BioTransplant Claims Two-Year Mismatched Transplant Survival

Researchers in the USA have shown that it is possible to transplant fully-mismatched kidneys from one nonhuman primate to another, and maintain graft survival for over two years, without chronic immunosuppression. The approach, carried out by researchers from the Massachusetts General Hospital, will form the basis of a human-to-human transplant system which will be tested by US firm BioTransplant.

The new approach, called AlloMune, rests on the stimulation of specific immune tolerance, and involves treating the recipients with an antibody (BTI-322) to remove mature immune cells, as well as the use of low-dose irradiation to make space for donor bone marrow. The researchers then inject the donor bone marrow, transplant the donor kidney and give a four-week course of immunosuppressive drugs. The aim is to engender a state of mixed chimerism, in which the immune system of the recipient regrows after partial ablation in the presence of both donor and recipient hematopoietic elements, and becomes tolerant to both.

In all seven of the primates tested, the graft survived for more than six months without the need for immunosuppression, and the longest survival was two years. In contrast, control recipients who did not receive the donor marrow rejected their new kidneys within two months.