# Soluble immune checkpoints reflect immune activation and treatment response in high-risk systemic sclerosis patients treated with plasma exchange

## TL;DR

Soluble immune checkpoints in high-risk systemic sclerosis patients correlate with immune activation and treatment response, offering potential as biomarkers.

## Contribution

Identifies soluble immune checkpoints as novel biomarkers for disease activity and treatment response in systemic sclerosis.

## Key findings

- Soluble immune checkpoints (sICPs) correlated with vascular dysfunction marker dp-ucMGP in systemic sclerosis patients.
- sICP levels significantly declined after 6 months of intensive immunosuppressive treatment.
- Classical cytokines showed weak correlations with disease severity compared to sICPs.

## Abstract

Systemic sclerosis (SSc) is an autoimmune disease characterized by immune dysregulation, vasculopathy, and fibrosis. High-risk patients, particularly those with diffuse cutaneous involvement (dcSSc) and interstitial lung disease (ILD), may benefit from early intensive immunosuppressive therapy during the inflammatory phase of the disease. We hypothesized that soluble immune checkpoints (sICPs) reflect immune activation and serve as biomarkers for disease activity and treatment response.

Plasma levels of 15 sICPs (including sPD-1, sTIM-3, sBTLA, sCD25, sCD137, sIDO), cytokines, B cell activating factor (BAFF) and dephosphorylated-uncarboxylated Matrix Gla Protein (dp-ucMGP) were analyzed in a prospective SSc cohort (n = 35). A high-risk subset (n = 14) received an intensified immunosuppressive regimen consisting of therapeutic plasma exchange (TPE), cyclophosphamide, and maintenance therapy with mycophenolate mofetil or rituximab in cases of intolerance. Samples were obtained at baseline, 6, and 12 months. Correlations with clinical variables and treatment response were assessed using non-parametric statistics and principal component analysis (PCA).

Patients selected for intensified treatment had a distinct inflammatory profile with elevated levels of sICPs and BAFF, while CRP levels did not differ. sICPs correlated positively with dp-ucMGP, indicating a link between vascular dysfunction and immune activation. Classical pro-inflammatory cytokines (e.g., IL-6, TNFα), however, showed weak correlations with disease severity. Longitudinal analysis showed a significant decline in most sICPs within 6 months of treatment, whereas cytokine levels remained stable. Survival and pulmonary function were preserved during a median follow-up of 4.5 years.

sICPs reflect T cell dysregulation and disease severity in SSc more accurately than classical cytokines. Early intervention in inflammatory, high-risk patients may prevent long-term clinical deterioration. The observed decline of sICPs following treatment supports their potential as early biomarkers of treatment response. Moreover, the correlation between sICPs and dp-ucMGP suggests a mechanistic link between vascular and immune pathology in SSc.