Thyroid stimulating monoclonal antibodies: overcoming the road blocks and the way forward

In 1956, Adams and Purves observed that Graves’ disease (GD) was directly caused by a factor present in serum (Adams & Purves, 1956). Subsequent studies showed that the responsible factor was an IgG and that these spontaneously arising autoantibodies induced hyperthyroidism by mimicking TSH stimulation of the TSH receptor, an unusual member of the glycoprotein hormone receptor family (reviewed in Rapoport et al ., 1998). The discovery of cell fusion for the purpose of generating monoclonal antibodies (Kohler & Milstein, 1975) was a key development for antibody characterization. In principle, monoclonal antibodies of any desired specificity could be generated by immunizing an animal with the antigen and fusing its splenic B lymphocytes with a myeloma cell line. Indeed, panels of mouse monoclonals to two major thyroid autoantigens, thyroglobulin (Tg) and the thyroid microsomal antigen/ thyroid peroxidase (TPO) were readily developed (for example Ruf et al ., 1985, 1989). Similarly, subsequent to the cloning of the TSHR (Nagayama et al ., 1989; Parmentier et al ., 1989; Frazier et al ., 1990; Misrahi et al ., 1990) and the generation of recombinant TSHR antigen, panels of TSHR monoclonal antibodies were produced. These murine monoclonals provided invaluable reagents (for example Loosfelt et al ., 1992; Harfst et al ., 1994; Seetharamaiah et al ., 1995; Nicholson et al ., 1996; Costagliola et al ., 1998; Davies et al ., 1998; Oda et al ., 2000). However, despite extensive efforts (published or unpublished) over many years by several different teams, none of these monoclonals alone or in combination stimulated the activity of thyrocytes or eukaryotic cells transfected with TSHR-cDNA. Other groups cloned human antibodies, some of which were reported as thyroid-stimulating antibodies (TSAb; reviewed in Rapoport et al ., 1998). However, these antibodies were inactive at low concentration (ng/ml range), one of the criteria that we described as essential to satisfy the ‘quest for the Holy Grail’ (McLachlan & Rapoport, 1996). In 2002, three different groups reported monoclonal TSAb generated from immunized mice or hamsters (Ando et al ., 2002; Costagliola et al ., 2002; Sanders et al ., 2002; summarized in Table 1). Six months later, an even greater achievement by one of these groups was the isolation of a human monoclonal TSAb from a Graves’ patient (Sanders et al ., 2003a) that did satisfy most of the criteria previously described (McLachlan & Rapoport, 1996). Four additional murine (Sanders et al ., 2003b) and a second hamster (Ando et al ., 2003) monoclonal TSAb were reported at international meetings in late 2003. Although the excitement associated with these successes may not have been immediately appreciated by all endocrinologists, the thyroid autoimmunity community heralded their significance in editorials (Costagliola & Vassart, 2002; Davies, 2002; Dayan, 2003). The information that will be revealed by these long-sought monoclonal TSAb has yet to be fully exploited. Nevertheless, at this stage, the success story raises several intriguing and important questions: What were the ‘road blocks’? How were they overcome? What are the properties of these TSAb? What epitopes do they recognize? How they can be used and, most importantly, what insight are they likely to provide?