Post-HCT rATG exposure <30 AU × day/mL was associated with lower NRM (overall and in patients who underwent HCT for malignant disorders), faster CD4⁺ IR, and higher OS rates. Post-HCT rATG exposure was not associated with risk of relapse in patients who underwent HCT for malignant disorders. The correlation between different levels of post-HCT rATG exposure and NRM in all patients (A), NRM in patients who underwent HCT for malignant disorders (B), and CD4⁺ IR (C). CD4⁺ IR was defined as CD4⁺ levels twice above 50 cells per µL at 2 consecutive measures within 100 days. (D) Correlation between CD4⁺ IR and NRM in all patients, demonstrating that patients who reconstitute CD4⁺ earlier have lower NRM. Note that this figure represents a landmark analysis starting 100 days after HCT. Therefore, only patients alive at 100 days after HCT were included in this specific analysis, which is 359 patients alive with known CD4⁺ IR status. (E-F) Correlation between different levels of post-HCT rATG exposure and OS (E) and relapse rates (F) in patients who underwent HCT for malignant disorders.