Allogeneic and homologous refer to tissue, bone marrow, or blood transplants from the same species, while autologous uses a person’s own tissue. Matching is important to prevent rejection, and close relatives are often sought for organ transplants. Autologous procedures use a person’s own tissue.
Allogeneic translates directly into the word homologous. Both are adjectives which mean to refer to tissue, bone marrow or blood, in any form of transplant or transfusion, i.e. of the same species. These terms are contrasted with autologous, which means using one of these tissues by the same person on the same person. A person having their own tissue retransplanted or replaced is having an autologous procedure. When you do an allogeneic transplant, the donated tissue comes from the same species, as opposed to any other form of animal species (xenograft) or from yourself (autologous).
In most cases, the transplantation of tissue, blood or other types of cells is allogeneic. This again means that some degree of matching must occur before putting what lived in another into one body. A blood donation also needs to be checked to confirm that it does not conflict with the recipient’s blood type. Rejection of an autologous blood transplant can occur if the blood is not fully matched. This doesn’t always mean that blood types have to match exactly. O positive blood may be able to receive most other blood types, but O negative blood usually can only receive O negative.
You may need more precise matching for things like allogeneic bone marrow transplant or organ transplants. This is why doctors will often look to family members for an appropriate match for bone marrow or organs that people can donate in whole or in part, such as kidneys or livers. The closer the match is, the less likely it is to refuse. Suitable matches are made outside the immediate family from time to time, and for some organ transplants, matches are almost always made outside the family, such as heart transplants.
What should be understood is that whether a transplant or transfusion originates in a person’s family or comes from outside of them, as long as it comes from another human being it is allogeneic. If it comes specifically from the person who needs the transplant/transfusion, it is described differently. Take, for example, a person who cannot have blood transplants. In this case a surgeon might decide to collect blood lost during surgery and transfuse it back into the person’s body. This would be autologous.
Similarly, bone marrow harvesting at birth, usually through umbilical cord harvesting, could give people who later develop cancer the ability to use their own marrow. It would be a perfect match. This would not be allogeneic but would be autologous. Collection of ova for subsequent fertilization could also be considered autologous, although once fertilized they would also be allogeneic, containing the genetic material of an additional person.
Simply put, homologous or allogeneic mean of the same species. The donor may or may not be a close relative. Close genetic matching is still usually very important, but that does not imply a relationship. Two things a homologue cannot be are the self or a member of another species.
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