Experimental transplantation of human umbilical cord blood (hUCB) mononuclear cells (MNCs) in rodent stroke models revealed the therapeutic potential of these cells. However, effective cells within the heterogeneous MNC population and their modes of action are still under discussion. MNCs and MNC fractions enriched (CD34(+)) or depleted (CD34(-)) for CD34-expressing stem/progenitor cells were isolated from hUCB. Cells were transplanted intravenously following middle cerebral artery occlusion in spontaneously hypertensive rats and directly or indirectly cocultivated with hippocampal slices previously subjected to oxygen and glucose deprivation. Application of saline solution or a human T-cell line served as controls. In vivo, MNCs, CD34(+) and CD34(-) cells reduced neurofunctional deficits and diminished lesion volume as determined by magnetic resonance imaging. MNCs were superior to other fractions. However, human cells could not be identified in brain tissue 29 days after stroke induction. Following direct application on postischemic hippocampal slices, MNCs reduced neural damage throughout a 3-day observation period. CD34(+) cells provided transient protection for 2 days. The CD34(-) fraction, in contrast to in vivo results, failed to reduce neural damage. Direct cocultivation of MNCs was superior to indirect cocultivation of equal cell numbers. Indirect application of up to 10-fold MNC concentrations enhanced neuroprotection to a level comparable to direct cocultivation. After direct application, MNCs migrated into the slices. Flow cytometric analysis of migrated cells revealed that the CD34(+) cells within MNCs were preferably attracted by damaged hippocampal tissue. Our study suggests that MNCs provide the most prominent neuroprotective effect, with CD34(+) cells seeming to be particularly involved in the protective action of MNCs. CD34(+) cells preferentially home to neural tissue in vitro, but are not superior concerning the overall effect, implying that there is another, still undiscovered, protective cell population. Furthermore, MNCs did not survive in the ischemic brain for longer periods without immunosuppression.

Background: One of the most promising options for treatment of stroke using adult stem cells are human umbilical cord blood (HUCB) cells that were already approved for therapeutic efficacy in vivo. However, complexity of animal models has thus far limited the understanding of beneficial cellular mechanisms. To address the influence of HUCB cells on neuronal tissue after stroke we established and employed a human in vitro model of neuronal hypoxia using fully differentiated vulnerable SH-SY5Y cells. These cells were incubated under an oxygen-reduced atmosphere (O 2 < 1%) for 48 hours. Subsequently, HUCB mononuclear cells (MNC) were added to post-hypoxic neuronal cultures. These cultures were characterized regarding to the development of apoptosis and necrosis over three days. Based on this we investigated the therapeutic influence of HUCB MNC on the progression of apoptotic cell death. The impact of HUCB cells and hypoxia on secretion of neuroprotective and inflammatory cytokines, chemokines and expression of adhesion molecules was proved.

Magnetic resonance imaging (MRI) of magnetically labeled stem cells has become a valuable tool in the understanding and evaluation of experimental stem cell-based therapies of degenerative central nervous system disorders. This comprehensive study assesses the impact of magnetic labeling of both human and rodent stem cell-containing populations on multiple biologic parameters as maintenance of stemness and oxidative stress levels. Cells were efficiently magnetically labeled with very small superparamagnetic iron oxide particles. Only under the condition of tailored labeling strategies can the impact of magnetic labeling on vitality, proliferation, pluripotency, and oxidative stress levels be minimized. In a rat model of Parkinson disease, magnetically labeled mouse embryonic stem cells were tracked by high-field MRI for 6 months. Significant interindividual differences concerning the spatial distribution of cells became evident. Histologically, transplanted green fluorescent protein-positive iron oxide-labeled cells were clearly identified. No significant increase in oxidative stress levels at the implantation site and no secondary uptake of magnetic label by host phagocytotic cells were observed. Our study strongly suggests that molecular MRI approaches must be carefully tailored to the respective cell population to exert minimal physiologic impact, ensuring the feasibility of this imaging approach for clinical applications.