Differential immune effects mediated by Toll-like receptors stimulation in precursor B-cell acute lymphoblastic leukaemia

Toll-like receptor-guided therapeutic intervention of human cancers: molecular and immunological perspectives

Toll-like receptors (TLRs) serve as the body's first line of defense, recognizing both pathogen-expressed molecules and host-derived molecules released from damaged or dying cells. The wide distribution of different cell types, ranging from epithelial to immune cells, highlights the crucial roles of TLRs in linking innate and adaptive immunity. Upon stimulation, TLRs binding mediates the expression of several adapter proteins and downstream kinases, that lead to the induction of several other signaling molecules such as key pro-inflammatory mediators. Indeed, extraordinary progress in immunobiological research has suggested that TLRs could represent promising targets for the therapeutic intervention of inflammation-associated diseases, autoimmune diseases, microbial infections as well as human cancers. So far, for the prevention and possible treatment of inflammatory diseases, various TLR antagonists/inhibitors have shown to be efficacious at several stages from pre-clinical evaluation to clinical trials. Therefore, the fascinating role of TLRs in modulating the human immune responses at innate as well as adaptive levels directed the scientists to opt for these immune sensor proteins as suitable targets for developing chemotherapeutics and immunotherapeutics against cancer. Hitherto, several TLR-targeting small molecules (e.g., Pam3CSK4, Poly (I:C), Poly (A:U)), chemical compounds, phytocompounds (e.g., Curcumin), peptides, and antibodies have been found to confer protection against several types of cancers. However, administration of inappropriate doses of such TLR-modulating therapeutics or a wrong infusion administration is reported to induce detrimental outcomes. This review summarizes the current findings on the molecular and structural biology of TLRs and gives an overview of the potency and promises of TLR-directed therapeutic strategies against cancers by discussing the findings from established and pipeline discoveries.

Spontaneous remission of acute lymphoblastic leukemia: A series of nine cases and a review of literature

AIMS

To report a series of acute lymphoblastic leukemia (ALL) cases with spontaneous remission and provide presenting clinical and pathologic information and details of clinical course to raise awareness among oncologists and patients.

METHODS

We identified and analyzed nine patients with ALL and spontaneous remission. Review of literature reveals an additional nine previously reported cases with similar clinical course.

RESULTS

All of these patients, ranging in age from 2 to 12 years of age, presented with inciting signs and symptoms of viral or bacterial infection. All of the patients showed varying percentages of lymphoblasts (.2% to 90%) in diagnostic bone marrow biopsy. All B-ALL cases shared a similar blast phenotype on flow cytometry with coexpression of CD19, CD10 and TdT and variable CD20 expression. All nine patients achieved spontaneous remission of their leukemia as confirmed by flow cytometry and/or bone marrow biopsy without chemotherapeutic intervention. Time to remission from presentation ranged from 1 to 8 weeks. After remission, all patients redeveloped ALL, and time from remission to reemergence ranged from 2 to 24 weeks.

CONCLUSION

Our series of cases and cases identified in literature show that ALL diagnosed with modern methods of flow cytometry and molecular analysis will recur within weeks to months from disappearance, usually with cytopenias, which provides a template for oncologic follow-up and testing in these patients.

Meta-analysis of microRNA profiling data does not reveal a consensus signature for B cell acute lymphoblastic leukemia

B cell acute lymphoblastic leukemia (B-ALL) is the most prevalent pediatric cancer. MicroRNAs (miRNAs) are 18-22nt non-coding transcripts shown to be essential for the development of many cancers. While some miRNAs are reportedly expressed differentially between healthy and B-ALL, no studies have reported a consensus miRNA signature. Therefore, we performed a reanalysis of five miRNA datasets to identify differentially expressed miRNAs (DEmiRs) and a meta-analysis of previously identified DEmiRs from 25 studies. Overall, the re-analysis showed that the DEmiR data clustered by platform and not by disease state. The meta-analysis also did not reveal a consensus miRNA signature as there were many miRNAs upregulated in some studies and downregulated in others. However, eight promising miRNAs (miR-181b, miR-128b, miR-181a, miR-128, miR-128a, miR-181c, miR-155, miR-142-3p, and miR-451) were identified from the meta-analysis, which could be the basis of future investigations. These analyses reveal that standardization of miRNA isolation and analysis is needed in B-ALL to enable cross-study comparisons and identify a consensus signature.

Continuous Complete Remission in Two Patients with Acute Lymphoblastic Leukemia and Severe Fungal Infection Following Short-Term, Dose-Reduced Chemotherapy

Spontaneous remission in acute lymphoblastic leukemia (ALL) is a rare phenomenon, which typically involves a pattern of feverish or septic disease followed by quick but mostly transient remission. We report on two male patients (46-year-old (pt. 1) and 19-year-old (pt. 2)) with CD20 positive, BCR-ABL negative common B-ALL. Patient 1 had received dexamethasone and cyclophosphamide (1.2 g) as a prephase therapy, followed by rituximab and a cumulative dose of 200 mg daunorubicin combined with 2 mg vincristine as an induction therapy. Patient 2 was treated with a reduced therapy regimen (Vincristine 1 mg, dexamethasone and 80 mg daunorubicin, 12-month mercaptopurine maintenance) due to (alcohol-related) toxic liver failure and pontine myelinolysis. Both patients developed severe septic disease just few days into induction treatment. Patient 1 suffered from pulmonary mycosis, which had to be resected eventually. Histological work-up revealed invasive mucor mycosis. Patient 2 presented with elevated serum aspergillus antigen and radiographic pulmonary lesions, indicative of pulmonary mycosis. In both patients, chemotherapy had to be interrupted and could not be resumed. Both patients recovered under broad antimicrobial, antifungal and prophylactic antiviral therapy and achieved molecular complete remission. At data cut-off remissions had been on-going for 34 months (pt. 1) and 8 years (pt. 2). Short-term, reduced intensity induction chemotherapy accompanied by severe fungal infections was followed by long-lasting continuous complete remissions in ALL. Thus, we hypothesize that infection-associated immunogenic responses may not only prevent early relapse of ALL but could also eradicate minimal residual disease. The effects of combined cytotoxic therapy and severe infection may also be mimicked by biomodulatory treatment strategies aiming at reorganizing pathologically altered cellular signaling networks. This could reduce toxicity and comorbidity in adult patients requiring leukemia treatment. Therefore, these two cases should encourage systematic studies on how leukemia stroma interaction can be harnessed to achieve long lasting control of ALL.

ETV6/RUNX1 Fusion Gene Abrogation Decreases the Oncogenicity of Tumour Cells in a Preclinical Model of Acute Lymphoblastic Leukaemia

BACKGROUND

The t(12;21)(p13;q22), which fuses ETV6 and RUNX1 genes, is the most common genetic abnormality in children with B-cell precursor acute lymphoblastic leukaemia. The implication of the fusion protein in leukemogenesis seems to be clear. However, its role in the maintenance of the disease continues to be controversial.

METHODS

Generation of an in vitroETV6/RUNX1 knock out model using the CRISPR/Cas9 gene editing system. Functional characterization by RNA sequencing, proliferation assays, apoptosis and pharmacologic studies, and generation of edited-cell xenograft model.

RESULTS

The expression of ETV6/RUNX1 fusion gene was completely eliminated, thus generating a powerful model on which to study the role of the fusion gene in leukemic cells. The loss of fusion gene expression led to the deregulation of biological processes affecting survival such as apoptosis resistance and cell proliferation capacity. Tumour cells showed higher levels of apoptosis, lower proliferation rate and a greater sensitivity to PI3K inhibitors in vitro along as a decrease in tumour growth in xenografts models after ETV6/RUNX1 fusion gene abrogation.

CONCLUSIONS

ETV6/RUNX1 fusion protein seems to play an important role in the maintenance of the leukemic phenotype and could thus become a potential therapeutic target.

Differential Depletion of Bone Marrow Resident B-ALL after Systemic Administration of Endosomal TLR Agonists

Acute lymphoblastic leukemia (ALL) is the most common pediatric malignancy. While frontline chemotherapy regimens are generally very effective, the prognosis for patients whose leukemia returns remains poor. The presence of measurable residual disease (MRD) in bone marrow at the completion of induction therapy is the strongest predictor of relapse, suggesting that strategies to eliminate the residual leukemic blasts from this niche could reduce the incidence of recurrence. We have previously reported that toll-like receptor (TLR) agonists achieve durable T cell-mediated protection in transplantable cell line-based models of B cell precursor leukemia (B-ALL). However, the successful application of TLR agonist therapy in an MRD setting would require the induction of anti-leukemic immune activity specifically in the bone marrow, a site of the chemotherapy-resistant leukemic blasts. In this study, we compare the organ-specific depletion of human and mouse primary B-ALL cells after systemic administration of endosomal TLR agonists. Despite comparable splenic responses, only the TLR9 agonist induced strong innate immune responses in the bone marrow and achieved a near-complete elimination of B-ALL cells. This pattern of response was associated with the most significantly prolonged disease-free survival. Overall, our findings identify innate immune activity in the bone marrow that is associated with durable TLR-induced protection against B-ALL outgrowth.

Heterogeneity of Toll-like receptor 9 signaling in B cell malignancies and its potential therapeutic application

Toll-like receptor 9 (TLR9) is expressed in a variety of B-cell malignancies and works as a bridge between innate and adaptive immunity. CpG oligodeoxynucleotides (CpG ODNs), TLR9 agonists, are able to induce anticancer immune responses and exert direct effects against cancer cells, serving as cancer therapeutic agents. Therefore, TLR9 might be a potential therapeutic target for drug development. However, several new evidences have revealed that direct effects of TLR9 agonists on B-cell malignancies is controversial. For example, CpG ODNs can induce apoptosis in certain type of chronic lymphocytic leukemia and lymphoma cells, while induce proliferation in multiple myeloma and other types of lymphoma cells. In this review, we summarize current understanding of the heterogeneity in responses of normal and malignant B cells to TLR9 agonists, due to differences in TLR9 expression levels, genetic alterations (such as MyD88 mutation), and signaling pathway activation. Especially, the downstream molecules of NF-κB signaling pathway play an important role in the heterogeneous response. In order to provide possibilities for therapeutic manipulation of TLR9 agonists in the treatment of these disorders, the preclinical and clinical advances in using CpG ODNs alone and in combination therapies are also summarized in this review.

Toll-like receptors targeting technology for the treatment of lymphoma

INTRODUCTION

The crucial role of Toll-like Receptors (TLRs) in innate and adaptive immune systems is well discussed in the literature. In cancer, TLRs act as a double-edged sword that can promote or suppress tumor growth. Areas covered: In this article, the authors uncover the potential role of TLRs in lymphomas, which are cancers related to the lymphatic system and blood cells. TLRs are de facto inflammation-inducing receptors that can either worsen disease or ameliorate lymphoma treatment. From this perspective, the usage of TLRs to modulate the immune system toward lymphoma regression is desirable. Various strategies have been used so far, and novel ways are being sought out to cure lymphoma. Expert opinion: TLR ligands have successfully been used to improve patient health; however, these receptors must be finely tuned to further optimize therapy. For a better outcome, novel specific ligands, improved pharmacodynamics, and unique targets should be discerned. Ligands with conjugated molecules, nanoparticles, and targeted drug delivery can highly optimize the therapy for lymphoma with various etiologies.

Toll-like receptors in the pathogenesis of human B cell malignancies

Toll-like receptors (TLRs) are important players in B-cell activation, maturation and memory and may be involved in the pathogenesis of B-cell lymphomas. Accumulating studies show differential expression in this heterogeneous group of cancers. Stimulation with TLR specific ligands, or agonists of their ligands, leads to aberrant responses in the malignant B-cells. According to current data, TLRs can be implicated in malignant transformation, tumor progression and immune evasion processes. Most of the studies focused on multiple myeloma and chronic lymphocytic leukemia, but in the last decade the putative role of TLRs in other types of B-cell lymphomas has gained much interest. The aim of this review is to discuss recent findings on the role of TLRs in normal B cell functioning and their role in the pathogenesis of B-cell malignancies.

Aberrant expression of functional BAFF-system receptors by malignant B-cell precursors impacts leukemia cell survival

Despite exhibiting oncogenic events, patient's leukemia cells are responsive and dependent on signals from their malignant bone marrow (BM) microenvironment, which modulate their survival, cell cycle progression, trafficking and resistance to chemotherapy. Identification of the signaling pathways mediating this leukemia/microenvironment interplay is critical for the development of novel molecular targeted therapies.

We observed that primary leukemia B-cell precursors aberrantly express receptors of the BAFF-system, BAFF-R, BCMA, and TACI. These receptors are functional as their ligation triggers activation of NF-κB, MAPK/JNK, and Akt signaling. Leukemia cells express surface BAFF and APRIL ligands, and soluble BAFF is significantly higher in leukemia patients in comparison to age-matched controls. Interestingly, leukemia cells also express surface APRIL, which seems to be encoded by APRIL-δ, a novel isoform that lacks the furin convertase domain. Importantly, we observed BM microenvironmental cells express the ligands BAFF and APRIL, including surface and secreted BAFF by BM endothelial cells. Functional studies showed that signals through BAFF-system receptors impact the survival and basal proliferation of leukemia B-cell precursors, and support the involvement of both homotypic and heterotypic mechanisms.

This study shows an unforeseen role for the BAFF-system in the biology of precursor B-cell leukemia, and suggests that the target disruption of BAFF signals may constitute a valid strategy for the treatment of this cancer.

In acute myeloid leukemia, B7-H1 (PD-L1) protection of blasts from cytotoxic T cells is induced by TLR ligands and interferon-gamma and can be reversed using MEK inhibitors

B7-H1 (PD-L1) is a B7-related protein that inhibits T-cell responses. B7-H1 participates in the immunoescape of cancer cells and is also involved in the long-term persistence of leukemic cells in a mouse model of leukemia. B7-H1 can be constitutively expressed by cancer cells, but is also induced by various stimuli. Therefore, we examined the constitutive and inducible expression of B7-H1 and the consequences of this expression in human acute myeloid leukemia (AML). We analyzed B7-H1 expression in a cohort of 79 patients with AML. In addition, we studied blast cells after incubation with interferon-gamma or toll-like receptors (TLR) ligands. Finally, we evaluated functionality of cytotoxic T-cell activity against blast cells. Expression of B7-H1 upon diagnosis was high in 18% of patients. Expression of TLR2, 4 and 9 was detected in one-third of AML samples. Expression of TLR2 and TLR4 ligands or IFN-γ induced by B7-H1 was found to protect AML cells from CTL-mediated lysis. Spontaneous B7-H1 expression was also found to be enhanced upon relapse in some patients. MEK inhibitors, including UO126 and AZD6244, reduced B7-H1 expression and restored CTL-mediated lysis of blast cells. In AML, B7-H1 expression by blasts represents a possible immune escape mechanism. The inducibility of B7-H1 expression by IFN-γ or TLR ligands suggests that various stimuli, either produced during the immune response against leukemia cells or released by infectious microorganisms, could protect leukemic cells from T cells. The efficacy of MEK inhibitors against B7-H1-mediated inhibition of CTLs suggests a possible cancer immunotherapy strategy using targeted drugs.

Highlights of the First International "Immunotherapy in Pediatric Oncology: Progress and Challenges" Meeting

The first annual conference on immunotherapy in pediatric oncology was held in Bethesda, MD, from September 9 to 10, 2008 to discuss the state-of-the-art of immunotherapeutic strategies currently being explored in pediatric oncology. Major topics included targeting cell surface receptors, understanding and improving T-cell-based therapies, augmenting innate immune strategies, and enhancing graft-versus-leukemia for pediatric malignancies. As can be seen in the summaries of the individual presentations, significant progress has been made in developing preclinical models of pediatric tumors and a variety of novel immunobiologic therapies are approaching, or already in, the clinic. Although there is much excitement about the potential utility of these agents, a great deal of challenges lie ahead in improving the efficacy of each of these modalities and getting them to patients in a timely fashion. The resulting discussions will hopefully lead to new collaborations and insight for further translational and clinical studies.

Novel molecular and cellular therapeutic targets in acute lymphoblastic leukemia and lymphoproliferative disease

While the outcome for pediatric patients with lymphoproliferative disorders (LPD) or lymphoid malignancies, such as acute lymphoblastic leukemia (ALL), has improved dramatically, patients often suffer from therapeutic sequelae. Additionally, despite intensified treatment, the prognosis remains dismal for patients with refractory or relapsed disease. Thus, novel biologically targeted treatment approaches are needed. These targets can be identified by understanding how a loss of lymphocyte homeostasis can result in LPD or ALL. Herein, we review potential molecular and cellular therapeutic strategies that (i) target key signaling networks (e.g., PI3K/AKT/mTOR, JAK/STAT, Notch1, and SRC kinase family-containing pathways) which regulate lymphocyte growth, survival, and function; (ii) block the interaction of ALL cells with stromal cells or lymphoid growth factors secreted by the bone marrow microenvironment; or (iii) stimulate innate and adaptive immune responses.

Toll-like receptors: lessons to learn from normal and malignant human B cells

The humoral immune system senses microbes via recognition of specific microbial molecular motifs by Toll-like receptors (TLRs). These encounters promote plasma cell differentiation and antibody production. Recent studies have demonstrated the importance of the TLR system in enhancing antibody-mediated defense against infections and maintaining memory B cells. These results have led the way to the design of vaccines that target B cells by engaging TLRs. In hematologic malignancies, cells often retain B cell-specific receptors and associated functions. Among these, TLRs are currently exploited to target different subclasses of B-cell leukemia, and TLR agonists are currently being evaluated in clinical trials. However, accumulating evidence suggests that endogenous TLR ligands or chronic infections promote tumor growth, thus providing a need for further investigations to decipher the exact function of TLRs in the B-cell lineage and in neoplastic B cells. The aim of this review is to present and discuss the latest advances with regard to the expression and function of TLRs in both healthy and malignant B cells. Special attention will be focused on the growth-promoting effects of TLR ligands on leukemic B cells and their potential clinical impact.