Stem Cell Graft Cellular Composition, Hematological and Immune Recovery in NHL Patients Mobilized with or without Plerixafor: A Prospective Comparison

Introduction:

Plerixafor, a reversible CXCR4 antagonist, may be used to enhance mobilization of CD34⁺ cells after G-CSF or chemotherapy plus G-CSF. There is a paucity of prospective data regarding cellular composition of grafts collected after plerixafor in chemomobilized patients. Also the data concerning hematopoietic or immune recovery after high-dose chemotherapy in plerixafor treated lymphoma patients is limited.

Patients and methods:

Thirty-one patients with NHL were included into this prospective study. There were 14 males and 17 females with a median age of 62 years (range 19 - 73). Altogether fourteen patients received plerixafor (plerixafor group) for poor or late mobilization whereas 17 did not (control group). All patients were mobilized with chemotherapy plus G-CSF. Cryopreserved graft samples were analyzed with flow cytometry for T and B cells (CD3/CD8/CD45/CD19) as well as for NK cells (CD3/CD16+CD56). Also CD34⁺ cell subclasses were analyzed (CD34/CD38/CD133). Complete blood counts were evaluated at +15 days, 1, 3, 6 and 12 months post-transplant. To evaluate immune reconstitution, flow cytometry of lymphocyte subsets (T, B, NK) was performed at 1, 3 and 6 months after the graft infusion with the same antibody panel as for graft analysis.

Results:

The median number of infused viable CD34⁺ cells was higher in the control group (3.1 x 10⁶/kg vs. 2.0 x 10⁶/kg, p = 0.036) (Table 1). The median percentage of the most primitive stem cells (CD34⁺CD133⁺CD38^-) in the grafts was higher in the plerixafor group (3.5 % vs 1.2 %, p = 0.001), but there was no significant difference in the absolute counts (0.07 x 10⁶/kg vs 0.05 x 10⁶/kg, p = 0.620). The median amounts of CD3⁺CD4⁺ and CD3⁺CD8⁺ T cell subsets, CD3⁺ and NK (CD3^-CD16/56⁺) cells were all significantly higher in the plerixafor group (Table 1).

The neutrophil counts at +15 days after the graft infusion were lower in the plerixafor group (2.1 x 10⁹/l vs. 4.8 x 10⁹/l, p = 0.013). Otherwise there was no significant difference in the hematological reconstitution between the groups. The immune reconstitution was comparable except for the higher number of NK cells in the plerixafor group at one month (0.4 x 10⁹/l vs. 0.1 x 10⁹/l, p = 0.001). Also a trend towards faster recovery of blood CD4⁺ T cells was observed after one month in the plerixafor group (0.2 x 10⁹/l vs. 0.1 x 10⁹/l, p = 0.097).

Conclusions:

This prospective study evaluating cellular composition of grafts confirms that the apheresis products collected from plerixafor-treated NHL patients contain a greater proportion of the more primitive stem cells and a greater number of T lymphocytes and NK cells compared to patients mobilized without plerixafor. Hematopoietic reconstitution was comparable between the groups except for slower neutrophil recovery in the plerixafor-group. Immune reconstitution was comparable but NK cell as well as CD4⁺ T cell recovery was faster in the plerixafor group. These results will be further evaluated in a larger set of patients. Also the possible effect of graft composition on the progression free and overall survival will be evaluated in the ongoing GOA (Graft and Outcome in Autologous transplantation) study.