Pre-HSCT emapalumab mitigates the risk of mixed chimerism associated with young age at the time of transplantation. (A) Minimum donor chimerism obtained within 1 year after HSCT stratified by age at the time of HSCT. (B) Five-year Kaplan-Meier survival estimates based on IFS (use of any cellular product or death). Chimerism levels were treated as continuous variables and compared via the Mann-Whitney U test. Survival curves were compared using the log-rank (Mantel-Cox) test. An XY plot by age and mixed chimerism and similar survival curves based on high-risk IFS and OS are shown in supplemental Figure 8. ∗∗P < .01. ns, not statistically significant.