Noninvasive transplant-rejection test?

Noninvasive transplant-rejection test?

An experimental method using radioactively labeled cells todetect the early stages of transplant rejection may be practical as either a replacement or a supplement to current techniques that require a series of heart-muscle biopsies, according to a report in the April CIRCULATION.

Researchers at Washington University School of Medicine inSt. Louis tracked blood lymphocytes labeled with the radioactive compound indium-111 and injected into 16 dogs that had received heart transplants. Infiltration of lymphocytes into a graft is a sign of early rejection, and preliminary work in St. Louis and elsewhere had suggested the protocol might be useful in a clinical setting.

After transplantation, blood was removed periodically fromeach dog, lymphocytes were separated out using a centrifuge and the cells were radiolabeled with indium-111. The labeled lymphocytes then were injected into the dog from which they had been drawn. Radioactivity in the heart was measured using a procedure called gamma scintigraphy, and biopsies were done at the same time for comparison.

Transplanted animals were divided into two groups: thosegiven the immunosuppressive drugs cyclosporine and prednisone, which are routinely used following transplantation, and those not given drugs to dampen the immune system's rejection of the graft. In dogs not receiving the drugs, infiltration of the graft by indium-111 lymphocytes began about six days after the transplant. No infiltration occurred in drugtreated animals, although labeled cells did appear within two days after the drug treatment was discontinued two weeks after surgery. Accumulation of the lymphocytes increased with time in heart recipients, but did not appear in animals not given transplants.

Although the method offers certain improvements overbiopsies, which require catheterization through the jugular vein, it presently requires more technician time and leadingedge technology. Authors of the report say that overexposure to radioactive materials is undesirable, pointing out that under current Food and Drug Administration standards for indium-111-labeled cells, four to five such assays per patient per year may be the allowable maximum. Despite these potential limitations, the scientists suggest that the technique may help monitor responses to immunosuppressive drugs, as well as determine when a biopsy is needed.