Longitudinal Characterization of Autoantibodies to the Thyrotropin Receptor (TRAb) During Alemtuzumab Therapy: Evidence that TRAb May Precede Thyroid Dysfunction by Many Years.

Abstract

Thyroid autoimmunity, especially Graves' disease or hypothyroidism with positive autoantibodies (TRAb) to the thyrotropin receptor (TSHR), occurs in 30-40% of patients with relapsing multiple sclerosis following treatment with alemtuzumab (ALTZ). ALTZ therapy therefore provides a unique opportunity to study the evolution of TRAb prior to clinical presentation. TRAb can stimulate (TSAb), block (TBAb), or not affect ("neutral") the TSHR function, causing hyperthyroidism, hypothyroidism, or euthyroidism, respectively. A longitudinal retrospective analysis was conducted of TRAb bioactivity over a period of nine years in 45 multiple sclerosis patients receiving ALTZ using available stored serum. Of these 45 patients, 31 developed thyroid dysfunction (TD) and 14 remained euthyroid despite being followed for a minimum of five years (NO-TD). The presence of TRAb was evaluated at standardized time points: (i) before ALTZ, (ii) latest time available following ALTZ and before TD onset, and (iii) following ALTZ during/after TD onset. Serum TRAb were detected by published in-house assays (ihTRAb): flow cytometry detecting any TSHR-binding TRAb, and luciferase bioassays detecting TSAb/TBAb bioactivity. Purified immunoglobulin G was used to verify TSAb/TBAb in selected hypothyroid cases. Standard clinical automated measurements of TRAb, antithyroid peroxidase autoantibodies (TPOAb), thyrotropin, free thyroxine, and free triiodothyronine were also collected. Before ALTZ, combined ihTRAb (positive with flow cytometry and/or luciferase bioassay) but not automated TRAb were present in 5/16 (31.2%) TD versus 0/14 (0%) NO-TD (p = 0.017). Detectable ihTRAb preceded TD development in 9/28 (32.1%) and by a median of 1.2 years (range 28 days-7.3 years). Combination testing of ihTRAb and TPOAb at baseline predicted 20% of subsequent cases of hyperthyroidism and 83% of hypothyroidism. Evidence is presented that TRAb measured with custom-made assays can be detected prior to any change in thyroid function in up to a third of cases of ALTZ-related TD. Furthermore, the presence of ihTRAb prior to ALTZ treatment was strongly predictive of subsequent TD. The findings suggest that a period of affinity maturation of TRAb may precede clinical disease onset in some cases. Combined testing of TPOAb and ihTRAb may increase the ability to predict those who will develop TD following ALTZ.