102. Maintenance of Remission is Influenced by HLA-DPB1*04:01 and Interaction with PR3225-239
Creators: name: Dhruti Chen1
name: McInnis1, Elizabeth
name: Wu1, Eveline
name: Stember1, Katherine
name: Hogan1, Susan
name: Yichun Hu1
name: Henderson1, Candace
name: Blazek1, Lauren
name: Mallal2, Simon
name: Karosiene, Edita
name: Bjoern Peters3
name: Sidney3, John
name: James4, Eddie
name: Kwok4, William
name: J. Charles Jennette1
name: Ciavatta1, Dominic
name: Falk1, Ronald
name: Free1, Meghan
Publisher: name: Zenodo
Year: 2022
Subjects: Vasculitis
ANCA
Abstracts
Giant Cell Arthritis
MPA
GPA
EGPA
Takayasu
IgA vasculitis

description: <strong>Background:</strong> GWAS identified the risk allele HLA-DPB1*04:01 in ANCA vasculitis and observational studies associate this risk allele with relapse. As HLA are the focal point of immune system initiation to antigen, these interactions can define immunological remission and/or antigen non-responsiveness. The specific HLA combined with the cognate peptide facilitates activation of an autoreactive immune response (including T and B cells). We hypothesized that PR3-ANCA vasculitis patients exhibit a specific interaction between cognate PR3 peptide and HLA-DPB1*04:01, and in the absence of this HLA-peptide interaction, long-term remission is achieved and maintained. <strong>Methods:</strong> ANCA vasculitis patients were followed longitudinally. Peripheral blood mononuclear cells (PBMCs) from patients and healthy controls with HLA-DPB1*04:01 were tested for HLA-DPB1*04:01 expression and interaction with a PR3 peptide identified via in silico and in vitro assays. Tetramers (HLA/peptide multimers) identified autoreactive T cells. <strong>Results</strong>: Carriers of the risk allele HLA-DPB1*04:01 were less likely to maintain remission in PR3-ANCA vasculitis, (HR for relapse 2.06 (1.01,4.20)). This effect was not observed in the MPO-ANCA or the combined patient cohort. We confirmed that mRNA and surface protein expression of HLA-DPB1 among patients and controls was not different, therefore we examined how highly specific peptide binding between HLA-DPB1*04:01 and PR3 may influence disease status. In silico predictions demonstrated strong affinity between PR3<sub>225-239 </sub>and HLA-DPB1*04:01 that was confirmed by in vitro binding. The interaction was tested in ex vivo flow cytometry studies of fluorescently labelled peptide and patient PBMCs. Patients in long-term remission off therapy had lower PR3 peptide and HLA overlap, indicating immunological remission (Figure). To further investigate the pathogenic role of HLA-DPB1*04:01, we utilized tetramers (HLA multimers) loaded with PR3<sub>225-239 </sub>to identify autoreactive CD4+ T cells in the circulation of patients (scrambled peptide MPO<sub>447-461</sub> as negative control). We examined tetramer positivity of PBMCs directly ex vivo versus 14 day expansion in vitro in response to specific peptides. CD4+ T cells were detectable by PR3-specific tetramers after 14 day in vitro expansion in response to PR3<sub>225-239</sub>. We found greater CD4+ T cell reactivity to PR3<sub>225-239</sub> compared to scrambled peptide in our cohort. This strengthened our conclusion that HLA-DPB1*04:01 and PR3<sub>225-239 </sub>drive the adaptive immune response in some patients with PR3-ANCA vasculitis. The CD4+ T cell response during active disease and remission was tested using paired samples. Despite limited paired samples, we found that in half of the active patients, T cell reactivity to PR3<sub>225-239</sub> was high only during periods of disease activity and exhibited low to no reactivity during disease remission. <strong>Conclusion:</strong> While the risk allele HLA-DPB1*04:01 has been previously associated with PR3-ANCA vasculitis, the biological underpinnings were unclear. These studies demonstrate that HLA-DPB1*04:01 and PR3<sub>225-239 </sub>affinity is dynamic and lack of interaction may be the basis for immunological remission. We hypothesized that it could determine the subsequent immune response of T cell activation and maintenance of immunological remission. We found that PR3<sub>225-239 </sub>presented by HLA-DPB1*04:01 is specifically recognized by autoreactive T cells and may explain why PR3-ANCA vasculitis patients with HLA-DPB1*04:01 are unable to maintain disease remission. <strong>Disclosures: </strong>J.C.J has the following disclosures: Grant support from Medimmune (2017-2019). E.Y.W. receives consulting and Advisory Board fees from Pharming Healthcare, Inc. and receives research funding from AstraZeneca and Bristol-Myers Squibb. All other authors have no financial conflicts of interest to disclose.