Autologous T-cell activation fosters ABT-199 resistance in chronic lymphocytic leukemia: rationale for a combined therapy with SYK inhibitors and anti-CD20 monoclonal antibodies

Evaluation of the novel therapeutic anti-CCR7 antibody CAP-100 as an add-on therapy in chronic lymphocytic leukemia patients receiving venetoclax

The Bruton's tyrosine kinase inhibitor ibrutinib and the B-cell lymphoma 2 anti-apoptotic protein inhibitor venetoclax provide high response rates in chronic lymphocytic leukemia (CLL). However, there is a growing number of patients that relapse after treatment or show refractory disease, thus new targets and agents are still needed. We have previously reported the chemokine receptor CCR7 as a relevant deregulated target in CLL and have developed CAP-100, a novel therapeutic anti-CCR7 antibody that is under evaluation for relapse/refractory CLL (NCT04704323). While CCR7 expression has been shown to be down-modulated in CLL patients treated with ibrutinib, whether venetoclax acts in a similar manner remains unaddressed. Here, we aimed to document the impact of venetoclax on CCR7 expression in CLL cells, as well as on the pre-clinical activity of CAP-100. To this end, we addressed CCR7 expression by flow cytometry and the antibody efficacy by means of in vitro chemotactic and antibody-dependent cell-mediated cytotoxicity (ADCC) assays. Our data indicate that venetoclax treatment did not significantly modify CCR7 expression pattern nor CAP-100 mechanisms of action. Together, these findings support CAP-100 as an adjuvant therapy to venetoclax that may introduce additional modes of action in CLL therapy.

Venetoclax resistance induced by activated T cells can be counteracted by sphingosine kinase inhibitors in chronic lymphocytic leukemia

The treatment of chronic lymphocytic leukemia (CLL) patients with venetoclax-based regimens has demonstrated efficacy and a safety profile, but the emergence of resistant cells and disease progression is a current complication. Therapeutic target of sphingosine kinases (SPHK) 1 and 2 has opened new opportunities in the treatment combinations of cancer patients. We previously reported that the dual SPHK1/2 inhibitor, SKI-II enhanced the in vitro cell death triggered by fludarabine, bendamustine or ibrutinib and reduced the activation and proliferation of chronic lymphocytic leukemia (CLL) cells. Since we previously showed that autologous activated T cells from CLL patients favor the activation of CLL cells and the generation of venetoclax resistance due to the upregulation of BCL-XL and MCL-1, we here aim to determine whether SPHK inhibitors affect this process. To this aim we employed the dual SPHK1/2 inhibitor SKI-II and opaganib, a SPHK2 inhibitor that is being studied in clinical trials. We found that SPHK inhibitors reduce the activation of CLL cells and the generation of venetoclax resistance induced by activated T cells mainly due to a reduced upregulation of BCL-XL. We also found that SPHK2 expression was enhanced in CLL cells by activated T cells of the same patient and the presence of venetoclax selects resistant cells with high levels of SPHK2. Of note, SPHK inhibitors were able to re-sensitize already resistant CLL cells to a second venetoclax treatment. Our results highlight the therapeutic potential of SPHK inhibitors in combination with venetoclax as a promising treatment option for the patients.

Natural Killer Cells in Chronic Lymphocytic Leukemia: Functional Impairment and Therapeutic Potential

Immunotherapy approaches have advanced rapidly in recent years. While the greatest therapeutic advances so far have been achieved with T cell therapies such as immune checkpoint blockade and CAR-T, recent advances in NK cell therapy have highlighted the therapeutic potential of these cells. Chronic lymphocytic leukemia (CLL), the most prevalent form of leukemia in Western countries, is a very immunosuppressive disease but still shows significant potential as a target of immunotherapy, including NK-based therapies. In addition to their antileukemia potential, NK cells are important immune effectors in the response to infections, which represent a major clinical concern for CLL patients. Here, we review the interactions between NK cells and CLL, describing functional changes and mechanisms of CLL-induced NK suppression, interactions with current therapeutic options, and the potential for therapeutic benefit using NK cell therapies.

Venetoclax enhances the efficacy of therapeutic antibodies in B-cell malignancies by augmenting tumor cell phagocytosis

Immunotherapy has evolved as a powerful tool for the treatment of B-cell malignancies, and patient outcomes have improved by combining therapeutic antibodies with conventional chemotherapy. Overexpression of antiapoptotic B-cell lymphoma 2 (Bcl-2) is associated with a poor prognosis, and increased levels have been described in patients with "double-hit" diffuse large B-cell lymphoma, a subgroup of Burkitt's lymphoma, and patients with pediatric acute lymphoblastic leukemia harboring a t(17;19) translocation. Here, we show that the addition of venetoclax (VEN), a specific Bcl-2 inhibitor, potently enhanced the efficacy of the therapeutic anti-CD20 antibody rituximab, anti-CD38 daratumumab, and anti-CD19-DE, a proprietary version of tafasitamab. This was because of an increase in antibody-dependent cellular phagocytosis by macrophages as shown in vitro and in vivo in cell lines and patient-derived xenograft models. Mechanistically, double-hit lymphoma cells subjected to VEN triggered phagocytosis in an apoptosis-independent manner. Our study identifies the combination of VEN and therapeutic antibodies as a promising novel strategy for the treatment of B-cell malignancies.

In Vitro and In Vivo Models of CLL–T Cell Interactions: Implications for Drug Testing

Simple Summary

Chronic lymphocytic leukemia (CLL) cells in the peripheral blood and lymphoid microenvironment display substantially different gene expression profiles and proliferative capaci-ty. It has been suggested that CLL–T-cell interactions are key pro-proliferative stimuli in immune niches. We review in vitro and in vivo model systems that mimic CLL-T-cell interactions to trigger CLL proliferation and study therapy resistance. We focus on studies describing the co-culture of leukemic cells with T cells, or supportive cell lines expressing T-cell factors, and simplified models of CLL cells’ stimulation with recombinant factors. In the second part, we summarize mouse models revealing the role of T cells in CLL biology and implications for generating patient-derived xenografts by co-transplanting leukemic cells with T cells.

Abstract

T cells are key components in environments that support chronic lymphocytic leukemia (CLL), activating CLL-cell proliferation and survival. Here, we review in vitro and in vivo model systems that mimic CLL–T-cell interactions, since these are critical for CLL-cell division and resistance to some types of therapy (such as DNA-damaging drugs or BH3-mimetic venetoclax). We discuss approaches for direct CLL-cell co-culture with autologous T cells, models utilizing supportive cell lines engineered to express T-cell factors (such as CD40L) or stimulating CLL cells with combinations of recombinant factors (CD40L, interleukins IL4 or IL21, INFγ) and additional B-cell receptor (BCR) activation with anti-IgM antibody. We also summarize strategies for CLL co-transplantation with autologous T cells into immunodeficient mice (NOD/SCID, NSG, NOG) to generate patient-derived xenografts (PDX) and the role of T cells in transgenic CLL mouse models based on TCL1 overexpression (Eµ-TCL1). We further discuss how these in vitro and in vivo models could be used to test drugs to uncover the effects of targeted therapies (such as inhibitors of BTK, PI3K, SYK, AKT, MEK, CDKs, BCL2, and proteasome) or chemotherapy (fludarabine and bendamustine) on CLL–T-cell interactions and CLL proliferation.

Aberrantly expressed Wnt5a in nurse-like cells drives resistance to Venetoclax in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of neoplastic B lymphocytes with high levels of Wnt5a in the plasma. Currently, the cell source of Wnt5a remains controversial. The receptor of Wnt5a is ROR1, whose expression is associated with disease progression and resistance to venetoclax, a BCL-2 inhibitor approved for the treatment of CLL. In this study, we found that the levels of Wnt5a in the plasma of CLL patients were positively correlated with absolute monocyte counts, but not lymphocyte counts. We cultured monocyte-derived nurse-like cells (NLCs) from patients with CLL, and detected Wnt5a expressed in NLCs. Flow cytometry and transwell assays showed that the antibody neutralizing Wnt5a inhibited the enhanced survival and migration in CLL cells co-cultured with NLCs. Furthermore, we performed a drug screening with CLL cells cultured with or without NLCs with a library containing 133 FDA-approved oncology drugs by using high-throughput flow cytometry. We observed a significant resistance to venetoclax in CLL cells co-cultured with NLCs. Immunoblot revealed the activation of NF-κB with enhanced expression of MCL-1 and BCL-XL in CLL cells co-cultured with NLCs. Neutralizing Wnt5a or blocking NF-κB pathway significantly decreased the expression of MCL-1 and BCL-XL, which leads to enhanced sensitivity to venetoclax in CLL cells co-cultured with NLCs. In conclusion, our data showed that NLCs could be one of the sources of Wnt5a detected in patients with CLL, and Wnt5a-induced NF-κB activation in the CLL microenvironment results in resistance to venetoclax in CLL cells.

Targeting the tumor microenvironment in chronic lymphocytic leukemia

The tumor microenvironment (TME) plays an essential role in the development, growth, and survival of the malignant B-cell clone in chronic lymphocytic leukemia (CLL). Within the proliferation niches of lymph nodes, bone marrow, and secondary lymphoid organs, a variety of phenotypically and functionally altered cell types, including T cells, natural killer cells, monocytes/macrophages, endothelial and mesenchymal stroma cells, provide crucial survival signals, along with CLL-cellinduced suppression of antitumor immune responses. The B-cell receptor pathway plays a pivotal role in mediating the interaction between CLL cells and the TME. However, an increasing number of additional components of the multifactorial TME are being discovered. Although the majority of therapeutic strategies employed in CLL hitherto have focused on targeting the leukemic cells, emerging evidence implies that modulation of microenvironmental cells and CLL-TME interactions by novel therapeutic agents significantly affect their clinical efficacy. Thus, improving our understanding of CLL-TME interactions and how they are affected by current therapeutic agents may improve and guide treatment strategies. Identification of novel TME interactions may also pave the road for the development of novel therapeutic strategies targeting the TME. In this review, we summarize current evidence on the effects of therapeutic agents on cells and interactions within the TME. With a growing demand for improved and personalized treatment options in CLL, this review aims at inspiring future exploration of smart drug combination strategies, translational studies, and novel therapeutic targets in clinical trials.

Venetoclax-resistant CLL cells show a highly activated and proliferative phenotype

Venetoclax treatment has demonstrated efficacy and a safety profile in chronic lymphocytic leukemia (CLL) patients, however the emergence of resistant cells is a current complication. We and others, previously reported that the activation of CLL cells by signals that mimic microenvironment stimuli favors the upregulation of anti-apoptotic proteins from B cell lymphoma-2 (BCL-2) family that are not targeted by venetoclax, reducing malignant cell sensitivity to the drug. We here studied venetoclax-resistant CLL cells generated in vitro by autologous activated T lymphocytes, and found that they showed an aggressive phenotype characterized by increased expression of activation and proliferation markers. Moreover, surviving cells expressed high levels of B cell lymphoma-extra-large (BCL-XL) and/or myeloid cell leukemia-1 (MCL-1), and a sustained resistance to a second treatment with the drug. Interestingly, the spleen tyrosine kinase (SYK) inhibitor entospletinib, and the phosphoinositide 3-kinase delta (PI3Kδ) inhibitor idelalisib, reduced T cell activation, impaired the generation of leukemic cells with this aggressive phenotype, and were able to restore CLL sensitivity to venetoclax. Our data highlight a novel combination to overcome resistance to venetoclax in CLL.

In Vitro Sensitivity to Venetoclax and Microenvironment Protection in Hairy Cell Leukemia

Current standard treatment of patients with hairy cell leukemia (HCL), a chronic B-cell neoplasia of low incidence that affects the elderly, is based on the administration of purine analogs such as cladribine. This chemotherapy approach shows satisfactory responses, but the disease relapses, often repeatedly. Venetoclax (ABT-199) is a Bcl-2 inhibitor currently approved for the treatment of chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML) in adult patients ineligible for intensive chemotherapy. Given that HCL cells express Bcl-2, our aim was to evaluate venetoclax as a potential therapy for HCL. We found that clinically relevant concentrations of venetoclax (0.1 and 1 µM) induced primary HCL cell apoptosis in vitro as measured by flow cytometry using Annexin V staining. As microenvironment induces resistance to venetoclax in CLL, we also evaluated its effect in HCL by testing the following stimuli: activated T lymphocytes, stromal cells, TLR-9 agonist CpG, and TLR-2 agonist PAM3. We found decreased levels of venetoclax-induced cytotoxicity in HCL cells exposed for 48 h to any of these stimuli, suggesting that leukemic B cells from HCL patients are sensitive to venetoclax, but this sensitivity can be overcome by signals from the microenvironment. We propose that the combination of venetoclax with drugs that target the microenvironment might improve its efficacy in HCL.

Venetoclax-based salvage therapy followed by Venetoclax and DLI maintenance vs. FLAG-Ida for relapsed or refractory acute myeloid leukemia after allogeneic stem cell transplantation

We retrospectively compared the outcomes of 20 patients receiving Venetoclax + low-dose Cytarabine + Actinomycin D (ACTIVE) with 29 patients receiving FLAG-Ida as salvage therapy for relapsed or refractory AML (R/R AML) after alloSCT. The groups were statistically balanced according to age, performance status, cytogenetics, and previous treatment. The overall response rate (CR + CRp + MLFS) of ACTIVE was 75% (15/20) in comparison to 66% (19/29) in the FLAG-Ida group (p = 0.542). The cumulative CR + CRp rate was significantly higher in the ACTIVE group compared to FLAG-Ida (70% (14/20) vs. 34% (10/29), respectively, p = 0.02). All three patients failing previous Venetoclax therapy and five out of seven patients with previous FLAG-Ida exposure achieved a CR/CRp after ACTIVE induction. ACTIVE patients survived longer compared to FLAG-Ida patients (13.1 vs. 5.1 months, respectively, p = 0.032). The treatment-related mortality was 0% in the ACTIVE group and 34% (10/29) in the FLAG-Ida patients (p = 0.003). The cumulative incidence of relapse did not differ between the two treatment groups. ACTIVE appears to have comparable antileukemic activity and lower toxicity compared to FLAG-Ida resulting in improved survival. Patients with Venetoclax or FLAG-Ida exposure responded to ACTIVE.

Immunomodulatory effects of different intravenous immunoglobulin preparations in chronic lymphocytic leukemia

Hypogammaglobulinemia is the most frequently observed immune defect in chronic lymphocytic leukemia (CLL). Although CLL patients usually have low serum levels of all isotypes (IgG, IgM and IgA), standard immunoglobulin (Ig) preparations for replacement therapy administrated to these patients contain more than 95% of IgG. Pentaglobin is an Ig preparation of intravenous application (IVIg) enriched with IgM and IgA (IVIgGMA), with the potential benefit to restore the Ig levels of all isotypes. Because IVIg preparations at high doses have well-documented anti-inflammatory and immunomodulatory effects, we aimed to evaluate the capacity of Pentaglobin and a standard IVIg preparation to affect leukemic and T cells from CLL patients. In contrast to standard IVIg, we found that IVIgGMA did not modify T cell activation and had a lower inhibitory effect on T cell proliferation. Regarding the activation of leukemic B cells through BCR, it was similarly reduced by both IVIgGMA and IVIgG. None of these IVIg preparations modified spontaneous apoptosis of T or leukemic B cells. However, the addition of IVIgGMA on in vitro cultures decreased the apoptosis of T cells induced by the BCL-2 inhibitor, venetoclax. Importantly, IVIgGMA did not impair venetoclax-induced apoptosis of leukemic B cells. Overall, our results add new data on the effects of different preparations of IVIg in CLL, and show that the IgM/IgA enriched preparation not only affects relevant mechanisms involved in CLL pathogenesis but also has a particular profile of immunomodulatory effects on T cells that deserves further investigation.

Of Lymph Nodes and CLL Cells: Deciphering the Role of CCR7 in the Pathogenesis of CLL and Understanding Its Potential as Therapeutic Target

The lymph node (LN) is an essential tissue for achieving effective immune responses but it is also critical in the pathogenesis of chronic lymphocytic leukemia (CLL). Within the multitude of signaling pathways aberrantly regulated in CLL the homeostatic axis composed by the chemokine receptor CCR7 and its ligands is the main driver for directing immune cells to home into the LN. In this literature review, we address the roles of CCR7 in the pathophysiology of CLL, and how this chemokine receptor is of critical importance to develop more rational and effective therapies for this malignancy.

Immunoregulatory effects of Lurbinectedin in chronic lymphocytic leukemia

Despite significant therapeutic improvements chronic lymphocytic leukemia (CLL) remains an incurable disease and there is a persistent pursuit of new treatment alternatives. Lurbinectedin, a selective inhibitor of active transcription of protein-coding genes, is currently in phase II/III clinical trials for solid tumors such as small-cell lung cancer (SCLC). In this study, we aimed to evaluate the activity of Lurbinectedin on circulating mononuclear cells from CLL patients and to determine whether Lurbinectedin could affect the cross-talk between B-CLL cells and the tumor microenvironment. We found that Lurbinectedin induced a dose- and time-dependent death in all cell types evaluated, with B cells, monocytes and monocytic myeloid derived suppressor cells (Mo-MDSC) being the most susceptible populations. At sub-apoptotic doses, Lurbinectedin decreased the expression of CCR7 in B-CLL cells and impaired their migration towards CCL19 and CCL21. Furthermore, low concentrations of Lurbinectedin stimulated the synthesis of pro-IL1β in monocytes and nurse-like cells, without inducing the inflammasome activation. Altogether, these results indicate that Lurbinectedin might have antitumor activity in CLL due to its direct action on leukemic cells in combination with its effects on the tumor microenvironment. Our findings encourage further investigation of Lurbinectedin as a potential therapy for CLL.

Spleen tyrosine kinase (SYK) blocks autophagic Tau degradation in vitro and in vivo

Spleen tyrosine kinase (SYK) plays a major role in inflammation and in adaptive immune responses and could therefore contribute to the neuroinflammation observed in various neurodegenerative diseases. Indeed, previously we have reported that SYK also regulates β-amyloid (Aβ) production and hyperphosphorylation of Tau protein involved in these diseases. Moreover, SYK hyperactivation occurs in a subset of activated microglia, in dystrophic neurites surrounding Aβ deposits, and in neurons affected by Tau pathology both in individuals with Alzheimer's disease (AD) and in AD mouse models. SYK activation increases Tau phosphorylation and accumulation, suggesting that SYK could be an attractive target for treating AD. However, the mechanism by which SYK affects Tau pathology is not clear. In this study, using cell biology and biochemical approaches, along with immunoprecipitation and immunoblotting, quantitative RT-PCR, and ELISAs, we found that SYK inhibition increases autophagic Tau degradation without impacting Tau production. Using neuron-like SH-SY5Y cells, we demonstrate that SYK acts upstream of the mammalian target of rapamycin (mTOR) pathway and that pharmacological inhibition or knockdown of SYK decreases mTOR pathway activation and increases autophagic Tau degradation. Interestingly, chronic SYK inhibition in a tauopathy mouse model profoundly reduced Tau accumulation, neuroinflammation, neuronal and synaptic loss, and also reversed defective autophagy. Our results further suggest that the SYK up-regulation observed in the brains of individuals with AD contributes to defective autophagic clearance leading to the accumulation of pathogenic Tau species. These findings further highlight SYK as a therapeutic target for the treatment of tauopathies and other neurodegenerative proteinopathies associated with defective autophagic clearance.