Letermovir Prophylaxis Duration Guided by CMV-Specific T-cell Monitoring After Allo-HSCT.

The purpose of this study is to evaluate the efficacy and safety of a personalized strategy for discontinuing Letermovir (a drug used to prevent Cytomegalovirus \[CMV\] infection) based on the recovery of the patient's own immune system. Cytomegalovirus (CMV) is a common and serious complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Currently, Letermovir is typically given as a standard prevention for about 100 days post-transplant. However, some patients may recover their CMV-specific immunity earlier, while others may need longer protection. In this study, researchers will use a dynamic monitoring technology (QuantiFERON-CMV) to detect the level of CMV-specific T-cells in patients. Participants will be randomly assigned to either the experimental group or the control group: Experimental Group: Letermovir discontinuation will be guided by T-cell recovery. If the test shows that the patient's CMV-specific T-cells have recovered, Letermovir may be stopped earlier than the standard 100 days. Control Group: Patients will receive the standard Letermovir prophylaxis for approximately 100 days, regardless of T-cell status. The study aims to determine if this immune-guided strategy can effectively prevent CMV infection while potentially reducing the duration of medication and associated costs, without increasing the risk of CMV disease.