Immunosuppressants are mainly used to prevent rejection after transplantation. It is generally based on the status of the disease before transplantation (to predict the probability of relapse after transplantation, e.g. T-acute lymphoid leukemia, which is prone to relapse after transplantation) and micro-residuals after transplantation and whether there is rejection after transplantation. If the doctor thinks the probability of relapse is high after transplantation, or if there is a high residual, the drug should be reduced as soon as possible. You can even stop the medication. If the residue is still high after stopping the drug and there is no rejection, use the drug to induce rejection, if the effect is not good, it is better to infuse donor cells and do immunotherapy. If acute rejection occurs, Wang Hengxiang of the Hematology Research Center of the Air Force General Hospital must check the concentration of anti-rejection drugs and keep the drug concentration within the therapeutic range, for example, cyclosporine between 150-250 (our hospital). At the same time, other drugs should be added.