PI3K p110δ inactivation antagonizes chronic lymphocytic leukemia and reverses T cell immune suppression

PI3K Inhibitors in Hematology: When One Door Closes…

The PI3K signaling pathway regulates key cellular processes and is one of the most aberrantly activated pathways in cancer. The class I PI3K catalytic subunits p110γ and p110δ are highly enriched in leukocytes, providing an additional rationale for targeting these PI3Ks in hematologic malignancies. In 2014, the PI3Kδ inhibitor idelalisib was the first of four PI3K inhibitors (PI3Ki) to receive regulatory approval for relapsed B-cell malignancies. This was followed by approvals of the pan-class I inhibitor copanlisib (2017), the dual PI3Kγ/δ inhibitor duvelisib (2018), and the PI3Kδ and casein kinase 1ε inhibitor umbralisib (2021). Copanlisib and umbralisib received accelerated approvals, whereas idelalisib and duvelisib received initial accelerated approvals followed by full approvals. The accelerated approvals were based on overall response rates; however, follow-up studies showed increased risk of death and serious side effects. Furthermore, the confirmatory trial with copanlisib failed to show an improvement in progression-free survival when compared with chemoimmunotherapy. These developments led to black box warnings for idelalisib and duvelisib and withdrawal of copanlisib and umbralisib from the market by their manufacturers. Given the uncertain future of this drug class, additional manufacturers terminated ongoing phase III trials with novel PI3Kis. In this study, we review the development and current status of PI3Kis in hematology, limitations to their use, and our perspective on whether there is a future for PI3Kis in hematology.

Lessons learned from the Eµ-TCL1 mouse model of CLL

The Eµ-TCL1 mouse model has been used for over 20 years to study the pathobiology of chronic lymphocytic leukemia (CLL) and for preclinical testing of novel therapies. A CLL-like disease develops with increasing age in these mice due to a B cell specific overexpression of human TCL1. The reliability of this model to mirror human CLL is controversially discussed, as none of the known driver mutations identified in patients are found in Eµ-TCL1 mice. It has to be acknowledged that this mouse model was key to develop targeted therapies that aim at inhibiting the constitutive B cell receptor (BCR) signaling, a main driver of CLL. Inhibitors of BCR signaling became standard-of-care for a large proportion of patients with CLL as they are highly effective. The Eµ-TCL1 model further advanced our understanding of CLL biology owed to studies that crossed this mouse line with various transgenic mouse models and demonstrated the relevance of CLL-cell intrinsic and -extrinsic drivers of disease. These studies were instrumental in showing the relevance of the tumor microenvironment in the lymphoid tissues for disease progression and immune escape in CLL. It became clear that CLL cells shape and rely on stromal and immune cells, and that immune suppressive mechanisms and T cell exhaustion contribute to CLL progression. Based on this knowledge, new immunotherapy strategies were clinically tested for CLL, but so far with disappointing results. As some of these therapies were effective in the Eµ-TCL1 mouse model, the question arose concerning the translatability of preclinical studies in these mice. The aim of this review is to summarize lessons we have learnt over the last decades by studying CLL-like disease in the Eµ-TCL1 mouse model. The article focuses on pitfalls and limitations of the model, as well as the gained knowledge and potential of using this model for the development of novel treatment strategies to achieve the goal of curing patients with CLL.

PI3Kδ Mediates Fibrosis by Patient-Derived Vitreous

The epithelial-mesenchymal transition (EMT) is a fundamental process in developing fibrotic diseases, including forming epiretinal membranes (ERMs). ERMs can result in irreversible vision loss. Previous research has demonstrated that vitreous (VIT) derived from patients with proliferative diabetic retinopathy can stimulate angiogenesis through the Axl/PI3K/Akt pathway. Building upon this knowledge, we aimed to explore the influence of VIT from patients with macular membranes in ARPE-19 cells. Our findings reveal that patient-derived VIT from individuals with macular membranes promotes EMT and phosphoinositide 3-kinase-delta (PI3Kδ) expression in ARPE-19 cells. To elucidate the function of PI3Kδ in the ERM, we conducted experiments involving the knockout of p110δ, a key subunit of PI3Kδ, and observed that its absence hinders EMT induced by patient-derived VIT. Moreover, p110δ depletion reduces cell proliferation and migration in ARPE-19 cells. Remarkably, these effects were further corroborated by applying the p110δ inhibitor idelalisib, which blocks fibrosis in the laser-induced fibrosis model. Collectively, our results propose that p110δ plays a critical role in the progression of ERMs. Consequently, targeting p110δ emerges as a promising therapeutic approach for mitigating fibrosis. These findings contribute to a better understanding of the underlying mechanisms involved in ERM formation and highlight the potential for p110δ-directed antifibrotic therapy in retinal diseases.

Development and Clinical Applications of PI3K/AKT/mTOR Pathway Inhibitors as a Therapeutic Option for Leukemias

Leukemias are hematological neoplasms characterized by dysregulations in several cellular signaling pathways, prominently including the PI3K/AKT/mTOR pathway. Since this pathway is associated with several important cellular mechanisms, such as proliferation, metabolism, survival, and cell death, its hyperactivation significantly contributes to the development of leukemias. In addition, it is a crucial prognostic factor, often correlated with therapeutic resistance. Changes in the PI3K/AKT/mTOR pathway are identified in more than 50% of cases of acute leukemia, especially in myeloid lineages. Furthermore, these changes are highly frequent in cases of chronic lymphocytic leukemia, especially those with a B cell phenotype, due to the correlation between the hyperactivation of B cell receptors and the abnormal activation of PI3Kδ. Thus, the search for new therapies that inhibit the activity of the PI3K/AKT/mTOR pathway has become the objective of several clinical studies that aim to replace conventional oncological treatments that have high rates of toxicities and low specificity with target-specific therapies offering improved patient quality of life. In this review we describe the PI3K/AKT/mTOR signal transduction pathway and its implications in leukemogenesis. Furthermore, we provide an overview of clinical trials that employed PI3K/AKT/mTOR inhibitors either as monotherapy or in combination with other cytotoxic agents for treating patients with various types of leukemias. The varying degrees of treatment efficacy are also reported.

PI3K/AKT/mTOR signaling transduction pathway and targeted therapies in cancer

The PI3K/AKT/mTOR (PAM) signaling pathway is a highly conserved signal transduction network in eukaryotic cells that promotes cell survival, cell growth, and cell cycle progression. Growth factor signalling to transcription factors in the PAM axis is highly regulated by multiple cross-interactions with several other signaling pathways, and dysregulation of signal transduction can predispose to cancer development. The PAM axis is the most frequently activated signaling pathway in human cancer and is often implicated in resistance to anticancer therapies. Dysfunction of components of this pathway such as hyperactivity of PI3K, loss of function of PTEN, and gain-of-function of AKT, are notorious drivers of treatment resistance and disease progression in cancer. In this review we highlight the major dysregulations in the PAM signaling pathway in cancer, and discuss the results of PI3K, AKT and mTOR inhibitors as monotherapy and in co-administation with other antineoplastic agents in clinical trials as a strategy for overcoming treatment resistance. Finally, the major mechanisms of resistance to PAM signaling targeted therapies, including PAM signaling in immunology and immunotherapies are also discussed.

Targeting the metabolism of tumor-infiltrating regulatory T cells

Although targeting the tumor metabolism is performed in cooperation with immunotherapy in the era of precision oncology, ignorance of immune cells' metabolism has resulted in unstable antitumor responses. Tumor-infiltrating regulatory T cells (TI-Tregs) are unique, overcoming the hypoxic, acidic, and nutrient-deficient tumor microenvironments (TMEs) and maintaining immunosuppressive functions. However, secondary autoimmunity caused by systemic Treg depletion remains the 'Sword of Damocles' for current Treg-targeted therapies. In this opinion piece, we propose that metabolically reprogrammed TI-Tregs might represent an obstacle to cancer therapies. Indeed, metabolism-based Treg-targeted therapy might provide higher selectivity for clearing TI-Tregs than traditional kinase/checkpoint inhibitors and chemokine/chemokine receptor blockade; it might also restore the efficacy of targeting the tumor metabolism and eliminate certain metabolic barriers to immunotherapy.

Duvelisib Eliminates CLL B Cells, Impairs CLL-Supporting Cells, and Overcomes Ibrutinib Resistance in a Xenograft Model

PURPOSE

Inhibitors of Bruton's tyrosine kinase (BTKi) and PI3K (PI3Ki) have significantly improved therapy of chronic lymphocytic leukemia (CLL). However, the emergence of resistance to BTKi has introduced an unmet therapeutic need. Hence, we sought evidence for essential roles of PI3K-δi and PI3K-γi in treatment-naïve and BTKi-refractory CLL.

EXPERIMENTAL DESIGN

Responses to PI3K-δi, PI3K-γi, and the dual-inhibitor duvelisib in each B, T, and myeloid cell compartments of CLL were studied in vitro, and in a xenograft mouse model using primary cells from treatment-naïve and ibrutinib-resistant patients, and finally, in a patient with ibrutinib-resistant CLL treated with duvelisib.

RESULTS

We demonstrate the essential roles of PI3K-δ for CLL B-cell survival and migration, of PI3K-γ for T-cell migration and macrophage polarization, and of dual inhibition of PI3K-δ,γ for efficacious reduction of leukemia burden. We also show that samples from patients whose disease progressed on ibrutinib were responsive to duvelisib therapy in a xenograft model, irrespective of BTK mutations. In support of this, we report a patient with ibrutinib-resistant CLL, bearing a clone with BTK and PLCγ2 mutations, who responded immediately to single-agent duvelisib with redistribution lymphocytosis followed by a partial clinical remission associated with modulation of T and myeloid cells.

CONCLUSIONS

Our data define the mechanism of action whereby dual inhibition of PI3K-δ,γ affects CLL B-cell numbers and T and myeloid cell pro-leukemia functions and support the use of duvelisib as a valuable approach for therapeutic interventions, including for patients refractory to BTKi.

LYN kinase programs stromal fibroblasts to facilitate leukemic survival via regulation of c-JUN and THBS1

Microenvironmental bystander cells are essential for the progression of chronic lymphocytic leukemia (CLL). We have discovered previously that LYN kinase promotes the formation of a microenvironmental niche for CLL. Here we provide mechanistic evidence that LYN regulates the polarization of stromal fibroblasts to support leukemic progression. LYN is overexpressed in fibroblasts of lymph nodes of CLL patients. LYN-deficient stromal cells reduce CLL growth in vivo. LYN-deficient fibroblasts show markedly reduced leukemia feeding capacity in vitro. Multi-omics profiling reveals that LYN regulates the polarization of fibroblasts towards an inflammatory cancer-associated phenotype through modulation of cytokine secretion and extracellular matrix composition. Mechanistically, LYN deletion reduces inflammatory signaling including reduction of c-JUN expression, which in turn augments the expression of Thrombospondin-1, which binds to CD47 thereby impairing CLL viability. Together, our findings suggest that LYN is essential for rewiring fibroblasts towards a leukemia-supportive phenotype.

Circulating Th17 T cells at treatment onset predict autoimmune toxicity of PI3Kδ inhibitors

PI3Kδ inhibitors are approved for the therapy of B cell malignancies, but their clinical use has been limited by unpredictable autoimmune toxicity, despite promising efficacy and evidence that toxicity is associated with improved clinical outcomes. Prior phenotypic evaluation by CyTOF has identified increases in activated CD8 T cells with activation of Th17 T cells, as well as decreases in Tregs, particularly in patients with toxicity. Here we sought to further understand the effects of idelalisib and duvelisib in vitro, and demonstrate that both idelalisib and duvelisib can inhibit T cell proliferation as well as Th1 and Treg differentiation in vitro, while promoting Th2 and Th17 differentiation. We further demonstrate directly using intracellular flow cytometry that autoimmune toxicity in patients is associated with higher absolute numbers of CD4 and CD8 T cells with Th17 differentiation in peripheral blood prior to therapy, and that gastrointestinal tissues from patients with active autoimmune complications of PI3Kδ inhibitors show infiltration with Th17+ T cells. These same tissues show depletion of Tregs as compared to CLL patients without toxicity, suggesting that loss of Tregs may be permissive for Th17 activation to lead to autoimmune toxicity. Clinical trials to restore this balance are warranted.

Safety and efficacy of dual PI3K-δ, γ inhibitor, duvelisib in patients with relapsed or refractory lymphoid neoplasms: A systematic review and meta-analysis of prospective clinical trials

Background

Duvelisib is the first FDA-approved oral dual inhibitor of phosphatidylinositol-3-kinase PI3K-delta (PI3K-δ) and PI3K-gamma (PI3K-γ). Although many clinical studies support the efficacy of duvelisib, the safety of duvelisib remains with great attention. This systematic review and meta-analysis aimed to evaluate the safety and efficacy of duvelisib in treating different relapsed or refractory (RR) lymphoid neoplasm types.

Methods

We searched prospective clinical trials from PUBMED, EMBASE, Cochrane Library, and ClinicalTrials.gov. For efficacy analysis, Overall response rate (ORR), complete response rate (CR), partial response rate (PR), rate of stable disease (SDR), rate of progressive disease (PDR), median progression-free survival (mPFS), 12-/24-month PFS, and 12-month overall survival (OS) were assessed. For safety analysis, the incidences of any grade and grade ≥3 adverse events (AEs), serious AEs, and treatment-related discontinuation and death were evaluated. Subgroup analysis based on the disease type was performed.

Results

We included 11 studies and 683 patients, including 305 chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), 187 B-cell indolent non-Hodgkin lymphoma (iNHL), 39 B-cell aggressive non-Hodgkin lymphoma (aNHL), and 152 T-cell non-Hodgkin lymphoma (T-NHL) patients. The pooled ORR in CLL/SLL, iNHL, aNHL and T-NHL was 70%, 70%, 28% and 47%, respectively. Additionally, the pooled ORR in CLL/SLL patients with or without TP53 mutation/17p-deletion (62% vs. 74%, p=0.45) and in follicular lymphoma (FL) or other iNHL (69% vs. 57%, p=0.38) had no significant differences. Mantle cell lymphoma (MCL) patients had higher pooled ORR than other aNHL (68% vs. 17%, p=0.04). Angioimmunoblastic TCL (AITL) patients had higher pooled ORR than other PTCL patients (67% vs. 42%, p=0.01). The pooled incidence of any grade, grade ≥3, serious AEs, treatment-related discontinuation and death was 99%, 79%, 63%, 33% and 3%, respectively. The most frequent any-grade AEs were diarrhea (47%), ALT/AST increase (39%), and neutropenia (38%). The most frequent grade ≥3 AEs were neutropenia (25%), ALT/AST increased (16%), diarrhea (12%), and anemia (12%).

Conclusion

Generally, duvelisib could offer favorable efficacy in patients with RR CLL/SLL, iNHL, MCL, and AITL. Risk and severity in duvelisib treatment may be mitigated through proper identification and management.

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.

Metabolic profiles of regulatory T cells and their adaptations to the tumor microenvironment: implications for antitumor immunity

Characterized by the expression of the critical transcription factor forkhead box protein P3, regulatory T (Treg) cells are an essential part of the immune system, with a dual effect on the pathogenesis of autoimmune diseases and cancer. Targeting Tregs to reestablish the proinflammatory and immunogenic tumor microenvironment (TME) is an increasingly attractive strategy for cancer treatment and has been emphasized in recent years. However, attempts have been significantly hindered by the subsequent autoimmunity after Treg ablation owing to systemic loss of their suppressive capacity. Cellular metabolic reprogramming is acknowledged as a hallmark of cancer, and emerging evidence suggests that elucidating the underlying mechanisms of how intratumoral Tregs acquire metabolic fitness and superior immunosuppression in the TME may contribute to clinical benefits. In this review, we discuss the common and distinct metabolic profiles of Tregs in peripheral tissues and the TME, as well as the differences between Tregs and other conventional T cells in their metabolic preferences. By focusing on the critical roles of different metabolic programs, such as glycolysis, oxidative phosphorylation, fatty acid oxidation, fatty acid synthesis, and amino acid metabolism, as well as their essential regulators in modulating Treg proliferation, migration, and function, we hope to provide new insights into Treg cell-targeted antitumor immunotherapies.

Regulatory T cells (Tregs) in lymphoid malignancies and the impact of novel therapies

Regulatory T cells (Tregs) are responsible for maintaining immune homeostasis by controlling immune responses. They can be characterized by concomitant expression of FoxP3, CD25 and inhibitory receptors such as PD-1 and CTLA-4. Tregs are key players in preventing autoimmunity and are dysregulated in cancer, where they facilitate tumor immune escape. B-cell lymphoid malignancies are a group of diseases with heterogenous molecular characteristics and clinical course. Treg levels are increased in patients with B-cell lymphoid malignancies and correlate with clinical outcomes. In this review, we discuss studies investigating Treg immunobiology in B-cell lymphoid malignancies, focusing on clinical correlations, mechanisms of accumulation, phenotype, and function. Overarching trends suggest that Tregs can be induced directly by tumor cells and recruited to the tumor microenvironment where they suppress antitumor immunity to facilitate disease progression. Further, we highlight studies showing that Tregs can be modulated by novel therapeutic agents such as immune checkpoint blockade and targeted therapies. Treg disruption by novel therapeutics may beneficially restore immune competence but has been associated with occurrence of adverse events. Strategies to achieve balance between these two outcomes will be paramount in the future to improve therapeutic efficacy and safety.

Idelalisib reduces regulatory T cells and activates T helper 17 cell differentiation in relapsed refractory patients with chronic lymphocytic leukaemia

Phosphatidylinositol 3 kinase (PI3K) inhibitors such as idelalisib have been associated with potentially severe autoimmune toxicity. In the present study, we demonstrate that relapsed refractory patients with chronic lymphocytic leukaemia treated with idelalisib rituximab on the phase III registration trial show uniform decrease in regulatory T cells (Tregs) and increase in CD8 T cells with treatment. Patients who do not develop toxicity show enrichment for T cells expressing multiple chemokine receptors, while those who do develop toxicity have an activated CD8 T cell population with T helper 17 cell differentiation at baseline, which then increases, leading to an increased CD8:Treg ratio that likely triggers autoimmune toxicity.

PI3K Targeting in Non-solid Cancer

Despite the therapeutic progress, relapse remains a major problem in the treatment of acute lymphoblastic leukemia (ALL). Most leukemia cells that survive chemotherapy are found in the bone marrow (BM), thus resistance to chemotherapy and other treatments may be partially attributed to pro-survival signaling to leukemic cells mediated by leukemia cell-microenvironment interactions. Adhesion of leukemia cells to BM stromal cells may lead to cell adhesion-mediated drug resistance (CAM-DR) mediating intracellular signaling changes that support survival of leukemia cells. In ALL and chronic lymphocytic leukemia (CLL), adhesion-mediated activation of the PI3K/AKT signaling pathway has been shown to be critical in CAM-DR. PI3K targeting inhibitors have been approved for CLL and have been evaluated preclinically in ALL. However, PI3K inhibition has yet to be approved for clinical use in ALL. Here, we review the role of PI3K signaling for normal hematopoietic and leukemia cells and summarize preclinical inhibitors of PI3K in ALL.

PI3Kδ Inhibitors as Immunomodulatory Agents for the Treatment of Lymphoma Patients

The development of small molecules able to block specific or multiple isoforms of phosphoinositide 3-kinases (PI3K) has already been an active field of research for many years in the cancer field. PI3Kδ inhibitors are among the targeted agents most extensively studied for the treatment of lymphoma patients and PI3Kδ inhibitors are already approved by regulatory agencies. More recently, it became clear that the anti-tumor activity of PI3K inhibitors might not be due only to a direct effect on the cancer cells but it can also be mediated via inhibition of the kinases in non-neoplastic cells present in the tumor microenvironment. T-cells represent an important component of the tumor microenvironment and they comprise different subpopulations that can have both anti- and pro-tumor effects. In this review article, we discuss the effects that PI3Kδ inhibitors exert on the immune system with a particular focus on the T-cell compartment.

PI3K inhibitors are finally coming of age

Overactive phosphoinositide 3-kinase (PI3K) in cancer and immune dysregulation has spurred extensive efforts to develop therapeutic PI3K inhibitors. Although progress has been hampered by issues such as poor drug tolerance and drug resistance, several PI3K inhibitors have now received regulatory approval - the PI3Kα isoform-selective inhibitor alpelisib for the treatment of breast cancer and inhibitors mainly aimed at the leukocyte-enriched PI3Kδ in B cell malignancies. In addition to targeting cancer cell-intrinsic PI3K activity, emerging evidence highlights the potential of PI3K inhibitors in cancer immunotherapy. This Review summarizes key discoveries that aid the clinical translation of PI3Kα and PI3Kδ inhibitors, highlighting lessons learnt and future opportunities.

Combined ibrutinib and venetoclax treatment vs single agents in the TCL1 mouse model for chronic lymphocytic leukemia

The covalent inhibitor of Bruton's tyrosine kinase ibrutinib and the specific Bcl-2 inhibitor venetoclax are both highly efficacious single agent drugs in the treatment of chronic lymphocytic leukemia (CLL). Based on their complementary modes of action, ibrutinib and venetoclax are hypothesized to act in synergistic fashion. Currently, it is unclear whether combined treatment is indeed superior to continuous single agent treatment, and what mechanisms could underlie resistance to combination treatment. In addition, effects of such treatment on the skewed T cell compartment characteristic for CLL are as yet unknown. In the murine Eµ-TCL1 adoptive transfer model, resembling aggressive CLL, we found that combined treatment resulted in deepest responses with longest duration due to a combination of decreased proliferation and increased induction of apoptosis. In addition, alterations in T cell subsets were most prominent upon combination treatment with increased naïve cells and reduced effector memory cells. Remarkably, effects of single agents but also combination treatment were eventually interrupted by relapse, and we found downregulation of BIM expression as a plausible cause of acquired drug resistance. Nevertheless, in this murine model, combination of venetoclax and ibrutinib has increased efficacy over single agents accompanied by a restoration of the T cell compartment.

Activation of the MAPK pathway mediates resistance to PI3K inhibitors in chronic lymphocytic leukemia

Inhibitors of Bruton tyrosine kinase (BTK) and phosphatidylinositol 3-kinase δ (PI3Kδ) that target the B-cell receptor (BCR) signaling pathway have revolutionized the treatment of chronic lymphocytic leukemia (CLL). Mutations associated with resistance to BTK inhibitors have been identified, but limited data are available on mechanisms of resistance to PI3Kδ inhibitors. Here we present findings from longitudinal whole-exome sequencing of cells from patients with multiply relapsed CLL (N = 28) enrolled in trials of PI3K inhibitors. The nonresponder subgroup was characterized by baseline activating mutations in MAP2K1, BRAF, and KRAS genes in 60% of patients. PI3Kδ inhibition failed to inhibit ERK phosphorylation (pERK) in nonresponder CLL cells with and without mutations, whereas treatment with a MEK inhibitor rescued ERK inhibition. Overexpression of MAP2K1 mutants in vitro led to increased basal and inducible pERK and resistance to idelalisib. These data demonstrate that MAPK/ERK activation plays a key role in resistance to PI3Kδ inhibitors in CLL and provide a rationale for therapy with a combination of PI3Kδ and ERK inhibitors.

Neutralizing interferon-α blocks inflammation-mediated vascular injury via PI3K and AMPK in systemic lupus erythematosus

Plasmacytoid dendritic cells (pDCs) play a key role in the initiation and amplification of systemic lupus erythematosus (SLE)-associated vascular injury. In this study, we found that dsDNA induced dose- and time-dependent increase in IFN-α and Toll-like receptor 7 (TLR7), TLR9 and IRF7 expression in pDCs. Co-cultured circulating endothelial cells (ECs) with activated pDCs significantly decreased proliferation, tube formation and migration in ECs. The elevated level of cellular IFN-α increased cell adhesion, promoted cell apoptosis, induced cell senescence and arrested cells at G0/G1 phase of endothelial progenitor cells (EPCs). Additionally, the co-culture system activated MAPK and inactivated PI3K. Pristane was used to establish a in vivo SLE-like mouse model. Importantly, we showed that INF-α-neutralizing antibody (IFN-α-NA) rescued all the changes induced by IFN-α in vitro and prevented vascular injury in pristane-induced SLE model in vivo. In conclusion, we confirmed that activated pDCs promoted vascular damage and the dysfunction of ECs/EPCs via IFN-α production. IFN-α-neutralizing antibody may be a clinical implication for preventing vascular injury. PI3K signalling and AMPK signalling were associated with SLE-associated vascular functions.

Immunomodulation by targeted anticancer agents

At odds with conventional chemotherapeutics, targeted anticancer agents are designed to inhibit precise molecular alterations that support oncogenesis or tumor progression. Despite such an elevated degree of molecular specificity, many clinically employed and experimental targeted anticancer agents also mediate immunostimulatory or immunosuppressive effects that (at least in some settings) influence therapeutic efficacy. Here, we discuss the main immunomodulatory effects of targeted anticancer agents and explore potential avenues to harness them in support of superior clinical efficacy.

Phosphoinositide 3-Kinase Signaling in the Tumor Microenvironment: What Do We Need to Consider When Treating Chronic Lymphocytic Leukemia With PI3K Inhibitors?

Phosphoinositide 3-kinases (PI3Ks) and their downstream proteins constitute a signaling pathway that is involved in both normal cell growth and malignant transformation of cells. Under physiological conditions, PI3K signaling regulates various cellular functions such as apoptosis, survival, proliferation, and growth, depending on the extracellular signals. A deterioration of these extracellular signals caused by mutational damage in oncogenes or growth factor receptors may result in hyperactivation of this signaling cascade, which is recognized as a hallmark of cancer. Although higher activation of PI3K pathway is common in many types of cancer, it has been therapeutically targeted for the first time in chronic lymphocytic leukemia (CLL), demonstrating its significance in B-cell receptor (BCR) signaling and malignant B-cell expansion. The biological activity of the PI3K pathway is not only limited to cancer cells but is also crucial for many components of the tumor microenvironment, as PI3K signaling regulates cytokine responses, and ensures the development and function of immune cells. Therefore, the success or failure of the PI3K inhibition is strongly related to microenvironmental stimuli. In this review, we outline the impacts of PI3K inhibition on the tumor microenvironment with a specific focus on CLL. Acknowledging the effects of PI3K inhibitor-based therapies on the tumor microenvironment in CLL can serve as a rationale for improved drug development, explain treatment-associated adverse events, and suggest novel combinatory treatment strategies in CLL.

Gene Expression and Resistance to Glucocorticoid-Induced Apoptosis in Acute Lymphoblastic Leukemia: A Brief Review and Update

BACKGROUND

Resistance to glucocorticoid (GC)-induced apoptosis in Acute Lymphoblastic Leukemia (ALL), is considered one of the major prognostic factors for the disease. Prednisolone is a corticosteroid and one of the most important agents in the treatment of acute lymphoblastic leukemia. The mechanics of GC resistance are largely unknown and intense ongoing research focuses on this topic.

AIM

The aim of the present study is to review some aspects of GC resistance in ALL, and in particular of Prednisolone, with emphasis on previous and present knowledge on gene expression and signaling pathways playing a role in the phenomenon.

METHODS

An electronic literature search was conducted by the authors from 1994 to June 2019. Original articles and systematic reviews selected, and the titles and abstracts of papers screened to determine whether they met the eligibility criteria, and full texts of the selected articles were retrieved.

RESULTS

Identification of gene targets responsible for glucocorticoid resistance may allow discovery of drugs, which in combination with glucocorticoids may increase the effectiveness of anti-leukemia therapies. The inherent plasticity of clinically evolving cancer justifies approaches to characterize and prevent undesirable activation of early oncogenic pathways.

CONCLUSION

Study of the pattern of intracellular signal pathway activation by anticancer drugs can lead to development of efficient treatment strategies by reducing detrimental secondary effects.

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

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

HDAC6 Inhibition Alleviates CLL-Induced T-Cell Dysfunction and Enhances Immune Checkpoint Blockade Efficacy in the Eμ-TCL1 Model

Development of chronic lymphocytic leukemia (CLL) is associated with severe immune dysfunction. T-cell exhaustion, immune checkpoint upregulation, and increase of regulatory T cells contribute to an immunosuppressive tumor microenvironment. As a result, CLL patients are severely susceptible to infectious complications that increase morbidity and mortality. CLL B-cell survival is highly dependent upon interaction with the supportive tumor microenvironment. It has been postulated that the reversal of T-cell dysfunction in CLL may be beneficial to reduce tumor burden. Previous studies have also highlighted roles for histone deacetylase 6 (HDAC6) in regulation of immune cell phenotype and function. Here, we report for the first time that HDAC6 inhibition exerts beneficial immunomodulatory effects on CLL B cells and alleviates CLL-induced immunosuppression of CLL T cells. In the Eμ-TCL1 adoptive transfer murine model, genetic silencing or inhibition of HDAC6 reduced surface expression of programmed death-ligand 1 (PD-L1) on CLL B cells and lowered interleukin-10 (IL-10) levels. This occurred concurrently with a bolstered T-cell phenotype, demonstrated by alteration of coinhibitory molecules and activation status. Analysis of mice with similar tumor burden indicated that the majority of T-cell changes elicited by silencing or inhibition of HDAC6 in vivo are likely secondary to decrease of tumor burden and immunomodulation of CLL B cells. The data reported here suggest that CLL B cell phenotype may be altered by HDAC6-mediated hyperacetylation of the chaperone heat shock protein 90 (HSP90) and subsequent inhibition of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway. Based on the beneficial immunomodulatory activity of HDAC6 inhibition, we rationalized that HDAC6 inhibitors could enhance immune checkpoint blockade in CLL. Conclusively, combination treatment with ACY738 augmented the antitumor efficacy of anti-PD-1 and anti-PD-L1 monoclonal antibodies in the Eμ-TCL1 adoptive transfer murine model. These combinatorial antitumor effects coincided with an increased cytotoxic CD8⁺ T-cell phenotype. Taken together, these data highlight a role for HDAC inhibitors in combination with immunotherapy and provides the rationale to investigate HDAC6 inhibition together with immune checkpoint blockade for treatment of CLL patients.

Class IA PI3Ks regulate subcellular and functional dynamics of IDO1

Knowledge of a protein's spatial dynamics at the subcellular level is key to understanding its function(s), interactions, and associated intracellular events. Indoleamine 2,3-dioxygenase 1 (IDO1) is a cytosolic enzyme that controls immune responses via tryptophan metabolism, mainly through its enzymic activity. When phosphorylated, however, IDO1 acts as a signaling molecule in plasmacytoid dendritic cells (pDCs), thus activating genomic effects, ultimately leading to long-lasting immunosuppression. Whether the two activities-namely, the catalytic and signaling functions-are spatially segregated has been unclear. We found that, under conditions favoring signaling rather than catabolic events, IDO1 shifts from the cytosol to early endosomes. The event requires interaction with class IA phosphoinositide 3-kinases (PI3Ks), which become activated, resulting in full expression of the immunoregulatory phenotype in vivo in pDCs as resulting from IDO1-dependent signaling events. Thus, IDO1's spatial dynamics meet the needs for short-acting as well as durable mechanisms of immune suppression, both under acute and chronic inflammatory conditions. These data expand the theoretical basis for an IDO1-centered therapy in inflammation and autoimmunity.

Emerging roles of class I PI3K inhibitors in modulating tumor microenvironment and immunity

Immune system-mediated tumor killing has revolutionized anti-tumor therapies, providing long-term and durable responses in some patients. The phosphoinositide 3-kinase (PI3K) pathway controls multiple biological processes and is frequently dysregulated in malignancies. Enormous efforts have been made to develop inhibitors against class I PI3K. Notably, with the increasing understanding of PI3K, it has been widely accepted that PI3K inhibition not only restrains tumor progression, but also reshapes the immunosuppressive tumor microenvironment. In this review, we focus on the pivotal roles of class I PI3Ks in adaptive and innate immune cells, as well as other stromal components. We discuss the modulation by PI3K inhibitors of the tumor-supportive microenvironment, including eliminating the regulatory immune cells, restoring cytotoxic cells or regulating angiogenesis. The potential combinations of PI3K inhibitors with other therapies to enhance the anti-tumor immunity are also described.

Control of T lymphocyte fate decisions by PI3K signaling

Virtually all aspects of T and B lymphocyte development, homeostasis, activation, and effector function are impacted by the interaction of their clonally distributed antigen receptors with antigens encountered in their respective environments. Antigen receptors mediate their effects by modulating intracellular signaling pathways that ultimately impinge on the cytoskeleton, bioenergetic pathways, transcription, and translation. Although these signaling pathways are rather well described at this point, especially those steps that are most receptor-proximal, how such pathways contribute to more quantitative aspects of lymphocyte function is still being elucidated. One of the signaling pathways that appears to be involved in this “tuning” process is controlled by the lipid kinase PI3K. Here we review recent key findings regarding both the triggering/enhancement of PI3K signals (via BCAP and ICOS) as well as their regulation (via PIK3IP1 and PHLPP) and how these signals integrate and determine cellular processes. Lymphocytes display tremendous functional plasticity, adjusting their metabolism and gene expression programs to specific conditions depending on their tissue of residence and the nature of the infectious threat to which they are responding. We give an overview of recent findings that have contributed to this model, with a focus on T cells, including what has been learned from patients with gain-of-function mutations in PI3K as well as lessons from cancer immunotherapy approaches.

Enhanced antitumor immunity through sequential targeting of PI3Kδ and LAG3

BACKGROUND

Despite striking successes, immunotherapies aimed at increasing cancer-specific T cell responses are unsuccessful in most patients with cancer. Inactivating regulatory T cells (Treg) by inhibiting the PI3Kδ signaling enzyme has shown promise in preclinical models of tumor immunity and is currently being tested in early phase clinical trials in solid tumors.

METHODS

Mice bearing 4T1 mammary tumors were orally administered a PI3Kδ inhibitor (PI-3065) daily and tumor growth, survival and T cell infiltrate were analyzed in the tumor microenvironment. A second treatment schedule comprised PI3Kδ inhibitor with anti-LAG3 antibodies administered sequentially 10 days later.

RESULTS

As observed in human immunotherapy trials with other agents, immunomodulation by PI3Kδ-blockade led to 4T1 tumor regressor and non-regressor mice. Tumor infiltrating T cells in regressors were metabolically fitter than those in non-regressors, with significant enrichments of antigen-specific CD8+ T cells, T cell factor 1 (TCF1)+ T cells and CD69- T cells, compatible with induction of a sustained tumor-specific T cell response. Treg numbers were significantly reduced in both regressor and non-regressor tumors compared with untreated tumors. The remaining Treg in non-regressor tumors were however significantly enriched with cells expressing the coinhibitory receptor LAG3, compared with Treg in regressor and untreated tumors. This striking difference prompted us to sequentially block PI3Kδ and LAG3. This combination enabled successful therapy of all mice, demonstrating the functional importance of LAG3 in non-regression of tumors on PI3Kδ inhibition therapy. Follow-up studies, performed using additional cancer cell lines, namely MC38 and CT26, indicated that a partial initial response to PI3Kδ inhibition is an essential prerequisite to a sequential therapeutic benefit of anti-LAG3 antibodies.

CONCLUSIONS

These data indicate that LAG3 is a key bottleneck to successful PI3Kδ-targeted immunotherapy and provide a rationale for combining PI3Kδ/LAG3 blockade in future clinical studies.

Idelalisib Rescues Natural Killer Cells from Monocyte-Induced Immunosuppression by Inhibiting NOX2-Derived Reactive Oxygen Species

The phosphatidylinositol-4,5-bisphosphate-3 kinase-δ (PI3Kδ) inhibitor idelalisib, used alone or in combination with anti-CD20, is clinically efficacious in B-cell lymphoma and chronic lymphocytic leukemia (CLL) by promoting apoptosis of malignant B cells. PI3K regulates the formation of reactive oxygen species (ROS) by the myeloid NADPH oxidase NOX2, but the role of PI3Kδ in myeloid cell-induced immunosuppression is unexplored. We assessed the effects of idelalisib on the spontaneous and IgG antibody-induced ROS production by human monocytes, on ROS-induced cell death of human natural killer (NK) cells, and on tumor cell clearance in an NK cell-dependent mouse model of metastasis. Idelalisib potently and efficiently inhibited the formation of NOX2-derived ROS from monocytes and rescued NK cells from ROS-induced cell death. Idelalisib also promoted NK cell cytotoxicity against anti-CD20-coated primary human CLL cells and cultured malignant B cells. Experiments using multiple PI3K inhibitors implicated the PI3Kδ isoform in regulating NOX2-induced ROS formation and immunosuppression. In B6 mice, systemic treatment with idelalisib significantly reduced the formation of lung metastases from intravenously injected melanoma cells but did not affect metastasis in B6.129S6-Cybbtm1Din (Nox2 ^-/-) mice or in NK cell-deficient mice. Our results imply that idelalisib rescues NK cells from NOX2/ROS-dependent immunosuppression and thus exerts antineoplastic efficacy beyond B-cell inhibition.

PI3Kδ inhibition reshapes follicular lymphoma-immune microenvironment cross talk and unleashes the activity of venetoclax

Despite idelalisib approval in relapsed follicular lymphoma (FL), a complete characterization of the immunomodulatory consequences of phosphatidylinositol 3-kinase δ (PI3Kδ) inhibition, biomarkers of response, and potential combinatorial therapies in FL remain to be established. Using ex vivo cocultures of FL patient biopsies and follicular dendritic cells (FDCs) to mimic the germinal center (n = 42), we uncovered that PI3Kδ inhibition interferes with FDC-induced genes related to angiogenesis, extracellular matrix formation, and transendothelial migration in a subset of FL samples, defining an 18-gene signature fingerprint of idelalisib sensitivity. A common hallmark of idelalisib found in all FL cases was its interference with the CD40/CD40L pathway and induced proliferation, together with the downregulation of proteins crucial for B-T-cell synapses, leading to an inefficient cross talk between FL cells and the supportive T-follicular helper cells (TFH). Moreover, idelalisib downmodulates the chemokine CCL22, hampering the recruitment of TFH and immunosupressive T-regulatory cells to the FL niche, leading to a less supportive and tolerogenic immune microenvironment. Finally, using BH3 profiling, we uncovered that FL-FDC and FL-macrophage cocultures augment tumor addiction to BCL-XL and MCL-1 or BFL-1, respectively, limiting the cytotoxic activity of the BCL-2 inhibitor venetoclax. Idelalisib restored FL dependence on BCL-2 and venetoclax activity. In summary, idelalisib exhibits a patient-dependent activity toward angiogenesis and lymphoma dissemination. In all FL cases, idelalisib exerts a general reshaping of the FL immune microenvironment and restores dependence on BCL-2, predisposing FL to cell death, providing a mechanistic rationale for investigating the combination of PI3Kδ inhibitors and venetoclax in clinical trials.

Phosphatidylinositol 3 Kinase δ Inhibitors: Present and Future

Inhibitors of PI3Kδ hold great potential for the therapy of chronic lymphocytic leukemia and B-cell malignancies. After initially exciting efficacy results with idelalisib, the first-in-class inhibitor, the emergence of unexpected and unpredictable autoimmune toxicities, worse in less heavily treated and younger patients, has decreased the use of the currently available inhibitors. Newer drugs in development are attempting to reduce toxicity with novel schedules and/or combinations. This article reviews the clinical data on efficacy and toxicity across the class and discusses ongoing efforts to understand and mitigate the likely on-target autoimmune toxicity.

T-cells in chronic lymphocytic leukemia: Guardians or drivers of disease?

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy, which is associated with profound alterations and defects in the immune system and a prevalent dependency on the microenvironmental niche. An abnormal T-cell compartment in the blood of CLL patients was already reported 40 years ago. Since then, our knowledge of T-cell characteristics in CLL has grown steadily, but the question of whether T-cells act as pro-tumoral bystander cells or possess anti-tumoral activity is still under debate. Increased numbers of CD4+ T-helper cell subsets are present in the blood of CLL patients, and T-helper cell cytokines have been shown to stimulate CLL cell survival and proliferation in vitro. In line with this, survival and growth of CLL cells in murine xenograft models have been shown to rely on activated CD4+ T-cells. This led to the hypothesis that T-cells are tumor-supportive in CLL. In recent years, evidence for an enrichment of antigen-experienced CD8+ T-cells in CLL has accumulated, and these cells have been shown to control leukemia in a CLL mouse model. Based on this, it was suggested that CD8+ T-cells recognize CLL-specific antigens and exert an anti-leukemia function. As described for other cancer entities, T-cells in CLL express multiple inhibitory receptors, such as PD-1, and lose their functional capacity, leading to an exhaustion phenotype which has been shown to be more severe in T-cells from secondary lymphoid organs compared with peripheral blood. This exhausted phenotype has been suggested to be causative for the poor response of CLL patients to CAR T-cell therapies. In addition, T-cells have been shown to be affected by drugs that are used to treat CLL, which likely impacts therapy response. This review provides an overview of the current knowledge about alterations of T-cells in CLL, including their distribution, function, and exhaustion state in blood and lymphoid organs, and touches also on the topic of how CLL drugs impact on the T-cell compartment and recent results of T-cell-based immunotherapy. We will discuss potential pathological roles of T-cell subsets in CLL and address the question of whether they foster progression or control of disease.

Meta-Analysis Reveals Significant Sex Differences in Chronic Lymphocytic Leukemia Progression in the Eµ-TCL1 Transgenic Mouse Model

The Eµ-TCL1 transgenic mouse model represents the most widely and extensively used animal model for chronic lymphocytic leukemia (CLL). In this report, we performed a meta-analysis of leukemia progression in over 300 individual Eµ-TCL1 transgenic mice and discovered a significantly accelerated disease progression in females compared to males. This difference is also reflected in an aggressive CLL mouse model with additional deletion of Tp53 besides the TCL1 transgene. Moreover, after serial adoptive transplantation of murine CLL cells, female recipients also succumbed to CLL earlier than male recipients. This sex-related disparity in the murine models is markedly contradictory to the human CLL condition. Thus, due to our observation we urge both careful consideration in the experimental design and accurate description of the Eµ-TCL1 transgenic cohorts in future studies.

Parsaclisib Is a Next-Generation Phosphoinositide 3-Kinase δ Inhibitor with Reduced Hepatotoxicity and Potent Antitumor and Immunomodulatory Activities in Models of B-Cell Malignancy

The clinical use of first-generation phosphoinositide 3-kinase (PI3K)δ inhibitors in B-cell malignancies is hampered by hepatotoxicity, requiring dose reduction, treatment interruption, and/or discontinuation of therapy. In addition, potential molecular mechanisms by which resistance to this class of drugs occurs have not been investigated. Parsaclisib (INCB050465) is a potent and selective next-generation PI3Kδ inhibitor that differs in structure from first-generation PI3Kδ inhibitors and has shown encouraging anti-B-cell tumor activity and reduced hepatotoxicity in phase 1/2 clinical studies. Here, we present preclinical data demonstrating parsaclisib as a potent inhibitor of PI3Kδ with over 1000-fold selectivity against other class 1 PI3K isozymes. Parsaclisib directly blocks PI3K signaling-mediated cell proliferation in B-cell lines in vitro and in vivo and indirectly controls tumor growth by lessening immunosuppression through regulatory T-cell inhibition in a syngeneic lymphoma model. Diffuse large B-cell lymphoma cell lines overexpressing MYC were insensitive to proliferation blockade via PI3Kδ signaling inhibition by parsaclisib, but their proliferative activities were reduced by suppression of MYC gene transcription. Molecular structure analysis of the first- and next-generation PI3Kδ inhibitors combined with clinical observation suggests that hepatotoxicity seen with the first-generation inhibitors could result from a structure-related off-target effect. Parsaclisib is currently being evaluated in multiple phase 2 clinical trials as a therapy against various hematologic malignancies of B-cell origin (NCT03126019, NCT02998476, NCT03235544, NCT03144674, and NCT02018861). SIGNIFICANCE STATEMENT: The preclinical properties described here provide the mechanism of action and support clinical investigations of parsaclisib as a therapy for B-cell malignancies. MYC overexpression was identified as a resistance mechanism to parsaclisib in DLBCL cells, which may be useful in guiding further translational studies for the selection of patients with DLBCL who might benefit from PI3Kδ inhibitor treatment in future trials. Hepatotoxicity associated with first-generation PI3Kδ inhibitors may be an off-target effect of that class of compounds.

Relevance function of microRNA-708 in the pathogenesis of cancer

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression post-transcriptionally responsible for regulating >70% of human genes. MicroRNA-708 (miR-708) is encoded in the intron 1 of the Odd Oz/ten-m homolog 4 (ODZ4) gene. Numerous researches have confirmed that the abnormal expressed miR-708 is involved in the regulation of multiple types of cancer. Notably, the expression level of miR-708 was higher in lung cancer, bladder cancer (BC) and colorectal cancer (CRC) cell lines while lower in hepatocellular carcinoma (HCC), prostate cancer (PC), gastric cancer (GC) and so on. This review provides a current view on the association between miR-708 and several cancers and focuses on the recent studies of miR-708 regulation, discussing its potential as an epigenetic biomarker and therapeutic target for these cancers. In particular, the regulated mechanisms and clinical application of miR-708 in these cancers are also discussed.

Immunotherapy for hematological malignancies

Tumor immune tolerance remains a major barrier for effective anti-cancer therapy. A growing number of pathways whereby solid tumors escape immune surveillance have been characterized (1). This progress led us to revisit the "hallmarks of cancer" and brought forward many promising immunotherapies. Every growing bodies of research have brought forward many exciting treatment strategies for hematological cancers like chimeric antigen receptor T cells (CAR-T cells) and immune checkpoint inhibitors. Given the distinct characteristics of the different cancers, some benefited profoundly from such therapies while some remain challenging for scientists and physicians. Here, we discuss the unique aspect of hematological malignancies, and briefly review the history, existing and future of immunotherapies for this group of cancer.

Formation of the Immunosuppressive Microenvironment of Classic Hodgkin Lymphoma and Therapeutic Approaches to Counter It

Classic Hodgkin lymphoma (cHL) is characterized by a few tumor cells surrounded by a protective, immunosuppressive tumor microenvironment composed of normal cells that are an active part of the disease. Hodgkin and Reed-Sternberg (HRS) cells evade the immune system through a variety of different mechanisms. They evade antitumor effector T cells and natural killer cells and promote T cell exhaustion. Using cytokines and extracellular vesicles, they recruit normal cells, induce their proliferation and "educate" (i.e. reprogram) them to become immunosuppressive and protumorigenic. Therefore, alternative treatment strategies are being developed to target not only tumor cells but also the tumor microenvironment. Here we summarize current knowledge on the ability of HRS cells to build their microenvironment and to educate normal cells to become immunosuppressive. We also describe therapeutic strategies to counteract formation of the tumor microenvironment and related processes leading to T cell exhaustion and repolarization of immunosuppressive tumor-associated macrophages.