Dendritic cells and regulation of graft-versus-host disease and graft-versus-leukemia activity.

Hematopoietic stem cell transplantation is the only curative treatment for many malignant hematologic diseases, with an often critical graft-versus-leukemia effect. Despite peritransplant prophylaxis, GVHD remains a significant cause of posthematopoietic stem cell transplantation morbidity and mortality. Traditional therapies have targeted T cells, yet immunostimulatory dendritic cells (DCs) are critical in the pathogenesis of GVHD. Furthermore, DCs also have tolerogenic properties. Monitoring of DC characteristics may be predictive of outcome, and therapies that target DCs are innovative and promising. DCs may be targeted in vivo or tolerogenic (tol) DCs may be generated in vitro and given in the peritransplant period. Other cellular therapies, notably regulatory T cells (T(reg)) and mesenchymal stem cells, mediate important effects through DCs and show promise for the prevention and treatment of GVHD in early human studies. Therapies are likely to be more effective if they have synergistic effects or target both DCs and T cells in vivo, such as tolDCs or T(reg). Given the effectiveness of tolDCs in experimental models of GVHD and their safety in early human studies for type 1 diabetes, it is crucial that tolDCs be investigated in the prevention and treatment of human GVHD while ensuring conservation of graft-versus-leukemia effects.