Background Elderly acute myeloid leukemia (AML) patients have poorer survival than younger individuals, a difference not fully explained by known genetic or disease factors. Immunosenescence likely contributes to worse therapeutic response and higher relapse. To investigate this, we analyzed scRNA-seq data from 63 bone marrow samples to characterize immune cell senescence in elderly AML and identify potential immunoregulatory targets.

Methods The scRNA-seq data for bone marrow samples consisted of both publicly available datasets and in-house data. Samples were categorized into four groups: young healthy controls (YHC), elderly healthy controls (EHC), young AML patients (YAML), and elderly AML patients (EAML). We first constructed a refined single-cell reference map of healthy controls (HCs). And leukemic cells from AML patients (AMLs) were identified by (1).a random forest model from van Galen et al. (2019), (2).inferCNV; (3).LSC scores. Subsequently, cell types in AMLs were assigned using a reference-based method. We then compared the proportions of cell types, transcription factor activity, and other key features between EAML and the other groups.

Results The proportion of immune cells in AMLs was significantly lower than that in HCs, indicating that the tumor microenvironment restricts immune cell abundance. However, the proportions of T and NK cells increased significantly with age in AMLs, whereas only a very slight increase was observed in HCs. Moreover, B cells showed increased significantly with age in AMLs but only a slight decrease in HCs, and neutrophils decreased significantly with age in AMLs but slightly increased in HCs.

We conducted an in-depth exploration of T cell subtypes in AMLs and HCs. The data revealed a significant increase in CD8+ T cells with age in AMLs (R²=0.29, p=0.002), while the levels remained almost consistent in HCs. Within the CD8+ T cell population, the CD8+ naïveT cells (CD8+ TN) showed a slight decrease with age in AMLs (R²=0.01, p=0.568), but a significant decrease was observed in HCs (R²=0.56, p<0.001). Indicates that the immune system in AMLs struggles to produce more CD8+ T cells. However, FOXO1transcription factor activity is lower in EAML than in YAML, indicating that CD8+ TN cells in EAML may be less able to restrain terminal effector differentiation. For CD8+ cytotoxic T lymphocytes (CD8+ CTL), no significant age-related increase in cell proportion was observed in AMLs, while a significant increase was apparent in HCs (R²=0.17, p=0.04). Strikingly, JUNBactivity, which is essential for cytotoxic T cell activation and antitumor function, was robust in CD8+ CTLs of HCs but markedly decreased in that of AMLs. However, JUNBactivity in CD8+ CTLs of EAML was higher than that in YAML, suggesting that impaired function of CD8+ CTLs is unlikely to be the primary factor contributing to the weakened immune response observed in elderly AML patients.

Moreover, CD8+ terminally differentiated effector memory T cells re-expressing CD45RA (CD8+ TEMRA) significantly increased with age in AMLs (R²=0.39, p<0.001), whereas only a slight increase was observed in HCs. Recent reports have shown that the accumulation of CD8+ TEMRA cells is detrimental to inflammation resistance. Transcription factor analysis revealed that CD8+ TEMRA cells in AMLs exhibited significant upregulation of PRDM1, EOMES, TBX21,and MAFcompared to HCs, suggesting a heightened inflammatory and anti-leukemic response. Notably, the activity of these transcription factors was higher in EAML patients than in YAML, indicating that the capacity for inflammation and tumor cell elimination may be attenuated in the EAML patients. The reduced anti-leukemic potential of CD8+ TEMRA cells in EAML, coupled with their age-associated increase in proportion, may reflect a compensatory mechanism in the aging immune system of EAML patients.

Conclusion Our current result reveals that elderly AML patients show a marked altered in cell abundance of key immune cell types, including impaired naïve and cytotoxic CD8+ T cell responses and the accumulation of less functional CD8+ TEMRA cells. These changes reflect weakened anti-leukemia immunity in the elderly, underscoring the need for further investigation into the immune landscape of elderly AML patients.

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2025
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