Reducing Post-Letermovir CMV Infection: Efficacy of an Immune-Reconstitution-Based Scoring System to Guide Prophylaxis Duration

Inclusion Criteria: * (1) Recipients who meet either of the following conditions: 1. CMV IgG-positive recipients undergoing HLA-haploidentical hematopoietic stem cell transplantation (HSCT). 2. CMV IgG-negative recipients receiving a graft from a CMV IgG-positive donor, and who have received letermovir as CMV prophylaxis post-transplant without prior discontinuation. * (2) Plasma CMV-DNA level below the lower limit of detection (local threshold: 400 copies/mL) within 5 days before enrollment. * (3) Age ≥ 18 years. * (4) Ability to provide written informed consent independently. * (5) Negative for HIV, HBV, and HCV. * (6) Written informed consent must be provided before initiation of any study procedure. Consent may be provided by the patient or a legally authorized representative if, in the investigator's judgment, obtaining consent directly from the patient is not in the patient's best medical interest. Exclusion Criteria: * (1) Prior clinical diagnosis of CMV infection, CMV disease, or CMV viremia before enrollment; * (2) Received ganciclovir, valganciclovir, foscarnet, acyclovir (oral dose \>3200 mg daily, or intravenous dose \>25 mg/kg daily), valacyclovir (oral dose \>3000 mg daily), or famciclovir (oral dose \>1500 mg daily) within 7 days before enrollment; * (3) Received the following treatments within 30 days before enrollment: cidofovir, CMV hyperimmune globulin, any experimental anti-CMV therapy or biologics; * (4) Presence of uncontrolled infection, requirement for mechanical ventilation, or hemodynamic instability at enrollment; * (5) Suffering from mental illness or other conditions that prevent compliance with study treatment and monitoring requirements; * (6) Inability or unwillingness to sign the informed consent form; * (7) Other special circumstances deemed ineligible by the investigator.