allograft
Meaning of allograft: Tissue moved from one person to another, which works well mechanically but is recognized as foreign by the recipient immune system.
Definition of allograft
An allograft is tissue or an organ transplanted from one individual to another of the same species who is not an identical twin. Kidneys, livers, hearts, corneas, bone, skin and heart valves are all transplanted this way. Because donor and recipient differ genetically, the recipient immune system treats the graft as foreign, so rejection is the central problem of allograft transplantation.
How does it differ from other grafts?
Grafts are classified by how closely the donor and recipient are related genetically, and that relationship predicts the immune response.
| Type | Donor | Rejection risk |
|---|---|---|
| Autograft | The same person | None |
| Isograft | An identical twin | None |
| Allograft | Another person | Present, needs suppression |
| Xenograft | Another species | Severe |
Why is it rejected?
Every cell carries surface proteins that act as an identity badge, encoded by a set of genes called the major histocompatibility complex. In humans these are the HLA proteins. Immune cells patrol constantly and destroy anything wearing the wrong badge. Donor and recipient are matched as closely as tests allow, and blood group compatibility is checked, but an exact match is rare outside identical twins. Medicines that damp down the immune response are therefore given long term. They keep the graft alive at the cost of weaker defense against infection and a raised risk of certain cancers.
Do all allografts behave the same way?
No, and the differences are large. Some tissue grafts are processed before use, stripped of living donor cells so that only the collagen framework remains. Transplanted bone and many heart valves work this way. They act as a scaffold that the recipient gradually replaces with their own cells, and they provoke little immune response. A living organ is different: it must keep functioning, so its cells cannot be removed, and continuous immune suppression is required. The cornea occupies a middle position, since the eye has limited immune surveillance of its own and corneal grafts often survive without systemic treatment.
Also known as
Used in a sentence
The defect was reconstructed with a bone allograft from a tissue bank.
Good to know
Processed allografts such as bone and heart valves contain no living donor cells and act as a scaffold, so they do not carry the rejection risk of a transplanted organ.
Word origin
Where “allograft” comes from
From the Greek allos, meaning other, joined to graft, from the Greek graphein by way of the Old French grafe.