Transplantation is that act of transferring cells, tissues or organs from one site to another. Transplant rejection is the process by which a transplant recipient’s immune system attacks the transplanted cells, tissues or organs (MedicinePlus). The main barrier today is rejection of transplanted organs which occurs as a result of cellmediated and humoral responsesby the recipient to antigens called Human Leukocyte Antigen (HLA). Transplant rejection occurs when transplanted tissues are rejected by the recipient’s immune system. The transplanted tissues are destroyed as a result. Several ways and methods have been devised to prevent tissue transplantation. This paper will critically review prevention of transplant rejection.
Cornea Transplantation is one of the major successful organ transplants in humans. This is especially due to the unique structure of the cornea, its absence of blood vessels and corneal lymphatic, allowing survival of corneal allograft.
During corneal eye transplant, the operation is carried out under anesthesia conditions and using a sedative. Drapes are then positioned around the eye and an eyelid is used to keep the eye open while it is lubricated to ward off dryness. The innermost part of the eye is the one involved in transplantation while portioning the patient’s eye using a trephine. This is then replaced using a cornea of the same size. After the operation the patient can then go home and come for follow-ups.
Corneal Graft Rejection
Mechanisms responsible for immunological privilege of the cornea are that the cornea lacks blood vessels, has no lymphatic, relative antigen presenting cells in the cornea, there is blood eye barrier and the presence Antigen Presenting Cells. This immune privilege is rare in many organisms but can be lost in some cases (Dr. Bali, et al.).
Sometimes after transplanting the cornea, there is a risk that the transplanted part will not be accepted by the recipient patient’s immune system leading to a ‘rejection.’ The cornea does not have blood cells and it is rare for rejection to occur, sometimes however rejection may occur leading to complications that may result to loss of sight in the affected eye (Europeans Medicines Agency).
Clinical presentation types
Patients who experience corneal graft rejection have the following symptoms: watery eyes, visual complaints, photophobia and redness in eyes (Dr. Bali, et al.). .
Prevention methods available
Prevention of graft rejection of immune-mediated rejection can be considered in terms of preoperative, intraoperative and postoperative factors. Preoperative factors are those measures geared towards preventing immune mediated allograft rejection. These are achieved by minimizing antigenic differences between the recipient and donor tissues by reduction of antigenic load of the donor tissue. Intraoperative are those factors that contribute to preventing corneal graft rejection include a careful surgical technique that tries to avoid decentralization of recipient bed cut, good graft apposition and optimal suturing. Postoperative factors are the ones that prevent immune mediated allograft rejection. Postoperative factors are achieved by alleviating host immune response to foreign donor tissue (Panda, et al., 2007).
According to Kostelná et al. (2010), prevention lies in early detection of the condition by observing any signs of inflammatory followed by appropriate therapy. Wright and Dhillon insist on the need to develop a means of disease prevention for those with the risk of corneal rejection because about 10 million patients undergo surgery in the world every year.
Reduction of antigenic load of donor tissue
Intraoperative factors that influence reduction of antigenic load include;
- Using a central cornea graft due to the fact that Langerhans cells are located in peripheral cornea.
- Removal of donor ephitalium reduces risk of rejection as ephitalium acts like a class I or II antigen.
- Exposure to Ultra violet rays as this reduces the rate of rejection by preventing activation of the T-cells due to depletion of Langerherhans cells.
- Establishing an anti-lymphatic strategy that will help in exit of antigen presenting cells and
- Depletion of local macrophages
- Gene therapy that can be modified while in storage for example ex vivo decreasing risk of potential systemic complications.
- Pretreatment of the graft
- Any other aspects like preservation of donor cornea, pretreatment with anti-lymphatic serum or with succinylated anti-lymphocytic globulin (Panda et al., 2007).
Minimizing Antigenic Differences between Host and Donor
Research has shown that HLA matching for allograft survival can be done in human cornea transplantation. HLA and ABO matching should be done to avoid or minimize future graft rejection. But the major complication here to graft rejection is due to a disparity between the donor and recipient. However, several studies have suggested that a beneficial effect of matching HLA antigens to the corneal graft survival. Many researchers are considering HLA matching for allograft survival (Panda et al., 2007).
Suppressing the hosts immune responses
To prevent cornea transplant rejection, that the role of immunosuppression in cornea can greatly be used for this purposes. This can be achieved by vascularization and immunosuppressive therapy. Vascularization however can be minimized by irridation, keratoplasty (tectonic), stem cell transplantation and topical corticosteroids. Corneal graft rejection with preoperative and postoperative has also been studied. This is by understanding that corneal graft rejection is just but a cell-mediated response that is controlled by CD4+ T cells and therefore occurs when the antiCD4 molecules are blocked (Panda et al., 2007).
During transplantation of cornea, the recipient may reject the organ from the donor although it is rare. The major cause of human allograft failure can be due to irreversible immune rejection of the transplanted cornea and the immunological process can cause reversible or irreversible damage and therefore it is prudent that prevention of transplant rejection is first observed. Corneal graft rejection encompasses complex series of responses involving recognition of histocompatibility. Thus the needs for systematic interventions are required. Prevention of corneal graft rejection hence is crucial and lies with reduction of donor antigenic tissue load. This in turn reduces host and donor incompatibility by suppressing the host immune response and by tissue matching. Early detection and use of therapy for prevention and management for of corneal graft rejection is also very crucial.