Delayed B-cell maturation with extra-follicular B-cell response and broad autoantibody repertoire are characteristic B-cell dysregulation signatures in patients with multi-lineage cytopenia

Abstract

IntroductionMulti-lineage cytopenia (m-IC) are increasingly recognized as presenting manifestation of inborn errors immunity (IEI). Although around 40% of these patients are associated with known IEI, the underlying immune anomalies at onset of m-IC are poorly understood. Recently, we published a unique immune signature characterized by abnormal expansion of circulating T-follicular helper cells (cTfh), increased T-cell activation and decreased naïve CD4+ T (Kumar et.al Blood 2022). Despite our improved understanding of T-cell immune abnormalities, the underlying B-cell dysfunction is largely undefined at onset of m-IC. MethodsIn this study, we enrolled 20 patients with pES, 30 patients with chronic ITP (cITP) and 18 healthy controls (HCs). High dimensional B cell immunophenotyping was performed to assess B-cell maturation, extrafollicular B cell development, and autoreactivity. Autoantibody profiling was performed using human protein microarrays. Multiplex immunofluorescence staining of lymph nodes was performed to evaluate germinal center reaction. ResultsWe observed that patients with m-IC had increased frequency of CD10+ immature B cells in comparison to cITP and HCs. Despite an expansion of cTfh and elevated levels of plasma CXCL13, we observed decreased frequency of CSMB which suggests underlying defects in B-cell maturation. While canonical B-cell maturation was defective, we noticed aberrant extrafollicular B-cell development characterized by significantly higher proportion of DN2 (CD11c+CD21low) and decreased proportion of DN1 (CD21+ CD11c-) populations (Figure 1A). However, the frequency of parent population i.e., double negative (DN) (IgD- CD27-) B-cells was similar across the cohorts. In addition, we also noted decreased proportion of CXCR5+ B cells in 30% of patients and overall skewed CXCR5 expression on B versus T cells. Furthermore, we noted increase in autoreactivity in B cells as evident by increase in proportion of 9G4+ B cells. To further assess auto-antibody driven pathophysiology, we evaluated the auto-antibody repertoire and found broad auto-antibody repertoire targeting several biological processes (Figure 1B). [Display omitted] ConclusionsTaken together, our findings identified broad B-cell immune abnormalities along with unique auto-antibody repertoire in patients with m-IC. In addition to enhancing our current knowledge of disease pathology, the utility of these findings could further help in disease monitoring and evaluating response to the therapeutics.