Allograft Cell Content and GVHD Differ in Murine Recipients of AMD3100 Versus G-CSF Mobilized Peripheral Blood Stem Cells.

G-CSF is currently the preferred agent to mobilize peripheral blood stem cells (PBSC) for allogeneic hematopoietic cell transplantation. AMD3100, a selective antagonist of SDF-1, has recently proven to rapidly mobilize hematopoietic stem cells in both humans and mice. It is currently unknown whether GVHD will differ in recipients of T-cell replete allografts mobilized with AMD3100 versus G-CSF. Therefore, we investigated the effects of AMD3100 on GVHD in a murine model of PBSC transplantation in which Balb/c recipients received 15x10⁶ splenocytes from allogeneic MHC matched B10.d2 mice following 950cGy of irradiation. Splenocytes from donor mice were harvested six hours after a single subcutaneous injection of AMD3100 (100μg). Controls consisted of Balb/c recipients of splenocytes harvested after five daily subcutaneous injections of G-CSF (10μg) or saline. In addition, one Balb/c cohort received splenocytes mobilized with the combination of G-CSF and AMD3100. Significantly higher numbers of stem cells (KLS cells; cKit+, lineage-, sca-1+) were mobilized after AMD3100 compared to saline controls (mean=32,300±3,900 vs. 14,700±4,900; p=0.02). The absolute number of KLS cells was significantly lower after AMD3100 mobilization compared to G-CSF (mean=52,400±8,600; p=0.03). No difference in number of KLS cells was observed in mice mobilized with AMD3100 and G-CSF compared to G-CSF alone. Splenocytes from G-CSF mobilized B10.d2 donors contained a significantly (p<0.01) lower percentage of T cells (15.9±3.1%) than AMD3100 mobilized donors (20.3±3.5%). The incidence of skin GVHD was higher in Balb/c recipients of AMD3100 mobilized splenocytes (19/20) compared to G-CSF mobilized splenocytes (5/18; p<0.01), while recipients of donors mobilized with the combination of G-CSF and AMD3100 had a slightly higher incidence of skin GVHD (9/20, p<0.01) compared to G-CSF alone. Using a cumulative clinical GVHD scoring system (maximum 9 points), the severity of GVHD was higher in mice receiving AMD3100 compared to mice receiving G-CSF (day +45 mean score=1.8 vs. 0.4 respectively; p<0.01) or G-CSF + AMD3100 (mean score=0.8; p=0.03) mobilized splenocytes. When the T cell dose was adjusted to equal numbers in all transplant groups, the difference in GVHD between cohorts was less pronounced; 8/8 (100%) in the AMD3100 recipient group compared to 4/9 (44%; p=0.03) in the G-CSF recipient group developed skin GVHD. Th1/Th2 serum cytokine profiles following mobilization were similar in all donor groups. Compared to G-CSF, AMD3100, given alone or in combination with G-CSF, mobilized comparable numbers of CD4/CD25+ regulatory T cells with similar MLR suppressive effects. In contrast, the percentage of memory T cells (CD62L-) was significantly increased in mice mobilized with G-CSF (89.1±3.0%) compared to AMD3100 (43.9±1.3%), potentially accounting for the lower incidence of GVHD in recipients of G-CSF mobilized PBSC. This murine model provides the first insight into differences in GVHD that may occur when allogeneic transplantation is performed using T-cell replete PBSC allografts mobilized with AMD3100. Whether the higher incidence of GVHD observed in recipients of AMD3100 mobilized PBSC will enhance graft vs. tumor effects in tumor bearing Balb/c recipients is currently under investigation.