Hematopoietic stem cell mobilizing agents G-CSF, cyclophosphamide or AMD3100 have distinct mechanisms of action on bone marrow HSC niches and bone formation

Abstract

The CXCR4 antagonist AMD3100 is progressively replacing cyclophosphamide (CYP) as adjuvant to granulocyte colonystimulating factor (G-CSF) to mobilize hematopoietic stem cells (HSC) for autologous transplants in patients who failed prior mobilization with G-CSF alone. It has recently emerged that G-CSF mediates HSC mobilization and inhibits bone formation via specific bone marrow (BM) macrophages. We compared the effect of these three mobilizing agents on BM macrophages, bone formation, osteoblasts, HSC niches and HSC reconstitution potential. Both G-CSF and CYP suppressed niche-supportive macrophages and osteoblasts, and inhibited expression of endosteal cytokines resulting in major impairment of HSC reconstitution potential remaining in the mobilized BM. In sharp contrast, although AMD3100 was effective at mobilizing HSC, it did not suppress osteoblasts, endosteal cytokine expression or reconstitution potential of HSC remaining in the mobilized BM.In conclusion, although G-CSF, CYP and AMD3100 efficiently mobilize HSC into the blood, their effects on HSC niches and bone formation are distinct with both G-CSF and CYP targeting HSC niche function and bone formation, whereas AMD3100 directly targets HSC without altering niche function or bone formation.

Mobilization with granulocyte colony-stimulating factor blocks medullar erythropoiesis by depleting F4/80+VCAM1+CD169+ER-HR3+Ly6G+ erythroid island macrophages in the mouse

“…Furthermore it has been recently demonstrated that this effect of G-CSF on HSC niches is mediated in part by a subset of BM macrophages [15][16][17]. In the mouse HSC niche supportive macrophages express the macrophage-specific antigen F4/80 together with the Ly-6G granulocyte antigen [16,18]. A separate report suggests that HSC niche supportive macrophages express CD169 also called M A N U S C R I P T…”

“…However whether F4/80 + Ly-6G + macrophages express CD169 has never been reported. G-CSF treatment depletes F4/80 + Ly-6G + macrophages in the BM [16,18], resulting in a concomitant loss of osteoblasts and bone formation, decreased expression of VCAM-1 and CXCL12, and HSC mobilization [15][16][17]. In support of this notion, three independent models of macrophage depletion result in HSPC mobilization in the mouse: 1) in macrophage Fas-induced apoptosis (MAFIA) transgenic mice, 2) by injection of clodronate-loaded liposomes into wild-type mice, or 3) following selective depletion of CD169 + macrophages in Siglec1 DTR/+ mice [15,16].…”

Myelosuppressive Therapies Significantly Increase Pro-Inflammatory Cytokines and Directly Cause Bone Loss

“…These results are consistent with other reports following cyclophosphamide, irradiation, or BMT therapy. (12)(13)(14) Studies have also shown that increases in the ratio between receptor activator of NF-kB ligand (RANKL) and osteoprotegerin (OPG) are associated with greater bone resorption in patients with metabolic or malignant bone diseases; (15) hence, we analyzed the expression of these transcripts in BM. We found the ratio of Rankl to Opg was significantly upregulated by day 7 after IRR þ BMT or 5-FU therapy (Fig.…”

Pretransplant Mobilization with Granulocyte Colony-Stimulating Factor Improves B-Cell Reconstitution by Lentiviral Vector Gene Therapy in SCID-X1 Mice

“…Since not all patients respond to G-CSF-induced HSC mobilization and need additional agents such as Plerixafor (AMD3100) to improve mobilization (Broxmeyer et al, 2005;DiPersio et al, 2009), combinations of mobilization agents that mobilize HSC by different mechanisms (Winkler et al, 2012) may further improve engraftment to levels similar to current cytoreductive conditioning. However, similar to Chen et al (2006), we have been unsuccessful using AMD3100 to obtain significant levels of engraftment following transplantation of clinically feasible stem cell numbers (unpublished results).…”