Successful Formation of a Chimeric Human Thymus Allograft Following Transplantation of Cultured Postnatal Human Thymus

Transplantation of cultured postnatal human thymus was performed in a patient with complete DiGeorge syndrome. Biopsy of the graft 3 mo after implantation revealed normal CD1⁺ thymocytes in thymic cortical epithelial regions and CD1^- thymocytes in thymic medullary epithelial regions, respectively. HLA analysis of graft thymocyte and thymic microenvironment components demonstrated that developing thymocytes and thymic macrophages were recipient derived, while thymic epithelial components were of donor origin. The patient, who initially had no T cells and had profoundly defective T cell function, developed normal T cell responses to mitogens and Ags, tolerance to donor in a mixed lymphocyte reaction, and normal Ab titers after tetanus toxoid and pneumovax immunization. Thus, transplantation of cultured postnatal human thymic tissue in humans can form functional chimeric thymic tissue, and may provide a strategy to reconstitute the peripheral T cell pool in select congenital and acquired immune deficiency syndromes.