ORGAN TRANSPLANTATION

ORGAN TRANSPLANTATION

Important points of transplantation, types, rejection, GHVD

Types of Transplants

a. According to source –

·       Between same species –

a.   Genetically identical (twin) isograft.

b.   Genetically different – allograft.

·       Between different species – heterograft or xenograft

b. According to site –

·       Orthotropic – when placed in normal anatomical position, e.g. skin graft.

·       Heterotropic – when placed in anatomically abnormal sites, e.g. thyroid placed in subcutaneous tissue, kidney placed in iliac fossa.

c. According to purpose –

·       Vital grafts – those living grafts which function physiologically, e.g. kidney or heart.

·       Static/structural graft – nonliving, provide only  a scaffolding on which new tissues are laid, e.g. bone/ artery.

 

 GRAFT REJECTION

Transplantation immunity is predominantly cell mediated

(T cell) but antibodies do play some role mainly in

hyperacute rejection.

Hyperacute Rejection

• Occurs within minutes to hours.

• Due to preformed antibodies against HLA class I

antigen of donor.

• Pathology – intravascular thrombosis and fibrinoid

necrosis of arterial walls.

• Such graft is called white graft.

• Most commonly seen after renal transplantation.

• It is avoidable by prior antibody detection and cross

matching.

Acute Rejection

• Occurs within 6 months.

• It is predominantly T cell mediated.

• Pathology – mononuclear cell infiltration.

• It is reversible by immunosuppressant therapy.

Chronic Rejection

• Occurs after 6 months.

• Due to both cell mediated and antibody mediated

effector mechanisms.

• Risk factor – most important risk factor for chronic

rejection is acute rejection.

• Pathology – vascular changes in the form of arterial

myointimal proliferation resulting in ischemia and

fibrosis.

• It is non-reversible.

Note: Liver is remarkably resistant to all types of graft

rejection.

Pretransplant Testing

1. Blood grouping (only ABO) and cross matching. Rh

groups need not to be tested.

2. HLA typing and matching – most important factor

of allograft survival is HLA compatibility.

HLA typing is done by microcytotoxicity test.

HLA groups important in transplant immunology are

HLA-DR > HLA-B > HLA-A.

HLA matching is not necessary before liver

transplantation.

Organ Donation

Most of the organs used for transplantation are obtained

from brainstem dead, heart-beating cadaveric donors.

Commonly used preservatives are – university of

Wisconsin solution and Eurocollins solution.

Pancreas Transplantation

For treatment of diabetes mellitus, isolated pancreatic islets

are transplanted into recipient liver by injection into portal

vein.

Liver Transplantation

First attempted by Starzl in 1963.

 Indications –

i. Chronic cirrhosis or chronic liver failure – most

common.

ii. Acute fulminant liver failure

iii. Metabolic liver diseases

iv. Primary hepatic malignancy.

Heart Transplantation

First performed by Christian Barnard in 1967.

First heart-lung transplantation was performed by Bruce

Reitz in 1981.

Indication – NYHA class III or IV disease in patients

< 65 years of age.

Contraindication – carboxyhemoglobin level > 20

percent, prior myocardial infarction and prolonged cardiac

arrest.

GRAFT-VERSUS-HOST DISEASE (GVHD)

It is the opposite of graft rejection. In GVHD, graft mounts

an immune reaction against the host antigens.

This occurs when immunologically competent cells are

introduced into recipients who are immunocompromised.

Occurs most commonly in allogenic bone marrow

transplantation.

Pathology:

• Acute GVHD causes epithelial cell necrosis in three

primary target organs – liver, skin and gut.

• Runt disease is an example of GVHD