Immunex Corp.'s colony stimulating factor fused to interleukin-3 is helping to establish a new mouse model for human bloodcell production, a model that also promises new approaches togene therapy.

University of Toronto researchers transplanted human bonemarrow into immune-deficient SCID mice, then gave theanimals mast cell growth factor and the fused GM-CSF-IL-3molecule that Seattle-based Immunex (NASDAQ:IMNX) callsPIXY321.

The factors greatly enhanced the extent of marrow grafting.Compared with untreated mice, the factors boosted the numberof human blood cells present by 10- to 100-fold, the scientistsreported in today's issue of Science.

While other procedures with SCID mice can partially re-createthe human blood system, this approach appears to uniquelyengraft the progenitors of all red and white cells in the blood.Stem cells, the originators of all blood cells, have been difficultto study and manipulate because they comprise only 1 percentof marrow cells.

The scientists found in the animals one of the most immatureprogenitors that can be detected by available assays.

The mice "expand the range of human diseases that can now bestudies in this model," the researchers said, and will "providean in vivo model to test gene therapy strategies targeted tostem cells rather than T cells."

BioWorld reported on Thursday that the Recombinant DNAAdvisory Committee of the National Institutes of Health gaveresearchers permission to use stem cells for the first time in agene therapy trial. The trial is aimed at curing adenosinedeaminase deficiency, an immune system disorder.

Repeated injections are necessary in the current approach,which uses cells to carry corrective genes into the body. Butstem cells, once altered genetically and successfully engrafted,would not have to be replaced. -- Roberta Friedman, Ph.D.

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