This multicenter prospective study seeks to determine if daratumumab given, prior to HLA-identical sibling donor transplantation using alemtuzumab, low dose total-body irradiation, and sirolimus, can prevent pure red blood cell aplasia with an acceptable safety profile in patients with anti-donor red blood cell antibodies, achieving an event-free survival similar to transplanted patients without such antibodies.

This study addresses an important question: Can daratumumab safely be administered prior to matched sibling donor (MSD) nonmyeloablative hematopoietic cell transplant (HCT) for SCD to avoid pure red blood cell aplasia in patients at risk of this complication? and thus achieve an event-free survival similar to patients without anti-donor red blood cell (RBC) antibodies?

Patients with anti-donor RBC antibodies, which includes patients with major ABO mismatch and other RBC alloantibodies against donor, have largely been excluded from the nonmyeloablative HCT approach given their risk of delayed donor RBC engraftment and/or hemolysis post-HCT. Exclusion of these patients limits access to less toxic curative therapies for this population at risk for toxicity due to their underlying multisystem disease. To address this need, we propose a multicenter clinical trial of Sickle cell disease Using a Nonmyeloablative approach: adding daratumumab for patients with anti-donor Red cell AntibodY (SUN-RAY). If successful, this trial will increase access to MSD nonmyeloablative HCT in SCD and will provide important safety and efficacy data for the use of daratumumab in the pre-HCT setting as well as in patients with SCD who have limited RBC donor options due to alloimmunization.

This is a phase 2 study given that the studied nonmyeloablative conditioning backbone (alemtuzumab, 300 cGY TBI, sirolimus) has been previously used effectively in both adults and children with SCD. Daratumumab will be added to this backbone with a washout period of 4 weeks prior to HCT infusion. Small case series have demonstrated that daratumumab is well tolerated either pre-HCT to treat patients with antibodies against mismatched donor HLA antigens, or post-HCT in patients with autoimmune cytopenias. The experience of the phase 2 clinical trial NCT03384654 studying daratumumab in pediatric acute lymphoblastic leukemia provides additional support for the safety and dosing of daratumumab for this study.

Inclusion Criteria:

General:

• Patients with SCD age 2-24.99 years who have a healthy HLA-identical sibling donor with major ABO incompatibility OR patients with RBC alloantibodies against other donor RBC antigens.
• Patients must have an absolute neutrophil count of 1 x 109/L and a platelet count of 100 x 109/L.
• Lansky/Karnofsky score of, at least, 70.

Patients with genotypes hemoglobin SS and Sβ0 thalassemia must have at least one of the following:

• History of an abnormal transcranial Doppler measurement defined as TCD velocity ≥200 cm/sec by the non-imaging technique measured at a minimum of two separate occasions.
• Progression of CNS vasculopathy on MRA determined to be secondary to SCD.
• History of cerebral infarction on brain MRI (overt stroke, or silent stroke if ≥3 mm in one dimension, visible in two planes on fluid-attenuated inversion recovery T2-weighted images).
• History of two or more episodes of Acute Chest Syndrome (ACS) in lifetime.
• History of three or more SCD pain events requiring treatment with an opiate or IV pain medication in lifetime.
• History of any hospitalization for a complication secondary to SCD (does NOT include empiric hospitalizations for fever only).
• History of two or more episodes of priapism.
• Administration of regular RBC transfusions (≥8 transfusions episodes in the previous 12 months).
• At least two episodes of splenic sequestration requiring red blood cell transfusion or splenectomy after at least one episode of splenic sequestration.

Patients with all other sickle genotypes (e.g. hemoglobin SC, Sβ+ thalassemia, etc.) must have at least one of the following:

• Clinically significant neurologic event (overt stroke).
• History of two or more episodes of ACS in the 2-year period preceding enrollment.
• History of three or more SCD pain events requiring treatment with an opiate or IV pain medication (inpatient or outpatient) in the 1-year period preceding enrollment.
• History of any hospitalization for SCD pain or ACS while receiving hydroxyurea treatment.
• History of two or more episodes of priapism (erection lasting ≥4 hours or requiring emergent medical care).
• Administration of regular RBC transfusions (≥8 transfusions in the previous 12 months)
• At least two episodes of splenic sequestration requiring red blood cell transfusion or splenectomy after at least one episode of splenic sequestration.

Exclusion Criteria:

• Life expectancy less than 6 month
• Pregnant or breastfeeding patients.
• Infectious Disease: Uncontrolled bacterial, viral or fungal infections (undergoing appropriate treatment and with progression of clinical symptoms) within 1 month prior to conditioning. Patients with febrile illness or suspected minor infection should await clinical resolution prior to starting conditioning. Patients with confirmed seropositivity for HIV and patients with active or resolved Hepatitis B or C determined by serology and/or NAAT are excluded.
• Liver: Direct (conjugated) bilirubin > 1.5 mg/dL. Transaminases >5x upper limit of normal for age.
• Cardiac: Left ventricular shortening fraction <25% or ejection fraction <50% by ECHO. Uncontrolled cardiac arrhythmia.
• Kidney: Estimated creatinine clearance less than 60 mL/min/1.73m2.
• Pulmonary function: Diffusion capacity of carbon monoxide (DLCO) <35% (adjusted for hemoglobin). Baseline oxygen saturation <94% at rest or PaO2 <70. Known moderate or severe persistent asthma within the past 2 years, or uncontrolled asthma of any classification.
• Heme: Available, medically suitable, and equivalent HLA-matched sibling donor, who does not have major ABO incompatibility or express RBC antigens against which the patient is alloimmunized.