CXCR4⁺CD45^- BMMNC subpopulation is superior to unfractionated BMMNCs for protection after ischemic stroke in mice

Cell-based therapy is considered to be a promising therapeutic strategy for stroke treatment. Although unfractionated bone marrow mononuclear cells (BMMNCs) have been tried in both preclinical and clinical trials, the effective subpopulations need to be identified. In this study, we used fluorescence-activated cell sorting to harvest the CXCR4⁺CD45⁺ and CXCR4⁺CD45^- BMMNC subpopulations from transgenic mice that express enhanced green fluorescent protein. We then allogeneically grafted unfractionated BMMNCs or a subpopulation into mice subjected to transient middle cerebral artery occlusion (tMCAO) and compared the effects on stroke outcomes. We found that CXCR4⁺CD45^- BMMNCs, but not CXCR4⁺CD45⁺ BMMNCs, more effectively reduced infarction volume and neurologic deficits than did unfractionated BMMNCs. Brain tissue from the ischemic hemisphere of mice treated with CXCR4⁺CD45^- BMMNCs had higher levels of vascular endothelial growth factor and lower levels of TNF-α than did tissue from mice treated with unfractionated BMMNCs. In contrast, CXCR4⁺CD45⁺ BMMNCs showed an increase in TNF-α. Additionally, CXCR4⁺CD45⁺ and CXCR4⁺CD45^- populations exhibited more robust migration into the lesion areas and were better able to express cell-specific markers of different linages than were the unfractionated BMMNCs. Endothelial and astrocyte cell markers did not colocalize with eGFP⁺ cells in the brains of tMCAO mice that received CXCR4⁺CD45⁺ BMMNCs. In vitro, the CXCR4⁺CD45^- BMMNCs expressed significantly more Oct-4 and Nanog mRNA than did the unfractionated BMMNCs. However, we did not detect gene expression of these two pluripotent markers in CXCR4⁺CD45⁺ BMMNCs. Taken together, our study shows for the first time that the CXCR4⁺CD45^- BMMNC subpopulation is superior to unfractionated BMMNCs in ameliorating cerebral damage in a mouse model of tMCAO and could represent a new therapeutic approach for stroke treatment.