CMV-TCIP Directed Letermovir Prophylaxis After Allo-SCT

Inclusion Criteria: * ≥ 18 years of age on the day of signing informed consent. * Karnofsky performance \>70% * Have documented seropositivity for CMV (either donor or recipient CMV IgG seropositivity) before AHCT. * Eligible for AHCT from an HLA-matched related, matched unrelated, mismatched unrelated or haploidentical donor using either bone marrow or peripheral blood stem cells. * Have undetectable CMV DNA from a plasma sample collected within 5 days prior to enrollment. * Must be within Day-10 thru Day+28 days of planned HSCT at the time of enrollment. * Be able to comply with medical recommendations or follow-up. * Has adequate organ functions determined by 1. Serum creatinine clearance ≥50 ml/min (calculated with Cockroft-Gault formula). 2. Bilirubin ≤1.5 mg/dl except for Gilbert's disease. 3. ALT or AST ≤200 IU/ml for adults. 4. Conjugated (direct) bilirubin \< 2x upper limit of normal. 5. Left ventricular ejection fraction ≥40%. 6. Diffusing capacity for carbon monoxide (DLCO) ≥ 50% predicted corrected for hemoglobin. Exclusion Criteria: * Has a history of CMV end-organ disease or CS-CMVi within 6 months prior to enrollment. * Received within 7 days prior to screening or plans to receive during the study any of the following: 1. Ganciclovir 2. Valganciclovir 3. Foscarnet 4. Acyclovir (\> 3200 mg PO per day or \> 25 mg/kg IV per day) 5. Valacyclovir (\> 3000 mg/day) 6. Famciclovir (\> 1500 mg/day) * Received within 30 days prior to screening or plans to receive during the study any of the following drugs: cidofovir, CMV hyper-immune globulin, any investigational CMV antiviral agent/biologic therapy. * Has suspected or known hypersensitivity to active or inactive ingredients of letermovir formulations. * Has an uncontrolled infection * Requires mechanical ventilation or is hemodynamically unstable