Vascular Composite Allotransplantation

NOMENCLATURE

What is an allograft?

Tissue transplantation between unrelated individuals of the same species.

What is an autograft?

Donor tissue, such as a skin graft, that comes from the same patient.

What is the term for a graft that comes from a genetically identical donor, such as an identical twin?

Isograft.

What is a xenograft?

A cross species graft, such as porcine skin grafts used as temporary skin substitutes or porcine or bovine acellular dermal matrices.

What is the difference between orthotopic and heterotopic transplants?

Orthotopic transplants are transferred into an anatomically similar site, whereas heterotopic transplants are transferred into a site different from their origin.

HISTORY

When was the first human organ transplantation?

Dr. Joseph Murray performed the first solid organ transplantation, a kidney, in 1954, between identical twin brothers.

What types of composite tissue allotransplantations have been performed?

Hand, lower extremities, face, abdominal wall, knee, flexor tendon apparatus, nerve, larynx, skeletal muscle, tongue, trachea, scalp, uterus, penis.

IMMUNOLOGY

Which antigens are the most immunogenic?

Major histocompatability complex (MHC) antigens. In humans, these are human leukocyte antigens (HLAs). HLAs reside on the surface of cells. HLA class I antigens are expressed on all nucleated cells, and class II antigens are only expressed on antigen presenting cells (APCs) such as B lymphocytes, monocytes, macrophages, dendritic cells (DCs), endothelial cells, and activated T cells.

What is hyperacute rejection?

ABO incompatibility and antibody incompatibility result in hyperacute rejection, which is mediated by the humoral immune system and occurs within minutes of transplantation.

What is acute rejection?

Acute rejection is caused by the direct pathway of allorecognition, in which donor APCs migrate to host lymphoid tissue and activate T cells. These T cells migrate to the graft and mediate graft rejection. Acute rejection occurs within weeks to months following transplant, and periodically at various time points later.

What is chronic rejection?

Chronic rejection occurs months to years after transplantation. It is contributed to by both direct and indirect pathways of allorecognition, although the indirect pathway is thought to be of greater significance in the pathogenesis of chronic graft rejection. In the indirect pathway, host APCs present processed donor antigens to host T cells. Intimal hypertrophy leading to lumen obliteration and ischemia are typical, as well as sclerotic skin changes.

Which is the most common type of rejection?

Acute rejection. Chronic rejection in vascular composite allotransplantation (VCA) is just being defined.

Which tissue type is most antigenic?

Skin and vascular endothelium is thought to be the most antigenic and immunoreactive tissue in VCA.

The vascularized muscle component of limb allografts may induce a cell-mediated response greater than the skin; however, muscle as a single component is less antigenic than skin.

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