<qa>  What is the goal of giving chemotherapy and total body irradiation before a donorRationale: Giving chemotherapy and total-body irradiation before a donor umbilical cord blood transplant helps stop the growth of cancer and abnormal cells and helps stop the patients immune system from rejecting the donors stem cells. When the healthy stem cells from the donors umbilical cord blood are injected into the patients bone marrow they may help make stem cells, red blood cells, white blood cells, and platelets. 