Patients with common variable immunodeficiency (CVID) can develop immune dysregulation complications such as autoimmunity, lymphoproliferation, enteritis, and malignancy, which cause significant morbidity and mortality. We aimed to (i) assess the potential of serum proteomics in stratifying patients with immune dysregulation using two independent cohorts and (ii) identify cytokine and chemokine signaling pathways that underlie immune dysregulation in CVID. A panel of 180 markers was measured in two multicenter CVID cohorts using Olink Protein Extension Assay technology. A classification algorithm was trained to distinguish CVID with immune dysregulation (CVIDid, n = 14) from CVID with infections only (CVIDio, n = 16) in the training cohort, and validated on a second testing cohort (CVIDid n = 23, CVIDio n = 24). Differential expression in both cohorts was used to determine relevant signaling pathways. An elastic net classifier using MILR1, LILRB4, IL10, IL12RB1, and CD83 could discriminate between CVIDid and CVIDio patients with a sensitivity of 0.83, specificity of 0.75, and area under the curve of 0.73 in an independent testing cohort. Activated pathways (fold change > 1.5, FDR-adjusted p < 0.05) in CVIDid included Th1 and Th17-associated signaling, as well as IL10 and other immune regulatory markers (LAG3, TNFRSF9, CD83). Targeted serum proteomics provided an accurate and reproducible tool to discriminate between patients with CVIDid and CVIDio. Cytokine profiles provided insight into activation of Th1 and Th17 pathways and indicate a possible role for chronic inflammation and exhaustion in immune dysregulation. These findings serve as a first step towards the development of biomarkers for immune dysregulation in CVID.

Abbreviations used ADA2-Adenosine deaminase2 CID-Combined immunodeficiency CNS-Central nervous system CSF-Cerebrospinal fluid CTLA4-Cytotoxic T-lymphocyteeassociated antigen 4 CVID-Common variable immunodeficiency DADA2-Deficiency of adenosine deaminase 2 HSCT-Hematopoietic stem cell transplantation ICD-International Statistical Classification of Diseases IgRT-Immunoglobulin replacement therapy ILD-Interstitial lung disease JCV-John Cunningham virus LRBA-LPS-responsive beige-like anchor protein MRI-Magnetic resonance imaging NGS-Next-generation sequencing PCR-Polymerase chain reaction PID-Primary immunodeficiency PML-Progressive multifocal leukoencephalopathy Treg-Regulatory T cellyet to be determined optimal maintenance therapy in case of relapse.

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