An allograft is a tissue graft from someone else, in contrast with an autograft, in which the donor and the recipient are the same person. Allografts are routinely used in many branches of medicine to do everything from replacing skin damaged by burns to giving someone with kidney failure a new kidney. Sources for allografts vary, with donor material usually being collected and stored by tissue banks, medical companies which specialize in retrieving, screening, and managing biological materials used in transplantation and grafting procedures.
In the case of an allograft, the donor material comes from a member of the same species, but the donor is not genetically identical to the recipient. As a result, the body of the recipient tends to reject the donor material, because it views the material as foreign. For this reason, recipients have to take medications to suppress their immune systems, and donor material is carefully screened to ensure that it matches the recipient as closely as possible. Blood typing is commonly the first step in screening, with additional screening tests determining the likelihood of allograft rejection.
Some allografts come from cadavers. A variety of donor tissue can be harvested from a dead body, including organs, skin, bone, and eye tissue. People who wish to donate tissue to benefit other people after their deaths can sign up for organ donor programs, and alert their families to their wish for their tissue to be harvested and used. In other cases, it is possible to take an allograft from a living person. Kidneys, for example, can be taken from living donors, most commonly relatives of the patient.
One of the advantages to using an allograft rather than an artificial replacement is that the tissue will eventually integrate into the body of the recipient if it is not rejected. In some cases, however, artificial tissue may be more suitable. For example, in some joint replacement surgeries, success rates with artificial joints and donor tissue are quite comparable. Because new progress is always being made, when patients know that they will be undergoing a medical procedure which involves a graft or artificial implant, they should talk with the surgeon about their options.
If donor tissue comes from an animal of a different species, it is known as a xenograft. One of the most famous types of xenograft involves heart valves from pigs which are used to replace failing valves in people. If a twin donates tissue to his or her twin, it is known as an isograft.