Timeline after first HSCT. Four groups of patients are included in this figure. (A) Patients who never experienced a reactivation or partial flare, did not have a second HSCT, and had a DC of ≤30% at last follow-up (I). Note that long-term event-free survival was possible in this group despite low DC levels. Patients who did not experience a reactivation or partial flare and received a second HSCT because of low DC (II). (B) Patients with a partial flare (III). Patients with systemic or isolated CNS reactivation (IV). The black part of the bar displays the time from first HSCT until the date when DC leveled off (ie, DC did not vary for >±10% anymore) and the following time until (I) last follow-up (green), (II) second HSCT (blue), (III) partial flare (purple), last follow-up (green), or second HSCT (blue), or (IV) reactivation (red). In some patients, the time when DC leveled off was after an event and is thus not shown. The DC (overall/CD3⁺/CD56⁺) at last follow-up (I), at second HSCT (II), at partial flare and last follow-up or second HSCT (III), and reactivation (IV) is provided. In P064, the absent DC for 5 years is shown, even though it became detectable again at last measurement (see the “Results” section for case description). *Patients with early-onset HLH during infancy (≤12 months of age), indicating a severe genetic defect. #A double heterozygous defect was found in this patient, 1 each for FHL3 and 5. CD3, T cell; CD56, NK cell; NA, not available.