Chemotherapy with stem cell transplantation is the only curative treatment  for leukemia patients.  Although originally developped to treat leukemia, this therapy is now under clinical investigation to treat patients  with metastatic lung cancer.  The benefit of such treatment is ascribed not only to the higher dose of chemotherapy administered to the patient, but also to the anti-tumor effect the transplant exerts on cancer cells. Unfortunately, graft-versus-host-disease (GVHD) is a serious complication that can induce severe immunosuppression.  As a result, patients that survive GVHD are typically at higher risk of lethal infections, disease recurrence and emergence of second malignant diseases. This grant seeks to understand the adverse effect of GVHD on immune reconstitution.