ABSTRACT
Infection is a frequent complication of hematopoietic stem cell transplants. It is due to a number of factors, including the underlying disease, the medical condition of the patient, the type of stem cell transplant (i.e. autologous or allogeneic), the source of stem cells infused (i.e. CD34-selected, T-cell-depleted, bone marrow, peripheral blood, or cord blood), the conditioning regimen (i.e. myeloablative or non-myeloablative), the development of graft-versus-host disease (GVHD), the use and type of prophylactic antibiotics, and the presence of latent infection and colonization of the patient at the time of transplant. For example, patients who are profoundly neutropenic for a prolonged period of time prior to high-dose therapy are more likely to have an increased risk for infection.1-3
There are two basic protective mechanisms that play a role in the risk of developing infections after transplant. One depends on non-specific defenses such as the integrity of the surface barriers of skin or the membranes of the respiratory, gastrointestinal, and urogenital systems. These natural barriers are easily damaged by high-dose therapy. In addition, the insertion of foreign objects, such as bladder catheters and central venous catheters, only increases the risk. The other major defense against infections is the immune system, either innate or adaptive. Innate protection results from such cells as granulocytes, monocytes/ macrophages, natural killer (NK) cells, and non-MHCrestricted γ/δ T cells. Complement may function in the expression of the innate system. The innate cells use a highly conserved limited pattern of recognition of foreign ‘non-self’ substances, i.e. antigens. In either an autologous or allogeneic transplant setting, the duration of neutropenia predisposes to bacterial infection.1-3 Early after either type of transplant, the
complement have yet been reported. The control of certain infections, especially viral, depends also on adaptive immune cells, such as HLA-restricted T cells. The adaptive system cannot operate independent of the innate system, and requires cells of the innate system such as dendritic cells, macrophages, and monocytes to present antigen and instruct the T and B cells how to react. The adaptive system works not only by attacking antigen presented on the correct HLA background but by also creating immunological memory.
