Aplastic anaemia (AA) is an immune-mediated bone marrow failure syndrome characterised by pancytopenia and progressive depletion of hematopoietic stem and progenitor cells.1 The incidence of AA in East Asia is two to three times higher than in Western countries, strongly suggesting that genetic background is a key factor in disease susceptibility.2, 3 The age distribution of AA exhibits peaks in children, young adults, and older adults (aged >60 years). Somatic mutation-driven clonal haematopoiesis, particularly mutations in genes such as DNMT3A, ASXL1 and RUNX1 associated with myelodysplastic syndrome (MDS) and acute myeloid leukaemia (AML), is more frequent in elderly patients and shows regional divergence between Japanese and American cohorts, with its frequency increasing with age.4 In addition, paroxysmal nocturnal haemoglobinuria (PNH) clones, acquired copy number-neutral loss of heterozygosity of the 6p arms (6pLOH), and telomere shortening have also been reported, particularly in elderly patients. In contrast, germline variants associated with inherited bone marrow failure syndromes (IBMFs) have been detected in a subset of young patients, while their exact causal role in disease pathogenesis remains unclear.5 These observations suggest that the pathogenic mechanisms underlying childhood AA may differ fundamentally from those in adults and remain largely unexplored. Existing research has centered the immunopathology of AA on the oligoclonal expansion and aberrant attack of cytotoxic T lymphocytes (CTLs) against hematopoietic stem cells.1 In this process, T helper 17 (Th17) cells play a crucial supportive role in modulating CTLs. By secreting cytokines such as IL-17 and IL-22, they directly stimulate the terminal differentiation of effector memory CD8+ T cells, enhancing their cytotoxic potential, while also suppressing the function and number of regulatory T cells (Tregs) through various mechanisms.6 Consequently, the imbalance between Th17 and Treg cells is widely recognised as a central event driving immune-mediated damage in AA. However, the upstream signals and programs that drive naïve T cells differentiate toward the pathogenic Th17 lineage remain unclear. Accumulating evidence indicates that the differentiation fate of T cells is not determined solely by genetic sequence but is co-regulated by epigenetic programming.7 In haematological malignancies, abnormal hypermethylation of CpG islands in promoter regions often leads to the silencing of tumour suppressor genes and is clearly associated with disease progression and poor prognosis. These findings suggest that epigenetic mechanisms, particularly DNA methylation, may serve as a link between genetic susceptibility, environmental factors, and abnormal T-cell immune responses in AA. Nevertheless, how the DNA methylome is altered in pediatric AA and how it contributes to T cell dysfunction remains a largely unexplored field. Based on the aforementioned knowledge gap, Lai et al.8 recently conducted a multi-omics study in pediatric AA, integrating flow cytometry, genome-wide DNA methylation sequencing, and single-cell RNA sequencing. Their study reaffirmed the central role of Th17/Treg imbalance in pediatric AA within an independent cohort, and shifted focus to the epigenetic drivers underlying this imbalance (Figure 1). The article revealed extensive DNA methylation variability in pediatric AA patients, with pathways enriched among these variable regions being closely related to T cell activation and differentiation. Furthermore, enrichment analysis of related genes pinpointed the JAK/STAT signalling pathway—a pathway crucial for lymphocyte activation, proliferation, and differentiation. Therefore, the study proposes that abnormal methylation states of key regulatory elements within this pathway could lead to dysregulated expression or activity, serving as a key upstream event that disrupts the downstream Th17/Treg balance and drives the immune dysregulation. Furthermore, naïve T cells with high expression of calcium/calmodulin-dependent protein kinase IV (CAMK4) are also significantly increased in the peripheral blood of pediatric AA patients, accounting for 10%–30% of total T cells, approximately 2.2- to 4.1-fold higher than in healthy controls.8, 9 CAMK4 is a key molecular node that integrates intracellular calcium signalling with gene transcription. It possesses a unique dual self-reinforcing mechanism that converts transient calcium pulses into sustained gene expression and protects the protein from ubiquitin-proteasome degradation.10 CAMK4 is regulated by the JAK/STAT signalling pathway, and drives the differentiation of naïve T cells toward Th17 cells via the AKT/mTOR/S6K and AKT-NF-κB signalling pathways, thereby enhancing IL-17 production. Simultaneously, CAMK4 phosphorylates CREMα, which represses IL-2 transcription, a cytokine essential for Treg survival and function—leading to reduced Treg numbers and suppressive capacity. This dual disruption of the Th17/Treg balance has been implicated in various autoimmune diseases. Building upon these discoveries, the study proposes an integrative hypothetical framework: Against a specific genetic background (e.g. susceptibility genes in East Asian populations), an as-yet-unidentified trigger (such as infection or drugs) may induce aberrant epigenetic programming in immune cells, particularly affecting the JAK/STAT signalling pathway in pediatric AA patients. This leads to activation of downstream effectors such as CAMK4, which, through its sustained self-reinforcing and Th17-promoting mechanisms, skews naïve T cells toward a pathogenic Th17 differentiation trajectory while suppressing Treg development. Collectively, these changes reshape the transcriptome of naïve T cells. This coordinated immune deviation may initiate an autoimmune attack against hematopoietic stem cells, ultimately resulting in bone marrow failure. In summary, this research represents an in-depth investigation into the pathogenesis of pediatric AA. It moves beyond merely describing the immune imbalance and attempts to uncover the programming-level error behind it by constructing a logical chain of “epigenetic alteration → signalling pathway abnormality → T-cell functional disorder”. This shift in perspective carries significant translational implications, suggesting that future therapeutic strategies for AA may include epigenetic drugs targeting abnormal DNA methylation or specific inhibitors blocking key signalling nodes like JAK/STAT and CAMK4.7 Such strategies aim to “reprogram” the erroneous immune response at its root, offering novel avenues for achieving precise disease treatment. Certainly, this framework requires future validation through larger-scale prospective studies and functional experiments to identify the most therapeutically valuable molecular targets for children with AA. Not applicable.
Lai et al. (Wed,) studied this question.