Donor and recipient CMV-serostatus is one of the risk factor for CMV infection in solid organ transplantation. Recipients with IgG positive anti-CMV are classified as low-risk patients since it is considered that patients also have specific cellular immunity against CMV. However, investigators group has published that around 25% of solid organ transplant candidates lack CMV-specific CD8+ T-cell response ("humoral/cellular mismatch") and they are at a higher risk of CMV replication after transplantation. The main goal of this study is to analyze the impact of the humoral/cellular mismatch in hematopoietic stem cell transplantation (HSCT) CMV-seropositive donors on the CMV reactivation after HSCT in CMVseropositive recipients. Investigators will study not only the incidence of CMV reactivation but also the severity (duration and peak viral load), CMV disease and survival. CMV-seropositive patients who receive a HSCT (bone marrow or peripheral blood) from related donors will be consecutively recruited from Reina Sofía Hospital (Córdoba) and Marqués de Valdecilla Hospital (Santander).