Abstract 2620: Differential Effects of Cyclosporine Regimens on Rat Brain Responses to Human Neural Cell Grafts

Abstract

Background Transplantation of neural cells is a promising stroke recovery therapy requiring animal model research, but rejection of human xenografts is an obstacle. While a variety of immunosupression strategies have been reported, few comparison data are available. We asked if different cyclosporine regimens would affect rat brain responses to human neural cell grafts. Methods Rats received intracerebral grafts of neural progenitors derived from human embryonic stem cells, and 6 rats each were randomized to 1 of 4 immunosupression groups: 1) SC (subcutaneous) group - cyclosporine 10 mg/kg/day SC starting 2 days prior to transplantation; 2) SC/PO (per os) group - the same injections for the first 7 days followed by 100 ug/ml in the drinking water; 3) PO group - only cyclosporine in the drinking water starting 2 days prior to transplantation; 4) Control - no immunosupression. Immunostaining, stereology, and optical densitometry were performed after 2 weeks for quantification of markers of human cells, neural cell types, and immune cells. Results More rats in the SC (6/6) and SC/PO (5/6) groups had surviving graft cells than the PO (1/6) and control (3/6) groups (p<0.05), with a trend toward more surviving graft cells as well. All rats with surviving graft cells showed co-labeling for the neural progenitor marker Nestin, and a minority of graft cells co-labeled for the cell division marker Ki67 and the neuronal marker MAP2. Optical densitometry showed more cellularity (p<0.05) and reactive astrocytosis (p<0.05) in grafted versus contralateral hemispheres, which was similar between groups. Areas of dead graft cell debris were seen in all groups; in these areas the human nuclear antigen was present in the cytoplasm of cells co-labeling for the microglia marker CD11b, suggesting that they had phagocytosed graft cells. Conclusions The survival of human neural cells in rat brains differed with immunosupression regimens, but immune cell infiltration, phagocytosis of graft cells, and reactive astrocytosis occurred in all groups. Frequent injections of laboratory animals is undesirable, and a compromise strategy of peri-transplant injections followed by mixing the drug in the drinking water showed good results to prevent graft cell rejection. Further research is needed to optimize the immunosupression approach for this application.