Grafting is the surgical process. This is the process of transplanting live tissues from one part of the body to another, from one person to another, or from one species to another. During this process, it generates a new blood supply through the transplanted tissues. Depends on the types of transplantation, the acceptance and rejection rate varies. This completely depends on the donor and recipient’s characteristics.
The graftings are classified according to the donor and recipient. Grafting is classified into four types. They are
Autograft → If the tissues or bones are transplanted from one part of the body to other parts of the body, within the same individual is Autograft.
Allograft → If the tissues/bones are transplanted from genetically different individuals, it is known as Allograft
Isograft → If the transplantation occurs between genetically identical individuals, ie. between identical twins, it is known as Isograft.
Xenograft → If the tissues/organ/bone transplantation occurs between the two different species, it is known as xenograft. For example between pig and human
Allograft meaning allogeneic transplantation or homograft. Allograft definition termed as the tissues or bones is transplanted between the genetically non identical individuals of the same species. Most of the donors and recipients of allografts may be relations. But allograft transplantation is possible only if both individuals have the same blood group. Allograft transplantation can commonly be used for the transplantations of skin, heart, liver, corneas, bone, bone marrow, and kidney.
The allogeneic means that the single source of cells is used to treat many patients. During the allogeneic transplantation, a person’s stem cells are replaced with the new healthy stem cells. Allogeneic therapy increases the risk of bringing out an immune response from the patient, and immunosuppressive therapies along with some combinational therapies for providing allogeneic processes.
Depending on the type of stem cells acquisition, the allogeneic tissue is classified into four types. They are listed below.
Unmodified Stem Cell Transplant
Cord Blood Transplants
Donor Lymphocyte Infusions (DLI)
During the unmodified, or conventional, stem cell transplantation. All the patients receive the stem cells as it is from the laboratory, without making any changes in it. These cells contain all immune cells like T cells. The unmodified stem cell transplants are better for people who have the risk of medicating the graft-versus-host disease.
During the T-cell depleted transplants, the T cells in the stem cells are taken out with suitable equipment in the laboratory. As the T-cells in donor stem cells can cause graft-versus-host disease to patients. After the removal of T-cells from stem cells, it contains remaining cells like blood-forming stem cells are provided to the patients. Then, the new T cells can be provided to the patients, which are less effective to cause graft versus host disease than the T-cells in actual stem cells. This reduces the complication of taking medication for graft versus host disease after transplantation.
The stem cells are taken from the umbilical cord and placenta of healthy newborn babies used for the cord blood transplant. Here, the chance of facing the risk of graft versus host disease after the coed blood transplantation is low. This is mainly because very close tissues in the umbilical cord match the patients and newborn donors. The people, who could not find the perfect matched donor can make use of Cord blood transplantation. The Memorial Sloan Kettering’s research explains well about cord blood transplantation.
People with certain types of cancer may come across stem cell transplantation. The physicians will slowly increase the amount of T-cells provided to the recipient from the donor. The controlled and minimum injecting of T cells has the ability to control the cancerous growth and reduces the risk of graft versus host disease.
Allograft rejection is mainly due to the recipient’s alloimmune response and donor tissue’s nonself antigens expression. The allograft rejections are mainly of three types.
Hyperacute rejection occurs immediately after the transplantation. This is completely because of mismatched antigens. These tissues must be removed as soon as possible to avoid tissue death. Hyperacute rejections are most commonly observed when the donor or recipient is in a different blood group. Hyperacute rejection can be avoided by concentrating while choosing the right donor using ABO compatibility. Every blood group has the anti donor human leukocyte antigen (HLA), which acts on other blood groups.
Acute rejection occurs at any time from the first week to 3 months after the transplantation. All the recipients experience a little percentage of acute rejection after transplantation. This acute rejection can be diagnosed by analyzing graft biopsy. This is mainly due to the immunological response of T cells and B cells.
Chronic rejection may occur or may not occur even after the year of transplantation. Mostly chronic rejection occurs during organ transplantation. The body's constant immune response against the organ leads to damage to the tissues or organs.
1. How Does Allograft Work?
Allograft rejection is the consequence of the recipient’s immune response to nonself antigen released by the donor tissues. Allograft tissues work on the principle of osteoconduction. Let’s imagine, a vine growing through a trellis. The allograft tissue also works in the same pattern. The Allograft chosen is similar to the scaffold, ie, trellis. It supports the bone formation cells i.e., the vine. They support the growth of new bones over time. Here, both antigen and an inductive stimulus required T cell activation. No single substance alone enough for stimulating the T-cell activation. The direct method is the recipient T cells react with the surface of donor cells. This pathway would activate host CD4 or DC8 T cells.
2. What is Allograft Bone Graft?
The two types of bone grafts are common in this field. One is allograft and the other autograft. For allograft, physicians use the bone collected from the deceased donor, or a cadaver, which is cleaned and stored in a tissue bank. For autograft, the doctors search and find the suitable replaceable bone inside the patients. Such as bones from ribs, hips, pelvis, or wrist are used for replacement.