III. To determine 1) if CMV-MVA Triplex increases levels, function and kinetics of CMV-specific T cell immunity in vaccinated compared to placebo treated human leukocyte antigen (HLA) A*0201, CMV seropositive HCT-recipients, 2) to determine whether vaccination induces adaptive natural killer (NK) cell population changes, and increase in the highly cytotoxic memory killer cell lectin-like receptor subfamily C, member 2 (NKG2C)+ NK cells, and 3) to explore GVHD biomarkers and compare between the vaccine and placebo groups.