Tumour-specific CD4 T cells eradicate melanoma via indirect recognition of tumour-derived antigen

Antimelanoma Effects of Alchemilla vulgaris: A Comprehensive In Vitro and In Vivo Study

Due to the rich ethnobotanical and growing evidence-based medicine records, the Alchemillae herba, i.e., the upper parts of the Lady's mantle (Alchemilla vulgaris L.), was used for the assessment of antimelanoma activity. The ethanolic extract of A. vulgaris strongly suppressed the viability of B16F1, B16F10, 518A2, and Fem-X cell lines. In contrast to the in vitro study, where the B16F1 cells were more sensitive to the treatment than the more aggressive counterpart B16F10, the results obtained in vivo using the corresponding syngeneic murine model were quite the opposite. The higher sensitivity of B16F10 tumors in vivo may be attributed to a more complex response to the extract compared to one triggered in vitro. In addition, the strong immunosuppressive microenvironment in the B16F1 model is impaired by the treatment, as evidenced by enhanced antigen-presenting potential of dendritic cells, influx and activity of CD4+ T and CD8+ T lymphocytes, decreased presence of T regulatory lymphocytes, and attenuation of anti-inflammatory cytokine production. All these effects are supported by the absence of systemic toxicity. A. vulgaris extract treatment results in a sustained and enhanced ability to reduce melanoma growth, followed by the restoration of innate and adopted antitumor immunity without affecting the overall physiology of the host.

CD4+ T cell immunity against cutaneous melanoma encompasses multifaceted MHC II-dependent responses

Whereas CD4+ T cells conventionally mediate antitumor immunity by providing help to CD8+ T cells, recent clinical studies have implied an important role for cytotoxic CD4+ T cells in cancer immunity. Using an orthotopic melanoma model, we provide a detailed account of antitumoral CD4+ T cell responses and their regulation by major histocompatibility complex class II (MHC II) in the skin. Intravital imaging revealed prominent interactions of CD4+ T cells with tumor debris-laden MHC II+ host antigen-presenting cells that accumulated around tumor cell nests, although direct recognition of MHC II+ melanoma cells alone could also promote CD4+ T cell control. CD4+ T cells stably suppressed or eradicated tumors even in the absence of other lymphocytes by using tumor necrosis factor-α and Fas ligand (FasL) but not perforin-mediated cytotoxicity. Interferon-γ was critical for protection, acting both directly on melanoma cells and via induction of nitric oxide synthase in myeloid cells. Our results illustrate multifaceted and context-specific aspects of MHC II-dependent CD4+ T cell immunity against cutaneous melanoma, emphasizing modulation of this axis as a potential avenue for immunotherapies.

MHCII restriction demonstrates B cells have very limited capacity to activate tumour-specific CD4+ T cells in vivo

There has been growing interest in the role of B cells in antitumour immunity and potential use in adoptive cellular therapies. To date, the success of such therapies is limited. The intrinsic capacity of B cells to specifically activate tumour-specific CD4+ T cells in vivo via TCR-dependent interactions remains poorly defined. We have developed an in vivo tumour model that utilizes MHCII I-E restriction which limits antigen presentation to tumour-specific CD4 T cells to either tumour-specific B cells or host myeloid antigen presenting cells (APCs) in lymphopenic RAG-/-mice. We have previously shown that these naive tumour-specific CD4+ T cells can successfully eradicate established tumours in this model when activated by host APCs. When naïve tumour-specific B cells are the only source of I-E+ APC, very limited proliferation of naïve CD4+ T cells is observed, whereas host I-E+ APCs are potent T cell activators. B cells pre-activated with an anti-CD40 agonistic antibody in vivo support increased T cell proliferation, although far less than host APCs. CD4+ T cells that have already differentiated to an effector/central memory phenotype proliferate more readily in response to naïve B cells, although still 100-fold less than in response to host APCs. This study demonstrates that even in a significantly lymphopenic environment, myeloid APCs are the dominant primary activators of tumour-specific T cells, in contrast to the very limited capacity of tumour-specific B cells. This suggests that future anti-tumour therapies that incorporate activated B cells should also include mechanisms that activate host APCs.

Methionine consumption by cancer cells drives a progressive upregulation of PD-1 expression in CD4 T cells

Programmed cell death protein 1 (PD-1), expressed on tumor-infiltrating T cells, is a T cell exhaustion marker. The mechanisms underlying PD-1 upregulation in CD4 T cells remain unknown. Here we develop nutrient-deprived media and a conditional knockout female mouse model to study the mechanism underlying PD-1 upregulation. Reduced methionine increases PD-1 expression on CD4 T cells. The genetic ablation of SLC43A2 in cancer cells restores methionine metabolism in CD4 T cells, increasing the intracellular levels of S-adenosylmethionine and yielding H3K79me2. Reduced H3K79me2 due to methionine deprivation downregulates AMPK, upregulates PD-1 expression and impairs antitumor immunity in CD4 T cells. Methionine supplementation restores H3K79 methylation and AMPK expression, lowering PD-1 levels. AMPK-deficient CD4 T cells exhibit increased endoplasmic reticulum stress and Xbp1s transcript levels. Our results demonstrate that AMPK is a methionine-dependent regulator of the epigenetic control of PD-1 expression in CD4 T cells, a metabolic checkpoint for CD4 T cell exhaustion.

Molecular, metabolic and functional CD4 T cell paralysis impedes tumor control

CD4 T cells are important effectors of anti-tumor immunity, yet the regulation of CD4 tumor-specific T (T TS ) cells during cancer development is still unclear. We demonstrate that CD4 T TS cells are initially primed in the tumor draining lymph node and begin to divide following tumor initiation. Distinct from CD8 T TS cells and previously defined exhaustion programs, CD4 T TS cell proliferation is rapidly frozen in place and differentiation stunted by a functional interplay of T regulatory cells and both intrinsic and extrinsic CTLA4 signaling. Together these mechanisms paralyze CD4 T TS cell differentiation, redirecting metabolic and cytokine production circuits, and reducing CD4 T TS cell accumulation in the tumor. Paralysis is actively maintained throughout cancer progression and CD4 T TS cells rapidly resume proliferation and functional differentiation when both suppressive reactions are alleviated. Strikingly, Treg depletion alone reciprocally induced CD4 T TS cells to themselves become tumor-specific Tregs, whereas CTLA4 blockade alone failed to promote T helper differentiation. Overcoming their paralysis established long-term tumor control, demonstrating a novel immune evasion mechanism that specifically cripples CD4 T TS cells to favor tumor progression.

HDAC inhibitor HPTA initiates anti-tumor response by CXCL9/10-recruited CXCR3+CD4+T cells against PAHs carcinogenicity

Polycyclic aromatic hydrocarbons (PAHs) exposure in food is closely associated with the occurrence and development of breast cancer, which may attribute to altered immunotoxicity and immune regulation. Currently, cancer immunotherapy aims to promote tumor-specific T cell responses, especially CD4⁺T helper cells (Th) for anti-tumor immunity. The histone deacetylase inhibitors (HDACis) are found to exert an anti-tumor effect by reshaping the tumor immune microenvironment, but the immune regulatory mechanism of HDACis in PAHs-induced breast tumor remains elusive. Here, using established breast cancer models induced by 7,12-dimethylbenz[a]anthracene (DMBA), a potent carcinogenic agent of PAH, the novel HDACi, 2-hexyl-4-pentylene acid (HPTA) exhibited anti-tumor effect by activating T lymphocytes immune function. HPTA recruited CXCR3⁺CD4⁺T cells into chemokines CXCL9/10-enriched tumor sites, the increased secretion of CXCL9/10 was regulated by the NF-κB-mediated pathway. Furthermore, HPTA promoted Th1 differentiation and assisted cytotoxic CD8⁺T cells in the elimination of breast cancer cells. These findings support the proposition of HPTA as a potential therapeutic in the treatment of PAHs-induced carcinogenicity.

Tailoring biomaterials and applications targeting tumor-associated macrophages in cancers

Tumor-associated macrophages (TAMs) play a critical role in supporting tumor growth and metastasis, taming host immunosurveillance, and augmenting therapeutic resistance. As the current treatment paradigms for cancers are generally insufficient to exterminate cancer cells, anti-cancer therapeutic strategies targeting TAMs have been developed. Since TAMs are highly heterogeneous and the pro-tumoral functions are mediated by phenotypes with canonical surface markers, TAM-associated materials exert anti-tumor functions by either inhibiting polarization to the pro-tumoral phenotype or decreasing the abundance of TAMs. Furthermore, TAMs in association with the immunosuppressive tumor microenvironment (TME) and tumor immunity have been extensively exploited in mounting evidence, and could act as carriers or accessory cells of anti-tumor biomaterials. Recently, a variety of TAM-based materials with the capacity to target and eliminate cancer cells have been increasingly developed for basic research and clinical practice. As various TAM-based biomaterials, including antibodies, nanoparticles, RNAs, etc., have been shown to have potential anti-tumor effects reversing the TME, in this review, we systematically summarize the current studies to fully interpret the specific properties and various effects of TAM-related biomaterials, highlighting the potential clinical applications of targeting the crosstalk among TAMs, tumor cells, and immune cells in anti-cancer therapy.

A phase I/II escalation trial design T-RAD: Treatment of metastatic lung cancer with mRNA-engineered T cells expressing a T cell receptor targeting human telomerase reverse transcriptase (hTERT)

Background

Adoptive cellular therapy (ACT) with genetically modified T cells aims to redirect T cells against resistant cancers through introduction of a T cell receptor (TCR). The Radium-4 TCR was isolated from a responding patient in a cancer vaccination study and recognizes the enzymatic component of human Telomerase Reverse Transcriptase (hTERT) presented on MHC class II (HLA-DP04). hTERT is a constitutively overexpressed tumor-associated antigen present in most human cancers, including non-small-cell lung cancer (NSCLC), which is the second most common type of cancer worldwide. Treatment alternatives for relapsing NSCLC are limited and survival is poor. To improve patient outcome we designed a TCR-based ACT study targeting hTERT.

Methods

T-RAD is a phase I/II study to evaluate the safety and efficacy of Radium-4 mRNA electroporated autologous T cells in the treatment of metastatic NSCLC with no other treatment option. Transient TCR expression is applied for safety considerations. Participants receive two intravenous injections with escalating doses of redirected T cells weekly for 6 consecutive weeks. Primary objectives are safety and tolerability. Secondary objectives include progression-free survival, time to progression, overall survival, patient reported outcomes and overall radiological response.

Discussion

Treatment for metastatic NSCLC is scarce and new personalized treatment options are in high demand. hTERT is a tumor target applicable to numerous cancer types. This proof-of-concept study will explore for the first time the safety and efficacy of TCR mRNA electroporated autologous T cells targeting hTERT. The T-RAD study will thus evaluate an attractive candidate for future immunotherapy of solid tumors.

Systemic CD4 Immunity and PD-L1/PD-1 Blockade Immunotherapy

PD-L1/PD-1 blockade immunotherapy has changed the therapeutic approaches for the treatment of many cancers. Nevertheless, the mechanisms underlying its efficacy or treatment failure are still unclear. Proficient systemic immunity seems to be a prerequisite for efficacy, as recently shown in patients and in mouse models. It is widely accepted that expansion of anti-tumor CD8 T cell populations is principally responsible for anti-tumor responses. In contrast, the role of CD4 T cells has been less studied. Here we review and discuss the evidence supporting the contribution of CD4 T cells to anti-tumor immunity, especially recent advances linking CD4 T cell subsets to efficacious PD-L1/PD-1 blockade immunotherapy. We also discuss the role of CD4 T cell memory subsets present in peripheral blood before the start of immunotherapies, and their utility as predictors of response.

Durable Responses to Anti-PD1 and Anti-CTLA4 in a Preclinical Model of Melanoma Displaying Key Immunotherapy Response Biomarkers

Simple Summary

Immunotherapy has improved the outcomes of patients with advanced melanoma, although many patients will progress while on treatment. Preclinical animal models provide valuable insights into immunotherapy response or resistance and can be used to test novel treatment combinations. The development of animal cancer models rarely involves the systematic analysis and inclusion of predictive biomarkers of immunotherapy response. This study describes a biomarker-driven workflow to generate a transplantable mouse melanoma model responsive to anti-PD1 and anti-CTLA4 immunotherapy. This model recapitulates human immunotherapy-responding tumor phenotypes and provides unique insights into the discrete mechanisms underlying the durability of response to immune checkpoint inhibitors.

Abstract

Immunotherapy has transformed the management of patients with advanced melanoma, with five-year overall survival rates reaching 52% for combination immunotherapies blocking the cytotoxic T-lymphocyte-associated antigen-4 (CTLA4) and programmed cell death-1 (PD1) immune axes. Yet, our understanding of local and systemic determinants of immunotherapy response and resistance is restrained by the paucity of preclinical models, particularly those for anti-PD1 monotherapy. We have therefore generated a novel murine model of melanoma by integrating key immunotherapy response biomarkers into the model development workflow. The resulting YUMM3.3^UVRc34 (BrafV600E; Cdkn2a–/–) model demonstrated high mutation burden and response to interferon (IFN)γ, including induced expression of antigen-presenting molecule MHC-I and the principal PD1 ligand PD-L1, consistent with phenotypes of human melanoma biopsies from patients subsequently responding to anti-PD1 monotherapy. Syngeneic immunosufficient mice bearing YUMM3.3^UVRc34 tumors demonstrated durable responses to anti-PD1, anti-CTLA4, or combined treatment. Immunotherapy responses were associated with early on-treatment changes in the tumor microenvironment and circulating T-cell subsets, and systemic immunological memory underlying protection from tumor recurrence. Local and systemic immunological landscapes associated with immunotherapy response in the YUMM3.3^UVRc34 melanoma model recapitulate immunotherapy responses observed in melanoma patients and identify discrete immunological mechanisms underlying the durability of responses to anti-PD1 and anti-CTLA4 treatments.

Core immune cell infiltration signatures identify molecular subtypes and promote precise checkpoint immunotherapy in cutaneous melanoma

Yutao Wang, China Medical University, ChinaThe tumor microenvironment (TME) has been shown to impact the prognosis of tumors in patients including cutaneous melanoma (CM); however, not all components of TME are important. Given the aforementioned situation, the functional immune cell contents correlated with CM patient prognosis are needed to optimize present predictive models and reflect the overall situation of TME. We developed a novel risk score named core tumor-infiltrating immune cell score (cTICscore), which showed certain advantages over existing biomarkers or TME-related signatures in predicting the prognosis of CM patients. Furthermore, we explored a new gene signature named cTILscore−related module gene score (cTMGs), based on four identified TME-associated genes (GCH1, GZMA, PSMB8, and PLAAT4) showing a close correlation with the cTICscore, which was generated by weighted gene co-expression network analysis and least absolute shrinkage and selection operator analysis to facilitate clinical application. Patients with low cTMGs had significantly better overall survival (OS, P = 0.002,< 0.001, = 0.002, and = 0.03, respectively) in the training and validating CM datasets. In addition, the area under the curve values used to predict the immune response in four CM cohorts were 0.723, 0.723, 0.754, and 0.792, respectively, and that in one gastric cohort was 0.764. Therefore, the four-gene signature, based on cTICscore, might improve prognostic information, serving as a predictive tool for CM patients receiving immunotherapy.cutaneous melanoma, tumor microenvironment, prognosis, immunotherapy, cTICscore

Comprehensive Gene Expression Analysis to Identify Differences and Similarities between Sex- and Stage-Stratified Melanoma Samples

Overall lower incidence and better prognosis are observed in female melanoma patients compared to males. As sex and stage differences in the context of melanoma gene expression are understudied, we aim to highlight them through statistical analysis of melanoma gene expression datasets. Data from seven online datasets, including normal skin, commonly acquired nevi, and melanomas, were collected and analyzed. Sex/stage-related differences were assessed using statistical analyses on survival, gene expression, and its variability. Significantly better overall survival in females was observed in stage I, II but not in stage III. Gene expression variability was significantly different between stages and sexes. Specifically, we observed a significantly lower variability in genes expressed in normal skin and nevi in females compared to males, as well as in female stage I, II melanomas. However, in stage III, variability was lower in males. Similarly, class comparison showed that the gene expression differences between sexes are most notable in non-melanoma followed by early-stage-melanoma samples. Sexual dimorphism is an important aspect to consider for a holistic understanding of early-stage melanomas, not only from the tumor characteristics but also from the gene expression points of view.

Roles of CD4+ T cells as mediators of antitumor immunity

It has been well established that CD8+ T cells serve as effector cells of the adaptive immune response against tumors, whereas CD4+ T cells either help or suppress the generation of CD8+ cytotoxic T cells. However, in several experimental models as well as in cancer patients, it has been shown that CD4+ T cells can also mediate antitumor immunity either directly by killing tumor cells or indirectly by activating innate immune cells or by reducing tumor angiogenesis. In this review, we discuss the growing evidence of this underappreciated role of CD4+ T cells as mediators of antitumor immunity.

MHC Class I Deficiency in Solid Tumors and Therapeutic Strategies to Overcome It

It is now well accepted that the immune system can control cancer growth. However, tumors escape immune-mediated control through multiple mechanisms and the downregulation or loss of major histocompatibility class (MHC)-I molecules is a common immune escape mechanism in many cancers. MHC-I molecules present antigenic peptides to cytotoxic T cells, and MHC-I loss can render tumor cells invisible to the immune system. In this review, we examine the dysregulation of MHC-I expression in cancer, explore the nature of MHC-I-bound antigenic peptides recognized by immune cells, and discuss therapeutic strategies that can be used to overcome MHC-I deficiency in solid tumors, with a focus on the role of natural killer (NK) cells and CD4 T cells.

IFN-γ Critically Enables the Intratumoural Infiltration of CXCR3+ CD8+ T Cells to Drive Squamous Cell Carcinoma Regression

Simple Summary

Cutaneous squamous cell carcinoma (SCC) is prevalent in aged individuals and individuals with compromised or weakened immune systems, indicating a close association between immune function and SCC control. The aim of our study was to uncover the identity of key immune subsets that mediate SCC control, and to elucidate the mechanistic role of the proinflammatory cytokine Interferon-gamma in this process. We established a SCC regressor model, which we used to determine that: (1) CD8⁺ T cells, not CD4⁺ T cells or NK cells, are essential for SCC regression; (2) the neutralisation of Interferon-gamma prevents CD8⁺ T cell infiltration and SCC regression; (3) CD8⁺ T cell migration into SCC critically depends upon Interferon-gamma-induced chemokine expression. Thus, our model can be used to understand the key immune mechanisms involved in SCC regression, which will support targeted investigations into the integrity of these mechanisms in patients with progressive disease.

Abstract

Ultraviolet (UV) radiation-induced tumours carry a high mutational load, are highly immunogenic, and often fail to grow when transplanted into normal, syngeneic mice. The aim of this study was to investigate factors critical for the immune-mediated rejection of cutaneous squamous cell carcinoma (SCC). In our rejection model, transplanted SCC establish and grow in mice immunosuppressed with tacrolimus. When tacrolimus is withdrawn, established SCC tumours subsequently undergo immune-mediated tumour rejection. Through the depletion of individual immune subsets at the time of tacrolimus withdrawal, we established a critical role for CD8⁺ T cells, but not CD4⁺ T cells, γδ T cells, or NK cells, in driving the regression of SCC. Regression was critically dependent on IFN-γ, although IFN-γ was not directly cytotoxic to SCC cells. IFN-γ-neutralisation abrogated SCC regression, significantly reduced CD8⁺ T cell-infiltration into SCC, and significantly impaired the secretion of CXCL9, CXCL10 and CCL5 within the tumour microenvironment. A strong positive correlation was revealed between CXCL10 expression and CD8⁺ T cell abundance in tumours. Indeed, blockade of the CXCL10 receptor CXCR3 at the time of tacrolimus withdrawal prevented CD8⁺ T cell infiltration and the regression of SCC. Chimeric models revealed an important role for immune cells as producers of IFN-γ, but not as recipients of IFN-γ signals via the IFN-γ receptor. Together, these findings suggest a key role for IFN-γ in driving the expression of chemokines within the tumour environment essential for the destruction of established SCC by CD8⁺ T cells.

Interleukin-33 modulates immune responses in cutaneous melanoma in a context-specific way

Controversial roles of interleukin-33 (IL-33) have been reported in melanoma from animal studies. We aimed to investigate the role of IL-33 in human cutaneous melanoma. RNA-seq data of 471 cases of cutaneous melanoma were retrieved from The Cancer Genome Atlas. The tumor microenvironment (TME) was deconstructed by the xCell algorithm using RNA-seq data. We evaluated the prognostic value of IL-33 and the relationship between IL-33 and immune components in TME. We also inferred the potential cellular sources of IL-33. All the analyses were conducted separately in three sub-cohorts, which are based on the biopsy sites of samples: primary melanoma; lymph node (LN) metastases; other metastases, including metastases to skin/soft tissue, or visceral sites. In the two metastasis sub-cohorts, IL-33 is associated with better prognosis and more active immune responses in the tumor. However, IL-33 is not a prognostic factor in the primary melanoma sub-cohort. Furthermore, we found that IL-33 is mainly derived from stromal cells in the metastasis sub-cohorts, and from epithelial cells/keratinocytes in the primary melanoma sub-cohort. These findings provide evidence for the context-specific anti-tumor effects of IL-33 in melanoma. And the distinct effects of IL-33 may be determined by the cellular sources of IL-33.

Systemic CD4 Immunity as a Key Contributor to PD-L1/PD-1 Blockade Immunotherapy Efficacy

PD-L1/PD-1 blockade immunotherapy has significantly improved treatment outcome for several cancer types compared to conventional cytotoxic therapies. However, the specific molecular and cellular mechanisms behind its efficacy are currently unclear. There is increasing evidence in murine models and in patients that unveil the key importance of systemic immunity to achieve clinical responses under several types of immunotherapy. Indeed, PD-L1/PD-1 blockade induces the expansion of systemic CD8+ PD-1+ T cell subpopulations which might be responsible for direct anti-tumor responses. However, the role of CD4+ T cells in PD-L1/PD-1 blockade-induced anti-tumor responses has been less documented. In this review we focus on the experimental data supporting the “often suspected” indispensable helper function of CD4 T cells towards CD8 effector anti-tumor responses in cancer; and particularly, we highlight the recently published studies uncovering the key contribution of systemic CD4 T cells to clinical efficacy in PD-L1/PD-1 blockade therapies. We conclude and propose that the presence of specific CD4 T cell memory subsets in peripheral blood before the initiation of treatments is a strong predictor of responses in non-small cell lung cancer patients. Therefore, development of new approaches to improve CD4 responses before PD-L1/PD-1 blockade therapy could be the solution to increase response rates and survival of patients.

Targeting Telomerase with an HLA Class II-Restricted TCR for Cancer Immunotherapy

T cell receptor (TCR)-engineered T cell therapy is a promising cancer treatment approach. Human telomerase reverse transcriptase (hTERT) is overexpressed in the majority of tumors and a potential target for adoptive cell therapy. We isolated a novel hTERT-specific TCR sequence, named Radium-4, from a clinically responding pancreatic cancer patient vaccinated with a long hTERT peptide. Radium-4 TCR-redirected primary CD4⁺ and CD8⁺ T cells demonstrated in vitro efficacy, producing inflammatory cytokines and killing hTERT⁺ melanoma cells in both 2D and 3D settings, as well as malignant, patient-derived ascites cells. Importantly, T cells expressing Radium-4 TCR displayed no toxicity against bone marrow stem cells or mature hematopoietic cells. Notably, Radium-4 TCR⁺ T cells also significantly reduced tumor growth and improved survival in a xenograft mouse model. Since hTERT is a universal cancer antigen, and the very frequently expressed HLA class II molecules presenting the hTERT peptide to this TCR provide a very high (>75%) population coverage, this TCR represents an attractive candidate for immunotherapy of solid tumors.

Tumor MHC Expression Guides First-Line Immunotherapy Selection in Melanoma

Simple Summary

Immunotherapy leads to durable responses in a proportion of patients with advanced melanoma. Combination immunotherapy is more efficacious than single-agent immunotherapy, yet it is associated with significant toxicity. Currently there are no robust biomarkers to guide first-line immunotherapy selection. We have developed a flow cytometry-based score, to quantify the expression of antigen-presenting molecules MHC-I and MHC-II on melanoma cells, that incorporates both the fraction of tumor cells expressing MHC molecules and the level of expression. We demonstrate that the evaluation of tumor cell surface MHC-I expression aids in treatment selection, with combination immunotherapy providing clinical benefit over single-agent immunotherapy in MHC-I low melanoma with poor immune cell infiltration.

Abstract

Immunotherapy targeting T-cell inhibitory receptors, namely programmed cell death-1 (PD-1) and/or cytotoxic T-lymphocyte associated protein-4 (CTLA-4), leads to durable responses in a proportion of patients with advanced metastatic melanoma. Combination immunotherapy results in higher rates of response compared to anti-PD-1 monotherapy, at the expense of higher toxicity. Currently, there are no robust molecular biomarkers for the selection of first-line immunotherapy. We used flow cytometry to profile pretreatment tumor biopsies from 36 melanoma patients treated with anti-PD-1 or combination (anti-PD-1 plus anti-CTLA-4) immunotherapy. A novel quantitative score was developed to determine the tumor cell expression of antigen-presenting MHC class I (MHC-I) molecules, and to correlate expression data with treatment response. Melanoma MHC-I expression was intact in all tumors derived from patients who demonstrated durable response to anti-PD-1 monotherapy. In contrast, melanoma MHC-I expression was low in 67% of tumors derived from patients with durable response to combination immunotherapy. Compared to MHC-I high tumors, MHC-I low tumors displayed reduced T-cell infiltration and a myeloid cell-enriched microenvironment. Our data emphasize the importance of robust MHC-I expression for anti-PD-1 monotherapy response and provide a rationale for the selection of combination immunotherapy as the first-line treatment in MHC-I low melanoma.

Imiquimod Exerts Antitumor Effects by Inducing Immunogenic Cell Death and Is Enhanced by the Glycolytic Inhibitor 2-Deoxyglucose

The induction of immunogenic cell death (ICD) in cancer cells triggers specific immune responses against the same cancer cells. Imiquimod (IMQ) is a synthetic ligand of toll-like receptor 7 that exerts antitumor activity by stimulating cell-mediated immunity or by directly inducing apoptosis. Whether IMQ causes tumors to undergo ICD and elicits a specific antitumor immune response is unknown. We demonstrated that IMQ-induced ICD-associated features, including the surface exposure of calreticulin and the secretion of adenosine triphosphate and HMGB1, were mediated by ROS and endoplasmic reticulum stress. In a B16F10 melanoma mouse model, vaccinating mice with IMQ-induced ICD cell lysate or directly injecting IMQ in situ reduced tumor growth that was mediated by inducing tumor-specific T-cell proliferation, promoting tumor-specific cytotoxic killing by CD8⁺ T cells, and increasing the infiltration of various immune cells into tumor lesions. The ICD-associated features were crucial in the induction of specific antitumor immunity in vivo. The glycolytic inhibitor 2-deoxyglucose enhanced IMQ-induced ICD-associated features and strengthened the antitumor immunity mediated by IMQ-induced ICD cell lysate in p53-mutant cancer cells, which were IMQ-resistant in vitro. We conclude that IMQ is an authentic ICD inducer and provide a concept connecting IMQ-induced cancer cell death and antitumor immune responses.

CD4+ T cells indirectly kill tumor cells via induction of cytotoxic macrophages in mouse models

It is well recognized that CD4⁺ T cells may play an important role in immunosurveillance and immunotherapy against cancer. However, the details of how these cells recognize and eliminate the tumor cells remain incompletely understood. For the past 25 years, we have focused on how CD4⁺ T cells reject multiple myeloma cells in a murine model (MOPC315). In our experimental system, the secreted tumor-specific antigen is taken up by tumor-infiltrating macrophages that process it and present a neoepitope [a V region-derived idiotypic (Id) peptide] on MHC class II molecules to Th1 cells. Stimulated Th1 cells produce IFNγ, which activates macrophages in a manner that elicits an M1-like, tumoricidal phenotype. Through an inducible nitric oxide synthetase (iNOS)-dependent mechanism, the M1 macrophages secrete nitric oxide (NO) that diffuses into neighboring tumor cells. Inside the tumor cells, NO-derived reactive nitrogen species, including peroxynitrite, causes nitrosylation of proteins and triggers apoptosis by the intrinsic apoptotic pathway. This mode of indirect tumor recognition by CD4⁺ T cells operates independently of MHC class II expression on cancer cells. However, secretion of the tumor-specific antigen, and uptake and MHCII presentation on macrophages, is required for rejection. Similar mechanisms can also be observed in a B-lymphoma model and in the unrelated B16 melanoma model. Our findings reveal a novel mechanism by which CD4⁺ T cells kill tumor cells indirectly via induction of intratumoral cytotoxic macrophages. The data suggest that induction of M1 polarization of tumor-infiltrating macrophages, by CD4⁺ T cells or through other means, could serve as an immunotherapeutic strategy.

Cognate Interaction With CD4+ T Cells Instructs Tumor-Associated Macrophages to Acquire M1-Like Phenotype

The immunosuppressive tumor microenvironment (TME) established by tumor cells, stromal cells and inhibitory immune cells counteracts the function of tumor reactive T cells. Tumor associated macrophages (TAMs) showing functional plasticity contribute to this process as so called M2-like macrophages can suppress the function of effector T cells and promote their differentiation into regulatory T cells (Tregs). Furthermore, tumor antigen specific CD4⁺ T effector cells can essentially sustain anti-tumoral immune responses as shown for various tumor entities, thus suggesting that cognate interaction between tumor antigen-specific CD4⁺ Th1 cells and TAMs might shift the intra-tumoral M1/M2 ratio toward M1. This study demonstrates repolarization of M2-like PECs upon MHC II-restricted interaction with tumor specific CD4⁺ Th1 cells in vitro as shown by extensive gene and protein expression analyses. Moreover, adoptive transfer of OVA-specific OT-II cells into C57BL/6 mice bearing OVA expressing IA^b−/− tumors resulted in increased accumulation of M1-like TAMs with enhanced M1 associated gene and protein expression profiles. Thus, this paper highlights a so far underestimated function of the CD4⁺ Th1/TAM axis in re-conditioning the immunosuppressive tumor microenvironment.

Combination of immune checkpoint blockade with DNA cancer vaccine induces potent antitumor immunity against P815 mastocytoma

DNA vaccination against cancer has become a promising strategy for inducing a specific and long-lasting antitumor immunity. However, DNA vaccines fail to generate potent immune responses when used as a single therapy. To enhance their activity into the tumor, a DNA vaccine against murine P815 mastocytoma was combined with antibodies directed against the immune checkpoints CTLA4 and PD1. The combination of these two strategies delayed tumor growth and enhanced specific antitumor immune cell infiltration in comparison to the corresponding single therapies. The combination also promoted IFNg, IL12 and granzyme B production in the tumor microenvironment and decreased the formation of liver metastasis in a very early phase of tumor development, enabling 90% survival. These results underline the complementarity of DNA vaccination and immune checkpoint blockers in inducing a potent immune response, by exploiting the generation of antigen-specific T cells by the vaccine and the ability of immune checkpoint blockers to enhance T cell activity and infiltration in the tumor. These findings suggest how and why a rational combination therapy can overcome the limits of DNA vaccination but could also allow responses to immune checkpoint blockers in a larger proportion of subjects.

Metformin exerts antitumor activity via induction of multiple death pathways in tumor cells and activation of a protective immune response

The antitumor effect of metformin has been demonstrated in several types of cancer; however, the mechanisms involved are incompletely understood. In this study, we showed that metformin acts directly on melanoma cells as well as on the tumor microenvironment, particularly in the context of the immune response. In vitro, metformin induces a complex interplay between apoptosis and autophagy in melanoma cells. The anti-metastatic activity of metformin in vivo was assessed in several mouse models challenged with B16F10 cells. Metformin's activity was, in part, immune system-dependent, whereas its antitumor properties were abrogated in immunodeficient (NSG) mice. Metformin treatment increased the number of lung CD8-effector-memory T and CD4⁺Foxp3⁺IL-10⁺ T cells in B16F10-transplanted mice. It also decreased the levels of Gr-1⁺CD11b⁺ and RORγ⁺ IL17⁺CD4⁺ cells in B16F10-injected mice and the anti-metastatic effect was impaired in RAG-1^−/− mice challenged with B16F10 cells, suggesting an important role for T cells in the protection induced by metformin. Finally, metformin in combination with the clinical metabolic agents rapamycin and sitagliptin showed a higher antitumor effect. The metformin/sitagliptin combination was effective in a BRAFV600E/PTEN tamoxifen-inducible murine melanoma model. Taken together, these results suggest that metformin has a pronounced effect on melanoma cells, including the induction of a strong protective immune response in the tumor microenvironment, leading to tumor growth control, and the combination with other metabolic agents may increase this effect.

The opposing roles of CD4+ T cells in anti-tumour immunity

Cancer immunotherapy focuses mainly on anti-tumour activity of CD8+ cytotoxic T lymphocytes (CTLs). CTLs can directly kill all tumour cell types, provided they carry recognizable antigens. However, CD4+ T cells also play important roles in anti-tumour immunity. CD4+ T cells can either suppress or promote the anti-tumour CTL response, either in secondary lymphoid organs or in the tumour. In this review, we highlight opposing mechanisms of conventional and regulatory T cells at both sites. We outline how current cancer immunotherapy strategies affect both subsets and how selective modulation of each subset is important to maximize the clinical response of cancer patients.

Groth B. Collaboration between tumor-specific CD4+ T cells and B cells in anti-cancer immunity

The role of B cells and antibodies in anti-tumor immunity is controversial, with both positive and negative effects reported in animal models and clinical studies. We developed a murine B16.F10 melanoma model to study the effects of collaboration between tumor-specific CD4⁺ T cells and B cells on tumor control. By incorporating T cell receptor transgenic T cells and B cell receptor isotype switching B cells, we were able to track the responses of tumor-reactive T and B cells and the development of anti-tumor antibodies in vivo. In the presence of tumor-specific B cells, the number of tumor-reactive CD4⁺ T cells was reduced in lymphoid tissues and the tumor itself, and this correlated with poor tumor control. B cells had little effect on the Th1 bias of the CD4⁺ T cell response, and the number of induced FoxP3⁺ regulatory cells (iTregs) generated from within the original naive CD4⁺ T cell inoculum was unrelated to the degree of B cell expansion. In response to CD4⁺ T cell help, B cells produced a range of isotype-switched anti-tumor antibodies, principally IgG1, IgG2a/c and IgG2b. In the absence of CD4⁺ T cells, B cells responded to agonistic anti-CD40 administration by switching to production of IgG2a/c and, to a lesser extent, IgG1, IgG3, IgA and IgE, which reduced the number of lung metastases after i.v. tumor inoculation but had no effect on the growth of subcutaneous tumors.

Periodically Pulsed Immunotherapy in a Mathematical Model of Tumor, CD4+ T Cells, and Antitumor Cytokine Interactions

Immunotherapy is one of the most recent approaches for controlling and curing malignant tumors. In this paper, we consider a mathematical model of periodically pulsed immunotherapy using CD4⁺ T cells and an antitumor cytokine. Mathematical analyses are performed to determine the threshold of a successful treatment. The interindividual variability is explored by one-, two-, and three-parameter bifurcation diagrams for a nontreatment case. Numerical simulation conducted in this paper shows that (i) the tumor can be regulated by administering CD4⁺ T cells alone in a patient with a strong immune system or who has been diagnosed at an early stage, (ii) immunotherapy with a large amount of an antitumor cytokine can boost the immune system to remit or even to suppress tumor cells completely, and (iii) through polytherapy the tumor can be kept at a smaller size with reduced dosages.

CD4 and CD8 T lymphocyte interplay in controlling tumor growth

The outstanding clinical success of immune checkpoint blockade has revived the interest in underlying mechanisms of the immune system that are capable of eliminating tumors even in advanced stages. In this scenario, CD4 and CD8 T cell responses are part of the cancer immune cycle and both populations significantly influence the clinical outcome. In general, the immune system has evolved several mechanisms to protect the host against cancer. Each of them has to be undermined or evaded during cancer development to enable tumor outgrowth. In this review, we give an overview of T lymphocyte-driven control of tumor growth and discuss the involved tumor-suppressive mechanisms of the immune system, such as senescence surveillance, cancer immunosurveillance, and cancer immunoediting with respect to recent clinical developments of immunotherapies. The main focus is on the currently existing knowledge about the CD4 and CD8 T lymphocyte interplay that mediates the control of tumor growth.

Epigenetic modulation in cancer immunotherapy

The success of immune checkpoint inhibitors in cancer immunotherapy has been widely heralded. However many cancer patients do not respond to immune checkpoint therapy and some relapse due to acquired tumor resistance. Epigenetic targeting may be beneficial in cancer immunotherapy by reversing immune avoidance and escape mechanisms employed by cancer cells, as well as by modulating immune cell differentiation and function. In this manuscript we review recent findings suggesting how epigenetics may be used to improve cancer immunotherapy. We focus on the inhibitors of the CTLA4 and PD1 immune checkpoints and epigenetic modifiers of histone acetylation and methylation and DNA methylation.