Biomedical Engineering Reference
In-Depth Information
cells) and humoral (B cell) responses. The cellular response results in allograft
infiltration and destruction by natural killer cells, cytotoxic T cells and macrophages
(Hayry, 1984). The humoral response results in cell lysis through both comple-
ment-dependent cell death and antibody-mediated cytotoxicity (Lee and Butler,
1997). Given the coordinated immune response to foreign antigen, allogeneic
transplantation without immunosuppression is only possible in transplants be-
tween identical twins (Murray
et al
., 1958; Burke
et al
., 1974).
5.4.3
Tolerance
Tolerance refers to the state of immunologic acceptance or unresponsiveness of
the recipient to the donor allograft or xenograft (Billingham
et al
., 1955) in the
absence of prolonged immunosuppression. Methods of attaining tolerance in adult
humans vary. One method employs the use of total body irradiation to remove
mature recipient T cells followed by donor bone marrow transplantation, prior to
organ transplantation. This induces a state of stable chimerism in which the
recipient is tolerant of both donor and recipient tissues. Further discussion of
tolerance is beyond the scope of this chapter
5.4.4 Allogeneic skin grafting techniques
Skin allografts were the first allograft organ transplants successfully achieved in
humans. However, skin is strongly antigenic and subject to almost inevitable
rejection in the absence of long-term immunosuppression. Current uses of allo-
graft skin among burn and plastic surgeons are threefold: the temporary coverage
of freshly excised wounds, use as an overlay on widely expanded autografts, and
its use to improve recipient bed quality and vascularity for a period of time prior to
autograft application (Blome-Eberwein
et al
., 2002; Moerman
et al
., 2002). In
addition to burns, allograft is used in cases of skin loss caused by trauma (full
thickness wounds with bone and/or tendon exposed), surgery (after the debride-
ment of extensive, necrotizing soft tissue infections), donor sites for autologous
skin grafts, reconstruction of critical facial defects, as temporary coverage (after
laser-resurfacing and dermabrasion), and in the cases of disease (as temporary
coverage for toxic epidermal necrolysis, congenital bullous epidermolysis, dia-
betic ulcers, venous ulcers, pressure and trophic ulcers).
Viable allograft is often regarded as the gold standard in temporary skin
coverage, possessing many of the qualities of the ideal wound dressing. The
characteristics of ideal large wound dressings include lack of antigenicity and
toxicity, reduced water permeability, heat retention, barrier to microorganisms,
pain reduction, firm adherence, protection of underlying tissue and resistance to
trauma, low cost and long shelf life with simple storage requirements (Pruitt and
Levine, 1984; Burd and Chiu, 2005) (
Table 5.1
). The extreme antigenicity of skin
inevitably results in the rejection of allograft.
