Laboratory for Pediatric Immunology, Department of Pediatrics, Leiden University Medical Center, Willem Alexander Children's Hospital, Leiden, Netherlands.
Department of Immunology, Leiden University Medical Center, Leiden, Netherlands.
Front Immunol. 2024 Aug 20;15:1328175. doi: 10.3389/fimmu.2024.1328175. eCollection 2024.
Pediatric patients with unexplained bone marrow failure (BMF) are often categorized as aplastic anemia (AA). Based on the accepted hypothesis of an auto-immune mechanism underlying AA, immune suppressive therapy (IST) might be effective. However, due to the lack of diagnostic tools to identify immune AA and prognostic markers to predict IST response together with the unequaled curative potential of hematopoietic stem cell transplantation (HSCT), most pediatric severe AA patients are momentarily treated by HSCT if available. Although several studies indicate oligoclonal T-cells with cytotoxic activities towards the hematopoietic stem cells, increasing evidence points towards defective inhibitory mechanisms failing to inhibit auto-reactive T-cells.
We aimed to investigate the role of NK- and B-cells in seven pediatric AA patients through a comprehensive analysis of paired bone marrow and peripheral blood samples with spectral flow cytometry in comparison to healthy age-matched bone marrow donors.
We observed a reduced absolute number of NK-cells in peripheral blood of AA patients with a skewed distribution towards CD56 NK-cells in a subgroup of patients. The enriched CD56 NK-cells had a lower expression of CD45RA and TIGIT and a higher expression of CD16, compared to healthy donors. Functional analysis revealed no differences in degranulation. However, IFN-γ production and perforin expression of NK-cells were reduced in the CD56-enriched patient group. The diminished NK-cell function in this subgroup might underly the auto-immunity. Importantly, NK-function of AA patients with reduced CD56 NK-cells was comparable to healthy donors. Also, B-cell counts were lower in AA patients. Subset analysis revealed a trend towards reduction of transitional B-cells in both absolute and relative numbers compared to healthy controls. As these cells were previously hypothesized as regulatory cells in AA, decreased numbers might be involved in defective inhibition of auto-reactive T-cells. Interestingly, even in patients with normal distribution of precursor B-cells, the transitional compartment was reduced, indicating partial differentiation failure from immature to transitional B-cells or a selective loss.
Our findings provide a base for future studies to unravel the role of transitional B-cells and CD56 NK-cells in larger cohorts of pediatric AA patients as diagnostic markers for immune AA and targets for therapeutic interventions.
患有原因不明骨髓衰竭（BMF）的儿科患者通常被归类为再生障碍性贫血（AA）。基于 AA 潜在的自身免疫机制的公认假说，免疫抑制疗法（IST）可能是有效的。然而，由于缺乏用于识别免疫性 AA 的诊断工具和预测 IST 反应的预后标志物，以及造血干细胞移植（HSCT）的无与伦比的治愈潜力，大多数儿科严重 AA 患者如果有 HSCT 可用，通常会立即接受 HSCT 治疗。尽管有几项研究表明具有细胞毒性活性的克隆性 T 细胞针对造血干细胞，但越来越多的证据表明，抑制自身反应性 T 细胞的抑制机制存在缺陷。
我们旨在通过光谱流式细胞术对来自 7 名 AA 患儿的配对骨髓和外周血样本进行全面分析，以研究 NK 细胞和 B 细胞在其中的作用，并与年龄匹配的健康骨髓供者进行比较。
我们观察到 AA 患者外周血中 NK 细胞的绝对数量减少，并且在亚组患者中 CD56 NK 细胞的分布呈偏斜。与健康供者相比，富集的 CD56 NK 细胞的 CD45RA 和 TIGIT 表达较低，而 CD16 表达较高。功能分析显示脱颗粒无差异。然而，在 CD56 富集的患者组中，NK 细胞 IFN-γ的产生和穿孔素的表达减少。在这个亚组中，NK 细胞功能的降低可能是自身免疫的基础。重要的是，AA 患者中 NK 细胞功能的减少与健康供者相比是相当的。此外，AA 患者的 B 细胞计数较低。亚组分析显示，与健康对照组相比，无论是绝对数还是相对数，过渡性 B 细胞的数量都有减少的趋势。由于这些细胞以前被假设为 AA 中的调节细胞，因此数量减少可能与自身反应性 T 细胞的抑制缺陷有关。有趣的是，即使在具有正常前体细胞 B 细胞分布的患者中，过渡细胞群也减少了，表明从未成熟到过渡 B 细胞的分化失败或选择性丢失。
我们的发现为未来的研究提供了基础，以在更大的儿科 AA 患者队列中阐明过渡性 B 细胞和 CD56 NK 细胞的作用，作为免疫性 AA 的诊断标志物和治疗干预的靶点。
