A major problem following transplantation is that the immune system of the recipient sees the grafted tissue as 'foreign' and attacks and destroys it. Historically, the focus of transplant immunology has mainly relied on targeting the mechanisms of specific (adaptive) immunity. However, there are emerging data that both rejection and tolerance are influenced by both nonspecific (innate) and adaptive immune responses.

A transplant experiment is to test the effect of environment by moving two species from their native environments into a common environment. The name was originally applied to experiments on plants, but is now equally applied to animals such as lizards, ants, and other organisms. Transplant experiments are often used to test if there is a genetic component to differences in populations. Advances in molecular biology have provided researchers with the ability to study genetic variation more directly. However, transplant experiments still have the advantages of being simple and requiring little technology. Common garden methods can be improved by combining evidence with genomic studies, the use of dense marker panel data, and modern statistical methods.

The major barriers to transplantation are as follows. Blood groups represent important transplantation barriers when blood is transfused because incompatible ABO blood group antigens of the donor are recognized by the recipient's natural antibodies. Secondly, Major histocompatibility antigens and the last one would be Minor histocompatibility antigens.

Organ donation is the donation of organs for human body or biological tissue after a living or dead person to a living recipient in need of transplantation. Near anybody can donate their organs. The determining factors are where and how a person dies, and the conditions of their organs and tissues. Though your age and medical past will be careful, you shouldn’t accept new, too old or not healthy enough to become a donor. Every year hundreds our people die though waiting for organ transplant or before they even get on to the transplant list. Now is serious absence of tissues the gap between the number of organs donated and the number of people waiting for a transplant is increasing.

Immunosuppression for organ transplants usually involves triple or quadruple drug treatment. The intensity of immunosuppression is initially high but tends to be reduced to a maintenance level that is determined by individual factors and the type of organ transplant. Immune suppressants in organ transplant are used for preventing organ rejection and reverse acute rejection in organ transplantation, prevent and treat graft-versus-host disease and minimize destruction of affected tissues in autoimmune and inflammatory diseases.