"By splicing jellyfish genes into white blood cells—nature’s front line against viral invaders—he created a biological sensor that glows in the presence of disease."
The "jellyfish genes" in question are probably GFP[1] (Green fluorescent protein), which has been spliced into many organisms. You can even buy fish with the gene[2].
[1] http://en.wikipedia.org/wiki/Green_fluorescent_protein [2] http://en.wikipedia.org/wiki/GloFish