Adult human mesenchymal stromal cells and the treatment of graft versus host disease.

Graft versus host disease is a difficult and potentially lethal complication of hematopoietic stem cell transplantation. It occurs with minor human leucocyte antigen (HLA) mismatch and is normally treated with corticosteroid and other immunosuppressive therapy. When it is refractory to steroid therapy, mortality approaches 80%. Mesenchymal stromal cells are rare cells found in bone marrow and other tissues. They can be expanded in culture and possess complex and diverse immunomodulatory activity. Moreover, human mesenchymal stromal cells carry low levels of class 1 and no class 2 HLA antigens, making them immunoprivileged and able to be used without HLA matching. Their use in steroid-refractory graft versus host disease was first described in 2004. Subsequently, they have been used in a number of Phase I and II trials in acute and chronic graft versus host disease trials with success. We discuss their mode of action, the results, their production, and potential dangers with a view to future application.