For the first time, living cells from humans have been transplanted successfully into mice, scientists reported yesterday, suggesting that it may become possible to do the opposite, using animal organs to cure human diseases.
By treating the human cells, "masking" them from the mouse's immune system, Dr. Denise Faustman said, she and colleagues at Massachusetts General Hospital in Boston were able to implant the cells without rejection and without using drugs to suppress the rodents' normal immunity. The transplanted beta cells from the pancreas survived in the mice and produced human insulin for months.
"We've been successful with what are considered in many ways the most difficult kind of transplants, from one species to another," she said. "We accomplished this without having to treat the mice with drugs."
Her report is published in this week's issue of Science.
The work has important implications for transplant medicine. Thousands of transplant operations for kidneys, livers and other vital organs are done in hospitals nationwide, and in each case, immune-suppressing drugs such as cyclosporine are needed to keep the body from rejecting the "foreign" tissues.
But suppressing immunity also disables the body's main line of defense. Patients become vulnerable to bacteria and viruses, as well as increased risk of cancer. There can also be side effects, such as kidney damage, from such drugs.
In addition to solving rejection problems, Dr. Faustman's interspecies transplant experiment might lead to an end to the chronic shortage of available organs. But using the new approach in humans, with cells or organs from animals, was not tried, and probably will not be possible for years, she said.
Normally, the mouse's immune system would identify human cells as "foreign" invaders and try to destroy them. The scientists treated the human cells with fragments of special antibodies that attached themselves to the human cells. This "masking" prevented the mouse's immune system from identifying the cells as foreign.
Dr. Faustman said that some of the mice given implants were killed for autopsy after 30 days and others after 200 days. None showed signs of rejecting the human cells. In fact, she said in a telephone interview, "we think the grafts became more stable with the passage of time."
Pathologist Paul Lacy, at Washington University in St. Louis, said the research "is a very interesting and important study." But he is not sure how long the implanted cells can be protected from rejection, or how, exactly, rejection is avoided.
"I don't know how that can be," he said. But "if this holds up, it could be used for treating human islet [beta] cells before they are implanted into diabetic patients. We would try to see if we can do the same thing in human-to-human transplants, without continuous immunosuppression."
Dr. Lacy and his colleagues have been attempting to replace diabetics' beta cells with human implants. Recently they found that the implants survive in patients who are immunosuppressed because of a kidney or other transplant operation.
Animal-to-human transplants have been tried and failed. In 1984 in California, a baboon's heart was used to replace Baby Fae's severely malformed heart. But she died a few days later as the baboon heart was being massively rejected.