aGVHD rATG exposure and mortality. Post-HCT high rATG exposure group (≥55 AU × day/mL) was associated with up to double the incidence of grade ≥2 aGVHD (HR, 2.28; 95% CI, 1.01-5.16 after adjustment for donor type) compared with the low rATG exposure group (<30 AU × day/mL). The proportion of deaths attributed to aGVHD and infection increased with higher post-HCT rATG exposures. (A) Correlation between different levels of post-HCT rATG exposures and aGVHD. Post-HCT rATG exposure of <30 AU × day/mL was associated with lower rates of GVHD. (B-D) Causes of mortality in the post-HCT rATG <30 AU × day/mL exposure group (B), 30-55 AU × day/mL exposure group (C), and ≥55 AU × day/mL exposure group (D). POD, progression of disease.