 At each visit after the NK cell infusion on Day -5, or as often as your study doctor thinks it is needed, you will be checked for possible reactions to the transplant and study drugs, including graft versus host disease GVHD. GVHD is a condition in which transplanted tissue attacks the body into which it is transplanted in patients receiving a stem cell transplant. Graft failure occurs when transplanted stem cells may not be able to grow and multiply in your body. If this happens, there will be a high risk of infections andor bleeding. If the number of white blood cells does not get back to high enough levels within 3 weeks after the transplant, more stem cells may need to be given. 