Manipulation of Haematopoietic Stem Cells with Integration Deficient Retroviral Vectors

The ability to grow haematopoietic stem cells (HSC) in culture would be valuable to expand sources where numbers of cells are limited (such as umbilical cord blood) for application in transplantation, ex vivo gene therapy and basic biological research. However, when grown in vitro, HSCs often die or differentiate into committed blood-cell types. Retro-viruses are useful tools for delivering genes to slowly or non-dividing cells, such as HSC. The aim of this project is to investigate the use of integration-deficient retroviral vectors for short-term delivery of genes to expand blood progenitor cell populations. A BSGT travel grant was awarded, enabling a visit to the Children's Hospital in Boston. A collaboration was initiated with Drs Mick Milsom and David Williams to investigate the feasibility of expressing HOXB4 from integration-defective retroviruses. This gene plays a prominent role in blood stem-cell biology, and overexpression of HOXB4 has been shown previously to enhance HSC self-renewal and enable in vivo and ex vivo expansion of HSCs in mice, dogs and non-human primates. However, there are concerns that permanent overexpression of HOXB4 can lead to cancer, and integrating viral vectors cause insertional mutagenesis. Application of integration-defective vectors for transient expression of the gene should theoretically be safer, although the efficacy is yet to be proven in this system. Experiments have shown the potential for this approach, and possible obstacles which need to be overcome to improve the system will be discussed.