Discovery of Antigen Specific CD4+ T cells in anti-3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) Immune Mediated Necrotizing Myopathy (IMNM)

Abstract

Abstract Anti-HMGCR+ IMNM is characterized by IgG antibodies against HMGCR and a strong association with HLA-DRB1* 11:01. Although this implicates HMGCR-specific CD4+ T cells in disease pathogenesis, no such cells have been identified thus far. Monocyte derived dendritic cells from 6 anti-HMGCR+ IMNM patients were incubated with HMGCR protein and presented peptides were identified using a natural antigen processing assay (NAPA). Briefly, HLA-DR/peptide complexes were isolated by immunoprecipitation and bound peptides were sequenced by mass spectrometry. HMGCR peptides corresponding to putative T cell epitopes were synthesized and used to stimulate peripheral blood mononuclear cells from: 10 anti-HMGCR+ IMNM patients, 10 dermatomyositis patients (DM), 5 HLA-DRB1* 11:01+ healthy controls (HC). HMGCR-reactive CD4+ T cells were identified by flow cytometry based on CD154 upregulation. A total of 7 different naturally processed HMGCR peptides were identified. The number of distinct peptides presented per patient ranged from 1 to 5, with 5 being presented by at least 2 patients. All HMGCR peptides elicited robust CD4+ T cell responses in 9/10 anti-HMGCR+ IMNM patients, compared to 4/10 DM patients (p=0.017), 1/5 of HC (p=0.0119). The anti-HMGCR+ IMNM patients responded to more epitopes (p=0.0163) and had higher total number of positive CD4+ T cell cells (p= 0.0001). Our findings represent the first report of antigen-specific CD4+ T cells in anti-HMGCR+ IMNM. Leveraging NAPA, we defined a core set of naturally presented HMGCR peptides defining precise immunologically relevant CD4+ T cell epitopes. Definition of these epitopes is key in understanding disease pathogenesis and will aid in the development of antigen-specific therapeutic tools. Supported by grants from Rheumatology Research Foundation and the Buck Foundation.