Purification of Adrenal Chromaffin Cells Increases Antinociceptive Efficacy of Xenotransplants without Immunosuppression

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Abstract
We have found that immunosuppression is necessary for the survival of xenogeneic adrenal medullary transplants. Because chromaffin cells are essentially nonimmunogenic, it is likely that the highly immunogenic “passenger” cells in the transplant preparation bring about rejection. This article describes a procedure that produces an essentially pure preparation of chromaffin cells for transplantation. Bovine adrenal medullary cells were isolated and differentially plated, resulting in a semipurified preparation of chromaffin cells. Ferromagnetic beads were added to the cell suspension, some of which were phagocytized by endothelial cells, which allowed their removal by exposure to a magnet. The remaining cells were then exposed to ferromagnetic beads coated with isolectin B4 from Griffonia simplicifolia and once again to a magnetic field. The “semipurified” preparation contained approximately 90% chromaffin cells, whereas the “highly purified” preparation was > 99.5% chromaffin cells as determined immunohistochemically. The immunogenicity of the two cell preparations was assessed in vitro by determining their capacity to evoke lymphocyte proliferation. Rat spleen lymphocytes were mixed with either a highly purified or semipurified population of bovine chromaffin cells. The results of this assay demonstrated that the highly purified preparation was a much weaker stimulant of lymphocyte proliferation than was the semipurified preparation and may demonstrate better graft survival in vivo. Transplantation via intrathecal catheter of either 80,000 or 250,000 cells from the highly or partially purified preparations onto the lumbar spinal cord of nonimmunosuppressed and nonnicotine-stimulated rats produced a cell number-dependent antinociception for both Aδ and C fiber-mediated thermonociception at 6 days after transplantation. After 6 days and up to 28 days, only the “highly purified” preparation showed antinociception. These results suggest that nearly complete purification of bovine chromaffin cells minimizes immunorejection of xenogeneic transplants of these cells.