Background and Purpose-Intravenously delivered human umbilical cord blood cells (HUCBC) have been previouslyshown to improve functional recovery of stroked rats. To extend these findings, we examined the behavioral recovery and stroke infarct volume in the presence of increasing doses of HUCBC after permanent middle cerebral artery occlusion (MCAO). Methods-Rats were subjected to MCAO and allowed to recover for 24 hours before intravenous infusion of 10 4 up to 3 to 5ϫ10 7 HUCBC. Behavioral tests (spontaneous activity, step test, elevated body swing test) were performed 1 week before MCAO and at 2 and 4 weeks after HUCBC infusion. On completion of behavioral testing, animals were euthanized and brain infarct volumes quantified. HUCBC were identified by immunofluorescence for human nuclei and by polymerase chain reaction (PCR) using primers specific for human glycerol 3-phosphate dehydrogenase. Results-At 4 weeks after infusion, there was a significant recovery in behavioral performance when 10 6 or more HUCBC were delivered (pϭ0.001 to pϭ0.05). Infarct volume measurements revealed an inverse relationship between HUCBC dose and damage volume, which reached significance at the higher HUCBC doses (10 7 cells, pϽ0.01; 3 to 5ϫ10 7 cells, pϽ0.05). Moreover, HUCBC were localized by immunohistochemistry and PCR analysis only in the injured brain hemisphere and spleen. Conclusions-These results extend previous observations of HUCBC infusion in the MCAO rat stroke model by demonstrating a dose relationship between HUCBC, behavioral improvement, and neuronal sparing.

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