Immunologic effects of human thymic stromal grafts and cell lines.

These experiments report a method of preparing stromal remnants from human thymus. The remnants were composed of epithelial cells, fibroblasts, and macrophages. They were grafted under the renal capsule of nude mice. Some of the grafts were reconstituted with lymphocytes to obtain the microscopic morphology of the thymus. The mice with reconstituted grafts survived in a conventional environment, had increased numbers of T cells in their spleen, and showed improvement of T-cell mediated immunologic function. This was measured by a positive allogeneic effect, a mixed lymphocyte reaction, and cell-mediated lysis. In vitro cell lines were established from thymic remnants of two separate individuals. These lines grew as attached monolayers. One of them was composed of fibroblasts. The other had an epithelial morphology. This epithelial cell line (HT-7) was shown to produce factors which promoted thymocyte differentiation in vitro.