DNA- and viral-mediated gene transfer in follicular cells: progress toward gene therapy of the thyroid.

The authors investigate the in vitro component of an ex situ strategy for gene transfer into the thyroid gland using DNA complex and retroviral vectors. Canine follicular cells harvested by unilateral lobectomy and grown in low-serum media proliferated in culture and retained their differentiated state as evidenced by morphology and thyroglobulin expression. Transient and "stable" gene transfer in thyroid cells were evaluated by comparing DNA and retroviral transduction techniques. Effective gene transfer and expression was demonstrated by histochemical staining for the marker gene product beta-galactosidase. The efficiency of transduction was assessed using an amphotropic retroviral vector carrying the neomycin resistance gene and semiquantitative polymerase chain reaction (PCR) identification of integrated proviral sequences. This analysis demonstrated a proviral frequency in transduced cultures of 10% to 30%. Transduced cells showed no change in morphology or growth patterns and maintained differentiated function as assessed by antibody staining for thyroglobulin. The thyroid gland is an attractive target for somatic gene therapy because of its large protein-synthetic capacity, sensitivity to hormonal regulation, and proportionately high blood flow. Follicular cell gene therapy may be useful not only for treating congenital or acquired diseases of the thyroid, but also disorders of circulating proteins such as hypopituitarism, hemophilia, and diabetes.