 Allogeneic hematopoietic cell transplantation offers high cure rates for patients with hematological and oncological diseases. Graft-versus-host disease attack of donors white blood cells on patients tissues is a serious complication also affecting the patients immune system. Therefore, patients in the early phase after allogeneic cell transplantation are at high risk for severe infectious complications. So far, no predictive biomarkers for the development of the chronic form of graft-versus-host disease are available. By analysing serially immune cell populations of the peripheral blood we will investigate whether certain subsets of cells are associated with development of chronic graft-versus-host disease. In addition, the patients immune regeneration will be evaluated by serial analyses of peripheral blood immune cell populations 3 months to 2 years after allogeneic cell transplantation. 