They used a modified version of the HIV virus to transfer a gene for neprilysin to neurons of genetically modified mice which produced human beta-amyloid.
For example, if a yeast cell was genetically modified to include a particular gene, this technique would allow the expression of that gene to come under precise control.
Glaxo has projects on everything from stem cells to gene therapy for rare immune diseases to an emerging area called epigenetics, which looks at how genes are modified.