Severe vaso-occlusive crisis. (A) Donor arm: severe vaso-occlusive crisis for each patient in the donor arm after biologic assignment, overlaid by the period before and after HCT. (B) No donor arm: severe vaso-occlusive crisis for each patient in the no donor arm after biologic assignment. Patient ID is in red if the severity criteria for pain were met at enrollment, and blue if the severity criteria for pain were not met at enrollment. Patients in gray did not respond about pain at enrollment. VOE, vasocclusive episode.