STRASBOURG, France _ The Dutch molecular biologist who clonedthe gene that launched human gene therapy worldwide, reportedanother "first" here at the J.-P. Lococq Gene Therapy Conference onThursday _ a stem-cell DNA transfer.Today, Dinko Valerio is managing director of IntroGene, the companyhe founded last year in Rijswijk, The Netherlands, to manufacture andmarket gene therapy products and processes.Several years ago, as his Ph.D. dissertation, he cloned the gene forhuman adenosine deaminase (ADA), which is lacking in children bornwith severe combined immunodeficiency (SCID). "My gene wasdistributed all over the world," Valerio told BioWorld Today.Two American girls with SCID were the first human subjects treatedwith a missing DNA sequence. They received copies of Valerio's genesequence at the National Institutes of Health.In an unpublished disclosure on Thursday, Valerio told conferenceparticipants of three SCID children (two French and one British) who,last March received injections of bone marrow stem cells transfectedex vivo with the ADA gene's cDNA. The stem cells were purified byCD34 cell enrichment, exposed to the retroviral vector with its ADAgene cargo, then reinfused into the patients."It represented the first use in the world of pluripotent hematopoieticstem cells in human gene therapy," Valerio said."This was based on preclinical work in mice and five years' experiencetransfusing stem cells in Rhesus monkeys." He added, "In theseprimates we have shown that we can safely and effectively introducetrue, long-term, reconstituted stem cells." As with the pioneeringAmerican SCID children, clinical evaluation of the Dutch gene therapytrial is clouded by the fact that all three young recipients receiveregular replacement of their missing enzyme in the form of bovinePEG-ADA, which keeps them healthy."But we have proof of the presence, in their circulating blood, of thenovel gene that we introduced into their stem cells," Valerie said. "Andin one of the three, the transfected stem cells went back to the bonemarrow compartment, homed there, and started generating new cells."In three years, or less, he expects the cells' progeny to repopulate theirhost's peripheral blood, thus restoring endogenous ADA function.Meanwhile, Valerio is planning clinical trials in the coming months toinoculate cancer patients whose stem cells are healthy with multidrugresistance genes. This will be followed by six or seven rounds ofchemotherapy, three weeks apart, in hopes that the transduced cells areselected for, and repopulate the hematopoietic system of those patients.The gene product will then "pump out the anti-tumor cytostatic drugs,"as he put it.Valerio's plan is to enroll 10 to 15 patients, each with non-Hodgkin'slymphoma, breast and bladder cancer, for treatment lasting 12 to 18months. "We're hoping there are fewer side effects," Valerio said."which might make it possible to increase the chemotherapy dosage."He expects to initiate the trials, all in the Netherlands, "before the endof the year. We have approval, and IntroGene is in the process ofmanufacturing the virus."Putting DNA Source Under The SkinArtificial organs will carry the gene for another genetically missingenzyme into the systems of six French infants with Hurler's syndrome,reported Jean-Michael Heard, who heads retroviral and gene transfer atthe Pasteur Institute in Paris. he described these synthetic, in-dwellingDNA carriers to the Thursday session on pre-clinical studies."Neo-organs," Heard explained, are confected of highly hydrophobicGortex synthetic fibers, treated with collagen, heparin basic fibroblastgrowth factor, obtained from yeast cells, and the cDNA gene for alpha-L-iduronidase. Such pseudo-organs, he explained, lodged by minorsurgery under the skin, on the omentum membrane in the peritonealcavity, have excellent blood supplies, proliferate capillaries and canexpress the deficient enzyme for long periods.He aims to implant from two to six such egg-sized creations in sixHurler infants, under 18 months of age who usually die of the geneticdisease before their 10th year. Hurler's affects one newborn in 50,000,Heard told BioWorld Today, "which means 15,000 to 20,000 are bornin France each year."Its horrendous stigmata include skeletal and facial deformation, grosslyswollen spleens and brain lesions. The defect is thought to reside onhuman chromosome 22. The only existing therapy is type-matchedbone marrow transplantation, which can help only half of the Hurler'spopulation, Heard said. The six trial patients will be treated at theNecker Hospital for Sick Children in Paris and DeBrousse Hospital inLyon.However, the proposed gene therapy trial is on hold, Heard said,because Farmitalia, the source of bfGF has stopped production. "Weare in discussion with several companies to supply us with the clinical-grade factor."Much later, after extended animal studies, Heard anticipates applyingthis technology to gene therapy of thalassemia. n
-- David N. Leff Science Editor
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