The effect of a short-course treatment with FK506 on the survivability of rat-to-mouse cross-species neural graft.

We examined the effect of a short-course treatment with a new immunosuppressive agent FK506 (FK) on the survivability of neural xenografts. Pieces of ventral mesencephalic tissues from rat embryos were transplanted into the right lateral ventricle of adult mice. The mice were either assigned to a 4-day FK (10 mg/kg/day) immunosuppressive scheme or were given no immunosuppression. The 4-day course treatment with FK was started on postoperative day 0, 2, 4, 6 or 8. The incidence of graft rejection 28 days after transplantation was 82%, 55%, 55%, 100% and 100% when FK was given on days 0-3, 2-5, 4-7, 6-9 and 8-11, respectively. As a separate group, we examined the cellular infiltration in neural xenografts of the non-immunosuppressed recipients at two different time points (3 days and 7 days) after transplantation. The infiltration of T-lymphocytes was not detected 3 days after transplantation, but had occurred by 7 days after transplantation. We speculate that FK is more effective in preventing the rejection of neural xenografts when it is given just before the initiation of the T-lymphocytic infiltration.