In recent years, the science and technology of organ transplantation have developed rapidly, which has been widely applied worldwide. However, multiple challenges remain to be resolved by clinicians, such as functional damage and immune rejection of transplant organs, immune deficiency caused by extensive use of immunosuppressants, chronic allograft dysfunction and adverse reactions. This article introduced relevant key research results published in 2021, taking the function and mechanism of immune cell subsets in the process of organ transplantation rejection or immune tolerance, and the research and application of new materials and drugs in organ transplantation as the main clues. The latest research progresses on regional immune response, especially the application of tissue-resident memory T cell in organ transplantation, were briefly summarized, and the future development of transplantation immunology was prospected.

Despite the rapid development of organ transplantation technique, the long-term survival and functional maintenance of transplant organs still depend on the massive use of immunosuppressants.At present, the rejection and infection after organ transplantation remain the major problem facing transplant surgeons and recipients. The basic research in the field of organ transplantation is still steadily advancing to further explore the basic biological principle of rejection and immune tolerance, resolve multiple pathophysiological questions in the process of clinical organ transplantation and provide basic theoretical basis and clinical intervention guidance for wider and more effective application of organ transplantation.In 2020, researchers have achieved significant progresses on a wide range of basic researches of organ transplantation, such as the fundamental principle of immune response, overcoming transplantation rejection and inducing transplantation immune tolerance, etc.In this article, novel attempts and progresses upon inducing transplantation immune tolerance in 2020 were reviewed from two perspectives including inhibition of immune cell function and suppression of immune signaling pathway, and the main development direction of immunology of organ transplantation in the future was prospected.