What is the difference in response to horse or rabbit antithymocyte globulin (ATG) in immunosuppressive therapy (IST) for aplastic anemia?

Updated: Jan 29, 2021
  • Author: Sameer Bakhshi, MD; Chief Editor: Emmanuel C Besa, MD  more...
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ATG can be derived from horses or rabbits. Scheinberg et al reported a large difference in the rate of hematologic response at 6 months in favor of horse ATG (68%), as compared with rabbit ATG (37%), in 120 patients with aplastic anemia. [92] Overall survival at 3 years also differed, with a survival rate of 96% in the horse-ATG group, compared with 76% in the rabbit-ATG group when data were censored at the time of stem-cell transplantation, and 94% versus 70% in the respective groups when stem-cell–transplantation events were not censored. [92]

A meta-analysis by Hayakawa et al of 13 studies comparing horse ATG with rabbit ATG for immunosuppressive therapy in severe aplastic anemia concluded that horse ATG results in a higher response rate (P=0.015); further, a sensitivity analysis showed higher early mortality with rabbit ATG. [93] Hence, these authors consider horse ATG the preferred choice in this setting.

However, other retrospective studies have failed to show significant differences between horse ATG and rabbit ATG. [90] In a study of 955 patients with aplastic anemia who received rabbit ATG and cyclosporine as first line treatment (492 patients treated from 2001 to 2008 and 463 treated from 2009 to 2012, responses rose from 37% at 90 days to 52% at 180 days and 65% at 365 days. Mortality within 90 days was 5.7% in the 2001-2008 arm and 2.4% in the 2009-2012 arm. Response rates at 6 months were highest in patients treated within 30 days after diagnosis, and in patients younger than 21 years. [94]

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