Soluble immune checkpoint factors reflect exhaustion of antitumor immunity and response to PD-1 blockade.

BACKGROUNDPrecise stratification of patients with non-small cell lung cancer (NSCLC) is needed for appropriate application of PD-1/PD-L1 blockade therapy.METHODSWe measured soluble forms of the immune-checkpoint molecules PD-L1, PD-1, and CTLA-4 in plasma of patients with advanced NSCLC before PD-1/PD-L1 blockade. A prospective biomarker-finding trial (cohort A) included 50 previously treated patients who received nivolumab. A retrospective observational study was performed for patients treated with any PD-1/PD-L1 blockade therapy (cohorts B and C), cytotoxic chemotherapy (cohort D), or targeted therapy (cohort E). Plasma samples from all patients were assayed for soluble immune-checkpoint molecules with a highly sensitive chemiluminescence-based assay.RESULTSNonresponsiveness to PD-1/PD-L1 blockade therapy was associated with higher concentrations of these soluble immune factors among patients with immune-reactive (hot) tumors. Such an association was not apparent for patients treated with cytotoxic chemotherapy or targeted therapy. Integrative analysis of tumor size, PD-L1 expression in tumor tissue (tPD-L1), and gene expression in tumor tissue and peripheral CD8+ T cells revealed that high concentrations of the 3 soluble immune factors were associated with hyper or terminal exhaustion of antitumor immunity. The combination of soluble PD-L1 (sPD-L1) and sCTLA-4 efficiently discriminated responsiveness to PD-1/PD-L1 blockade among patients with immune-reactive tumors.CONCLUSIONCombinations of soluble immune factors might be able to identify patients unlikely to respond to PD-1/PD-L1 blockade as a result of terminal exhaustion of antitumor immunity. Our data suggest that such a combination better predicts, along with tPD-L1, for the response of patients with NSCLC.TRIAL REGISTRATIONUMIN000019674.FUNDINGThis study was funded by Ono Pharmaceutical Co. Ltd. and Sysmex Corporation.

Vascularization of the adult mouse lung grafted onto the chick chorioallantoic membrane.

In the later stages of angiogenesis, the vascular sprout transitions into a functional vessel by fusing with a target vessel. Although this process appears to routinely occur in embryonic tissue, the biologic rules for sprout fusion and lumenization in adult regenerating tissue are unknown. To investigate this process, we grafted portions of the regenerating post-pneumonectomy lung onto the chick chorioallantoic membrane (CAM). Grafts from all 4 lobes of the post-pneumonectomy right lung demonstrated peri-graft angiogenesis as reflected by fluorescent plasma markers; however, fluorescent microsphere perfusion primarily occurred in the lobe of the lung that is the dominant site of post-pneumonectomy angiogenesis-namely, the cardiac lobe. Vascularization of the cardiac lobe grafts was confirmed by active tissue growth (p < .05). Functional vascular connections between the cardiac lobe and the CAM vascular network were demonstrated by confocal fluorescence microscopy as well as corrosion casting and scanning electron microscopy (SEM). Bulk transcriptional profiling of the cardiac lobe demonstrated the enhanced expression of many genes relative to alveolar epithelial cell (CD11b-/CD31-) control cells, but only the upregulation of Ereg and Fgf6 compared to the less well-vascularized right upper lobe. The growth of actively regenerating non-neoplastic adult tissue on the CAM demonstrates that functional lumenization can occur between species (mouse and chick) and across the developmental spectrum (adult and embryo).

The combination of soluble forms of PD-1 and PD-L1 as a predictive marker of PD-1 blockade in patients with advanced cancers: a multicenter retrospective study.

Introduction: The clinical relevance of soluble forms of programmed cell death-1 (sPD-1) and programmed cell death-ligand 1 (sPD-L1) remains unclear. We here investigated the relation between the efficacy of PD-1 blockade and pretreatment plasma levels of sPD-1 and sPD-L1 across a broad range of cancer types. Methods: We retrospectively analyzed clinical data from 171 patients with advanced solid tumors who received nivolumab or pembrolizumab monotherapy regardless of treatment line. The concentrations of sPD-1 and sPD-L1 were measured with a fully automated immunoassay (HISCL system). Results: The study subjects comprised patients with head and neck cancer (n = 50), urothelial cancer (n = 42), renal cell cancer (n = 37), gastric cancer (n = 20), esophageal cancer (n = 10), malignant pleural mesothelioma (n = 6), or microsatellite instability-high tumors (n = 6). High or low levels of sPD-1 or sPD-L1 were not significantly associated with progression-free survival (PFS) or overall survival (OS) for PD-1 blockade in the entire study population. Comparison of treatment outcomes according to combinations of high or low sPD-1 and sPD-L1 levels, however, revealed that patients with low sPD-1 and high sPD-L1 concentrations had a significantly poorer PFS (HR of 1.79 [95% CI, 1.13-2.83], p = 0.01) and a tendency toward poorer OS (HR of 1.70 [95% CI, 0.99-2.91], p = 0.05) compared with all other patients. Conclusion: Our findings suggest that the combination of low sPD-1 and high sPD-L1 levels is a potential negative biomarker for PD-1 blockade therapy.

Lack of Association of Plasma Levels of Soluble Programmed Cell Death Protein 1, Programmed Death-Ligand 1, and CTLA-4 With Survival for Stage II to IIIA NSCLC After Complete Resection and Adjuvant Chemotherapy.

Introduction: Perioperative treatment in NSCLC has gained marked attention with the introduction of immune checkpoint inhibitors. Such a paradigm shift has given us additional opportunities to evaluate potential biomarkers in patients with these curable disease stages. Methods: This study (WJOG12319LTR) was designed as a biomarker study to evaluate whether soluble immune markers were prognostic or predictive on relapse-free survival in patients with stage II to IIIA NSCLC who underwent complete resection and adjuvant chemotherapy with cisplatin plus S-1, which is an oral fluoropyrimidine formulation that consists of tegafur, gimeracil, and oteracil, or S-1 alone in the previous WJOG4107 study. Archived plasma samples were assayed for soluble (s) forms of programmed cell death protein 1 (sPD-1), programmed death-ligand 1(sPD-L1), and CTLA-4 (sCTLA-4) with the highly sensitive HISCL system. Using time-dependent receiver operating characteristic curve analysis, the area under the curves were derived and optimal cutoff values were determined. Using the cutoff values, whether the marker was prognostic or predictive was assessed by survival analysis. Results: A total of 150 patients were included in the study. The time-dependent receiver operating characteristics analysis revealed that the area under the curves for sPD-1, sPD-L1, and sCTLA-4 were 0.54, 0.51, and 0.58, respectively. The survival analysis did not reject that hazard ratios were 1 in terms of the soluble immune marker and the treatment-marker interaction for all three markers. Conclusions: There was no proof that circulating concentrations of sPD-1, sPD-L1, and sCTLA-4 were prognostic or predictive factors of the outcome for adjuvant chemotherapy after complete resection in patients with NSCLC.

Spermidine - an old molecule with a new age-defying immune function.

Polyamines - putrescine, spermidine, and spermine - are widely distributed aliphatic compounds known to regulate important biological processes in prokaryotic and eukaryotic cells. Therefore, spermidine insufficiency is associated with various physio-pathological processes, such as aging and cancers. Recent advances in immuno-metabolism and immunotherapy shed new light on the role of spermidine in immune cell regulation and anticancer responses. Here, we review novel works demonstrating that spermidine is produced by collective metabolic pathways of gut bacteria, bacteria-host co-metabolism, and by the host cells, including activated immune cells. We highlight the effectiveness of spermidine in enhancing antitumor responses in aged animals otherwise nonresponsive to immune checkpoint therapy and propose that spermidine supplementation could be used to enhance the efficacy of anti-PD-1 treatment.

Insights from a 30-year journey: function, regulation and therapeutic modulation of PD1.

PD1 was originally discovered in 1992 as a molecule associated with activation-induced cell death in T cells. Over the past 30 years, it was found that PD1 has a critical role in avoiding overactivation-induced cell death and autoimmunity, whereas its inhibition unleashes anticancer immunity. Here, we outline the journey from the discovery of PD1 to its role as a breakthrough target in cancer immunotherapy. We describe its regulation and function and examine how a mechanistic understanding of PD1 signalling suggests a central function in setting the T cell activation threshold, thereby controlling T cell proliferation, differentiation, exhaustion and metabolic status. This threshold theory, in combination with new insights into T cell metabolism and a better understanding of immune cell modulation by the microbiota, can provide guidance for the development of efficient combination therapies. Moreover, we discuss the mechanisms underlying immune-related adverse events after PD1-targeted therapy and their possible treatment.

Soluble programmed cell death ligand 1 predicts prognosis for gastric cancer patients treated with nivolumab: Blood-based biomarker analysis for the DELIVER trial.

BACKGROUND: The clinical value of soluble forms of programmed cell death-1 (sPD-1), PD ligand 1 (sPD-L1) and cytotoxic T lymphocyte-associated protein-4 (sCTLA-4) for gastric cancer (GC) patients treated with nivolumab monotherapy has remained unknown. METHODS: Blood samples collected before nivolumab treatment from 439 GC patients enrolled in the DELIVER (Japan Clinical Cancer Research Organisation GC-08) trial were analysed for sPD-1, sPD-L1 and sCTLA-4. Corresponding baseline clinical data were also retrieved. RESULTS: Higher plasma levels of sPD-1 (hazard ratio [HR] = 1.27, p = 0.020), sPD-L1 (HR = 1.86, p < 0.001) and sCTLA-4 (HR = 1.33, p = 0.008) were significantly associated with shorter overall survival (OS), whereas only higher sPD-L1 levels was significantly associated with shorter progression-free survival (HR = 1.30, p = 0.008). The sPD-L1 concentration was significantly associated with the Glasgow prognostic score (GPS) (p < 0.001), but both sPD-L1 (HR = 1.67, p < 0.001) and GPS (HR = 1.39, p = 0.009 for GPS 0 versus 1; HR = 1.95, p < 0.001 for GPS 0 versus 2) were independently associated with OS. Patients with a GPS of 0 and low sPD-L1 thus showed the longest OS (median, 12.0 months) and those with a GPS of 2 and high sPD-L1 showed the shortest OS (median, 3.1 months), yielding a HR of 3.69 (p < 0.001). CONCLUSION: Baseline sPD-L1 levels have the potential to predict survival for advanced GC patients treated with nivolumab, with the prognostic accuracy of sPD-L1 being improved by its combination with GPS.

Combination bezafibrate and nivolumab treatment of patients with advanced non-small cell lung cancer.

Despite the success of cancer immunotherapies such as programmed cell death-1 (PD-1) and PD-1 ligand 1 (PD-L1) inhibitors, patients often develop resistance. New combination therapies with PD-1/PD-L1 inhibitors are needed to overcome this issue. Bezafibrate, a ligand of peroxisome proliferator-activated receptor-γ coactivator 1α/peroxisome proliferator-activated receptor complexes, has shown a synergistic antitumor effect with PD-1 blockade in mice that is mediated by activation of mitochondria in T cells. We have therefore now performed a phase 1 trial (UMIN000017854) of bezafibrate with nivolumab in previously treated patients with advanced non-small cell lung cancer. The primary end point was the percentage of patients who experience dose-limiting toxicity, and this combination regimen was found to be well tolerated. Preplanned comprehensive analysis of plasma metabolites and gene expression in peripheral cytotoxic T cells indicated that bezafibrate promoted T cell function through up-regulation of mitochondrial metabolism including fatty acid oxidation and may thereby have prolonged the duration of response. This combination strategy targeting T cell metabolism thus has the potential to maintain antitumor activity of immune checkpoint inhibitors and warrants further validation.

Chemical induction of splice-neoantigens attenuates tumor growth in a preclinical model of colorectal cancer.

Neoantigen production is a determinant of cancer immunotherapy. However, the expansion of neoantigen abundance for cancer therapeutics is technically challenging. Here, we report that the synthetic compound RECTAS can induce the production of splice-neoantigens that could be used to boost antitumor immune responses. RECTAS suppressed tumor growth in a CD8+ T cell- and tumor major histocompatibility complex class I-dependent manner and enhanced immune checkpoint blockade efficacy. Subsequent transcriptome analysis and validation for immunogenicity identified six splice-neoantigen candidates whose expression was induced by RECTAS treatment. Vaccination of the identified neoepitopes elicited T cell responses capable of killing cancer cells in vitro, in addition to suppression of tumor growth in vivo upon sensitization with RECTAS. Collectively, these results provide support for the further development of splice variant-inducing treatments for cancer immunotherapy.

Spermidine activates mitochondrial trifunctional protein and improves antitumor immunity in mice.

Spermidine (SPD) delays age-related pathologies in various organisms. SPD supplementation overcame the impaired immunotherapy against tumors in aged mice by increasing mitochondrial function and activating CD8+ T cells. Treatment of naïve CD8+ T cells with SPD acutely enhanced fatty acid oxidation. SPD conjugated to beads bound to the mitochondrial trifunctional protein (MTP). In the MTP complex, synthesized and purified from Escherichia coli, SPD bound to the α and ß subunits of MTP with strong affinity and allosterically enhanced their enzymatic activities. T cell-specific deletion of the MTP α subunit abolished enhancement of programmed cell death protein 1 (PD-1) blockade immunotherapy by SPD, indicating that MTP is required for SPD-dependent T cell activation.

B cell-derived GABA elicits IL-10+ macrophages to limit anti-tumour immunity.

Small, soluble metabolites not only are essential intermediates in intracellular biochemical processes, but can also influence neighbouring cells when released into the extracellular milieu1-3. Here we identify the metabolite and neurotransmitter GABA as a candidate signalling molecule synthesized and secreted by activated B cells and plasma cells. We show that B cell-derived GABA promotes monocyte differentiation into anti-inflammatory macrophages that secrete interleukin-10 and inhibit CD8+ T cell killer function. In mice, B cell deficiency or B cell-specific inactivation of the GABA-generating enzyme GAD67 enhances anti-tumour responses. Our study reveals that, in addition to cytokines and membrane proteins, small metabolites derived from B-lineage cells have immunoregulatory functions, which may be pharmaceutical targets allowing fine-tuning of immune responses.

Critical role of the CD44lowCD62Llow CD8+ T cell subset in restoring antitumor immunity in aged mice.

CD8+ T cells play a central role in antitumor immune responses that kill cancer cells directly. In aged individuals, CD8+ T cell immunity is strongly suppressed, which is associated with cancer and other age-related diseases. The mechanism underlying this age-related decrease in immune function remains largely unknown. This study investigated the role of T cell function in age-related unresponsiveness to PD-1 blockade cancer therapy. We found inefficient generation of CD44lowCD62Llow CD8+ T cell subset (P4) in draining lymph nodes of tumor-bearing aged mice. In vitro stimulation of naive CD8+ T cells first generated P4 cells, followed by effector/memory T cells. The P4 cells contained a unique set of genes related to enzymes involved in one-carbon (1C) metabolism, which is critical to antigen-specific T cell activation and mitochondrial function. Consistent with this finding, 1C-metabolism-related gene expression and mitochondrial respiration were down-regulated in aged CD8+ T cells compared with young CD8+ T cells. In aged OVA-specific T cell receptor (TCR) transgenic mice, ZAP-70 was not activated, even after inoculation with OVA-expressing tumor cells. The attenuation of TCR signaling appeared to be due to elevated expression of CD45RB phosphatase in aged CD8+ T cells. Surprisingly, strong stimulation by nonself cell injection into aged PD-1-deficient mice restored normal levels of CD45RB and ameliorated the emergence of P4 cells and 1C metabolic enzyme expression in CD8+ T cells, and antitumor activity. These findings indicate that impaired induction of the P4 subset may be responsible for the age-related resistance to PD-1 blockade, which can be rescued by strong TCR stimulation.

Inherited PD-1 deficiency underlies tuberculosis and autoimmunity in a child.

The pathophysiology of adverse events following programmed cell death protein 1 (PD-1) blockade, including tuberculosis (TB) and autoimmunity, remains poorly characterized. We studied a patient with inherited PD-1 deficiency and TB who died of pulmonary autoimmunity. The patient's leukocytes did not express PD-1 or respond to PD-1-mediated suppression. The patient's lymphocytes produced only small amounts of interferon (IFN)-γ upon mycobacterial stimuli, similarly to patients with inborn errors of IFN-γ production who are vulnerable to TB. This phenotype resulted from a combined depletion of Vδ2+ γδ T, mucosal-associated invariant T and CD56bright natural killer lymphocytes and dysfunction of other T lymphocyte subsets. Moreover, the patient displayed hepatosplenomegaly and an expansion of total, activated and RORγT+ CD4-CD8- double-negative αß T cells, similar to patients with STAT3 gain-of-function mutations who display lymphoproliferative autoimmunity. This phenotype resulted from excessive amounts of STAT3-activating cytokines interleukin (IL)-6 and IL-23 produced by activated T lymphocytes and monocytes, and the STAT3-dependent expression of RORγT by activated T lymphocytes. Our work highlights the indispensable role of human PD-1 in governing both antimycobacterial immunity and self-tolerance, while identifying potentially actionable molecular targets for the diagnostic and therapeutic management of TB and autoimmunity in patients on PD-1 blockade.

Immune metabolism in PD-1 blockade-based cancer immunotherapy.

Energy metabolism plays an important role in proliferating cells. Recent reports indicate that metabolic regulation or metabolic products can control immune cell differentiation, fate and reactions. Cancer immunotherapy based on blockade of programmed cell death protein 1 (PD-1) has been used worldwide, but a significant fraction of patients remain unresponsive. Therefore, clarifying the mechanisms and overcoming the unresponsiveness are urgent issues. Because cancer immunity consists of interactions between the cancer and host immune cells, there has recently been a focus on the metabolic interactions and/or competition between the tumor and the immune system to address these issues. Cancer cells render their microenvironment immunosuppressive, driving T-cell dysfunction or exhaustion, which is advantageous for cancer cell survival. However, accumulating mechanistic evidence of T-cell and cancer cell metabolism has gradually revealed that controlling the metabolic pathways of either type of cell can overcome T-cell dysfunction and reprogram the metabolic balance in the tumor microenvironment. Here, we summarize the role of immune metabolism in T-cell-based immune surveillance and cancer immune escape. This new concept has boosted the development of combination therapy and predictive biomarkers in cancer immunotherapy with immune checkpoint inhibitors.

Circulation of gut-preactivated naïve CD8+ T cells enhances antitumor immunity in B cell-defective mice.

The gut microbiome has garnered attention as an effective target to boost immunity and improve cancer immunotherapy. We found that B cell-defective (BCD) mice, such as µ-membrane targeted deletion (µMT) and activation-induced cytidine deaminase (AID) knockouts (KOs), have elevated antitumor immunity under specific pathogen-free but not germ-free conditions. Microbial dysbiosis in these BCD mice enriched the type I IFN (IFN) signature in mucosal CD8+ T cells, resulting in up-regulation of the type I IFN-inducible protein stem cell antigen-1 (Sca-1). Among CD8+ T cells, naïve cells predominantly circulate from the gut to the periphery, and those that had migrated from the mesenteric lymph nodes (mLNs) to the periphery had significantly higher expression of Sca-1. The gut-educated Sca-1+ naïve subset is endowed with enhanced mitochondrial activity and antitumor effector potential. The heterogeneity and functional versatility of the systemic naïve CD8+ T cell compartment was revealed by single-cell analysis and functional assays of CD8+ T cell subpopulations. These results indicate one of the potential mechanisms through which microbial dysbiosis regulates antitumor immunity.

[Synergistic Effect of Immune Checkpoint Blockade Inhibition Therapy by Modulating T Cell Metabolism].

Immune checkpoint blockade inhibition is a therapy which interferes with inhibitory signals placed upon immune cells, thereby eliciting anti-tumor responses. Although programmed death-1(PD-1)blockade therapy has been shown to be highly effective in clinical use, certain population of patients still fail to respond. Therefore, it is critical to determine how therapeutic efficacy of checkpoint inhibition can be enhanced. Recently, it has been shown that intracellular metabolism plays an important role in T cell differentiation and function. Because an effective tumor response relies on the differentiation of tumor-responsive effector cytotoxic T lymphocytes(CTLs), understanding such mechanisms will be essential for developing an improved therapeutic approach. Experiments on tumor-bearing mice have displayed strong anti-tumor responses upon combination therapy ofPD -1 blockade and enhanced mitochondrial metabolism, through increased production ofreactive oxygen species(ROS); upregulation ofmechanistic target ofrapamycin(mTOR)and AMP-activated protein kinase(AMPK); and upregulation ofperoxisome proliferator-activated receptor gamma coactivator 1-alpha(PGC-1a). In addition, the use of bezafibrate, a peroxisome proliferator-activated receptor(PPAR)agonist, in combination with PD-1 blockade resulted in improved effector function in CTLs. In this review, we will explore the mechanism behind T cell metabolism under the context ofcheckpoint blockade therapy, as well as how modulating T cell metabolism yields synergistic anti-tumor effects in combination with PD-1 blockade therapy.

PD-L1 is induced on the hepatocyte surface via CKLF-like MARVEL transmembrane domain-containing protein 6 up-regulation by the anti-HBV drug Entecavir.

Chronic hepatitis B is now controllable when treated with nucleoside reverse transcriptase inhibitors (NRTIs), which inhibit hepatitis B virus (HBV) replication. However, once the NRTIs are discontinued, most patients relapse, necessitating lifelong NRTIs treatment. HBV infection relapse is assumed to be caused by the persistent existence of covalently closed circular DNA (cccDNA) in the nuclei of infected hepatocytes. The mechanism by which cccDNA-positive hepatocytes escape immune surveillance during NRTIs treatment remains elusive. Entecavir (ETV), a commonly used NRTI, post-transcriptionally up-regulates programmed cell death-ligand 1 (PD-L1), an immune checkpoint molecule, on the cell surface of hepatocytes regardless of HBV infection. Up-regulation by ETV depends on up-regulation of CKLF-like MARVEL transmembrane domain-containing 6, a newly identified potent regulator of PD-L1 expression on the cell surface. ETV-treated hepatic cells suppressed the activity of primary CD3 T cells and programmed cell death protein-1 (PD-1)-over-expressed Jurkat cells. Finally, ETV induces PD-L1 in primary hepatocytes infected by HBV. These results provide evidence that ETV considerably up-regulates PD-L1 on the cell surface of infected hepatocytes, which may be one of the mechanisms by which infected hepatocytes subvert immune surveillance.

Tumors attenuating the mitochondrial activity in T cells escape from PD-1 blockade therapy.

PD-1 blockade therapy has revolutionized cancer treatments. However, a substantial population of patients is unresponsive. To rescue unresponsive patients, the mechanism of unresponsiveness to PD-1 blockade therapy must be elucidated. Using a 'bilateral tumor model' where responsive and unresponsive tumors were inoculated into different sides of the mouse belly, we demonstrated that unresponsive tumors can be categorized into two groups: with and without systemic immunosuppressive property (SIP). The SIP-positive tumors released uncharacterized, non-proteinaceous small molecules that inhibited mitochondrial activation and T cell proliferation. By contrast, the SIP-negative B16 tumor escaped from immunity by losing MHC class I expression. Unresponsiveness of SIP-positive tumors was partially overcome by improving the mitochondrial function with a mitochondrial activator; this was not successful for B16, which employs immune ignorance. These results demonstrated that the 'bilateral tumor model' was useful for stratifying tumors to investigate the mechanism of unresponsiveness and develop a strategy for proper combination therapy.

Immunotherapy is a fast-emerging treatment area that turns the body's own immune system against cancer. One powerful group of treatments are the PD-1 blockers. PD-1 is an inducible protein that is sometimes found on healthy immune cells called T cells and normally acts to stop T cells mistakenly attacking healthy cells. However, it can also prevent T cells attacking cancer. This happens when cancer cells make a protein called PD-1 ligand, which interacts with PD-1 to switch off nearby T cells. Antibodies that block PD-1 or PD-1 ligand can reactivate T cells, allowing them to destroy the cancer, but this PD-1 blocking therapy currently works in less than half of all patients who receive the treatment. To mount a successful defense against cancer, a T cell needs to be able to perform two key tasks: recognize cancer cells and prepare to attack. T cells are alerted to the presence of the disease by MHC class I proteins on the surface of cancer cells holding up small fragments of molecules that are tell-tale sign that the cell is cancerous. To prepare to attack, a T cell depends on its mitochondria ­ the powerhouses of the cell ­ to send a cascade of signals inside the T cell that help it to activate and multiply. It is possible that cancer cells escape PD-1 blocking treatments by interfering with either one of these two tasks. They may either hide their MHC class I proteins to become invisible to passing T cells ­ a phenomenon known as "local immune ignorance"; or they may release long-range molecules to stop T cells preparing to attack ­ "systemic immune suppression". To explore these options further, Kumar, Chamoto et al. developed a new tumor model in mice. Each mouse had two tumors, one that responded to PD-1 blocking treatment and one that did not. The idea was that, if the unresponsive tumor was simply hiding from passing T cells, its presence should not affect the other tumor. But, if it was releasing molecules to block T-cell activation, the other tumor could become unresponsive to PD-1 blocking treatment too. Kumar, Chamoto et al. examined different types of unresponsive tumor in this model system and found that they fell into two groups. The first group simply hid themselves from nearby T cells, while the second group released molecules to dampen all T cells. The identity of these molecules is unknown, but further experiments suggested that they likely work by blocking the mitochondria in T cells. In mice with these tumors, drugs that boosted mitochondria activity made anti-PD-1 treatment more effective. If the findings in this mouse model parallel those in humans, it could open a new research area for immunotherapy. The next step is for researchers need to identify the molecule responsible for systemic immune suppression. This could help to make PD-1 blocking treatments more effective in people who do not currently respond.

PD-L1/L2 protein levels rapidly increase on monocytes via trogocytosis from tumor cells in classical Hodgkin lymphoma.

In classical Hodgkin lymphoma (cHL)-characterized by the presence of Hodgkin and Reed-Sternberg (HRS) cells-tumor-associated macrophages (TAMs) play a pivotal role in tumor formation. However, the significance of direct contact between HRS cells and TAMs has not been elucidated. HRS cells and TAMs are known to express PD-L1, which leads to PD-1+ CD4+ T cell exhaustion in cHL. Here, we found that PD-L1/L2 expression was elevated in monocytes co-cultured with HRS cells within 1 h, but not in monocytes cultured with supernatants of HRS cells. Immunofluorescence analysis of PD-L1/L2 revealed that their upregulation resulted in membrane transfer called "trogocytosis" from HRS cells to monocytes. PD-L1/L2 upregulation was not observed in monocytes co-cultured with PD-L1/L2-deficient HRS cells, validating the hypothesis that there is a direct transfer of PD-L1/L2 from HRS cells to monocytes. In the patients, both ligands (PD-L1/L2) were upregulated in TAMs in contact with HRS cells, but not in TAMs distant from HRS cells, suggesting that trogocytosis occurs in cHL patients. Taken together, trogocytosis may be one of the mechanisms that induces rapid upregulation of PD-L1/L2 in monocytes to evade antitumor immunity through the suppression of T cells as mediated by MHC antigen presentation.

Current issues and perspectives in PD-1 blockade cancer immunotherapy.

Programmed cell death 1 (PD-1) signal receptor blockade has revolutionized the field of cancer therapy. Despite their considerable potential for treating certain cancers, drugs targeting PD-1 still present two main drawbacks: the substantial number of unresponsive patients and/or patients showing recurrences, and side effects associated with the autoimmune response. These drawbacks highlight the need for further investigation of the mechanisms underlying the therapeutic effects, as well as the need to develop novel biomarkers to predict the lack of treatment response and to monitor potential adverse events. Combination therapy is a promising approach to improve the efficacy of PD-1 blockade therapy. Considering the increasing number of patients with cancer worldwide, solving the above issues is central to the field of cancer immunotherapy. In this review, we discuss these issues and clinical perspectives associated with PD-1 blockade cancer immunotherapy.