Invited Editorial: Epitope Discovery for Inflammatory Myopathy Treatment




Terrance O’Hanlon

Environmental Autoimmunity Group, National Institute of Environmental Health Sciences, USA

The idiopathic inflammatory myopathies (IIM) are heterogeneous autoimmune diseases that share the common features of muscle inflammation and weakness. In addition to muscle, these systemic connective tissue diseases may also affect the skin, joints, gastrointestinal tract, lungs and other organ systems. The IIM are the most common acquired myopathies in adults, result in incurable, progressively disabling disease with significant morbidity and mortality and high socioeconomic costs.

Polymyositis and Dermatomyositis (i.e., myositis with associated skin rashes) are the most frequent clinical subtypes of IIM and are thought to involve distinct etiopathogenic mechanisms. Polymyositis is characterized by oligoclonal, antigen-restricted CD8+ T cell muscle infiltrates that damage myocytes via perforin-mediated cytotoxicity. In contrast, dermatomyositis involves a primary vasculopathy, perivascular accumulations of B and CD4+ T lymphocytes and dendritic cells, and complement-mediated vascular endothelial cell damage.

In addition to these immunohistopathologic differences, approximately one-third of myositis patients manufacture myositis-specific autoantibodies (MSA) directed against different components of the protein biosynthetic pathway including several amino-acyl tRNA synthetases, translational elongation factors, and signal recognition particle. Most prevalent among these are autoantibodies targeting the histidyl-tRNA synthetase protein (HRS); commonly referred to as anti-Jo-1 autoantibodies and detected in ~20% of all myositis patients.

While the pathologic significance of the MSAs remains unclear, considerable interest exists in defining immunodominant T cell epitopes of the anti-Jo-1 antigen. To this end, we utilized the ProImmune REVEAL® Class II Rapid Epitope Discovery System to investigate the potential binding of overlapping, synthetic peptides spanning the entire anti-Jo-1 antigen molecule (Module 1: PEPscreen® Custom Peptide Library Synthesis). To date, our studies with ProImmune have resulted in the successful identification of several candidate T cell epitopes in binding assays with the IIM associated genetic risk factor HLA-DRB1*03:01 (Module 2: Class II MHC-Peptide Binding Assay). Moreover, our T cell epitope discovery data were enhanced further by equilibrium binding assays measuring precise rates of kinetic association (Ka) and disassociation (Kd) of peptide MHC Class II complexes (Class II Complete Rate and Stability Assays). Currently, our studies with ProImmune have progressed to the functional validation phase of the anti-Jo-1 T cell epitope discovery project. Herein we plan to use a combination of cellular assays (e.g., ELISpot and T cell proliferation) using myositis patient-derived peripheral blood cells to examine clonal expansion of antigen-specific, MHC Class II restricted T cells.