WASHINGTON _ Doctors who last week drippedbaboon cells into AIDS patient Jeff Getty now mustgrapple with a new challenge _ perfecting tests that candetermine whether the patient has become infected with ababoon virus.
Scientists have long known that at least 150 diseases canspread from animals to humans. Among them are rabies,hantavirus and herpesvirus B _ three of the most virulentdisease-causing organisms known to afflict humans.
But until the recent surge of interest in usingxenotransplants as a comparatively plentiful source ofscarce replacements for human organs and tissues,scientists have had little motivation to tackle the toughtask of making diagnostics for such a high-risk enterprise.
Doctors say the risk of transmission in the Getty case isunknown, but it may be enhanced by the 38-year-old SanFranciscan's deteriorating immune system, and the factthat the transplanted bone marrow cells were drippeddirectly into his bloodstream.
The baboon that was sacrificed for this experiment wasknown to be infected with a retrovirus _ baboonendogenous retrovirus (BEV), which infects all cells ofall baboons _ and baboon versions of cytomegalovirusand Epstein Barr Virus.
It was one of the rare baboons not infected with Foamyvirus, a retrovirus which in humans is considered asuspect in chronic fatigue syndrome.
Louisa Chapman, an epidemiologist in the retrovirusbranch of the Centers for Disease Control and Prevention(CDC) in Atlanta, said the agency has attempted to adapta "generic" test that identifies reverse transcriptase foruse in the Getty case. Researchers hope the test wouldidentify baboon endogenous retrovirus if it takes hold inGetty's system.
The challenge in this case is finding some way to adaptthe test so that it responds only to reverse transcriptase(RT) in BEV and not in Getty's HIV, when specimens ofhis blood, saliva and semen are added to the reagents.
Walid Heneine, at the CDC, has taken on the task, using ageneric RT test that is a "million-fold" more sensitivethan other generic retrovirus screening tests. To obtainBEV-specific results, Heneine added an inhibitor that isspecific for HIV reverse transcriptase, and, if it works asintended, should eliminate it from the test result.
Another CDC researcher, Diane Pardy, has adaptedpolymerase chain reaction (PCR) technology to search forthe virus itself.
Baboon endogenous virus is regarded as a "chimera,"meaning that was formed from other retroviruses overeons, and passed through generations in offspring.
Although humans are not believed to be at risk of gettinginfected with this virus under ordinary circumstances,some researchers worry that the Getty experiment "issetting up a situation where BEV can be transmitted tohumans," Chapman said.
The reason is found in a simple laboratory test.
When BEV is cultivated in a mixture of baboon andhuman tissues, human cells also become infected.
Chapman said CDC will test Getty's saliva and semen forthe next year or more, at regular intervals, to determinewhether humans are capable of transmitting BEV oncethey become infected.
Developing tests to guard against the baboon versions ofEBV and CMV are even more complicated, she said.Researchers are limited to using PCR to try to isolate theviruses. No one knows how successful that effort will be.
Jonathan Allan, a primate virologist at the SouthwestFoundation for Primate Research in San Antonio, said,"There's no way to know whether Baboon EBV would beinfectious in humans. I would assume it would beinfectious because there is a fairly wide host range intissue culture."
Allan describes himself as an opponent of baboon-to-human transplants because, he said, "You can't makebaboon transplants safe. How can you pick up unknownagents with the diagnostics that are available? It'sabsurd."
Although the FDA has responsibility for approving suchexperiments, CDC officials have publicly expressedconcerns about going forward with the research.
An eminent CDC researcher and a voting member of theFDA's Biologic Response Modifiers AdvisoryCommittee, Harold Jaffe, expressed specific concernsabout the Getty experiment at the advisory committee'smeeting in July. But once the FDA approved theexperiment, Chapman said, the agency felt an urgentresponsibility to monitor Getty "for infections that mighthave public health significance." n
-- Steve Sternberg Special To BioWorld Today
(c) 1997 American Health Consultants. All rights reserved.