Immunotherapy and immunoprophylaxis in bone marrow transplantation

Abstract

Immunotherapy can be defined as treatment directed at augmenting host immune defence mechanisms. Non-antimicrobial therapies and immunoprophylaxis in bone marrow transplantation (BMT) can be subdivided into three broad categories: passive immunotherapy with intravenous immunoglobulin (IVIG); cytokine therapy; and anti-endotoxin-directed treatments. Most studies using IVIG in BMT are prophylactic and suffer from variability in study design, type of IVIG and dosing regimens. Various effects on viral and bacterial infections and graft-versus-host disease (GVHD) have been reported but few if any have shown benefit in terms of improved patient survival. Moreover the immunomodulatory effect of immunoglobulin G preparations is frequently overlooked. With the exception of cytomegalovirus (CMV) pneumonitis, there is little evidence of benefit in the treatment of established infections and the relative benefits of hyperimmune preparations are poorly established. The development of haemopoietic growth factors has led to the widespread use of cytokines in BMT. The benefits of these agents both in the prevention of fever and infection and as adjuvants to standard antimicrobial therapy in established infection (e.g. invasive mycoses) are rapidly becoming apparent. Both human recombinant granulocyte-macrophage colony-stimulating factor (rhGM-CSF) and granulocyte colony-stimulating factor (rhG-CSF) have been shown to accelerate granulocyte recovery following BMT and reduce fever days, antibiotic usage and hospitalization. RhGM-CSF appears superior in these respects. The roles of interleukin 1 (IL1), IL3, IL6 and interferons are also under evaluation. As with the much publicised studies using anti-endotoxin antibodies as therapy in sepsis, there is little evidence of benefit in the few studies performed in BMT patients. Other strategies using prophylactic IVIG enriched for anti-endotoxin antibodies appear more promising. The concept of neutralizing the production of cytokines with monoclonal antibodies, receptor antagonists or other biological modifiers, is mainly directed at reducing tissue damage during the preparative regimen with the aim of reducing subsequent GVHD. Any effect this may have on infectious complications such as CMV disease has yet to be investigated. Cloned T cells cytotoxic against CMV have also been developed and studies using these preparations are underway.