B7-DC-Ig enhances vaccine effect by a novel mechanism dependent on PD-1 expression level on T cell subsets

Generating immunogenomic data-guided virtual patients using a QSP model to predict response of advanced NSCLC to PD-L1 inhibition

Generating realistic virtual patients from a limited amount of patient data is one of the major challenges for quantitative systems pharmacology modeling in immuno-oncology. Quantitative systems pharmacology (QSP) is a mathematical modeling methodology that integrates mechanistic knowledge of biological systems to investigate dynamics in a whole system during disease progression and drug treatment. In the present analysis, we parameterized our previously published QSP model of the cancer-immunity cycle to non-small cell lung cancer (NSCLC) and generated a virtual patient cohort to predict clinical response to PD-L1 inhibition in NSCLC. The virtual patient generation was guided by immunogenomic data from iAtlas portal and population pharmacokinetic data of durvalumab, a PD-L1 inhibitor. With virtual patients generated following the immunogenomic data distribution, our model predicted a response rate of 18.6% (95% bootstrap confidence interval: 13.3-24.2%) and identified CD8/Treg ratio as a potential predictive biomarker in addition to PD-L1 expression and tumor mutational burden. We demonstrated that omics data served as a reliable resource for virtual patient generation techniques in immuno-oncology using QSP models.

Generating immunogenomic data-guided virtual patients using a QSP model to predict response of advanced NSCLC to PD-L1 inhibition

Generating realistic virtual patients from a limited amount of patient data is one of the major challenges for quantitative systems pharmacology modeling in immuno-oncology. Quantitative systems pharmacology (QSP) is a mathematical modeling methodology that integrates mechanistic knowledge of biological systems to investigate dynamics in a whole system during disease progression and drug treatment. In the present analysis, we parameterized our previously published QSP model of the cancer-immunity cycle to non-small cell lung cancer (NSCLC) and generated a virtual patient cohort to predict clinical response to PD-L1 inhibition in NSCLC. The virtual patient generation was guided by immunogenomic data from iAtlas portal and population pharmacokinetic data of durvalumab, a PD-L1 inhibitor. With virtual patients generated following the immunogenomic data distribution, our model predicted a response rate of 18.6% (95% bootstrap confidence interval: 13.3-24.2%) and identified CD8/Treg ratio as a potential predictive biomarker in addition to PD-L1 expression and tumor mutational burden. We demonstrated that omics data served as a reliable resource for virtual patient generation techniques in immuno-oncology using QSP models.

Laparoscopic-Assisted Colorectal Resection Can Reduce the Inhibition of Immune Function Compared with Conventional Open Surgery: A Retrospective Clinical Study

Background: Immune function is an important indicator for assessing postoperative recovery and long-term survival in patients with malignancy, and laparoscopic surgery is thought to have a less suppressive effect on the immune response than open surgery. This study aimed to investigate this effect in a retrospective clinical study. Methods: In this retrospective clinical study, we enrolled 63 patients with colorectal cancer in the Department of General Surgery of the First Affiliated Hospital of Soochow University and assessed the changes in their postoperative immune function by measuring CD3+T, CD4+T, CD8+T lymphocytes, and CD4+/CD8+ ratio. Results: Compared with open surgery, laparoscopic colorectal surgery was effective in improving the postoperative decline in immune function. We determined that the number of CD4+, CD8+T lymphocytes, and the CD4+/CD8+ ratio was not significantly reduced in the laparoscopic group. Conclusion: Laparoscopic-assisted colorectal resection can reduce the inhibition of immune functions compared with conventional open surgery.

Dynamics of tumor-associated macrophages in a quantitative systems pharmacology model of immunotherapy in triple-negative breast cancer

Quantitative systems pharmacology (QSP) modeling is an emerging mechanistic computational approach that couples drug pharmacokinetics/pharmacodynamics and the course of disease progression. It has begun to play important roles in drug development for complex diseases such as cancer, including triple-negative breast cancer (TNBC). The combination of the anti-PD-L1 antibody atezolizumab and nab-paclitaxel has shown clinical activity in advanced TNBC with PD-L1-positive tumor-infiltrating immune cells. As tumor-associated macrophages (TAMs) serve as major contributors to the immuno-suppressive tumor microenvironment, we incorporated the dynamics of TAMs into our previously published QSP model to investigate their impact on cancer treatment. We show that through proper calibration, the model captures the macrophage heterogeneity in the tumor microenvironment while maintaining its predictive power of the trial results at the population level. Despite its high mechanistic complexity, the modularized QSP platform can be readily reproduced, expanded for new species of interest, and applied in clinical trial simulation.

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A mechanistic model of quantitative systems pharmacology in immuno-oncology

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Dynamics of tumor-associated macrophages are integrated into our previous work

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Conducting in silico clinical trials to predict clinical response to cancer therapy

L2pB1 Cells Contribute to Tumor Growth Inhibition

Natural IgM (nIgM) antibodies play critical roles in cancer immunosurveillance. However, the role of B-1 B cells, the lymphocytes that produce nIgM, remains to be elucidated. L2pB1 cells, a subpopulation of B-1 B cells, have a unique poly-self-reactive nIgM repertoire and are capable of phagocytosis, potent antigen presentation, and immunomodulation. Using an inducible knock-in and knockout mouse model, we investigated the effect of the loss of L2pB1 cells in a B16F10 melanoma model. Our results show active tumor infiltration of L2pB1 cells in wild type mice, and conversely, depletion of L2pB1 cells results in larger tumor mass and increased angiogenesis. In vitro analysis revealed that L2pB1 cells contribute to the growth inhibition of melanoma cells in both 2D cell culture and 3D tumor spheroids. Similar effects were observed in an MC38 murine colon cancer model. Moreover, our data suggest that one of the ways that L2pB1 cells can induce tumor cell death is via lipoptosis. Lastly, we tested whether L2pB1 cell-derived monoclonal nIgM antibodies can specifically recognize tumor spheroids. Nine of the 28 nIgM-secreting L2pB1 clones demonstrated specific binding to tumor spheroids but did not bind control murine embryonic fibroblasts. Our study provides evidence that L2pB1 cells contribute to cancer immunity through their unique nIgM repertoire, tumor recognition, and lipoptosis. Taken together, because of their ability to recognize common features of tumors that are independent of genetic mutations, L2pB1 cells and their nIgM could be potential candidates for cancer treatment that can overcome tumor heterogeneity-associated drug resistance.

Programmed cell death ligand-1: A dynamic immune checkpoint in cancer therapy

Antibody-based immunotherapies play a pivotal role in cancer research with efficient achievements in tumor suppression. Tumor survival is assisted by modulation of immune checkpoints to create imbalances between immune cells and cancer cell's environment. The modulation results in T-cell signal inhibition ultimately inert its proliferation and activation against various tumor cells. PD-L1, a 40 kDa transmembrane protein of B7 family, binds with PD-1 on the membrane of T cells which results in inhibition of T-cell proliferation and activation. PD-L1/PD-1 pathway has generated novel target sites for antibodies that can block PD-L1/PD-1 interactions. The blockage results in T-cell proliferation and tumor cell suppression. The PD-L1 immune checkpoint strategies' development, expression and regulations, signal inhibitions, and developmental stages of PD-L1/PD-1 antibodies are briefly discussed here in this review. All this information will provide a base for new therapeutic development against PD-L1 and PD-1 immune checkpoint interactions and will make available promising treatment options.

T cells with high PD-1 expression are associated with lower HIV-specific immune responses despite long-term antiretroviral therapy

OBJECTIVE

We evaluated frequencies of T cells with high PD-1 expression (PD-1) before and after long-term effective antiretroviral therapy (ART), and determined if frequencies on-ART correlated positively with measures of HIV persistence and negatively with HIV-specific responses.

METHODS

We enrolled individuals who started ART during chronic infection and had durable suppression of viremia for at least 4 years (N = 99). We assessed PD-1 T-cell frequencies at timepoints pre-ART and on-ART using flow cytometry, and evaluated how frequencies on-ART are associated with measures of HIV persistence, HIV-specific immune responses, and immune activation levels.

RESULTS

Pre-ART, PD-1 CD4 T cells correlated positively with viremia and negatively with CD4 T-cell count. At year 1 on-ART, %PD-1 CD4 T cells decreased but then remained stable at 4 and 6-15 years on-ART, whereas %PD-1 CD8 T cells on-ART remained similar to pre-ART. PD-1 CD4 T cells correlated positively with HIV DNA pre-ART and on-ART, and with CD4 T-cell activation on-ART. PD-1 CD4 T cells negatively correlated with HIV Gag-specific and Env-specific T-cell responses but not with CMV-specific or EBV-specific responses. PD-1 CD8 T cells trended towards a negative correlation with responses to Gag and Env, but not to CMV and EBV.

CONCLUSION

PD-1 T cells persist in blood despite prolonged suppression on ART, correlate with HIV DNA levels, and are associated with lower HIV-specific T-cell responses but not CMV-specific or EBV-specific responses, suggesting that these cells are HIV-specific. The findings support evaluating PD-1 blockade strategies for their effect on HIV persistence and HIV-specific immunity.

PD-1 blockade in subprimed CD8 cells induces dysfunctional PD-1+CD38hi cells and anti-PD-1 resistance

Understanding resistance to antibody to programmed cell death protein 1 (PD-1; anti-PD-1) is crucial for the development of reversal strategies. In anti-PD-1-resistant models, simultaneous anti-PD-1 and vaccine therapy reversed resistance, while PD-1 blockade before antigen priming abolished therapeutic outcomes. This was due to induction of dysfunctional PD-1⁺CD38^hi CD8⁺ cells by PD-1 blockade in suboptimally primed CD8 cell conditions induced by tumors. This results in erroneous T cell receptor signaling and unresponsiveness to antigenic restimulation. On the other hand, PD-1 blockade of optimally primed CD8 cells prevented the induction of dysfunctional CD8 cells, reversing resistance. Depleting PD-1⁺CD38^hi CD8⁺ cells enhanced therapeutic outcomes. Furthermore, non-responding patients showed more PD-1⁺CD38⁺CD8⁺ cells in tumor and blood than responders. In conclusion, the status of CD8⁺ T cell priming is a major contributor to anti-PD-1 therapeutic resistance. PD-1 blockade in unprimed or suboptimally primed CD8 cells induces resistance through the induction of PD-1⁺CD38^hi CD8⁺ cells that is reversed by optimal priming. PD-1⁺CD38^hi CD8⁺ cells serve as a predictive and therapeutic biomarker for anti-PD-1 treatment. Sequencing of anti-PD-1 and vaccine is crucial for successful therapy.

Hepatic expression of programmed death-1 (PD-1) and its ligand, PD-L1, in children with autoimmune hepatitis: relation to treatment response

AIM OF THE STUDY

Autoimmune hepatitis (AIH) is characterized histologically by aggressive inflammation with interface hepatitis and prominent lymphoplasmacytic infiltration. Programmed death-1 (PD-1) is expressed on activated lymphocytes. Engagement of PD-1 by its ligand PD-L1 leads to cell apoptosis and death. We aimed to evaluate the immunohistochemical expression of PD-1 and PD-L1 in children with AIH, and its relation to treatment outcome.

MATERIAL AND METHODS

Pre-treatment liver biopsies of 31 children with AIH were compared to 30 children with chronic hepatitis C virus (HCV) infection as a control group. PD-1 was evaluated in lymphocytes, while PD-L1 was evaluated in lymphocytes, hepatocytes, biliary epithelial cells, sinusoidal endothelial cells and Kupffer cells. All AIH patients received the standard treatment.

RESULTS

The mean PD-1 was significantly higher in AIH than HCV patients (29.19 ±18.5% vs. 15.2 ±10.1%; p = 0.002) while there was no statistically significant difference as regards PD-L1 on lymphocytes (p = 0.853). Neither PD-1 nor PD-L1 correlated with either liver fibrosis or the inflammatory activity (p > 0.05 for all). PD-1/PD-L1 ratio was significantly higher in AIH compared to HCV patients and in non-responder AIH patients compared to responders (46.9 vs. 6.58). PD-1 expression was comparable in both responders and non-responders (p = 0.813), while PD-L1 was significantly upregulated in responders (4.17 ±3.15% vs. 0.63 ±1.3%; p = 0.046). PD-L1 expression on hepatocytes, biliary epithelial cells, sinusoidal endothelial cells and Kupffer cells was comparable in AIH and HCV groups.

CONCLUSIONS

PD-1/PD-L1 ratio, which reflects immune aggression, was significantly higher in AIH compared to HCV patients and in non-responder AIH patients compared to responders.

Immune checkpoint blockade and its combination therapy with small-molecule inhibitors for cancer treatment

Initially understood for its physiological maintenance of self-tolerance, the immune checkpoint molecule has recently been recognized as a promising anti-cancer target. There has been considerable interest in the biology and the action mechanism of the immune checkpoint therapy, and their incorporation with other therapeutic regimens. Recently the small-molecule inhibitor (SMI) has been identified as an attractive combination partner for immune checkpoint inhibitors (ICIs) and is becoming a novel direction for the field of combination drug design. In this review, we provide a systematic discussion of the biology and function of major immune checkpoint molecules, and their interactions with corresponding targeting agents. With both preclinical studies and clinical trials, we especially highlight the ICI + SMI combination, with its recent advances as well as its application challenges.

Posttranscriptional Control of PD-L1 Expression by 17β-Estradiol via PI3K/Akt Signaling Pathway in ERα-Positive Cancer Cell Lines

OBJECTIVE

Estrogen is a well-known oncogenic driver in endometrial (ECs) and breast cancers (BCs). Programmed cell death protein 1 (PD-1) and its ligands PD-1 Ligand 1 (PD-L1) and PD-L2 have been shown to mediate immune evasion of the tumor cells. The purpose of the present study was to assess the effects of estrogen on PD-L1 and PD-L2 expression in EC and BC cell lines.

METHODS

17β-Estradiol (E2)-induced expression of PD-L1 and PD-L2 and possible signaling pathway were investigated in EC and BC cells. Coculture of T cells and cancer cells with E2 stimulation was performed to assess the functions of T cells.

RESULTS

We found that E2 increased expression of PD-L1, but not PD-L2, protein via activation of phosphoinositide 3-kinase (PI3K)/Akt pathway in Ishikawa and Michigan Cancer Foundation-7 (MCF-7) cells. Phosphoinositide 3-kinase and Akt inhibitors could block E2's effects. 17β-Estradiol did not increase PD-L1 mRNA transcription, but stabilized PD-L1 mRNA. 17β-Estradiol's effects were only observed in estrogen receptor α (ERα)-positive Ishikawa and MCF-7 cells, but not in ERα-negative MDA-MB-231 cells. Coculture of Ishikawa or MCF-7 cells with T cells inhibited expression of interferon-γ and interleukin-2 and increased BCL-2-interacting mediator of cell death expression in the presence of E2.

CONCLUSIONS

This study provides the first evidence that estrogen upregulates PD-L1 protein expression in ERα-positive EC and BC cells to suppress immune functions of T cells in the tumor microenvironment, demonstrating a new mechanism of how estrogen drives cancer progression.

Antigen-Specific Antitumor Responses Induced by OX40 Agonist Are Enhanced by the IDO Inhibitor Indoximod

Although an immune response to tumors may be generated using vaccines, so far, this approach has only shown minimal clinical success. This is attributed to the tendency of cancer to escape immune surveillance via multiple immune suppressive mechanisms. Successful cancer immunotherapy requires targeting these inhibitory mechanisms along with enhancement of antigen-specific immune responses to promote sustained tumor-specific immunity. Here, we evaluated the effect of indoximod, an inhibitor of the immunosuppressive indoleamine-(2,3)-dioxygenase (IDO) pathway, on antitumor efficacy of anti-OX40 agonist in the context of vaccine in the IDO^- TC-1 tumor model. We demonstrate that although the addition of anti-OX40 to the vaccine moderately enhances therapeutic efficacy, incorporation of indoximod into this treatment leads to enhanced tumor regression and cure of established tumors in 60% of treated mice. We show that the mechanisms by which the IDO inhibitor leads to this therapeutic potency include (i) an increment of vaccine-induced tumor-infiltrating effector T cells that is facilitated by anti-OX40 and (ii) a decrease of IDO enzyme activity produced by nontumor cells within the tumor microenvironment that results in enhancement of the specificity and the functionality of vaccine-induced effector T cells. Our findings suggest a translatable strategy to enhance the overall efficacy of cancer immunotherapy. Cancer Immunol Res; 6(2); 201-8. ©2018 AACR.

Recurrent glioma clinical trial, CheckMate-143: the game is not over yet

Glioblastoma (GBM) is the most common, and aggressive, primary brain tumor in adults. With a median patient survival of less than two years, GBM represents one of the biggest therapeutic challenges of the modern era. Even with the best available treatment, recurrence rates are nearly 100% and therapeutic options at the time of relapse are extremely limited. Nivolumab, an anti-programmed cell death-1 (PD-1) monoclonal antibody, has provided significant clinical benefits in the treatment of various advanced cancers and represented a promising therapy for primary and recurrent GBM. CheckMate 143 (NCT 02017717) was the first large randomized clinical trial of PD pathway inhibition in the setting of GBM, including a comparison of nivolumab and the anti-VEGF antibody, bevacizumab, in the treatment of recurrent disease. However, preliminary results, recently announced in a WFNOS 2017 abstract, demonstrated a failure of nivolumab to prolong overall survival of patients with recurrent GBM, and this arm of the trial was prematurely closed. In this review, we discuss the basic concepts underlying the rational to target PD pathway in GBM, address implications of using immune checkpoint inhibitors in central nervous system malignancies, provide a rationale for possible reasons contributing to the failure of nivolumab to prolong survival in patients with recurrent disease, and analyze the future role of immune checkpoint inhibitors in the treatment of GBM.

Prokaryotic expression of the extracellular domain of porcine programmed death 1 (PD-1) and its ligand PD-L1 and identification of the binding with peripheral blood mononuclear cells in vitro

Programmed cell death protein 1 (PD-1), a costimulatory molecule of the CD28 family, has 2 ligands, PD-L1 and PD-L2. Our previous studies showed that the expression of PD-1 and PD-L1 is up-regulated during viral infection in pigs. Extensive studies have shown that blockade of the PD-1/PD-L1 pathways by anti-PD-L1 antibody or soluble PD-1 restores exhausted T-cells in humans and mice. In the present study the extracellular domains of PD-1 and PD-L1 were used to evaluate the binding of PD-1 and PD-L1 with peripheral blood mononuclear cells (PBMCs). We amplified the cDNA encoding the extracellular domains of PD-1 and PD-L1 to construct recombinant expression plasmids and obtain soluble recombinant proteins, which were then labeled with fluorescein isothiocyanate (FITC). The His-ExPD-1 and His-ExPD-L1 recombinant proteins were expressed in the form of inclusion bodies with a relative molecular weight of 33.0 and 45.0 kDa, respectively. We then prepared polyclonal antibodies against the proteins with a multi-antiserum titer of 1:102 400. Binding of the proteins with PBMCs was evaluated by flow cytometry. The fluorescence signals of His-ExPD-1-FITC and His-ExPD-L1-FITC were greater than those for the FITC control. These results suggest that the soluble recombinant proteins may be used to prepare monoclonal antibodies to block the PD-1/PD-L1 pathway.

T cell costimulatory receptor CD28 is a primary target for PD-1-mediated inhibition

Programmed cell death-1 (PD-1) is a coinhibitory receptor that suppresses T cell activation and is an important cancer immunotherapy target. Upon activation by its ligand PD-L1, PD-1 is thought to suppress signaling through the T cell receptor (TCR). By titrating PD-1 signaling in a biochemical reconstitution system, we demonstrate that the co-receptor CD28 is strongly preferred over the TCR as a target for dephosphorylation by PD-1-recruited Shp2 phosphatase. We also show that CD28, but not the TCR, is preferentially dephosphorylated in response to PD-1 activation by PD-L1 in an intact cell system. These results reveal that PD-1 suppresses T cell function primarily by inactivating CD28 signaling, suggesting that costimulatory pathways play key roles in regulating effector T cell function and responses to anti-PD-L1/PD-1 therapy.

PD-L1, PD-L2 and PD-1 expression in metastatic melanoma: Correlation with tumor-infiltrating immune cells and clinical outcome

Therapeutic blockade of PD-1/PD-L1 can have dramatic therapeutic benefit in some patients; however, the prognostic associations of PD-1 and its ligands, in the absence of therapeutic blockade have not been definitively addressed. In particular, associations of PD-L2 with immune infiltrates and with outcome have yet to be explored. We hypothesized that surface expression of both PD-L1 and PD-L2 by melanoma cells would be associated with immune cell infiltration and with overall patient survival, independent of checkpoint blockade therapy. We also characterized the heterogeneity of their distribution within a tumor and within tumors of the same patient. Tissue microarrays of metastatic melanoma samples from 147 patients were quantified for CD8⁺, CD45, CD4⁺, CD3, CD163, CD20, CD138, FoxP3, PD-1, PD-L1 and PD-L2 markers by immunohistochemistry. Relationships between the proportions of PD-L1 and PD-L2 expressing tumor cells with the immune cell count, distribution (immunotype) and patient survival were studied. Expressions of both PD-L1 and PD-L2 correlated significantly with increasing densities of immune cells in the tumor specimens and with immunotype. Positive PD-L2 expression was associated with improved overall survival and the simultaneous positive expression of both PD-1 ligands showed a higher association with survival. Significant heterogeneity of PD-L1 and PD-L2 expressions within tumors were observed, however, they were less pronounced with PD-L2. In conclusion, both are markers of immune infiltration and PD-L2, alone or in combination with PD-L1, is a marker for prognosis in metastatic melanoma patients. Larger tumor samples yield more reliable assessments of PD-L1/L2 expression.

PD-L1-specific T cells

Recently, there has been an increased focus on the immune checkpoint protein PD-1 and its ligand PD-L1 due to the discovery that blocking the PD-1/PD-L1 pathway with monoclonal antibodies elicits striking clinical results in many different malignancies. We have described naturally occurring PD-L1-specific T cells that recognize both PD-L1-expressing immune cells and malignant cells. Thus, PD-L1-specific T cells have the ability to modulate adaptive immune reactions by reacting to regulatory cells. Thus, utilization of PD-L1-derived T cell epitopes may represent an attractive vaccination strategy for targeting the tumor microenvironment and for boosting the clinical effects of additional anticancer immunotherapy. This review summarizes present information about PD-L1 as a T cell antigen, depicts the initial findings about the function of PD-L1-specific T cells in the adjustment of immune responses, and discusses future opportunities.

Targeting the programmed death-1/programmed death-ligand 1 axis in lymphoma

PURPOSE OF REVIEW

The development of 'immune checkpoint inhibitors' or drugs targeting the programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) axis has been a stunning success of cancer immunotherapy. This review provides a timely overview of the biology and function of the PD-1 pathway and discusses the rationale for therapeutic inhibition of this pathway in lymphoma.

RECENT FINDINGS

Recent studies have evaluated the prevalence and prognostic implications of PD-1, PD-L1/2 expression in various lymphoma subtypes. We present an overview of the clinical trials evaluating pidilizumab, nivolumab, and pembrolizumab in patients with lymphoid malignancies, and highlight some of the more promising agents in this class, currently in development. Finally, we discuss biomarkers that may predict response to therapy in patients with lymphoma across these clinical trials.

SUMMARY

A plethora of clinical trials are in progress testing immune checkpoint inhibitors in many subtypes of lymphoma, which will define their role both as a monotherapy and in combination with other biologic agents.

Old-School Chemotherapy in Immunotherapeutic Combination in Cancer, A Low-cost Drug Repurposed

Cancer immunotherapy has proven to be a potent treatment modality. Although often successful in generating antitumor immune responses, cancer immunotherapy is frequently hindered by tumor immune-escape mechanisms. Among immunosuppressive strategies within the tumor microenvironment, suppressive immune regulatory cells play a key role in promoting tumor progression through inhibiting the effector arm of the immune response. Targeting these suppressive cells can greatly enhance antitumor immune therapies, hence augmenting a highly effective therapeutic antitumor response. Several approaches are being tested to enhance the effector arm of the immune system while simultaneously inhibiting the suppressor arm. Some of these approaches are none other than traditional drugs repurposed as immune modulators. Cyclophosphamide, an old-school chemotherapeutic agent used across a wide range of malignancies, was found to be a potent immune modulator that targets suppressive regulatory immune cells within the tumor microenvironment while enhancing effector cells. Preclinical and clinical findings have confirmed the ability of low doses of cyclophosphamide to selectively deplete regulatory T cells while enhancing effector and memory cytotoxic T cells within the tumor microenvironment. These immune effects translate to suppressed tumor growth and enhanced survival, evidence of antitumor therapeutic efficacy. This article discusses the reincarnation of cyclophosphamide as an immune modulator that augments novel immunotherapeutic approaches. Cancer Immunol Res; 4(5); 377-82. ©2016 AACR.

ADAP and SKAP55 deficiency suppresses PD-1 expression in CD8+ cytotoxic T lymphocytes for enhanced anti-tumor immunotherapy

PD-1 negatively regulates CD8(+) cytotoxic T lymphocytes (CTL) cytotoxicity and anti-tumor immunity. However, it is not fully understood how PD-1 expression on CD8(+) CTL is regulated during anti-tumor immunotherapy. In this study, we have identified that the ADAP-SKAP55 signaling module reduced CD8(+) CTL cytotoxicity and enhanced PD-1 expression in a Fyn-, Ca(2+)-, and NFATc1-dependent manner. In DC vaccine-based tumor prevention and therapeutic models, knockout of SKAP55 or ADAP showed a heightened protection from tumor formation or metastases in mice and reduced PD-1 expression in CD8(+) effector cells. Interestingly, CTLA-4 levels and the percentages of tumor infiltrating CD4(+)Foxp3(+) Tregs remained unchanged. Furthermore, adoptive transfer of SKAP55-deficient or ADAP-deficient CD8(+) CTLs significantly blocked tumor growth and increased anti-tumor immunity. Pretreatment of wild-type CD8(+) CTLs with the NFATc1 inhibitor CsA could also downregulate PD-1 expression and enhance anti-tumor therapeutic efficacy. Together, we propose that targeting the unrecognized ADAP-SKAP55-NFATc1-PD-1 pathway might increase efficacy of anti-tumor immunotherapy.

Future perspectives in melanoma research: meeting report from the "Melanoma Bridge": Napoli, December 3rd-6th 2014

The fourth "Melanoma Bridge Meeting" took place in Naples, December 3-6th, 2014. The four topics discussed at this meeting were: Molecular and Immunological Advances, Combination Therapies, News in Immunotherapy, and Tumor Microenvironment and Biomarkers. Until recently systemic therapy for metastatic melanoma patients was ineffective, but recent advances in tumor biology and immunology have led to the development of new targeted and immunotherapeutic agents that prolong progression-free survival (PFS) and overall survival (OS). New therapies, such as mitogen-activated protein kinase (MAPK) pathway inhibitors as well as other signaling pathway inhibitors, are being tested in patients with metastatic melanoma either as monotherapy or in combination, and all have yielded promising results. These include inhibitors of receptor tyrosine kinases (BRAF, MEK, and VEGFR), the phosphatidylinositol 3 kinase (PI3K) pathway [PI3K, AKT, mammalian target of rapamycin (mTOR)], activators of apoptotic pathway, and the cell cycle inhibitors (CDK4/6). Various locoregional interventions including radiotherapy and surgery are still valid approaches in treatment of advanced melanoma that can be integrated with novel therapies. Intrinsic, adaptive and acquired resistance occur with targeted therapy such as BRAF inhibitors, where most responses are short-lived. Given that the reactivation of the MAPK pathway through several distinct mechanisms is responsible for the majority of acquired resistance, it is logical to combine BRAF inhibitors with inhibitors of targets downstream in the MAPK pathway. For example, combination of BRAF/MEK inhibitors (e.g., dabrafenib/trametinib) have been demonstrated to improve survival compared to monotherapy. Application of novel technologies such sequencing have proven useful as a tool for identification of MAPK pathway-alternative resistance mechanism and designing other combinatorial therapies such as those between BRAF and AKT inhibitors. Improved survival rates have also been observed with immune-targeted therapy for patients with metastatic melanoma. Immune-modulating antibodies came to the forefront with anti-CTLA-4, programmed cell death-1 (PD-1) and PD-1 ligand 1 (PD-L1) pathway blocking antibodies that result in durable responses in a subset of melanoma patients. Agents targeting other immune inhibitory (e.g., Tim-3) or immune stimulating (e.g., CD137) receptors and other approaches such as adoptive cell transfer demonstrate clinical benefit in patients with melanoma as well. These agents are being studied in combination with targeted therapies in attempt to produce longer-term responses than those more typically seen with targeted therapy. Other combinations with cytotoxic chemotherapy and inhibitors of angiogenesis are changing the evolving landscape of therapeutic options and are being evaluated to prevent or delay resistance and to further improve survival rates for this patient population. This meeting's specific focus was on advances in combination of targeted therapy and immunotherapy. Both combination targeted therapy approaches and different immunotherapies were discussed. Similarly to the previous meetings, the importance of biomarkers for clinical application as markers for diagnosis, prognosis and prediction of treatment response was an integral part of the meeting. The overall emphasis on biomarkers supports novel concepts toward integrating biomarkers into contemporary clinical management of patients with melanoma across the entire spectrum of disease stage. Translation of the knowledge gained from the biology of tumor microenvironment across different tumors represents a bridge to impact on prognosis and response to therapy in melanoma.

Human Cancer Immunotherapy with PD-1/PD-L1 Blockade

The ligation of programmed cell death-1 (PD-1) to its ligands PD-L1 and PD-L2 counteracts T-cell activation, which is critical in immune tolerance. The persistent high expression of PD-1 and PD-L1 are also observed on tumor-infiltrating lymphocytes and various tumor cells, maintaining the highly suppressive microenvironment in tumor sites and promoting tumor malignancies. The blockade of PD-1 axis with PD-L2 fusion protein or monoclonal antibodies against either PD-1 or PD-L1 has been clinically evaluated in various tumor types. This short review summarizes the progress of PD-1 axis blockade in clinical trials to evaluate its effectiveness in the antitumor immunotherapy.

Development of PD-1/PD-L1 Pathway in Tumor Immune Microenvironment and Treatment for Non-Small Cell Lung Cancer

Lung cancer is currently the leading cause of cancer-related death in worldwide, non-small cell lung cancer (NSCLC) accounts for about 85% of all lung cancers. Surgery, platinum-based chemotherapy, molecular targeted agents and radiotherapy are the main treatment of NSCLC. With the strategies of treatment constantly improving, the prognosis of NSCLC patients is not as good as before, new sort of treatments are needed to be exploited. Programmed death 1 (PD-1) and its ligand PD-L1 play a key role in tumor immune escape and the formation of tumor microenvironment, closely related with tumor generation and development. Blockading the PD-1/PD-L1 pathway could reverse the tumor microenvironment and enhance the endogenous antitumor immune responses. Utilizing the PD-1 and/or PD-L1 inhibitors has shown benefits in clinical trials of NSCLC. In this review, we discuss the basic principle of PD-1/PD-L1 pathway and its role in the tumorigenesis and development of NSCLC. The clinical development of PD-1/PD-L1 pathway inhibitors and the main problems in the present studies and the research direction in the future will also be discussed.

Programmed death-1 & its ligands: promising targets for cancer immunotherapy

Novel strategies for cancer treatment involving blockade of immune inhibitors have shown significant progress toward understanding the molecular mechanism of tumor immune evasion. The preclinical findings and clinical responses associated with programmed death-1 (PD-1) and PD-ligand pathway blockade seem promising, making these targets highly sought for cancer immunotherapy. In fact, the anti-PD-1 antibodies, pembrolizumab and nivolumab, were recently approved by the US FDA for the treatment of unresectable and metastatic melanoma resistant to anticytotoxic T-lymphocyte antigen-4 antibody (ipilimumab) and BRAF inhibitor. Here, we discuss strategies of combining PD-1/PD-ligand interaction inhibitors with other immune checkpoint modulators and standard-of-care therapy to break immune tolerance and induce a potent antitumor activity, which is currently a research area of key scientific pursuit.

Animal models for viral infection and cell exhaustion

PURPOSE OF REVIEW

Despite eliciting an early antiviral T cell response, HIV-specific T cells are unable to prevent disease progression, partly because of their loss of effector functions, known as T cell exhaustion. Restoring this T cell functionality represents a critical step for regaining immunological control of HIV-1 replication, and may be fundamental for the development of a functional cure for HIV. In this context, the use of animal models is invaluable for evaluating the efficacy and mechanisms of novel therapeutics aimed at reinvigorating T cell functions.

RECENT FINDINGS

Although nonhuman primates continue to be a mainstay for studying HIV pathogenesis and therapies, recent advances in humanized mouse models have improved their ability to recapitulate the features of cell exhaustion during HIV infection. Targeting coinhibitory receptors in HIV-infected and simian immunodeficiency virus (SIV)-infected animals has resulted in viral load reductions, presumably by reinvigorating the effector functions of T cells. Additionally, studies combining programmed death-1 (PD-1) blockade with suppressive antiretroviral therapy provide further support to the use of coinhibitory receptor blockades in restoring T cell function by delaying viral load rebound upon antiretroviral therapy interruption. Future in-vivo studies should build on recent in-vitro data, supporting the simultaneous targeting of multiple regulators of cell exhaustion.

SUMMARY

In this review, we describe the most recent advances in the use of animal models for the study of cell exhaustion following HIV/SIV infection. These findings suggest that the use of animal models is increasingly critical in translating immunotherapeutics into clinical practice.

[Immunotherapy in non-small cell lung cancer: inhibition of PD1/PDL1 pathway]

Despite recent advances in targeted therapy of non-small cell lung cancer (NSCLC), many patients do not benefit from these therapies. Inhibition of PD1/PDL1 is an interesting therapeutic target which restores the immune system against tumor cells. PD1 is located on lymphocytes and PDL1 on the antigen presenting cells. PD1 and PDL1 are co-inhibition molecules and their interaction results in immune tolerance against tumor cells. Anti-PD1 and anti-PDL1 antibodies have been developed to restore immune system in solid cancer including NSCLC. In phase I, studies assessing nivolumab, an anti-PD1 antibody, objective responses were observed in 13 to 18% of NSCLC patients failing previous treatment. The data obtained with anti-PDL1 antibodies is similar with objective responses ranging from 6 to 22%. The encouraging results of phase I/II studies must be confirmed in ongoing phase III studies. Anti-PD1 and anti-PDL1 antibodies exposed to new adverse events including auto-immune diseases whose support is not codified. Questions about treatment duration and criteria evaluation are not resolved. These treatments pave the way for immunomodulation in NSCLC treatment.

Human cancer immunotherapy with antibodies to the PD-1 and PD-L1 pathway

The programmed death 1 (PD-1) receptor and its ligands programmed death ligand 1 (PD-L1) and PD-L2, members of the CD28 and B7 families, play critical roles in T cell coinhibition and exhaustion. Overexpression of PD-L1 and PD-1 on tumor cells and tumor-infiltrating lymphocytes, respectively, correlates with poor disease outcome in some human cancers. Monoclonal antibodies (mAbs) blockading the PD-1/PD-L1 pathway have been developed for cancer immunotherapy via enhancing T cell functions. Clinical trials with mAbs to PD-1 and PD-L1 have shown impressive response rates in patients, particularly for melanoma, non-small-cell lung cancer (NSCLC), renal cell carcinoma (RCC), and bladder cancer. Further studies are needed to dissect the mechanisms of variable response rate, to identify biomarkers for clinical response, to develop small-molecule inhibitors, and to combine these treatments with other therapies.

Fusion protein of mutant B7-DC and Fc enhances the antitumor immune effect of GM-CSF-secreting whole-cell vaccine

B7-DC [also known as programmed death ligand 2 (PD-L2)] is a costimulatory molecule expressed predominantly on dendritic cells (DCs) and macrophages. In addition to its coinhibitory receptor, programmed death receptor 1 (PD-1), evidence suggests that B7-DC interacts with an unidentified costimulatory receptor on T cells. B7-DC mutants with selective binding capacity for the costimulatory receptor may be effective in stimulating antitumor immune responses, while avoiding the inhibitory effects of PD-1. In this study, we concomitantly administered a GM-CSF-secreting whole-cell vaccine together with a fusion protein of mutant B7-DC and Fc portion (mB7-DC-Fc), which binds selectively to the costimulatory receptor. This lead to an increased number of tumor antigen-specific cytotoxic T lymphocytes both in the spleen and at the tumor site and complete elimination of established tumors in vivo. In addition, mB7-DC-Fc increased IFN-γ and IL-2 production and decreased IL-4 and IL-10 production in vitro, indicating that mB7-DC-Fc tips the Th1/Th2 balance toward Th1 dominance, which is more favorable for antitumor immunity. Furthermore, mB7-DC-Fc decreased the PD-1(+) proportion of CD8(+) T cells in vitro and tumor-infiltrating CD8(+) T cells in vivo, suggesting that mB7-DC-Fc may maintain tumor-infiltrating CD8(+) T cells in a nonexhausted state. In conclusion, mB7-DC-Fc administration during the T-cell priming phase enhances antitumor effects of vaccine by generating more tumor antigen-specific cytotoxic T lymphocytes and leading to their accumulation at the tumor site. We suggest that this combination approach may be a promising strategy for antitumor immunotherapy.

Blocking tumor escape in hematologic malignancies: the anti-PD-1 strategy

Immunotherapy remains an important tool for treatment of hematologic malignancies. The Programmed Death-1 (PD-1) immune checkpoint pathway has emerged as a mechanism of tumor evasion from the anti-tumor immune response. The recent development of anti-PD-1 monoclonal antibodies has offered a targeted approach to cancer therapy. Several agents are in various stages of development and have shown clinical responses across a broad spectrum of both solid and hematologic malignancies. The use of anti-PD-1 therapy in hematologic malignancies is limited but has demonstrated clinical responses in relapsed/refractory disease following multiple lines of therapy. PD-1 blockade may reduce relapse rates for patients who fail to obtain a complete remission prior to autologous hematopoietic cell transplant. The role of the PD-1 pathway for tumor escape is reviewed. We explore the use of anti-PD-1 therapy in hematologic malignancies. The proposed mechanism of PD-1 blockade as a modulator of the innate and acquired immune response is considered. Finally, the challenges of anti-PD-1 therapy and the future direction of investigation in this area are reviewed.

Influence of PD-L1 cross-linking on cell death in PD-L1-expressing cell lines and bovine lymphocytes

Programmed death-ligand 1 (PD-L1) blockade is accepted as a novel strategy for the reactivation of exhausted T cells that express programmed death-1 (PD-1). However, the mechanism of PD-L1-mediated inhibitory signalling after PD-L1 cross-linking by anti-PD-L1 monoclonal antibody (mAb) or PD-1-immunogloblin fusion protein (PD-1-Ig) is still unknown, although it may induce cell death of PD-L1(+) cells required for regular immune reactions. In this study, PD-1-Ig or anti-PD-L1 mAb treatment was tested in cell lines that expressed PD-L1 and bovine lymphocytes to investigate whether the treatment induces immune reactivation or PD-L1-mediated cell death. PD-L1 cross-linking by PD-1-Ig or anti-PD-L1 mAb primarily increased the number of dead cells in PD-L1(high) cells, but not in PD-L1(low) cells; these cells were prepared from Cos-7 cells in which bovine PD-L1 expression was induced by transfection. The PD-L1-mediated cell death also occurred in Cos-7 and HeLa cells transfected with vectors only encoding the extracellular region of PD-L1. In bovine lymphocytes, the anti-PD-L1 mAb treatment up-regulated interferon-γ (IFN-γ) production, whereas PD-1-Ig treatment decreased this cytokine production and cell proliferation. The IFN-γ production in B-cell-depleted peripheral blood mononuclear cells was not reduced by PD-1-Ig treatment and the percentages of dead cells in PD-L1(+) B cells were increased by PD-1-Ig treatment, indicating that PD-1-Ig-induced immunosuppression in bovine lymphocytes could be caused by PD-L1-mediated B-cell death. This study provides novel information for the understanding of signalling through PD-L1.

Considerations for combined immune checkpoint modulation and radiation treatment

Recent advances indicate that new therapeutic strategies for the treatment of malignancies will be realized from combined radiation treatment and immune checkpoint modulation. Numerous biophysical properties must be considered for effective biologic development, including affinity, selectivity, oligomeric state and valency. High-resolution structural characterization contributes to our understanding of these properties and can lead to the realization of proteins with unique in vitro activities and novel in vivo therapeutic functions. In this article we focus on the importance of these factors for new potential biologics and consider these in the context of combination therapies with physical modalities, including radiation therapy. In particular, we examine the consequences of altered avidities and subset-specific ligand density on the rational modification of biological function in the immunoglobulin and tumor necrosis factor superfamilies and for new optimized combination therapies.

Identification and characterization of bovine programmed death-ligand 2

Previous reports from this group have indicated that the immunoinhibitory programmed death (PD)-1 receptor and its ligand, PD-L1, are involved in the mechanism of immune evasion of bovine chronic infection. However, no functional analysis of bovine PD-L2 in cattle has been reported. Thus, in this study, the molecular function of bovine PD-L2 was analyzed in vitro. Recombinant PD-L2 (PD-L2-Ig), which comprises an extracellular domain of bovine PD-L2 fused to the Fc portion of rabbit IgG1, was prepared based on the cloned cDNA sequence for bovine PD-L2. Bovine PD-L2-Ig bound to bovine PD-1-expressing cells and addition of soluble bovine PD-1-Ig clearly inhibited the binding of PD-L2-Ig to membrane PD-1 in a dose-dependent manner. Cell proliferation and IFN-γ production were significantly enhanced in the presence of PD-L2-Ig in peripheral blood mononuclear cells (PBMCs) from cattle. Moreover, PD-L2-Ig significantly enhanced IFN-γ production from virus envelope peptides-stimulated PBMCs derived from bovine leukemia virus-infected cattle. Interestingly, PD-L2-Ig-induced IFN-γ production was further enhanced by treatment with anti-bovine PD-1 antibody. These data suggest potential applications of bovine PD-L2-Ig as a therapy for bovine diseases.

RGMb is a novel binding partner for PD-L2 and its engagement with PD-L2 promotes respiratory tolerance

Interaction between the inhibitory molecule PD-L2 on dendritic cells and repulsive guidance molecule b (RGMb) on lung macrophages is required to establish respiratory tolerance.

We report that programmed death ligand 2 (PD-L2), a known ligand of PD-1, also binds to repulsive guidance molecule b (RGMb), which was originally identified in the nervous system as a co-receptor for bone morphogenetic proteins (BMPs). PD-L2 and BMP-2/4 bind to distinct sites on RGMb. Normal resting lung interstitial macrophages and alveolar epithelial cells express high levels of RGMb mRNA, whereas lung dendritic cells express PD-L2. Blockade of the RGMb–PD-L2 interaction markedly impaired the development of respiratory tolerance by interfering with the initial T cell expansion required for respiratory tolerance. Experiments with PD-L2–deficient mice showed that PD-L2 expression on non–T cells was critical for respiratory tolerance, but expression on T cells was not required. Because PD-L2 binds to both PD-1, which inhibits antitumor immunity, and to RGMb, which regulates respiratory immunity, targeting the PD-L2 pathway has therapeutic potential for asthma, cancer, and other immune-mediated disorders. Understanding this pathway may provide insights into how to optimally modulate the PD-1 pathway in cancer immunotherapy while minimizing adverse events.

RGMb is a novel binding partner for PD-L2 and its engagement with PD-L2 promotes respiratory tolerance

We report that programmed death ligand 2 (PD-L2), a known ligand of PD-1, also binds to repulsive guidance molecule b (RGMb), which was originally identified in the nervous system as a co-receptor for bone morphogenetic proteins (BMPs). PD-L2 and BMP-2/4 bind to distinct sites on RGMb. Normal resting lung interstitial macrophages and alveolar epithelial cells express high levels of RGMb mRNA, whereas lung dendritic cells express PD-L2. Blockade of the RGMb-PD-L2 interaction markedly impaired the development of respiratory tolerance by interfering with the initial T cell expansion required for respiratory tolerance. Experiments with PD-L2-deficient mice showed that PD-L2 expression on non-T cells was critical for respiratory tolerance, but expression on T cells was not required. Because PD-L2 binds to both PD-1, which inhibits antitumor immunity, and to RGMb, which regulates respiratory immunity, targeting the PD-L2 pathway has therapeutic potential for asthma, cancer, and other immune-mediated disorders. Understanding this pathway may provide insights into how to optimally modulate the PD-1 pathway in cancer immunotherapy while minimizing adverse events.

Immune targeting of PD-1(hi) expressing cells during and after antiretroviral therapy in SIV-infected rhesus macaques

High-level T cell expression of PD-1 during SIV infection is correlated with impaired proliferation and function. We evaluated the phenotype and distribution of T cells and Tregs during antiretroviral therapy plus PD-1 modulation (using a B7-DC-Ig fusion protein) and post-ART. Chronically SIV-infected rhesus macaques received: 11 weeks of ART (Group A); 11 weeks of ART plus B7-DC-Ig (Group B); 11 weeks of ART plus B7-DC-Ig, then 12 weeks of B7-DC-Ig alone (Group C). Continuous B7-DC-Ig treatment (Group C) decreased rebound viremia post-ART compared to pre-ART levels, associated with decreased PD-1(hi) expressing T cells and Tregs in PBMCs, and PD-1(hi) Tregs in lymph nodes. It transiently decreased expression of Ki67 and α4β7 in PBMC CD4(+) and CD8(+) Tregs for up to 8 weeks post-ART and maintained Ag-specific T-cell responses at low levels. Continued immune modulation targeting PD-1(hi) cells during and post-ART helps maintain lower viremia, keeps a favorable T cell/Treg repertoire and modulates antigen-specific responses.

Immunological responses to a multi-peptide vaccine targeting cancer-testis antigens and VEGFRs in advanced pancreatic cancer patients

The prognosis of patients with advanced pancreatic cancer is extremely poor and there are only a few standard treatments. Here, we report the results of a Phase I clinical trial to investigate the safety, immunostimulatory effects, and antineoplastic activity of a multi-target vaccine composed of four distinct peptides derived from cancer-testis (CT) antigens and vascular endothelial growth factor receptors (VEGFRs). Nine patients with unresectable, advanced pancreatic cancer who were refractory to standard chemotherapy were enrolled. Each patient was vaccinated with HLA-A*2402-restricted peptides derived from the CT antigens kinesin family member 20A (KIF20A) and cell division cycle-associated 1 (CDCA1) as well as from VEGFR1 and VEGFR2 subcutaneously once a week, and disease progression was evaluated up to 6 mo later. Adverse events were assessed using the Common Terminology Criteria for Adverse Events v. 3.0. Immunological responses were monitored by ELISPOT assays and flow cytometry based on peptide-specific dextramers. The clinical outcomes that were measured were tumor response, progression-free survival (PFS) and overall survival (OS). In general, the multi-peptide vaccine was well-tolerated, and no grade 3 or 4 adverse events were observed upon vaccination. Peptide-specific T-cell responses were detected in all 9 patients, and clinical benefits were observed in four of them. Median PFS and OS were 90 and 207 d, respectively. The elicitation of multiple and robust peptide-specific T-cell responses as well as the status of host lymphocytes may be useful prognostic factors among patients with advanced pancreatic cancer treated with peptide-based anticancer vaccines.

Anti-PD-1 antibody significantly increases therapeutic efficacy of Listeria monocytogenes (Lm)-LLO immunotherapy

Background

One of the significant tumor immune escape mechanisms and substantial barrier for successful immunotherapy is tumor-mediated inhibition of immune response through cell-to-cell or receptor/ligand interactions. Programmed death receptor-1 (PD-1) interaction with its ligands, PD-L1 and PD-L2, is one of the important strategies that many tumors employ to escape immune surveillance. Upon PD-Ls binding to PD-1, T cell receptor (TCR) signaling is dampened, causing inhibition of proliferation, decreased cytokine production, anergy and/or apoptosis. Thus PD-Ls expression by tumor cells serves as a protective mechanism, leading to suppression of tumor-infiltrating lymphocytes in the tumor microenvironment. Lm-LLO immunotherapies have been shown to be therapeutically effective due to their ability to induce potent antigen-specific immune responses. However, it has been demonstrated that infection with Lm leads to up-regulation of PD-L1 on mouse immune cells that can inhibit effector T cells through PD-1/PD-L1 pathway.

Methods

Therapeutic and immune efficacy of Listeria-based vaccine (Lm-LLO-E7) in combination with anti-PD-1 antibody was tested in E7 antigen expressing TC-1 mouse tumor model. Tumor growth, survival, as well as peripheral and tumor-infiltrating immune cell profiles after immunotherapy were assessed.

Results

Here we demonstrate that the combination of an Lm-LLO immunotherapy with anti-PD-1 antibody that blocks PD-1/PD-L1 interaction, significantly improves immune and therapeutic efficacy of treatment in TC-1 mouse tumor model. Importantly, we show that in addition to significant reduction of regulatory T cells (Treg) and myeloid-derived suppressor cells (MDSC) in both spleen and tumor microenvironment that are mediated solely by the Lm-LLO immunotherapy, the addition of anti-PD-1 antibody to the treatment results in significant increase of antigen-specific immune responses in periphery and CD8 T cell infiltration into the tumor. As a result, this combinational treatment leads to significant inhibition of tumor growth and prolonged survival/complete regression of tumors in treated animals.

We also demonstrate that in vitro infection with Lm results in significant upregulation of surface PD-L1 expression on human monocyte-derived dendritic cells suggesting the translational capacity of this finding.

Conclusions

Our findings demonstrate that combination of Lm-LLO-based vaccine with blocking of PD-1/PD-L1 interaction is a feasible approach with clinical translation potential that can lead to overall enhancement of the efficacy of anti-tumor immunotherapy.

Antagonist antibodies to PD-1 and B7-H1 (PD-L1) in the treatment of advanced human cancer

The immune suppressive molecule programmed death-1 (PD-1) is upregulated in activated T lymphocytes and inhibits T-cell function upon binding to its ligands B7-H1 (PD-L1, CD274) and B7-DC (PD-L2, CD273). Substantial experimental data from in vitro cell culture systems and animal models, and more recently from clinical trials, indicate that PD-1/PD-1-ligand interactions are a major mechanism of immune suppression within the tumor microenvironment. Initial clinical studies of antibodies directed against PD-1 and B7-H1 showed both an encouraging safety profile and remarkable antitumor activity in subsets of patients with metastatic disease, including malignancies--such as lung cancer--which were previously thought to be unresponsive to immunotherapy. Preliminary data have suggested a correlation between tumor membrane B7-H1 expression and clinical response to anti-PD-1 antibodies. Several key challenges remain to optimize development of PD-1/B7-H1 pathway blockade, including defining the biologic significance of all potential ligand-receptor interactions in the tumor microenvironment, developing more accurate predictive biomarkers of response, determining the breadth of activity in human malignancies, and developing rational combinations of therapy that address key mechanisms involved in positive and negative regulation of antitumor immune responses.

Focus on the target: the tumor microenvironment, Society for Immunotherapy of Cancer Annual Meeting Workshop, October 24th-25th 2012

The Workshop associated with the 27th Annual Meeting of the Society for Immunotherapy of Cancer (SITC), North Bethesda, MD, October 24-25, 2012 focused on targeting the tumor microenvironment as part of an integrative approach to immune-based cancer therapy.