Comparison Of Autologous Microparticles and Fucosyltransferase-7 For Adhesion Improvement Of Hematopoietic Stem Cells To Bone Marrow Endothelial Cells In a Microfluidic Flow Chamber

The improvement of graft function and time to engraftment might help to reduce infection-related mortality in stem cell transplantation (SCT). While the concept of stem cells fucosylation for accelerated engraftment has already reached clinical study phase (for cord blood transplantation; NCT01471067), own previous work has shown an association between engraftment time and circulating microparticles bearing P-Selectin and P-Selectin glycoprotein ligand 1 (PSGL-1). PSGL-1 contains the sialyl Lewis x (CD15s) antigen that requires fucosylation for optimal binding of P- and E-Selectin on endothelial cells. We therefore hypothesized that addition of microparticles (MP) might enhance adhesion of human stem cells (HSC) to bone marrow endothelial cells and that MP might have synergistic effects in combination with stem cell fucosylation. HSC were obtained from apheresis products of allogeneic donors, purified by Ficoll and magnetic bead separation for CD34, stained with calcein AM and perfused through an automated microfluidic flow chamber (Bioflux 200, Fluxionbio, USA) covered with a confluent layer of an immortalized human bone marrow endothelial cell line (HBMEC). Photos (and videos) were taken using a fluorescence microscope at start, 5 min and 10 min and analyzed for adherent HSC across the whole chamber (about 1.5 sqmm) using ImageJ software. Autologous MP were generated by addition of calcimycin to apheresis and isolation of MP by centrifugation. For control experiments, one part of the MP solution was passed through a 0,2µm-filter to remove MP. MP concentration (mean: 1362/µl) was assessed by detection of Annexin V binding in flow cytometry, using TrucountBeads® for quantification. Fucosylation was performed by 1h incubation of isolated CD34+ stem cells with GDP-fucose and fucosyltransferase 7 (FUT7). Successful fucosylation was controlled by CD15s staining of HSC in flow cytometry. Results of seven experiments (in duplicate) demonstrated the highest number of adherent HSC in the MPpositiv/FUT7negativ preparation (median: 32 HSC/sqmm; range: 15-78), followed by MPpositiv/FUT7positiv (30 HSC/sqmm; range: 16-38), MPnegativ/FUT7positiv (median: 25/sqmm; range: 11-27) and MPnegativ/FUT7negativ (20 HSC/sqmm; range: 0-22). Comparison of the MPpositiv/FUT7negativ and MPnegativ/FUT7negativ as well as the MPpositiv/FUT7positiv and MPpositiv/FUT7negativ preparations showed statistically significant differences in Wilcoxon rank test (p<.05) while comparison of MPpositiv/FUT7positiv vs. MPnegativ/FUT7positiv and MPnegativ/FUT7positiv vs. MPnegativ/FUT7negativ preparations did not. In summary, these results demonstrate that MP can improve HSC adhesion to bone marrow endothelial cells similar to fucosylation. The effect of fucosylation on HSC adhesion appears to be mediated by MP. However, there is not a synergistic effect between MP and fucosylation.