Process and procedural adjustments to improve CD34+ collection efficiency of hematopoietic progenitor cell collections in sickle cell disease

Abstract

Background: Adequate CD34+ collection efficiency (CE) is critical to achieve target CD34+ cell doses in hematopoietic progenitor cell (HPC) collections. Autologous HPC collection in sickle cell disease (SCD) is associated with unstable collection interfaces and low CD34+ CEs. We hypothesized that variables specific to SCD, activation of blood cells and elevated viscosity, might contribute to these issues and made adjustments to the collection process and procedure to address our hypothesis. Study design and methods: In two patients with SCD undergoing autologous HPC collection on our clinical trial (NCT02193191), we therefore implemented adjustments to the process and procedure in the following areas: proximity of RBC exchange to HPC collection, the type of anticoagulation, and the packing factor setting.Results: There was no collection interface instability. Our CD34+ CE1s were high at 70% and 51%, and granulocyte CE, platelet CE, and product granulocyte % were remarkably low. Product hematocrits were not as high as previously reported to be required to obtain adequate CEs. Interestingly, one HPC product showed a hemoglobin S (HbS) of 91% at the same time that the peripheral blood (PB) showed a HbS of 22%. Discussion: Adjustments to the HPC collection process and procedure were associated with adequate CD34+ CEs and low granulocyte and platelet contamination in HPC products from SCD patients. Given the discrepancy in the percentage of sickle RBCs in the product versus the PB, we hypothesize that CD34+ cells and RBCs may aggregate. Our interventions and hypothesis should be further investigated in larger studies.

Optimizing haematopoietic stem and progenitor cell apheresis collection from plerixafor‐mobilized patients with sickle cell disease

“…Esrick et al adjusted the depth of the collection toward the RBC layer by using 5%–10% interface collection, and the CEs of two collections exceeded 40% 3 . Avecilla et al lowered CP to 15–25 and 17–25 for two patients, and reached a CE1 of 70% and 51% respectively 8 . In this study, we identified the optimal collection depth to capture SCD HSPCs and achieved highly efficient apheresis collection.…”

“…HbS < 10%, does not necessarily improve CE either 3 . Avecilla et al reported that percentage of HbS of a HSPC product was 91, whereas percentage of HbS of the HSPC donor's peripheral blood was 22, indicating that sickle RBCs could have a similar sedimentation rate as HSPCs or form aggregates with HSPCs 8 . Hence, sickle RBCs, even when present at a low percentage, can profoundly affect HSPC collection, and adjusting the apheresis setting is needed.…”

“…3 Avecilla et al lowered CP to 15-25 and 17-25 for two patients, and reached a CE1 of 70% and 51% respectively. 8 In this study, we identified the optimal collection depth to capture SCD HSPCs and achieved highly efficient apheresis collection.…”

“…[4][5][6] These cellular aggregates alter densitybased cell separation during apheresis collection, causing HSPCs to travel deep into the buffy coat, close to the RBC layer. 2,3,7,8 Therefore, HSPCs are not efficiently captured in SCD patients with standard apheresis collection optimized for non-SCD individuals. 3 SCD is also characterized by a hypercoagulable state with increased activation of platelets and coagulation cascade.…”

“…SCD patients are known to have high levels of circulating red blood cell (RBC)–neutrophil /monocyte, and platelet–neutrophil/monocyte aggregates, even at steady state 4–6 . These cellular aggregates alter density‐based cell separation during apheresis collection, causing HSPCs to travel deep into the buffy coat, close to the RBC layer 2,3,7,8 . Therefore, HSPCs are not efficiently captured in SCD patients with standard apheresis collection optimized for non‐SCD individuals 3 .…”