A Common Pituitary Autoantibody in Two Patients with Immune Checkpoint Inhibitor-Mediated Hypophysitis: ZCCHC8

ABSTRACT Objective Hypophysitis is an increasingly recognized adverse effect of immune checkpoint inhibitor (ICI) therapy for malignancy. However, the mechanisms through which ICIs induce hypophysitis are largely unknown. We aim to describe 2 cases of ICI-mediated hypophysitis and perform autoantibody profiling on serial samples from these patients to determine if common autoantibodies could be identified. Methods We describe 2 cases of patients with metastatic urothelial cancer who received ICI therapy and subsequently developed severe fatigue, prompting a hormonal workup consistent with hypopituitarism. Patient 1 received the ICI ipilimumab (anti-cytotoxic T-lymphocyte-associated protein 4) and patient 2 received the ICI pembrolizumab (anti-programmed cell death protein 1). Both patients had serial seromic immune biomarker profiling using high-density protein arrays before and after developing hypophysitis. Once a common autoantibody was found, zinc finger CCHC-type containing 8 (ZCCHC8), we used immunohistochemistry to assess its presence in pituitary tissue. Results Of a limited number of increased autoantibodies detected, those to ZCCHC8 were the only common antibodies to increase at least 3-fold post-hypophysitis in both patients. Using immunohistochemistry staining, we show for the first time that ZCCHC8 is expressed in pituitary gland tissue. Conclusion Seromic profiling identified a common autoantibody, ZCCHC8, in 2 patients who developed hypophysitis on ICI therapy, and other serial autoantibody increases in each patient. These findings warrant validation in other cohorts to determine if the response is to self or tumor antigen, and may reveal novel insights into pituitary gland physiology and the pathogenesis of ICI-mediated hypophysitis.