Busulfan/Clofarabine + Allogeneic Stem Cell Transplantation

This research is a phase II clinical trial. Phase II clinical trials test the effectiveness of an investigational intervention to learn whether it works in treating a specific cancer. "Investigational" means that the study intervention is still being studied and that research doctors are trying to find out more about it. It also means that the FDA has not yet approved this study intervention for your type of cancer. All participants on this study are treated in an identical manner. The investigators are doing this study because there continues to be a significant risk of relapse of disease after reduced intensity transplantation. In studies which have compared transplants using high-doses of chemotherapy and/or radiation versus reduced intensity transplants, patients undergoing reduced intensity transplants appear to have higher rates of relapse, but lower rates of toxicity and complication. This study attempts to utilize clofarabine, a newer chemotherapy agent shown to be quite active in AML, ALL, and MDS, to increase the anti-tumor effects of the conditioning regimen without accumulating unacceptable toxicity. The reduced intensity allogeneic stem cell transplantation procedure involves giving you chemotherapy in relatively less intense doses to suppress your immune system. This is followed by an infusion of healthy blood stem cells from a matched related donor or a matched unrelated volunteer donor. It is hoped that these donor cells can eventually then attack any cancer cells which remain. In this research study, the investigators are looking to see how well this new combination of busulfan and clofarabine works in reduced intensity allogeneic stem cell transplantation. By "works" the investigators mean to analyze safety, ability of donor cells to engraft (take hold), as well as measures of complications including toxicity, infections, graft-vs-host disease (GVHD), and relapse.