In the third approved trial of gene transfer in humans, St. JudeChildren's Research Hospital researchers have reimplanted achild's marrow cells containing markers that will enable themto track response to cancer therapy.

The marrow, containing markers delivered using a vectorsupplied by Genetic Therapy Inc., was implanted into an 11-year-old leukemia patient, the Memphis hospital and thecompany announced Tuesday.

The trial is the first approved gene transfer protocolperformed outside of the National Institutes of Health and thefirst involving marrow cells. Genetic Therapy of Gaithersburg,Md., supplied the vectors for the other two trials as well, saidMarc Schneebaum, chief financial officer.

The marker is a gene conferring resistance to neomycin. It willhelp researchers track the marrow cells to see if relapsescome from failure of the therapy or from hidden cancer in themarrow. Typically, marrow is culled from a patient beforeintensive therapy destroys marrow along with cancer cells.Following therapy, the saved marrow is reimplanted.

If the patient relapses in the St. Jude trial, polymerase chainreaction as well as culturing of the marrow cells in thepresence of neomycin will be used to determine whether themarker is present.

If occult cancer in the marrow indeed contributes to failure,the marker should help scientists figure out how to purgemarrow more effectively, Dr. Malcom Brenner of St. Jude toldBioWorld.

The marker is carried into about 10 percent of both normal andtumor cells, as stable incorporation only occurs if the cell iscaught actively dividing, Brenner said.

The neomycin gene was culled from a bacterium and engineeredinto a mouse retrovirus, which functions as the vector. Theretrovirus has been "heavily modified so it can't reproduce,"Brenner said. Concerns about implanting gene-altered marrowmade the approval process especially prolonged, he said.

In two weeks, a child with neuroblastoma will also receivemarked marrow, Brenner said.

The vector's developer, Dusty Miller of the Fred HutchinsonCancer Center in Seattle, published data but did not apply for apatent, according to Schneebaum. The company has filed forpatents on other vector constructs it has created, which thecompany has not yet tested in human trials, he said.

Genetic Therapy stock (NASDAQ:GTII) closed unchanged at$8.50.

-- Roberta Friedman, Ph.D. Special to BioWorld

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