Type 1 diabetes results from the selective destruction of insulin-producing beta 
cells in the islets of Langerhans, and autoimmune T cells are thought to be the 
mediators of this destruction. T cells are also responsible for allorejection 
once the islets are transplanted into a patient to reduce the negative 
consequences of a lack of insulin. To better understand these processes, we have 
developed a transgenic mouse expressing proinsulin II tagged with a live-cell 
fluorescent reporter protein, Timer. Timer protein is unique because it changes 
color from green to red in the first 24 h after synthesis. With this marker, 
insulin synthesis can be carefully monitored through fluorescent changes over 
time. To complement this new biotechnological research tool, we designed a body 
window to allow for in vivo imaging over time of the islets transplanted under 
the kidney capsule. The window device, which is sutured to replace the 
underlying skin and body wall over the site of islet transplantation, may be 
used to simultaneously observe beta cells and T cells that have been labeled 
with a fluorochrome distinguishable from Timer. The imaging of both 
insulin-producing cells and T cells may be carried out repeatedly for a week or 
more with no need for repeated surgery, while preserving the life of the studied 
animal.