The mice were SCID mice. They have no adaptive immune system to speak of. I made another post in this thread and included some links.

This is a very incredible result though. Even if immunosuppressants are required, think of all the non-patient outcomes: easily sourced human SC-beta cells for research and high throughput study. This stuff can be grown at volume, and the techniques will only improve. The results will also inform research into other cell lines. Bottom line, this is yet another step forward for stem cell tech.