Partial engraftment following plerixafor rescue after failed sibling donor peripheral blood stem cell harvest

Rarely, healthy donors fail adequate peripheral blood stem cell (PBSC) mobilization. If the recipient has already received conditioning chemotherapy, this can result in the donor undergoing urgent marrow harvest under general anesthesia. Plerixafor is a novel CXCR4 antagonist, licensed for autologous PBSC harvest (PBSCH) in patients who failed mobilization with granulocyte-colony-stimulating factor (G-CSF) alone. Experience using plerixafor in healthy allogeneic donors failing G-CSF mobilization is scarce.

A 65-year-old patient was referred for a reduced-intensity conditioning sibling allograft for relapsed follicular lymphoma. She received fludarabine, melphalan, and alemtuzumab conditioning. Her 68-year-old brother was fully HLA matched. PBSCH was planned on Day -1 after 4 days of 10 μg/kg G-CSF. Day 1 PBSCH collected an inadequate number of CD34+ 0.35 × 10(6) /kg cells. Despite increasing G-CSF (16 μg/kg), Day 2 yielded 0.33 × 10(6) /kg CD34+ cells, giving a suboptimal total dose. He proceeded to a third PBSCH day after plerixafor (0.24 mg/kg) and G-CSF (16 μg/kg) were given the evening before. A total of 1.79 × 10(6) /kg CD34+ cells were harvested, giving a total dose of 2.46 × 10(6) /kg CD34+ cells. After initial neutrophil engraftment on Day +13, the patient's neutrophils gradually decreased to 0.02 × 10(9) /L by Day +74. A marrow aspirate on Day +81 was markedly hypocellular. Total white blood cell chimerism was near 100% donor on Days +32, +74, and +102. Despite chimeric-only engraftment, the patient remains platelet and red blood cell transfusion dependent.

Rescue plerixafor to assist PBSCH in healthy allogeneic donors has been effective in terms of CD34+ cell number mobilized. It is unclear whether the partial engraftment seen was coincidental or related to a difference in PBSC quality.