Regulatory T Cells of G-CSF Mobilized Stem Cell Donors Qualify for Clinical Applications,

Abstract 4055

Recent clinical studies demonstrate the high potency of human regulatory T cells (Tregs) to control graft-versus-host disease following hematopoietic stem cell transplantation (SCT). Isolation of Tregs after recombinant G-CSF induced mobilization of stem cells would simplify the design of clinical trials in allogeneic SCT. However, there is growing evidence that G-CSF also exerts profound immune modulatory effects in the adaptive immune system. Therefore, we analyzed Tregs isolated by FACS based cell sorting from stem cell donors before (n=8) and after (n=13) G-CSF administration regarding their phenotype, stability, functional and expansion properties. Absolute CD4+ T cell (3.2 fold increase of mean after G-CSF; p<0.05) and CD4+CD25hi Treg cell numbers (4.1 fold increase of mean after G-CSF; p<0.01) were significantly increased after G-CSF administration. Analysis of the Foxp3 TSDR demethylation level displays a stable Foxp3 phenotype of G-CSF encountered Tregs (mean value 97.1% vs. 95.0 % after G-CSF administration). Moreover, the CD4+CD25hi Tregs of G-CSF treated SC donors suppress the proliferation of effector T cells with no significant differences to Tregs isolated from healthy donors before G-CSF treatment (mean values 42.1% vs. 49.9% after G-CSF administration at a Treg/ T effector cell ratio of 1:1). In vitro expansion of Tregs isolated after G-CSF application with anti-CD3 and anti-CD28 dynabeads in the presence of interleukin-2 led to comparable cell numbers as for the stimulation of control Treg cells. However, differences could be detected for the thymic derived marker molecule CD31 and those associated with activation (LAP, CD69, CD62L) and migration (CxCR3) as detected by FACS analysis. Our results show no significant differences regarding suppressive function and stability of Tregs isolated from stem cell donors before and after G-CSF administration. These data support the application of G-CSF mobilized Tregs for clinical trials which in turn opens up new possibilities for the adoptive transfer of Tregs in HSCT.