Immune checkpoint molecules performance in ANCA vasculitis.

Objective: The PD-1 axis promotes protection against autoimmunity. Immune checkpoint (IC) molecules performance in anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) remains unknown. This study aims to assess the IC pathway's role in the AAV's pathophysiology.

Methods: We recruited 88 AAV from our centre as a discovery cohort (acute=42, remission=46) and 30 patients from another institution for external validation (acute=16, remission=14).Serum, urine and peripheral blood mononuclear cells (PBMCs) were collected. In vitro IC molecules production by lymphocytes was studied with and without MPO/PR3 antigen stimulus. Cell culture supernatant (SN) was obtained by centrifugation. PD-1, PD-L1 and PD-L2 concentrations were assessed in serum (s), urine (u) and SN of AAV and healthy controls (HC) using a multiplex assay. PD-1 and PD-L1's expression was analysed in six diagnostic kidney biopsies.

Results: uPD-1 and uPD-L2's concentration was lower in AAV than HC (p<0.0001, p=0.0075). Acute patients exhibited lower uPD-L2 levels compared with those in remission (p=0.036). Similarly, PBMCs showed reduced PD-1 production than HC (stimulated group p=0.04, unstimulated p=0.0074). Furthermore, patients with inflammatory renal lesions had fewer PD-1-positive interstitial cells/staining intensity compared with those with sclerotic lesions. Contradictorily, sPD-1 and sPD-L1's concentration was higher in AAV than HC (p=0.007, p<0.0001) with acute patients exhibiting elevated sPD-1 levels compared with those in remission (p=0.0051). Serum and urine findings were confirmed in the validation cohort.

Conclusions: Results in urine, SN and histology suggest IC pathway abolition during acute disease restored in remission and contribute to understand PD-1 axis's role in AAV proposing it as a new biomarker of disease activity.