In Vivo Recruitment of Hematopoietic Cells Using Stromal Cell-Derived Factor 1 Alpha-Loaded Heparinized Three-Dimensional Collagen Scaffolds

Implantable three-dimensional (3D) constructs to engineer tissue have great therapeutic potential in regenerative medicine and immunotherapy. However, autonomous recruitment of cells into the engineered scaffold in vivo is hampered by lack of attracting scaffolds. As a first step to engineering immune tissue, 3D collagen scaffolds were investigated for their ability to enhance in vivo recruitment and growth of various hematopoietic cells. Scaffolds containing immobilized heparin to trap the stem cell chemo-attractant stromal cell-derived factor 1 alpha (SDF1 alpha) were implanted subcutaneously into C57B16 mice, and influx of cells was monitored using immunohistochemistry. Five weeks post-implantation, heparinized scaffolds were always populated by cells, but incorporating SDF1 alpha considerably stimulated recruitment of cells. SDF1 alpha could not exert this effect when the formation of a SDF1 alpha gradient was abrogated. Scaffolds were mainly populated by CD11b+ and CD11c+ myeloid cells and fibroblasts. One week after implantation, scaffolds harbored only low numbers of cells. Apparently, not all CXCR4-expressing cells, like large numbers of granulocytes, migrate into the scaffold, but retransplantation of a 1-week-old scaffold from a CD45.2(+) into a CD45.1(+) mouse yielded a scaffold harboring mainly CD45.2(+) cells after 5 weeks. These data confirm that only a few progenitor cells are recruited early after implantation. These cells then proliferate and differentiate along different lineages and determine the outcome after 5 weeks.