this modern era, many attempts have been made to transplant tissues and
organs from one person to another or even occasionally from lower
animals to humans. However, the normal human immune response can cause
a rejection of the transplant.
An isograft is the transplant of tissue
or organ from one identical twin to another. An allograft is the
transplant from one human to another or from one animal to another of the same species. A xenograft is the transplant from animal to human or
from an animal of one species to another species.
Rejection is the consequence of the recipient's allo-immune response to the non-self antigens expressed by donor tissues. In
hyperacute rejection, transplant patients are serologically
presensitized to alloantigens (ie, graft antigens are recognized as
nonself). Hyperacute rejection manifests within minutes to hours of
graft implantation. Hyperacute rejection has become relatively rare
since the introduction of routine pretransplantation screening of graft
recipients for antidonor antibodies. In acute rejection, can occur within 24 hours of transplantation and occur over a period of days to weeks. chronic
rejection, usually occurs months or years after the transplant. No
currently accepted therapeutic strategy exists for chronic rejection.
is a condition that can occur following bone marrow transplant. The
condition may be acute or chronic, mild or severe. Severe cases can
often be life-threatening. Bone marrow transplants are done to
treat and cure certain types of leukemia or other cancers that have
invaded the bone marrow. Experimental bone marrow transplants are also
performed to treat non-malignant conditions, such as sickle cell anemia.In
the transplant, the host's bone marrow is first destroyed with
chemotherapy or radiation. Then the host receives replacement bone
marrow from a donor. Most recipients undergo allogeneic transplants,
which means they receive genetically matched bone marrow from a donor,
usually a close family member or occasionally someone outside the
family who has been found to be a match. Sometimes, autologous
transplants are performed. Here, the person is given back his or her
own marrow once it has been purged of malignant cells.While the
goal of bone marrow transplantation is to eradicate tumor cells and
thus the cancer, drugs are also given to suppress the host's immune
system to permit the new donor marrow to implant without being
destroyed by the host's immune system.Varying degrees of
graft-versus-host disease are viewed as an expected complication of
bone marrow transplantation since tissue typing can find close, but not
perfect, tissue matches between donor and recipien.
Only identical twins have identical
Acute: Skin rash, diarhhea, abnormal liver function tests,
increased susceptibility to infection. Symptoms usually begin within 2
months after transplantation.Chronic: Skin rash, dermatitis, hair
loss, liver damage, dry eyes and dry mouth, increased susceptibility to
infections, possible lung and gastrointestinal disorders. Symptoms
start more than 3 months after transplant.
Treatment consists of suppressing the immune response. Treatment of acute GVHD includes use of high-dose corticosteroids.
(blood group) and HLA (tissue antigen) typing before transplantation.
Compatible family donors can further decrease the risk.Anti-rejection drugs
Because the patient's immune system recognizes the new organ as
a foreign tissue, it's normal for the immune system to try to reject
the organ. Drugs (immunosuppressants) help suppress the immune system
to prevent or reverse rejection. Although researchers continue to study
new drugs, these are the most common drugs used to prevent organ
rejection: 1. Cyclosporine. 2. Prednisone. 3. Azathioprine. 4. Tacrolor
FK506. 5. Mycophate mofetil. 6. Sirolimus. 7. OKT3.
Xenotransplantation is the transplantation of living cells, tissues
and organs from one species to another species. This was performed in
the early 20th century and was soon abandoned due to rapid death of the
recipient. Since the first experimental xenotransplantation, various
organs from rabbit, pig, goats, lambs and non-human primates were used.
Transplant rejection is the consequence of the host immune system
response. It can be hyperacute, acute and chronic. The term
graft-versus host disease is used to describe the complications that
follow a bone marrow transplant. It can be treated by anti-rejection
drugs and prevented by HLA typing. Xenotransplantation is an exciting
experiment and involves transplant between one species to another