The first human trial of insulin-producing cells that have been gene-edited to evade immune attack is a success so far. The cells have survived and produced insulin for a month after being injected into a 42-year-old man with type 1 diabetes early in December.

As a precaution, only a small number of insulin-producing beta cells were injected into a forearm muscle in this initial test, so the man still needs insulin injections. It also remains to be seen how long the…