CD34⁺ Subclasses of Blood Stem Cell Grafts Collected After Plerixafor Injection in Non-Hodgkin Lymphoma (NHL) Patients Mobilizing Poorly with Chemotherapy Plus G-CSF

Mobilization of blood stem cells is difficult in a subgroup of patients with standard methods. Plerixafor, a CXCR4 antagonist, has been used for stem cell mobilization in combination with G-CSF for some years. Mobilization method used may affect not only efficacy of stem cell mobilization and collection but also graft content which on the other hand may have effect on post-transplant outcomes. No data is available on CD34⁺ subclasses in grafts collected after plerixafor administration in patients who mobilize poorly with chemotherapy plus G-CSF.

Patients and Methods: Altogether blood stem cell grafts collected from 26 NHL patients were studies. Thirteen patients (8 M, 5 F, median age 51 yrs) were mobilized with a combination of chemotherapy and G-CSF ad received plerixafor due to poor mobilization followed by stem cell apheressis. Thirteen patients (10 M, 3 F, median age 56 yrs) were mobilized with chemotherapy plus G-CSF without plerixafor and served as controls. Samples from the first collection after plerixafor and from the first apheresis of control patients were studied by flow cytometry using the following antibodies: CD34, CD38, CD 117, CD133, CD19 and CD45. Viability of CD34⁺ cells after freezing was assessed with 7-aminoactinomycin D staining. Also in vitro growth of granulocyte/macrophage progenitors (GM-CFU) were assessed from all grafts. Patients were followed after high-dose chemotherapy in regard to hematopoietic reconstitution.

The number of viable cells in the grafts was comparable between the plerixafor and the control groups (Table 1). The number of the most primitive stem cells (CD34⁺CD38⁻CD133⁺) was higher in plerixafor mobilized grafts (Table 1). Most of the CD34⁺ cells were myeloid progenitors, as defined by their CD117 antigen co-expression. No differences in GM-CFU were observed between the groups. All except one patient had received high-dose therapy. The median number of CD34⁺ cells collected from the patients was comparable (3.1 vs. 3.3 × 10⁶/kg). The median time to reach neutrophils > 10 × 10⁹/L was 10 days from the stem cell infusion in both groups and time to unsupported platelets was also comparable (16 d vs. 13 d). Platelet counts at 1 month, 3 months and 6 months were comparable between the groups. Absolute lymphocyte counts were higher in plerixafor group but the differences were not statistically significant. One early toxic death occurred in the plerixafor mobilized group and one death due to disease recurrence in both groups with a median follow-up of 301 and 348 days from stem cell infusion in prelixafor and control groups, respectively.

Plerixafor added to chemomobilization in NHL patients resulted in higher number of the most primitive CD34⁺ cells in the graft with comparable in vitro growth and engraftment potential after BEAM chemotherapy when compared to patients mobilized without plerixafor. Longer follow-up of higher patient numbers are needed to evaluate whether differences in graft content have an effect on patient outcomes.

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