Prenatally harvested cells for cardiovascular tissue engineering: fabrication of autologous implants prior to birth.

Using the principal of tissue engineering, several groups have demonstrated the feasibility of creating heart valves, blood vessels, and myocardial structures using autologous cells and biodegradable scaffold materials. In the current cardiovascular clinical scenario, the main medical need for a tissue engineering solution is in the field of pediatric applications treating congenital heart disease. In these young patients, the introduction of autologous viable and growing replacement structures, such as tissue engineered heart valves and vessels, would substantially reduce today's severe therapeutic limitations, which are mainly due to the need for repeat reoperations to adapt the current artificial prostheses to somatic growth. Based on high resolution imaging techniques, an increasing number of defects are diagnosed already prior to birth around week 20. For interventions, cells should be obtained already during pregnancy to provide tissue engineered implants either at birth or even prenatally. In our recent studies human fetal mesenchymal stem cells were isolated from routinely sampled prenatal amniotic fluid or chorionic villus specimens and expanded in vitro. Fresh and cryopreserved samples were used. After phenotyping and genotyping, cells were seeded onto synthetic biodegradable scaffolds and conditioned in a bioreactor. Leaflets were endothelialized with either amniotic fluid- or umbilical cord blood-derived endothelial progenitor cells and conditioned. Resulting tissues were analyzed by histology, immunohistochemistry, biochemistry (amounts of extracellular matrix, DNA), mechanical testing, and scanning electron microscopy (SEM) and were compared with native neonatal heart valve leaflets. Genotyping confirmed their fetal origin, and fresh versus cryopreserved cells showed comparable myofibroblast-like phenotypes. Neo-tissues exhibited organization, cell phenotypes, extracellular matrix production, and DNA content comparable to their native counterparts. Leaflet surfaces were covered with functional endothelia. SEM showed morphologically cellular distribution throughout the polymer and smooth surfaces. Mechanical profiles approximated those of native heart valves. These in vitro studies demonstrated the principal feasibility of using various human cell types isolated from fetal sources for cardiovascular tissue engineering. Umbilical cord blood-, amniotic fluid- and chorionic villi-derived cells have shown promising potential for the clinical realization of this congenital tissue engineering approach. Based on these results, future research must aim at further investigation as well as preclinical evaluation of prenatally harvested stem- or progenitor cells with regard to their potential for clinical use.

Clodronate-liposome-mediated depletion of tumour-associated macrophages: a new and highly effective antiangiogenic therapy approach.

Tumour-associated macrophages, TAMs, play a pivotal role in tumour growth and metastasis by promoting tumour angiogenesis. Treatment with clodronate encapsulated in liposomes (clodrolip) efficiently depleted these phagocytic cells in the murine F9 teratocarcinoma and human A673 rhabdomyosarcoma mouse tumour models resulting in significant inhibition of tumour growth ranging from 75 to >92%, depending on therapy and schedule. Tumour inhibition was accompanied by a drastic reduction in blood vessel density in the tumour tissue. Vascular endothelial growth factor (VEGF) is one of the major inducers of tumour angiogenesis and is also required for macrophage recruitment. The strongest effects were observed with the combination therapy of clodrolip and a VEGF-neutralising antibody, whereas free clodronate was not significantly active. Immunohistologic evaluation of the tumours showed significant depletion of F4/80+ and MOMA-1+ and a less pronounced depletion of CD11b+ TAMs. Blood vessel staining (CD31) and quantification of the vessels as well as TAMs and tumour-associated dendritic cells (TADCs) in the A673 model showed reduction rates of 85 to >94%, even 9 days after the end of therapy. In addition, CD11c+ TADCs, which have been shown to potentially differentiate into endothelial-like cells upon stimulation by tumour released growth and differentiation factors, were similarly reduced by clodrolip or antibody treatment. These results validate clodrolip therapy in combination with angiogenesis inhibitors as a promising novel strategy for an indirect cancer therapy aimed at the haematopoietic precursor cells that stimulate tumour growth and dissemination and as a tool to study the role of macrophages and dendritic cells in tumorigenesis.