Abstract
Synthesis of factor VIII by liver sinusoidal endothelial cells has been documented, and liver transplantation for end stage liver disease has been shown to cure concomitant hemophilia A. Given the irreversible nature of liver transplantation, the spleen is an alternate organ of interest in transplant therapy to cure hemophilia A. Factor VIII gene expression in the spleen has been documented by RT-PCR (
Hollestelle, M. J. et al, 2001, Thromb Haemost 86:855–61
), and a recent report of living related splenic transplantation for hemophilia A has shown symptom-free survival up to 4 years (Jiang, H. C. et al, 2006, Transplant Proc 38:1483
). However, it is unclear which cell populations in the spleen synthesize factor VIII. Immunohistochemistry of murine spleen showed factor VIII staining of the sinusoidal endothelial cells as expected. Surprisingly, clusters of large mononuclear cells in the red pulp also intensely stained for factor VIII. CD31 staining revealed same pattern of sinusoidal endothelial cells and large mononuclear cells in the red pulp. Single cell suspensions of murine spleen analyzed by flow cytometry corroborated significant factor VIII expression (47–70% of all splenic cells). At least 60% of splenic cells were CD31+ CD45+, and these CD31+ CD45+ cells showed significant factor VIII expression (38–48%). When CD31+ cells were depleted by magnetic cell sorting, there was still a subgroup of cells expressing factor VIII (approximately 50%). In summary, we have shown that a significant proportion of splenic cells synthesize factor VIII by flow cytometry and immunohistochemistry. In addition to the sinusoidal endothelial cells, CD31+ CD45+ cells (possibly the large mononuclear cells seen on immunohistochemistry) contribute to splenic synthesis of factor VIII. Based on CD31 depletion study, there is still an unidentified group of cells (CD31-) that contributes to factor VIII synthesis. Further characterization of these cells and an in vivo study in a murine hemophilia A model have been initiated. We conclude that the spleen is a viable source of factor VIII and may be useful in cell-based and/or organ transplant therapy of hemophilia A.Disclosure: No relevant conflicts of interest to declare.
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2006, The American Society of Hematology
2006
