Adaptive Autoimmunity in Pediatric Acute-Onset Neuropsychiatric Syndrome

About This Grant

Project Summary Pediatric Acute-Onset Neuropsychiatric Syndrome (PANS) is characterized by a variety of psychiatric manifestations, particularly Obsessive-Compulsive Disorder (OCD) which affects 1-4% of children worldwide. Symptoms often begin suddenly following an infection (e.g. streptococcal throat infection). PANS is highly heterogenous and PANS etiology remains poorly understood. Thus, biomarkers identified in PANS patients, even only a subset, could provide valuable insights. It has been hypothesized that PANS is driven by a post-infectious immune process, and clinical observations suggest a role for autoimmunity in PANS etiology. PANS features both systemic and CNS inflammation, which informs our central hypothesis --- a subset of PANS involves functional autoantibodies (AAbs) that alter CNS immunity by affecting the blood brain barrier (BBB), immune trafficking, and immune cell activity, as investigated in 2 Revised Specific Aims. In Aim 1, we will measure functional properties of anti-interferon-λ and other AAbs in serum and CSF using a panel of cell-based receptor blocking assays. We discovered PANS patients with high-titer, serum anti-interferon-lambda (IFN-λ) IgG with blocking activity. We further hypothesize that additional functional AAbs against related molecules exist and could play a role in PANS pathogenesis. We will develop and validate blocking assays for promising anti-cytokine antibodies (ACA) where blocking assays have not been described. Sera and CSF with blocking activity will be fractionated and assessed for IgG blocking activity. Longitudinal serum samples from all PANS patients with IFN-λ-blocking IgG, and other PANS patients with blocking ACA, will then be characterized in Aim 2. Aim 2 will characterize B cell repertoires and clone human recombinant monoclonal antibodies (rMAbs) from sorted B cells from ACA+ PANS patients. We will take advantage of a large, existing, well-curated PANS Biobank that houses cryopreserved peripheral blood mononuclear cells (PBMCs) collected contemporaneously with the serum used in Aim 1. Antigen-specific B cell repertoires will be analyzed using an antigen tetramer-baiting enrichment strategy followed by single cell RNA sequencing. Paired heavy and light chain immunoglobulin genes will be cloned from single B cells to produce rMAbs, which will be subject to antigenic target analysis methods in Aim 1. rMAbs specific for the cytokine of interest will be tested in functional assays described in Aim 1. Although beyond the scope of this proposal, rMAbs will serve as “tool compounds” for future experiments measuring the functional effects of the cytokine and ACA on BBB permeability, mechanisms using in vivo animal models and analyzing cross-reactive microbial epitopes. Mapping rMAb binding sites on autoantigens, including all three IFN-λ isoforms, can also be performed. Our studies will enable characterization of functional AAbs and creation of rMAbs that can be used for mechanistic studies. Our work could provide mechanistic insights into PANS and support use of early immune-modulating interventions (IVIG or B cell-depleting therapies) in a subset of PANS patients with pathogenic ACA.