Lympho-myeloid chimerism achieved by spleen graft of green fluorescent protein transgenic rat in a combined pancreas transplantation model (TI03-029)

BACKGROUND: Multilineage chimerism is a promising strategy to induce donor-specific tolerance. Because the beneficial effect of splenic grafting on tolerance induction is well known, we studied long-term hematopoietic chimerism and the fate of donor-derived cells after allogenic pancreas/spleen transplantation. METHODS: Green fluorescent protein (GFP) transgenic (Tg) Wistar rats were donors and combined pancreas/spleen transplantation (PST) or pancreas transplantation (PT) alone was performed on recipient LEW rats. Graft survival was compared between these two groups and the fate of donor-derived GFP(+) cells was analyzed by flow cytometry. In this system, the donor-derived cells were clearly defined as having lymphocytic or granulocytic lineage by cell size. T-cell subsets of GFP(+) and GFP(-) cells in long graft-surviving rats were also characterized. RESULTS: The survival period of the grafted pancreas in PST rats was significantly longer than that of PT rats (P<0.001). Three of seven PST rats survived >250 days. The chimeric level of donor-derived GFP(+) cells in the recipient peripheral blood was markedly higher in PST rats. In rats with long-surviving grafts, overall peripheral blood chimerism was more than 5%, and both lymphocytes and granulocytes generated from the grafted spleen were stable. T-cell subsets in the recipient LEW rats varied according to the type of cells. CD4(+)CD8(+) subsets decreased in the GFP(+) cells and CD4(-)CD8(+) subsets increased in the GFP(-) (LEW) cells. CONCLUSION: We confirmed the combination effect of the grafted spleen on pancreatic graft survival. Donor lymphocytic and granulocytic lineages were generated in the recipients with long-surviving graft. It suggested that multilineage chimerism was often induced by the spleen graft and protected the pancreatic graft against rejection for a long period.