sC5b-9 levels are lower in abatacept cohort at day +14 post-HSCT. (A) Pretransplant sC5b-9 values are similar between abatacept and no-abatacept cohorts, indicating similar complement activation status before proceeding with HSCT. (B) Day +7 post-HSCT sC5b-9 values are similar between abatacept and no-abatacept cohort. (C) Day +14 post-HSCT sC5b-9 values are higher in the no-abatacept cohort than in the abatacept cohort, suggesting lower complement activation in the abatacept cohort.