Deposition of collagen type I onto skeletal endothelium reveals a new role for blood vessels in regulating bone morphology.

Recently, blood vessels have been implicated in the morphogenesis of various organs. The vasculature is also known to be essential for endochondral bone development, yet the underlying mechanism has remained elusive. We show that a unique composition of blood vessels facilitates the role of the endothelium in bone mineralization and morphogenesis. Immunostaining and electron microscopy showed that the endothelium in developing bones lacks basement membrane, which normally isolates the blood vessel from its surroundings. Further analysis revealed the presence of collagen type I on the endothelial wall of these vessels. Because collagen type I is the main component of the osteoid, we hypothesized that the bone vasculature guides the formation of the collagenous template and consequently of the mature bone. Indeed, some of the bone vessels were found to undergo mineralization. Moreover, the vascular pattern at each embryonic stage prefigured the mineral distribution pattern observed one day later. Finally, perturbation of vascular patterning by overexpressing Vegf in osteoblasts resulted in abnormal bone morphology, supporting a role for blood vessels in bone morphogenesis. These data reveal the unique composition of the endothelium in developing bones and indicate that vascular patterning plays a role in determining bone shape by forming a template for deposition of bone matrix.

Substrate-bound CCL21 and ICAM1 combined with soluble IL-6 collectively augment the expansion of antigen-specific murine CD4+ T cells.

Immune processes within the complex microenvironment of the lymph node involve multiple intercellular, cell-matrix, and paracrine interactions, resulting in the expansion of antigen-specific T cells. Inspired by the lymph node microenvironment, we aimed to develop an ex vivo "synthetic immune niche" (SIN), which could effectively stimulate the proliferation of antigen-activated CD4+ T cells. This engineered SIN consisted of surfaces coated with the chemokine C-C motif ligand 21 (CCL21) and with the intercellular adhesion molecule 1 (ICAM1), coupled with the soluble cytokine interleukin 6 (IL-6) added to the culture medium. When activated by ovalbumin-loaded dendritic cells, OT-II T cells growing on regular uncoated culture plates form nonadherent, dynamic clusters around the dendritic cells. We found that functionalization of the plate surface with CCL21 and ICAM1 and the addition of IL-6 to the medium dramatically increases T-cell proliferation and transforms the culture topology from that of suspended 3-dimensional cell clusters into a firm, substrate-attached monolayer of cells. Our findings demonstrate that the components of this SIN collectively modulate T-cell interactions and augment both the proliferation and survival of T cells in an antigen-specific manner, potentially serving as a powerful approach for expanding immunotherapeutic T cells.