Additional Study Information: The purpose of this study is to see if investigational drug CSJ148 is safe and if it can prevent HCMV infection during the first 98 days after stem cell transplant. Information about any side effect that the study drug can cause will also be collected.Study group will be made up of 6 patients. All patients in this group will receive the study drug, CSJ148. The patient and the study doctor will know what the patient has been given.Study group 2 will be made up of 80 patients. All patients in the cohort will receive either study drug, CSJ148 or placebo. Placebo contains no active study drug. There is a 1 in 3 chance the patient will receive placebo during cohort 2 of the study. The patient and the study doctor will not know what the patient has been given, but the study doctor can find out if there is an emergency.In all dosing groups, an IV line will be used to administer either study drug, CSJ148 or placebo, and blood samples will be taken from a second line to measure study drug levels.The IV administration procedure takes approximately 2 hours and 15 minutes.