Pro-angiogenic effect of RANTES-loaded polysaccharide-based microparticles for a mouse ischemia therapy.

Peripheral arterial disease results from the chronic obstruction of arteries leading to critical hindlimb ischemia. The aim was to develop a new therapeutic strategy of revascularization by using biodegradable and biocompatible polysaccharides-based microparticles (MP) to treat the mouse hindlimb ischemia. For this purpose, we deliver the pro-angiogenic chemokine Regulated upon Activation, Normal T-cell Expressed and Secreted (RANTES)/CCL5 in the mouse ischemic hindlimb, in solution or incorporated into polysaccharide-based microparticles. We demonstrate that RANTES-loaded microparticles improve the clinical score, induce the revascularization and the muscle regeneration in injured mice limb. To decipher the mechanisms underlying RANTES effects in vivo, we demonstrate that RANTES increases the spreading, the migration of human endothelial progenitor cells (EPC) and the formation of vascular network. The main receptors of RANTES i.e. CCR5, syndecan-4 and CD44 expressed at endothelial progenitor cell surface are involved in RANTES-induced in vitro biological effects on EPC. By using two RANTES mutants, [E66A]-RANTES with impaired ability to oligomerize, and [44AANA47]-RANTES mutated in the main RANTES-glycosaminoglycan binding site, we demonstrate that both chemokine oligomerization and binding site to glycosaminoglycans are essential for RANTES-induced angiogenesis in vitro. Herein we improved the muscle regeneration and revascularization after RANTES-loaded MP local injection in mice hindlimb ischemia.

18F-FDG labelling of hematopoietic stem cells: Dynamic study of bone marrow homing by PET-CT imaging and impact on cell functionality.

PURPOSE OF THE STUDY: After transplantation, cord blood (CB) hematopoietic stem and progenitor cells (HSPCs) are able to home to the bone marrow niche and to reconstitute the hematopoietic system. PET-CT imaging may be a useful method to monitor this parameter in different conditions. The aim of our study was to set up an efficient method for HSPC radiolabelling with [18F] fluorodeoxyglucose (18F-FDG) and to follow early HSPC homing through PET-CT in mice. MATERIALS AND METHODS: Purified CB HSPCs were radiolabelled with 18F-FDG at 37° C with various conditions of cell concentration, incubation time and radioactivity concentration in order to define the in vitro condition that allows both sufficient 18F-FDG uptake to get high quality PET imaging, and preservation of HSPC viability and functional properties during 3h after radiolabelling. Then, 24h after 2.25Gy irradiation, eight NOD-scid/γc-/- mice were injected with 18F-FDG-labelled HSPCs, the biodistribution of which was followed using micro-PET-CT. RESULTS: The optimal incubation time was 45min with a stability of 48.3%±12.8% after 180min. The radio-uptake rate we obtained was 7.2%±1.7% with an activity of 5.6±2.1 MBq. Three hours after radiolabelling, viability was 96.7%±3.4%. Fifteen hours after radiolabelling, cell viability was 64.0%±2.3%, migration ability diminished from 51.0%±23.6% to 12.0%±9.1%, clonogenic capacity was null, and long-term engraftment in NSG mice also decreased compared to unlabelled cells. Micro-PET-CT experiments showed an accumulation of radiolabelled HSPCs for 2.5h after injection in the bone marrow and a slight elution of 18F-FDG. CONCLUSION: The activity of the obtained 18F-FDG-labelled HSPCs was sufficient to perform the micro-PET-CT imaging. Although the radiolabelling had a significant toxicity on HSPCs 15h after labelling, this technique allowed monitoring the beginning of HSPC homing into the bone marrow.

Stem cells for the treatment of heart failure.

Stem cell-based therapy is currently tested in several trials of chronic heart failure. The main question is to determine how its implementation could be extended to standard clinical practice. To answer this question, it is helpful to capitalize on the three main lessons drawn from the accumulated experience, both in the laboratory and in the clinics. Regarding the cell type, the best outcomes seem to be achieved by cells the phenotype of which closely matches that of the target tissue. This argues in favor of the use of cardiac-committed cells among which the pluripotent stem cell-derived cardiac progeny is particularly attractive. Regarding the mechanism of action, there has been a major paradigm shift whereby cells are no longer expected to structurally integrate within the recipient myocardium but rather to release biomolecules that foster endogenous repair processes. This implies to focus on early cell retention, rather than on sustained cell survival, so that the cells reside in the target tissue long enough and in sufficient amounts to deliver the factors underpinning their action. Biomaterials are here critical adjuncts to optimize this residency time. Furthermore, the paracrine hypothesis gives more flexibility for using allogeneic cells in that targeting an only transient engraftment requires to delay, and no longer to avoid, rejection, which, in turn, should simplify immunomodulation regimens. Regarding manufacturing, a broad dissemination of cardiac cell therapy requires the development of automated systems allowing to yield highly reproducible cell products. This further emphasizes the interest of allogeneic cells because of their suitability for industrially-relevant and cost-effective scale-up and quality control procedures. At the end, definite confirmation that the effects of cells can be recapitulated by the factors they secrete could lead to acellular therapies whereby factors alone (possibly clustered in extracellular vesicles) would be delivered to the patient. The production process of these cell-derived biologics would then be closer to that of a pharmaceutical compound, which could streamline the manufacturing and regulatory paths and thereby facilitate an expended clinical use.

Esophageal tissue engineering: Current status and perspectives.

Tissue engineering, which consists of the combination and in vivo implantation of elements required for tissue remodeling toward a specific organ phenotype, could be an alternative for classical techniques of esophageal replacement. The current hybrid approach entails creation of an esophageal substitute composed of an acellular matrix and autologous epithelial and muscle cells provides the most successful results. Current research is based on the use of mesenchymal stem cells, whose potential for differentiation and proangioogenic, immune-modulator and anti-inflammatory properties are important assets. In the near future, esophageal substitutes could be constructed from acellular "intelligent matrices" that contain the molecules necessary for tissue regeneration; this should allow circumvention of the implantation step and still obtain standardized in vivo biological responses. At present, tissue engineering applications to esophageal replacement are limited to enlargement plasties with absorbable, non-cellular matrices. Nevertheless, the application of existing clinical techniques for replacement of other organs by tissue engineering in combination with a multiplication of translational research protocols for esophageal replacement in large animals should soon pave the way for health agencies to authorize clinical trials.

Cord blood-circulating endothelial progenitors for treatment of vascular diseases.

Adult peripheral blood (PB) endothelial progenitor cells (EPC) are produced in the bone marrow and are able to integrate vascular structures in sites of neoangiogenesis. EPCs thus represent a potential therapeutic tool for ischaemic diseases. However, use of autologous EPCs in cell therapy is limited by their rarity in adult PB. Cord blood (CB) contains more EPCs than PB, and they are functional after expansion. They form primary colonies that give rise to secondary colonies, each yielding more than 10(7) cells after few passages. The number of endothelial cells obtained from one unit of CB is compatible with potential clinical application. EPC colonies can be securely produced, expanded and cryopreserved in close culture devices and endothelial cells produced in these conditions are functional as shown in different in vitro and in vivo assays. As CB EPC-derived endothelial cells would be allogeneic to patients, it would be of interest to prepare them from ready-existing CB banks. We show that not all frozen CB units from a CB bank are able to generate EPC colonies in culture, and when they do so, number of colonies is lower than that obtained with fresh CB units. However, endothelial cells derived from frozen CB have the same phenotypical and functional properties than those derived from fresh CB. This indicates that CB cryopreservation should be improved to preserve integrity of stem cells other than haematopoietic ones. Feasibility of using CB for clinical applications will be validated in porcine models of ischaemia.

Microbial contamination of BM products before and after processing: a report of incidence and immediate adverse events in 257 grafts.

BACKGROUND: The incidence and potential clinical consequences of bacterial contamination of autologous and allogeneic BM products remains open to question. We report our experience of bacterial contamination of BM grafts and adverse events that occurred after transplantation. METHODS: From January 2003 to February 2006, 257 BM harvests were processed and infused at our institution. Analysis of microbial contamination incidence before and after processing, sensitivity spectra of isolated bacteria and adverse events after graft infusion were analyzed. RESULTS: Nineteen of 257 BM (7.4%) were contaminated. Coagulase-negative Staphylococcus (n=9) and Propionibacterium acnes (n=6) were the most frequently isolated microorganisms. Two of nine coagulase-negative staphylococci were found to be resistant to erythromycin and two of six P. acnes to fosfomycin and gentamycin. The frequency and severity of immediate adverse events reported in patients receiving a contaminated graft were similar to those observed in patients receiving a non-contaminated product. No major adverse sequelae occurred after infusion of contaminated grafts. Finally, none of the patients transplanted with a contaminated graft developed bacteriemia that could have been related to the isolated microorganism. DISCUSSION: Microbial contamination of BM progenitor cell grafts does not induce severe clinical complications or infectious diseases after infusion. The vast majority of isolated pathogens were skin contaminants.

Recovery, viability and clinical toxicity of thawed and washed haematopoietic progenitor cells: analysis of 952 autologous peripheral blood stem cell transplantations.

Cryopreservation and thawing of haematopoietic stem cells are associated with cell loss and infusion-related toxicities. We analysed viability, total nucleated cell (TNC) and CD34+ cell recovery, and infusion-related toxicities of 952 thawed and washed products. Mean TNC and CD34+ viable cells recoveries were 55.9+/-18.6 and 98.0+/-36.5%, respectively. Mean cell viability was 68.25+/-18.9%. TNC recovery was correlated with viability but independent of the initial nucleated cell concentration. No difference in TNC recovery or viability was observed according to underlying diseases, except for myeloma, for which these variables were significantly lower (P<0.05). CD34+ cell recovery was not correlated with viability or CD34+ initial count and was similar for all diseases. Cryostorage duration was not associated with cell loss. Immediate adverse events occurred in 169 patients (19%) and were moderate (grade I or II) for the majority of patients. Clinical toxicity was associated with a higher infused cell number and the presence of clumps in infused bags. The washing procedure of cell products lead to a low rate of adverse events, but patients transplanted with high cell numbers or bags in which clumps were identified are predisposed to such complications.