Characterization of autoantibodies and their triggers in myelin oligodendrocyte glycoprotein antibody-associated disease

Mounting evidence points to a pivotal role of autoantibodies in the pathophysiology of demyelinating disorders of the central nervous system (CNS). In the clinical management of patients, autoantibodies are used as diagnostic biomarkers. The triggers and mechanisms behind the complex autoimmune responses, however, are not yet fully understood. Myelin oligodendrocyte glycoprotein (MOG) antibody associated disease (MOGAD) is a recently classified demyelinating CNS disease characterized by the presence of autoantibodies against MOG, a protein expressed solely in the CNS. The diagnosis of MOGAD is associated with several challenges, and the pathophysiology of the disease remains elusive.
This PhD thesis comprises three specific aims: (1) to address challenges in the diagnosis of MOGAD in light of the recently published MOGAD diagnostic criteria, (2) to explore MOG reactive autoantibodies of the immunoglobulin A (IgA) isotype as a potential biomarker in CNS demyelinating disease, and (3) to investigate post infectious and vaccine related triggers in MOGAD through the cloning and in depth characterization of antibodies from patients.
To enable the characterization of MOG reactive antibody responses in patients, we used a flow cytometry assay with live cells expressing human MOG (hMOG). To identify and clone autoantibodies, we enriched and isolated MOG-reactive B cells from patients using a customized assay with cells expressing fluorescence labeled hMOG. In vitro techniques were used to characterize antibody reactivities to a panel of self- and foreign antigens, and single cell sequencing experiments were performed to decipher the immune cell origin and phenotype of the autoreactive antibodies.
Addressing the first aim of this thesis, we found that the performance of the MOGAD diagnostic criteria resulted in discordant diagnoses of MOGAD in some cases, and the performance of MOG antibody testing with different methods gave diverse results in a subset of the samples. Investigating a different patient cohort, MOG antibodies were only detected in rare cases of patients with psychiatric disease. In the second aim of this thesis, we identified MOG antibodies of the IgA isotype in a subgroup of patients with demyelinating diseases. Notably, these patients presented with distinct clinical features compared to patients who were seropositive for MOG antibodies of the immunoglobulin G isotype. As part of the third aim, we cloned MOG reactive antibodies from different donors. Although the majority of the monoclonal antibodies did not react against other antigens, one antibody derived from a patient with post-vaccination development of MOGAD showed cross reactivity to hMOG and tetanus toxoid. We were able to delineate the B cell phenotype of the B cells that produced this antibody clone.
The results of this thesis underscore the need to identify additional biomarkers to facilitate the differential diagnosis of MOGAD and propose MOG-IgA as a potential novel biomarker in patients with demyelinating disorders. The cloning and characterization of patient derived MOG-reactive antibodies provides important insight into their specificity and function and lays the groundwork for future investigations regarding their pathogenic role in neuroinflammation.