Human Delayed-Type Hypersensitivity Reaction in a SCID Mouse Engrafted with Human T Cells and Autologous Skin

We have developed an animal model to study human delayed-type hypersensitivity reactions occurring in a human environment within a mouse host. Human skin was graften onto the backs and autologous human immune cells were injected into the peritoneal cavity of mice with severe combined immunodeficiency. Seven and 14 d after grafting, 2–50% of total white blood and spleen cells were of human origin. Mouse spleen-derived human T cells from tetanus toxoid as measured by [³H] thymidine uptake, and the strength of this proliferative response equaled that with pre-graft T cells from the same donor. Proliferation was blocked with monoclonal antibodies to human but not to mouse major histocompatibility complex antigens and with anti-human CD4 monoclonal antibodies. In vivo Vaccination of mice with tetanus toxoid did not enhance proliferation of mouse spleen-derived human T cells in response to antigen. Injection of tetanus toxoid into the human skin graft caused a perivascular human CD4⁺/CD25⁺ T-cell infiltrate, which was not present when tetanus toxoid was injected into adjacent mouse skin. We conclude that human T cells grafted into mice with severe combined immunodeficiency retain their function, but not mouse skin as homing sites, and that human T-cell responses depend on the human micro-environment. This model lends itself to studies of endothelium-T-cell interaction, T-cell activation within skin, and chronic inflammatory skin diseases.