Inside this Month
Authors: Robert M. Frederickson
Journal: Molecular Therapy (2003)

Human embryonic stem (hES) cells can grow indefinitely in culture, yet retain the ability to dif- ferentiate into any type of cell. The exploitation of these cells for regenerative medicine depends on the development of technologies to manipulate these cells genetically in vitro. In this issue, Benjamin Ruebinoff and colleagues demonstrate stable transduction of hES cells with self-inactivat- ing, HIV-1-based gene vectors expressing green fluorescent protein. Importantly, the modified cells retained both their capacity for self-renewal and their pluripotent potential, suggesting the vectors will be useful to engineer human stem cells for both therapeutic applications and stem cell research. A major drawback of alphaviral vectors is that they strongly inhibit host protein synthesis, lead- ing to apoptotic cell death of trans- duced cells. In this issue, Kenneth Lundstrom and colleagues character- ize new Semliki Forest Virus repli- cons that have been engineered to reduced vector cytotoxicity. Previously described point mutations in nonstructural protein 2 (nsP2) were combined to produce new vec- tors with reduced cytotoxicity, and which improved cell survival and enhanced transgene expression in neuronal cells and hippocampal slices. The morphology and physiol- ogy of transduced neuronal cells were also better conserved. Conditionally replicating aden- oviruses are therapeutic agents that replicate only in tumor cells. Animal models are essential to evalu- ate new cancer therapies, yet human adenoviruses are unable to replicate in nonhuman cells. While the tumor cells are often of human origin, the stromal and support cells are not, limiting the ability of current pre- clinical models to assess the effec- tiveness and safety of the therapy. In this issue, Akseli Hemminki and col- leagues present a new test system for conditionally replicating adenovirus- es based on canine adenviruses. The authors engineered canine viruses that only replicate in dog osteocarcinoma cells. The translational potential of the sys- tem will ultimately depend on the simi- larity of the viruses, tumors and immune responses between dogs and humans. Allergic asthma is believed to be caused by a dysregulated, T helper-2 lymphocyte (Th2)-biased immune response. Th2 cytokines IL- 13 and IL-4 play important roles in asthma pathogenesis, and interfer- ence with their action can alleviate symptoms in a mouse model. A recombinant IL-4 receptor antago- nist, IL-4RA, has been shown to be effective in a murine model, and a human form of the protein is now being tested in clinical trials. In this issue, John Murphy and colleagues investigate the possibility of deliver- ing the therapeutic by gene therapy via an adeno-associated viral vector. The Herpes Simplex Virus (HSV) amplicon is a useful vector to deliver gene therapeutics to the cen- tral nervous system (CNS): It is neurotropic, can carry large genetic payloads and is easy to manipulate. However, in vivo delivery of HSV amplicons exposes the recipient to foreign antigens, such as virion com- ponents and viral proteins expressed by the associated helper virus. In this issue, John Olschowka and colleagues detail the innate immune response resulting from delivery of HSV-1-based vectors to the CNS. They document that helper-virus free amplicon preparations gave rise to a less deleterious immune response profile due to the absence of helper virus gene expression.