The role of placental-derived adherent stromal cell (PLX-PAD) in the treatment of critical limb ischemia.

BACKGROUND AIMS: Mesenchymal stromal cells (MSC) are spindle-shaped plastic-adherent cells isolated from bone marrow (BM), adipose tissue and other organs, including the placenta. Autologous BM-derived MSC have been studied in animals with experimentally induced critical limb ischemia (CLI) as a model of end-stage peripheral vascular disease. While demonstrating therapeutic benefit, the use of these cells is limited by the need to surgically extract BM and the fear of thrombosis secondary to the use of granulocyte-colony-stimulating factor (G-CSF) to mobilize the cells. METHODS: We studied the use of placental-derived adherent stromal cells (ASC) in a standard limb ischemia model of male Balb/c mice. These placental-derived cells, termed PLX-PAD, share the adherence and marker expression of BM-derived MSC but lack their differentiation potential. PLX-PAD are isolated from human placenta following a Caesarean section and cultured in a bioreactor, termed the PluriX System. The PluriX System provides a three-dimensional (3-D) microenvironment that enables the large-scale growth of these cells. PLX-PAD are stable adhesive cells that can be expanded in vitro without the loss of phenotype and without showing signs of karyotypic changes. RESULTS: The intramuscular (i.m.) administration of PLX-PAD in our model significantly improved blood flow (BF) (P=0.0008), increased capillary density (P=0.021), reduced oxidative stress (P=0.034) and reduced endothelial damage (P=0.004), while increasing limb function versus the administration of a phosphate-buffered saline (PBS) control vehicle in the affected limb. CONCLUSIONS: Allogeneic placental-derived ASC may provide an off-the-shelf supply of therapeutic cells that would need no histocompatible tissue matching and be potentially less expensive and considerably more convenient than BM or adipose-derived MSC.

Safety and biodistribution profile of placental-derived mesenchymal stromal cells (PLX-PAD) following intramuscular delivery.

The administration of mesenchymal stromal cells (MSCs) provides an exciting emerging therapeutic modality for the treatment of peripheral arterial disease, a condition that is associated with critical limb ischemia as its end stage. Placental-derived MSCs, termed PLX-PAD cells, are stable adhesive stromal cells isolated from full-term human placentae, cultured on carriers, and expanded in a bioreactor called the PluriX. These cells can be expanded in vitro without phenotypic or karyotypic changes. We studied the safety and biodistribution properties of PLX-PAD cells following intramuscular administration in NOD/SCID mice. No significant clinical signs, hematological and biochemical parameters, or major pathological changes were found in PLX-PAD-treated animals in comparison to vehicle controls. Several animals in the control and PLX-PAD-treated groups developed thymic malignant lymphoma, first seen after one month, as expected in this mouse strain. In addition, both groups developed spontaneous mesenteric vessel inflammation. Real-time quantitative polymerase chain reaction (RT-qPCR) demonstrated that distribution of PLX-PAD cells was confined to the injection site. Placental-derived MSCs remained in this site with gradual decrease in concentration during a three-month period. In view of these data, we conclude that the administration of PLX-PAD cells is not associated with any adverse effects in NOD/SCID mice.

Spontaneous aortitis in the Balb/c mouse.

We examined whether high incidence rates (18%-56%) of inflammation in the root of the aorta detected in a Balb/c mouse model for hind limb ischemia were related to the surgical procedure. Twenty mice underwent ligation of the femoral artery; incidences of aortic root inflammation were compared to those observed in controls. We used a multiple-section sampling method to increase the sensitivity of the diagnostic rates. Although a cumulative incidence of 12.5% was found, no difference was seen in the overall incidence rates between the control and the surgically treated groups. Evaluation of blood levels of inflammatory cytokines showed that ligation of the femoral artery produced higher levels of interleukin-6 in the surgically transected group of mice. The development of spontaneous arteritis in this strain must be considered in future studies.

Placental-derived and expanded mesenchymal stromal cells (PLX-I) to enhance the engraftment of hematopoietic stem cells derived from umbilical cord blood.

For the past 40 years, bone marrow transplantation (BMT) has become standard therapy to re-establish marrow function in patients with damaged or defective bone marrow. A human leukocyte antigen-matched sibling is the donor of choice for patients needing transplantation of allogeneic hematopoietic stem cells (HSCs). As most patients do not have an acceptable matched, related donor, the National Marrow Donor Program has been established to match volunteer bone marrow donors with potential recipients who require BMT. Although transplantation of HSCs from an unrelated donor can be an effective therapy for a variety of malignant and non-malignant diseases, it remains complicated because of treatment-related morbidity and mortality, which has led to the investigation of alternative sources of HSCs such as umbilical cord blood (UCB). This review highlights the advantages and disadvantages of UCB and recent developments that address its disadvantages. This includes the use of a placenta-expanded mesenchymal stromal cell product (PLX-I) being developed by Pluristem Therapeutics, Inc. and our opinion about the potential of this product.

Structure--function studies of the recombinant protein bioemulsifier AlnA.

Acinetobacter radioresistens KA53 produces an extracellular bioemulsifier, referred to as alasan. The surface active component of alasan is a 35.77 kDa protein AlnA. Although AlnA and the Escherichia coli outer membrane protein A (OmpA) have a high amino acid sequence homology, E. coli OmpA has no emulsifying activity. Comparison of the amino acid sequences of AlnA and E. coli OmpA revealed four hydrophobic regions in AlnA that were absent in E. coli OmpA. Deletions and substitutions (with the homologous OmpA sequence) were constructed in each of the four hydrophobic regions of AlnA by site-directed polymerase chain reaction (PCR) mutagenesis, using the overlap PCR method. Analysis of the emulsifying activities of the mutated AlnA molecules demonstrated that all four hydrophobic regions were necessary for emulsifying activity. However, most of the inactive mutated proteins still adhered avidly to hexadecane. These findings indicate that in addition to binding to hydrocarbons, the protein emulsifier must form a specific structure on the surface of the hydrocarbon that prevents coalescence of oil droplets. This is the first structure-function study of a protein bioemulsifer.

The active component of the bioemulsifier alasan from Acinetobacter radioresistens KA53 is an OmpA-like protein.

The bioemulsifier of Acinetobacter radioresistens KA53, referred to as alasan, is a high-molecular-weight complex of polysaccharide and protein. Recently, one of the alasan proteins, with an apparent molecular mass of 45 kDa, was purified and shown to constitute most of the emulsifying activity. The N-terminal sequence of the 45-kDa protein showed high homology to an OmpA-like protein from Acinetobacter spp. In the research described here the gene coding for the 45-kDa protein was cloned, sequenced, and expressed in Escherichia coli. Recombinant protein AlnA (35.77 kDa without the leader sequence) had an amino acid sequence homologous to that of E. coli OmpA and contained 70% of the specific (hydrocarbon-in-water) emulsifying activity of the native 45-kDa protein and 2.4 times that of the alasan complex. In addition to their emulsifying activity, both the native 45-kDa protein and the recombinant AlnA were highly effective in solubilizing phenanthrene, ca. 80 microg per mg of protein, corresponding to 15 to 19 molecules of phenanthrene per molecule of protein. E. coli OmpA had no significant emulsifying or phenanthrene-solubilizing activity. The production of a recombinant surface-active protein (emulsification and solubilization of hydrocarbons in water) from a defined gene makes possible for the first time structure-function studies of a bioemulsan.