title: Horse versus rabbit antithymocyte globulin in acquired aplastic anemia.
abstract: In severe acquired aplastic anemia, hematopoietic failure is the result of immune-mediated destruction of bone marrow stem and progenitor cells. Immunosuppressive therapy with antithymocyte globulin (ATG) plus cyclosporine is an effective alternative to stem-cell transplantation and improves blood counts and survival. Although horse ATG is the standard therapy, rabbit ATG is more potent in depleting peripheral-blood lymphocytes and is preferred in other clinical circumstances.
  
  
  
  From December 2005 through July 2010, we performed a randomized trial comparing these two ATG formulations in conventional regimens. Patients were treated at a single facility. The primary outcome was hematologic response at 6 months, as determined by blood counts. The study was designed to enroll 60 patients each for the rabbit-ATG and horse-ATG groups and was powered to detect a difference of 25 percentage points in the response rate.
  
  
  
  A large, unexpected difference was observed in the rate of hematologic response at 6 months in favor of horse ATG (68%; 95% confidence interval [CI], 56 to 80) as compared with rabbit ATG (37%; 95% CI, 24 to 49; P<0.001). Overall survival at 3 years also differed, with a survival rate of 96% (95% CI, 90 to 100) in the horse-ATG group as compared with 76% (95% CI, 61 to 95) in the rabbit-ATG group (P=0.04) when data were censored at the time of stem-cell transplantation, and 94% (95% CI, 88 to 100) as compared with 70% (95% CI, 56 to 86; P=0.008) in the respective groups when stem-cell-transplantation events were not censored.
  
  
  
  In a randomized study, rabbit ATG was inferior to horse ATG as a first treatment for severe aplastic anemia, as indicated by hematologic response and survival. (Funded by the Intramural Research Program of the National Institutes of Health; ClinicalTrials.gov number, NCT00260689.).
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, Bethesda, MD, USA. scheinbp@mail.nih.gov
authors.forename: Phillip
authors.initials: P
authors.lastname: Scheinberg
authors.forename: Olga
authors.initials: O
authors.lastname: Nunez
authors.forename: Barbara
authors.initials: B
authors.lastname: Weinstein
authors.forename: Priscila
authors.initials: P
authors.lastname: Scheinberg
authors.forename: Angélique
authors.initials: A
authors.lastname: Biancotto
authors.forename: Colin O
authors.initials: CO
authors.lastname: Wu
authors.forename: Neal S
authors.initials: NS
authors.lastname: Young
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000741:Anemia, Aplastic / Q000097:blood / Q000188:drug therapy* / Q000401:mortality / Q000628:therapy; D000818:Animals; D000961:Antilymphocyte Serum / Q000009:adverse effects / Q000627:therapeutic use*; D001772:Blood Cell Count; D002648:Child; D002675:Child, Preschool; D005260:Female; D006736:Horses; D006801:Humans; D007166:Immunosuppressive Agents / Q000009:adverse effects / Q000627:therapeutic use*; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D011817:Rabbits; D033581:Stem Cell Transplantation; D015996:Survival Rate; D055815:Young Adult
chemical_list: D000961:Antilymphocyte Serum; D007166:Immunosuppressive Agents