Development of thymus autografts under the kidney capsule in the pig: A new ''organ'' for xenotransplantation

Ten piglets, 7 to 16 weeks old, were partially thymectomised and 1 to 4 cm(3) of minced thymic fragments autografted under the renal capsule. They were sacrificed, respectively, after 2, 4, 6, 8, 12, and 20 weeks. After 2 weeks, irregular whitish zones are present under the renal capsule. They were composed principally of two cell types: the first type was characterized by small round basophilic nuclei and little cytoplasm typical of lymphocytes; the second cell type had larger ovoid nuclei and a large vacuolised cytoplasm. Each cell type could be found in separate lobules or mixed in variable proportion in the same structure. The thymic autografts grew to form a layer up to 4 mm thick after 20 weeks. In the meantime, at the beginning of 4th week, the lobular structure became well organized with the cell type presenting large nuclei and cytoplasm being restricted to the center of the lobules while lymphocytes composed a peripheral layer. Hassal corpuscles (HC) appeared in the center of the lobules. Immunohistochemical labeling with anti-cytokeratin mono- and polyclonal Ab and with anti-neurophysin polyclonal Ab displayed all the characteristics of normal functional thymic microenvironment. It is proposed that this novel experimental preparation ending up as a neo-organ (thyme-kidney) be used for xenotransplantation in an attempt to produce specific xenotolerance.