Hematopoietic stem cell mobilization for gene therapy of adult patients with severe β-thalassemia: results of clinical trials using G-CSF or plerixafor in splenectomized and nonsplenectomized subjects

Abstract

The safety and efficacy of hematopoietic stem cell (HSC) mobilization was investigated in adult splenectomized (SPL) and non-SPL patients with thalassemia major, in two clinical trials, using different mobilization modes: granulocyte-colony-stimulating factor (G-CSF)-alone, G-CSF following pretreatment with hydroxyurea (HU), plerixafor-alone. G-CSF-mobilization was both safe and effective in non-SPL patients. However, in SPL patients the procedure resulted in excessive response to G-CSF, expressed as early hyperleukocytosis necessitating significant dose reduction, and suboptimal CD34(+) cells yields. One-month HU-pretreatment prevented hyperleukocytosis and allowed successful CD34(+) cell collections when an optimal washout period was maintained, but it significantly prolonged the mobilization procedure. Plerixafor resulted in rapid and effective mobilization in both SPL and non-SPL patients and was well-tolerated. For gene therapy of thalassemia, G-CSF or Plerixafor could be used as mobilization agents in non-SPL patients whereas Plerixafor appears to be the mobilization agent of choice in SPL adult thalassemics in terms of safety and efficacy.

Figures

Figure 1

CD34+ cell yield. (a) Non-SPL patients. The yields from non-SPL subjects, in total 2 aphereses, are shown individually in bars. Left panel: G-CSF-treated subjects; middle panel: HU+G-CSF-treated subjects; right panel: plerixafor-treated subjects. The mobilization outcome in the HU+G-CSF-treated group is directly correlated with the length of the washout period after HU (gray line). (b) SPL patients. The yields from SPL subjects, in total 2 aphereses, are shown individually in bars. Left panel: G-CSF-treated subjects; left-middle panel: HU+G-CSF-treated subjects; right-middle panel: Plerixafor-treated subjects; right panel: Plerixafor+G-CSF-treated subject. The mobilization outcome in the HU+G-CSF-treated group is directly correlated with the length of the washout period after HU (gray line). The primary y-axis represents the CD34+ cell yield ×106/kg and the secondary y-axis the days of washout period after HU-pretreatment. P25 and P04/P25 (**) is the same patient mobilized initially with G-CSF and later with Plerixafor+G-CSF. Patients P02 (*) and P04/P25 (**) reached the target cell dose in 1 apheresis. G-CSF, granulocyte-colony stimulating factor; HU, hydroxyurea; non-SPL, nonsplenectomized; SPL, splenectomized.

Figure 2

Kinetics of white blood cells (WBCs) and peripheral blood CD34+ cells in splenectomized (SPL) patients and the mean yield of CD34+ cells per patient per apheresis. (a) Kinetics of WBCs and peripheral blood CD34+ cells in the SPL patients treated with G-CSF or HU+G-CSF (with the long washout period) or plerixafor. (b) The mean yield per patient per apheresis in SPL subjects treated with granulocyte-colony stimulating factor (G-CSF), HU+G-CSF (with the long washout period), plerixafor and plerixafor + G-CSF. (c) The mean yield per patient per apheresis in non-SPL subjects treated with G-CSF, HU+G-CSF (with the long washout period), and plerixafor. *P = 0.02 versus G-CSF, #P = 0.09 versus G-CSF. HU, hydroxyurea.

Figure 3

Suggested HSC mobilization algorithm for patients with thalassemia. (a) Nonsplenectomized patients. Non-SPL patients with spleen volume <800 cm3 (arbitrary cutoff) could be mobilized with G-CSF whereas patients with excessive splenomegaly (>800 cm3) would better receive Plerixafor which results in significantly less splenic enlargement. (b) Splenectomized patients. SPL patients with baseline WBC <30.0 × 103/µl (arbitrary cutoff) could be mobilized with Plerixafor which triggers less leukocytosis compared to G-CSF, whereas SPL patients with >30.0 × 103/µl baseline WBCs would better receive pretreatment with HU (with the optimal washout interval) to reduce WBCs before mobilization, either with Plerixafor or low-dose G-CSF. HSC, hematopoietic stem cell; HU, hydroxyurea; non-SPL, nonsplenectomized; SPL, splenectomized.