WASHINGTON _ The baboon-to-human bone marrow transplantthat was attempted two months ago to save the life of AIDS activistJeff Getty has been a limited success.
Yolanda Colson, a surgeon at the University of Pittsburgh and amember of the transplant team, told BioWorld Today that as a PhaseI clinical study the transplant "had reached its first goal of showingthat the procedure was safe."
Phil Noguchi, whose FDA Division of Cellular and Gene Therapiesregulates xenotransplants, said that the transplant "has failed toachieve its intended therapeutic effect to get engraftment.
"At this point there is no evidence of transmission of endogenousvirus from the baboon but we will continue to follow this over thelong-term," he said.
Noguchi said the agency "is pleased the experiment is continuing andthat its result will help shape how we will approach the next one."
Bone marrow recipient Jeff Getty so far does not appear to havecontracted any virus from the baboon, a concern voiced by someexperts in xenotransplantation late last year. (See BioWorld Today,Dec. 1, 1995, p. 1.) They were concerned about the danger oftransmission of the foamy virus, an organism that is feared to belethal in humans. The issue was confounded by the fact that there areno reliable assays available to determine if a virus had beentransmitted.
The premise behind the transplant was that stem cells from thebaboon would grow in Getty's bone marrow, boosting his immuneresponse to attack the AIDS virus. Researchers thought that becausebaboons do not contract AIDS their stem cells would confer somesort of immunity.
In addition, the transplant team used a new technology that involvedadding facilitator cells to encourage engraftment. Previous baboonbone marrow transplants failed because the host rejected the cells,according to a University of Pittsburgh spokeswoman.
Colson said a polymerase chain reaction (PCR) of Getty's bloodfound no trace of the DNA from the male baboon's Y chromosome.PCR can detect as few as one in a million cells, but "the cells did notcross from species to species." Colson said.
She estimated that because Getty was administered a low dose ofchemotherapy and radiation to quell his immune system prior to thetransplant, his immune response remained robust enough to destroythe baboon cells. "It is likely that we did not give enough radiationand chemotherapy to make space for the bone marrow to engraft,"Colson said.
"There is a fine balance between conditioning enough not to rejectthe marrow but not to do serious damage to an already immunecompromised patient," she explained.
"If we had to do it again we would err on the he side of conditioningless," she added.
The confounding outcome of the procedure is that Getty feels betteras the result of it. "There is a theory that the conditioning contributedto this outcome or it may be unrelated," said Colson.
The transplant was approved by the FDA after considerablediscussion of the public health risks. (See BioWorld Today, July 17,1995, p. 1.) The FDA is expected soon to release guidelines that setout a new paradigm for future xenotransplants that regulate species tospecies transplants now under development by many biotech firms,Noguchi said. n
-- Michele L. Robinson Washington Editor
(c) 1997 American Health Consultants. All rights reserved.