Chronic lymphocytic leukemia cells in a lymph node microenvironment depict molecular signature associated with an aggressive disease

Stromal cells engineered to express T cell factors induce robust CLL cell proliferation in vitro and in PDX co-transplantations allowing the identification of RAF inhibitors as anti-proliferative drugs

Several in vitro models have been developed to mimic chronic lymphocytic leukemia (CLL) proliferation in immune niches; however, they typically do not induce robust proliferation. We prepared a novel model based on mimicking T-cell signals in vitro and in patient-derived xenografts (PDXs). Six supportive cell lines were prepared by engineering HS5 stromal cells with stable expression of human CD40L, IL4, IL21, and their combinations. Co-culture with HS5 expressing CD40L and IL4 in combination led to mild CLL cell proliferation (median 7% at day 7), while the HS5 expressing CD40L, IL4, and IL21 led to unprecedented proliferation rate (median 44%). The co-cultures mimicked the gene expression fingerprint of lymph node CLL cells (MYC, NFκB, and E2F signatures) and revealed novel vulnerabilities in CLL-T-cell-induced proliferation. Drug testing in co-cultures revealed for the first time that pan-RAF inhibitors fully block CLL proliferation. The co-culture model can be downscaled to five microliter volume for large drug screening purposes or upscaled to CLL PDXs by HS5-CD40L-IL4 ± IL21 co-transplantation. Co-transplanting NSG mice with purified CLL cells and HS5-CD40L-IL4 or HS5-CD40L-IL4-IL21 cells on collagen-based scaffold led to 47% or 82% engraftment efficacy, respectively, with ~20% of PDXs being clonally related to CLL, potentially overcoming the need to co-transplant autologous T-cells in PDXs.

Role of the tumor microenvironment in CLL pathogenesis

Chronic lymphocytic leukemia (CLL) cells extensively interact with and depend on their surrounding tumor microenvironment (TME). The TME encompasses a heterogeneous array of cell types, soluble signals, and extracellular vesicles, which contribute significantly to CLL pathogenesis. CLL cells and the TME cooperatively generate a chronic inflammatory milieu, which reciprocally reprograms the TME and activates a signaling network within CLL cells, promoting their survival and proliferation. Additionally, the inflammatory milieu exerts chemotactic effects, attracting CLL cells and other immune cells to the lymphoid tissues. The intricate CLL-TME interactions also facilitate immune evasion and compromise leukemic cell surveillance. We also review recent advances that have shed light on additional aspects that are substantially influenced by the CLL-TME interplay.

Novel Spirocyclic Dimer, SpiD3, Targets Chronic Lymphocytic Leukemia Survival Pathways with Potent Preclinical Effects

Chronic lymphocytic leukemia (CLL) cell survival and growth is fueled by the induction of B-cell receptor (BCR) signaling within the tumor microenvironment (TME) driving activation of NFκB signaling and the unfolded protein response (UPR). Malignant cells have higher basal levels of UPR posing a unique therapeutic window to combat CLL cell growth using pharmacologic agents that induce accumulation of misfolded proteins. Frontline CLL therapeutics that directly target BCR signaling such as Bruton tyrosine kinase (BTK) inhibitors (e.g., ibrutinib) have enhanced patient survival. However, resistance mechanisms wherein tumor cells bypass BTK inhibition through acquired BTK mutations, and/or activation of alternative survival mechanisms have rendered ibrutinib ineffective, imposing the need for novel therapeutics. We evaluated SpiD3, a novel spirocyclic dimer, in CLL cell lines, patient-derived CLL samples, ibrutinib-resistant CLL cells, and in the Eµ-TCL1 mouse model. Our integrated multi-omics and functional analyses revealed BCR signaling, NFκB signaling, and endoplasmic reticulum stress among the top pathways modulated by SpiD3. This was accompanied by marked upregulation of the UPR and inhibition of global protein synthesis in CLL cell lines and patient-derived CLL cells. In ibrutinib-resistant CLL cells, SpiD3 retained its antileukemic effects, mirrored in reduced activation of key proliferative pathways (e.g., PRAS, ERK, MYC). Translationally, we observed reduced tumor burden in SpiD3-treated Eµ-TCL1 mice. Our findings reveal that SpiD3 exploits critical vulnerabilities in CLL cells including NFκB signaling and the UPR, culminating in profound antitumor properties independent of TME stimuli.

SIGNIFICANCE

SpiD3 demonstrates cytotoxicity in CLL partially through inhibition of NFκB signaling independent of tumor-supportive stimuli. By inducing the accumulation of unfolded proteins, SpiD3 activates the UPR and hinders protein synthesis in CLL cells. Overall, SpiD3 exploits critical CLL vulnerabilities (i.e., the NFκB pathway and UPR) highlighting its use in drug-resistant CLL.

Factors associated with long-term outcomes of CD19 CAR T-cell therapy for relapsed/refractory CLL

High response rates have been reported after CD19-targeted chimeric antigen receptor-modified (CD19 CAR) T-cell therapy for relapsed/refractory (R/R) chronic lymphocytic leukemia (CLL), yet the factors associated with duration of response in this setting are poorly characterized. We analyzed long-term outcomes in 47 patients with R/R CLL and/or Richter transformation treated on our phase 1/2 clinical trial of CD19 CAR T-cell therapy with an updated median follow-up of 79.6 months. Median progression-free survival (PFS) was 8.9 months, and the 6-year PFS was 17.8%. Maximum standardized uptake value (hazard ratio [HR], 1.15; 95% confidence interval [CI], 1.07-1.23; P < .001) and bulky disease (≥5 cm; HR, 2.12; 95% CI, 1.06-4.26; P = .034) before lymphodepletion were associated with shorter PFS. Day +28 complete response by positron emission tomography-computed tomography (HR, 0.13; 95% CI, 0.04-0.40; P < .001), day +28 measurable residual disease (MRD) negativity by multiparameter flow cytometry (HR, 0.08; 95% CI, 0.03-0.22; P < .001), day +28 MRD negativity by next-generation sequencing (HR, 0.21; 95% CI, 0.08-0.51; P < .001), higher peak CD8+ CAR T-cell expansion (HR, 0.49; 95% CI; 0.36-0.68; P < .001), higher peak CD4+ CAR T-cell expansion (HR, 0.47; 95% CI; 0.33-0.69; P < .001), and longer CAR T-cell persistence (HR, 0.56; 95% CI, 0.44-0.72; P < .001) were associated with longer PFS. The 6-year duration of response and overall survival were 26.4% and 31.2%, respectively. CD19 CAR T-cell therapy achieved durable responses with curative potential in a subset of patients with R/R CLL. This trial was registered at www.clinicaltrials.gov as #NCT01865617.

MALAT1 expression is associated with aggressive behavior in indolent B-cell neoplasms

MALAT1 long non-coding RNA has oncogenic roles but has been poorly studied in indolent B-cell neoplasms. Here, MALAT1 expression was analyzed using RNA-seq, microarrays or qRT-PCR in primary samples from clinico-biological subtypes of chronic lymphocytic leukemia (CLL, n = 266), paired Richter transformation (RT, n = 6) and follicular lymphoma (FL, n = 61). In peripheral blood (PB) CLL samples, high MALAT1 expression was associated with a significantly shorter time to treatment independently from other known prognostic factors. Coding genes expressed in association with MALAT1 in CLL were predominantly related to oncogenic pathways stimulated in the lymph node (LN) microenvironment. In RT paired samples, MALAT1 levels were lower, concordant with their acquired increased independency of external signals. Moreover, MALAT1 levels in paired PB/LN CLLs were similar, suggesting that the prognostic value of MALAT1 expression in PB is mirroring expression differences already present in LN. Similarly, high MALAT1 expression in FL predicted for a shorter progression-free survival, in association with expression pathways promoting FL pathogenesis. In summary, MALAT1 expression is related to pathophysiology and more aggressive clinical behavior of indolent B-cell neoplasms. Particularly in CLL, its levels could be a surrogate marker of the microenvironment stimulation and may contribute to refine the clinical management of these patients.

PP2A modulation overcomes multidrug resistance in chronic lymphocytic leukemia via mPTP-dependent apoptosis

Targeted therapies such as venetoclax (VEN) (Bcl-2 inhibitor) have revolutionized the treatment of chronic lymphocytic leukemia (CLL). We previously reported that persister CLL cells in treated patients overexpress multiple antiapoptotic proteins and display resistance to proapoptotic agents. Here, we demonstrated that multidrug-resistant CLL cells in vivo exhibited apoptosis restriction at a pre-mitochondrial level due to insufficient activation of the Bax and Bak (Bax/Bak) proteins. Co-immunoprecipitation analyses with selective BH domain antagonists revealed that the pleiotropic proapoptotic protein (Bim) was prevented from activating Bax/Bak by "switching" interactions to other upregulated antiapoptotic proteins (Mcl-1, Bcl-xL, Bcl-2). Hence, treatments that bypass Bax/Bak restriction are required to deplete these resistant cells in patients. Protein phosphatase 2A (PP2A) contributes to oncogenesis and treatment resistance. We observed that small-molecule activator of PP2A (SMAP) induced cytotoxicity in multiple cancer cell lines and CLL samples, including multidrug-resistant leukemia and lymphoma cells. The SMAP (DT-061) activated apoptosis in multidrug-resistant CLL cells through induction of mitochondrial permeability transition pores, independent of Bax/Bak. DT-061 inhibited the growth of wild-type and Bax/Bak double-knockout, multidrug-resistant CLL cells in a xenograft mouse model. Collectively, we discovered multidrug-resistant CLL cells in patients and validated a pharmacologically tractable pathway to deplete this reservoir.

Enhanced Costimulatory Signaling Improves CAR T-cell Effector Responses in CLL

CD19-redirected chimeric antigen receptor (CAR) T cells have shown remarkable activity against B-cell cancers. While second-generation CARs induce complete remission in >80% of patients with acute lymphoblastic leukemia, similar monotherapy induces long-term remissions in only 26% of patients with chronic lymphocytic leukemia (CLL). This disparity is attributed to cell-intrinsic effector defects in autologous CLL-derived T cells. However, the mechanisms by which leukemic cells impact CAR T-cell potency are poorly understood. Herein we describe an in vitro assay that recapitulates endogenous CLL-mediated T-cell defects in healthy donor CAR T cells. Contact with CLL cells insufficiently activates, but does not irreversibly impair, CAR T-cell function. This state is rescuable by strong antigenic stimulation or IL2, and is not driven by immune suppression. Rather, this activation defect is attributable to low levels of costimulatory molecules on CLL cells, and exogenous costimulation enhanced CAR T-cell activation. We next assessed the stimulatory phenotype of CLL cells derived from different niches within the same patient. Lymph node (LN)-derived CLL cells had a strong costimulatory phenotype and promoted better CAR T-cell degranulation and cytokine production than matched peripheral blood CLL cells. Finally, in vitro CD40L-activated CLL cells acquired a costimulatory phenotype similar to the LN-derived tumor and stimulated improved CAR T-cell proliferation, cytokine production, and cytotoxicity. Together, these data identify insufficient activation as a driver of poor CAR T-cell responses in CLL. The costimulatory phenotype of CLL cells drives differential CAR T-cell responses, and can be augmented by improving costimulatory signaling.

Significance

CLL cells insufficiently activate CAR T cells, driven by low levels of costimulatory molecules on the tumor. LN-derived CLL cells are more costimulatory and mediate enhanced CAR T-cell killing. This costimulatory phenotype can be modeled via CD40 L activation, and the activated tumor promotes stronger CAR T-cell responses.

Drug-microenvironment perturbations reveal resistance mechanisms and prognostic subgroups in CLL

The tumour microenvironment and genetic alterations collectively influence drug efficacy in cancer, but current evidence is limited and systematic analyses are lacking. Using chronic lymphocytic leukaemia (CLL) as a model disease, we investigated the influence of 17 microenvironmental stimuli on 12 drugs in 192 genetically characterised patient samples. Based on microenvironmental response, we identified four subgroups with distinct clinical outcomes beyond known prognostic markers. Response to multiple microenvironmental stimuli was amplified in trisomy 12 samples. Trisomy 12 was associated with a distinct epigenetic signature. Bromodomain inhibition reversed this epigenetic profile and could be used to target microenvironmental signalling in trisomy 12 CLL. We quantified the impact of microenvironmental stimuli on drug response and their dependence on genetic alterations, identifying interleukin 4 (IL4) and Toll-like receptor (TLR) stimulation as the strongest actuators of drug resistance. IL4 and TLR signalling activity was increased in CLL-infiltrated lymph nodes compared with healthy samples. High IL4 activity correlated with faster disease progression. The publicly available dataset can facilitate the investigation of cell-extrinsic mechanisms of drug resistance and disease progression.

A Ferroptosis Molecular Subtype-Related Signature for Predicting Prognosis and Response to Chemotherapy in Patients with Chronic Lymphocytic Leukemia

Ferroptosis is a type of regulated cell death catalyzed by the iron-dependent accumulation of lipid hydroperoxides to lethal levels. Chronic lymphocytic leukemia (CLL) is a chronic lymphoproliferative disorder. However, the understanding of ferroptosis in CLL remains largely poor. In this study, we investigated the stratification and prognostic role of ferroptosis-related genes in CLL patients of ICGC cohort. We obtained fourteen genes with prognostic value by screening 110 ferroptosis-related genes (FRGs). Based on the expression profiles of these 14 genes, we classified CLL patients into two clusters. Most of the FRGs were highly expressed in cluster 1, and cluster 1 was associated with better overall survival (OS). Subsequently, we developed an eight-gene signature (TP63, STEAP3, NQO1, ELAVL1, PRKAA1, HELLS, FANCD2, and CDKN2A) by using LASSO analysis. This risk signature divided CLL patients into high- and low-risk groups. We used Cox regression analysis and ROC analysis demonstrated the risk signature was reliable and robust. And we validated the risk model in an external cohort (GSE22762). We also conducted enrichment analysis and genomic mutation analysis. Finally, we explored the potential effect of chemotherapy between the two risk groups. Our study contributed to understanding the role of ferroptosis in CLL and facilitated personalized and precision treatment.

Elastin MIcrofibriL INterfacer1 (EMILIN-1) is an alternative prosurvival VLA-4 ligand in chronic lymphocytic leukemia

CD49d, the α4 chain of the VLA-4 integrin, is a negative prognosticator in chronic lymphocytic leukemia (CLL) with a key role in CLL cell-microenvironment interactions mainly occurring via its ligands VCAM-1 and fibronectin. In the present study, we focused on EMILIN-1 (Elastin-MIcrofibriL-INterfacer-1), an alternative VLA-4 ligand whose role has been so far reported only in non-hematological settings, by investigating: i) the distribution of EMILIN-1 in CLL-involved tissues; ii) the capability of EMILIN-1 to operate, via its globular C1q (gC1q) domain, as additional adhesion ligand in CLL; iii) the functional meaning of EMILIN-1 gC1q/VLA-4 interactions in CLL. EMILIN-1 is widely present in the CLL-involved areas of bone marrow biopsies (BMBs) without difference between CD49d negative and positive cases, displaying at least three different expression patterns: "fibrillar", "dot-like" and "mixed". The lack in CLL-BMB of neutrophil elastase, whose proteolytic activity degrades EMILIN-1 and impairs EMILIN-1 function, suggests full functional EMILIN-1 in CLL independently of its expression pattern. Functionally, EMILIN-1 gC1q domain promotes adhesion of CLL cells through specific interaction with VLA-4, and releases pro-survival signals for CLL cells, as demonstrated by enhanced ERK and AKT phosphorylation and impairment of in-vitro-induced apoptosis. EMILIN-1/VLA-4 interaction can efficiently contribute to the maintenance of the neoplastic clone in CLL.

Extrinsic interactions in the microenvironment in vivo activate an antiapoptotic multidrug-resistant phenotype in CLL

The Bcl-2 inhibitor venetoclax has yielded exceptional clinical responses in chronic lymphocytic leukemia (CLL). However, de novo resistance can result in failure to achieve negative minimal residual disease and predicts poor treatment outcomes. Consequently, additional proapoptotic drugs, such as inhibitors of Mcl-1 and Bcl-xL, are in development. By profiling antiapoptotic proteins using flow cytometry, we find that leukemic B cells that recently emigrated from the lymph node (CD69+/CXCR4Low) in vivo are enriched for cell clusters simultaneously overexpressing multiple antiapoptotic proteins (Mcl-1High/Bcl-xLHigh/Bcl-2High) in both treated and treatment-naive CLL patients. These cells exhibited antiapoptotic resistance to multiple BH-domain antagonists, including inhibitors of Bcl-2, Mcl-1, and Bcl-xL, when tested as single agents in a flow cytometry-based functional assay. Antiapoptotic multidrug resistance declines ex vivo, consistent with resistance being generated in vivo by extrinsic microenvironmental interactions. Surviving "persister" cells in patients undergoing venetoclax treatment are enriched for CLL cells displaying the functional and molecular properties of microenvironmentally induced multidrug resistance. Overcoming this resistance required simultaneous inhibition of multiple antiapoptotic proteins, with potential for unwanted toxicities. Using a drug screen performed using patient peripheral blood mononuclear cells cultured in an ex vivo microenvironment model, we identify novel venetoclax drug combinations that induce selective cytotoxicity in multidrug-resistant CLL cells. Thus, we demonstrate that antiapoptotic multidrug-resistant CLL cells exist in patients de novo and show that these cells persist during proapoptotic treatment, such as venetoclax. We validate clinically actionable approaches to selectively deplete this reservoir in patients.

A Tissue Counterpart to Monoclonal B-Cell Lymphocytosis

CONTEXT.—

B-cell clones discovered in tissue biopsies, without overt lymphoma, may represent a tissue counterpart to peripheral blood monoclonal B-cell lymphocytosis (MBL), herein termed tMBL.

OBJECTIVE.—

To characterize the clinicopathologic features of tMBL.

DESIGN.—

During a 10-year period, we retrospectively identified non-bone marrow/peripheral blood cases with monotypic B cells detected by tissue-based flow cytometry, but without an identifiable lymphomatous infiltrate on routine histopathology. We excluded cases with prior diagnosis of chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma or MBL.

RESULTS.—

Fifty-four cases were identified (35 lymph node, 3 splenic, and 16 soft tissue/viscera). Forty-six cases were CLL-type, 2 were atypical CLL, and 6 were non-CLL. tMBL was detectable by immunohistochemistry in 14 cases (26%, all CLL-type). Concurrent blood flow cytometry, available in 10 cases, showed 4 with low-count MBL (3 CLL-type, 1 with non-CLL-type), 5 with high-count MBL (all CLL-type), and 1 case negative for clonal population. With median follow-up of 51 months, 2 patients had progression of disease (CLL, 68.7 months; and diffuse large B-cell lymphoma, 5.9 months). Patients with IHC-detectable tMBL had increased monoclonal B cells per total lymphocyte events (P = .01), morphologic evidence of bone marrow involvement (P = .04), higher white blood cell count (P = .02), and increased absolute lymphocyte count (P = .02).

CONCLUSIONS.—

tMBL spans an immunophenotypic spectrum similar to MBL, is detectable by immunohistochemistry in a minority of cases (often CLL immunophenotype), and is likely systemic in most cases. Development of overt lymphoma is uncommon but may occur, warranting clinical follow-up.

Constitutive activation of Lyn kinase enhances BCR responsiveness, but not the development of CLL in Eµ-TCL1 mice

The treatment of chronic lymphocytic leukemia (CLL) has been improved dramatically by inhibitors targeting B-cell receptor (BCR)-associated kinases. The tyrosine kinase Lyn is a key modulator of BCR signaling and shows increased expression and activity in CLL. To evaluate the functional relevance of Lyn for CLL, we generated a conditional knockin mouse model harboring a gain-of-function mutation of the Lyn gene (LynY508F), which was specifically expressed in the B-cell lineage (Lynup-B). Kinase activity profiling revealed an enhanced responsiveness to BCR stimulation in Lynup-B B cells. When crossing Lynup-B mice with Eµ-TCL1 mice (TCL1tg/wt), a transgenic mouse model for CLL, the resulting TCL1tg/wt Lynup-B mice showed no significant change of hepatomegaly, splenomegaly, bone marrow infiltration, or overall survival when compared with TCL1tg/wt mice. Our data also suggested that TCL1 expression has partially masked the effect of the Lynup-B mutation, because the BCR response was only slightly increased in TCL1tg/wt Lynup-B compared with TCL1tg/wt. In contrast, TCL1tg/wt Lynup-B were protected at various degrees against spontaneous apoptosis in vitro and upon treatment with kinase inhibitors targeting the BCR. Collectively, and consistent with our previous data in a Lyn-deficient CLL model, these data lend further suggest that an increased activation of Lyn kinase in B cells does not appear to be a major driver of leukemia progression and the level of increased BCR responsiveness induced by Lynup-B is insufficient to induce clear changes to CLL pathogenesis in vivo.

Modeling the Leukemia Microenviroment In Vitro

Over the last decade, the active role of the microenvironment in the pathogenesis, development and drug resistance of B cell malignancies has been clearly established. It is known that the tissue microenvironment promotes proliferation and drug resistance of leukemic cells suggesting that successful treatments of B cell malignancies must target the leukemic cells within these compartments. However, the cross-talk occurring between cancer cells and the tissue microenvironment still needs to be fully elucidated. In solid tumors, this lack of knowledge has led to the development of new and more complex in vitro models able to successfully mimic the in vivo settings, while only a few simplified models are available for haematological cancers, commonly relying only on the co-culture with stabilized stromal cells and/or the addition of limited cocktails of cytokines. Here, we will review the known cellular and molecular interactions occurring between monoclonal B lymphocytes and their tissue microenvironment and the current literature describing innovative in vitro models developed in particular to study chronic lymphocytic leukemia (CLL). We will also elaborate on the possibility to further improve such systems based on the current knowledge of the key molecules/signals present in the microenvironment. In particular, we think that future models should be developed as 3D culture systems with a higher level of cellular and molecular complexity, to replicate microenvironmental-induced signaling. We believe that innovative 3D-models may therefore improve the knowledge on pathogenic mechanisms leading to the dissemination and homing of leukemia cells and consequently the identification of therapeutic targets.

Association of Common Variants of TNFSF13 and TNFRSF13B Genes with CLL Risk and Clinical Picture, as Well as Expression of Their Products-APRIL and TACI Molecules

Interactions between APRIL (TNFSF13) and its receptor TACI (TNFRSF13B) are implicated in providing survival benefits for chronic lymphocytic leukaemia (CLL) cells. Here we explored the relationship between TNFSF13 and TNFRSF13B SNPs and expression of APRIL and TACI molecules and performed extended case-control study to evaluate earlier observations. Expression of APRIL and TACI was detected by FACS for 72 and 145 patients, respectively, and soluble APRIL was measured by ELISA in plasma of 122 patients. Genotypes were determined in 439 CLL patients and 477 control subjects with TaqMan Assays or restriction fragment length polymorphism (RFLP). The rs4968210GG genotype of TNFSF13 was associated with a lower percentage of CD19⁺APRIL⁺ cells in CLL patients when compared to (AA + GA) genotypes (p-value = 0.027). Homozygosity at rs11078355 TNFRSF13B was associated with higher CD19⁺ TACI⁺ cell percentage in CLL patients (p-value = 0.036). The analysis of extended groups of patients and healthy controls confirmed the association of TNFSF13 rs3803800AA genotype with a higher CLL risk (OR = 2.13; CI95% = 1.21; 3.75; p-value = 0.007), while the possession of TNFRSF13B rs4985726G allele (CG + GG) genotype was associated with lower risk of CLL (OR = 0.69; CI95% = 0.51; 0.95; p-value = 0.02). Genetic variants of TNFSF13 and TNFRSF13B may have an impact on APRIL and TACI expression and may be considered as possible CLL risk factors.

Wright A. Differential B-Cell Receptor Signaling Requirement for Adhesion of Mantle Cell Lymphoma Cells to Stromal Cells

Interactions between lymphoma cells and stromal cells play a key role in promoting tumor survival and development of drug resistance. We identified differences in key signaling pathways between the JeKo-1 and REC-1 mantle cell lymphoma (MCL) cell lines, displaying different patterns of stromal cell adhesion and chemotaxis towards stroma-conditioned medium. The identified adhesion-regulated genes reciprocated important aspects of microenvironment-mediated gene modulation in MCL patients. Five-hundred and ninety genes were differently regulated between the cell lines upon adhesion to stromal cells, while 32 genes were similarly regulated in both cell lines. Regulation of B-cell Receptor (BCR) signature genes in adherent cells was specific for JeKo-1. Inhibition of BCR using siRNA or clinically approved inhibitors, Ibrutinib and Acalabrutinib, decreased adhesion of JeKo-1, but not REC-1 cells. Cell surface levels of chemokine receptor CXCR4 were higher in JeKo-1, facilitating migration and adhesion of JeKo-1 but not REC-1 cells. Surface levels of ICAM1 adhesion protein differ for REC-1 and JeKo-1. While ICAM1 played a positive role in adherence of both cell lines to stromal cells, S1PR1 had an inhibitory effect. Our results provide a model framework for further investigation of mechanistic differences in patient-response to new pathway-specific drugs.

New roles for B cell receptor associated kinases: when the B cell is not the target

Targeting of B cell receptor associated kinases (BAKs), such as Bruton's tyrosine kinase (BTK) or phosphoinositol-3-kinase (PI3K) delta, by specific inhibitors has revolutionized the therapy of B lymphoid malignancies. BAKs are critical signaling transducers of BCR signaling and seem relevant in B cell lymphoma pathogenesis. The functional relevance of BTK for lymphoid malignancies is strongly supported by the observation that resistance to therapy in CLL patients treated with BTK inhibitors such as ibrutinib is often associated with mutations in genes coding for BTK or Phospholipase-C gamma (PLCɣ). In some contrast, next generation sequencing data show that BAKs are mutated at very low frequency in treatment-naïve B cell lymphomas. Therefore, it remains debatable whether BAKs are essential drivers for lymphoma development. In addition, results obtained by targeted deletion of BAKs such as Lyn and Btk in murine CLL models suggest that BAKs may be essential to shape the dialogue between malignant B cells and the tumor microenvironment (TME). Since BAKs are expressed in multiple cell types, BAK inhibitors may disrupt the lymphoma supportive microenvironment. This concept also explains the typical response to BAK inhibitor treatment, characterized by a long-lasting increase of peripheral blood lymphoid cells, due to a redistribution from the lymphoid homing compartments. In addition, BAK inhibitors have shown some efficacy in solid tumors, probably through mediator cells in the TME. This review summarizes and validates the evidence for BAK inhibitors being part of a class of agents that modulate the (hematopoietic) microenvironment of cancers.

SLAMF1/CD150 in hematologic malignancies: Silent marker or active player?

SLAMF1/CD150 receptor is a founder of signaling lymphocyte activation molecule (SLAM) family of cell-surface receptors. It is widely expressed on cells within hematopoietic system. In hematologic malignancies CD150 cell surface expression is restricted to cutaneous T-cell lymphomas, few types of B-cell non-Hodgkin's lymphoma, near half of cases of chronic lymphocytic leukemia, Hodgkin's lymphoma, and multiple myeloma. Differential expression among various types of hematological malignancies allows considering CD150 as diagnostical and potential prognostic marker. Moreover, CD150 may be a target for antibody-based or measles virus oncolytic therapy. Due to CD150 signaling properties it is involved in regulation of malignant cell fate decision and tumor microenvironment in Hodgkin's lymphoma and chronic lymphocytic leukemia. This review summarizes evidence for the important role of CD150 in pathogenesis of hematologic malignancies.

CUDC-907 blocks multiple pro-survival signals and abrogates microenvironment protection in CLL

CUDC‐907, a dual PI3K/HDAC inhibitor, has been proposed to have therapeutic potential in hematopoietic malignancies. However, the molecular mechanisms of its effects in chronic lymphocytic leukaemia (CLL) remain elusive. We show that CLL cells are sensitive to CUDC‐907, even under conditions similar to the protective microenvironment of proliferation centres. CUDC‐907 inhibited PI3K/AKT and HDAC activity, as expected, but also suppressed RAF/MEK/ERK and STAT3 signalling and reduced the expression of anti‐apoptotic BCL‐2 family proteins BCL‐2, BCL‐xL, and MCL‐1. Moreover, CUDC‐907 downregulated cytokines BAFF and APRIL and their receptors BAFFR, TACI, and BCMA, thus blocking BAFF‐induced NF‐κB signalling. T cell chemokines CCL3/4/17/22 and phosphorylation of CXCR4 were also reduced by CUDC‐907. These data indicated that CUDC‐907 abrogates different protective signals and suggested that it might sensitize CLL cells to other drugs. Indeed, combinations of low concentrations of CUDC‐907 with inhibitors of BCL2, BTK, or the NF‐κB pathway showed a potent synergistic effect. Our data indicate that, apart from its known functions, CUDC‐907 blocks multiple pro‐survival pathways to overcome microenvironment protection in CLL cells. This provides a rationale to evaluate the clinical relevance of CUDC‐907 in combination therapies with other targeted inhibitors.

Mechanistic Insights into CpG DNA and IL-15 Synergy in Promoting B Cell Chronic Lymphocytic Leukemia Clonal Expansion

Malignant cell growth within patients with B cell chronic lymphocytic leukemia (B-CLL) is largely restricted to lymphoid tissues, particularly lymph nodes. The recent in vitro finding that TLR-9 ligand (oligodeoxynucleotide [ODN]) and IL-15 exhibit strong synergy in promoting B-CLL growth may be particularly relevant to growth in these sites. This study shows IL-15-producing cells are prevalent within B-CLL-infiltrated lymph nodes and, using purified B-CLL cells from blood, investigates the mechanism for ODN and IL-15 synergy in driving B-CLL growth. ODN boosts baseline levels of phospho-RelA(S529) in B-CLL and promotes NF-κB-driven increases in IL15RA and IL2RB mRNA, followed by elevated IL-15Rα and IL-2/IL-15Rβ (CD122) protein. IL-15→CD122 signaling during a critical interval, 20 to 36-48 h following initial ODN exposure, is required for optimal induction of the cycling process. Furthermore, experiments with neutralizing anti-IL-15 and anti-CD122 mAbs indicate that clonal expansion requires continued IL-15/CD122 signaling during cycling. The latter is consistent with evidence of heightened IL2RB mRNA in the fraction of recently proliferated B-CLL cells within patient peripheral blood. Compromised ODN+IL-15 growth with limited cell density is consistent with a role for upregulated IL-15Rα in facilitating homotypic trans IL-15 signaling, although there may be other explanations. Together, the findings show that ODN and IL-15 elicit temporally distinct signals that function in a coordinated manner to drive B-CLL clonal expansion.

Imipenem and normal saline with cyclophosphamide have positive effects on the intestinal barrier in rats with sepsis

BACKGROUND

Sepsis is a life-threatening organ dysfunction caused the dysregulation of host inflammatory response and immunosuppression to infection Early recognition and intervention are hence of paramount importance. In this respect the "sepsis bundle" was proposed in 2004 to be instituted in cases of suspected sepsis.

OBJECTIVE AND HYPOTHESIS

We hypothesised that a combination treatment of the sepsis bundle with cyclophosphamide would improve the function of the intestinal mucosa and enhance survival in rats with induced sepsis.

METHODS AND RESULTS

Sprague-Dawley rats were divided into 5 different groups: sham, cecal ligation and puncture (CLP), cyclophosphamide (CTX), imipenem+normal saline (NS) and imipenem+NS+CTX. Cecal ligation and puncture were used for inducing the polymicrobial sepsis. Western-blot was used to measure the occludin protein, and ELISA for examining the plasma level of cytokines IL-6, IL-10 and TNF-α. TUNEL assay for testing the intestinal mucosal apoptosis, and hematoxylin-eosin staining for observing the intestinal mucosal changes. The permeability of intestinal mucosa was determined by the plasma level of FD-70. The results showed that the combination treatment of the sepsis bundle with cyclophosphamide attenuated cytokine levels, inhibited epithelial cell apoptosis and improved the function of the intestinal barrier. The survival rate of the group treated with the combined therapy was significantly higher than that of the other groups.

CONCLUSION

The combination treatment of sepsis bundle with cyclophosphamide improves the function of the intestinal barrier and enhances survival in septic rats.

Subtype assignment of CLL based on B-cell subset associated gene signatures from normal bone marrow - A proof of concept study

Diagnostic and prognostic evaluation of chronic lymphocytic leukemia (CLL) involves blood cell counts, immunophenotyping, IgVH mutation status, and cytogenetic analyses. We generated B-cell associated gene-signatures (BAGS) based on six naturally occurring B-cell subsets within normal bone marrow. Our hypothesis is that by segregating CLL according to BAGS, we can identify subtypes with prognostic implications in support of pathogenetic value of BAGS. Microarray-based gene-expression samples from eight independent CLL cohorts (1,024 untreated patients) were BAGS-stratified into pre-BI, pre-BII, immature, naïve, memory, or plasma cell subtypes; the majority falling within the memory (24.5-45.8%) or naïve (14.5-32.3%) categories. For a subset of CLL patients (n = 296), time to treatment (TTT) was shorter amongst early differentiation subtypes (pre-BI/pre-BII/immature) compared to late subtypes (memory/plasma cell, HR: 0.53 [0.35-0.78]). Particularly, pre-BII subtype patients had the shortest TTT among all subtypes. Correlates derived for BAGS subtype and IgVH mutation (n = 405) revealed an elevated mutation frequency in late vs. early subtypes (71% vs. 45%, P < .001). Predictions for BAGS subtype resistance towards rituximab and cyclophosphamide varied for rituximab, whereas all subtypes were sensitive to cyclophosphamide. This study supports our hypothesis that BAGS-subtyping may be of tangible prognostic and pathogenetic value for CLL patients.

Mixed-species RNAseq analysis of human lymphoma cells adhering to mouse stromal cells identifies a core gene set that is also differentially expressed in the lymph node microenvironment of mantle cell lymphoma and chronic lymphocytic leukemia patients

A subset of hematologic cancer patients is refractory to treatment or suffers relapse, due in part to minimal residual disease, whereby some cancer cells survive treatment. Cell-adhesion-mediated drug resistance is an important mechanism, whereby cancer cells receive survival signals via interaction with e.g. stromal cells. No genome-wide studies of in vitro systems have yet been performed to compare gene expression in different cell subsets within a co-culture and cells grown separately. Using RNA sequencing and species-specific read mapping, we compared transcript levels in human Jeko-1 mantle cell lymphoma cells stably adhered to mouse MS-5 stromal cells or in suspension within a co-culture or cultured separately as well as in stromal cells in co-culture or in separate culture. From 1050 differentially expressed transcripts in adherent mantle cell lymphoma cells, we identified 24 functional categories that together represent four main functional themes, anti-apoptosis, B-cell signaling, cell adhesion/migration and early mitosis. A comparison with previous mantle cell lymphoma and chronic lymphocytic leukemia studies, of gene expression differences between lymph node and blood, identified 116 genes that are differentially expressed in all three studies. From these genes, we suggest a core set of genes (CCL3, CCL4, DUSP4, ETV5, ICAM1, IL15RA, IL21R, IL4I1, MFSD2A, NFKB1, NFKBIE, SEMA7A, TMEM2) characteristic of cells undergoing cell-adhesion-mediated microenvironment signaling in mantle cell lymphoma/chronic lymphocytic leukemia. The model system developed and characterized here together with the core gene set will be useful for future studies of pathways that mediate increased cancer cell survival and drug resistance mechanisms.

Tumor necrosis factor receptor signaling is a driver of chronic lymphocytic leukemia that can be therapeutically targeted by the flavonoid wogonin

Chronic lymphocytic leukemia is a malignancy of mature B cells that strongly depend on microenvironmental factors, and their deprivation has been identified as a promising treatment approach for this incurable disease. Cytokine array screening of 247 chronic lymphocytic leukemia serum samples revealed elevated levels of tumor necrosis factor (TNF) receptor-1 which were associated with poor clinical outcome. We detected a microenvironment-induced expression of TNF receptor-1 in chronic lymphocytic leukemia cells in vitro, and an aberrantly high expression of this receptor in the proliferation centers of patients’ lymph nodes. Stimulation of TNF receptor-1 with TNF-α enhanced nuclear factor κ-light-chain-enhancer of activated B cells (NFκB) activity and viability of chronic lymphocytic leukemia cells, which was inhibited by wogonin. The therapeutic effects of wogonin were analyzed in mice after adoptive transfer of Eμ-T-cell leukemia 1 (TCL1) leukemic cells. Wogonin treatment prevented leukemia development when given early after transplantation. The treatment of full-blown leukemia resulted in the loss of the TNF receptor-1 on chronic lymphocytic leukemia cells and their mobilization to blood. Targeting TNF receptor-1 signaling is therefore proposed for the treatment of chronic lymphocytic leukemia.

Wnt signalling pathways in chronic lymphocytic leukaemia and B-cell lymphomas

In this review, we discuss the intricate roles of the Wnt signalling network in the development and progression of mature B-cell-derived haematological malignancies, with a focus on chronic lymphocytic leukaemia (CLL) and related B-cell lymphomas. We review the current literature and highlight the differences between the β-catenin-dependent and -independent branches of Wnt signalling. Special attention is paid to the role of the non-canonical Wnt/planar cell polarity (PCP) pathway, mediated by the Wnt-5-receptor tyrosine kinase-like orphan receptor (ROR1)-Dishevelled signalling axis in CLL. This is mainly because the Wnt/PCP co-receptor ROR1 was found to be overexpressed in CLL and the Wnt/PCP pathway contributes to numerous aspects of CLL pathogenesis. We also discuss the possibilities of therapeutically targeting the Wnt signalling pathways as an approach to disrupt the crucial interaction between malignant cells and their micro-environment. We also advocate the need for research in this direction for other lymphomas, namely, diffuse large B-cell lymphoma, Hodgkin lymphoma, mantle cell lymphoma, Burkitt lymphoma and follicular lymphoma where the Wnt signalling pathway probably plays a similar role.

LINKED ARTICLES

This article is part of a themed section on WNT Signalling: Mechanisms and Therapeutic Opportunities. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.24/issuetoc.

Revisiting the role of interleukin-8 in chronic lymphocytic leukemia

The proliferation and survival of malignant B cells in chronic lymphocytic leukemia (CLL) depend on signals from the microenvironment in lymphoid tissues. Among a plethora of soluble factors, IL-8 has been considered one of the most relevant to support CLL B cell progression in an autocrine fashion, even though the expression of IL-8 receptors, CXCR1 and CXCR2, on leukemic B cells has not been reported. Here we show that circulating CLL B cells neither express CXCR1 or CXCR2 nor they respond to exogenous IL-8 when cultured in vitro alone or in the presence of monocytes/nurse-like cells. By intracellular staining and ELISA we show that highly purified CLL B cells do not produce IL-8 spontaneously or upon activation through the B cell receptor. By contrast, we found that a minor proportion (<0.5%) of contaminating monocytes in enriched suspensions of leukemic cells might be the actual source of IL-8 due to their strong capacity to release this cytokine. Altogether our results indicate that CLL B cells are not able to secrete or respond to IL-8 and highlight the importance of methodological details in in vitro experiments.

Regulation of MAPK signaling and implications in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a heterogeneous B cell malignancy that still remains incurable. Recent studies have highlighted cellular and non-cellular components of the tissue microenvironment in CLL that help nurture the growth of leukemic cells by providing the necessary stimuli for their proliferation and survival. The diverse stimuli in the specialized tissue microenvironment of CLL lead to constitutive activation of several signaling pathways that includes B cell receptor signaling and the associated mitogen-activated protein kinase (MAPK) signaling. Recent findings have described aberrant activation of MAPK signaling and its interactions with other cellular signaling pathways in the pathogenesis of CLL. These studies have shed light on the deregulated molecular mechanisms contributing to hyperactivation of MAPK signaling and provided avenues for therapeutic options for aggressive CLL. In this review, we describe and discuss the current status of our understanding into the role of MAPK signaling in the pathogenesis of CLL.

Chronic lymphocytic leukemia cells are active participants in microenvironmental cross-talk

The importance of the tumor microenvironment in chronic lymphocytic leukemia is widely accepted. Nevertheless, the understanding of the complex interplay between the various types of bystander cells and chronic lymphocytic leukemia cells is incomplete. Numerous studies have indicated that bystander cells provide chronic lymphocytic leukemia-supportive functions, but it has also become clear that chronic lymphocytic leukemia cells actively engage in the formation of a supportive tumor microenvironment through several cross-talk mechanisms. In this review, we describe how chronic lymphocytic leukemia cells participate in this interplay by inducing migration and tumor-supportive differentiation of bystander cells. Furthermore, chronic lymphocytic leukemia-mediated alterations in the interactions between bystander cells are discussed. Upon bystander cell interaction, chronic lymphocytic leukemia cells secrete cytokines and chemokines such as migratory factors [chemokine (C-C motif) ligand 22 and chemokine (CC motif) ligand 2], which result in further recruitment of T cells but also of monocyte-derived cells. Within the tumor microenvironment, chronic lymphocytic leukemia cells induce differentiation towards a tumor-supportive M2 phenotype of monocyte-derived cells and suppress phagocytosis, but also induce increased numbers of supportive regulatory T cells. Like other tumor types, the differentiation of stromal cells towards supportive cancer-associated fibroblasts is critically dependent on chronic lymphocytic leukemia-derived factors such as exosomes and platelet-derived growth factor. Lastly, both chronic lymphocytic leukemia and bystander cells induce a tolerogenic tumor microenvironment; chronic lymphocytic leukemia-secreted cytokines, such as interleukin-10, suppress cytotoxic T-cell functions, while chronic lymphocytic leukemia-associated monocyte-derived cells contribute to suppression of T-cell function by producing the immune checkpoint factor, programmed cell death-ligand 1. Deeper understanding of the active involvement and cross-talk of chronic lymphocytic leukemia cells in shaping the tumor microenvironment may offer novel clues for designing therapeutic strategies.

Microenvironmental agonists generate de novo phenotypic resistance to combined ibrutinib plus venetoclax in CLL and MCL

De novo resistance and rapid recurrence often characterize responses of B-cell malignancies to ibrutinib (IBR), indicating a need to develop drug combinations that block compensatory survival signaling and give deeper, more durable responses. To identify such combinations, we previously performed a combinatorial drug screen and identified the Bcl-2 inhibitor venetoclax (VEN) as a promising partner for combination with IBR in Mantle Cell Lymphoma (MCL). We have opened a multi-institutional clinical trial to test this combination. However, analysis of primary samples from patients with MCL as well as chronic lymphocytic leukemia (CLL) revealed unexpected heterogeneous de novo resistance even to the IBR+VEN combination. In the current study, we demonstrate that resistance to the combination can be generated by microenvironmental agonists: IL-10, CD40L and, most potently, CpG-oligodeoxynucleotides (CpG-ODN), which is a surrogate for unmethylated DNA and a specific agonist for TLR9 signaling. Incubation with these agonists caused robust activation of NF-κB signaling, especially alternative NF-κB, which led to enhanced expression of the anti-apoptotic proteins Mcl-1, Bcl-xL, and survivin, thus decreasing dependence on Bcl-2. Inhibitors of NF-κB signaling blocked overexpression of these anti-apoptotic proteins and overcame resistance. Inhibitors of Mcl-1, Bcl-xL, or survivin also overcame this resistance, and showed synergistic benefit with the IBR+VEN combination. We conclude that microenvironmental factors, particularly the TLR9 agonist, can generate de novo resistance to the IBR+VEN combination in CLL and MCL cells. This signaling pathway presents targets for overcoming drug resistance induced by extrinsic microenvironmental factors in diverse B-cell malignancies.

Drug Discovery Testing Compounds in Patient Samples by Automated Flow Cytometry

Functional ex vivo assays that predict a patient’s clinical response to anticancer drugs for guiding cancer treatment have long been a goal, but few have yet proved to be reliable. To address this, we have developed an automated flow cytometry platform for drug screening that evaluates multiple endpoints with a robust data analysis system that can capture the complex mechanisms of action across different compounds. This system, called PharmaFlow, is used to test peripheral blood or bone marrow samples from patients diagnosed with hematological malignancies. Functional assays that use the whole sample, retaining all the microenvironmental components contained in the sample, offer an approach to ex vivo testing that may give results that are clinically relevant. This new approach can help to predict the patients’ response to existing treatments or to drugs under development, for hematological malignancies or other tumors. In addition, relevant biomarkers can be identified that determine the patient’s sensitivity, resistance, or toxicity to a given treatment. We propose that this approach, which better recapitulates the human microenvironment, constitutes a more predictive assay for personalized medicine and preclinical drug discovery.

LYN Kinase in the Tumor Microenvironment Is Essential for the Progression of Chronic Lymphocytic Leukemia

Survival of chronic lymphocytic leukemia (CLL) cells strictly depends on the support of an appropriate tumor microenvironment. Here, we demonstrate that LYN kinase is essential for CLL progression. Lyn deficiency results in a significantly reduced CLL burden in vivo. Loss of Lyn within leukemic cells reduces B cell receptor (BCR) signaling including BTK phosphorylation, but surprisingly does not affect leukemic cell expansion. Instead, syngeneic CLL transplantation of CLL cells into Lyn- or Btk-deficient recipients results in a strongly delayed leukemic progression and prolonged survival. Moreover, Lyn deficiency in macrophages hinders nursing functions for CLL cells, which is mediated by direct contact rather than secretion of soluble factors. Taken together, LYN and BTK seem essential for the formation of a microenvironment supporting leukemic growth.

Suppression of chronic lymphocytic leukemia progression by CXCR4 inhibitor WZ811

CXCR4 is a chemokine and chemokine receptor pair playing critical roles in tumorigenesis. Overexpression of C-X-C chemokine receptor type 4 (CXCR4) is a hallmark of many hematological malignancies including acute myeloid leukemia, chronic lymphocytic leukemia and non-Hodgkin's lymphoma, and generally correlates with a poor prognosis. A highly potent competitive antagonist of CXCR4, WZ811, recently has been identified with suppression of cancer cells aggressive in a variety of cancers. However, the effects of WZ811 on chronic lymphocytic leukemia cells have not yet been defined. The effect of WZ811 on chronic lymphocytic leukemia cells TF-1 and UT-7 cells in proliferation, colony formation, and cell migration in vitro were measured respectively. Decreased in cell viability, colony formation, migration, and survival with cell cycle arrest and higher sensitivity to docetaxel in vitro was observed upon WZ811 treatment. In mouse xenograft models developed with human leukemia cells, WZ811 exhibited tumor growth inhibition. Collectively, we have demonstrated that CXCR4 inhibition by WZ811 has the potential for the treatment of human hematological malignancies. This study demonstrated that WZ811 may be a novel approach in the treatment of chronic lymphocytic leukemia.

Pro-survival signal inhibition by CDK inhibitor dinaciclib in Chronic Lymphocytic Leukaemia

Dinaciclib is a cyclin-dependent kinase inhibitor with clinical potential in different cancers, including chronic lymphocytic leukaemia (CLL). In order to better understand its cytotoxic action, we characterized its effects on signalling pathways important for the survival of CLL cells. We found that dinaciclib induced apoptosis through the activation of caspases 8 and 9, which was independent of the presence of cytokines to mimic the environment of proliferation centres or IGVH mutation status. Moreover, treatment with dinaciclib led to the inhibition of oncogenic pathways normally activated in stimulated CLL cells, such as STAT3, NF-κB, p38, PI3K/AKT and RAF/MEK/ERK. Dinaciclib was also able to block the expression of anti-apoptotic proteins of the BCL2 family such as MCL1 and BCL-xL (also termed BCL2L1). Finally, we showed that low concentrations of dinaciclib enhanced cell sensitivity to ibrutinib and the BCL2 inhibitor ABT-199, two drugs with known effects on CLL. Taken together, our data show that dinaciclib targets multiple pro-survival signalling pathways in CLL, which provides a mechanistic explanation for its potent induction of apoptosis. They also support a therapeutic application of cyclin-dependent kinase inhibitors in CLL in combination with other relevant targeted therapies.

Modulation of B-cell receptor and microenvironment signaling by a guanine exchange factor in B-cell malignancies

OBJECTIVE

Chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL) cells over-express a guanine exchange factor (GEF), Rasgrf-1. This GEF increases active Ras as it catalyzes the removal of GDP from Ras so that GTP can bind and activate Ras. This study aims to study the mechanism of action of Rasgrf-1 in B-cell malignancies.

METHODS

N-terminus truncated Rasgrf-1 variants have a higher GEF activity as compared to the full-length transcript therefore a MCL cell line with stable over-expression of truncated Rasgrf-1 was established. The B-cell receptor (BCR) and chemokine signaling pathways were compared in the Rasgrf-1 over-expressing and a control transfected cell line.

RESULTS

Cells over-expressing truncated form of Rasgrf-1 have a higher proliferative rate as compared to control transfected cells. BCR was activated by lower concentrations of anti-IgM antibody in Rasgrf-1 over-expressing cells as compared to control cells indicating that these cells are more sensitive to BCR signaling. BCR signaling also phosphorylates Rasgrf-1 that further increases its GEF function and amplifies BCR signaling. This activation of Rasgrf-1 in over-expressing cells resulted in a higher expression of phospho-ERK, AKT, BTK and PKC-alpha as compared to control cells. Besides BCR, Rasgrf-1 over-expressing cells were also more sensitive to microenvironment stimuli as determined by resistance to apoptosis, chemotaxis and ERK pathway activation.

CONCLUSIONS

This GEF protein sensitizes B-cells to BCR and chemokine mediated signaling and also upregulates a number of other signaling pathways which promotes growth and survival of these cells.

Regulatory B lymphocyte functions should be considered in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is characterized by an abnormal expansion of mature B cells in the bone marrow and their accumulation in blood and secondary lymphoid organs. Tumor CLL cells share expression of various surface molecules with many subsets of B cells and have several common characteristics with regulatory B cells (B regs). However, the identification of B regs and their role in CLL remain elusive. The aim of this review is to summarize recent works regarding the regulatory and phenotypic characteristic of B regs and their associated effects on the immune system. It is also meant to highlight their potential importance with regards to the immunotherapeutic response.

C–C motif ligand 11 reduction in CLL patients serum after vitamin D supplementation

Background: Vitamin D (VD) deficiency results in a worse prognosis in patients with chronic lymphocytic leukemia (CLL) and may affect the production of cytokines. Nonetheless, there is the lack of studies dealing with VD supplementation and its impact on chemokines in CLL patients.

Aim: The primary endpoint of our interventional study was to evaluate the effect of cholecalciferol supplementation on serum chemokines levels in CLL patients.

Materials and methods: Eighteen subjects with CLL were enrolled for the study. Six-month-long cholecalciferol supplementation was performed in CLL patients with serum 25-OH-D₃ levels below 30 ng/ml. Cytokines levels were assessed at the beginning of the study and after 6 months. Baseline measurements of cytokines were compared to those in apparently healthy controls.

Results: Increased levels of CCL2, CCL3, CCL4, CXCL8, CXCL10, TNFα, bFGF, G-CSF, and VEGF were found in CLL patients in comparison with the healthy controls. In the course of the VD supplementation a decrease in serum levels of chemokines CCL11, CCL3, and cytokine PDGF-BB was observed. The decrease of CCL11 was found in CLL patients on VD supplementation solely, whereas the decrease of CCL3 and PDGF-BB was observed in CLL subjects on both chemotherapy and VD supplementation.

Conclusion: The VD supplementation may exert beneficial effect on chemokines levels in CLL patients with VD deficiency.

Chronic lymphocytic leukemia (CLL)-Then and now

The field of chronic lymphocytic leukemia (CLL) has witnessed considerable change since the time clinical staging was introduced in clinical practice in 1975. Over the years, the prognostication in CLL has expanded with the addition in late 90s of mutational status of variable region of immunoglobulin heavy chain (IGHV), and chromosomal analyses using fluorescent in situ hybridization (FISH). More recently, stereotypy of BCR (B cell receptor) and whole exome sequencing (WES) based discovery of specific mutations such as NOTCH1, TP53, SF3B1, XPO-1, BIRC3, ATM, and RPS15 further refined the current prognostication system in CLL. In therapy, the field of CLL has seen major changes from oral chlorambucil and steroids prior to 1980s, to chemo-immunotherapy (CIT) with fludarabine, cyclophosphamide, rituximab (FCR) to the orally administered targeted therapeutic agents inhibiting kinases in the B cell receptor (BCR) signaling pathway such as Ibrutinib (BTK inhibitor) and Idelalisib (p110 PI3Kδ inhibitor) and novel anti-CD20 mAb's (monoclonal antibodies) such as obinutuzumab. This progress is continuing and other targeted therapeutics such as Bcl2 antagonists (Venetoclax or ABT-199) and finally chimeric antigen receptor against T cells (CART) are in the process of being developed. This review is an attempt to summarize the major benchmarks in the prognostication and in the therapy of CLL. The topic allocated to us by Dr Ayalew Tefferi and Dr Carlo Brugnara is very appropriate to reminisce what our understanding of chronic lymphocytic leukemia (CLL) was in 1976 and how rapidly have the advances occurring in this field affected the patients with CLL.

Microenvironment interactions and B-cell receptor signaling in Chronic Lymphocytic Leukemia: Implications for disease pathogenesis and treatment

Chronic Lymphocytic Leukemia (CLL) is a malignancy of mature B lymphocytes which are highly dependent on interactions with the tissue microenvironment for their survival and proliferation. Critical components of the microenvironment are monocyte-derived nurselike cells (NLCs), mesenchymal stromal cells, T cells and NK cells, which communicate with CLL cells through a complex network of adhesion molecules, chemokine receptors, tumor necrosis factor (TNF) family members, and soluble factors. (Auto-) antigens and/or autonomous mechanisms activate the B-cell receptor (BCR) and its downstream signaling cascade in secondary lymphatic tissues, playing a central pathogenetic role in CLL. Novel small molecule inhibitors, including the Bruton's tyrosine kinase (BTK) inhibitor ibrutinib and the phosphoinositide-3-kinase delta (PI3Kδ) inhibitor idelalisib, target BCR signaling and have become the most successful new therapeutics in this disease. We here review the cellular and molecular characteristics of CLL cells, and discuss the cellular components and key pathways involved in the cross-talk with their microenvironment. We also highlight the relevant novel treatment strategies, focusing on immunomodulatory agents and BCR signaling inhibitors and how these treatments disrupt CLL-microenvironment interactions. This article is part of a Special Issue entitled: Tumor Microenvironment Regulation of Cancer Cell Survival, Metastasis, Inflammation, and Immune Surveillance edited by Peter Ruvolo and Gregg L. Semenza.

Premalignant cell dynamics in indolent B-cell malignancies

PURPOSE OF REVIEW

Follicular lymphoma and chronic lymphocytic leukemia (CLL) are indolent B-cell malignancies characterized by a long preclinical phase and frequent relapses once treatment is initiated. The present review gathers recent findings on the occurrence, relevance, and dynamics of premalignant cells in the development of follicular lymphoma and CLL.

RECENT FINDINGS

The frequency of circulating cells bearing the follicular lymphoma hallmark translocation t(14;18) in healthy persons is correlated to the risk of developing follicular lymphoma later in life. Chronic B-cell receptor stimulation induces cyclic re-entries of BCL2 B cells into germinal centers that propagate clonal evolution and early follicular lymphoma progression. The lymph node microenvironment is a key activation/proliferation niche for malignant cells in CLL, also active in its preclinical antecedent monoclonal B-cell lymphocytosis.

SUMMARY

Considering recent studies of premalignant cells in both diseases and of their putative normal cell counterparts, we propose different models of premalignant evolution for the two pathologies. Before overt follicular lymphoma, t(14;18) B cells exploit the dynamics of memory B cells to re-enter multiple times into local or distant germinal centers, gather activation/proliferation signals, and gain additional mutations to progress to malignant lymphoma. In monoclonal B-cell lymphocytosis, CLL-like activated/memory B cells follow cycles of germinal center-independent activation/proliferation in lymph node. Finally, we discuss the next level genetic and functional analyses that should result in a better understanding of the origins and mechanisms of frequent relapses in follicular lymphoma and CLL.

ILK Induction in Lymphoid Organs by a TNFα-NF-κB-Regulated Pathway Promotes the Development of Chronic Lymphocytic Leukemia

The proliferation of chronic lymphocytic leukemia (CLL) cells requires communication with the lymphoid organ microenvironment. Integrin-linked kinase (ILK) is a multifunctional intracellular adaptor protein that transmits extracellular signals to regulate malignant cell motility, metastasis, and cell-cycle progression, but is poorly characterized in hematologic malignancies. In this study, we investigated the role of ILK in the context of CLL and observed high ILK expression in patient samples, particularly in tumor cells harboring prognostic high-risk markers such as unmutated IGHV genes, high Zap70, or CD38 expression, or a signature of recent proliferation. We also found increased numbers of Ki67 (MKI67)-positive cells in regions of enhanced ILK expression in lymph nodes from CLL patients. Using coculture conditions mimicking the proliferative lymph node microenvironment, we detected a parallel induction of ILK and cyclin D1 (CCND1) expression in CLL cells that was dependent on the activation of NF-κB signaling by soluble TNFα. The newly synthesized ILK protein colocalized to centrosomal structures and was required for correct centrosome clustering and mitotic spindle organization. Furthermore, we established a mouse model of CLL in which B-cell-specific genetic ablation of ILK resulted in decelerated leukemia development due to reduced organ infiltration and proliferation of CLL cells. Collectively, our findings describe a TNFα-NF-κB-mediated mechanism by which ILK expression is induced in the lymph node microenvironment and propose that ILK promotes leukemogenesis by enabling CLL cells to cope with centrosomal defects acquired during malignant transformation. Cancer Res; 76(8); 2186-96. ©2016 AACR.

TCL1 transgenic mouse model as a tool for the study of therapeutic targets and microenvironment in human B-cell chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy with a mature phenotype. In spite of its relatively indolent nature, no radical cure is as yet available. CLL is not associated with either a unique cytogenetic or a molecular defect, which might have been a potential therapeutic target. Instead, several factors are involved in disease development, such as environmental signals which interact with genetic abnormalities to promote survival, proliferation and an immune surveillance escape. Among these, PI3-Kinase signal pathway alterations are nowadays considered to be clearly important. The TCL1 gene, an AKT co-activator, is the cause of a mature T-cell leukemia, as well as being highly expressed in all B-CLL. A TCL1 transgenic mouse which reproduces leukemia with a distinct immunophenotype and similar to the course of the human B-CLL was developed several years ago and is widely used by many groups. This is a review of the CLL biology arising from work of many independent investigators who have used TCL1 transgenic mouse model focusing on pathogenetic, microenviroment and therapeutic targets.

Sprouty 2: a novel attenuator of B-cell receptor and MAPK-Erk signaling in CLL

Clinical heterogeneity is a major barrier to effective treatment of chronic lymphocytic leukemia (CLL). Emerging evidence suggests that constitutive activation of various signaling pathways like mitogen-activated protein kinase-extracellular signal-regulated kinase (MAPK-Erk) signaling plays a role in the heterogeneous clinical outcome of CLL patients. In this study, we have investigated the role of Sprouty (SPRY)2 as a negative regulator of receptor and nonreceptor tyrosine kinase signaling in the pathogenesis of CLL. We show that SPRY2 expression is significantly decreased in CLL cells, particularly from poor-prognosis patients compared with those from good-prognosis patients. Overexpression of SPRY2 in CLL cells from poor-prognosis patients increased their apoptosis. Conversely, downregulation of SPRY2 in CLL cells from good-prognosis patients resulted in increased proliferation. Furthermore, CLL cells with low SPRY2 expression grew more rapidly in a xenograft model of CLL. Strikingly, B-cell-specific transgenic overexpression of spry2 in mice led to a decrease in the frequency of B1 cells, the precursors of CLL cells in rodents. Mechanistically, we show that SPRY2 attenuates the B-cell receptor (BCR) and MAPK-Erk signaling by binding to and antagonizing the activities of RAF1, BRAF, and spleen tyrosine kinase (SYK) in normal B cells and CLL cells. We also show that SPRY2 is targeted by microRNA-21, which in turn leads to increased activity of Syk and Erk in CLL cells. Taken together, these results establish SPRY2 as a critical negative regulator of BCR-mediated MAPK-Erk signaling in CLL, thereby providing one of the molecular mechanisms to explain the clinical heterogeneity of CLL.

Conserved Molecular Underpinnings and Characterization of a Role for Caveolin-1 in the Tumor Microenvironment of Mature T-Cell Lymphomas

Neoplasms of extra-thymic T-cell origin represent a rare and difficult population characterized by poor clinical outcome, aggressive presentation, and poorly defined molecular characteristics. Much work has been done to gain greater insights into distinguishing features among malignant subtypes, but there also exists a need to identify unifying characteristics to assist in rapid diagnosis and subsequent potential treatment. Herein, we investigated gene expression data of five different mature T-cell lymphoma subtypes (n = 187) and found 21 genes to be up- and down-regulated across all malignancies in comparison to healthy CD4⁺ and CD8⁺ T-cell controls (n = 52). From these results, we sought to characterize a role for caveolin-1 (CAV1), a gene with previous description in the progression of both solid and hematological tumors. Caveolin-1 was upregulated, albeit with a heterogeneous nature, across all mature T-cell lymphoma subtypes, a finding confirmed using immunohistochemical staining on an independent sampling of mature T-cell lymphoma biopsies (n = 65 cases). Further, stratifying malignant samples in accordance with high and low CAV1 expression revealed that higher expression of CAV1 in mature T-cell lymphomas is analogous with an enhanced inflammatory and invasive gene expression profile. Taken together, these results demonstrate a role for CAV1 in the tumor microenvironment of mature T-cell malignancies and point toward potential prognostic implications.

Absence of caveolin-1 leads to delayed development of chronic lymphocytic leukemia in Eμ-TCL1 mouse model

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in the United States. The tissue microenvironment, specifically the lymph nodes, influences the biological and clinical behavior of CLL cells. Gene expression profiling of CLL cells from peripheral blood, bone marrow, and lymph nodes revealed Cav-1 as one of the genes that might be involved in the pathogenesis of CLL. We have previously reported that the knockdown of Cav-1 in primary CLL cells exhibits a significant decrease in cell migration and immune synapse formation. However, the precise role of Cav-1 in CLL initiation and progression in vivo is not known. Therefore, we decreased the expression of Cav-1 in vivo by breeding Eμ-TCL1 with cav-1 knockout mice. We observed a significant decrease in the number of CLL cells and rate of proliferation of CLL cells in spleen, liver, and bone marrow from Eμ-TCL1-Cav1(-/+) and Eμ-TCL1-Cav1(-/-) mice as compared with Eμ-TCL1 mice. In addition, there was a significant increase in survival of Eμ-TCL1-Cav1(-/+) and Eμ-TCL1-Cav1(-/-) compared with Eμ-TCL1 mice. Mechanistically, we observed a decrease in MAPK-Erk signaling measured by p-Erk levels in Eμ-TCL1-Cav1(-/+) mice when compared with Eμ-TCL1-Cav(wt/wt). Together these results indicate that decreased Cav-1 in Eμ-TCL1 mice significantly delays the onset of CLL and decreases leukemic progression by inhibiting MAPK-Erk signaling, suggesting a role for Cav-1 in the proliferation and progression of CLL.

Mechanisms of PD-L1/PD-1-mediated CD8 T-cell dysfunction in the context of aging-related immune defects in the Eµ-TCL1 CLL mouse model

T-cell defects, immune suppression, and poor antitumor immune responses are hallmarks of chronic lymphocytic leukemia (CLL), and PD-1/PD-L1 inhibitory signaling has emerged as a major immunosuppressive mechanism. However, the effect of different microenvironments and the confounding influence of aging are poorly understood. The current study uses the Eμ-TCL1 mouse model, which replicates human T-cell defects, as a preclinical platform to longitudinally examine patterns of T-cell dysfunction alongside developing CLL and in different microenvironments, with a focus on PD-1/PD-L1 interactions. The development of CLL was significantly associated with changes in T-cell phenotype across all organs and function. Although partly mirrored in aging wild-type mice, CLL-specific T-cell changes were identified. Murine CLL cells highly expressed PD-L1 and PD-L2 in all organs, with high PD-L1 expression in the spleen. CD3(+)CD8(+) T cells from leukemic and aging healthy mice highly expressed PD-1, identifying aging as a confounder, but adoptive transfer experiments demonstrated CLL-specific PD-1 induction. Direct comparisons of PD-1 expression and function between aging CLL mice and controls identified PD-1(+) T cells in CLL as a heterogeneous population with variable effector function. This is highly relevant for therapeutic targeting of CD8(+) T cells, showing the potential of reprogramming and selective subset expansion to restore antitumor immunity.