Multimodal investigations of trans-endothelial cell trafficking under condition of disrupted blood-brain barrier integrity

Background: Stem cells or immune cells targeting the central nervous system (CNS) bear significant promises for patients affected by CNS disorders. Brain or spinal cord delivery of therapeutic cells is limited by the blood-brain barrier (BBB) which remains one of the recognized rate-limiting steps. Osmotic BBB disruption (BBBD) has been shown to improve small molecule chemotherapy for brain tumors, but successful delivery of cells in conjunction with BBBD has never been reported. We have used a clinically relevant model (pig) of BBBD to attempt brain delivery of TALL-104, a human leukemic T cell line. TALL-104 cells are potent tumor killers and have demonstrated potential for systemic tumor therapy. The pig model used is analogous to the clinical BBBD procedure. Cells were injected in the carotid artery after labeling with the MRI T1 contrast agent GdHPDO3A. Contrast CT scans were used to quantify BBBD and MRI was used to detect Gd++-loaded cells in the brain. Transcranial Doppler was used to monitor cerebral blood flow. EEG recordings were used to detect seizures. Immunocytochemical detection (Cresyl Violet, anti-human CD8 for TALL-104, Evans Blue for BBB damage, GFAP and NEUN) was performed. Results: At the concentration used TALL-104 cells were tolerated. Incomplete BBBD did not allow cell entry into the brain. MRI scans at 24 and 48 hours post-injection allowed visualization of topographically segregated cells in the hemisphere that underwent successful BBBD. Perivascular location of TALL-104 was confirmed in the BBBD hemisphere by Cresyl violet and CD8 immunocytochemistry. No significant alteration in CBF or EEG activity was recorded during cell injections. Conclusions: Our data show that targeted CNS cell therapy requires blood-brain barrier disruption. MRI-detectable cytotoxic anti-neoplastic cells can be forced to transverse the BBB and accumulate in the perivascular space. The virtual absence of toxicity, the high anti-tumor activity of TALL-104, and the clinical feasibility of human osmotic BBBD suggest that this approach may be adopted to treat brain or spinal cord tumors. In addition, BBBD may favor CNS entry of other cells that normally lack CNS tropism.