By David N. Leff
Among the great life-saving feats of the last half-century, organ transplantation ranks high. But while replacement hearts, lungs, livers and kidneys prolong their recipients' life expectancy, the gift grafts take a toll on the quality of that life.
The foreign tissues installed in a patient's body exact a form of lifelong molecular blackmail called immunosuppression. Without it, the organ's new host mounts a furious toxic cleansing — rejection — to rid itself of the alien intruder.
But with immunosuppression, drugs such as cyclosporine expose the donor organ's new owner to the constant threat of infection. And cyclosporine has other adverse side effects, from excessive hairiness to high blood pressure, tremor, gum overgrowth and kidney dysfunction.
That's why transplant immunologists the world over are striving to devise strategies that will avoid graft rejection without the need for chronic immunosuppression.
What they are looking to create is a state of tolerance between host and donor cells, something like the immunological equivalent of the Oslo peace accord between Israel and the Palestinians, or the Dayton agreement among Serbs, Croats and Bosnians. Neither of these pacts proposed to kindle friendliness between the adversaries, merely peaceful coexistence.
That's what Japanese transplant scientists report they have achieved, in the current issue of the Proceedings of the National [U.S.] Academy of Sciences (PNAS), dated June 9, 1998. Their research paper bears the title: "A strategy for organ allografts without using immunosuppressants or irradiation."
Of the article's 15 co-authors, the sole American is pioneer immunologist Robert Good, who, as an academy member, sponsored PNAS' acceptance of the manuscript. Good is on the faculty of the University of South Florida, in St. Petersburg.
"These are experiments in mice," he told BioWorld Today, "and they are highly reproducible in mice. If all of the paper's results can be reproduced in a larger experimental animal," he continued, "then they should be adaptable to a human. There's nothing in their strategy that precludes that."
But Good added a caveat: "This is tricky, because we don't understand the exact mechanism that is operating in their strategy."
Four Steps To Tolerance
The paper's senior author is immunologist Susumu Ikehara, chief of pathology at Kansai Medical University in Osaka, Japan. "Ikehara has been working on chimerism [coexistence of disparate cells] for a number of years," Good observed, "and induction of a tolerance state under a variety of circumstances."
Good went on, "I've been involved in extensive collaborative work with Ikehara since 1977. He worked in my laboratory for three years." So did several of the PNAS' lead co-authors, among them experimental transplant biologist Haruo Morita.
Good has been working on the issue of tolerance induction, he recalled, "ever since 1956. when we first showed that we could produce immune tolerance in adult mice."
Ikehara and his colleagues summed up in four steps their strategic game plan to tolerize mice against foreign donor skin grafts:
1. "Inject T cells from the spleen of the donor, to facilitate acceptance of the allogeneic [same-species but non-self] engraftment.
2. "Induce donor-specific anergy [immune non-responsiveness] in the cytotoxic T lymphocytes [CTLs] of the recipient." [CTLs are killer cells that attack and destroy donor organs by acute rejection.]
3. "T helper type 2 cells become the dominant T cells in the recipients that are accepting the skin transplants.
4. "A lasting chimerism (microchimerism) is established in these recipients."
The young female mice in the teams' experiments, slated to receive the skin grafts from rodents of a different, immune-incompatible strain, on Day One had a quantity of donor bone-marrow cells and spleen cells injected into their portal veins.
"The portal venous route," Good pointed out, "has an especial influence, particularly in producing immunological unresponsiveness."
The murine patients also got two injections of low-dose cyclosporine A, to prime their immune systems against the impending non-self skin grafts. These consisted of full-thickness oblongs of skin, one centimeter by 1.5 centimeters, excised from the backs of donor mice, and rendered hairless by plucking and depilation.
On day seven, these donor-organ surrogates were stitched to graft beds on the recipients' chests.
From Murine Skin To Porcine Kidney
Two weeks later, the grafts had "taken," with no sign of rejection, in all of the treated mice, and their subsequent survival lasted beyond 350 days — about half of a mouse's normal life span — and still counting.
"Luxurious hair-growth was observed," the PNAS paper reported, "and it was counterpoint to the normal hair growth."
A control contingent of animals, which received grafts without the prior tolerance-inducing injections, had lost the donated tissue to rejection by 14 days after transplantation.
The successful cohort received a second skin donation 238 days after the first, and its survival to date is more than 100 days.
Having proven their point with skin, the Japanese transplanters segued into the pancreas, a tissue closer to the organ-transplant mainstream. "Allopancreatic tissues transplanted under the renal capsules of recipient mice," their PNAS paper reported, "have been accepted and associated with production of lasting immunologic tolerance."
What's more, in these pancreatic experiments, the team performed the transplant not on Day Seven, as with the initial skin grafts, but on Day One, simultaneously with the portal-vein injections.
"A single-day protocol may become important in the future," the co-authors predict, "because it might prove more applicable to organ transplantation in humans than a protocol that requires several days to complete."
So might xenotransplantation — growing organs in animals such as pigs to meet growing human replacement needs.
Haruo Morita, co-leading author of the PNAS paper, told BioWorld Today, in a brief telephone conversation, that his Kansai group — at their new transplantation center — has recently applied their skin-graft protocol to pigs, "with very good results. The transplantation," he said, "has already survived 200 days."
As for potential organ xenotransplants, "we have already tried it in pigs now," Morita observed. "For example, kidney is better accepted than small bowel."
Good was at a ceremony in Tokyo last month on May 13, to receive an imperial award, the Order of the Sacred Treasure, Gold and Silver Stars, conferred by the emperor of Japan. The distinction honors Good's "great achievements in academic research, and further development of scientific exchange between the U.S. and Japan." *