Globoid cell leukodystrophy (GCL or Krabbe disease) is a recessive disease 
caused by mutations of the lysosomal enzyme galactocerebrosidase (GALC) and 
twitcher is the murine model of GCL. We have prepared retroviral packaging cell 
lines to transduce the GALC gene. Retroviral transduction restored GALC activity 
in GCL fibroblasts and increased such activity to very high levels in 
immortalized neural progenitor cells (ST14A cells). GALC activity was also 
normalized in twitcher fibroblasts co-cultured with ST14A cells over-expressing 
GALC, demonstrating that this enzyme is secreted and can be imported efficiently 
by GALC-deficient cells. These results give the necessary background to evaluate 
the therapeutic effect in twitcher of brain grafting of neural progenitor cells 
engineered to release high levels of GALC.