LYMPHODEPLETING EFFECTS AND SAFETY OF PENTOSTATIN FOR NONMYELOABLATIVE ALLOGENEIC STEM-CELL TRANSPLANTATION 1 STEVEN Z. PAVLETIC, 2,8 R. GREGORY BOCIEK, 2 JAMES M. FORAN, 2 RONALD J. RUBOCKI, 3 CHARLES A. KUSZYNSKI, 3 JAMES L. WISECARVER, 3 LORI HATCHER, 3 DAVID M. LUCAS, 7 JOHN C. BYRD, 7 MICHAEL R. GREVER, 7 SHANTARAM S. JOSHI, 4 PENNY HARDIMAN, 2 LYNETTE M. SMITH, 5 TIMOTHY R. MCGUIRE, 6 PHILIP J. BIERMAN, 2 JULIE M. VOSE, 2 JAMES O. ARMITAGE, 2 AND JAMES E. TALMADGE 3 Nonmyeloablative allogeneic stem-cell transplanta- tion (alloNST) is the focus of investigations searching for less-toxic transplantation regimens. We report studies on the kinetics of lymphodepletion and safety of pentostatin (PT) conditioning in alloNST. Patients with hematologic malignancy received mobilized blood from human leukocyte antigen-matched related (n4) or unrelated (n8) donors. PT 4 mg/m 2 was ad- ministered on days 21, 20, and 19 and 200 cGy of total-body irradiation was administered on day 1, followed by cyclosporine A and mycophenolate mofetil. Mononuclear cell adenosine deaminase after PT was inhibited 84%. The absolute CD3  cells de- creased significantly by day 7 (49%) and CD19  cells declined 92% by day 1. CD4  cells were depressed more than CD8  cells. Neutrophils and monocytes were minimally affected by PT. Median posttransplant peripheral blood chimerism on day 70 showed 95% donor leukocytes and 82.5% donor CD3 lymphocytes. PT demonstrated lymphodepleting effects and prom- ising safety, supporting alloNST as early as 7 days after initiation of PT. Recently, interest has grown in reduced-intensity nonmy- eloablative allogeneic hematopoietic stem-cell transplanta- tion (alloNST) regimens that rely on immunosuppression to secure engraftment with minimal toxicity (1). Pentostatin (PT) is a purine nucleoside analog approved for the treatment of hairy cell leukemia where it is used at low doses of 4 mg/m 2 /day that cause few side effects and minimal myelo- suppression (2). PT is also a potent immunosuppressive agent inducing adenosine deaminase (ADA) inhibition, a mechanism of action different from other nucleoside analogs such as fludarabine or cladribine. PT has also been reported to induce CD4 + cell suppression as early as 3 to 6 weeks after administration (3). Currently, PT is being explored as a novel immunosuppres- sant for alloNST in empiric combinations with chemother- apy, irradiation, or other immunosuppressive approaches where the exact contribution of PT to the overall regimen is difficult to determine (4–6). Little is known about the immu- nosuppressive effects that occur within days after PT admin- istration, the time frame critical to allogeneic transplant. We report a pilot study of alloNST, designed to evaluate the short-term kinetics of lymphodepletion by PT and its safety and effects on engraftment. We used a modification of an established low-dose total-body irradiation regimen with the addition of PT 3 weeks before stem-cell infusion (7). All patients were ineligible for conventional allogeneic stem-cell transplantation because of advanced age, decreased organ function, or poor performance status. PT was admin- istered intravenously at 4 mg/m 2 /day for 3 days on days -21, -20, and -19, with day 0 being the day of hematopoietic blood stem-cell infusion. Total-body irradiation (200 cGy) was administered in a single fraction on day -1. Cyclosporine A was administered intravenously at 2.0 mg/kg every 12 hr on days -1, 0, and +1 and then converted to oral administration at a 1:1 ratio; target therapeutic levels were 200 to 300 ng/L. Cyclosporine A was tapered starting on day +70 if no graft- versus-host disease (GVHD) occurred. Mycophenolate mofetil was administered orally from day 0 to +27 twice daily at 15 mg/kg. Growth factors were not administered during the first 28 days posttransplant. Twelve patients aged 21 to 69 years (median, 59 years) received transplants from related (n=4) or unrelated (n=8) donors (Table 1). All unrelated donors were matched at the allele level for the human leukocyte antigen (HLA)-A, HLA-B, HLA-C, HLA-DRB1, and HLA-DQ loci except patient 13, whose donor was allele mismatched at both HLA-C loci. Hematologic toxicity during the 3 weeks after PT admin- istration was mild. A transient neutropenia was observed with a median neutrophil count of 892/L (range, 300 – 4,080/ L) at the lowest point, which occurred 7 days after starting PT (day -14), resulting in a 57% depression compared with the absolute neutrophil counts at baseline. Platelets de- creased only 12% from the baseline; the lowest median plate- let count was 10810 3 /L (range, 37–38110 3 /L) and oc- curred on day -1. Lymphopenia was the predominant hematologic effect, with an 80% maximal decrease from base- 1 This study was supported in part by research funding from SuperGen and Immunex through investigator-initiated grants awarded to S.Z.P. One of the co-authors (M.R.G.) served as consul- tant for SuperGen. 2 Department of Internal Medicine, Section of Oncology/Hematol- ogy, University of Nebraska Medical Center, Omaha, NE. 3 Department of Pathology and Microbiology, University of Ne- braska Medical Center, Omaha, NE. 4 Department of Genetics, Cell Biology and Anatomy, University of Nebraska Medical Center, Omaha, NE. 5 Department of Preventive and Societal Medicine, University of Nebraska Medical Center, Omaha, NE. 6 College of Pharmacy, University of Nebraska Medical Center, Omaha, NE. 7 Department of Internal Medicine, The Ohio State University, Columbus, OH. 8 Address correspondence to: Steven Z. Pavletic, M.D., Graft-ver- sus-Host and Autoimmunity Unit, Experimental Transplantation and Immunology Branch, National Cancer Institute, Building 10, Room 12S241, 10 Center Drive, Bethesda, MD 20892-1907. E-mail: pavletis@mail.nih.gov. Received 24 April 2003. Revision requested 19 May 2003. Accepted 5 June 2003. DOI: 10.1097/01.TP.0000084869.08639.A0 BRIEF COMMUNICATIONS September 15, 2003 877