Combination of PD-1/PD-L1 checkpoint inhibition and dendritic cell therapy in mice models and in patients with mesothelioma.

Immunotherapy with anti-PD1/PD-L1 is effective in only a subgroup of patients with malignant pleural mesothelioma (MPM). We investigated the efficacy of a combination of anti-PD1/PD-L1 and dendritic cell (DC) therapy to optimally induce effective anti-tumor immunity in MPM in both humans and mice. Data of nine MPM patients treated with DC therapy and sequential anti-PD1 treatment were collected and analyzed for progression-free survival (PFS) and overall survival (OS). Survival and T-cell responses were monitored in AC29 mesothelioma-bearing mice treated concurrently with the combination therapy; additionally, the role of the tumor-draining lymph node (TDLN) was investigated. The combination therapy resulted in a median OS and PFS of 17.7 and 8.0 months, respectively. Grade 3 to 4 treatment-related adverse events had not been reported. Survival of the mesothelioma-bearing mice treated with the combination therapy was longer than that of untreated mice, and coincided with improved T-cell activation in peripheral blood and less T-cell exhaustion in end stage tumors. Comparable results were obtained when solely the TDLN was targeted. We concluded that this combination therapy is safe and shows promising OS and PFS. The murine data support that PD-L1 treatment may reinvigorate the T-cell responses induced by DC therapy, which may primarily be the result of TDLN targeting.

Correction to: Role of Bruton's tyrosine kinase in B cells and malignancies.

Following publication of the original article [1], the authors reported an error in Table 1.

Role of Bruton's tyrosine kinase in B cells and malignancies.

Bruton's tyrosine kinase (BTK) is a non-receptor kinase that plays a crucial role in oncogenic signaling that is critical for proliferation and survival of leukemic cells in many B cell malignancies. BTK was initially shown to be defective in the primary immunodeficiency X-linked agammaglobulinemia (XLA) and is essential both for B cell development and function of mature B cells. Shortly after its discovery, BTK was placed in the signal transduction pathway downstream of the B cell antigen receptor (BCR). More recently, small-molecule inhibitors of this kinase have shown excellent anti-tumor activity, first in animal models and subsequently in clinical studies. In particular, the orally administered irreversible BTK inhibitor ibrutinib is associated with high response rates in patients with relapsed/refractory chronic lymphocytic leukemia (CLL) and mantle-cell lymphoma (MCL), including patients with high-risk genetic lesions. Because ibrutinib is generally well tolerated and shows durable single-agent efficacy, it was rapidly approved for first-line treatment of patients with CLL in 2016. To date, evidence is accumulating for efficacy of ibrutinib in various other B cell malignancies. BTK inhibition has molecular effects beyond its classic role in BCR signaling. These involve B cell-intrinsic signaling pathways central to cellular survival, proliferation or retention in supportive lymphoid niches. Moreover, BTK functions in several myeloid cell populations representing important components of the tumor microenvironment. As a result, there is currently a considerable interest in BTK inhibition as an anti-cancer therapy, not only in B cell malignancies but also in solid tumors. Efficacy of BTK inhibition as a single agent therapy is strong, but resistance may develop, fueling the development of combination therapies that improve clinical responses. In this review, we discuss the role of BTK in B cell differentiation and B cell malignancies and highlight the importance of BTK inhibition in cancer therapy.

Overcoming immune checkpoint blockade resistance in solid tumors with intermittent ITK inhibition.

Cytotoxic CD8 + T cell (CTL) exhaustion is driven by chronic antigen stimulation. Reversing CTL exhaustion with immune checkpoint blockade (ICB) has provided clinical benefits in different types of cancer. We, therefore, investigated whether modulating chronic antigen stimulation and T-cell receptor (TCR) signaling with an IL2-inducible T-cell kinase (ITK) inhibitor, could confer ICB responsiveness to ICB resistant solid tumors. In vivo intermittent treatment of 3 ICB-resistant solid tumor (melanoma, mesothelioma or pancreatic cancer) with ITK inhibitor significantly improved ICB therapy. ITK inhibition directly reinvigorate exhausted CTL in vitro as it enhanced cytokine production, decreased inhibitory receptor expression, and downregulated the transcription factor TOX. Our study demonstrates that intermittent ITK inhibition can be used to directly ameliorate CTL exhaustion and enhance immunotherapies even in solid tumors that are ICB resistant.

PD-L1 checkpoint blockade promotes regulatory T cell activity that underlies therapy resistance.

Despite the clinical success of immune checkpoint blockade (ICB), in certain cancer types, most patients with cancer do not respond well. Furthermore, in patients for whom ICB is initially successful, this is often short-lived because of the development of resistance to ICB. The mechanisms underlying primary or secondary ICB resistance are incompletely understood. Here, we identified preferential activation and enhanced suppressive capacity of regulatory T cells (Treg cells) in αPD-L1 therapy-resistant solid tumor-bearing mice. Treg cell depletion reversed resistance to αPD-L1 with concomitant expansion of effector T cells. Moreover, we found that tumor-infiltrating Treg cells in human patients with skin cancer, and in patients with non-small cell lung cancer, up-regulated a suppressive transcriptional gene program after ICB treatment, which correlated with lack of treatment response. αPD-1/PD-L1-induced PD-1+ Treg cell activation was also seen in peripheral blood of patients with lung cancer and mesothelioma, especially in nonresponders. Together, these data reveal that treatment with αPD-1 and αPD-L1 unleashes the immunosuppressive role of Treg cells, resulting in therapy resistance, suggesting that Treg cell targeting is an important adjunct strategy to enhance therapeutic efficacy.

Low-Dose JAK3 Inhibition Improves Antitumor T-Cell Immunity and Immunotherapy Efficacy.

Terminal T-cell exhaustion poses a significant barrier to effective anticancer immunotherapy efficacy, with current drugs aimed at reversing exhaustion being limited. Recent investigations into the molecular drivers of T-cell exhaustion have led to the identification of chronic IL2 receptor (IL2R)-STAT5 pathway signaling in mediating T-cell exhaustion. We targeted the key downstream IL2R-intermediate JAK 3 using a clinically relevant highly specific JAK3-inhibitor (JAK3i; PF-06651600) that potently inhibited STAT5-phosphorylation in vitro. Whereas pulsed high-dose JAK3i administration inhibited antitumor T-cell effector function, low-dose chronic JAK3i significantly improved T-cell responses and decreased tumor load in mouse models of solid cancer. Low-dose JAK3i combined with cellular and peptide vaccine strategies further decreased tumor load compared with both monotherapies alone. Collectively, these results identify JAK3 as a novel and promising target for combination immunotherapy.

Switch-maintenance gemcitabine after first-line chemotherapy in patients with malignant mesothelioma (NVALT19): an investigator-initiated, randomised, open-label, phase 2 trial.

BACKGROUND: Almost all patients with malignant mesothelioma eventually have disease progression after first-line therapy. Previous studies have investigated maintenance therapy, but none has shown a great effect. We aimed to assess the efficacy and safety of switch-maintenance gemcitabine in patients with malignant mesothelioma without disease progression after first-line chemotherapy. METHODS: We did a randomised, open-label, phase 2 trial in 18 hospitals in the Netherlands (NVALT19). We recruited patients aged older than 18 years with unresectable malignant mesothelioma with no evidence of disease progression after at least four cycles of first-line chemotherapy (with platinum and pemetrexed), who had a WHO performance status of 0-2, adequate organ function, and measurable or evaluable disease. Exclusion criteria were active uncontrolled infection or severe cardiac dysfunction, serious disabling conditions, symptomatic CNS metastases, radiotherapy within 2 weeks before enrolment, and concomitant use of any other drugs under investigation. Patients were randomly assigned (1:1), using the minimisation method, to maintenance intravenous gemcitabine (1250 mg/m2 on days 1 and 8, in cycles of 21 days) plus supportive care, or to best supportive care alone, until disease progression, unacceptable toxicity, serious intercurrent illness, patient request for discontinuation, or need for any other anticancer agent, except for palliative radiotherapy. A CT scan of the thorax or abdomen (or both) and pulmonary function tests were done at baseline and repeated every 6 weeks. The primary outcome was progression-free survival in the intention-to-treat population. Safety was analysed in all participants who received one or more doses of the study drug or had at least one visit for supportive care. Recruitment is now closed; treatment and follow-up are ongoing. This study is registered with the Netherlands Trial Registry, NTR4132/NL3847. FINDINGS: Between March 20, 2014, and Feb 27, 2019, 130 patients were enrolled and randomly assigned to gemcitabine plus supportive care (65 patients [50%]) or supportive care alone (65 patients [50%]). No patients were lost to follow-up; median follow-up was 36·5 months (95% CI 34·2 to not reached), and one patient in the supportive care group withdrew consent. Progression-free survival was significantly longer in the gemcitabine group (median 6·2 months [95% CI 4·6-8·7]) than in the supportive care group (3·2 months [2·8-4·1]; hazard ratio [HR] 0·48 [95% CI 0·33-0·71]; p=0·0002). The benefit was confirmed by masked independent central review (HR 0·49 [0·33-0·72]; p=0·0002). Grade 3-4 adverse events occurred in 33 (52%) of 64 patients in the gemcitabine group and in ten (16%) of 62 patients in the supportive care group. The most frequent adverse events were anaemia, neutropenia, fatigue or asthenia, pain, and infection in the gemcitabine group, and pain, infection, and cough or dyspnoea in the supportive care group. One patient (2%) in the gemcitabine group died, due to a treatment-related infection. INTERPRETATION: Switch-maintenance gemcitabine, after first-line chemotherapy, significantly prolonged progression-free survival compared with best supportive care alone, among patients with malignant mesothelioma. This study confirms the activity of gemcitabine in treating malignant mesothelioma. FUNDING: Dutch Cancer Society (Koningin Wilhelmina Fonds voor de Nederlandse Kankerbestrijding) and Stichting NVALT studies.

Immune monitoring in mesothelioma patients identifies novel immune-modulatory functions of gemcitabine associating with clinical response.

BACKGROUND: Gemcitabine is a frequently used chemotherapeutic agent but its effects on the immune system are incompletely understood. Recently, the randomized NVALT19-trial revealed that maintenance gemcitabine after first-line chemotherapy significantly prolonged progression-free survival (PFS) compared to best supportive care (BSC) in malignant mesothelioma. Whether these effects are paralleled by changes in circulating immune cell subsets is currently unknown. These analyses could offer improved mechanistic insights into the effects of gemcitabine on the host and guide development of effective combination therapies in mesothelioma. METHODS: We stained peripheral blood mononuclear cells (PBMCs) and myeloid-derived suppressor cells (MDSCs) at baseline and 3 weeks following start of gemcitabine or BSC treatment in a subgroup of mesothelioma patients included in the NVALT19-trial. In total, 24 paired samples including both MDSCs and PBMCs were included. We performed multicolour flow-cytometry to assess co-inhibitory and-stimulatory receptor- and cytokine expression and matched these parameters with PFS and OS. FINDINGS: Gemcitabine treatment was significantly associated with an increased NK-cell- and decreased T-regulatory cell proliferation whereas the opposite occurred in control patients. Furthermore, myeloid-derived suppressor cells (MDSCs) frequencies were lower in gemcitabine-treated patients and this correlated with increased T-cell proliferation following treatment. Whereas gemcitabine variably altered co-inhibitory receptor expression, co-stimulatory molecules including ICOS, CD28 and HLA-DR were uniformly increased across CD4+ T-helper, CD8+ T- and NK-cells. Although preliminary in nature, the increase in NK-cell proliferation and PD-1 expression in T cells following gemcitabine treatment was associated with improved PFS and OS. INTERPRETATION: Gemcitabine treatment was associated with widespread effects on circulating immune cells of mesothelioma patients with responding patients displaying increased NK-cell and PD-1 + T-cell proliferation. These exploratory data provide a platform for future on treatment-biomarker development and novel combination treatment strategies.

Dendritic cell vaccination and CD40-agonist combination therapy licenses T cell-dependent antitumor immunity in a pancreatic carcinoma murine model.

BACKGROUND: Pancreatic ductal adenocarcinoma (PDAC) is notoriously resistant to treatment including checkpoint-blockade immunotherapy. We hypothesized that a bimodal treatment approach consisting of dendritic cell (DC) vaccination to prime tumor-specific T cells, and a strategy to reprogram the desmoplastic tumor microenvironment (TME) would be needed to break tolerance to these pancreatic cancers. As a proof-of-concept, we investigated the efficacy of combined DC vaccination with CD40-agonistic antibodies in a poorly immunogenic murine model of PDAC. Based on the rationale that mesothelioma and pancreatic cancer share a number of tumor associated antigens, the DCs were loaded with either pancreatic or mesothelioma tumor lysates. METHODS: Immune-competent mice with subcutaneously or orthotopically growing KrasG12D/+;Trp53R172H/+;Pdx-1-Cre (KPC) PDAC tumors were vaccinated with syngeneic bone marrow-derived DCs loaded with either pancreatic cancer (KPC) or mesothelioma (AE17) lysate and consequently treated with FGK45 (CD40 agonist). Tumor progression was monitored and immune responses in TME and lymphoid organs were analyzed using multicolor flow cytometry and NanoString analyzes. RESULTS: Mesothelioma-lysate loaded DCs generated cross-reactive tumor-antigen-specific T-cell responses to pancreatic cancer and induced delayed tumor outgrowth when provided as prophylactic vaccine. In established disease, combination with stimulating CD40 antibody was necessary to improve survival, while anti-CD40 alone was ineffective. Extensive analysis of the TME showed that anti-CD40 monotherapy did improve CD8 +T cell infiltration, but these essential effector cells displayed hallmarks of exhaustion, including PD-1, TIM-3 and NKG2A. Combination therapy induced a strong change in tumor transcriptome and mitigated the expression of inhibitory markers on CD8 +T cells. CONCLUSION: These results demonstrate the potency of DC therapy in combination with CD40-stimulation for the treatment of pancreatic cancer and provide directions for near future clinical trials.

The PD-1/PD-L1-Checkpoint Restrains T cell Immunity in Tumor-Draining Lymph Nodes.

PD-1/PD-L1-checkpoint blockade therapy is generally thought to relieve tumor cell-mediated suppression in the tumor microenvironment but PD-L1 is also expressed on non-tumor macrophages and conventional dendritic cells (cDCs). Here we show in mouse tumor models that tumor-draining lymph nodes (TDLNs) are enriched for tumor-specific PD-1+ T cells which closely associate with PD-L1+ cDCs. TDLN-targeted PD-L1-blockade induces enhanced anti-tumor T cell immunity by seeding the tumor site with progenitor-exhausted T cells, resulting in improved tumor control. Moreover, we show that abundant PD-1/PD-L1-interactions in TDLNs of nonmetastatic melanoma patients, but not those in corresponding tumors, associate with early distant disease recurrence. These findings point at a critical role for PD-L1 expression in TDLNs in governing systemic anti-tumor immunity, identifying high-risk patient groups amendable to adjuvant PD-1/PD-L1-blockade therapy.

Current State of Dendritic Cell-Based Immunotherapy: Opportunities for in vitro Antigen Loading of Different DC Subsets?

Dendritic cell (DC) based cancer immunotherapy aims at the activation of the immune system, and in particular tumor-specific cytotoxic T lymphocytes (CTLs) to eradicate the tumor. DCs represent a heterogeneous cell population, including conventional DCs (cDCs), consisting of cDC1s, cDC2s, plasmacytoid DCs (pDCs), and monocyte-derived DCs (moDCs). These DC subsets differ both in ontogeny and functional properties, such as the capacity to induce CD4+ and CD8+ T-cell activation. MoDCs are most frequently used for vaccination purposes, based on technical aspects such as availability and in vitro expansion. However, whether moDCs are superior over other DC subsets in inducing anti-tumor immune responses, is unknown, and likely depends on tumor type and composition of the tumor microenvironment. In this review, we discuss cellular aspects essential for DC vaccination efficacy, and the most recent findings on different DC subsets that could be used for DC-based cancer immunotherapy. This can prove valuable for the future design of more effective DC vaccines by choosing different DC subsets, and sheds light on the working mechanism of DC immunotherapy.

Combination Strategies to Optimize Efficacy of Dendritic Cell-Based Immunotherapy.

Dendritic cells (DCs) are antigen-presenting cells (APCs) that are essential for the activation of immune responses. In various malignancies, these immunostimulatory properties are exploited by DC-therapy, aiming at the induction of effective anti-tumor immunity by vaccination with ex vivo antigen-loaded DCs. Depending on the type of DC-therapy used, long-term clinical efficacy upon DC-therapy remains restricted to a proportion of patients, likely due to lack of immunogenicity of tumor cells, presence of a stromal compartment, and the suppressive tumor microenvironment (TME), thereby leading to the development of resistance. In order to circumvent tumor-induced suppressive mechanisms and unleash the full potential of DC-therapy, considerable efforts have been made to combine DC-therapy with chemotherapy, radiotherapy or with checkpoint inhibitors. These combination strategies could enhance tumor immunogenicity, stimulate endogenous DCs following immunogenic cell death, improve infiltration of cytotoxic T lymphocytes (CTLs) or specifically deplete immunosuppressive cells in the TME, such as regulatory T-cells and myeloid-derived suppressor cells. In this review, different strategies of combining DC-therapy with immunomodulatory treatments will be discussed. These strategies and insights will improve and guide DC-based combination immunotherapies with the aim of further improving patient prognosis and care.

Immunotherapeutic strategies in non-small-cell lung cancer: the present and the future.

Non-small cell lung cancer (NSCLC) is still the leading cause of cancer death worldwide, with a poor prognosis. In the era of immunotherapies, the field is rapidly changing, and the clinician needs to be aware of the current state and future perspectives of immunotherapeutic strategies. In this review, we discuss the current status of immune checkpoint inhibitors, cancer vaccines and cellular therapies specifically in NSCLC. Last but not least, we will discuss rational combination strategies that are promising for the near future.

Depletion of Tumor-Associated Macrophages with a CSF-1R Kinase Inhibitor Enhances Antitumor Immunity and Survival Induced by DC Immunotherapy.

New immunotherapeutic strategies are needed to induce effective antitumor immunity in all cancer patients. Malignant mesothelioma is characterized by a poor prognosis and resistance to conventional therapies. Infiltration of tumor-associated macrophages (TAM) is prominent in mesothelioma and is linked to immune suppression, angiogenesis, and tumor aggressiveness. Therefore, TAM depletion could potentially reactivate antitumor immunity. We show that M-CSFR inhibition using the CSF-1R kinase inhibitor PLX3397 (pexidartinib) effectively reduced numbers of TAMs, circulating nonclassical monocytes, as well as amount of neoangiogenesis and ascites in mesothelioma mouse models, but did not improve survival. When combined with dendritic cell vaccination, survival was synergistically enhanced with a concomitant decrease in TAMs and an increase in CD8+ T-cell numbers and functionality. Total as well as tumor antigen-specific CD8+ T cells in tumor tissue of mice treated with combination therapy showed reduced surface expression of the programmed cell death protein-1 (PD-1), a phenomenon associated with T-cell exhaustion. Finally, mice treated with combination therapy were protected from tumor rechallenge and displayed superior T-cell memory responses. We report that decreasing local TAM-mediated immune suppression without immune activation does not improve survival. However, combination of TAM-mediated immune suppression with dendritic cell immunotherapy generates robust and durable antitumor immunity. These findings provide insights into the interaction between immunotherapy-induced antitumor T cells and TAMs and offer a therapeutic strategy for mesothelioma treatment. Cancer Immunol Res; 5(7); 535-46. ©2017 AACR.

Rationally combining immunotherapies to improve efficacy of immune checkpoint blockade in solid tumors.

With the widespread application of immune checkpoint blocking antibodies (ICBs) for the treatment of advanced cancer, immunotherapy has proven to be capable of yielding unparalleled clinical results. However, despite the initial success of ICB-treatment, still a minority of patients experience durable responses to ICB therapy. A plethora of mechanisms underlie ICB resistance ranging from low immunogenicity, inadequate generation or recruitment of tumor-specific T cells or local suppression by stromal cells to acquired genetic alterations leading to immune escape. Increasing the response rates to ICBs requires insight into the mechanisms underlying resistance and the subsequent design of rational therapeutic combinations on a per patient basis. In this review, we aim to establish order into the mechanisms governing primary and secondary ICB resistance, offer therapeutic options to circumvent different modes of resistance and plea for a personalized medicine approach to maximize immunotherapeutic benefit for all cancer patients.

Efficacy of Tumor Vaccines and Cellular Immunotherapies in Non-Small-Cell Lung Cancer: A Systematic Review and Meta-Analysis.

PURPOSE: Programmed cell death protein-1- checkpoint blockers have recently been approved as second-line treatment for advanced non-small-cell lung cancer (NSCLC). Unfortunately, only a subgroup of patients responds and shows long-term survival to these therapies. Tumor vaccines and cellular immunotherapies could synergize with checkpoint blockade, but which of these treatments is most efficacious is unknown. In this meta-analysis, we assessed the efficacy of tumor vaccination and cellular immunotherapy in NSCLC. METHODS: We searched for randomized controlled trials (RCTs) investigating cellular immunotherapy or vaccines in NSCLC. We used random effects models to analyze overall survival (OS) and progression-free survival (PFS), expressed as hazard ratios (HRs), and differences in time (months). The effect of immunotherapy type, disease stage, tumor histology, and concurrent chemotherapy was assessed using subgroup analysis and meta-regression. All procedures were performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. RESULTS: We identified 18 RCTs that matched our selection criteria; these included a total of 6,756 patients. Immunotherapy extended NSCLC survival and PFS, expressed as HR (OS: HR, 0.81, 95% CI, 0.70 to 0.94, P = .01; PFS: HR, 0.83, 95% CI, 0.72 to 0.95, P = .006) and month difference (OS: difference, 5.43 months, 95% CI, 3.20 to 7.65, P < .005; PFS: difference, 3.24 months, 95% CI, 1.61 to 4.88, P < .005). Cellular therapies outperformed tumor vaccines (OS as HR: P = .005, month difference: P < .001; PFS as HR: P = .001, month difference: P = .004). There was a benefit of immunotherapy in low-stage compared with high-stage NSCLC and with concurrent administration of chemotherapy only in one of four outcome measures evaluated (PFS in months: P = .01 and PFS as HR: P = .031, respectively). There was no significant effect of tumor histology on survival or PFS. CONCLUSION: Tumor vaccines and cellular immunotherapies enhanced OS and PFS in NSCLC. Cellular immunotherapy was found to be more effective than tumor vaccination. These findings have implications for future studies investigating combination immunotherapy in NSCLC.