Method of Mobilization: Implication on Cell Subsets in the Graft and Immune Reconstitution Post Autologous Hematopoietic Cell Transplantation (AHCT)

Method of Mobilization: Implication on Cell Subsets in The Graft and Immune Reconstitution post Autologous Hematopoietic Cell Transplantation (AHCT)

The optimal mobilization method for either myeloma or lymphoma patients undergoing AHCT is still debatable and strategies for graft collection vary between different institutions. Plerixafor, a CXCR4 antagonist is used for peripheral blood stem cell mobilization in multiple myeloma and non-Hodgkins lymphoma patients requiring AHCT. The effect of plerixafor on graft composition has scarce data that are based mostly on cryopreserved samples. Moreover; the effect of plerixafor on immune reconstitution and hematologic recovery post AHCT has not been well evaluated. The goal of our study was to compare graft composition, hematologic and immune reconstitution recovery among patients mobilized with plerixafor plus G-CSF to those mobilized with G-CSF alone.

Methods: 49 patients eligible for AHCT were enrolled on a single arm prospective trial at a single transplant center. All patients were mobilized with G-CSF 10µg/kg/day for 4 consecutive days. A peripheral blood CD34 level of <20/µl on day 4 was used as a cutoff to use plerixafor 0.24mg/kg in addition to G-CSf on 9pm of the fourth day. Peripheral blood collection was started on day 5 and was continued till the target dose is achieved or a minimum CD 34+ cell dose of >2x10⁶ cells/Kg was obtained after 3 collection days. Samples from the freshly collected graft and patients' peripheral blood on days +30 and +60 were analyzed by flow cytometry (BD FACSCanto II) . A single platform assay was used (Beckman-Coulter Stem kit) via a ISHAGE protocol. The antibody cocktail contained the following pre-conjugated monoclonal antibodies: CD56-PE (Miltenyi Biotech, Auburn, CA), CD3-APC, CD16-FITC, (Beckman Coulter, Brea, CA), CD19-PE-CY7 (BD Biosciences, San Jose, CA). Data were acquired using BD FACSCanto II (BD Biosciences) and analyzed with the FACSDiva software (BD Biosciences) to quantify CD3+ T cells, CD3+ CD56+ NK-like T cells, CD56+ CD16+ and CD56+ CD16- NK cells as well as CD19+ B cells.

Results: 49 patients with a median age of 58 years (range 21-75) were mobilized with either G-CSF alone (N=16) or plerixafor +G-CSF (G+P)(N=33).The median number of collection days was 1.42 and 1.81 (p=0.2) and the median collected CD34+ dose was 8.28x10⁶/kg and 5.24x10⁶ /kg (p=022) in the G+P and G-CSF alone groups respectively. Both groups had similar times to neutrophil and platelet engraftment. The graft analysis showed a white blood count of 309x10⁹/l and 262x10⁹/l (p=0.38), median percentage of CD34+ cells of 0.75% and 0.73% (p=0.81), percentage of CD3+ T cells of 25.6% and 22% (p=0.6) in the G+P and G-CSF alone groups resepectively. Both groups had similar proportions of CD3+, CD4+,CD8+, NK, NKT and iNKT cells in the mobilized grafts. Peripheral blood samples at day +30 and day +60 were analyzed for T cell markers and hematologic recovery (table 1). There was no significant difference between absolute lymphocyte counts, NK cell counts, T cells and absolute neutrophil count.

Conclusion: Plerixafor when combined with G-CSF helps in achieving mobilization goals in patients predicted to be poor mobilizers based on peripheral CD34 levels. The addition of plerixafor doesn't not seem to affect T cell composition of the graft and yields similar hematologic and immune recovery when compared to mobilization with G-CSF alone.