The object of the invention is to provide an immunological reconstitution promoter or a prophylactic agent for infections for use in allogeneic hematopoietic stem cell transplantation therapy for tumors. The promoter or prophylactic agent enables the amelioration of delayed immune reconstitution or the prevention of infection following transplantation, while maintaining the GVT effect of allogeneic hematopoietic stem cell transplantation. Specifically, in a transplant patient in whom immune reconstitution is delayed, such reconstitution can be promoted by administering, at an early stage following transplantation, a substance capable of depleting CD4+ cells. Early completion of infection management in the patient and improvement in the survival rate are anticipated as a result. In addition, the risk of complications associated with allogeneic hematopoietic stem cell transplantation is reduced, enabling more widespread use of this therapy.
