Pentostatin and Alemtuzumab as a Preparative Regimen for Allogeneic Peripheral Blood Stem Cell Transplantation

Primary Objectives of the study: * To determine the efficacy of a preparative regimen of pentostatin and alemtuzumab plus related or unrelated allogeneic peripheral blood stem cell transplantation (PBSCT) in inducing durable donor lymphohematopoietic cell chimerism (defined as at least 50% donor cells in the peripheral blood) by 100 days after PBSCT (day +100) in subjects with high-risk malignancies who are at high risk for morbidity and mortality with conventional intensive pre-transplant conditioning regimens. * To determine the safety of a preparative regimen of pentostatin and alemtuzumab plus related or unrelated allogeneic PBSCT, as measured by the non-relapse mortality at day +100 in the study subject population.