A new step in understanding stem cell mobilization in patients with Fanconi anemia: A bridge to gene therapy

Background: Fanconi anemia (FA) is an inherited disorder characterized clinically by congenital abnormalities, progressive bone marrow failure (BMF), and a predisposition to malignancy. Gene therapy (GT) of FA, via the infusion of gene-corrected peripheral blood (PB) autologous hematopoietic stem cells (HSCs), may constitute a cure for BMF. GT bypasses the donor restrictions and adverse events associated with allogenic HSC transplantation. However, adequate harvesting of PB-HSCs is a crucial determinant of successful engraftment in gene therapy. Harvesting the low numbers of HSCs in patients with FA is particularly challenging.

Study design and methods: This open-label phase I/II trial evaluates the feasibility and safety of co-administration of G-CSF and plerixafor in patients with FA for the mobilization and harvesting of peripheral HSCs, intending to use them in a gene therapy trial. Patients with mutations in the FANCA gene received two subcutaneous injections of G-CSF (6 μg/kg × 2/d from D1 to D8. Plerixafor (0.24 mg/kg/d) was administered 2 h before apheresis (from D5 onward).

Results: CD34⁺ cells were mobilized for four patients quickly but transiently after the plerixafor injection. One patient had a CD34⁺ cell count of over 100/μl; the mobilization peaked 2 h after the injection and lasted for more than 9 h. There were no short-term adverse events associated with the mobilization or harvesting procedures.

Conclusion: Our data in patients with FA show that the mobilization of HSCs with G-CSF and plerixafor is safe and more efficient in younger individuals without BMF.