ACUTE HUMAN VS MOUSE GRAFT VS HOST-DISEASE IN NORMAL AND IMMUNODEFICIENT MICE

Recent reports of persistent engraftment of human lymphocytes and myeloid cells in hereditary immunodeficient severe combined immunodeficient mice (SCID) and beige athymic nude X-linked immunodeficiency (Bg/Nu/XID) mice have raised the question of why attempts to graft human cells into artificially immunosuppressed normal mice have failed so far. In the present study we provide evidence that this difference is due to the absence of natural antibodies in the mutant mice. We demonstrate that human PBL can be grafted in normal mice immunosuppressed by heavy doses of total body irradiation, provided the transplant is performed when the recipients lack natural antibodies in their serum, e.g. as in newborn normal mice, in mice treated with anti-mouse IgM antibody from birth, and in 3-week-old B cell-deficient CBA/N mice. In all cases, large numbers of human PBL were required. Under these conditions an acute and fatal graft vs. host disease (GVHD) developed in the recipients, regardless of whether these were artificially immunosuppressed or hereditary immunodeficient. The clinical manifestations and the histopathology of this xenogeneic acute GVHD are quite different from those of allogeneic GVHD. The former is primarily confined to the hematolymphoid tissues and locations close to accumulations of proliferating lymphoblasts, such as the peritoneal cavity in case of i.p. transplantation. The discordant xenogeneic GVHD is induced by human T lymphocytes and can be abrogated by treatment with anti-human T cell serum.