Background Lymphocytes play a critical role in immune responses, and changes in their quantity and function are closely related to infection risk. Different chemotherapy regimens may have varying effects on lymphocyte subpopulations, and understanding this is crucial for optimizing treatment protocols and improving patient survival. With the advancement of single-cell RNA sequencing technology, it is now possible to more accurately depict the impact of chemotherapy on the immune system, providing theoretical support for immune recovery and infection control. This study aims to compare the effects of low-dose and standard-dose chemotherapy regimens in the treatment of pediatric AML on lymphocyte subpopulations, and analyze their relationship with infection susceptibility and immune function.

Method We analyzed the clinical data of 400 pediatric AML patients from a single center who received the CALSⅢ-AML-2018 protocol (a randomized, phase III, non-inferiority clinical trial, registration number: ChiCTR1800015883). We compared the adverse events according to CTCAE 5.0 during induction I, as well as the peripheral blood lymphocyte subpopulation counts and proportions on day 26 (time point of bone marrow assessment), between the low-dose (LDC) group (cytarabine, 10 mg/m² and mitoxantrone or idarubicin, concurrently administered with G-CSF, 5 μg/kg) and the standard-dose (SDC) group (cytarabine, 100 mg/m², daunorubicin, and etoposide). We conducted single-cell transcriptome sequencing on bone marrow samples from 12 patients (4 in the LDC group, 8 in the SDC group) on day 26 and compared the differentially expressed genes (DEGs) associated with lymphocytes in the LDC/SDC groups in both infection and non-infection subgroups and analyzed the intersecting genes among these subgroups.

Results There were no statistically significant differences in baseline characteristics between the LDC and SDC groups (P > 0.05). However, during induction I, the infection incidence in the LDC group was lower than that in the SDC group, with notable differences in febrile neutropenia (53.5% vs. 60.5%), lung or sinus infection (21.0% vs. 27.5%), and mucosal infection (8.5% vs. 12.5%). On day 26, the LDC group exhibited significantly higher peripheral blood lymphocyte counts (P = 0.004), CD3+ counts (P = 0.021), CD4+ counts (P = 0.043), CD8+ counts (P = 0.014), B cell counts (P < 0.001), NK cell counts (P = 0.032), and B cell percentages (P < 0.001), compared to the SDC group. The single-cell sequencing results show significant differential gene expression between the LDC group and the SDC group in B cells (990 genes), CD4+ memory T cells (1518 genes), CD8+ memory T cells (1602 genes), native T cells (2100 genes), Pro B cells (102 genes), Pre B cells (2 genes), plasma cells (1674 genes), NK cells (1498 genes), and early lymphoid cells (464 genes), as well as between the infection and non-infection groups. Regardless of infection status, LDC group showed differential gene expression in CD4+ memory T cells (21 genes), CD8+ memory T cells (19 genes), Naive T cells (24 genes), plasma cells (8 genes), and NK cells (21 genes) compared to SDC group. Among the differential intersecting genes in the LDC group (infection vs. non-infection), SDC group (infection vs. non-infection), infection group (LDC vs. SDC), and non-infection group (LDC vs. SDC), the following were observed: upregulated GMPR expression in CD4+ memory T cells, upregulated MPEG1 and JCHAIN expression in CD8+ memory T cells, PTAFR expression in naive T cells, and SLC7A7 expression in NK cells.

ConclusionsCompared to the SDC regimen, the LDC regimen can reduce the incidence of infections during induction remission, which may be attributed to better immune recovery in the LDC group. Infection appears to have a substantial impact on post-chemotherapy immune recovery, with B cells, Pro B cells, and Pre B cells being particularly susceptible to immune suppression. The chemotherapy regimen and infection status have a significant impact on the gene expression of lymphocyte subpopulations, which may be closely related to the regulation of immune responses and susceptibility to infections. In addition, we identified inherent intersecting genes that regulate the recovery of different lymphocyte subpopulations, independent of infection and chemotherapy factors.

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2025
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