Baboon marrow patient shows no sign of infection
Special Report
Baboon marrow patient shows no sign of infection
Standard precautions, positive-pressure isolation
Baboon bone marrow and human tissues have failed to engraft as hoped in a highly publicized xenotransplant conducted last year on an AIDS patient, who is nonetheless doing well and shows no signs of xenogeneic infection related to the procedure, according to an infectious disease consultant on the case.
Baboon bone marrow cells are resistant to infection with HIV, and thus could potentially be used to reconstitute the immune system against the disease if they can be engrafted in humans. The baboon bone marrow transplant was done on Dec. 14, 1995, and the failure of cell engraftment was reported the following February.
’The bone marrow did not permanently engraft, so from that standpoint it did not work,” says Marian Michaels, MD, MPH, assistant professor of pediatrics and surgery at the Universtiy of Pittsburgh School of Medicine, a member of the IOM xenotransplantation committee, and an infectious disease consultant on the case, which was conducted at the University of California at San Francisco. ’The patient, on the other hand, did quite well better than he had in previous years.”
Patient monitored for life with PCR
It remains unclear whether the pre-transplant medical and immunosuppressive drug ’conditioning” necessary to conduct the procedure or some aspect of the baboon marrow contributed to the positive effect, which has resulted in formerly ineffective AIDS drug therapy now showing positive results. The patient was slated for another medical follow-up, but at nine months out showed no signs of infection related to the xenograft, she says. The clinical evaluation to look for signs of infection includes culturing blood, sputum, and urine for presence of a viral pathogen. The patient will be monitored for life through testing that includes the use of polymerase chain reaction (PCR) for known baboon and human pathogens as well as any signs of xenogeneic infection caused by a new virus.
’Even though he is not having any specific symptoms or signs, when he comes in and has these specimens obtained, we put them on different cell lines that we know will grow primate viruses as well as human viruses and culture them,” Michaels says. ’Even if there is no cytopathic effect, we freeze everything so they are stored and archived. To be able to retrospectively look and learn is critical.”
As an infectious disease consultant on two prior baboon-to-human liver xenotransplants at the University of Pittsburgh in the early 90s, Michael developed screening and infection control protocols similar to those recommended in the draft federal guidelines for xenotransplant programs. The baboon marrow recipient, for example, was hospitalized for three weeks following the procedure in an intensive care isolation room. Since respiratory transmission is probably the least likely route of infection from a xenotransplant patient to workers and other patients, the isolation room for the bone marrow case was under positive pressure to the adjacent hallway rather than the negative pressure rooms typically used to contain airborne infectious agents like tuberculosis. Negative pressure rooms can pull other airborne organisms in when doors are opened and closed, putting such immune-suppressed patients at potential risk of infection.
’I felt putting that patient on negative pressure [isolation] was actually putting him at more danger,” she says. ’So we opted to put the patient in a single isolation room and limit the number of visitors just like we would with any intensive care unit patient or a bone marrow transplant patient.”
Had the patient developed signs of respiratory infection such as a cough, negative pressure isolation would have been implemented to minimize the possibility of transmission, she adds.
In terms of hospital personnel, routine standard precautions were reinforced, including an emphasis on handwashing before and after touching the patient or touching equipment in the room. As with recommended standard or universal precautions, gloves and gowns were donned for any procedure that may involve soiling, and masks or eye protection if there was any potential splash or spray to the face, she adds.
’Really, universal precautions are pretty damn good,” she says.
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