Objectives

Many cellular therapies for sickle cell disease (SCD) rely on the in vitro manipulation of cells to effect genetic changes in hope of curative therapies through stem cell transplantation. One of the major impediments in the field is the availability of SCD derived stem cells for testing of gene targeting therapies. The purpose of this collection is to provide a bank of frozen blood derived stem cells that can be made available to scientists in the SCD field. A central repository allows for a standardized cell pool to be used by many different laboratories and thus enable comparisons of in vitro manipulation.

Background

Cellular therapy for treating the hemoglobinopathy associated with SCD is developing at a rapid pace, with multiple approaches in development. Most of the therapeutic approaches that use stem cell transplantation will require preclinical testing of the modified HSC, to establish and validate the in vitro procedures. Emerging therapies include gene addition of beta globin, Bcl11a modification as well as other gene and base editing techniques performed at many academic and industry research laboratories.

To develop these novel cell therapies, there is a need for both healthy and SCD CD34+ cells for use in preclinical development and in validation of these therapeutic approaches. One of the challenges in obtaining SCD CD34+ HSCs is that mobilization and collection of these cells is challenging due to technical limitations of the apheresis procedure. Moreover, peripheral blood mobilization of stem cells in SCD patients is limited to plerixafor as G-CSF is contraindicated in SCD thus obtaining relatively fewer cells at collection. Taken together, there are very few centers that can potentially assemble SCD stem cell donors and have the expertise to successfully collect CD34+ cells for research use.

Participants

Volunteers with SCD were recruited as donors for collection of peripheral blood stem cells by apheresis. Inclusion criteria included: Diagnosis of sickle cell disease with genotype HbSS, HbS/beta thalassemia, age 18-45 years, receiving regularly-scheduled blood transfusions or exchange transfusions as part of existing medical care, adequate hematologic parameters, organ function and performance status. Exclusion criteria included subjects on concurrent hydroxyurea treatment, with uncontrolled illness, known myelodysplasia of the bone marrow, pregnancy or breastfeeding and/or receipt of an investigational study drug or procedure within 90 days of enrollment.

Design

Volunteers were treated with plerixafor, a drug shown to safely mobilize peripheral blood (PB) CD34+ cells in people with SCD. The collected blood cells will be purified by magnetic separation using CD34 beads, validated, frozen. CD34 positive cells are frozen in aliquots immediately after purification. A portion of cells from the CD34 negative fraction were also aliquoted and frozen and are available for request.

Conclusions

The plerixafor-mobilized apheresis units from subjects with sickle cell disease were collected and CD34+ cell isolation was conducted under standard operating procedures described in detail elsewhere (1) and in the manual of operations.

1. Esrick EB, Manis JP, Daley H, Baricordi C, Trébéden-Negre H, Pierciey FJ, Armant M, Nikiforow S, Heeney MM, London WB, Biasco L, Asmal M, Williams DA, Biffi A. Successful hematopoietic stem cell mobilization and apheresis collection using plerixafor alone in sickle cell patients. Blood Adv. 2018 Oct 9;2(19):2505-2512. doi: 10.1182/bloodadvances.2018016725. PMID: 30282642; PMCID: PMC6177648.

Additional Details

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