfected parasites that were no longer expressing the luciferase remained PCR positive for luciferase DNA for 8 weeks learn more following electroporation. This finding is similar to that reported by Yuan et al. (24). These results also indicated that the electroporation protocol described was either insufficient to deliver the transgene to the germline or that the transgene was not

integrated at high frequency to be able to be detected in transgenic F1 parasites. Most of the aforementioned strategies for the introduction of transgenes into parasitic helminths result in transient, nonheritable expression of the gene of interest. For many gene expression and functional studies, this may be sufficient; however, for other types of studies such as the investigation into cellular and molecular aspects of the host immune response to the parasite, heritable expression is required. Whilst techniques for transgenesis in the free-living nematode Caenorhabditis elegans have been established for decades, heritable transgene expression in parasitic worms is still in its

infancy, although significant inroads are being made into achieving this. It is unlikely that transfection with plasmid-based constructs, as Roscovitine described in many of the reports above, will result in chromosomal integration of transgenes. However, a way forward to achieve this aim is to use gene therapy-type approaches utilizing retroviruses (e.g. gamma retroviruses or lentiviruses),

retrotransposons or transposons, which enhance the likelihood of development of heritable, transgenic lines of schistosomes. This is particularly likely if germline cells can be targeted for transduction. In addition, retroviruses or transposons can be used to transfer gene cassettes for the production of siRNAs, thereby combining a powerful knock-down technology with an efficient delivery system offering the possibility for heritable RNAi targeting specific host cell genes (25,26). Together with colleagues, 3-mercaptopyruvate sulfurtransferase we have made the first attempts down this track and reported the use of retroviruses and transposons to transduce schistosomes (27,28). In Kines et al., we produced replication incompetent Moloney murine leukaemia virus (MMLV) virions that were pseudotyped with vesicular stomatitis virus glycoprotein (VSVG) carrying a luciferase reporter gene. Virions co-cultured with schistosomes interacted with the tegument of the worms and immunofluorescence studies indicated that the retroviral capsid and RNA genome were released within the surface cells.