What is Grafting?
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.
Classification of Grafting
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 Definition
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.
Allogeneic Tissue
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.
Types of Allogeneic Tissue
Depending on the type of stem cells acquisition, the allogeneic tissue is classified into four types. They are listed below.
Unmodified Stem Cell Transplant
T-Cell-Depleted Transplants
Cord Blood Transplants
Donor Lymphocyte Infusions (DLI)
Unmodified Stem Cell Transplant
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.
T-Cell-Depleted Transplant
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.
Cord Blood Transplant
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.
Donor Lymphocyte Infusions (DLI)
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
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
Acute Rejection
Chronic Rejection
Hyperacute Rejection:
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:
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:
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.
FAQs on Allograft
1. What is an allograft in Biology?
An allograft, also known as a homograft, is a type of tissue or organ transplant from one individual to another genetically non-identical individual of the same species. For a successful transplantation, the donor and recipient must have compatible blood types and closely matched tissue markers (HLA antigens) to minimise the risk of immune rejection.
2. What is the difference between an autograft, allograft, isograft, and xenograft?
The main difference between these graft types lies in the source of the transplanted tissue. As per NCERT concepts for the 2025-26 syllabus, the types are:
- Autograft: Tissue is moved from one part of the body to another on the same person. There is no risk of immune rejection.
- Allograft: Tissue is transplanted between two genetically different individuals of the same species (e.g., human to human).
- Isograft: Tissue is transplanted between two genetically identical individuals, such as identical twins.
- Xenograft: Tissue is transplanted between individuals of different species (e.g., a pig heart valve transplanted into a human).
3. What are some common examples of allografts used in medicine?
Allografts are widely used to treat various medical conditions. Common examples include:
- Organ Transplants: Such as kidney, liver, heart, and lung transplants from a deceased or living donor.
- Bone Grafts: Used in spinal fusion, joint reconstruction, and filling bone voids after trauma or surgery.
- Skin Grafts: Used to treat severe burns, where skin from a cadaver provides a temporary protective covering.
- Corneal Transplants: To restore vision in patients with damaged corneas.
- Tendon and Ligament Grafts: For reconstructing torn ligaments, like the ACL in the knee.
4. How does an allograft work in the body, for example in a bone graft?
An allograft primarily works through a process called osteoconduction. You can think of the allograft bone as a natural scaffold or a trellis. It doesn't grow on its own but provides the perfect framework for the recipient's own bone-forming cells to migrate into, populate, and build new bone over time. This process allows the patient's body to gradually replace the graft material with its own healthy, living tissue, ultimately healing the defect.
5. Why is tissue matching so important for a successful allograft?
Tissue matching is critical because the human immune system is designed to recognise and attack any cells it identifies as foreign. Every person's cells have unique surface markers called Human Leukocyte Antigens (HLA). If the donor's HLA type is very different from the recipient's, the recipient's immune system will identify the allograft as an invader and launch an attack, leading to graft rejection. Close matching of HLA and blood groups (ABO compatibility) significantly reduces the intensity of this immune response, increasing the chances of the graft surviving.
6. What are the main types of allograft rejection a patient might face?
Allograft rejection is primarily classified based on the timing and the part of the immune system involved. The three main types are:
- Hyperacute Rejection: This happens within minutes to hours after the transplant. It is caused by pre-existing antibodies in the recipient's blood that immediately attack the donor tissue, often due to ABO blood type incompatibility.
- Acute Rejection: This typically occurs from the first week to about three months post-transplant. It is mainly caused by the recipient's T-cells recognising the graft as foreign and attacking it.
- Chronic Rejection: This is a slow, progressive form of rejection that occurs over many months or even years. It involves a long-term immune response that gradually damages the blood vessels and tissues of the transplanted organ, leading to its eventual failure.
7. Why must patients take immunosuppressive drugs after an allograft procedure?
Even with good tissue matching, the recipient's immune system will still recognise an allograft as foreign to some extent. Immunosuppressive drugs are essential medications that weaken or suppress the patient's immune system. Their primary role is to prevent the body's immune cells (like T-cells and B-cells) from attacking and destroying the transplanted tissue or organ. Patients usually need to take these drugs for the entire lifetime of the graft to prevent both acute and chronic rejection, ensuring its long-term function and survival.
