Background: Multiple sclerosis (MS) may occur before the age of 18. Differentiation between paediatric MS (PedMS) and other demyelinating syndromes (ODSs) is challenging. In adult with MS, the kappa free light chain (KFLC) index has proven to be a reliable marker of intrathecal Ig synthesis. Objective: To assess the diagnostic value of the KFLC index in a cohort of patients with paediatric-onset, inflammatory disorders of the CNS. Methods: We included 73 patients and divided them into four groups: PedMS ( n = 16), ODS ( n = 17), encephalitis and/or inflammatory epilepsy (EE, n = 15), and controls without inflammatory CNS diseases ( n = 25). The KFLC index was calculated and compared with the results of the oligoclonal bands determination. Results: The KFLC index was higher in the PedMS group (median (interquartile range (IQR)): 150.9 (41.02–310.6)) than in the ODS (3.37 (2.22–8.11)), the EE (5.53 (2.31–25.81)) and the control group (3.41 (2.27–5.08)), respectively. The best KFLC index cut-off for differentiating between patients with PedMS and controls was 6.83 (sensitivity: 100%; specificity: 92%). A KFLC index over 93.77 indicated that the patient is very likely to have PedMS (sensitivity: 68%; specificity: 100%). Conclusion: The KFLC index is a reliable tool for the diagnosis of MS in a paediatric population.

Calcineurin inhibitors have improved graft survival in solid-organ transplantation but their use is limited by toxicity, requiring a switch to another immunosuppressor in some cases. Belatacept is one option that has been shown to improve graft and patient survival despite being associated with a higher risk of acute cellular rejection. This risk of acute cellular rejection is correlated with the presence of belatacept-resistant T cells. We performed a transcriptomic analysis of in vitro-activated cells to identify pathways affected by belatacept in belatacept-sensitive cells (CD4⁺CD57⁻) but not in belatacept-resistant CD4⁺CD57⁺ T cells. mTOR was significantly downregulated in belatacept-sensitive but not belatacept-resistant T cells. The inhibition of mTOR strongly decreases the activation and cytotoxicity of CD4⁺CD57⁺ cells. In humans, the use of a combination of mTOR inhibitor and belatacept prevents graft rejection and decreases the expression of activation markers on CD4 and CD8 T cells. mTOR inhibition decreases the functioning of belatacept-resistant CD4⁺CD57⁺ T cells in vitro and in vivo. It could potentially be used in association with belatacept to prevent acute cellular rejection in cases of calcineurin intolerance.

Hematopoiesis is a dynamic, adaptive process that governs blood and immune cell production through coordinated self-renewal, proliferation and differentiation. Shaped by intrinsic cell heterogeneity, environmental cues and physiological demands, it ensures effective blood cell production under both steady-state and stress conditions. Advances in single-cell and lineage-tracing technologies have shifted the traditional hierarchical view of hematopoiesis toward a flexible, interconnected network. B cell development exemplifies this plasticity, involving coordinated genetic and environmental signals to generate diverse subsets. Beyond the classical common lymphoid progenitors (CLP)-dependent model, B cells can also arise through alternative pathways, including direct differentiation from HSCs or at extramedullary sites like the spleen. Environmental signals and niche-specific factors support this diversity. Bipotent progenitors linking B lymphoid and myeloid (macrophage/osteoclast) fates have been identified in both fetal and adult hematopoiesis, revealing overlapping lineage potential and developmental flexibility. Moreover, mature B cells exhibit functional adaptability. B2 cells can convert into B1 cells under certain conditions, while CD11b⁺ myeloid-like B cells (M-B cells) emerge during emergency myelopoiesis, highlighting functional plasticity beyond antibody production. This evolving understanding redefines B cells as versatile immunoregulatory players, especially during inflammation and immune stress and opens new avenues for therapeutic interventions in immunity and hematologic disorders.

Objectives Given that method validation is mandatory for compliance with the International Organization for Standardization (ISO) 15,189 standard requirements, we evaluated the analytical performance of the AQUIOS CL system (Beckman Coulter) and compared it with two bead-based flow cytometry (FCM) protocols (BD FACSCAnto^TM-II and Beckman Coulter DxFLEX). There are no comparative literature data on standardized protocols for counting lymphocyte subsets on the new-generation cytometer DxFLEX. Methods We evaluated the AQUIOS CL’s performance with regard to accuracy, linearity and stability by using dedicated control cell samples and patient samples. We also compared the lymphocyte counts measured on the AQUIOS CL (n=69 samples) with those measured on the BD FACSCAnto^TM-II and DxFLEX FCM systems. For 61 samples, FCM results were compared with those measured on the XN-3000 Sysmex hematology analyzer. Results AQUIOS CL showed acceptable performance – even outside the manufacturer’s quantification ranges- and strong correlations with bead-based FCM methods. The FCM techniques and the XN-3000 gave similar absolute lymphocyte counts, although values in samples with intense lymphocytosis (B cell lymphoma/leukemia) were underestimated. Conclusions The AQUIOS CL flow cytometer is a time-saving, single-platform system with good performance, especially when the manufacturer’s instructions for use are followed. However, AQUIOS CL’s possible limitations and pitfalls impose validation of a bead-based FCM method for immunophenotyping verification or as a back-up system. Although the DxFLEX flow cytometer is more time-consuming to use, it can provide standardized lymphocyte subset counts in case of aberrant results on AQUIOS CL or in the event of equipment failure.

Recombinant human erythropoietin (EPO) is widely used to treat anemia. EPO has immunomodulatory effects extending beyond erythropoiesis, but its impact on lympho-hematopoiesis remains insufficiently explored. The objective of this study was to investigate B lymphopoiesis in the context of hyper-EPOemia-induced stress hematopoiesis. Using an EPO supplementation model in C57BL/6 mice, we found that EPO exerts contrasting effects on early B cell development. EPO supplementation promotes the transition from common lymphoid progenitors (CLPs) to pre-pro-B cells but impairs the pre-pro-B to pro-B transition, in part by downregulating interleukin-7 (IL-7) receptor expression. Remarkably, EPO promotes the emergence of atypical B cell precursors, including M-CSFR/CD115-expressing CLPs and CD11b and CD16/32-expressing pre-pro-B cells. Gene expression profiling revealed that EPO reprograms early B cell precursors, upregulating myeloid-type genes, while downregulating B lymphoid identity genes. In conclusion, our results show that hyper-EPOemia interferes with the earliest stages of B cell development, while promoting the emergence of mixed-lineage "myeloid-like" B cells.