Increased percentages of circulating T follicular helper cells associate with disease subtype and activity in pediatric immune cytopenias.

Immune thrombocytopenia (ITP), warm autoimmune hemolytic anemia (wAIHA), and Evans syndrome (ES) have unpredictable disease activity and are sometimes associated with monogenetic disorders and/or extra-hematologic autoimmunity. ITP and immune neutropenia remain diagnoses of exclusion, hindering the diagnosis of ES in patients with multiple cytopenias. As there are no predictors of immunological comorbidities in these patients, it is difficult to determine who would benefit from genetic testing and/or evaluations for extra-hematologic autoimmunity. As circulating CD4+ T follicular helper (cTfh) cells promote autoimmunity, we quantified cTfh cells, associated clinical characteristics, and transcriptional signatures in a cohort of 153 pediatric patients with immune cytopenias (85 with ITP, 26 with wAIHA, and 42 with ES). cTfh cell percentages exceeding 9.5% had 76% sensitivity and 86% specificity for distinguishing ES from ITP or wAIHA, irrespective of disease activity, with a positive predictive value of 0.68 and negative predictive value of 0.91. Increased percentages of cTfh cells were associated with active cytopenia and decreased with treatment in patients with improving cytopenias over time, suggesting the utility of cTfh measurement for clinical monitoring. Increased percentages of cTfh cells were also associated with underlying immune disorders and extra-hematologic autoimmunity, thus identifying patients who would benefit from more extensive immunological evaluation. Single-cell RNA-sequencing of cTfh cells and plasma cytokines revealed increased interferon-α/β and interferon-γ signaling in patients with active wAIHA and ES, respectively. These results not only uncover immunological pathways differentiating subtypes of immune cytopenias, but also demonstrate applications of existing clinical tests in diagnosing immune cytopenias and in identifying patients who require more extensive evaluation for immunological comorbidities.