Method of Mobilization: Implication on Cell Subsets in the Graft and Immune Reconstitution Post Autologous Hematopoietic Cell Transplantation (AHCT)
Authors: Solh Melhem M. , Kristin Rathmann , chang-Fong Sauvi , Oyer Jeremiah , Ahmed Wesam B. , Copik Alicja J , Khaled Yasser 
Published: October 2019

Abstract
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.
Table 1: Immune Reconstitution at Day 30 and Day 60 post Autologous Transplantation Treatment Group G-CSF (N=16) Plerixafor + G-CSF (N=33) P-value G-CSF (N=16) Plerixafor + G-CSF (N=33) P-value Day 30 Day 60 WBC 5.08 5.41 0.873 4.94 5.38 0.654 HGB 10.86 11.19 0.353 11.22 11.17 0.757 HCT 32.35 33.66 0.321 33.36 33.53 0.565 PLT 119.88 161.42 0.068 166.94 173.73 0.949 Abs Lymph 1.09 1.44 0.296 1.41 1.50 0.974 % NK 26.14 30.38 0.277 11.53 20.09 0.095 Abs NK 0.31 0.35 0.186 0.17 0.21 0.470 % T cell 67 60 0.183 76.15 67.39 0.340 Abs T cell 0.72 0.96 0.717 1.35 .82 0.095 NKT%* 5.28 3.33 8.25 3.38 B cell % 2.38 1.52 0.922 2.63 5.58 0.424 Abs. Neut count 2.99 2.64 0.488 2.85 3.01 0.848

Disclosures
No relevant conflicts of interest to declare.