High proportions of CD4⁺ T cells among residual bone marrow T cells in childhood acute lymphoblastic leukemia are associated with favorable early responses

Contribution of the TIME in BCP-ALL: the basis for novel approaches therapeutics

The bone marrow (BM) niche is a microenvironment where both immune and non-immune cells functionally interact with hematopoietic stem cells (HSC) and more differentiated progenitors, contributing to the regulation of hematopoiesis. It is regulated by various signaling molecules such as cytokines, chemokines, and adhesion molecules in its microenvironment. However, despite the strict regulation of BM signals to maintain their steady state, accumulating evidence in B-cell precursor acute lymphoblastic leukemia (BCP-ALL) indicates that leukemic cells can disrupt the physiological hematopoietic niche in the BM, creating a new leukemia-supportive microenvironment. This environment favors immunological evasion mechanisms and the interaction of these cells with the development and progression of BCP-ALL. With a growing understanding of the tumor immune microenvironment (TIME) in the development and progression of BCP-ALL, current strategies focused on "re-editing" TIME to promote antitumor immunity have been developed. In this review, we summarize how TIME cells are disrupted by the presence of leukemic cells, evading immunosurveillance mechanisms in the BCP-ALL model. We also explore the crosstalk between TIME and leukemic cells that leads to treatment resistance, along with the most promising immuno-therapy strategies. Understanding and further research into the role of the BM microenvironment in leukemia progression and relapse are crucial for developing more effective treatments and reducing patient mortality.

Residual Bone Marrow T & NK-Cells at Diagnosis in Pediatric Pre-B-ALL: A Case-Control Study

Background

Mature bone marrow T lymphocytes and NK may have a special relevance in the control of the malignant growth.

Objective

We aimed to assess the percentage of the residual BM T-cells, (T-helper -T-cytotoxic- NKT) and the NK cells of childhood precursor B-lymphoblastic leukemia (B-ALL) as an indicator of innate and adaptive immunity in these patients.

Subjects and Methods

This study was conducted on 40 B-ALL patients, and 40 apparently healthy matched children served as a control group. The flow cytometry was used to assess the percentage of the residual BM T-cells (T-helper, T-cytotoxic and NKT), and the NK cells.

Results

Compared with the control group, the percentage of the residual BM T-cells, its subtypes (T-helper, T-cytotoxic), and NKT cells in addition to the NK cells was significantly decreased in Group IA, and Group IB, but there was no significant difference between Group IA and Group IB in all studied parameters. In terms of the CD4/CD8 ratio, there was a significant increase in Group IA as compared to the control group (P < 0.026), but there were no significant statistical differences in CD4/CD8 ratio between Groups IB, and the control. Likewise, in CD4/CD8 ratio between groups IA, and Groups IB (P > 0.05). The percentage of NK, and NKT cells shows a significant increase in Hepatomegaly and Splenomegaly, as compared to non-Hepatomegaly and non-Splenomegaly patients of Groups IB (P < 0.05). However, there was a significant increase in statistical differences in the percentage of NKT cell between non-Splenomegaly, as compared to Splenomegaly patients of Group IA (P < 0.05). Additionally, there is a negative correlation between B.M Blast% to CD4/CD8 ratio and NK%, but there is no significant correlation between B.M Blast% to NK T% in the group 1 A.

The Bone Marrow Niche in B-Cell Acute Lymphoblastic Leukemia: The Role of Microenvironment from Pre-Leukemia to Overt Leukemia

Genetic lesions predisposing to pediatric B-cell acute lymphoblastic leukemia (B-ALL) arise in utero, generating a clinically silent pre-leukemic phase. We here reviewed the role of the surrounding bone marrow (BM) microenvironment in the persistence and transformation of pre-leukemic clones into fully leukemic cells. In this context, inflammation has been highlighted as a crucial microenvironmental stimulus able to promote genetic instability, leading to the disease manifestation. Moreover, we focused on the cross-talk between the bulk of leukemic cells with the surrounding microenvironment, which creates a “corrupted” BM malignant niche, unfavorable for healthy hematopoietic precursors. In detail, several cell subsets, including stromal, endothelial cells, osteoblasts and immune cells, composing the peculiar leukemic niche, can actively interact with B-ALL blasts. Through deregulated molecular pathways they are able to influence leukemia development, survival, chemoresistance, migratory and invasive properties. The concept that the pre-leukemic and leukemic cell survival and evolution are strictly dependent both on genetic lesions and on the external signals coming from the microenvironment paves the way to a new idea of dual targeting therapeutic strategy.

T Cell Subsets During Early Life and Their Implication in the Treatment of Childhood Acute Lymphoblastic Leukemia

The immune system plays a major role in recognizing and eliminating malignant cells, and this has been exploited in the development of immunotherapies aimed at either activating or reactivating the anti-tumor activity of a patient's immune system. A wide range of therapeutic approaches involving T lymphocytes, such as programmed cell death protein ligand-1 (PDL-1) inhibitors, cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) blockers, and CD19-targeted T-cell therapy through chimeric antigen receptor (CAR)-T cells or CD19/CD3 bi-specific T-cell engagers, have been introduced to the field of oncology, leading to significant improvements in overall survival of adult cancer patients. During the past few years, the availability and approval of T-cell based immunotherapies have become a reality also for the treatment of childhood cancers. However, the distribution, ratio of regulatory to effector cells and the quality of T-cell responses early in life are distinct from those during adolescence and adulthood, raising the possibility that these differences impact the efficacy of immunotherapy. Herein we provide a brief overview of the properties of conventional T cell subsets during early life. Focusing on the most common cancer type during childhood, acute lymphoblastic leukemia (ALL), we describe how current conventional therapies used against ALL influence the T-cell compartment of small children. We describe early life T-cell responses in relation to immunotherapies engaging T-cell anticancer reactivity and present our opinion that it is not only immaturity of the adaptive immune system, but also the impact of an immunosuppressive environment that may prove disadvantageous in the setting of immunotherapies targeting pediatric cancer cells.

Association of absolute lymphocyte count and peripheral blood lymphocyte subsets percentage with minimal residual disease at the end of induction in pediatric B cell acute lymphoblastic leukemia

Absolute lymphocyte count (ALC) has been associated with overall survival (OS) and event-free survival, but we do not know if ALC is associated with minimal residual disease (MRD) at the end of induction (EOI) and whether it can be used as surrogate marker in resource limited settings. Immunological differences between MRD-positive and MRD-negative B ALL patients at the EOI are not known at present. This prospective study evaluated the association of ALC and peripheral blood lymphocyte subset percentage at the EOI with MRD. ALC was done at baseline, day 8, and day 15 and at EOI. Assessment for MRD and peripheral blood lymphocyte subset was done at EOI. In 2-year study duration, 197 B cell acute lymphoblastic leukemia (ALL) patients were recruited out of which 150 were analyzed. Peripheral lymphocyte subset percentage was available for 58 patients. We found that ALC at baseline, day 8, day 15, and EOI was not associated with MRD. Day 8 ALC was significantly higher in poor steroid responders (day 8 blasts > 1 × 10⁹ cells/l) (p < 0.0001). At the EOI, CD4^-CD8⁺ cell percentage in peripheral blood were significantly higher in MRD-positive patients than MRD-negative patients (p = 0.01). Our study suggests that ALC at any point is not a surrogate marker for MRD. Immunologically MRD-positive and MRD-negative patients differ in CD4^-CD8⁺ cells. The role of CD8⁺T and TCRαβCD3⁺T cells in eliminating residual leukemic cells need to be studied further by functional assays.

CD4+CD25highCD127low/-FoxP3 + Regulatory T-Cell Population in Acute Leukemias: A Review of the Literature

Regulatory T-cells (Tregs) are a very important subtype of lymphocytes when it comes to self-control in the human immunological system. Tregs are decisive not only in the protection against destruction of own tissues by autoimmune immunocompetent cells but also in the immunological answer to developing cancers. On the other hand, Tregs could be responsible for the progression of acute and chronic leukemias. In our study, we review publications available in the PUMED database concerning acute leukemia, with a particular emphasis on child's leukemias. The percentage of regulatory T-lymphocytes in peripheral blood and bone marrow was elevated compared to those in healthy individuals and correlated with progressive disease. Regulatory T-cells taken from children diagnosed with leukemia showed a higher suppressive capability, which was confirmed by detecting elevated levels of secreted IL-10 and TGF-beta. The possibility of pharmacological intervention in the self-control of the immunological system is now under extensive investigation in many human cancers. Presumably, Treg cells could be a vital part of targeted therapies. Routine Treg determination could be used to assess the severity of disease and prognosis in children with acute lymphoblastic leukemia. This proposition results from the fact that in some studies, higher percentage of Treg cells in peripheral blood was demonstrated. However, observations confirming these facts are scarce; thus, extrapolating them to the population of children with hematological malignancies needs to be verified in additional studies.

CD4+CD25highCD127low/-FoxP3+ Regulatory T Cell Subpopulations in the Bone Marrow and Peripheral Blood of Children with ALL: Brief Report

CD4⁺CD25^highCD127^low/-FoxP₃⁺ regulatory T cells (Tregs) are currently under extensive investigation in childhood acute lymphoblastic leukemia (ALL) and in other human cancers. Usually, Treg cells maintain the immune cell homeostasis. This small subset of T cells has been, in fact, considered to be involved in the pathogenesis of autoimmune diseases and progression of acute and chronic leukemias. However, whether Treg dysregulation in CLL and ALL plays a key role or it rather represents a simple epiphenomenon is still a matter of debate. Treg cells have been proposed as a prognostic indicator of the clinical course of the disease and might also be used for targeted immune therapy. Our study revealed statistically higher percentage of Treg cells in the bone marrow than in peripheral blood in the group of 42 children with acute lymphoblastic leukemia. By analyzing Treg subpopulations, it was shown that only memory Tregs in contact with leukemic antigens showed statistically significant differences. We noticed a low negative correlation between Treg cells in the bone marrow and the percentage of blasts (R = -0.36) as well as a moderate correlation between Treg cells in the bone marrow and Hb level (R = +0.41) in peripheral blood before therapy. The number of peripheral blood blasts on day 8th correlates negatively (R = -0.36) with Tregs. Furthermore, statistical analysis revealed low negative correlation between the number of Tregs in the bone marrow and the minimal residual disease measured on day 15th, the percentage of blasts in the bone marrow and leukocytosis after 15 days of chemotherapy. These results indicate the influence of Tregs on the final therapeutic effect.

Absolute lymphocyte counts at end of induction correlate with distinct immune cell compartments in pediatric B cell precursor acute lymphoblastic leukemia

Several retrospective studies in children with B cell precursor (BCP) acute lymphoblastic leukemia (ALL) provided clinical evidence that higher absolute lymphocyte counts (ALC) early into treatment significantly correlated with improved relapse-free and overall survival. It still remains unknown, however, whether the predictive role of higher ALCs reflects general bone marrow recovery or a more specific attribute of immune function. To investigate this question, we implemented a prospective observational cohort study in 20 children with BCP ALL on day 29 (D29) of induction chemotherapy and immunophenotyped their lymphoid (T, B and natural killer cells) and myeloid (neutrophils, monocytes, dendritic cells) compartments. In a first evaluation of a cohort treated with Children's Oncology Group-based induction chemotherapy, the immune cell compartments were differentially depleted at D29. Neither gender, risk status, minimal residual disease, nor bone marrow recovery markers correlated with D29 ALC. In contrast, both CD3+ T cell and dendritic cell compartments, which did not correlate with age, significantly correlated with D29 ALC (p < 0.0001). In addition, subset complexity of cellular immune compartments was preserved at D29. This study reveals that D29 ALC significantly correlates with distinct immune cell compartments but not with bone marrow recovery markers, suggesting that higher D29 ALCs may contribute to leukemia control by inducing specific host immune activity.

Non-tumour bone marrow lymphocytes correlate with improved overall survival in childhood acute lymphoblastic leukaemia

Composition of tumour immune cell infiltrates correlates with response to treatment and overall survival (OS) in several cancer settings. We retrospectively examined immune cells present in diagnostic bone marrow aspirates from paediatric patients with B-cell acute lymphoblastic leukaemia. Our analysis identified a sub-group (∼30% of patients) with >2.37% CD20 and >6.05% CD7 expression, which had 100% OS, and a sub-group (∼30% of patients) with ≤2.37% CD20 and ≤6.05% CD7 expression at increased risk of treatment failure (66.7% OS, P < 0.05). Immune cell infiltrate at diagnosis may predict treatment response and could provide a means to enhance immediate treatment risk stratification.

Developmental exposure to 2,3,7,8 tetrachlorodibenzo-p-dioxin attenuates later-life Notch1-mediated T cell development and leukemogenesis

Over half of T cell acute lymphoblastic leukemia (T-ALL) patients have activating mutations in the Notch gene. Moreover, the contaminant 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) is a known carcinogen that mediates its toxicity through the aryl hydrocarbon receptor (AHR), and crosstalk between activated AHR and Notch signaling pathways has previously been observed. Given the importance of Notch signaling in thymocyte development and T-ALL disease progression, we hypothesized that the activated AHR potentiates disease initiation and progression in an in vivo model of Notch1-induced thymoma. This hypothesis was tested utilizing adult and developmental exposure paradigms to TCDD in mice expressing a constitutively active Notch1 transgene (Notch(ICN-TG)). Following exposure of adult Notch(ICN-TG) mice to a single high dose of TCDD, we observed a significant increase in the efficiency of CD8 thymocyte generation. We next exposed pregnant mice to 3μg/kg of TCDD throughout gestation and lactation to elucidate effects of developmental AHR activation on later-life T cell development and T-ALL-like thymoma susceptibility induced by Notch1. We found that the vehicle-exposed Notch(ICN-TG) offspring have a peripheral T cell pool heavily biased toward the CD4 lineage, while TCDD-exposed Notch(ICN-TG) offspring were biased toward the CD8 lineage. Furthermore, while the vehicle-exposed NotchICN-TG mice showed increased splenomegaly and B to T cell ratios indicative of disease, mice developmentally exposed to TCDD were largely protected from disease. These studies support a model where developmental AHR activation attenuates later-life Notch1-dependent impacts on thymocyte development and disease progression.