Overcoming T cell exhaustion in infection and cancer

Combination of CD40 Agonism and CSF-1R Blockade Reconditions Tumor-Associated Macrophages and Drives Potent Antitumor Immunity

Efficacious antitumor immune responses must overcome multiple suppressive mechanisms in the tumor microenvironment to control cancer progression. In this study, we demonstrate that dual targeting of suppressive myeloid populations by inhibiting CSF-1/CSF-1R signaling and activation of antigen-presenting cells with agonist anti-CD40 treatment confers superior antitumor efficacy and increased survival compared with monotherapy treatment in preclinical tumor models. Concurrent CSF-1R blockade and CD40 agonism lead to profound changes in the composition of immune infiltrates, causing an overall decrease in immunosuppressive cells and a shift toward a more inflammatory milieu. Anti-CD40/anti-CSF-1R-treated tumors contain decreased tumor-associated macrophages and Foxp3⁺ regulatory T cells. This combination approach increases maturation and differentiation of proinflammatory macrophages and dendritic cells and also drives potent priming of effector T cells in draining lymph nodes. As a result, tumor-infiltrating effector T cells exhibit improved responses to tumor antigen rechallenge. These studies show that combining therapeutic approaches may simultaneously remove inhibitory immune populations and sustain endogenous antitumor immune responses to successfully impair cancer progression. Cancer Immunol Res; 5(12); 1109-21. ©2017 AACR.

Mechanisms of Mixed Chimerism-Based Transplant Tolerance

Immune responses to allografts represent a major barrier in organ transplantation. Immune tolerance to avoid chronic immunosuppression is a critical goal in the field, recently achieved in the clinic by combining bone marrow transplantation (BMT) with kidney transplantation following non-myeloablative conditioning. At high levels of chimerism such protocols can permit central deletional tolerance, but with a significant risk of graft-versus-host (GVH) disease (GVHD). By contrast, transient chimerism-based tolerance is devoid of GVHD risk and appears to initially depend on regulatory T cells (Tregs) followed by gradual, presumably peripheral, clonal deletion of donor-reactive T cells. Here we review recent mechanistic insights into tolerance and the development of more robust and safer protocols for tolerance induction that will be guided by innovative immune monitoring tools.

Checkpoint inhibitor-induced uveitis: a case series

PURPOSE

Checkpoint inhibitors are now a common treatment modality for metastatic cancer. In this manuscript, we describe the clinical features and management of autoimmune non-infectious uveitis induced by this class of drugs.

METHODS

Seven patients undergoing checkpoint inhibitor treatment for metastatic cancer from uveitis practices at three tertiary referral centers.

RESULTS

All seven patients developed various severities of ocular inflammatory disease while taking checkpoint inhibitors for metastatic disease.

CONCLUSIONS

Checkpoint inhibitors may induce autoimmune uveitis. Ocular complaints should prompt an early evaluation by an ophthalmologist.

Offspring's Tolerance of Mother Goes Viral

Pregnancy uniquely allows genetically discordant tissues of the mother and child to intimately coexist in harmony. In this issue of Immunity, Ou and colleagues show that hepatitis B virus exploits these naturally occurring immune tolerance pathways to establish persistent postnatal infection in offspring.

Comprehensive Mass Cytometry Analysis of Cell Cycle, Activation, and Coinhibitory Receptors Expression in CD4 T Cells from Healthy and HIV-Infected Individuals

RATIONALE

Mass cytometry allows large multiplex analysis of cell cycle stages together with differentiation, activation, and exhaustion markers, allowing further assessment of the quiescence status of resting CD4 T cells.

METHODS

Peripheral blood CD4 T lymphocytes from 8 individuals, 4 healthy donors, and 4 HIV-infected on antiretroviral treatment (T) were stained with the same 26 monoclonal antibodies and dyes targeting surface and intracellular markers of differentiation, activation, exhaustion, and cell cycle stages. Samples were run on a CYTOF-2.

RESULTS

Patterns of naïve [TN] CD4 T cells strongly differed from all other memory subsets central-memory (CM), transitional-memory (TM), effector-memory (EM), and terminally differentiated RA-expressing (TEMRA) subsets, while stem-cell memory (SCM) and T follicular-helper cells (TfH) were close to CM and TM cells with the highest percentages in cell cycle. EM and TEMRA were the most altered by HIV infection, with an increased frequency of activated and cycling cells. Activation markers and coinhibitory receptor expression differed among cell cycle stages, with HLA-DR fitting better than CD25 or CD38 with cycle, and opposite PD-1 gradients along differentiation and cell cycle. "Resting" DR-CD25- CD4+ T cells contained similar amounts of cells in G1 than the activated DR ± CD25± ones but three fold lower cells in S-G2-M.

CONCLUSION

This broad multiplex mass cytometry analysis demonstrates some subsets of the so-called "resting" CD25-DR- CD4+ T cells contain noticeable amounts of cells into cycle or expressing coinhibitory receptors, opening new avenues for a redefinition of resting peripheral blood CD4 T cells harboring the HIV reservoirs. © 2016 International Clinical Cytometry Society.

Exhaustion of T lymphocytes in the tumor microenvironment: Significance and effective mechanisms

T lymphocytes play crucial roles in adaptive immune responses to tumors. However, due to different tolerance mechanisms and inhibitory effects of the tumor microenvironment (TME) on T cells, responses to tumors are insufficient. In fact, cellular and molecular suppressive mechanisms repress T cell responses in the TME, resulting in senescent, anergic and exhausted lymphocytes. Exhaustion is a poor responsive status of T cells, with up-regulated expression of inhibitory receptors, decreased production of effective cytokines, and reduced cytotoxic activity. Low immunogenicity of tumor antigens and inadequate presentation of tumor-specific antigens results in inappropriate activation of naive T lymphocytes against tumor antigens. Moreover, when effector cytotoxic T cells enter TME, they encounter a complicated network of cells and cytokines that suppress their effectiveness and turn them into exhausted T cells. Thus, the mechanism of T cell exhaustion in cancer is different from that in chronic infections. In this review we will discuss the main components such as inhibitory receptors, inflammatory cells, stromal cells, cytokine milieu as well as environmental and metabolic conditions in TME which play role in development of exhaustion. Furthermore, recent therapeutic methods available to overcome exhaustion will be discussed.

Coinhibitory Receptor Expression and Immune Checkpoint Blockade: Maintaining a Balance in CD8+ T Cell Responses to Chronic Viral Infections and Cancer

In cancer and chronic viral infections, T cells are exposed to persistent antigen stimulation. This results in expression of multiple inhibitory receptors also called “immune checkpoints” by T cells. Although these inhibitory receptors under normal conditions maintain self-tolerance and prevent immunopathology, their sustained expression deteriorates T cell function: a phenomenon called exhaustion. Recent advances in cancer immunotherapy involve blockade of cytotoxic T lymphocyte antigen-4 and programmed cell death 1 in order to reverse T cell exhaustion and reinvigorate immunity, which has translated to dramatic clinical remission in many cases of metastatic melanoma and lung cancer. With the paucity of therapeutic vaccines against chronic infections such as HIV, HPV, hepatitis B, and hepatitis C, such adjunct checkpoint blockade strategies are required including the blockade of other inhibitory receptors such as T cell immunoreceptor with immunoglobulin (Ig) and immunoreceptor tyrosine-based inhibitory motif domains, T cell Ig and mucin-domain containing-3, lymphocyte activation gene 3, and V-domain Ig-containing suppressor of T cell activation. The nature of different chronic viral infections and cancers is likely to influence the level, composition, and pattern of inhibitory receptors expressed by responding T cells. This will have implications for checkpoint antibody blockade strategies employed for treating tumors and chronic viral infections. Here, we review recent advances that provide a clearer insight into the role of coinhibitory receptor expression in T cell exhaustion and reveal novel antibody-blockade therapeutic targets for chronic viral infections and cancer. Understanding the mechanism of T cell exhaustion in response to chronic virus infections and cancer as well as the nature of restored T cell responses will contribute to further improvement of immune checkpoint blockade strategies.

Impaired polyfunctionality of CD8+ T cells in severe sepsis patients with human cytomegalovirus reactivation

Human cytomegalovirus (HCMV) establishes a lifelong chronic latent infection and often reactivates in immunocompromised patients. In addition, HCMV reactivates in patients with sepsis or other critical illnesses, particularly in patients with poor prognoses. However, the immunological characteristics of sepsis patients with HCMV reactivation have not been elucidated. In the present study, we examined T-cell responses in severe sepsis patients with and without HCMV reactivation. First, HCMV pp65-specific T-cell functions were assessed by intracellular cytokine staining (ICS) for IFN-γ, TNF-α, and MIP-1β and by CD107a staining. We analyzed the ICS data for each function individually and found no difference between the patient groups. However, the relative frequency of polyfunctional CD8⁺ T cells was significantly decreased in sepsis patients with HCMV reactivation. Next, we examined programmed cell death protein 1 (PD-1) expression. It was significantly increased in the CD8⁺ T-cell population in severe sepsis patients with HCMV reactivation, indicating CD8⁺ T-cell exhaustion. Interestingly, the frequency of PD-1⁺ cells in the CD8⁺ T-cell population was inversely correlated with the relative frequency of polyfunctional CD8⁺ T cells. Herein, we demonstrate that HCMV reactivation in severe sepsis patients is associated with PD-1 expression and impaired polyfunctionality of CD8⁺ T cells.

PD-1 Blockade Promotes Epitope Spreading in Anticancer CD8+ T Cell Responses by Preventing Fratricidal Death of Subdominant Clones To Relieve Immunodomination

The interactions between programmed death-1 (PD-1) and its ligands hamper tumor-specific CD8⁺ T cell (T_CD8) responses, and PD-1-based "checkpoint inhibitors" have shown promise in certain cancers, thus revitalizing interest in immunotherapy. PD-1-targeted therapies reverse T_CD8 exhaustion/anergy. However, whether they alter the epitope breadth of T_CD8 responses remains unclear. This is an important question because subdominant T_CD8 are more likely than immunodominant clones to escape tolerance mechanisms and may contribute to protective anticancer immunity. We have addressed this question in an in vivo model of T_CD8 responses to well-defined epitopes of a clinically relevant oncoprotein, large T Ag. We found that unlike other coinhibitory molecules (CTLA-4, LAG-3, TIM-3), PD-1 was highly expressed by subdominant T_CD8, which correlated with their propensity to favorably respond to PD-1/PD-1 ligand-1 (PD-L1)-blocking Abs. PD-1 blockade increased the size of subdominant T_CD8 clones at the peak of their primary response, and it also sustained their presence, thus giving rise to an enlarged memory pool. The expanded population was fully functional as judged by IFN-γ production and MHC class I-restricted cytotoxicity. The selective increase in subdominant T_CD8 clonal size was due to their enhanced survival, not proliferation. Further mechanistic studies utilizing peptide-pulsed dendritic cells, recombinant vaccinia viruses encoding full-length T Ag or epitope mingenes, and tumor cells expressing T Ag variants revealed that anti-PD-1 invigorates subdominant T_CD8 responses by relieving their lysis-dependent suppression by immunodominant T_CD8 To our knowledge, our work constitutes the first report that interfering with PD-1 signaling potentiates epitope spreading in tumor-specific responses, a finding with clear implications for cancer immunotherapy and vaccination.

Anti-CD137 Suppresses Tumor Growth by Blocking Reverse Signaling by CD137 Ligand

CD137 (4-1BB) is a T-cell costimulatory molecule, and agonstic CD137 antibodies are currently being evaluated in the clinic as cancer immunotherapy. Recently, it was found that CD137^-/- mice or mice injected with agonistic anti-CD137 antibodies exhibit heightened antitumor responses, contrary to expectations based on other knowledge of CD137 function. Here, we report findings related to reverse signaling by CD137 ligand (CD137L) in antigen-presenting dendritic cells (DC) in tumors that address these paradoxical results. Specifically, CD137L suppressed intratumoral differentiation of IL12-producing CD103⁺ DC and type 1 tumor-associated macrophages (TAM). Differentiation of these cell types is important because they are required to generate IFNγ-producing CD8⁺ cytotoxic T lymphocytes (Tc1). Notably, CD137L blockade increased levels of IL12 and IFNγ, which promoted intratumoral differentiation of IFNγ-producing Tc1, IL12-producing CD103⁺ DC, and type 1 TAM within tumors. Our results offer an explanation for the paradoxical effects of CD137 blockade, based on differential immunomodulatory effects of CD137 signaling and reverse signaling in T cells and DC, respectively. Further, they show how CD137L blockade can seed a forward-feedback loop for activation of CD103⁺ DC/type 1 TAM and Tc1 that can create a self-perpetuating cycle of highly effective immunosurveillance. Cancer Res; 77(21); 5989-6000. ©2017 AACR.

Lag-3, Tim-3, and TIGIT: Co-inhibitory Receptors with Specialized Functions in Immune Regulation

Co-inhibitory receptors, such as CTLA-4 and PD-1, have an important role in regulating T cell responses and have proven to be effective targets in the setting of chronic diseases where constitutive co-inhibitory receptor expression on T cells dampens effector T cell responses. Unfortunately, many patients still fail to respond to therapies that target CTLA-4 and PD-1. The next wave of co-inhibitory receptor targets that are being explored in clinical trials include Lag-3, Tim-3, and TIGIT. These receptors, although they belong to the same class of receptors as PD-1 and CTLA-4, exhibit unique functions, especially at tissue sites where they regulate distinct aspects of immunity. Increased understanding of the specialized functions of these receptors will inform the rational application of therapies that target these receptors to the clinic.

Peripheral Autoimmune Regulator Induces Exhaustion of CD4+ and CD8+ Effector T Cells to Attenuate Autoimmune Diabetes in Non-Obese Diabetic Mice

Autoimmune regulator (Aire) is one of the most crucial genes expressed in the thymus, where it orchestrates the promiscuous expression and presentation of tissue-specific antigens during thymocyte selection. The presence of Aire-expressing cells outside the thymus points toward its plausible extrathymic functions; however, the relative contribution of Aire-expressing cells of hematopoietic origin and their role in the modulation of autoimmune diseases are still obscure. Here, we report that non-obese diabetic mice with transgenic Aire expression under the control of the CD11c (integrin alpha X) promoter were significantly protected from autoimmune diabetes compared with their non-transgenic littermates. The protective effect of Aire transgene was mediated primarily by an increase in the “exhausted” populations of CD4⁺ and CD8⁺ T cells, both demonstrating poor expressions of interferon-γ and tumor necrosis factor-α. Both CD4⁺ and CD8⁺ effector T cells in transgenic mice displayed distinctive and differential expression of T-bet and Eomesodermin, respectively, in conjunction with high expression of programmed cell death protein-1 and other exhaustion-associated markers. Importantly, transgenic Aire expression did not result in any detectable changes in the population of Foxp3⁺ regulatory T (Treg) cells. Co-transfer experiments also demonstrated that Aire transgenic dendritic cells, as a “stand-alone” cell population, had the potential to suppress effector T cells in vivo without the support of Treg cells, but eventually failed to prevent the diabetogenesis in recipient mice. In conclusion, our study suggests that apart from its role in clonal deletion of autoreactive T cells or clonal diversion to Treg lineage, Aire can also contribute to tolerance by forcing effector T cells into a state of exhaustion with poor effector functions, thereby effectively containing autoimmune diseases.

PD-1 expression on tumor-specific T cells: Friend or foe for immunotherapy?

Inhibitory properties of PD-1 receptor engagement on activated T cells are well established in physiologic and pathological contexts. In cancer, the use of checkpoint blockade, such as anti-PD-1 antibodies, becomes progressively a reference treatment of a growing number of tumors. Nonetheless, it is also established that PD-1 expression on antigen-specific T cells reflects the functional avidity and anti-tumor reactivity of these T cells. We will discuss this dual significance of PD-1 expression on tumor-specific T cells, due to a complex regulation and the opportunity to exploit this expression to define, monitor and exploit tumor-reactive T cells for immunotherapy purposes.

Functional T cells targeting tumor-associated antigens are predictive for recurrence-free survival of patients with radically operated non-small cell lung cancer

In this prospective study, we examined postoperative follow-up and preoperative IFN-γ T cell responses against 14 non-small cell lung cancer (NSCLC)-associated antigens in the blood of 51 patients with NSCLC, 7 patients with benign pulmonary tumors, and 10 tumor-free patients by enzyme-linked immunospot assay. The phenotype and function of T cells specific for tumor-associated antigens (TAAs) in the blood or tumor tissue of 9 NSCLC patients were characterized in detail using TNF-α, IL-2, and IFN-γ cytokine capture assays. We found that circulating TAA-specific T cells were significantly enriched in NSCLC compared with tumor-free patients. The most frequently recognized TAAs were Aurora kinase A, HER2/neu, NY-ESO-1, and p53. TNF-α was the most abundant cytokine secreted by TAA-specific T cells in the blood as well as by in situ-activated tumor-infiltrating lymphocytes, most of which were effector memory cells. The absence of TAA-reactive T cells identified patients at higher risk of tumor recurrence, irrespective of tumor stage (OR = 8.76, 95% CI: 1.57-34.79, p = 0.008). We conclude that pre-existing TAA-reactive circulating T cells are a strong independent prognostic factor for recurrence-free survival. These data may help discriminating high-risk from low-risk patients, improving prognostication, and redirecting adjuvant therapy. Our findings suggest the therapeutic relevance of Aurora kinase A, HER2/neu, NY-ESO-1, and p53 as targets for immunotherapy. This study is registered on Clinicaltrials.gov with trial identification number: NCT02515760.

The Inhibitory Signaling Receptor Protocadherin-18 Regulates Tumor-Infiltrating CD8+ T-cell Function

Cancers are infiltrated with antitumor CD8⁺ T cells that arise during tumor growth, but are defective in effector phase functions because of the suppressive microenvironment. The reactivation of TILs can result in tumor destruction, showing that lytic dysfunction in CD8⁺ tumor-infiltrating lymphocytes (TIL) permits tumor growth. Like all memory T cells, TILs express inhibitory signaling receptors (aka checkpoint inhibitor molecules) that downregulate TCR-mediated signal transduction upon TIL interaction with cells expressing cognate ligands, thereby restricting cell activation and preventing the effector phase. Previously, we identified a novel murine CD8⁺ TIL inhibitory signaling receptor, protocadherin-18, and showed that it interacts with p56^lck kinase to abrogate proximal TCR signaling. Here, we show that TILs from mice deleted in protocadherin-18 had enhanced antitumor activity and that coblockade of PD-1 and protocadherin-18 in wild-type mice significantly enhanced TIL effector phase function. These results define an important role for protocadherin-18 in antitumor T-cell activity. Cancer Immunol Res; 5(10); 920-8. ©2017 AACR.

Metabolic reprogramming and apoptosis sensitivity: Defining the contours of a T cell response

An effective adaptive immune response hinges on the rapid clonal expansion of T cells in response to antigen. The sensitivity of these T cells to programmed cell death (i.e. apoptosis) is carefully calibrated at various stages to ensure a robust yet measured reaction that resolves without inflicting unintended damage to host tissues. To meet bioenergetic demands associated with vigorous proliferation, acquisition of effector functions, and memory formation, T cells also undergo dynamic changes in their metabolism at every stage of this response. In this review, we focus on relatively recent studies that illuminate intimate links between metabolic programs and apoptosis sensitivity in T cells. We then examine how these connections ultimately influence T cell survival and function within the metabolically taxing environs of the tumor microenvironment.

New approaches for the enhancement of chimeric antigen receptors for the treatment of HIV

HIV infection continues to be a life-long chronic disease in spite of the success of antiretroviral therapy (ART) in controlling viral replication and preventing disease progression. However, because of the high cost of treatment, severe side effects, and inefficiency in curing the disease with ART, there is a call for alternative therapies that will provide a functional cure for HIV. Cytotoxic T lymphocytes (CTLs) are vital in the control and clearance of viral infections and therefore immune-based therapies have attempted to engineer HIV-specific CTLs that would be able to clear the infection from the body. The development of chimeric antigen receptors (CARs) provides an opportunity to engineer superior HIV-specific CTLs that will be independent of the major histocompatibility complex for target recognition. A CD4-based CAR has been previously tested in clinical trials to test the antiviral efficacy of peripheral T cells armed with this CD4-based CAR. The results from these clinical trials showed the safety and feasibility of CAR T cell therapy for HIV infection; however, minimal antiviral efficacy was seen. In this review, we will discuss the various strategies being developed to enhance the therapeutic potency of anti-HIV CARs with the goal of generating superior antiviral responses that will lead to life-long HIV immunity and clearance of the virus from the body.

HLA-mediated tumor escape mechanisms that may impair immunotherapy clinical outcomes via T-cell activation

Although the immune system provides protection from cancer by means of immunosurveillance, which serves a major function in eliminating cancer cells, it may also lead to cancer immunoediting, molding tumor immunogenicity. Cancer cells exploit several molecular mechanisms to thwart immune-mediated death by disabling cellular components of the immune system associated with tumor recognition and rejection. Human leukocyte antigen (HLA) molecules are mandatory for the immune recognition and subsequent killing of neoplastic cells by the immune system, as tumor antigens must be presented in an HLA-restricted manner to be recognized by T-cell receptors. Impaired HLA-I expression prevents the activation of cytotoxic immune mechanisms, whereas impaired HLA-II expression affects the antigen-presenting capability of antigen presenting cells. Aberrant HLA-G expression by cancer cells favors immune escape by inhibiting the activities of virtually all immune cells. The development of cancer therapies based on T-cell activation must consider these HLA-associated immune evasion mechanisms, as alterations in their expression occur early and frequently in the majority of types of cancer, and have an adverse impact on the clinical response to immunotherapy. Herein, the concept of altered HLA expression as a mechanism exploited by tumors to escape immune control and induce an immunosuppressive environment is reviewed. A number of novel clinical immunotherapeutic approaches used for cancer treatment are also reviewed, and strategies for overcoming the limitations of these immunotherapeutic interventions are proposed.

Programmed Cell Death-1/Programmed Death-ligand 1 Pathway: A New Target for Sepsis

OBJECTIVE

Sepsis remains a leading cause of death in many Intensive Care Units worldwide. Immunosuppression has been a primary focus of sepsis research as a key pathophysiological mechanism. Given the important role of the negative costimulatory molecules programmed cell death-1 (PD-1) and programmed death-ligand 1 (PD-L1) in the occurrence of immunosuppression during sepsis, we reviewed literatures related to the PD-1/PD-L1 pathway to examine its potential as a new target for sepsis treatment.

DATA SOURCES

Studies of the association between PD-1/PD-L1 and sepsis published up to January 31, 2017, were obtained by searching the PubMed database.

STUDY SELECTION

English language studies, including those based on animal models, clinical research, and reviews, with data related to PD-1/PD-L1 and sepsis, were evaluated.

RESULTS

Immunomodulatory therapeutics could reverse the deactivation of immune cells caused by sepsis and restore immune cell activation and function. Blockade of the PD-1/PD-L1 pathway could reduce the exhaustion of T-cells and enhance the proliferation and activation of T-cells.

CONCLUSIONS

The anti-PD-1/PD-L1 pathway shows promise as a new target for sepsis treatment. This review provides a basis for clinical trials and future studies aimed at revaluating the efficacy and safety of this targeted approach.

Small-molecule inhibitors of PD-1/PD-L1 immune checkpoint alleviate the PD-L1-induced exhaustion of T-cells

Antibodies targeting the PD-1/PD-L1 immune checkpoint achieved spectacular success in anticancer therapy in the recent years. In contrast, no small molecules with cellular activity have been reported so far. Here we provide evidence that small molecules are capable of alleviating the PD-1/PD-L1 immune checkpoint-mediated exhaustion of Jurkat T-lymphocytes. The two optimized small-molecule inhibitors of the PD-1/PD-L1 interaction, BMS-1001 and BMS-1166, developed by Bristol-Myers Squibb, bind to human PD-L1 and block its interaction with PD-1, when tested on isolated proteins. The compounds present low toxicity towards tested cell lines and block the interaction of soluble PD-L1 with the cell surface-expressed PD-1. As a result, BMS-1001 and BMS-1166 alleviate the inhibitory effect of the soluble PD-L1 on the T-cell receptor-mediated activation of T-lymphocytes. Moreover, the compounds were effective in attenuating the inhibitory effect of the cell surface-associated PD-L1. We also determined the X-ray structures of the complexes of BMS-1001 and BMS-1166 with PD-L1, which revealed features that may be responsible for increased potency of the compounds compared to their predecessors. Further development may lead to the design of an anticancer therapy based on the orally delivered immune checkpoint inhibition.

Tissue-resident memory features are linked to the magnitude of cytotoxic T cell responses in human lung cancer

Therapies that boost the anti-tumor responses of cytotoxic T lymphocytes (CTLs) have shown promise; however, clinical responses to the immunotherapeutic agents currently available vary considerably, and the molecular basis of this is unclear. We performed transcriptomic profiling of tumor-infiltrating CTLs from treatment-naive patients with lung cancer to define the molecular features associated with the robustness of anti-tumor immune responses. We observed considerable heterogeneity in the expression of molecules associated with activation of the T cell antigen receptor (TCR) and of immunological-checkpoint molecules such as 4-1BB, PD-1 and TIM-3. Tumors with a high density of CTLs showed enrichment for transcripts linked to tissue-resident memory cells (TRM cells), such as CD103, and CTLs from CD103hi tumors displayed features of enhanced cytotoxicity. A greater density of TRM cells in tumors was predictive of a better survival outcome in lung cancer, and this effect was independent of that conferred by CTL density. Here we define the 'molecular fingerprint' of tumor-infiltrating CTLs and identify potentially new targets for immunotherapy.

Extracellular Vesicles Transfer the Receptor Programmed Death-1 in Rheumatoid Arthritis

Introduction

Extracellular vesicles (EVs) have been recognized as route of communication in the microenvironment. They transfer proteins and microRNAs (miRNAs) between cells, and possess immunoregulatory properties. However, their role in immune-mediated diseases remains to be elucidated. We hypothesized a role for EVs in the rheumatoid arthritis (RA) joint, potentially involving the development of T cell exhaustion and transfer of the co-inhibitory receptor programmed death 1 (PD-1).

Methods

Synovial fluid mononuclear cells (SFMCs) and peripheral blood mononuclear cells (PBMCs) from RA patients were investigated for PD-1 and other markers of T cell inhibition. EVs were isolated from RA plasma and synovial fluid. In addition, healthy control (HC) and RA PBMCs and SFMCs were cultured to produce EVs. These were isolated and investigated by immunogold electron microscopy (EM) and also co-cultured with lymphocytes and PD-1 negative cells to investigate their functions. Finally, the miRNA expression profiles were assessed in EVs isolated from RA and HC cell cultures.

Results

Cells from the RA joint expressed several T cell co-inhibitory receptors, including PD-1, TIM-3, and Tigit. ELISA demonstrated the presence of PD-1 in EVs from RA plasma and synovial fluid. Immunogold EM visualized PD-1 expression by EVs. Co-culturing lymphocytes and the PD-1 negative cell line, U937 with EVs resulted in an induction of PD-1 on these cells. Moreover, EVs from RA PBMCs increased proliferation in lymphocytes when co-cultured with these. All EVs contained miRNAs associated with PD-1 and other markers of T cell inhibition and the content was significantly lower in EVs from RA PBMCs than HC PBMCs. Stimulation of the cells increased the miRNA expression. However, EVs isolated from stimulated RA SFMCs did not change their miRNA expression profile to the same extend.

Conclusion

EVs carrying both the PD-1 receptor and miRNAs associated with T cell inhibition were present in RA cell cultures. Upon stimulation, these miRNAs failed to be upregulated in EVs from RA SFMCs. This was in line with increased expression of T cell co-inhibitory markers on SFMCs. In conclusion, we suggest EVs to play a significant role in the RA microenvironment, potentially favoring the progression of T cell exhaustion.

Partially exhausted tumor-infiltrating lymphocytes predict response to combination immunotherapy

BACKGROUND

Programmed death 1 (PD-1) inhibition activates partially exhausted cytotoxic T lymphocytes (peCTLs) and induces tumor regression. We previously showed that the peCTL fraction predicts response to anti-PD-1 monotherapy. Here, we sought to correlate peCTL and regulatory T lymphocyte (Treg) levels with response to combination immunotherapy, and with demographic/disease characteristics, in metastatic melanoma patients.

METHODS

Pretreatment melanoma samples underwent multiparameter flow cytometric analysis. Patients were treated with anti-PD-1 monotherapy or combination therapy, and responses determined by Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1) criteria. peCTL and Treg levels across demographic/disease variables were compared. Low versus high peCTL (≤20% vs. >20%) were defined from a previous study.

RESULTS

One hundred and two melanoma patients were identified. The peCTL fraction was higher in responders than nonresponders. Low peCTL correlated with female sex and liver metastasis, but not with lactate dehydrogenase (LDH), tumor stage, or age. While overall response rates (ORRs) to anti-PD-1 monotherapy and combination therapy were similar in high-peCTL patients, low-peCTL patients given combination therapy demonstrated higher ORRs than those who received monotherapy. Treg levels were not associated with these factors nor with response.

CONCLUSION

In melanoma, pretreatment peCTL fraction is reduced in women and in patients with liver metastasis. In low-peCTL patients, anti-PD-1 combination therapy is associated with significantly higher ORR than anti-PD-1 monotherapy. Fewer tumor-infiltrating peCTLs may be required to achieve response to combination immunotherapy.

TRIAL REGISTRATION

UCSF IRB Protocol 138510FUNDING. NIH DP2-AR068130, K08-AR062064, AR066821, and Burroughs Wellcome CAMS-1010934 (M.D.R.). Amoroso and Cook Fund, and the Parker Institute for Cancer Immunotherapy (A.I.D.).

Tumor-associated immune aggregates in oral cancer: Their cellular composition and potential prognostic significance

There is growing evidence supporting the importance of immune microenvironment in cancer development and progression, especially with the rapid development of immunotherapy. Presence of immune cell aggregates in solid tumors has been associated with clinical outcomes, but little is known about the immune microenvironment in oral squamous cell carcinoma (OSCC), which has high morbidity and mortality. Based on our preliminary observation, we hypothesize that there is the presence of tumor-associated immune aggregates (TaIAs) during oral cancer development. Adapting to the dynamic change of the composition of cellular membership and co-evolving with the tumor at invasion fronts, these TaIAs, either pro-inflammatory or immune suppressive, are associated with clinical consequences. With the unique access to a set of prospectively collected, highly annotated OSCC surgical samples and the use of multi-color immunostaining of key immune cells, the confirmation of our hypothesis may shed light of the underlying biology related to OSCC and the knowledge learned can potentially be used to identify prognostic markers, response predictive markers for immunotherapies, as well as novel therapeutic targets.

Limitations and opportunities for immune checkpoint inhibitors in pediatric malignancies

Immune checkpoint inhibitors (ICI) have shown great promise in a wide spectrum of adult solid and hematological malignancies, achieving objective tumor responses and prolonging survival. However, there is limited clinical success amongst pediatric patients. In this review, we summarize the current understanding of ICI and present an up-to-date overview of recent and ongoing clinical trials of ICI in pediatric malignancies. In addition, we will discuss immunologic and clinical difficulties in this young population, as well as future prospects for combination of ICI with other immune-based and conventional treatments.

Hepatic IFIT3 predicts interferon-α therapeutic response in patients of hepatocellular carcinoma

Adjuvant interferon-α (IFN-α) therapy is used to control certain types of cancer in clinics. For hepatocellular carcinoma (HCC), IFN-α therapy is effective in only a subgroup of patients; therefore, identifying biomarkers to predict the response to IFN-α therapy is of high significance and clinical utility. As the induced IFN-stimulated gene expression following IFN-α treatment plays pivotal roles in IFN-α effects, we screened IFN-stimulated gene expression in HCC tissues and found that several IFN-stimulated genes were significantly decreased in HCC. Interestingly, expression of IFN-induced protein with tetratricopeptide repeats (IFIT) family members, including IFIT1, IFIT2, IFIT3, and IFIT5, was decreased in HCC tissues. We further analyzed the expression of IFIT family members in HCC and their roles in patients' responses to IFN-α therapy in two independent randomized controlled IFN-α therapy clinical trials of HCC patients. We found that higher expression of IFIT3, but not other IFITs, in HCC tissues predicts better response to IFN-α therapy, suggesting that IFIT3 may be a useful predictor of the response to IFN-α therapy in HCC patients. Mechanistically, IFIT3 enhanced the antitumor effects of IFN-α by promoting IFN-α effector responses both in vitro and in vivo. IFIT3 could bind signal transducer and activator of transcription 1 (STAT1) and STAT2 to enhance STAT1-STAT2 heterodimerization and nuclear translocation upon IFN-α treatment, thus promoting IFN-α effector signaling.

CONCLUSION

Higher IFIT3 expression in HCC tissues predicts better response to IFN-α therapy in HCC patients; IFIT3 promotes IFN-α effector responses and therapeutic effects by strengthening IFN-α effector signaling in HCC. (Hepatology 2017;66:152-166).

Predominance of weakly cytotoxic, T-betLowEomesNeg CD8+ T-cells in human gastrointestinal mucosa: implications for HIV infection

The gastrointestinal mucosa is an important site of HIV acquisition, viral replication, and pathogenesis. Immune cells in mucosal tissues frequently differ in phenotype and function from their non-mucosal counterparts. Although perforin-mediated cytotoxicity as measured in blood is a recognized correlate of HIV immune control, its role in gastrointestinal tissues is unknown. We sought to elucidate the cytotoxic features of rectal mucosal CD8⁺ T-cells in HIV infected and uninfected subjects. Perforin expression and lytic capacity were significantly reduced in rectal CD8⁺ T-cells compared with their blood counterparts, regardless of HIV clinical status; granzyme B (GrzB) was reduced to a lesser extent. Mucosal perforin and GrzB expression were higher in participants not on antiretroviral therapy compared with those on therapy and controls. Reduction in perforin and GrzB was not explained by differences in memory/effector subsets. Expression of T-bet and Eomesodermin was significantly lower in gut CD8⁺ T-cells compared with blood, and in vitro neutralization of TGF-β partially restored perforin expression in gut CD8⁺ T-cells. These findings suggest that rectal CD8⁺ T-cells are primarily non-cytotoxic, and phenotypically shaped by the tissue microenvironment. Further elucidation of rectal immune responses to HIV will inform the development of vaccines and immunotherapies targeted to mucosal tissues.

Generating long-lived CD8(+) T-cell memory: Insights from epigenetic programs

T-cell-based immunological memory has the potential to provide the host with life-long protection against pathogen reexposure and thus offers tremendous promise for the design of vaccines targeting chronic infections or cancer. In order to exploit this potential in the design of new vaccines, it is necessary to understand how and when memory T cells acquire their poised effector potential, and moreover, how they maintain these properties during homeostatic proliferation. To gain insight into the persistent nature of memory T-cell functions, investigators have turned their attention to epigenetic mechanisms. Recent efforts have revealed that many of the properties acquired among memory T cells are coupled to stable changes in DNA methylation and histone modifications. Furthermore, it has recently been reported that the delineating features among memory T cells subsets are also linked to distinct epigenetic events, such as permissive and repressive histone modifications and DNA methylation programs, providing exciting new hypotheses regarding their cellular ancestry. Here, we review recent studies focused on epigenetic programs acquired during effector and memory T-cell differentiation and discuss how these data may shed new light on the developmental path for generating long-lived CD8(+) T-cell memory.

Metabolic programming in chronically stimulated T cells: Lessons from cancer and viral infections

T-cell metabolism is central to the shaping of a successful immune response. However, there are pathological situations where T cells are rendered dysfunctional and incapable of eliminating infected or transformed cells. Here, we review the current knowledge on T-cell metabolism and how persistent antigenic stimulation, in the form of cancer and chronic viral infection, modifies both metabolic and functional pathways in T cells.

Designed Ankyrin Repeat Proteins as Her2 Targeting Domains in Chimeric Antigen Receptor-Engineered T Cells

Chimeric antigen receptor (CAR) engineering is a branch of cancer immunotherapy that equips immune cells to target tumor antigens expressed on the cell surface using antibody-derived single-chain variable fragments (scFvs). However, other antibody mimetics, such as designed ankyrin repeat proteins (DARPins), can also serve as antigen-binding domains in CARs. This study shows that CAR-engineered T (CAR-T) cells utilizing Her2-targeting DARPins G3 and 929 can target human epidermal growth factor receptor 2 (Her2)-overexpressing cancer cells as effectively as CAR-T cells with the scFv 4D5 in vitro, and G3 CAR-T cells can slow or eliminate tumor growth in vivo as effectively as 4D5 CAR-T cells. Some DARPins may offer an attractive alternative to scFv usage in CARs, as they are smaller, thermodynamically stable, poorly immunogenic, and can be generated with different binding properties from DARPin libraries.

Adoptive cell therapy using PD-1+ myeloma-reactive T cells eliminates established myeloma in mice

Background

Adoptive cellular therapy (ACT) with cancer antigen-reactive T cells following lymphodepletive pre-conditioning has emerged as a potentially curative therapy for patients with advanced cancers. However, identification and enrichment of appropriate T cell subsets for cancer eradication remains a major challenge for hematologic cancers.

Methods

PD-1⁺ and PD-1⁻ T cell subsets from myeloma-bearing mice were sorted and analyzed for myeloma reactivity in vitro. In addition, the T cells were activated and expanded in culture and given to syngeneic myeloma-bearing mice as ACT.

Results

Myeloma-reactive T cells were enriched in the PD-1⁺ cell subset. Similar results were also observed in a mouse AML model. PD-1⁺ T cells from myeloma-bearing mice were found to be functional, they could be activated and expanded ex vivo, and they maintained their anti-myeloma reactivity after expansion. Adoptive transfer of ex vivo-expanded PD-1⁺ T cells together with a PD-L1 blocking antibody eliminated established myeloma in Rag-deficient mice. Both CD8 and CD4 T cell subsets were important for eradicating myeloma. Adoptively transferred PD-1⁺ T cells persisted in recipient mice and were able to mount an adaptive memory immune response.

Conclusions

These results demonstrate that PD-1 is a biomarker for functional myeloma-specific T cells, and that activated and expanded PD-1⁺ T cells can be effective as ACT for myeloma. Furthermore, this strategy could be useful for treating other hematologic cancers.

Blimp-1 impairs T cell function via upregulation of TIGIT and PD-1 in patients with acute myeloid leukemia

Background

T cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif (ITIM) domain (TIGIT) and programmed cell death protein 1 (PD-1) are important inhibitory receptors that associate with T cell exhaustion in acute myeloid leukemia (AML). In this study, we aimed to determine the underlying transcriptional mechanisms regulating these inhibitory pathways. Specifically, we investigated the role of transcription factor B lymphocyte-induced maturation protein 1 (Blimp-1) in T cell response and transcriptional regulation of TIGIT and PD-1 in AML.

Methods

Peripheral blood samples collected from patients with AML were used in this study. Blimp-1 expression was examined by flow cytometry. The correlation of Blimp-1 expression to clinical characteristics of AML patients was analyzed. Phenotypic and functional studies of Blimp-1-expressing T cells were performed using flow cytometry-based assays. Luciferase reporter assays and ChIP assays were applied to assess direct binding and transcription activity of Blimp-1. Using siRNA to silence Blimp-1, we further elucidated the regulatory role of Blimp-1 in the TIGIT and PD-1 expression and T cell immune response.

Results

Blimp-1 expression is elevated in T cells from AML patients. Consistent with exhaustion, Blimp-1⁺ T cells upregulate multiple inhibitory receptors including PD-1 and TIGIT. In addition, they are functionally impaired manifested by low cytokine production and decreased cytotoxicity capacity. Importantly, the functional defect is reversed by inhibition of Blimp-1 via siRNA knockdown. Furthermore, Blimp-1 binds to the promoters of PD-1 and TIGIT and positively regulates their expression.

Conclusions

Our study demonstrates an important inhibitory effect of Blimp-1 on T cell response in AML; thus, targeting Blimp-1 and its regulated molecules to improve the immune response may provide effective leukemia therapeutics.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-017-0486-z) contains supplementary material, which is available to authorized users.

Overcoming resistance to targeted therapy with immunotherapy and combination therapy for metastatic melanoma

Resistance to targeted therapy is an ongoing problem for the successful treatment of Stage IV metastatic melanoma. For many patients, the use of targeted therapies, such as BRAF kinase inhibitors, were initially promising yet resistance inevitably occurred. Even after combining BRAF kinase inhibitors with MEK pathway inhibitors to offset re-activation of the MAP kinase pathway, resistance is still documented. Similarly, outcomes with immune checkpoint inhibitors as monotherapy were optimistic for some patients without relapse or progression, yet the majority of patients undergoing monotherapy have progressive disease. Will immunotherapy and combination therapy trials overcome resistance in metastatic melanoma? In an effort to treat resistant disease, new clinical trials evaluating the combination of immunotherapy with other therapies, such as kinase inhibitors, adoptive cell therapy, chimeric CD40 ligand to boost costimulation, or a tumor-specific oncolytic virus enhancing granulocyte macrophage colony-stimulating factor (GM-CSF) expression, are currently underway. Updated studies on the mechanisms of resistance, immune escape and options to reinvigorate immune cells support the continued discovery of new and improved forms of therapy.

Tumor cell-derived lactate induces TAZ-dependent upregulation of PD-L1 through GPR81 in human lung cancer cells

The clinical success of immunotherapy that inhibits the negative immune regulatory pathway programmed cell death protein 1/PD-1 ligand (PD-1/PD-L1) has initiated a new era in the treatment of metastatic cancer. PD-L1 expression is upregulated in many solid tumors including lung cancer and functions predominantly in lactate-enriched tumor microenvironments. Here, we provided evidence for PD-L1 induction in response to lactate stimulation in lung cancer cells. Lactate-induced PD-L1 induction was mediated by its receptor GPR81. The silencing of GPR81 signaling in lung cancer cells resulted in a decrease in PD-L1 protein levels and functional inactivation of PD-L1 promoter activity. In addition, GPR81-mediated upregulation of PD-L1 in glucose-stimulated lung cancer cells that recapitulates the enhanced glycolysis in vivo was dependent on lactate dehydrogenase A (LDHA). We also demonstrated that activation of GPR81 decreases intracellular cAMP levels and inhibits protein kinase A (PKA) activity, leading to activation of the transcriptional coactivator TAZ. Interaction of TAZ with the transcription factor TEAD was essential for TAZ activation of PD-L1 and induction of its expression. Furthermore, we found that lactate-induced activation of PD-L1 in tumor cells led to reduced production of interferon-γ and induction of apoptosis of cocultured Jurkat T-cell leukemia cells. Our findings reveal an unexpected role of lactate in contributing to tumor cell protection from cytotoxic T-cell targeting and establishes a direct connection between tumor cell metabolic reprograming and tumor evasion from the immune response.

Transcriptional and epigenetic regulation of T cell hyporesponsiveness

Naive CD8⁺ T cells differentiate into effector and memory cytolytic T cells (CTLs) during an acute infection. In contrast, in scenarios of persistent antigen stimulation, such as chronic infections and cancer, antigen-specific CTLs show a gradual decrease in effector function, a phenomenon that has been termed CD8⁺ T cell "exhaustion" or "dysfunction." Another hyporesponsive state, termed "anergy", is observed when T cells are activated in the absence of positive costimulatory signals. Among the many negative regulators induced in hyporesponsive T cells are inhibitory cell-surface receptors, such as PD-1, LAG-3, CTLA-4, and TIM-3; "checkpoint blockade" therapies that involve treatment of patients with cancer with blocking antibodies to those receptors show considerable promise in the clinic because the blocking antibodies can mitigate hyporesponsiveness and promote tumor rejection. In this review, we describe recent advances in our molecular understanding of these hyporesponsive states. We review evidence for the involvement of diverse transcription factors, metabolic programs, and chromatin accessibility changes in hyporesponsive T cells, and we discuss how checkpoint blockade therapies affect the molecular program of CD8⁺ T cell exhaustion.

Cancer immunotherapy by targeting immune checkpoints: mechanism of T cell dysfunction in cancer immunity and new therapeutic targets

Immune checkpoints or coinhibitory receptors, such as cytotoxic T lymphocyte antigen (CTLA)-4 and programmed death (PD)-1, play important roles in regulating T cell responses, and they were proven to be effective targets in treating cancer. In chronic viral infections and cancer, T cells are chronically exposed to persistent antigen stimulation. This is often associated with deterioration of T cell function with constitutive activation of immune checkpoints, a state called ‘exhaustion’, which is commonly associated with inefficient control of tumors and persistent viral infections. Immune checkpoint blockade can reinvigorate dysfunctional/exhausted T cells by restoring immunity to eliminate cancer or virus-infected cells. These immune checkpoint blocking antibodies have moved immunotherapy into a new era, and they represent paradigm-shifting therapeutic strategies for cancer treatment. A clearer understanding of the regulatory roles of these receptors and elucidation of the mechanisms of T cell dysfunction will provide more insights for rational design and development of cancer therapies that target immune checkpoints. This article reviews recent advance(s) in molecular understanding of T cell dysfunction in tumor microenvironments. In addition, we also discuss new immune checkpoint targets in cancer therapy.

Epigenetic Strategies to Boost Cancer Immunotherapies

Recently, immunotherapeutic approaches have shown impressive responses in a subset of cancer patients. However, the rate of success is low and a large percentage of treated patients do not experience clinical benefits. Therefore, additional strategies are needed to improve responses and select responsive patients. Emerging data suggest that epigenetic drugs can improve the responses to immunotherapy. Understanding the mechanisms of resistance to immunotherapy and the epigenetic events that take place during immune evasion is critical to providing a rational combined use of immunotherapies and epigenetic drugs. This review focuses in the epigenetic mechanisms involved in the responses to immunotherapy and how current drugs that target epigenetic regulators impact on them.

Chimeric PD-1:28 Receptor Upgrades Low-Avidity T cells and Restores Effector Function of Tumor-Infiltrating Lymphocytes for Adoptive Cell Therapy

Inherent intermediate- to low-affinity T-cell receptors (TCR) that develop during the natural course of immune responses may not allow sufficient activation for tumor elimination, making the majority of T cells suboptimal for adoptive T-cell therapy (ATT). TCR affinity enhancement has been implemented to provide stronger T-cell activity but carries the risk of creating undesired cross-reactivity leading to potential serious adverse effects in clinical application. We demonstrate here that engineering of low-avidity T cells recognizing a naturally processed and presented tumor-associated antigen with a chimeric PD-1:28 receptor increases effector function to levels seen with high-avidity T cells of identical specificity. Upgrading the function of low-avidity T cells without changing the TCR affinity will allow a large arsenal of low-avidity T cells previously thought to be therapeutically inefficient to be considered for ATT. PD-1:28 engineering reinstated Th1 function in tumor-infiltrating lymphocytes that had been functionally disabled in the human renal cell carcinoma environment without unleashing undesired Th2 cytokines or IL10. Involved mechanisms may be correlated to restoration of ERK and AKT signaling pathways. In mouse tumor models of ATT, PD-1:28 engineering enabled low-avidity T cells to proliferate stronger and prevented PD-L1 upregulation and Th2 polarization in the tumor milieu. Engineered T cells combined with checkpoint blockade secreted significantly more IFNγ compared with T cells without PD-1:28, suggesting a beneficial combination with checkpoint blockade therapy or other therapeutic strategies. Altogether, the supportive effects of PD-1:28 engineering on T-cell function make it an attractive tool for ATT. Cancer Res; 77(13); 3577-90. ©2017 AACR.

In vivo photolabeling of tumor-infiltrating cells reveals highly regulated egress of T-cell subsets from tumors

Immune therapy is rapidly gaining prominence in the clinic as a major weapon against cancer. Whereas much attention has been focused on the infiltration of tumors by immune cells, the subsequent fate of these infiltrates remains largely unexplored. We therefore established a photoconversion-based model that allowed us to label tumor-infiltrating immune cells and follow their migration. Using this system, we identified a population of tumor-experienced cells that emigrate from primary tumors to draining lymph nodes via afferent lymphatic vessels. Although the majority of tumor-infiltrating cells were myeloid, T cells made up the largest population of tumor-egressing leukocytes. Strikingly, the subset composition of tumor-egressing T cells was greatly skewed compared with those that had infiltrated the tumor and those resident in the draining lymph node. Some T-cell subsets such as CD8⁺ T cells emigrated more readily; others including CD4^-CD8^- T cells were preferentially retained, suggesting that specific mechanisms guide immune cell egress from tumors. Furthermore, tumor-egressing T cells were more activated and displayed enhanced effector function in comparison with their lymph node counterparts. Finally, we demonstrated that tumor-infiltrating T cells migrate to distant secondary tumors and draining lymph nodes, highlighting a mechanism whereby tumor-experienced effector T cells may mediate antitumor immunity at metastatic sites. Thus, our results provide insights into migration and function of tumor-infiltrating immune cells and the role of these cells in tumor immunity outside of primary tumor deposits.

Mechanisms of Immune Tolerance in Leukemia and Lymphoma

The mechanisms through which immune responses are generated against solid cancers are well characterized and knowledge of the immune evasion pathways exploited by these malignancies has grown considerably. However, for hematological cancers, which develop and disseminate quite differently than solid tumors, the pathways that regulate immune activation or tolerance are less clear. Growing evidence suggests that, while numerous immune escape pathways are shared between hematological and solid malignancies, several unique pathways are exploited by leukemia and lymphoma. Below we discuss immune evasion mechanisms in leukemia and lymphoma, highlighting key differences from solid tumors. A more complete characterization of the mechanisms of immune tolerance in hematological malignancies is critical to inform the development of future immunotherapeutic approaches.

Tumor Interferon Signaling Regulates a Multigenic Resistance Program to Immune Checkpoint Blockade

Therapeutic blocking of the PD1 pathway results in significant tumor responses, but resistance is common. We demonstrate that prolonged interferon signaling orchestrates PDL1-dependent and PDL1-independent resistance to immune checkpoint blockade (ICB) and to combinations such as radiation plus anti-CTLA4. Persistent type II interferon signaling allows tumors to acquire STAT1-related epigenomic changes and augments expression of interferon-stimulated genes and ligands for multiple T cell inhibitory receptors. Both type I and II interferons maintain this resistance program. Crippling the program genetically or pharmacologically interferes with multiple inhibitory pathways and expands distinct T cell populations with improved function despite expressing markers of severe exhaustion. Consequently, tumors resistant to multi-agent ICB are rendered responsive to ICB monotherapy. Finally, we observe that biomarkers for interferon-driven resistance associate with clinical progression after anti-PD1 therapy. Thus, the duration of tumor interferon signaling augments adaptive resistance and inhibition of the interferon response bypasses requirements for combinatorial ICB therapies.

Amplification of N-Myc is associated with a T-cell-poor microenvironment in metastatic neuroblastoma restraining interferon pathway activity and chemokine expression

Immune checkpoint inhibitors have significantly improved the treatment of several cancers. T-cell infiltration and the number of neoantigens caused by tumor-specific mutations are correlated to favorable responses in cancers with a high mutation load. Accordingly, checkpoint immunotherapy is thought to be less effective in tumors with low mutation frequencies such as neuroblastoma, a neuroendocrine tumor of early childhood with poor outcome of the high-risk disease group. However, spontaneous regressions and paraneoplastic syndromes seen in neuroblastoma patients suggest substantial immunogenicity. Using an integrative transcriptomic approach, we investigated the molecular characteristics of T-cell infiltration in primary neuroblastomas as an indicator of pre-existing immune responses and potential responsiveness to checkpoint inhibition. Here, we report that a T-cell-poor microenvironment in primary metastatic neuroblastomas is associated with genomic amplification of the MYCN (N-Myc) proto-oncogene. These tumors exhibited lower interferon pathway activity and chemokine expression in line with reduced immune cell infiltration. Importantly, we identified a global role for N-Myc in the suppression of interferon and pro-inflammatory pathways in human and murine neuroblastoma cell lines. N-Myc depletion potently enhanced targeted interferon pathway activation by a small molecule agonist of the cGAS-STING innate immune pathway. This promoted chemokine expression including Cxcl10 and T-cell recruitment in microfluidics migration assays. Hence, our data suggest N-Myc inhibition plus targeted IFN activation as adjuvant strategy to enforce cytotoxic T-cell recruitment in MYCN-amplified neuroblastomas.

Proliferation of PD-1+ CD8 T cells in peripheral blood after PD-1-targeted therapy in lung cancer patients

Exhausted T cells in chronic infections and cancer have sustained expression of the inhibitory receptor programmed cell death 1 (PD-1). Therapies that block the PD-1 pathway have shown promising clinical results in a significant number of advanced-stage cancer patients. Nonetheless, a better understanding of the immunological responses induced by PD-1 blockade in cancer patients is lacking. Identification of predictive biomarkers is a priority in the field, but whether peripheral blood analysis can provide biomarkers to monitor or predict patients' responses to treatment remains to be resolved. In this study, we analyzed longitudinal blood samples from advanced stage non-small cell lung cancer (NSCLC) patients (n = 29) receiving PD-1-targeted therapies. We detected an increase in Ki-67+ PD-1+ CD8 T cells following therapy in ∼70% of patients, and most responses were induced after the first or second treatment cycle. This T-cell activation was not indiscriminate because we observed only minimal effects on EBV-specific CD8 T cells, suggesting that responding cells may be tumor specific. These proliferating CD8 T cells had an effector-like phenotype (HLA-DR⁺, CD38⁺, Bcl-2^lo), expressed costimulatory molecules (CD28, CD27, ICOS), and had high levels of PD-1 and coexpression of CTLA-4. We found that 70% of patients with disease progression had either a delayed or absent PD-1+ CD8 T-cell response, whereas 80% of patients with clinical benefit exhibited PD-1+ CD8 T-cell responses within 4 wk of treatment initiation. Our results suggest that peripheral blood analysis may provide valuable insights into NSCLC patients' responses to PD-1-targeted therapies.

Mitochondrial Control and Guidance of Cellular Activities of T Cells

Immune cells protect us against infection and cancer cells, as well as functioning during healing processes to support tissue repairing and regeneration. These behaviors require that upon stimulation from immune activation the appropriate subsets of immune cells are generated. In addition to activation-induced signaling cascades, metabolic reprogramming (profound changes in metabolic pathways) also provides a novel form of regulation to control the formation of desirable immune responses. Immune cells encounter various nutrient compositions by circulating in bloodstream and infiltrating into peripheral tissues; therefore, proper engagement of metabolic pathways is critical to fulfill the metabolic demands of immune cells. Metabolic pathways are tightly regulated mainly via mitochondrial dynamics and the activities of the tricarboxylic acid cycle and the electron transport chain. In this review, we will discuss how metabolic reprogramming influences activation, effector functions, and lineage polarization in T cells, with a particular focus on mitochondria-regulated metabolic checkpoints. Additionally, we will further explore how in various diseases deregulation and manipulation of mitochondrial regulation can occur and be exploited. Furthermore, we will discuss how this knowledge can facilitate the design of immunotherapies.

Immune checkpoints and their inhibition in cancer and infectious diseases

The development of chronic infections and cancer is facilitated by a variety of immune subversion mechanisms, such as the production of anti-inflammatory cytokines, induction of regulatory T (Treg) cells, and expression of immune checkpoint molecules, including CTLA-4 and PD-1. CTLA-4, expressed on T cells, interacts with CD80/CD86, thereby limiting T-cell activation and leading to anergy. PD-1 is predominantly expressed on T cells and its interaction with PD-L1 and PD-L2 expressed on antigen-presenting cells (APCs) and tumors sends a negative signal to T cells, which can lead to T-cell exhaustion. Given their role in suppressing effector T-cell responses, immune checkpoints are being targeted for the treatment of cancer. Indeed, antibodies binding to CTLA-4, PD-1, or PD-L1 have shown remarkable efficacy, especially in combination therapies, for a number of cancers and have been licensed for the treatment of melanoma, nonsmall cell lung cancer, and renal and bladder cancers. Moreover, immune checkpoint inhibitors have been shown to enhance ex vivo effector T-cell responses from patients with chronic viral, bacterial, or parasitic infection, including HIV, tuberculosis, and malaria. Although the data from clinical trials in infectious diseases are still sparse, these inhibitors have great potential for treating chronic infections, especially when combined with therapeutic vaccines.

T-cell invigoration to tumour burden ratio associated with anti-PD-1 response

Despite the success of monotherapies based on blockade of programmed cell death 1 (PD-1) in human melanoma, most patients do not experience durable clinical benefit. Pre-existing T-cell infiltration and/or the presence of PD-L1 in tumours may be used as indicators of clinical response; however, blood-based profiling to understand the mechanisms of PD-1 blockade has not been widely explored. Here we use immune profiling of peripheral blood from patients with stage IV melanoma before and after treatment with the PD-1-targeting antibody pembrolizumab and identify pharmacodynamic changes in circulating exhausted-phenotype CD8 T cells (T_ex cells). Most of the patients demonstrated an immunological response to pembrolizumab. Clinical failure in many patients was not solely due to an inability to induce immune reinvigoration, but rather resulted from an imbalance between T-cell reinvigoration and tumour burden. The magnitude of reinvigoration of circulating T_ex cells determined in relation to pretreatment tumour burden correlated with clinical response. By focused profiling of a mechanistically relevant circulating T-cell subpopulation calibrated to pretreatment disease burden, we identify a clinically accessible potential on-treatment predictor of response to PD-1 blockade.

Hurdles to the Development of Effective HBV Immunotherapies and HCV Vaccines

Chronic infections with HBV and HCV continue to be major public health problems, with hundreds of millions of people infected worldwide; this is despite the availability of both an effective prophylactic HBV vaccine for more than 3 decades and potent direct antivirals for HBV and, more recently, HCV infection. Consequently, development of HBV immunotherapies and prophylactic HCV vaccines remains extremely urgent, but limited funding and significant gaps in our understanding of the correlates of immune protection pose serious hurdles for the development of novel immune-based interventions. Here we discuss immunological questions related to HBV and HCV, some shared and some pertinent to only 1 of the viruses, that should be addressed for the rational design of HBV immunotherapies and HCV vaccines.

CRISPR/Cas9-mediated PD-1 disruption enhances anti-tumor efficacy of human chimeric antigen receptor T cells

Immunotherapies with chimeric antigen receptor (CAR) T cells and checkpoint inhibitors (including antibodies that antagonize programmed cell death protein 1 [PD-1]) have both opened new avenues for cancer treatment, but the clinical potential of combined disruption of inhibitory checkpoints and CAR T cell therapy remains incompletely explored. Here we show that programmed death ligand 1 (PD-L1) expression on tumor cells can render human CAR T cells (anti-CD19 4-1BBζ) hypo-functional, resulting in impaired tumor clearance in a sub-cutaneous xenograft model. To overcome this suppressed anti-tumor response, we developed a protocol for combined Cas9 ribonucleoprotein (Cas9 RNP)-mediated gene editing and lentiviral transduction to generate PD-1 deficient anti-CD19 CAR T cells. Pdcd1 (PD-1) disruption augmented CAR T cell mediated killing of tumor cells in vitro and enhanced clearance of PD-L1+ tumor xenografts in vivo. This study demonstrates improved therapeutic efficacy of Cas9-edited CAR T cells and highlights the potential of precision genome engineering to enhance next-generation cell therapies.