Injectable living marrow stromal cell-based autologous tissue engineered heart valves: first experiences with a one-step intervention in primates.

AIMS: A living heart valve with regeneration capacity based on autologous cells and minimally invasive implantation technology would represent a substantial improvement upon contemporary heart valve prostheses. This study investigates the feasibility of injectable, marrow stromal cell-based, autologous, living tissue engineered heart valves (TEHV) generated and implanted in a one-step intervention in non-human primates. METHODS AND RESULTS: Trileaflet heart valves were fabricated from non-woven biodegradable synthetic composite scaffolds and integrated into self-expanding nitinol stents. During the same intervention autologous bone marrow-derived mononuclear cells were harvested, seeded onto the scaffold matrix, and implanted transapically as pulmonary valve replacements into non-human primates (n = 6). The transapical implantations were successful in all animals and the overall procedure time from cell harvest to TEHV implantation was 118 ± 17 min. In vivo functionality assessed by echocardiography revealed preserved valvular structures and adequate functionality up to 4 weeks post implantation. Substantial cellular remodelling and in-growth into the scaffold materials resulted in layered, endothelialized tissues as visualized by histology and immunohistochemistry. Biomechanical analysis showed non-linear stress-strain curves of the leaflets, indicating replacement of the initial biodegradable matrix by living tissue. CONCLUSION: Here, we provide a novel concept demonstrating that heart valve tissue engineering based on a minimally invasive technique for both cell harvest and valve delivery as a one-step intervention is feasible in non-human primates. This innovative approach may overcome the limitations of contemporary surgical and interventional bioprosthetic heart valve prostheses.

Ang-2 and PDGF-BB cooperatively stimulate human peripheral blood monocyte fibrinolysis.

Angiopoietin-2 (Ang-2) is a growth factor, which was identified originally as playing a critical role in vessel remodeling during angiogenesis. More recent evidence has indicated additional involvement in vascular homeostatic responses such as coagulation and inflammation, which are central to wound healing. We therefore determined whether a relationship existed between Ang-2 and monocytes, one of the initial cell types to be recruited to a wound, in the context of fibrin clot invasion. Ang-2 significantly increased monocyte invasion of fibrin in the presence of serum. In the absence of serum, it required a combination of Ang-2 and platelet-derived growth factor BB (PDGF-BB) to increase invasion by threefold. Furthermore, it was shown that the heightened invasion was dependent on serine proteases and matrix metalloproteinases (MMPs) and that the combination of Ang-2 and PDGF-BB increased urokinase plasminogen-activator receptor expression, as well as MMP-9 and membrane type 1 MMP expression. These data give further credence to the concept of Ang-2 as a key regulator of several essential phases of wound healing.

Cell specific ingrowth hydrogels.

Extracellular mimetic hydrogels formed from peptide crosslinkers and polyethylene glycol monomers permit cell-controlled invasion. The use of matrix metalloproteinase specific peptides might further allow for selective control of different cell-type invasion. In this study, the invasion of fibroblasts and vascular smooth muscle cells (VSMC) into hydrogels polymerised with either a peptide generally permissive for matrix metalloproteinase (MMP) degradation or peptides preferentially cleaved by MMP-14 or MMP-9 enzymes were compared. The two cell-types invaded the MMP permissive hydrogel equally. However, invasion of VSMC into MMP-14 selective peptide crosslinked hydrogels was diametrically opposite in nature to that of fibroblasts whereby VSMC showed a two-fold increase into these hydrogels relative to that observed in permissive hydrogels whilst fibroblasts had a relative two-fold decrease (p < 0.01). These findings are suggestive that invasion and growth of different cell-types in engineered synthetic extracellular matrix mimics may be controlled selectively by the choice of protease specific peptide crosslinker and this could have general utility in tissue regenerative and engineering approaches.

Off-the-shelf human decellularized tissue-engineered heart valves in a non-human primate model.

Heart valve tissue engineering based on decellularized xenogenic or allogenic starter matrices has shown promising first clinical results. However, the availability of healthy homologous donor valves is limited and xenogenic materials are associated with infectious and immunologic risks. To address such limitations, biodegradable synthetic materials have been successfully used for the creation of living autologous tissue-engineered heart valves (TEHVs) in vitro. Since these classical tissue engineering technologies necessitate substantial infrastructure and logistics, we recently introduced decellularized TEHVs (dTEHVs), based on biodegradable synthetic materials and vascular-derived cells, and successfully created a potential off-the-shelf starter matrix for guided tissue regeneration. Here, we investigate the host repopulation capacity of such dTEHVs in a non-human primate model with up to 8 weeks follow-up. After minimally invasive delivery into the orthotopic pulmonary position, dTEHVs revealed mobile and thin leaflets after 8 weeks of follow-up. Furthermore, mild-moderate valvular insufficiency and relative leaflet shortening were detected. However, in comparison to the decellularized human native heart valve control - representing currently used homografts - dTEHVs showed remarkable rapid cellular repopulation. Given this substantial in situ remodeling capacity, these results suggest that human cell-derived bioengineered decellularized materials represent a promising and clinically relevant starter matrix for heart valve tissue engineering. These biomaterials may ultimately overcome the limitations of currently used valve replacements by providing homologous, non-immunogenic, off-the-shelf replacement constructs.