Nadine Varin-Blank

The tumor microenvironment (TME) plays a key role in driving tumor progression, metastasis, and resistance to therapy. The TME is a highly variable ecosystem composed of both cancer and surrounding normal cells, immune survey cells and the extracellular matrix, also composed of signaling molecules that mediate interactions between them. Blood cancer cells pose a unique challenge because of their circulation and widespread distribution along with their capacity to invade various niches, interacting with a wide range of host cells such as fibroblasts, immune cells, endothelial cells, and adipocytes. Metabolism reprogramming in this tumor context, notably referring to elevated cholesterol and fatty acid metabolism, emerges as a crucial event in shaping an immune-suppressive microenvironment that promotes tumor progression. Cholesterol and fatty acids are supplied by both de novo biosynthesis and exogenous uptake from lipoproteins. Lipoproteins are pseudo-micellar structures, designed to transport essential water-insoluble metabolites, including triacylglycerols and cholesterol, in the plasma, lymph, and interstitial fluids. A number of studies have reported abnormal circulating lipoprotein levels in leukemic patients and have suggested that lipoproteins are key for cancer cells to thrive. However, the role of lipoprotein metabolism in cancer cells in the context of the TME is still incompletely discussed so far. The aim of this review is to consider the importance of lipoprotein metabolism in shaping the tumor microenvironment in the context of hematological malignancies.

The bone marrow microenvironment is a dynamic and complex niche that plays a central role in the development, progression, and therapeutic resistance of leukemia. Among the various stromal and immune cells that compose this microenvironment, adipocytes are increasingly recognized as active participants rather than passive bystanders. These cells contribute to leukemia pathophysiology by supplying leukemic cells with vital metabolic fuels such as free fatty acids and glutamine, which support cellular bioenergetics and biosynthesis. Furthermore, adipocytes secrete adipokines—including leptin, adiponectin, and others—that influence leukemic cell proliferation, apoptosis, and chemoresistance. Leukemic cells, in turn, are not merely recipients of these signals, but actively remodel the marrow niche to their advantage. They can suppress adipogenesis, inhibit the differentiation of mesenchymal stem cells into adipocytes, or reprogram existing adipocytes to adopt a tumor-supportive phenotype. These transformed adipocytes may enhance leukemic cell survival, dampen immune responses, and create a metabolic sanctuary that enables resistance to standard chemotherapies. This reciprocal and dynamic interaction between leukemic cells and adipocytes contributes significantly to minimal residual disease and relapse, posing a major challenge for durable remission. Recent advances in tissue engineering—such as organ-on-chip and 3D co-culture systems—offer promising platforms to recapitulate and study these leukemia–adipocyte interactions with high fidelity. These models facilitate mechanistic insights and provide a foundation for developing novel therapeutic strategies aimed at disrupting the metabolic and paracrine crosstalk within the leukemic niche. Targeting the adipocyte–leukemia axis represents a compelling and underexplored avenue for improving leukemia treatment by sensitizing malignant cells to existing therapies and overcoming the protective influence of the bone marrow microenvironment.

In the microenvironment, cell interactions are established between different cell types to regulate their migration, survival and activation. β-Catenin is a multifunctional protein that stabilizes cell–cell interactions and regulates cell survival through its transcriptional activity. We used chronic lymphocytic leukemia (CLL) cells as a cellular model to study the role of β-catenin in regulating the adhesion of tumor cells to their microenvironment, which is necessary for tumor cell survival and accumulation. When co-cultured with a stromal cell line (HS-5), a fraction of the CLL cells adhere to stromal cells in a dynamic fashion regulated by the different levels of β-catenin expression. In non-adherent cells, β-catenin is stabilized in the cytosol and translocates into the nucleus, increasing the expression of cyclin D1. In adherent cells, the level of cytosolic β-catenin is low but membrane β-catenin helps to stabilize the adhesion of CLL to stromal cells. Indeed, the overexpression of β-catenin enhances the interaction of CLL with HS-5 cells, suggesting that this protein behaves as a regulator of cell adhesion to the stromal component and of the transcriptional regulation of cell survival. Inhibitors that block the stabilization of β-catenin alter this equilibrium and effectively disrupt the support that CLL cells receive from the cross-talk with the stroma.

Chronic Lymphocytic Leukemia (CLL) is a heterogeneous B cell neoplasm ranging from indolent to rapidly progressive disease. Leukemic cell subsets with regulatory properties evade immune clearance; however, the contribution of such subsets during CLL progression is not completely elucidated. Here, we report that CLL B cells crosstalk with their immune counterparts, notably by promoting the regulatory T (Treg) cell compartment and shaping several helper T (Th) subsets. Among various constitutively- and BCR/CD40-mediated factors secreted, tumour subsets co-express two important immunoregulatory cytokines, IL10 and TGFβ1, both associated with a memory B cell phenotype. Neutralizing secreted IL10 or inhibiting the TGFβ signalling pathway demonstrated that these cytokines are mainly involved in Th- and Treg differentiation/maintenance. In line with the regulatory subsets, we also demonstrated that a CLL B cell population expresses FOXP3, a marker of regulatory T cells. Analysis of IL10, TGFβ1 and FOXP3 positive subpopulations frequencies in CLL samples discriminated 2 clusters of untreated CLL patients that were significantly different in Tregs frequency and time-to-treatment. Since this distinction was pertinent to disease progression, the regulatory profiling provides a new rationale for patient stratification and sheds light on immune dysfunction in CLL.

Tumor microenvironment exerts a critical role in sustaining homing, retention, and survival of chronic lymphocytic leukemia (CLL) cells in secondary lymphoid organs. Such conditions foster immune surveillance escape and resistance to therapies. The physiological microenvironment is rendered tumor permissive by an interplay of chemokines, chemokine receptors, and adhesion molecules as well as by direct interactions between malignant lymphocytes and stromal cells, T cells, and specialized macrophages referred to as nurselike cells (NLCs). To characterize this complex interplay, we investigated the altered architecture on CLL lymph nodes biopsies and observed a dramatic loss of tissue subcompartments and stromal cell networks as compared with nonmalignant lymph nodes. A supplemental high density of CD68+ cells expressing the homeostatic chemokine CCL21 was randomly distributed. Using an imaging flow cytometry approach, CCL21 mRNA and the corresponding protein were observed in single CD68+ NLCs differentiated in vitro from CLL peripheral blood mononuclear cells. The chemokine was sequestered at the NLC membrane, helping capture of CCR7-high-expressing CLL B cells. Inhibiting the CCL21/CCR7 interaction by blocking antibodies or using therapeutic ibrutinib altered the adhesion of leukemic cells. Our results indicate NLCs as providers of an alternative source of CCL21, taking over the physiological task of follicular reticular cells, whose network is deeply altered in CLL lymph nodes. By retaining malignant B cells, CCL21 provides a protective environment for their niching and survival, thus allowing tumor evasion and resistance to treatment. These findings argue for a specific targeting or reeducation of NLCs as a new immunotherapy strategy for this disease.

B-cell receptor (BCR) signaling pathways and interactions with the tumor microenvironment account for mantle cell lymphoma (MCL) cells survival in lymphoid organs. In several MCL cases, the WNT/β-catenin canonical pathway is activated and β–catenin accumulates into the nucleus. As both BCR and β-catenin are important mediators of cell survival and interaction with the microenvironment, we investigated the crosstalk between BCR and WNT/β-catenin signaling and analyzed their impact on cellular homeostasis as well as their targeting by specific inhibitors. β-catenin was detected in all leukemic MCL samples and its level of expression rapidly increased upon BCR stimulation. This stabilization was hampered by the BCR-pathway inhibitor Ibrutinib, supporting β-catenin as an effector of the BCR signaling. In parallel, MCL cells as compared with normal B cells expressed elevated levels of WNT16, a NF-κB target gene. Its expression increased further upon BCR stimulation to participate to the stabilization of β-catenin. Upon BCR stimulation, β-catenin translocated into the nucleus but did not induce a Wnt-like transcriptional response, i.e., TCF/LEF dependent. β-catenin rather participated to the regulation of NF-κB transcriptional targets, such as IL6, IL8, and IL1. Oligo pull down and chromatin immunoprecipitation experiments demonstrated that β-catenin is part of a protein complex that binds the NF-κB DNA consensus sequence, strengthening the idea of an association between the two proteins. An inhibitor targeting β-catenin transcriptional interactions hindered both NF-κB DNA recruitment and induced primary MCL cells apoptosis. Thus, β-catenin likely represents another player through which BCR signaling impacts on MCL cell survival.

Endoplasmic reticulum (ER) calcium storage and release play important roles in B lymphocyte maturation, survival, antigen-dependent cell activation and immunoglobulin synthesis. Calcium is accumulated in the endoplasmic reticulum (ER) by Sarco/Endoplasmic Reticulum Calcium ATPases (SERCA enzymes). Because lymphocyte function is critically dependent on SERCA activity, it is important to understand qualitative and quantitative changes of SERCA protein expression that occur during B lymphoid differentiation and leukemogenesis. In this work we investigated the modulation of SERCA expression during the pharmacologically induced differentiation of leukemic precursor B lymphoblast cell lines that carry the E2A-PBX1 fusion oncoprotein. Changes of SERCA levels during differentiation were determined and compared to those of established early B lymphoid differentiation markers. SERCA expression of the cells was compared to that of mature B cell lines as well, and the effect of the direct inhibition of SERCA-dependent calcium transport on the differentiation process was investigated. We show that E2A-PBX1+ leukemia cells simultaneously express SERCA2 and SERCA3-type calcium pumps; however, their SERCA3 expression is markedly inferior to that of mature B cells. Activation of protein kinase C enzymes by phorbol ester leads to phenotypic differentiation of the cells, and this is accompanied by the induction of SERCA3 expression. Direct pharmacological inhibition of SERCA-dependent calcium transport during phorbol ester treatment interferes with the differentiation process. These data show that the calcium pump composition of the ER is concurrent with increased SERCA3 expression during the differentiation of precursor B acute lymphoblastic leukemia cells, that a cross-talk exists between SERCA function and the control of differentiation, and that SERCA3 may constitute an interesting new marker for the study of early B cell phenotype.

Objective: To study the role of B lymphocytes in systemic sclerosis (SSc).Methods: Peripheral B cell subpopulations and the production of interleukin‐6 (IL‐6) and transforming growth factor β (TGFβ) were analyzed using flow cytometry and multiplex assay. The fibroblast proliferation rate upon incubation with supernatants from B cells isolated from SSc patients or healthy controls was assessed using XTT, bromodeoxyuridine, and Ki‐67. Collagen production was assessed using a collagen assay.Results: Ninety untreated patients (12 males) fulfilling the American College of Rheumatology/European League Against Rheumatism criteria for SSc (23 with diffuse cutaneous SSc [dcSSc] and 67 with limited cutaneous SSc [lcSSc]) and 30 healthy controls were recruited. Increased proportions of B cells expressing CD69 and CD95 were identified among the patients with SSc. B lymphocytes from dcSSc patients versus lcSSc patients and healthy controls expressed increased proportion of cells positive for CD5 (mean ± SD 24.12 ± 7.93% versus 14.09 ± 6.58% [P = 0.03] and 14.21 ± 5.34% [P = 0.01]), CD86 (39.89 ± 22.11% versus 17.72 ± 13.98% [P = 0.0007] and 11.68 ± 11.09% [P < 0.001]), IL‐6 receptor (IL‐6R; 33.64 ± 23.12% versus 17.91 ± 13.62% [P < 0.0001] and 12.08 ± 8.68% [P = 0.0009]), or IL‐21R (32.55 ± 20.19% versus 5.76 ± 4.40% [P < 0.0001] and 5.93 ± 3.29% [P < 0.0001]). In addition, the levels of IL‐6 (mean ± SD 314.3 ± 317.8 pg/ml versus 6.10 ± 2.58 pg/ml; P = 0.0007) and TGFβ (mean ± SD 1,020 ± 569 pg/ml versus 163.8 ± 98.69 pg/ml; P = 0.001) secreted by B lymphocytes from patients with SSc were increased compared to healthy controls. Fibroblast proliferation and collagen production were also significantly increased in the presence of B cell supernatant from SSc patients as compared to healthy controls.Conclusion: The numbers of activated B cells were increased in SSc patients, and the up‐regulation of CD5, CD86, IL‐6R, and IL‐21R discriminated between patients with dcSSc and those with lcSSc. Peripheral B lymphocytes from SSc patients secreted both IL‐6 and TGFβ, and they activated fibroblasts in vitro.