**2.1 Autograft and isograft**

Autograft means 'self-tissue' and refers to where on organ is transferred from one body site to another within the same individual. In recent years, auto-liver transplantation has been operated in some centres, but the number does not exceed one hundred because the operation technique is very complex and difficult. The autograft is a promising graft and has two advantages: (1) the graft is a tissue or organ already belong to the recipient who has spontaneous tolerance to the graft and so may avoid taking immunosuppressive drugs; (2) liver shortage is rapidly becoming a major restricting factor on the development of liver transplantation, and autografts avoid this problem. An isograft is a tissue or organ which is transferred between genetically identical individuals, e.g., liver transplantation between identical twins or grafts between mice of the same in-bred strain. This graft has the same advantages as the autograft, and it is not necessary to apply immunosuppressive regimens to the recipients. In particular, with the development of living donor liver transplantation, this is an excellent graft. Nevertheless, the isograft is fairly uncommon and far from universal.

#### **2.2 Allograft**

76 Liver Transplantation – Basic Issues

these mechanisms is important, as it aids in the understanding of the clinical features of rejection and – hence – in making an early diagnosis and delivering appropriate treatment. Knowledge of these mechanisms is also critical in developing strategies to minimise rejection and in developing new drugs and treatments that blunt the effects of the immune system on transplanted organs, thereby ensuring the longer survival of these organs. The

Grafts of different species can cause different degrees of immune response to recipients. Generally, the greater the difference between the species, the more likely that it is that there will be a stronger immunological rejection. Accordingly, this section will discuss the types of graft. Liver grafts often mainly consist of four types: autograft, isograft, allograft and xenograft (Figure 1). The definitions and features of all grafts will be now be described in detail and the effects of different grafts on the body's immune system also will be

Autograft means 'self-tissue' and refers to where on organ is transferred from one body site to another within the same individual. In recent years, auto-liver transplantation has been operated in some centres, but the number does not exceed one hundred because the operation technique is very complex and difficult. The autograft is a promising graft and has two advantages: (1) the graft is a tissue or organ already belong to the recipient who has spontaneous tolerance to the graft and so may avoid taking immunosuppressive drugs; (2) liver shortage is rapidly becoming a major restricting factor on the development of liver transplantation, and autografts avoid this problem. An isograft is a tissue or organ which is transferred between genetically identical individuals, e.g., liver transplantation between identical twins or grafts between mice of the same in-bred strain. This graft has the same advantages as the autograft, and it is not necessary to apply immunosuppressive regimens to the recipients. In particular, with the development of living donor liver transplantation,

next chapter will elaborate on various aspects of liver transplantation immunology.

**2. Types of grafts** 

Fig. 1. Types of grafts

**2.1 Autograft and isograft** 

introduced.

An allograft is a tissue or organ which has been transferred between genetically different members of the same species. Allografts account for many human transplants, including those from cadaveric, living-related and living-unrelated donors. It is also called an allogeneic graft or a homograft. With regard to liver transplantation, most grafts are allografts. The graft may cause acute rejection and chronic rejection, and as such surgeons have to select the optimal match so as to reduce the occurrence of rejection by the ABO group and the HLA system.

### **2.3 Xenograft**

A xenograft is a tissue or organ which has been transferred between different species. Donor shortage imposes the main restricting factor on liver transplantation and the continual growth of transplantation has led to significant organ shortages for a long time. At present in China – which is a country with a high incidence of liver disease – almost 3,000,000 patients develop some degree of liver cirrhosis, and about 10% of patients deteriorate to end-stage liver cirrhosis or liver cancer. As such, clinicians are often faced with the difficult prospect of rationing organs. Furthermore, liver transplantation in urgent cases is usually delayed – occasionally with fatal outcomes – until a suitable liver becomes available. Using animals as liver donors is a theoretically attractive solution, because it offers a potentially inexhaustible source of liver. This is of particular relevance for patients with fulminant liver failure who require urgent transplantation. Another potential use of xenografts lies in the fact that some animals are immune to certain viruses which may re-infect a human liver transplant (hepatitis being a case in point). Xenografts have been applied in the clinical region. Starzl's team transplanted two baboon livers into human subjects at Pittsburgh (Starzl et al., 1993). Although they did so with good graft function (and this may well result in the further development of this approach) the graft is confronted with some problems. The first is a problem of theory, such that only about fifty-percent of people support xenotransplantation. The second – and the biggest – problem is one of rejection, since xenotransplantation often causes hyperacute rejection and leads to graft dysfunction.
