Is the Brain an "Immunologically Privileged Site"?

previously investigated this concept by using intracerebral tumor homografts and intracerebral tumor isografts to sensitized animals and concluded that probably due to variable genetic relations and other factors not yet completely understood, the brain is only partially privileged in tumor transplantation experiments in various strains of inbred mice.5 In that study, using a transplantable glioma arising in C57BL/6J mice, it was shown that this tumor was rejected when transplanted to the subcutaneous tissues of six other strains of inbred mice. When transplanted to the brains of these same strains of mice, the tumor grew in 10 to 35% of those mouse strains, although it had been rejected in 100% of the subcutaneous transplants. The rejection of the cerebral homotransplants was characterized by an unusual hyaline de¬ generation of the neoplastic cells without any significant inflammatory or typical immune response. When the homotransplant was carried out to mice specifically sensitized by prior skin grafting with C57BL/6J skin, the cerebral homograft rejection was char¬ acterized by the unusual hyaline degenera¬ tion and the typical immune inflammatory response. Isografts to animals sensitized by prior inoculation with glioma and adjuvant were rejected with a typical immune rejec¬ tion in the brain.5 The purpose of the present investigation is to examine further this concept and its corollary, Is the brain immunologically competent to respond to homograft chal¬ lenge ? Our observations in this study would in¬ dicate that the exposure of the host to an intracerebral or subcutaneous glioma cured by radiation provides a significant degree of immunity to a later intracerebral or subcutaneous implant.