Triple immunosuppression protects murine intracerebral, hippocampal xenografts in adult rat hosts: effects on cellular infiltration, major histocompatibility complex antigen induction and blood-brain barrier leakage.

Recently we reported protection of intracerebral mouse to rat hippocampal xenografts upon treatment with a combination of cyclosporin A, prednisolone and azathioprine. These findings are now supported in an extended analysis of graft-infiltrating cells. Host T-cell and macrophage infiltration and the immunocytochemical level of cellular expression of major histocompatibility complex class I and II antigens, measured by densitometric analysis, were compared between recipient rats receiving cyclosporin A alone or cyclosporin A in combination with prednisolone and azathioprine. The combination therapy resulted in a much improved survival of the xenografted hippocampal tissue with preservation of organotypic granule and pyramidal cell layers. Graft infiltration by T-cells and macrophages was significantly lower and the level of major histocompatibility complex class I and II antigen expression by the infiltrating cells markedly reduced. Lower expression of donor-type major histocompatibility complex class I antigen was also found in the xenografts in the trimedicated recipients, together with reduced blood brain barrier leakage and astrogliosis at the host-graft interface. The results demonstrate the benefits of using combined immunosuppressive strategies for protection of histoincompatible brain xenografts in the central nervous system.