Encapsulated thymic epithelial cells as a potential treatment for immunodeficiencies.

The epithelial cells of the thymus produce hormones that have been implicated in the maturation of T lymphocytes. Thymic epithelial cells can be encapsulated in a permselective polymer membrane that allows the passage of thymic hormones, but prevents the entry of antibodies, complement, cells, and viruses. A pure culture of thymic epithelial cells, identified as such by transmission electron microscopy and keratin staining, was obtained by low temperature organ culture of fetal mouse thymus. These cells remained intact and produced physiologic amounts of the thymic hormone thymosin alpha-1 after encapsulation in a permselective polymer membrane and in vitro culture for 5 days. An encapsulated implant of thymic epithelial cells may therefore promote reconstitution of an immune system in immunodeficiency diseases without allowing the rejection or destruction of the thymic tissue.