Effect of FK-506 on xenografted human Graves' thyroid tissue in severe combined immunodeficient mice

Objective. We studied the macrolide antibiotic FK-506, an immunosuppressive agent, in an attempt to ameliorate the lesion of autoimmune thyroid disease in human thyroid tissue xenografted into severe combined immunodeficient (SCID) mice. It was not felt appropriate to employ this agent directly in patients with autoimmune thyroid disease because adequate therapeutic modalities are available and the introduction of new, experimental agents could not be justified. Moreover, the study of the tissue before and after treatment could not have been undertaken directly in patients. Design. Human thyroid xenografts from four patients with Graves' disease and two normal persons were xenografted Ento SCID mice. Two weeks after xenografting, human immunoglobulin G (IgG) was detectable in all SCID mice xenografted with Graves' thyroid tissue. Mice Were divided into two groups with human IgG levels similar to each other. Mice in the first group were treated with FK-506 daily for 6 weeks; mice in the second (similar) group were given phosphate-buffered saline (PBS) only (control group). Measurements. Blood samples were taken every 2 weeks from the tail veins for human IgG, thyroid stimulating antibody, thyroperoxidase antibodies, thyroglobulin antibodies, and interferon-gamma (IFN-γ). Affer 8 weeks treatment, animals were sacrificed; thyroid tissue was examined histologically and for thyrocyte HLA-DR expression. FK-506 was also added to thyrocytes in in-vitro tissue culture conditions. Results. After 4-6 weeks of FK-506 therapy, human IgG, all thyroid antibodies and IFN-γ were suppressed, while the levels remained elevated in the control group. Lymphocytic infiltration virtually disappeared in the human thyroid tissue of the FK-506-treated mice and thyrocyte HLA-DR expression markedly declined; in the control mice, lymphocytic infiltration remained heavy and HLADR expression remained high. On the other hand, FK-506 added directly to thyrocytes in vitro (without lymphocytes) did not reduce thyrocyte HLA-DR expression. Conclusions. FK-506 appears to suppress the activation of intrathyroidal lymphocytes, but not thyrocytes. From these observations, it is concluded that this agent, by its action on intrathyroidal lymphocytes, is able to ameliorate the immunologically mediated histological and serological disturbance in human autoimmune thyroid disease, at least under these circumstances.