Functional and clinical relevance of VLA-4 (CD49d/CD29) in ibrutinib-treated chronic lymphocytic leukemia

Early reappearance of intraclonal proliferative subpopulations in ibrutinib-resistant chronic lymphocytic leukemia

The Bruton's tyrosine kinase (BTK) inhibitor ibrutinib represents an effective strategy for treatment of chronic lymphocytic leukemia (CLL), nevertheless about 30% of patients eventually undergo disease progression. Here we investigated by flow cytometry the long-term modulation of the CLL CXCR4dim/CD5bright proliferative fraction (PF), its correlation with therapeutic outcome and emergence of ibrutinib resistance. By longitudinal tracking, the PF, initially suppressed by ibrutinib, reappeared upon early disease progression, without association with lymphocyte count or serum beta-2-microglobulin. Somatic mutations of BTK/PLCG2, detected in 57% of progressing cases, were significantly enriched in PF with a 3-fold greater allele frequency than the non-PF fraction, suggesting a BTK/PLCG2-mutated reservoir resident within the proliferative compartments. PF increase was also present in BTK/PLCG2-unmutated cases at progression, indicating that PF evaluation could represent a marker of CLL progression under ibrutinib. Furthermore, we evidence different transcriptomic profiles of PF at progression in cases with or without BTK/PLCG2 mutations, suggestive of a reactivation of B-cell receptor signaling or the emergence of bypass signaling through MYC and/or Toll-Like-Receptor-9. Clinically, longitudinal monitoring of the CXCR4dim/CD5bright PF by flow cytometry may provide a simple tool helping to intercept CLL progression under ibrutinib therapy.

Prognostication in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most common type of leukemia in Western countries. CLL is a highly heterogeneous disease: some patients may never require therapy and others relapse several times after different therapeutic strategies. Therefore, in CLL, prognostic markers are essential to capture high-risk patients for different clinical endpoints including early treatment requirement, early progression after BTK or BCL2 inhibitors and Richter transformation. In early stage CLL, different biological and clinical biomarkers have been identified to predict time to treatment requirement that could be used to identify the most appropriate population for early intervention clinical trial. However, at the moment, the standard of care for early stage CLL remains watch & wait since no survival benefit has been identified in clinical trials with chemoimmunotherapy and with BTK inhibitors. In patients requiring treatment TP53 disruptions identify high-risk patients who benefit the most from long-term continuous therapy with BTKi. On the opposite side of the spectrum, IGHV mutated patients devoid of TP53 disruption benefit the most from fixed-duration therapy with venetoclax-obinutuzumab. In between, the highly heterogenous subgroup of patients with IGHV unmutated genes represents the group in which further efforts are needed to identify additional prognostic biomarkers aimed at selecting patients who can benefit from fixed-duration and patients who can benefit from long term BTKi therapy. In the context of the aggressive transformation of CLL, namely Richter syndrome, the clonal relationship to the CLL counterpart represents the strongest prognostic biomarker. Clonally related Richter syndrome still represents an unmet clinical need which requires further efforts to identify new therapeutic strategies.

ERBB4-Mediated Signaling Is a Mediator of Resistance to PI3K and BTK Inhibitors in B-cell Lymphoid Neoplasms

BTK and PI3K inhibitors are among the drugs approved for the treatment of patients with lymphoid neoplasms. Although active, their ability to lead to long-lasting complete remission is rather limited, especially in the lymphoma setting. This indicates that tumor cells often develop resistance to the drugs. We started from a marginal zone lymphoma cell line, Karpas-1718, kept under prolonged exposure to the PI3Kδ inhibitor idelalisib until acquisition of resistance, or with no drug. Cells underwent transcriptome, miRNA and methylation profiling, whole-exome sequencing, and pharmacologic screening, which led to the identification of the overexpression of ERBB4 and its ligands HBEGF and NRG2 in the resistant cells. Cellular and genetic experiments demonstrated the involvement of this axis in blocking the antitumor activity of various BTK/PI3K inhibitors, currently used in the clinical setting. Addition of recombinant HBEGF induced resistance to BTK/PI3K inhibitors in parental cells and in additional lymphoma models. Combination with the ERBB inhibitor lapatinib was beneficial in resistant cells and in other lymphoma models already expressing the identified resistance factors. An epigenetic reprogramming sustained the expression of the resistance-related factors, and pretreatment with demethylating agents or EZH2 inhibitors overcame the resistance. Resistance factors were also shown to be expressed in clinical specimens. In conclusion, we showed that the overexpression of ERBB4 and its ligands represents a novel mechanism of resistance for lymphoma cells to bypass the antitumor activity of BTK and PI3K inhibitors and that targeted pharmacologic interventions can restore sensitivity to the small molecules.

Lymphocyte migration and retention properties affected by ibrutinib in chronic lymphocytic leukemia

The Bruton tyrosine kinase (BTK) inhibitor ibrutinib is widely used for treatment of patients with relapsed/refractory or treatment-naïve chronic lymphocytic leukemia (CLL). A prominent effect of ibrutinib is to disrupt the retention of CLL cells from supportive lymphoid tissues, by altering BTK-dependent adhesion and migration. To further explore the mechanism of action of ibrutinib and its potential impact on non-leukemic cells, we quantified multiple motility and adhesion parameters of human primary CLL cells and non-leukemic lymphoid cells. In vitro, ibrutinib affected CCL19-, CXCL12- and CXCL13-evoked migration behavior of CLL cells and non-neoplastic lymphocytes, by reducing both motility speed and directionality. De-phosphorylation of BTK induced by ibrutinib in CLL cells was associated with defective polarization over fibronectin and inability to assemble the immunological synapse upon B-cell receptor engagement. In patients' samples collected during a 6-month monitoring of therapy, chemokine-evoked migration was repressed in CLL cells and marginally reduced in T cells. This was accompanied by profound modulation of the expression of chemokine receptors and adhesion molecules. Remarkably, the relative expression of the receptors governing lymph node entry (CCR7) versus exit (S1PR1) stood out as a reliable predictive marker of the clinically relevant treatment-induced lymphocytosis. Together, our data reveal a multifaceted modulation of motility and adhesive properties of ibrutinib on both CLL leukemic cell and T-cell populations and point to intrinsic differences in CLL recirculation properties as an underlying cause for variability in treatment response.

CD49d in chronic lymphocytic leukemia: a molecule with multiple regulation layers. Comment to "Sialylation regulates migration in chronic lymphocytic leukemia"

Not available.

Identification of the Axis β-Catenin-BTK in the Dynamic Adhesion of Chronic Lymphocytic Leukemia Cells to Their 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.

Comparison of the blood immune repertoire with clinical features in chronic lymphocytic leukemia patients treated with chemoimmunotherapy or ibrutinib

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of CD19+ CD5+ clonal B lymphocytes in the blood, bone marrow, and peripheral lymphoid organs. Treatment options for patients range from historical chemoimmunotherapy (CIT) to small molecule inhibitors targeting pro-survival pathways in leukemic B cells, such as the Bruton's tyrosine kinase inhibitor ibrutinib (IBR). Using biobanked blood samples obtained pre-therapy and at standard response evaluation timepoints, we performed an in-depth evaluation of the blood innate and adaptive immune compartments between pentostatin-based CIT and IBR and looked for correlations with clinical sequelae. CD4+ conventional T cells and CD8+ cytotoxic T cells responded similarly to CIT and IBR, although exhaustion status differed. Both treatments dramatically increased the prevalence and functional status of monocyte, dendritic cell, and natural killer cell subsets. As expected, both regimens reduced clonal B cell levels however, we observed no substantial recovery of normal B cells. Although improvements in most immune subsets were observed with CIT and IBR at response evaluation, both patient groups remained susceptible to infections and secondary malignancies during the study.

Egress of resident memory T cells from tissue with neoadjuvant immunotherapy: Implications for systemic anti-tumor immunity

INTRODUCTION

Resident memory T (TRM) cells are embedded in peripheral tissue and capable of acting as sentinels that can respond quickly to repeat pathogen exposure as part of an endogenous anti-microbial immune response. Recent evidence suggests that chronic antigen exposure and other microenvironment cues may promote the development of TRM cells within solid tumors as well, and that this TRM phenotype can sequester tumor-specific T cells into tumors and out of circulation resulting in limited systemic antitumor immunity. Here, we perform a review of the published English literature and describe tissue-specific mediators of TRM cell differentiation in states of infection and malignancy with special focus on the role of TGF-β and how targeting TGF-β signaling could be used as a therapeutical approach to promote tumor systemic immunity.

DISCUSSION

The presence of TRM cells with antigen specificity to neoepitopes in tumors associates with positive clinical prognosis and greater responsiveness to immunotherapy. Recent evidence indicates that solid tumors may act as reservoirs for tumor specific TRM cells and limit their circulation - possibly resulting in impaired systemic antitumor immunity. TRM cells utilize specific mechanisms to egress from peripheral tissues into circulation and other peripheral sites, and emerging evidence indicates that immunotherapeutic approaches may initiate these processes and increase systemic antitumor immunity.

CONCLUSIONS

Reversing tumor sequestration of tumor-specific T cells prior to surgical removal or radiation of tumor may increase systemic antitumor immunity. This finding may underlie the improved recurrence free survival observed with neoadjuvant immunotherapy in clinical trials.

The Role of the Microenvironment and Cell Adhesion Molecules in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy whose progression largely depends on the lymph node and bone marrow microenvironment. Indeed, CLL cells actively proliferate in specific regions of these anatomical compartments, known as proliferation centers, while being quiescent in the blood stream. Hence, CLL cell adhesion and migration into these protective niches are critical for CLL pathophysiology. CLL cells are lodged in their microenvironment through a series of molecular interactions that are mediated by cellular adhesion molecules and their counter receptors. The importance of these adhesion molecules in the clinic is demonstrated by the correlation between the expression levels of some of them, in particular CD49d, and the prognostic likelihood. Furthermore, novel therapeutic agents, such as ibrutinib, impair the functions of these adhesion molecules, leading to an egress of CLL cells from the lymph nodes and bone marrow into the circulation together with an inhibition of homing into these survival niches, thereby preventing disease progression. Several adhesion molecules have been shown to participate in CLL adhesion and migration. Their importance also stems from the observation that they are involved in promoting, directly or indirectly, survival signals that sustain CLL proliferation and limit the efficacy of standard and novel chemotherapeutic drugs, a process known as cell adhesion-mediated drug resistance. In this respect, many studies have elucidated the molecular mechanisms underlying cell adhesion-mediated drug resistance, which have highlighted different signaling pathways that may represent potential therapeutic targets. Here, we review the role of the microenvironment and the adhesion molecules that have been shown to be important in CLL and their impact on transendothelial migration and cell-mediated drug resistance. We also discuss how novel therapeutic compounds modulate the function of this important class of molecules.

BCR/Integrin Interaction in CLL: A Physiologic Remnant with Clinical Relevance

CD49d, the alpha chain of the very late antigen-4 (VLA-4) integrin, has a negative prognostic impact in chronic lymphocytic leukemia treated with the Bruton's tyrosine kinase (BTK) inhibitors, ibrutinib and acalabrutinib. Despite BTK inhibition, VLA-4 remains inside-out activated via B-cell receptor, an activation dampened by phosphoinositide 3-kinase inhibitors. Evaluation of CD49d expression in patients starting BTK inhibitor therapy may improve their prognostic stratification. See related article by Alsadhan et al., p. 3612.

CD49d Expression Identifies a Biologically Distinct Subtype of Chronic Lymphocytic Leukemia with Inferior Progression-Free Survival on BTK Inhibitor Therapy

PURPOSE

To determine the role of CD49d for response to Bruton's tyrosine kinase inhibitors (BTKi) in patients with chronic lymphocytic leukemia (CLL).

PATIENTS AND METHODS

In patients treated with acalabrutinib (n = 48), CD49d expression, VLA-4 integrin activation, and tumor transcriptomes of CLL cells were assessed. Clinical responses to BTKis were investigated in acalabrutinib- (n = 48; NCT02337829) and ibrutinib-treated (n = 73; NCT01500733) patients.

RESULTS

In patients treated with acalabrutinib, treatment-induced lymphocytosis was comparable for both subgroups but resolved more rapidly for CD49d+ cases. Acalabrutinib inhibited constitutive VLA-4 activation but was insufficient to block BCR and CXCR4-mediated inside-out activation. Transcriptomes of CD49d+ and CD49d- cases were compared using RNA sequencing at baseline and at 1 and 6 months on treatment. Gene set enrichment analysis revealed increased constitutive NF-κB and JAK-STAT signaling, enhanced survival, adhesion, and migratory capacity in CD49d+ over CD49d- CLL that was maintained during therapy. In the combined cohorts of 121 BTKi-treated patients, 48 (39.7%) progressed on treatment with BTK and/or PLCG2 mutations detected in 87% of CLL progressions. Consistent with a recent report, homogeneous and bimodal CD49d-positive cases (the latter having concurrent CD49d+ and CD49d- CLL subpopulations, irrespective of the traditional 30% cutoff value) had a shorter time to progression of 6.6 years, whereas 90% of cases homogenously CD49d- were estimated progression-free at 8 years (P = 0.0004).

CONCLUSIONS

CD49d/VLA-4 emerges as a microenvironmental factor that contributes to BTKi resistance in CLL. The prognostic value of CD49d is improved by considering bimodal CD49d expression. See related commentary by Tissino et al., p. 3560.

Prognostic Markers in the Era of Targeted Therapies

BACKGROUND

Small molecules targeting Bruton's tyrosine kinase (BTK) and B-cell lymphoma-2 have become the standard of care for the treatment of chronic lymphocytic leukemia (CLL), replacing chemoimmunotherapy (CIT) in most clinical settings. Ongoing trials explore targeted combinations and minimal residual disease-driven treatment cessation. These dramatic shifts in the current and upcoming treatment landscape of CLL raise the need to reevaluate existing prognostic markers and develop novel ones.

SUMMARY

This review examines prognostic markers in CLL patients treated with standard and investigational targeted therapies. Specifically, initial treatment of TP53 aberrant patients with a BTK inhibitor can achieve 70% progression-free survival (PFS) at 5 years, outperforming the 15% 5-year PFS with a CIT regimen containing fludarabine, cyclophosphamide, and rituximab (FCR). The prognostic implications of the immunoglobulin heavy chain variable gene (IGHV) mutation status have also changed. Unmutated IGHV is associated with inferior PFS and overall survival after FCR and inferior PFS with fixed-duration therapy with venetoclax and anti-CD20 monoclonal antibody but not with continuous BTK inhibitor treatment.

KEY MESSAGES

(1) Genetic variables (e.g., TP53 aberration, IGHV mutation, complex karyotype) have a prognostic significance in CLL patients treated with targeted therapy. (2) Understanding the prognostic and predictive values of these markers is critical for the development of a risk-adapted treatment strategy in CLL.

ERBB4-mediated signaling is a mediator of resistance to BTK and PI3K inhibitors in B cell lymphoid neoplasms

BTK and PI3K inhibitors are among the drugs approved for the treatment of patients with lymphoid neoplasms. Although active, their ability to lead as single agents to long-lasting complete remission is rather limited especially in the lymphoma setting. This indicates that tumor cells often develop resistance to the drugs. Here, we show that the overexpression of ERBB4 and its ligands represents a modality for B cell neoplastic cells to bypass the anti-tumor activity of BTK and PI3K inhibitors and that targeted pharmacological interventions can restore sensitivity to the small molecules. We started from a marginal zone lymphoma (MZL) cell line, Karpas-1718, kept under prolonged exposure to the PI3Kδ inhibitor idelalisib until acquisition of resistance, or with no drug. Cells underwent transcriptome, miRNA and methylation profiling, whole exome sequencing, and pharmacological screening which led to the identification of the overexpression of ERBB4 and its ligands HBEGF and NRG2 in the resistant cells. Cellular and genetic experiments demonstrated the involvement of this axis in blocking the anti-tumor activity of various BTK and PI3K inhibitors, currently used in the clinical setting. Addition of recombinant HBEGF induced resistance to BTK and PI3K inhibitors in parental cells but also in additional lymphoma models. Combination with the ERBB inhibitor lapatinib was beneficial in resistant cells and in other lymphoma models already expressing the identified resistance factors. Multi-omics analysis underlined that an epigenetic reprogramming affected the expression of the resistance-related factors, and pretreatment with demethylating agents or EZH2 inhibitors overcame the resistance. Resistance factors were shown to be expressed in clinical samples, further extending the findings of the study. In conclusions, we identified a novel ERBB4-driven mechanism of resistance to BTK and PI3K inhibitors and treatments that appear to overcome it.

Key points

A mechanism of secondary resistance to the PI3Kδ and BTK inhibitors in B cell neoplasms driven by secreted factors.Resistance can be reverted by targeting ERBB signaling.

High surface IgM levels associate with shorter response to ibrutinib and BTK bypass in patients with CLL

Chronic lymphocytic leukemia (CLL) cells have variably low surface IgM (sIgM) levels/signaling capacity, influenced by chronic antigen engagement at tissue sites. Within these low levels, CLL with relatively high sIgM (CLLhigh) progresses more rapidly than CLL with low sIgM (CLLlow). During ibrutinib therapy, surviving CLL cells redistribute into the peripheral blood and can recover sIgM expression. Return of CLL cells to tissue may eventually recur, where cells with high sIgM could promote tumor growth. We analyzed time to new treatment (TTNT) following ibrutinib in 70 patients with CLL (median follow-up of 66 months) and correlated it with pretreatment sIgM levels and signaling characteristics. Pretreatment sIgM levels correlated with signaling capacity, as measured by intracellular Ca2+ mobilization (iCa2+), in vitro (r = 0.70; P < .0001). High sIgM levels/signaling strongly correlated with short TTNT (P < .05), and 36% of patients with CLLhigh vs 8% of patients with CLLlow progressed to require a new treatment. In vitro, capacity of ibrutinib to inhibit sIgM-mediated signaling inversely correlated with pretherapy sIgM levels (r = -0.68; P = .01) or iCa2+ (r = -0.71; P = .009). In patients, sIgM-mediated iCa2+ and ERK phosphorylation levels were reduced by ibrutinib therapy but not abolished. The residual signaling capacity downstream of BTK was associated with high expression of sIgM, whereas it was minimal when sIgM expression was low (P < .05). These results suggested that high sIgM levels facilitated CLL cell resistance to ibrutinib in patients. The CLL cells, surviving in the periphery with high sIgM expression, include a dangerous fraction that is able to migrate to tissue and receive proliferative stimuli, which may require targeting by combined approaches.

Revealing a Phenotypical Appearance of Ibrutinib Resistance in Patients With Chronic Lymphocytic Leukaemia by Flow Cytometry

Background: Ibrutinib is widely known as an effective and well-tolerated therapeutical choice of the chronic lymphocytic leukaemia (CLL). However, acquired resistance may occur during the treatment, causing relapse. Early detection of ibrutinib resistance is an important issue, therefore we aimed to find phenotypic markers on CLL cells the expression of which may correlate with the appearance of ibrutinib resistance.

Methods: We examined 28 patients’ peripheral blood (PB) samples (treatment naïve, ibrutinib sensitive, clinically ibrutinib resistant). The surface markers’ expression (CD27, CD69, CD86, CD184, CD185) were measured by flow cytometry. Furthermore, the BTK^C481S resistance mutation was assessed by digital droplet PCR. Moreover, the CLL cells’ phenotype of a patient with acquired ibrutinib resistance was observed during the ibrutinib treatment.

Results: The expression of CD27 (p = 0.030) and CD86 (p = 0.031) became higher in the clinically resistant cohort than in the ibrutinib sensitive cohort. Besides, we found that high CD86 and CD27 expressions were accompanied by BTK^C481S mutation. Our prospective study showed that the increase of the expression of CD27, CD69 and CD86 was noticed ahead of the clinical resistance with 3 months.

Conclusion: Our study suggests that the changes of the expression of these markers could indicate ibrutinib resistance and the examination of these phenotypic changes may become a part of the patients’ follow-up in the future.

Integrin Signaling Shaping BTK-Inhibitor Resistance

Integrins are adhesion molecules that function as anchors in retaining tumor cells in supportive tissues and facilitating metastasis. Beta1 integrins are known to contribute to cell adhesion-mediated drug resistance in cancer. Very late antigen-4 (VLA-4), a CD49d/CD29 heterodimer, is a beta1 integrin implicated in therapy resistance in both solid tumors and haematological malignancies such as chronic lymphocytic leukemia (CLL). A complex inside-out signaling mechanism activates VLA-4, which might include several therapeutic targets for CLL. Treatment regimens for this disease have recently shifted towards novel agents targeting BCR signaling. Bruton’s tyrosine kinase (BTK) is a component of B cell receptor signaling and BTK inhibitors such as ibrutinib are highly successful; however, their limitations include indefinite drug administration, the development of therapy resistance, and toxicities. VLA-4 might be activated independently of BTK, resulting in an ongoing interaction of CD49d-expressing leukemic cells with their surrounding tissue, which may reduce the success of therapy with BTK inhibitors and increases the need for alternative therapies. In this context, we discuss the inside-out signaling cascade culminating in VLA-4 activation, consider the advantages and disadvantages of BTK inhibitors in CLL and elucidate the mechanisms behind cell adhesion-mediated drug resistance.

[The correlation of CD49d expression pattern with molecular genetics and hotspot gene mutants in patients with chronic lymphocytic leukemia]

Objective: To explore the correlation of CD49d expression patterns with molecular genetics and hotspot gene mutants in patients with chronic lymphocytic leukemia. Methods: The expression of CD49d was detected by flow cytometry and grouped into homogeneous, bimodal, negative and positive expression. Panel fluorescence in situ hybridization (FISH) was used for molecular genetics analysis and next-generation sequencing (NGS) was conducted for gene mutation detection. Results: There were 43 patients (23.89% ) with positive CD49d expression, 137 patients (76.11% ) with negative CD49d expression, 96 patients (53.33% ) with homogeneous CD49d expression and 84 patients (46.67% ) with bimodal CD49d expression. Compared with patients in the CD49d negative group, patients in the CD49d positive group had higher Rai stage (P=0.048) and higher proportion of spleen enlargement (P=0.030) . Compared with patients with homogeneous expression of CD49d, patients with bimodal expression of CD49d had a higher proportion of spleen enlargement (P=0.009) . The expression rate of 11q22- in bimodal CD49d(-) group was significantly higher than that in homogeneous CD49d(-) group (24.29% vs 10.45% , P=0.043) . The incidence of +12 in homogeneous CD49d group was higher than that in bimodal CD49d group (16.67% vs 5.95% , P=0.035) . The incidence of +12 in homogeneous CD49d(+) group was higher than that in bimodal CD49d(-) group (17.24% vs 4.29% , P=0.045) . The incidence of +12 in homogeneous CD49d(-) group was higher than that in bimodal CD49d(-) group (16.42% vs 4.29% , P=0.024) . BIRC3 mutation rate in CD49d positive group was higher than that in CD49d negative group (11.63% vs 2.92% , P=0.037) . Conclusion: There were significant correlations between CD49d and 11q22-, +12 and BIRC3 gene mutation. Patients with bimodal CD49d were more correlated with poor prognosis indexes.

Ibrutinib Does Not Impact CCR7-Mediated Homeostatic Migration in T-Cells from Chronic Lymphocytic Leukemia Patients

Bruton's tyrosine kinase inhibitor ibrutinib has significantly changed treatment landscape in chronic lymphocytic leukemia (CLL). Growing evidence supports ibrutinib to work beyond the effect on tumor cells by means of, for example, restoring functionality of the T-cell compartment and increasing circulating T-cell numbers. Recent evidence suggests T-cell enhanced expansion, rather than increased egress from secondary lymphoid organs (SLO), as a root cause for ibrutinib-induced lymphocytosis. However, whether the latter physiological change is also a consequence of a forced retention in blood remains undisclosed. Since CCR7 is the main chemokine receptor taking over the homing of T-cells from peripheral compartments to lymph nodes and other SLO, we aimed to investigate the impact of ibrutinib on CCR7 functionality in T-cells. To this end, we documented receptor expression in T-cells from a large cohort of ibrutinib-treated CLL patients, and performed different in vivo and in vitro migration models. Overall, our data confirm that CCR7 expression or receptor-mediated migration in CLL T-cells is not affected by ibrutinib. Furthermore, it does not modulate CCR7-driven homing nor nodal interstitial migration. Together, our results support that ibrutinib-induced CLL T-cell accumulation in the blood stream is not derived from an impairment of CCR7-driven recirculation between the SLO and bloodstream, and therefore T-cell expansion is the most plausible cause.

The scaffold protein NEDD9 is necessary for leukemia-cell migration and disease progression in a mouse model of chronic lymphocytic leukemia

The scaffold protein NEDD9 is frequently upregulated and hyperphosphorylated in cancers, and is associated with poor clinical outcome. NEDD9 promotes B-cell adhesion, migration and chemotaxis, pivotal processes for malignant development. We show that global or B-cell-specific deletion of Nedd9 in chronic lymphocytic leukemia (CLL) mouse models delayed CLL development, markedly reduced disease burden and resulted in significant survival benefit. NEDD9 was required for efficient CLL cell homing, chemotaxis, migration and adhesion. In CLL patients, peripheral NEDD9 expression was associated with adhesion and migration signatures as well as leukocyte count. Additionally, CLL lymph nodes frequently expressed high NEDD9 levels, with a subset of patients showing NEDD9 expression enriched in the CLL proliferation centers. Blocking activity of prominent NEDD9 effectors, including AURKA and HDAC6, effectively reduced CLL cell migration and chemotaxis. Collectively, our study provides evidence for a functional role of NEDD9 in CLL pathogenesis that involves intrinsic defects in adhesion, migration and homing.

Elucidation of Focal Adhesion Kinase as a Modulator of Migration and Invasion and as a Potential Therapeutic Target in Chronic Lymphocytic Leukemia

The retention and re-migration of Chronic Lymphocytic Leukemia cells into cytoprotective and proliferative lymphoid niches is thought to contribute to the development of resistance, leading to subsequent disease relapse. The aim of this study was to elucidate the molecular processes that govern CLL cell migration to elicit a more complete inhibition of tumor cell migration. We compared the phenotypic and transcriptional changes induced in CLL cells using two distinct models designed to recapitulate the peripheral circulation, CLL cell migration across an endothelial barrier, and the lymph node interaction between CLL cells and activated T cells. Initially, CLL cells were co-cultured with CD40L-expressing fibroblasts and exhibited an activated B-cell phenotype, and their transcriptional signatures demonstrated the upregulation of pro-survival and anti-apoptotic genes and overrepresentation of the NF-κB signaling pathway. Using our dynamic circulating model, we were able to study the transcriptomics and miRNomics associated with CLL migration. More than 3000 genes were altered when CLL cells underwent transendothelial migration, with an overrepresentation of adhesion and cell migration gene sets. From this analysis, an upregulation of the FAK signaling pathway was observed. Importantly, PTK2 (FAK) gene expression was significantly upregulated in migrating CLL cells (PTK2 Fold-change = 4.9). Here we demonstrate that TLR9 agonism increased levels of p-FAK (p ≤ 0.05), which could be prevented by pharmacological inhibition of FAK with defactinib (p ≤ 0.01). Furthermore, a reduction in CLL cell migration and invasion was observed when FAK was inhibited (p ≤ 0.0001), supporting a role for FAK in both CLL migration and tissue invasion. When taken together, our data highlights the potential for combining FAK inhibition with current targeted therapies as a more effective treatment regime for CLL.

In vitro and in vivo effects of AVA4746, a novel competitive antagonist of the ligand binding of VLA-4, in B-cell acute lymphoblastic leukemia

Treatment of resistant or recurrent acute lymphoblastic leukemia (ALL) remains a challenge. It was previously demonstrated that the adhesion molecule integrin α4, referred to hereafter as α4, mediates the cell adhesion-mediated drug resistance (CAM-DR) of B-cell ALL by binding to vascular cell adhesion molecule-1 (VCAM-1) on bone marrow stroma. In addition, it was previously observed that the blockade of α4 with natalizumab or inhibition using the small molecule antagonist TBC3486 sensitized relapsed ALL cells to chemotherapy. However, α4-targeted therapy is not clinically available for the treatment of leukemia to date. In the present study, the use of a novel non-peptidic small molecule integrin α4 antagonist, AVA4746, as a potential new approach to combat drug-resistant B-ALL was explored. An in vitro co-culture = model of primary B-ALL cells and an in vivo xenograft model of patient-derived B-ALL cells were utilized for evaluation of AVA4746. VLA-4 conformation activation, cell adhesion/de-adhesion, endothelial tube formation, in vivo leukemia cell mobilization and survival assays were performed. AVA4746 exhibited high affinity for binding to B-ALL cells, where it also efficiently blocked ligand-binding to VCAM-1. In addition, AVA4746 caused the functional de-adhesion of primary B-ALL cells from VCAM-1. Inhibition of α4 using AVA4746 also prevented angiogenesis in vitro and when applied in combination with chemotherapy consisting of Vincristine, Dexamethasone and L-asparaginase, it prolonged the survival of ~33% of the mice in an in vivo xenograft model of B-ALL. These data implicate the potential of targeting the α4-VCAM-1 interaction using AVA4746 for the treatment of drug-resistant B-lineage ALL.

Kindlin-3 maintains marginal zone B cells but confines follicular B cell activation and differentiation

Integrin-mediated interactions between hematopoietic cells and their microenvironment are important for the development and function of immune cells. Here, the role of the integrin adaptor Kindlin-3 in B cell homeostasis is studied. Comparing the individual steps of B cell development in B cell-specific Kindlin-3 or alpha4 integrin knockout mice, we found in both conditions a phenotype of reduced late immature, mature, and recirculating B cells in the bone marrow. In the spleen, constitutive B cell-specific Kindlin-3 knockout caused a loss of marginal zone B cells and an unexpected expansion of follicular B cells. Alpha4 integrin deficiency did not induce this phenotype. In Kindlin-3 knockout B cells VLA-4 as well as LFA-1-mediated adhesion was abrogated, and short-term homing of these cells in vivo was redirected to the spleen. Upon inducible Kindlin-3 knockout, marginal zone B cells were lost due to defective retention within 2 weeks, while follicular B cell numbers were unaltered. Kindlin-3 deficient follicular B cells displayed higher IgD, CD40, CD44, CXCR5, and EBI2 levels, and elevated PI3K signaling upon CXCR5 stimulation. They also showed transcriptional signatures of spontaneous follicular B cell activation. This activation manifested in scattered germinal centers in situ, early plasmablasts differentiation, and signs of IgG class switch.

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.

Artificial intelligence models in chronic lymphocytic leukemia - recommendations toward state-of-the-art

Artificial intelligence (AI), machine learning and predictive modeling are becoming enabling technologies in many day-to-day applications. Translation of these advances to the patient's bedside for AI assisted interventions is not yet the norm. With specific emphasis on CLL, here, we review the progress of prognostic models in hematology and highlight sources of stagnation that may be limiting significant improvements in prognostication in the near future. We discuss issues related to performance, trust, modeling simplicity, and prognostic marker robustness and find that the major limiting factor in progressing toward state-of-the-art prognostication within the hematological community, is not the lack of able AI algorithms but rather, the lack of their adoption. Current models in CLL still deal with the 'average' patient while the use of patient-centric approaches remains absent. Using lessons from research areas where machine learning has become an enabling technology, we derive recommendations and propose methods for achieving state-of-the-art predictions in modeling health data, that can be readily adopted by the CLL modeling community.

Impaired nodal shrinkage and apoptosis define the independent adverse outcome of NOTCH1 mutated patients under ibrutinib therapy in chronic lymphocytic leukaemia

The introduction of agents inhibiting the B-cell receptor-associated kinases such as ibrutinib has dramatically changed treatments algorithms of chronic lymphocytic leukemia (CLL) as well as the role of different adverse prognosticators. We evaluated the efficacy of ibrutinib as a single agent, in a real-life context, in 180 patients with CLL mostly pretreated, recruited from three independent cohorts from Italy. Patients received 420 mg oral ibrutinib once daily until progression or occurrence of unacceptable side effects. Seventy-three patients discontinued ibrutinib for progression or for adverse events. NOTCH1 mutations (NOTCH1 M) were correlated with a reduced redistribution lymphocytosis, calculated at 3 months on ibrutinib (P=0.022). Moreover, NOTCH1 M patients showed inferior nodal response at 6 months on ibrutinib compared to NOTCH1 wild-type patients (P<0.0001). Significant shorter progression free survival (PFS) and overall survival (OS) were observed in NOTCH1 M patients (P=0.00002 and P=0.001). Interestingly, NOTCH1 M plus a lower BAX/BCL-2 ratio identified a CLL subset showing the worst PFS and OS (P=0.0002 and P=0.005). In multivariate analysis of PFS and OS, NOTCH1 M were confirmed an independent prognosticator (P=0.00006 and P=0.0039). In conclusion, NOTCH1 M are strongly associated with a lower BAX/BCL-2 ratio, consistent with defective apoptosis, lower redistribution lymphocytosis and lower nodal shrinkage under ibrutinib treatment, this last paramter being responsible for partial responses, subsequent relapses, as well as shorter PFS and OS. Either new small molecule combination approaches or antibodies targeting NOTCH1 could be future therapeutic options for NOTCH1 M patients.

Recent Advances in BTK Inhibitors for the Treatment of Inflammatory and Autoimmune Diseases

Bruton’s tyrosine kinase (BTK) plays a crucial role in B-cell receptor and Fc receptor signaling pathways. BTK is also involved in the regulation of Toll-like receptors and chemokine receptors. Given the central role of BTK in immunity, BTK inhibition represents a promising therapeutic approach for the treatment of inflammatory and autoimmune diseases. Great efforts have been made in developing BTK inhibitors for potential clinical applications in inflammatory and autoimmune diseases. This review covers the recent development of BTK inhibitors at preclinical and clinical stages in treating these diseases. Individual examples of three types of inhibitors, namely covalent irreversible inhibitors, covalent reversible inhibitors, and non-covalent reversible inhibitors, are discussed with a focus on their structure, bioactivity and selectivity. Contrary to expectations, reversible BTK inhibitors have not yielded a significant breakthrough so far. The development of covalent, irreversible BTK inhibitors has progressed more rapidly. Many candidates entered different stages of clinical trials; tolebrutinib and evobrutinib are undergoing phase 3 clinical evaluation. Rilzabrutinib, a covalent reversible BTK inhibitor, is now in phase 3 clinical trials and also offers a promising future. An analysis of the protein–inhibitor interactions based on published co-crystal structures provides useful clues for the rational design of safe and effective small-molecule BTK inhibitors.

Polymeric nanomedicines targeting hematological malignancies

Hematological malignancies (HMs) typically persisting in the blood, lymphoma, and/or bone marrow invalidate surgery and local treatments clinically used for solid tumors. The presence and drug resistance nature of cancer stem cells (CSCs) further lends HMs hard to cure. The development of new treatments like molecular targeted drugs and antibodies has improved the clinical outcomes for HMs but only to a certain extent, due to issues of low bioavailability, moderate response, occurrence of drug resistance, and/or dose-limiting toxicities. In the past years, polymeric nanomedicines targeting HMs including refractory and relapsed lymphoma, leukemia and multiple myeloma have emerged as a promising chemotherapeutic approach that is shown capable of overcoming drug resistance, delivering drugs not only to cancer cells but also CSCs, and increasing therapeutic index by lessening drug-associated adverse effects. In addition, polymeric nanomedicines have shown to potentiate next-generation anticancer modalities such as therapeutic proteins and nucleic acids in effectively treating HMs. In this review, we highlight recent advance in targeted polymeric nanoformulations that are coated with varying ligands (e.g. cancer cell membrane proteins, antibodies, transferrin, hyaluronic acid, aptamer, peptide, and folate) and loaded with different therapeutic agents (e.g. chemotherapeutics, molecular targeted drugs, therapeutic antibodies, nucleic acid drugs, and apoptotic proteins) for directing to distinct targets (e.g. CD19, CD20, CD22, CD30, CD38, CD44, CD64, CXCR, FLT3, VLA-4, and bone marrow microenvironment) in HMs. The advantages and potential challenges of different designs are discussed.

The ubiquitous role of spleen tyrosine kinase (Syk) in gut diseases: From mucosal immunity to targeted therapy

Spleen tyrosine kinase (Syk) is a cytoplasmic non-receptor protein tyrosine kinase expressed in a variety of cells and play crucial roles in signal transduction. Syk mediates downstream signaling by recruiting to the dually phosphorylated immunoreceptor tyrosine-based activation motifs (ITAMs) of the transmembrane adaptor molecule or the receptor chain itself. In gut diseases, Syk is observed to be expressed in intestinal epithelial cells, monocytes/macrophages, dendritic cells and mast cells. Activation of Syk in these cells can modulate intestinal mucosal immune response by promoting inflammatory cytokines and chemokines production, thus regulating gut homeostasis. Due to the restriction of specificity and selectivity for the development of Syk inhibitors, only a few such inhibitors are available in gut diseases, including intestinal ischemia/reperfusion damage, infectious disease, inflammatory bowel disease, etc. The promising outcomes of Syk inhibitors from both preclinical and clinical studies have shown to attenuate the progression of gut diseases thereby indicating a great potential in the development of Syk targeted therapy for treatment of gut diseases. This review depicts the characterization of Syk, summarizes the signal pathways of Syk, and discusses its potential targeted therapy for gut diseases.

CD44 engagement enhances acute myeloid leukemia cell adhesion to the bone marrow microenvironment by increasing VLA-4 avidity

Adhesive properties of leukemia cells shape the degree of organ infiltration and the extent of leukocytosis. CD44 and the integrin VLA-4, a CD49d/CD29 heterodimer, are important factors in progenitor cell adhesion in bone marrow. Here, we report their cooperation in acute myeloid leukemia (AML) by a novel non-classical CD44-mediated way of inside-out VLA-4 activation. In primary AML bone marrow samples from patients and the OCI-AML3 cell line, CD44 engagement by hyaluronan induced inside-out activation of VLA-4 resulting in enhanced leukemia cell adhesion on VCAM-1. This was independent of VLA-4 affinity regulation but based on ligand-induced integrin clustering on the cell surface. CD44-induced VLA-4 activation could be inhibited by the Src family kinase inhibitor PP2 and the multikinase inhibitor midostaurin. As a further consequence, the increased adhesion on VCAM-1 allowed AML cells to bind stromal cells strongly. Thereby, the VLA-4/VCAM-1 interaction promoted activation of Akt, MAPK, NF-kB and mTOR signaling and decreased AML cell apoptosis. Collectively, our investigations provide a mechanistic description of an unusual CD44 function in regulating VLA-4 avidity in AML, enhancing AML cell retention in the supportive bone marrow microenvironment.

TP53 Mutations with Low Variant Allele Frequency Predict Short Survival in Chronic Lymphocytic Leukemia

PURPOSE

In chronic lymphocytic leukemia (CLL), TP53 mutations are associated with reduced survival and resistance to standard chemoimmunotherapy (CIT). Nevertheless, the clinical impact of subclonal TP53 mutations below 10% to 15% variant allele frequency (VAF) remains unclear.

EXPERIMENTAL DESIGN

Using a training/validation approach, we retrospectively analyzed the clinical and biological features of TP53 mutations above (high-VAF) or below (low-VAF) the previously reported 10.0% VAF threshold, as determined by deep next-generation sequencing. Clinical impact of low-VAF TP53 mutations was also confirmed in a cohort (n = 251) of CLL treated with fludarabine-cyclophosphamide-rituximab (FCR) or FCR-like regimens from two UK trials.

RESULTS

In the training cohort, 97 of 684 patients bore 152 TP53 mutations, while in the validation cohort, 71 of 536 patients had 109 TP53 mutations. In both cohorts, patients with the TP53 mutation experienced significantly shorter overall survival (OS) than TP53 wild-type patients, regardless of the TP53 mutation VAF. By combining TP53 mutation and 17p13.1 deletion (del17p) data in the total cohort (n = 1,220), 113 cases were TP53 mutated only (73/113 with low-VAF mutations), 55 del17p/TP53 mutated (3/55 with low-VAF mutations), 20 del17p only, and 1,032 (84.6%) TP53 wild-type. A model including low-VAF cases outperformed the canonical model, which considered only high-VAF cases (c-indices 0.643 vs. 0.603, P < 0.0001), and improved the prognostic risk stratification of CLL International Prognostic Index. Clinical results were confirmed in CIT-treated cases (n = 552) from the retrospective cohort, and the UK trials cohort.

CONCLUSIONS

TP53 mutations affected OS regardless of VAF. This finding can be used to update the definition of TP53 mutated CLL for clinical purposes.

Leukaemia: a model metastatic disease

In contrast to solid cancers, which often require genetic modifications and complex cellular reprogramming for effective metastatic dissemination, leukaemic cells uniquely possess the innate ability for migration and invasion. Dedifferentiated, malignant leukocytes retain the benign leukocytes' capacity for cell motility and survival in the circulation, while acquiring the potential for rapid and uncontrolled cell division. For these reasons, leukaemias, although not traditionally considered as metastatic diseases, are in fact models of highly efficient metastatic spread. Accordingly, they are often aggressive and challenging diseases to treat. In this Perspective, we discuss the key molecular processes that facilitate metastasis in a variety of leukaemic subtypes, the clinical significance of leukaemic invasion into specific tissues and the current pipeline of treatments targeting leukaemia metastasis.

Inhibition of B-cell receptor signaling disrupts cell adhesion in mantle cell lymphoma via RAC2

Inhibition of the B-cell receptor (BCR) signaling pathway is highly effective in B-cell neoplasia through Bruton tyrosine kinase inhibition by ibrutinib. Ibrutinib also disrupts cell adhesion between a tumor and its microenvironment. However, it is largely unknown how BCR signaling is linked to cell adhesion. We observed that intrinsic sensitivities of mantle cell lymphoma (MCL) cell lines to ibrutinib correlated well with their cell adhesion phenotype. RNA-sequencing revealed that BCR and cell adhesion signatures were simultaneously downregulated by ibrutinib in the ibrutinib-sensitive, but not ibrutinib-resistant, cells. Among the differentially expressed genes, RAC2, part of the BCR signature and a known regulator of cell adhesion, was downregulated at both the RNA and protein levels by ibrutinib only in sensitive cells. RAC2 physically associated with B-cell linker protein (BLNK), a BCR adaptor molecule, uniquely in sensitive cells. RAC2 reduction using RNA interference and CRISPR impaired cell adhesion, whereas RAC2 overexpression reversed ibrutinib-induced cell adhesion impairment. In a xenograft mouse model, mice treated with ibrutinib exhibited slower tumor growth, with reduced RAC2 expression in tissue. Finally, RAC2 was expressed in ∼65% of human primary MCL tumors, and RAC2 suppression by ibrutinib resulted in cell adhesion impairment. These findings, made with cell lines, a xenograft model, and human primary lymphoma tumors, uncover a novel link between BCR signaling and cell adhesion. This study highlights the importance of RAC2 and cell adhesion in MCL pathogenesis and drug development.

B Cell Receptor signaling and genetic lesions in TP53 and CDKN2A/CDKN2B cooperate in Richter Transformation

B cell receptor (BCR) signals play a critical role in the pathogenesis of chronic lymphocytic leukemia (CLL), but their role in regulating CLL cell proliferation has still not been firmly established. Unlike normal B cells, CLL cells do not proliferate in vitro upon engagement of the BCR, suggesting that CLL cell proliferation is regulated by other signals from the microenvironment, such as those provided by Toll-like receptors or T cells. Here, we report that BCR engagement of human and murine CLL cells induces several positive regulators of the cell cycle, but simultaneously induces the negative regulators CDKN1A, CDKN2A and CDKN2B, which block cell cycle progression. We further show that introduction of genetic lesions that downregulate these cell cycle inhibitors, such as inactivating lesions in CDKN2A, CDKN2B and the CDKN1A regulator TP53, leads to more aggressive disease in a murine in vivo CLL model and spontaneous proliferation in vitro that is BCR-dependent but independent of costimulatory signals. Importantly, inactivating lesions in CDKN2A, CDKN2B and TP53 frequently co-occur in Richter syndrome, and BCR stimulation of human Richter syndrome cells with such lesions is sufficient to induce proliferation. We also show that tumor cells with combined TP53 and CDKN2A/2B abnormalities remain sensitive to BCR inhibitor treatment and are synergistically sensitive to the combination of a BCR and CDK4/6 inhibitor both in vitro and in vivo. These data provide evidence that BCR signals are directly involved in driving CLL cell proliferation and reveal a novel mechanism of Richter transformation.

FoxO1-GAB1 axis regulates homing capacity and tonic AKT activity in chronic lymphocytic leukemia

Recirculation of chronic lymphocytic leukemia (CLL) cells between the peripheral blood and lymphoid niches plays a critical role in disease pathophysiology, and inhibiting this process is one of the major mechanisms of action for B-cell receptor (BCR) inhibitors such as ibrutinib and idelalisib. Migration is a complex process guided by chemokine receptors and integrins. However, it remains largely unknown how CLL cells integrate multiple migratory signals while balancing survival in the peripheral blood and the decision to return to immune niches. Our study provided evidence that CXCR4/CD5 intraclonal subpopulations can be used to study the regulation of migration of CLL cells. We performed RNA profiling of CXCR4dimCD5bright vs CXCR4brightCD5dim CLL cells and identified differential expression of dozens of molecules with a putative function in cell migration. GRB2-associated binding protein 1 (GAB1) positively regulated CLL cell homing capacity of CXCR4brightCD5dim cells. Gradual GAB1 accumulation in CLL cells outside immune niches was mediated by FoxO1-induced transcriptional GAB1 activation. Upregulation of GAB1 also played an important role in maintaining basal phosphatidylinositol 3-kinase (PI3K) activity and the "tonic" AKT phosphorylation required to sustain the survival of resting CLL B cells. This finding is important during ibrutinib therapy, because CLL cells induce the FoxO1-GAB1-pAKT axis, which represents an adaptation mechanism to the inability to home to immune niches. We have demonstrated that GAB1 can be targeted therapeutically by novel GAB1 inhibitors, alone or in combination with BTK inhibition. GAB1 inhibitors induce CLL cell apoptosis, impair cell migration, inhibit tonic or BCR-induced AKT phosphorylation, and block compensatory AKT activity during ibrutinib therapy.

Intensity of antigen expression reflects IGHV mutational status and Dohner-defined prognostic categories in chronic lymphocytic leukemia, monoclonal B-cell lymphocytosis, and small lymphocytic lymphoma

We demonstrate the prognostic utility of antigen quantitation in chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) and monoclonal B-cell lymphocytosis (MBL). Median antibody-bound-per-cell (ABC) of CD20, CD22, CD25, CD19, and %CD38(+) was determined in CLL (185/208), SLL (8/208) and MBL (15/208) cases by flow cytometry, then compared to Dohner-classification, immunoglobulin status (mutated, IGHV-M; unmutated, IGHV-U), CLL-IPI risk and time to first treatment (TTFT). Trisomy 12 cases showed increased %CD38-expression (p = .0379). Higher %CD38 was observed in IGHV-U versus IGHV-M (p = .0003). CD20ABC was increased in IGHV-U versus IGHV-M (p = .006). Del13q cases demonstrated lower CD22ABC (p = .0198). Cases without cytogenetic abnormality exhibited higher CD19ABC (p = .0295) and CD22ABC (p = .0078). Del17p cases demonstrated lower CD25ABC (p = .0097). High and very-high CLL-IPI risk groups were associated with high CD38-expression (p = .02) and low CD25ABC (p = .0004). Shortened TTFT was associated with high CD38-expression (p < .0001). Interestingly, high CD25ABC trended toward shortened TTFT (p = .07). Quantitative antigen expression reflects CLL-IPI risk groups and Dohner-classification.

The future of laboratory testing in chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is a malignant lymphoproliferative disorder characterised by the accumulation of dysfunctional B-lymphocytes in the blood and lymphoid tissues. It is a clonally complex disease with a high degree of both intra-tumoural and inter-patient heterogeneity. This variability leads to a wide range of clinical outcomes and highlights the critical need for accurate prognostic tests in CLL. With the advent of a range of new targeted agents for CLL in recent years, there is also a clinical need for improved predictive tests to therapy. This review of laboratory testing in CLL focuses on emerging technologies for prognostication including single nucleotide polymorphism microarray for karyotypic analysis, targeted next generation sequencing analysis of the immunoglobulin heavy chain variable region gene as well as genes recurrently mutated in the disease such as TP53, and detection of minimal residual disease.

Comparison of ibrutinib and idelalisib plus rituximab in real-life relapsed/resistant chronic lymphocytic leukemia cases

OBJECTIVES

To compare the capacity of ibrutinib (IB) and idelalisib-rituximab (IDELA-R) of prolonging overall survival (OS) as in CLL patients, previously treated with chemotherapy only.

METHODS

A real-life cohort of 675 cases has been identified and investigated in the database of the groups participating in the study.

RESULTS

At an unadjusted univariate analysis, a significant death risk reduction was observed favoring IB (IDELA-R vs IB HR = 0.5, 95% CI = 0.36-0.71) although with some limitations due to the non-randomized and retrospective nature of the study and to the lower number of patients in the IDELA-R group (112 cases) related to the current prescribing practice. To overcome the potential problem of confounding by indication, we adjusted the association between the type of therapy and mortality for all variables significantly associated with OS at Cox univariate analysis. Furthermore, those variables, differently distributed between the two study groups, were introduced into the multivariate Cox model to improve the effectiveness of the analysis. By introducing all these variables into the multiple Cox regression model, we confirmed the protective effect of IB vs IDELA-R (HR = 0.67, 95% CI = 0.45-0.98, P = .04) independent of potential confounders.

CONCLUSIONS

Although our analysis presents some constraints, that is, the unavailability of additional potential confounders, and the retrospective nature of the study, this observation may be of help for the daily clinical practice, particularly in the absence of randomized trials comparing the two schedules.

Incorporating molecular biomarkers into the continuum of care in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a mature B-cell malignancy characterized by marked heterogeneity. Discoveries in disease biology over the past two decades have helped explain clinical variability and heralded the arrival of the targeted therapy era. In this article, we review improvements in risk stratification which have coincided with this progress, including individual biomarkers and their incorporation into prognostic models. Amidst an ever-expanding list of biomarkers, we seek to bring focus to the essential tests to improve patient care and counseling at particular times in the disease course, beginning with prognosis at diagnosis. The majority of patients do not require treatment at the time of diagnosis, making time-to-first-treatment a key initial prognostic concern. Prognostic and predictive biomarkers are then considered at subsequent major junctures, including at the time of treatment initiation, while on therapy, and at the time of relapse on novel agents.

Longitudinal CITE-Seq profiling of chronic lymphocytic leukemia during ibrutinib treatment: evolution of leukemic and immune cells at relapse

BACKGROUND

Ibrutinib, an irreversible Bruton Tyrosine Kinase (BTK) inhibitor, has revolutionized Chronic Lymphocytic Leukemia (CLL) treatment, but resistances to ibrutinib have emerged, whether related or not to BTK mutations. Patterns of CLL evolution under ibrutinib therapy are well characterized for the leukemic cells but not for their microenvironment.

METHODS

Here, we addressed this question at the single cell level of both transcriptome and immune-phenotype. The PBMCs from a CLL patient were monitored during ibrutinib treatment using Cellular Indexing of Transcriptomes and Epitopes by sequencing (CITE-Seq) technology.

RESULTS

This unveiled that the short clinical relapse of this patient driven by BTK mutation is associated with intraclonal heterogeneity in B leukemic cells and up-regulation of common signaling pathways induced by ibrutinib in both B leukemic cells and immune cells. This approach also pinpointed a subset of leukemic cells present before treatment and highly enriched during progression under ibrutinib. These latter exhibit an original gene signature including up-regulated BCR, MYC-activated, and other targetable pathways. Meanwhile, although ibrutinib differentially affected the exhaustion of T lymphocytes, this treatment enhanced the T cell cytotoxicity even during disease progression.

CONCLUSIONS

These results could open new alternative of therapeutic strategies for ibrutinib-refractory CLL patients, based on immunotherapy or targeting B leukemic cells themselves.

CD49d promotes disease progression in chronic lymphocytic leukemia: new insights from CD49d bimodal expression

CD49d is a remarkable prognostic biomarker of chronic lymphocytic leukemia (CLL). The cutoff value for the extensively validated 30% of positive CLL cells is able to separate CLL patients into 2 subgroups with different prognoses, but it does not consider the pattern of CD49d expression. In the present study, we analyzed a cohort of 1630 CLL samples and identified the presence of ∼20% of CLL cases (n = 313) characterized by a bimodal expression of CD49d, that is, concomitant presence of a CD49d+ subpopulation and a CD49d- subpopulation. At variance with the highly stable CD49d expression observed in CLL patients with a homogeneous pattern of CD49d expression, CD49d bimodal CLL showed a higher level of variability in sequential samples, and an increase in the CD49d+ subpopulation over time after therapy. The CD49d+ subpopulation from CD49d bimodal CLL displayed higher levels of proliferation compared with the CD49d- cells; and was more highly represented in the bone marrow compared with peripheral blood (PB), and in PB CLL subsets expressing the CXCR4dim/CD5bright phenotype, known to be enriched in proliferative cells. From a clinical standpoint, CLL patients with CD49d bimodal expression, regardless of whether the CD49d+ subpopulation exceeded the 30% cutoff or not, experienced clinical behavior similar to CD49d+ CLL, both in chemoimmunotherapy (n = 1522) and in ibrutinib (n = 158) settings. Altogether, these results suggest that CD49d can drive disease progression in CLL, and that the pattern of CD49d expression should also be considered to improve the prognostic impact of this biomarker in CLL.

Genetic and Non-Genetic Mechanisms of Resistance to BCR Signaling Inhibitors in B Cell Malignancies

The approval of BTK and PI3K inhibitors (ibrutinib, idelalisib) represents a revolution in the therapy of B cell malignancies such as chronic lymphocytic leukemia (CLL), mantle-cell lymphoma (MCL), diffuse large B cell lymphoma (DLBCL), follicular lymphoma (FL), or Waldenström's macroglobulinemia (WM). However, these "BCR inhibitors" function by interfering with B cell pathophysiology in a more complex way than anticipated, and resistance develops through multiple mechanisms. In ibrutinib treated patients, the most commonly described resistance-mechanism is a mutation in BTK itself, which prevents the covalent binding of ibrutinib, or a mutation in PLCG2, which acts to bypass the dependency on BTK at the BCR signalosome. However, additional genetic aberrations leading to resistance are being described (such as mutations in the CARD11, CCND1, BIRC3, TRAF2, TRAF3, TNFAIP3, loss of chromosomal region 6q or 8p, a gain of Toll-like receptor (TLR)/MYD88 signaling or gain of 2p chromosomal region). Furthermore, relative resistance to BTK inhibitors can be caused by non-genetic adaptive mechanisms leading to compensatory pro-survival pathway activation. For instance, PI3K/mTOR/Akt, NFkB and MAPK activation, BCL2, MYC, and XPO1 upregulation or PTEN downregulation lead to B cell survival despite BTK inhibition. Resistance could also arise from activating microenvironmental pathways such as chemokine or integrin signaling via CXCR4 or VLA4 upregulation, respectively. Defining these compensatory pro-survival mechanisms can help to develop novel therapeutic combinations of BTK inhibitors with other inhibitors (such as BH3-mimetic venetoclax, XPO1 inhibitor selinexor, mTOR, or MEK inhibitors). The mechanisms of resistance to PI3K inhibitors remain relatively unclear, but some studies point to MAPK signaling upregulation via both genetic and non-genetic changes, which could be co-targeted therapeutically. Alternatively, drugs mimicking the BTK/PI3K inhibition effect can be used to prevent adhesion and/or malignant B cell migration (chemokine and integrin inhibitors) or to block the pro-proliferative T cell signals in the microenvironment (such as IL4/STAT signaling inhibitors). Here we review the genetic and non-genetic mechanisms of resistance and adaptation to the first generation of BTK and PI3K inhibitors (ibrutinib and idelalisib, respectively), and discuss possible combinatorial therapeutic strategies to overcome resistance or to increase clinical efficacy.

Prediction of Outcome in Patients With Chronic Lymphocytic Leukemia Treated With Ibrutinib: Development and Validation of a Four-Factor Prognostic Model

PURPOSE

Randomized trials established the superiority of ibrutinib-based therapy over chemoimmunotherapy in chronic lymphocytic leukemia. Durability of progression-free survival (PFS) with ibrutinib can vary by patient subgroup. Clinical tools for prognostication and risk-stratification are needed.

PATIENTS AND METHODS

Patients treated with ibrutinib in phase II and III trials provided the discovery data set and were subdivided into discovery and internal validation cohorts. An external validation cohort included 84 patients enrolled in our investigator-initiated phase II trial. Univariable analysis of 18 pretreatment parameters was performed using PFS and overall survival (OS) end-points. Multivariable analysis and machine-learning algorithms identified four factors for a prognostic model that was validated in internal and external cohorts.

RESULTS

Factors independently associated with inferior PFS and OS were as follows: TP53 aberration, prior treatment, β-2 microglobulin ≥ 5 mg/L, and lactate dehydrogenase > 250 U/L. Each of these four factors contributed one point to a prognostic model that stratified patients into three risk groups: three to four points, high risk; two points, intermediate risk; zero to one point, low risk. The 3-year PFS rates for all 804 patients combined were 47%, 74%, and 87% for the high-, the intermediate-, and the low-risk group, respectively (P < .0001). The 3-year OS rates were 63%, 83%, and 93%, respectively (P < .0001). The model remained significant when applied to treatment-naïve and relapsed/refractory cohorts individually. For 84 patients in the external cohort, BTK and PLCG2 mutations were tested cross-sectionally and at progression. The cumulative incidences of mutations were strongly correlated with the model. In the external cohort, Richter's transformation occurred in 17% of the high-risk group, and in no patient in the low-risk group.

CONCLUSION

Patients at increased risk of ibrutinib failure can be identified at treatment initiation and considered for clinical trials.

Recent progress of prognostic biomarkers and risk scoring systems in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most prevalent adult leukemia with high heterogeneity in the western world. Thus, investigators identified a number of prognostic biomarkers and scoring systems to guide treatment decisions and validated them in the context of immunochemotherapy. A better understanding of prognostic biomarkers, including serum markers, flow cytometry outcomes, IGHV mutation status, microRNAs, chromosome aberrations and gene mutations, have contributed to prognosis in CLL. Del17p/ TP53 mutation, NOTCH1 mutation, CD49d, IGHV mutation status, complex karyotypes and microRNAs were reported to be of predictive values to guide clinical decisions. Based on the biomarkers above, classic prognostic models, such as the Rai and Binet staging systems, MDACC nomogram, GCLLSG model and CLL-IPI, were developed to improve risk stratification and tailor treatment intensity. Considering the presence of novel agents, many investigators validated the conventional prognostic biomarkers in the setting of novel agents and only TP53 mutation status/del 17p and CD49d expression were reported to be of prognostic value. Whether other prognostic indicators and models can be used in the context of novel agents, further studies are required.

Importance of Crosstalk Between Chronic Lymphocytic Leukemia Cells and the Stromal Microenvironment: Direct Contact, Soluble Factors, and Extracellular Vesicles

Chronic lymphocytic leukemia (CLL) is caused by the accumulation of malignant B cells due to a defect in apoptosis and the presence of small population of proliferating cells principally in the lymph nodes. The abnormal survival of CLL B cells is explained by a plethora of supportive stimuli produced by the surrounding cells of the microenvironment, including follicular dendritic cells (FDCs), and mesenchymal stromal cells (MSCs). This crosstalk between malignant cells and normal cells can take place directly by cell-to-cell contact (assisted by adhesion molecules such as VLA-4 or CD100), indirectly by soluble factors (chemokines such as CXCL12, CXCL13, or CCL2) interacting with their receptors or by the exchange of material (protein, microRNAs or long non-coding RNAs) via extracellular vesicles. These different communication methods lead to different activation pathways (including BCR and NFκB pathways), gene expression modifications (chemokines, antiapoptotic protein increase, prognostic biomarkers), chemotaxis, homing in lymphoid tissues and survival of leukemic cells. In addition, these interactions are bidirectional, and CLL cells can manipulate the normal surrounding stromal cells in different ways to establish a supportive microenvironment. Here, we review this complex crosstalk between CLL cells and stromal cells, focusing on the different types of interactions, activated pathways, treatment strategies to disrupt this bidirectional communication, and the prognostic impact of these induced modifications.

Mechanisms of B Cell Receptor Activation and Responses to B Cell Receptor Inhibitors in B Cell Malignancies

The B cell receptor (BCR) pathway has been identified as a potential therapeutic target in a number of common B cell malignancies, including chronic lymphocytic leukemia, diffuse large B cell lymphoma, Burkitt lymphoma, follicular lymphoma, mantle cell lymphoma, marginal zone B cell lymphoma, and Waldenstrom's macroglobulinemia. This finding has resulted in the development of numerous drugs that target this pathway, including various inhibitors of the kinases BTK, PI3K, and SYK. Several of these drugs have been approved in recent years for clinical use, resulting in a profound change in the way these diseases are currently being treated. However, the response rates and durability of responses vary largely across the different disease entities, suggesting a different proportion of patients with an activated BCR pathway and different mechanisms of BCR pathway activation. Indeed, several antigen-dependent and antigen-independent mechanisms have recently been described and shown to result in the activation of distinct downstream signaling pathways. The purpose of this review is to provide an overview of the mechanisms responsible for the activation of the BCR pathway in different B cell malignancies and to correlate these mechanisms with clinical responses to treatment with BCR inhibitors.

An Updated Perspective on Current Prognostic and Predictive Biomarkers in Chronic Lymphocytic Leukemia in the Context of Chemoimmunotherapy and Novel Targeted Therapy

Chronic lymphocytic leukemia (CLL) is a heterogeneous disease with a variable clinical course. Novel biomarkers discovered over the past 20 years have revolutionized the way clinicians approach prognostication and treatment especially in the chemotherapy-free era. Herein, we review the best established prognostic and predictive biomarkers in the setting of chemoimmunotherapy (CIT) and novel targeted therapy. We propose that TP53 disruption (defined as either TP53 mutation or chromosome 17p deletion), unmutated immunoglobulin heavy chain variable region gene status (UM IGHV), NOTCH1 mutation, and CD49d expression are the strongest prognosticators of disease progression and overall survival in the field of novel biomarkers including recurrent gene mutations. We also highlight the predictive role of TP53 disruption, UM IGHV, and NOTCH1 mutation in the setting of CIT and TP53 disruption and CD49d expression in the setting of novel targeted therapy employing B-cell receptor (BCR) and B-cell lymphoma-2 (BCL2) inhibition. Finally, we discuss future directions in the field of biomarker development to identify those with relapsed/refractory disease at risk for progression despite treatment with novel therapies.