Tissue and Organ Homotransplantation
Homotransplantation is the transfer of tissue from one individual to another of the same species. Before 1944 homotransplantation of skin had been achieved permanently only between identical twins. While temporary survival of skin between nonrelated individuals had been reported, permanent survivals were unkonwn. In that year, Peter Brian Medawar reported that a second homograft of skin from the same donor rabbit to the same recipient rabbit was rejected more rapidly than the first. His observation suggested that a sensitivity reaction was stimulated in the recipient rabbit—possibly similar to the better-understood antigen-antibody reaction against a foreign protein. Widespread interest was aroused among plastic surgeons, internists, immunologists, and others to find a solution to this challenging and potentially far-reaching problem. A prolonged survival of skin grafts has been reported in the seriously burned individual who lacks ability to produce antibodies in abundance. In addition, similar survivals have been reported in individuals suffering from agam-maglobulinemia, a condition in which antibodies cannot be produced; and in persons whose ability to produce antibodies has been decreased by X-ray irradiation.
A sequel has been the successful transfer of a functioning kidney as a lifesaving measure from one of identical twins to his twin brother ill with a fatal kidney disease. Not only have there been a number of successes between identical twins, but also successes in the transfer of a kidney between nonidentical members of the same family as the resistance of the recipient has been reduced by irradiation. Because there are close relationships between homotransplant survivals and problems of the growth and homo-transplant rejection and control of cancer, many studies on homotransplantation are being carried out on lower animals. Interesting peculiarities exist in certain animal strains—for example, in dizygotic freemartin cattle, nonidentical male and female twins that share a common circulation in utero and are "tolerant" to one another's skin graft. Rupert E. Billingham has duplicated this condition in the mouse.
The rejection of a homograft is unrelated to blood types, and no skin types have yet been demonstrated. Since rejection requires contact with the cells of the host, the homograft can be protected if it is enclosed in a diffusion chamber from which cells are excluded.