Abstract

Background: Mobilization of hematopoietic stem cells (HSCs) in mice and man can be induced using G-CSF (G) or by the use of chemokines and chemokine receptor antagonists. Recent preclinical and clinical data using the bicyclam AMD3100 (A) suggests that the combination of G+A results in significantly improved yields of HSCs compared to G alone in both mice and man (

Blood.
2005
;
106
:
1867
). In humans, optimal mobilization of HSCs occurs 6–9 h after subcutaneous (s.c.) A. These mobilization kinetics necessitate the somewhat undesirable administration of A the evening before the first day of apheresis.

Methods: We assessed the kinetics of HSC mobilization in mice and man after IV or s.c. administration of A. Human donors were initially mobilized with increasing doses of IV A (80, 160, 240 or 320 μg/kg). After 4 days of drug clearance, the same donors were then mobilized with a single s.c. dose of A (240 μg/kg) and collected cells were used as a source of HSCs for HLA-matched sibling recipients undergoing single dose (550 cGy) TBI and cytoxan allogeneic HSC transplantation (

Devine et. al.
Blood
.
2006
;
108
:
53
).

Results: Peak mobilization of mouse CFU-GM occurred 3 h after s.c A (5 mg/kg; 15–18-fold; n=5) and 0.5–1 h after IV A (1–3 μg/kg; 10–12-fold; n=3). Identical CFU-GM kinetics were observed after mice were first given G (250 μg/kg) for 4 days then administered either s.c. A (250–500 fold in 3 h; n=3) or IV A (170–350 fold n=3). To date, 6 normal HLA-matched sib donors have been treated with 80 μg/kg (n=3) or 160 μg/kg (n=3) IV A over 30 minutes followed 4 days later by 240 μg/kg s.c. A. Peak mobilization of CD34+ cells occurred 1–4 h after 80 μg/kg IV A, 4–6 h after 160 μg/kg IV A, and 9 h after s.c. A. The more rapid kinetics of CD34 mobilization after IV A is in contrast to the kinetics of s.c. A in autologous transplant patients receiving both G and A (

J Clin. Oncol.
2004
;
22
:
1095
) and in normal volunteers receiving A alone (∼9 hours;
Blood
.
2003
;
102
:
2728
). This data suggests that IV A not only mobilizes HSCs from mouse and man more quickly than s.c. A, but also, that the peak of mobilization may be enhanced (6.4-fold at 160 uμg/kg IV vs. 5.2-fold for 240 μg/kg s.c.) and prolonged (5.7 fold at 160 μg/kg IV vs. 3.8 fold for 240 μg/kg s.c. at 6 h post-A) after IV A. IV A also induced: (i.) a more rapid and greater peak of CD19+ B cell mobilization (6-fold at 1 h and 6.7-fold at 4 h) than s.c. A (2.2-fold at 6 h), (ii.) a modest increase in CD4+ and CD8+ CD3+ T cell mobilization (3.2-fold vs. 1.1-fold for sc A at 6h) and (iii.) no significant changes in Treg, NK, CMV-specific CD8, and γδ T cells. To identify genes that are differentially expressed following G or A mobilization, we performed RNA profiling analyses using Affymatrix U133+2 arrays and RNA isolated from purified (>95%) CD34+ HSCs obtained from 5 individual normal donors mobilized sequentially with A and G. Of note, CXCR4, CCR9, ALCAM, ICAM, and CEECAM1 were expressed more abundantly in all A mobilized CD34+ cells while mucin, Integrin α 6, Integrin α 2b, and CEACAM1 were more abundantly expressed in all G-mobilized CD34+ cells.

Conclusions: IV A results in more rapid and prolonged mobilization of mouse HSC and human CD34+ cells compared to s.c. A. IV A was not associated with any adverse events in the 6 donors mobilized at the first two IV dose levels. The enhanced and more rapid mobilization of CD34+ cells by IV A may have significant applications for the optimal collection of peripheral blood HSC products.

Author notes

Disclosure:Honoraria Information: Dr. DiPersio received honoraria from AnorMed, Genzyme, and MGI Pharma.