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INTRODUCTION
Vascularized composite allotransplantation (VCA) is an up and coming clinical modality in the realm
of reconstructive microsurgery. Being able to replace tissues like for like en bloc is absolutely crucial and
empowers the surgeon to achieve the most optimal outcome. However, the greater goal of VCA is the ability
of the reconstructive surgeon to not only restore form but also function. Functional restoration could
arguably be the epitome of reconstruction where the quality of lives are improved not only from external
appearance but rather also allow the patients to get back to their activities of daily living.

Trauma remains a significant burden in today’s society with many resulting in soft tissue defects. Other
causes of soft tissue defects include congenital deformities and neoplastic conditions. Much of the previous
methods for reconstruction include prosthesis or sequential flaps that obliterate and attempted to restore the
form of a tissue defect. However, this is often inadequate and is lacking in function. VCA differs from solid
organ transplantation (SOT) where tissues of varying antigenicity are transplanted en bloc. This results in
issues of varying rejection rates. In particular, skin which is often a component of VCA transplants such
[1]
as the hand and face has the highest antigenicity of all body tissue types . As such, rejection faced by skin
component is high and the recipient or patient is dependent on a high constant level of immunosuppression.
Skin contains dendritic cells such as Langerhans cells that have strong immunogenic properties and it has
been shown that some of these cells of donor origin reside in the epidermis decades after the transplantation .
[2]

Chronic immunosuppression itself carries deleterious effects in the long run. Patients face opportunistic
infections and an increased risk of malignancy from the decreased immunity that is usually present to
prevent and take on a surveillance role. As such, one has to carefully weigh up the pro and cons when
deciding the perform VCA on a patient. The patient should also be able to finance a lifelong requirement of
immunosuppressive drugs which are often costly and have a high dropout rate due to the side effects.

Much of the research at present in VCA is on better improving the safety profile of such procedures,
especially with the need for the improvement in immunosuppressive regimens. By decreasing our reliance
on immunosuppressive drugs, we increase the acceptability of such a procedure as the downside of
immunosuppression can be deleterious. The ultimate goal in transplant science would be to achieve allograft
tolerance. Tolerance to an allograft is a phenomenon where the recipient body does not recognize the foreign
antigens from the donor and hence will accept the graft. Immunosuppressive drugs can hence be reduced
or even omitted. In order for this process to occur, immunological manipulation and re-education of the
recipient’s immune system has to occur. Several strategies already show promise in this respect and will
be discussed in this article. Varying tissue types also have varying levels of inducibility with regards to
tolerance formation. In particular, due to the varying tissue types of differing antigenicity in VCA, tolerance
is often difficult to achieve.

A brief history of VCA
VCA has come a long way since its first conception back in AD 348. It has always been a goal of mankind to
be able to replace like with like where allograft transplantation en bloc of a gangrenous leg of an elder church
sacristan was performed by two brothers known as the miracle of Cosmas and Damian . Previously known
[3]
as composite tissue allotransplantation (CTA), VCA in the past started off with transplantation between
identical twins which obviated the need for immunosuppression, which is the bane of VCA and is a focus of
intense research at present.

The first-hand allotransplantation was performed in 1964 in Ecuador where a first generation drug regimen
was provided. This included steroids and azathioprine initially. However, the hand allograft still was rejected
2 weeks later. Allografted tendons had been performed using non-vascularized techniques to replace lost or
nonfunctional upper extremity flexor tendons but end results were unacceptable due to the lack of viability