Observational Clinical Study of Letermovir for Preventing CMV Infection After Allo-HSCT

Participants will be categorized into high-risk and intermediate-risk groups based on risk factors for CMV infection.Initiate letemovir prophylaxis on day +1 in high-risk patients and on days +7 to +14 in non-high-risk patients.(240 mg, qd in patients with concomitant cyclosporine; 480 mg, qd in patients with concomitant tacrolimus) to +100 days. For patients with comorbid GVHD who require intensive immunosuppression, consider extending the regimen to +200 days.