Bone marrow T helper cells with a Th1 phenotype induce activation and proliferation of leukemic cells in precursor B acute lymphoblastic leukemia patients

Overexpression of Potential Markers of Regulatory and Exhausted CD8+ T Cells in the Peripheral Blood Mononuclear Cells of Patients with B-Acute Lymphoblastic Leukemia

B-acute lymphoblastic leukemia (B-ALL) is one of the most common pediatric cancers, wherein regulatory T cells (Treg) and exhausted CD8⁺ T cells may be important in its development and maintenance. In this bioinformatics study, we evaluated the expression of 20 Treg/CD8 exhaustion markers and their possible roles in patients with B-ALL. The mRNA expression values of peripheral blood mononuclear cell samples from 25 patients with B-ALL and 93 healthy subjects (HSs) were downloaded from publicly available datasets. Treg/CD8 exhaustion marker expression was normalized with that of the T cell signature and correlated with the expression of Ki-67, regulatory transcription factors (FoxP3, Helios), cytokines (IL-10, TGF-β), CD8⁺ markers (CD8α chain, CD8β chain), and CD8⁺ activation markers (Granzyme B, Granulysin). The mean expression level of 19 Treg/CD8 exhaustion markers was higher in the patients than in the HSs. In patients, the expression of five markers (CD39, CTLA-4, TNFR2, TIGIT, and TIM-3) correlated positively with Ki-67, FoxP3, and IL-10 expression. Moreover, the expression of some of them correlated positively with Helios or TGF-β. Our results suggested that Treg/CD8⁺ T cells expressing CD39, CTLA-4, TNFR2, TIGIT, and TIM-3 favor B-ALL progression, and targeted immunotherapy against these markers could be a promising approach for treating B-ALL.

In Utero Development and Immunosurveillance of B Cell Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is the most frequent type of pediatric cancer with a peak incidence at 2–5 years of age. ALL frequently begins in utero with the emergence of clinically silent, preleukemic cells. Underlying leukemia-predisposing germline and acquired somatic mutations define distinct ALL subtypes that vary dramatically in treatment outcomes. In addition to genetic predisposition, a second hit, which usually occurs postnatally, is required for development of overt leukemia in most ALL subtypes. An untrained, dysregulated immune response, possibly due to an abnormal response to infection, may be an important co-factor triggering the onset of leukemia. Furthermore, the involvement of natural killer (NK) cells and T helper (Th) cells in controlling the preleukemic cells has been discussed. Identifying the cell of origin of the preleukemia-initiating event might give additional insights into potential options for prevention. Modulation of the immune system to achieve prolonged immunosurveillance of the preleukemic clone that eventually dies out in later years might present a future directive. Herein, we review the concepts of prenatal origin as well as potential preventive approaches to pediatric B cell precursor (BCP) ALL.

Alteration of the immune environment in bone marrow from children with recurrent B cell precursor acute lymphoblastic leukemia

Due to the considerable success of cancer immunotherapy for leukemia, the tumor immune environment has become a focus of intense research; however, there are few reports on the dynamics of the tumor immune environment in leukemia. Here, we analyzed the tumor immune environment in pediatric B cell precursor acute lymphoblastic leukemia by analyzing serial bone marrow samples from nine patients with primary and recurrent disease by mass cytometry using 39 immunophenotype markers, and transcriptome analysis. High‐dimensional single‐cell mass cytometry analysis elucidated a dynamic shift of T cells from naïve to effector subsets, and clarified that, during relapse, the tumor immune environment comprised a T helper 1‐polarized immune profile, together with an increased number of effector regulatory T cells. These results were confirmed in a validation cohort using conventional flow cytometry. Furthermore, RNA transcriptome analysis identified the upregulation of immune‐related pathways in B cell precursor acute lymphoblastic leukemia cells during relapse, suggesting interaction with the surrounding environment. In conclusion, a tumor immune environment characterized by a T helper 1‐polarized immune profile, with an increased number of effector regulatory T cells, could contribute to the pathophysiology of recurrent B cell precursor acute lymphoblastic leukemia. This information could contribute to the development of effective immunotherapeutic approaches against B cell precursor acute lymphoblastic leukemia relapse.

Support of BCP-ALL-cells by autologous bone marrow Th-cells involves induction of AID expression but not widespread AID off-target mutagenesis

B-cell precursor acute lymphoblastic leukemia (BCP-ALL) is the most common childhood malignancy. The two-step BCP-ALL pathogenesis requires in utero-induced chromosomal aberrations and additional mutagenic events for overt leukemia. In mouse models, activation-induced cytidine deaminase (AID/AICDA) was suggested to contribute to BCP-ALL pathogenesis by off-target mutagenic activity. The role of AID in patients, however, remains unclear. Moreover, AID is usually not expressed in precursor B-cells but in germinal center B-cells, where it is induced upon T-helper (Th) cell stimulation. We have previously demonstrated that autologous Th-cells supportively interacted with BCP-ALL-cells. Here, we hypothesize that this interaction additionally induces AID expression in BCP-ALL-cells, leading to off-target mutagenic activity. We show that co-culture with autologous bone marrow Th-cells induced high AICDA expression in primary BCP-ALL-cells. This induction was mediated by a mechanism similar to the induction in mature B-cells involving IL-13/Stat6, CD40L/NF-κB and TGFβ/Smad2/3 signaling. Even though Th-cell-induced AID seemed to be active in vitro in a BCP-ALL reporter cell line, extensive mutational signature analysis revealed no major contribution of AID activity to the mutational landscape in BCP-ALL patients. AID activity was neither detected in mutation clusters nor in known AID targets. Moreover, no recurrently mutated gene showed a relevant enrichment of mutations in the AID motif. Together, the lack of AID-induced mutational consequences argues towards a Th-cell-promoted yet AID-independent BCP-ALL pathogenesis and favors therapeutic research focusing on Th-cell-derived support of BCP-ALL-cells rather than AID-induced effects.