MBL deficient patients will be randomized in a ratio of 2:2:1 to receive up to 4 weekly i.v. infusions of rhMBL at a dose of 0.5 mg/kg or 1.0 mg/kg, or standard anti-infectious prophylactic therapy alone. A total of 20 patients will be treated in each of the rhMBL arms, and 10 patients will receive best standard supportive prophylactic therapy but not rhMBL. All patients are to receive anti-infectious prophylactic supportive therapy as per institutional standards.