Stable engraftment of allogeneic T lymphocytes in a patient with severe combined immunodeficiency following a transfusion with unirradiated blood. Specific recognition of host histocompatibility antigens and engraftment failure of a bone marrow transplant HLA-identical to the host.

We have analyzed the immunocompetence of blood donor-derived, allogeneic T cells that had engrafted in a patient with severe combined immunodeficiency following transfusion with unirradiated blood. The blood donor T cells multiply and persist in the patients' bone marrow and peripheral blood over several months without leading to a graft-versus-host disease. The allogeneic T cells can be expanded in vitro and restimulated by cells expressing host HLA-DR antigens. The presence of blood donor-derived T cells prevented engraftment of a bone marrow graft from an HLA-identical sibling; in contrast, engraftment and immunological reconstitution by bone marrow donor-derived cells was seen following elimination of the allogeneic T cells in vivo. We conclude that the allogeneic T cells sensitized against host histocompatibility antigens were responsible for bone marrow graft failure, even though this sensitization did not lead to a graft-versus-host disease.