Trafficking of high avidity HER-2/neu-specific T cells into HER-2/neu-expressing tumors after depletion of effector/memory-like regulatory T cells

Signatures of recent activation identify a circulating T cell compartment containing tumor-specific antigen receptors with high avidity

T cell receptor (TCR) avidity is assumed to be a major determinant of the spatiotemporal fate and protective capacity of tumor-specific T cells. However, monitoring polyclonal T cell responses with known TCR avidities in vivo over space and time remains challenging. Here, we investigated the fate and functionality of tumor neoantigen-specific T cells with TCRs of distinct avidities in a well-established, reductionist preclinical tumor model and human patients with melanoma. To this end, we used polyclonal T cell transfers with in-depth characterized TCRs together with flow cytometric phenotyping in mice inoculated with MC38 OVA tumors. Transfer of T cells from retrogenic mice harboring TCRs with high avidity resulted in best tumor protection. Unexpectedly, we found that both high- and low-avidity T cells are similarly abundant within the tumor and adopt concordant phenotypic signs of exhaustion. Outside the tumor, high-avidity TCR T cells were not generally overrepresented but, instead, selectively enriched in T cell populations with intermediate PD-1 protein expression. Single-cell sequencing of neoantigen-specific T cells from two patients with melanoma-combined with transgenic reexpression of identified TCRs by CRISPR-Cas9-mediated orthotopic TCR replacement-revealed high-functionality TCRs to be enriched in T cells with RNA signatures of recent activation. Furthermore, of 130 surface protein candidates, PD-1 surface expression was most consistently enriched in functional TCRs. Together, our findings show that tumor-reactive TCRs with high protective capacity circulating in peripheral blood are characterized by a signature of recent activation.

Robust antigen-specific CD8 T cell tolerance to a model prostate cancer neoantigen

Immunotherapy has shown limited success in prostate cancer; this may be partially explained by its immunosuppressive tumor microenvironment (TME). Although androgen-deprivation therapy (ADT), the most common treatment for prostate cancer, initially promotes a robust T cell infiltrate, T cell responses are later attenuated. Based on the castration-sensitive Myc-CaP model, we developed an antigen-specific system to study CD8 T cell tolerance to prostate tumors. This model is unique in that CD8 T cells recognize a bona-fide tumor antigen (Her-2/neu), rather than an overexpressed xenogenic antigen like chicken ovalbumin or influenza hemagglutinin. Using this novel model, we demonstrate robust tolerance that is not alleviated by TLR agonists or ADT. This model may serve as a novel and useful tool to further interrogate methods by which to augment anti-tumor cancer immune responses to prostate cancer.

Significance

Prostate cancer is a leading cause of cancer-related death in men worldwide, with an estimated 33,000 deaths projected in the U.S. in 2020. Although primary (localized) tumors can be cured by surgery or radiation, approximately 40% of patients eventually develop recurrent disease. While initially responsive to androgen-deprivation, many patients with recurrent prostate cancer eventually progress to a more advanced disease state known as metastatic castration-resistant prostate cancer (mCRPC); this is the lethal phenotype. These studies describe a novel androgen-responsive murine cell line that expresses a bona-fide tumor antigen (Her-2/neu). Pre-clinical work with this model shows robust and antigen-specific CD8 T cell tolerance, providing a novel preclinical model to study CD8 T cell tolerance to prostate tumors.

T-cell receptor affinity in the age of cancer immunotherapy

The strength of the interaction between T-cell receptors (TCRs) and their ligands, peptide/major histocompatibility complex complexes (pMHCs), is one of the most frequently discussed and investigated features of T cells in immuno-oncology today. Although there are many molecules on the surface of T cells that interact with ligands on other cells, the TCR/pMHC is the only receptor-ligand pair that offers antigen specificity and dictates the functional response of the T cell. The strength of the TCR/pMHC interaction, along with the environment in which this interaction takes place, is key to how the T cell will respond. The TCR repertoire of T cells that interact with tumor-associated antigens is vast, although typically of low affinity. Here, we focus on the low-affinity interactions between TCRs from CD8+ T cells and different models used in immuno-oncology.

Targeting Cancer with Genetically Engineered TCR T Cells

The adoptive cell transfer (ACT) of genetically engineered T cell receptor (TCR) T cells is one of the burgeoning fields of immunotherapy, with promising results in current clinical trials. Presently, clinicaltrials.gov has over 200 active trials involving adoptive cell therapy. The ACT of genetically engineered T cells not only allows the ability to select for TCRs with desired properties such as high-affinity receptors and tumor reactivity but to further enhance those receptors allowing for better targeting and killing of cancer cells in patients. Moreover, the addition of genetic material, including cytokines and cytokine receptors, can increase the survival and persistence of the T cell allowing for complete and sustained remission of cancer targets. The potential for improvement in adoptive cell therapy is limitless, with genetic modifications targeting to improve weaknesses of ACT and to thus enhance receptor affinity and functional avidity of the genetically engineered T cells.

Immune-Checkpoint Blockade Opposes CD8+ T-cell Suppression in Human and Murine Cancer

Immune-checkpoint blockade enhances antitumor responses against cancers. One cancer type that is sensitive to checkpoint blockade is squamous cell carcinoma of the head and neck (SCCHN), which we use here to study limitations of this treatment modality. We observed that CD8⁺ tumor-infiltrating lymphocytes (TILs) in SCCHN and melanoma express excess immune checkpoints components PD-1 and Tim-3 and are also CD27^-/CD28^-, a phenotype we previously associated with immune dysfunction and suppression. In ex vivo experiments, patients' CD8⁺ TILs with this phenotype suppressed proliferation of autologous peripheral blood T cells. Similar phenotype and function of TILs was observed in the TC-1 mouse tumor model. Treatment of TC-1 tumors with anti-PD-1 or anti-Tim-3 slowed tumor growth in vivo and reversed the suppressive function of multi-checkpoint⁺ CD8⁺ TIL. Similarly, treatment of both human and mouse PD-1⁺ Tim-3⁺ CD8⁺ TILs with anticheckpoint antibodies ex vivo reversed their suppressive function. These suppressive CD8⁺ TILs from mice and humans expressed ligands for PD-1 and Tim-3 and exerted their suppressive function via IL10 and close contact. To model therapeutic strategies, we combined anti-PD-1 blockade with IL7 cytokine therapy or with transfer of antigen-specific T cells. Both strategies resulted in synergistic antitumor effects and reduced suppressor cell function. These findings enhance our understanding of checkpoint blockade in cancer treatment and identify strategies to promote synergistic activities in the context of other immunotherapies.

A CD40 Agonist and PD-1 Antagonist Antibody Reprogram the Microenvironment of Nonimmunogenic Tumors to Allow T-cell-Mediated Anticancer Activity

In cancers with tumor-infiltrating lymphocytes (TILs), monoclonal antibodies (mAbs) that block immune checkpoints such as CTLA-4 and PD-1/PD-L1 promote antitumor T-cell immunity. Unfortunately, most cancers fail to respond to single-agent immunotherapies. T regulatory cells, myeloid derived suppressor cells (MDSCs), and extensive stromal networks within the tumor microenvironment (TME) dampen antitumor immune responses by preventing T-cell infiltration and/or activation. Few studies have explored combinations of immune-checkpoint antibodies that target multiple suppressive cell populations within the TME, and fewer have studied the combinations of both agonist and antagonist mAbs on changes within the TME. Here, we test the hypothesis that combining a T-cell-inducing vaccine with both a PD-1 antagonist and CD40 agonist mAbs (triple therapy) will induce T-cell priming and TIL activation in mouse models of nonimmunogenic solid malignancies. In an orthotopic breast cancer model and both subcutaneous and metastatic pancreatic cancer mouse models, only triple therapy was able to eradicate most tumors. The survival benefit was accompanied by significant tumor infiltration of IFNγ-, Granzyme B-, and TNFα-secreting effector T cells. Further characterization of immune populations was carried out by high-dimensional flow-cytometric clustering analysis and visualized by t-distributed stochastic neighbor embedding (t-SNE). Triple therapy also resulted in increased infiltration of dendritic cells, maturation of antigen-presenting cells, and a significant decrease in granulocytic MDSCs. These studies reveal that combination CD40 agonist and PD-1 antagonist mAbs reprogram immune resistant tumors in favor of antitumor immunity.

Entinostat Converts Immune-Resistant Breast and Pancreatic Cancers into Checkpoint-Responsive Tumors by Reprogramming Tumor-Infiltrating MDSCs

Immune-checkpoint inhibition (ICI) has revolutionized treatment in cancers that are naturally immunogenic by enabling infiltration of T cells into the tumor microenvironment (TME) and promoting cytotoxic signaling pathways. Tumors possessing complex immunosuppressive TMEs such as breast and pancreatic cancers present unique therapeutic obstacles as response rates to ICI remain low. Such tumors often recruit myeloid-derived suppressor cells (MDSCs), whose functioning prohibits both T-cell activation and infiltration. We attempted to sensitize these tumors to ICI using epigenetic modulation to target MDSC trafficking and function to foster a less immunosuppressive TME. We showed that combining a histone deacetylase inhibitor, entinostat (ENT), with anti-PD-1, anti-CTLA-4, or both significantly improved tumor-free survival in both the HER2/neu transgenic breast cancer and the Panc02 metastatic pancreatic cancer mouse models. Using flow cytometry, gene-expression profiling, and ex vivo functional assays, we characterized populations of tumor-infiltrating lymphocytes (TILs) and MDSCs, as well as their functional capabilities. We showed that addition of ENT to checkpoint inhibition led to significantly decreased suppression by granulocytic MDSCs in the TME of both tumor types. We also demonstrated an increase in activated granzyme-B-producing CD8+ T effector cells in mice treated with combination therapy. Gene-expression profiling of both MDSCs and TILs identified significant changes in immune-related pathways. In summary, addition of ENT to ICI significantly altered infiltration and function of innate immune cells, allowing for a more robust adaptive immune response. These findings provide a rationale for combination therapy in patients with immune-resistant tumors, including breast and pancreatic cancers.

Definitive activation of endogenous antitumor immunity by repetitive cycles of cyclophosphamide with interspersed Toll-like receptor agonists

Many cancers both evoke and subvert endogenous anti-tumor immunity. However, immunosuppression can be therapeutically reversed in subsets of cancer patients by treatments such as checkpoint inhibitors or Toll-like receptor agonists (TLRa). Moreover, chemotherapy can leukodeplete immunosuppressive host elements, including myeloid-derived suppressor cells (MDSCs) and regulatory T-cells (Tregs). We hypothesized that chemotherapy-induced leukodepletion could be immunopotentiated by co-administering TLRa to emulate a life-threatening infection. Combining CpG (ODN 1826) or CpG+poly(I:C) with cyclophosphamide (CY) resulted in uniquely well-tolerated therapeutic synergy, permanently eradicating advanced mouse tumors including 4T1 (breast), Panc02 (pancreas) and CT26 (colorectal). Definitive treatment required endogenous CD8+ and CD4+ IFNγ-producing T-cells. Tumor-specific IFNγ-producing T-cells persisted during CY-induced leukopenia, whereas Tregs were progressively eliminated, especially intratumorally. Spleen-associated MDSCs were cyclically depleted by CY+TLRa treatment, with residual monocytic MDSCs requiring only continued exposure to CpG or CpG+IFNγ to effectively attack malignant cells while sparing non-transformed cells. Such tumor destruction occurred despite upregulated tumor expression of Programmed Death Ligand-1, but could be blocked by clodronate-loaded liposomes to deplete phagocytic cells or by nitric oxide synthase inhibitors. CY+TLRa also induced tumoricidal myeloid cells in naive mice, indicating that CY+TLRa's immunomodulatory impacts occurred in the complete absence of tumor-bearing, and that tumor-induced MDSCs were not an essential source of tumoricidal myeloid precursors. Repetitive CY+TLRa can therefore modulate endogenous immunity to eradicate advanced tumors without vaccinations or adoptive T-cell therapy. Human blood monocytes could be rendered similarly tumoricidal during in vitro activation with TLRa+IFNγ, underscoring the potential therapeutic relevance of these mouse tumor studies to cancer patients.

Immunotherapy for breast cancer: past, present, and future

Immunotherapy has shown promise in many solid tumors including melanoma and non-small cell lung cancer with an evolving role in breast cancer. Immunotherapy encompasses a wide range of therapies including immune checkpoint inhibition, monoclonal antibodies, bispecific antibodies, vaccinations, antibody-drug conjugates, and identifying other emerging interventions targeting the tumor microenvironment. Increasing efficacy of these treatments in breast cancer patients requires identification of better biomarkers to guide patient selection; recognizing when to initiate these therapies in multi-modality treatment plans; establishing novel assays to monitor immune-mediated responses; and creating combined systemic therapy options incorporating conventional treatments such as chemotherapy and endocrine therapy. This review will focus on the current role and future directions of many of these immunotherapies in breast cancer, as well as highlighting clinical trials that are investigating several of these active issues.

Human HER2 overexpressing mouse breast cancer cell lines derived from MMTV.f.HuHER2 mice: characterization and use in a model of metastatic breast cancer

Preclinical evaluation of therapeutic agents against metastatic breast cancer require cell lines and animal models that recapitulate clinical metastatic breast cancer as much as possible. We have previously used cell lines derived from the neu-N transgenic model to investigate anti-neu targeting of metastatic breast cancer using an alpha-emitter labeled antibody reactive with the rat variant of HER2/neu expressed by the neu-N model. To investigate alpha-particle emitter targeting of metastatic breast cancer using clinically relevant, commercially available anti-HER2/neu antibodies, we have developed cell lines derived from primary tumors and lung metastases from HuHER2 transgenic mice. We extracted primary mammary gland tumors, isolated the epithelial breast cancer cells, and established seven different cell lines. We also established 2 different cell lines from spontaneous lung metastases and cell lines from a serial transplantation of tumor tissues in HuHER2 transgenic mice. HuHER2 protein was overexpressed in all of the established cell lines. The mRNA level of ER (estrogen receptor) and PR (progesterone receptor) was relatively low in the cell lines compared to normal mammary gland (MG). As EMT markers, the expression of E-Cadherin in the cell lines was downregulated while the expression of TWIST1 and Vimentin were upregulated, relative to MG. Furthermore, trastuzumab directly inhibited cellular viability. Biodistribution studies with ¹¹¹In-DTPA-trastuzumab in HuHER2 cell tumor xenografts demonstrated specific targeting with a clinically relevant antibody. Collectively, these cell lines show all the hallmarks of highly aggressive, metastatic breast cancer and are being used to evaluate combination therapy with alpha-particle emitter labeled HER2/neu reactive antibodies.

A STING Agonist Given with OX40 Receptor and PD-L1 Modulators Primes Immunity and Reduces Tumor Growth in Tolerized Mice

Stimulator of interferon genes (STING) signaling induces IFNβ production by intratumoral dendritic cells (DC), driving T-cell priming and recruitment into the tumor microenvironment (TME). We examined to what extent preexisting antigen-specific tolerance influenced the efficacy of in situ delivery of a potent STING-activating cyclic dinucleotide (CDN), ADU S-100, against established HER-2⁺ breast tumors. ADU S-100 induced HER-2-specific CD8⁺ T-cell priming and durable tumor clearance in 100% of nontolerant parental FVB/N mice. In contrast, ADU S-100 did not sufficiently prime HER-2-specific CD8⁺ T cells in tolerant neu/N mice, resulting in only delayed tumor growth and tumor clearance in 10% of the mice. No differences in IFNβ production, DC priming, or HER-2-specific CD8⁺ T-cell trafficking were detected between FVB/N and neu/N mice. However, activation and expansion of HER-2-specific CD8⁺ T cells were defective in neu/N mice. Immune cell infiltrates of untreated tumor-bearing neu/N mice expressed high numbers of PD1 and OX40 receptors on their CD8⁺ T cells, and PD-L1 was highly expressed on both myeloid and tumor cells. Modulating PD-L1 and OX40 receptor signaling combined with intratumoral ADU S-100 administration enhanced HER-2-specific CD8⁺ T-cell activity, clearing tumors in 40% of neu/N mice. Thus, intratumoral STING agonists could potently prime tumor antigen-specific CD8⁺ T-cell responses, and adding PD-L1 blockade and OX40 receptor activation can overcome antigen-enforced immune tolerance to induce tumor regression. Cancer Immunol Res; 5(6); 468-79. ©2017 AACR.

Sorafenib combined with HER-2 targeted vaccination can promote effective T cell immunity in vivo

The tumor microenvironment (TME) is established and maintained through complex interactions between tumor cells and host stromal elements. Therefore, therapies that target multiple cellular components of the tumor may be most effective. Sorafenib, a multi-kinase inhibitor, alters signaling pathways in both tumor cells and host stromal cells. Thus, we explored the potential immune-modulating effects of sorafenib in a murine HER-2-(neu) overexpressing breast tumor model alone and in combination with a HER-2 targeted granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting vaccine (3T3neuGM). In vitro, sorafenib inhibited the growth of HER-2 overexpressing NT2.5 tumor cells, inducing apoptosis. Sorafenib also interfered with ERK MAPK, p38 MAPK, and STAT3 signaling, as well as cyclin D expression, but did not affect HER-2 or AKT signaling. In vivo, single agent sorafenib disrupted the tumor-associated vasculature and induced tumor cell apoptosis, effectively inducing the regression of established NT2.5 tumors in immune competent FVB/N mice. Immune depletion studies demonstrated that both CD4⁺ and CD8⁺ T cells were required for tumor regression. Sorafenib treatment did not impact the rate of tumor clearance induced by vaccination with 3T3neuGM in tumor-bearing FVB/N mice relative to either sorafenib treatment or vaccination alone. In vivo studies further demonstrated that sorafenib enhanced the accumulation of both CD4⁺ and CD8⁺ T cells into the TME of vaccinated mice. Together, these findings suggest that GM-CSF-secreting cellular immunotherapy may be integrated with sorafenib without impairing vaccine-based immune responses.

Aberrant Glycosylation of Anchor-Optimized MUC1 Peptides Can Enhance Antigen Binding Affinity and Reverse Tolerance to Cytotoxic T Lymphocytes

Cancer vaccines have often failed to live up to their promise, although recent results with checkpoint inhibitors are reviving hopes that they will soon fulfill their promise. Although mutation-specific vaccines are under development, there is still high interest in an off-the-shelf vaccine to a ubiquitous antigen, such as MUC1, which is aberrantly expressed on most solid and many hematological tumors, including more than 90% of breast carcinomas. Clinical trials for MUC1 have shown variable success, likely because of immunological tolerance to a self-antigen and to poor immunogenicity of tandem repeat peptides. We hypothesized that MUC1 peptides could be optimized, relying on heteroclitic optimizations of potential anchor amino acids with and without tumor-specific glycosylation of the peptides. We have identified novel MUC1 class I peptides that bind to HLA-A*0201 molecules with significantly higher affinity and function than the native MUC1 peptides. These peptides elicited CTLs from normal donors, as well as breast cancer patients, which were highly effective in killing MUC1-expressing MCF-7 breast cancer cells. Each peptide elicited lytic responses in greater than 6/8 of normal individuals and 3/3 breast cancer patients. The CTLs generated against the glycosylated-anchor modified peptides cross reacted with the native MUC1 peptide, STAPPVHNV, suggesting these analog peptides may offer substantial improvement in the design of epitope-based vaccines.

Identifying Individual T Cell Receptors of Optimal Avidity for Tumor Antigens

Cytotoxic T cells recognize, via their T cell receptors (TCRs), small antigenic peptides presented by the major histocompatibility complex (pMHC) on the surface of professional antigen-presenting cells and infected or malignant cells. The efficiency of T cell triggering critically depends on TCR binding to cognate pMHC, i.e., the TCR–pMHC structural avidity. The binding and kinetic attributes of this interaction are key parameters for protective T cell-mediated immunity, with stronger TCR–pMHC interactions conferring superior T cell activation and responsiveness than weaker ones. However, high-avidity TCRs are not always available, particularly among self/tumor antigen-specific T cells, most of which are eliminated by central and peripheral deletion mechanisms. Consequently, systematic assessment of T cell avidity can greatly help distinguishing protective from non-protective T cells. Here, we review novel strategies to assess TCR–pMHC interaction kinetics, enabling the identification of the functionally most-relevant T cells. We also discuss the significance of these technologies in determining which cells within a naturally occurring polyclonal tumor-specific T cell response would offer the best clinical benefit for use in adoptive therapies, with or without T cell engineering.

Control of CD8 T-Cell Infiltration into Tumors by Vasculature and Microenvironment

CD8 T-cells are a critical brake on the initial development of tumors. In established tumors, the presence of CD8 T-cells is correlated with a positive patient prognosis, although immunosuppressive mechanisms limit their effectiveness and they are rarely curative without manipulation. Cancer immunotherapies aim to shift the balance back to dominant antitumor immunity through antibody blockade of immunosuppressive signaling pathways, vaccination, and adoptive transfer of activated or engineered T-cells. These approaches have yielded striking responses in small subsets of patients with solid tumors, most notably those with melanoma. Importantly, the subset of patients who respond to vaccination or immunosuppression blockade therapies are those with CD8 T-cells present in the tumor prior to initiating therapy. While current adoptive cell therapy approaches can be dramatically effective, they require infusion of extremely large numbers of T-cells, but the number that actually infiltrates the tumor is very small. Thus, poor representation of CD8 T-cells in tumors is a fundamental hurdle to successful immunotherapy, over and above the well-established barrier of immunosuppression. In this review, we discuss the factors that determine whether immune cells are present in tumors, with a focus on the representation of cytotoxic CD8 T-cells. We emphasize the critically important role of tumor-associated vasculature as a gateway that enables the active infiltration of both effector and naïve CD8 T-cells that exert antitumor activity. We also discuss strategies to enhance the gateway function and extend the effectiveness of immunotherapies to a broader set of cancer patients.

Galectin-3 Shapes Antitumor Immune Responses by Suppressing CD8+ T Cells via LAG-3 and Inhibiting Expansion of Plasmacytoid Dendritic Cells

Galectin-3 is a 31-kDa lectin that modulates T-cell responses through several mechanisms, including apoptosis, T-cell receptor (TCR) cross-linking, and TCR downregulation. We found that patients with pancreatic ductal adenocarcinoma (PDA) who responded to a granulocyte-macrophage colony-stimulating factor-secreting allogeneic PDA vaccine developed neutralizing antibodies to galectin-3 after immunization. We show that galectin-3 binds activated antigen-committed CD8(+) T cells only in the tumor microenvironment. Galectin-3-deficient mice exhibit improved CD8(+) T-cell effector function and increased expression of several inflammatory genes. Galectin-3 binds to LAG-3, and LAG-3 expression is necessary for galectin-3-mediated suppression of CD8(+) T cells in vitro. Lastly, galectin-3-deficient mice have elevated levels of circulating plasmacytoid dendritic cells, which are superior to conventional dendritic cells in activating CD8(+) T cells. Thus, inhibiting galectin-3 in conjunction with CD8(+) T-cell-directed immunotherapies should enhance the tumor-specific immune response.

Enhancement of T cell recruitment and infiltration into tumours

Studies have documented that cancer patients with tumours which are highly infiltrated with cytotoxic T lymphocytes show enhanced survival rates. The ultimate goal of cancer immunotherapy is to elicit high-avidity tumour-specific T cells to migrate and kill malignant tumours. Novel antibody therapies such as ipilumimab (a cytotoxic T lymphocyte antigen-4 blocking antibody) show enhanced T cell infiltration into the tumour tissue and increased survival. More conventional therapies such as chemotherapy or anti-angiogenic therapy and recent therapies with oncolytic viruses have been shown to alter the tumour microenvironment and thereby lead to enhanced T cell infiltration. Understanding the mechanisms involved in the migration of high-avidity tumour-specific T cells into tumours will support and provide solutions for the optimization of therapeutic options in cancer immunotherapy.

Targeting the right regulatory T-cell population for tumor immunotherapy

Regulatory T cells (Tregs) that suppress tumor-specific T cell-mediated immune responses are the subject of an intense wave of investigation. We recently reported that a subset of Tregs, namely effector/memory CD25(low) cells, are responsible for suppressing high avidity tumor-specific T cells in mouse mammary tumors. Here, we discuss additional findings that clarify this mechanism of Treg-mediated immunosuppression.

Harnessing the immune system for the treatment of breast cancer

Standard treatment options for breast cancer include surgery, chemotherapy, radiation, and targeted therapies, such as adjuvant hormonal therapy and monoclonal antibodies. Recently, the recognition that chronic inflammation in the tumor microenvironment promotes tumor growth and survival during different stages of breast cancer development has led to the development of novel immunotherapies. Several immunotherapeutic strategies have been studied both preclinically and clinically and already have been shown to enhance the efficacy of conventional treatment modalities. Therefore, therapies targeting the immune system may represent a promising next-generation approach for the treatment of breast cancers. This review will discuss recent findings that elucidate the roles of suppressive immune cells and proinflammatory cytokines and chemokines in the tumor-promoting microenvironment, and the most current immunotherapeutic strategies in breast cancer.

A feasibility study of cyclophosphamide, trastuzumab, and an allogeneic GM-CSF-secreting breast tumor vaccine for HER2+ metastatic breast cancer

Granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting tumor vaccines are bioactive, but limited by disease burden and immune tolerance. Cyclophosphamide augments vaccine activity in tolerant neu mice and in patients with metastatic breast cancer. HER2-specific monoclonal antibodies (mAb) enhance vaccine activity in neu mice. We hypothesized that cyclophosphamide-modulated vaccination with HER2-specific mAb safely induces relevant HER2-specific immunity in neu mice and patients with HER2+ metastatic breast cancer. Adding both cyclophosphamide and the HER2-specific mAb 7.16.4 to vaccination maximized HER2-specific CD8+ T-cell immunity and tumor-free survival in neu transgenic mice. We, therefore, conducted a single-arm feasibility study of cyclophosphamide, an allogeneic HER2+ GM-CSF-secreting breast tumor vaccine, and weekly trastuzumab in 20 patients with HER2+ metastatic breast cancer. Primary clinical trial objectives were safety and clinical benefit, in which clinical benefit represents complete response + partial response + stable disease. Secondary study objectives were to assess HER2-specific T-cell responses by delayed type hypersensitivity (DTH) and intracellular cytokine staining. Patients received three monthly vaccinations, with a boost 6 to 8 months from trial entry. This combination immunotherapy was safe, with clinical benefit rates at 6 months and 1 year of 55% [95% confidence interval (CI), 32%-77%; P = 0.013] and 40% (95% CI, 19%-64%), respectively. Median progression-free survival and overall survival durations were 7 months (95% CI, 4-16) and 42 months (95% CI, 22-70), respectively. Increased HER2-specific DTH developed in 7 of 20 patients [of whom 4 had clinical benefit (95% CI, 18-90)], with a trend toward longer progression-free survival and overall survival in DTH responders. Polyfunctional HER2-specific CD8+ T cells progressively expanded across vaccination cycles. Further investigation of cyclophosphamide-modulated vaccination with trastuzumab is warranted.

Pilot study of a novel combination of two therapeutic vaccines in advanced non-small-cell lung cancer patients

Cancer vaccines contain tumor antigens in a pro-inflammatory context with the purpose to generate potent antitumor immune responses. However, tumor cells develop different immunosuppressive mechanisms that limit the effectiveness of an anticancer immune response. Therefore, therapeutic vaccine treatment alone is usually not sufficient to generate tumor regression or survival improvement, especially in the advanced disease scenario in which most clinical studies have been conducted. Combining cancer vaccines with different anticancer therapies such as chemotherapy, radiotherapy and other immunotherapeutic agents has had different levels of success. However, the combination of cancer vaccines with different mechanisms of action has not been explored in clinical trials. To address this issue, the current review summarizes the main clinical and immunological results obtained with two different therapeutic vaccines used in advanced non-small-cell lung cancer patients, inducing an immune response against epidermal growth factor (CIMAvax-EGF) and NGcGM3 ganglioside (racotumomab). We also discuss preliminary findings obtained in a trial of combination of these two vaccines and future challenges with these therapies.

Immunotherapy converts nonimmunogenic pancreatic tumors into immunogenic foci of immune regulation

Pancreatic ductal adenocarcinoma (PDAC) is considered a "nonimmunogenic" neoplasm. Single-agent immunotherapies have failed to demonstrate significant clinical activity in PDAC and other "nonimmunogenic" tumors, in part due to a complex tumor microenvironment (TME) that provides a formidable barrier to immune infiltration and function. We designed a neoadjuvant and adjuvant clinical trial comparing an irradiated, granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting, allogeneic PDAC vaccine (GVAX) given as a single agent or in combination with low-dose cyclophosphamide to deplete regulatory T cells (Treg) as a means to study how the TME is altered by immunotherapy. Examination of resected PDACs revealed the formation of vaccine-induced intratumoral tertiary lymphoid aggregates in 33 of 39 patients 2 weeks after vaccine treatment. Immunohistochemical analysis showed these aggregates to be regulatory structures of adaptive immunity. Microarray analysis of microdissected aggregates identified gene-expression signatures in five signaling pathways involved in regulating immune-cell activation and trafficking that were associated with improved postvaccination responses. A suppressed Treg pathway and an enhanced Th17 pathway within these aggregates were associated with improved survival, enhanced postvaccination mesothelin-specific T-cell responses, and increased intratumoral Teff:Treg ratios. This study provides the first example of immune-based therapy converting a "nonimmunogenic" neoplasm into an "immunogenic" neoplasm by inducing infiltration of T cells and development of tertiary lymphoid structures in the TME. Post-GVAX T-cell infiltration and aggregate formation resulted in the upregulation of immunosuppressive regulatory mechanisms, including the PD-1-PD-L1 pathway, suggesting that patients with vaccine-primed PDAC may be better candidates than vaccine-naïve patients for immune checkpoint and other immunomodulatory therapies.

A Listeria vaccine and depletion of T-regulatory cells activate immunity against early stage pancreatic intraepithelial neoplasms and prolong survival of mice

BACKGROUND & AIMS

Premalignant lesions and early stage tumors contain immunosuppressive microenvironments that create barriers for cancer vaccines. Kras(G12D/+);Trp53(R172H/+);Pdx-1-Cre (KPC) mice, which express an activated form of Kras in pancreatic tissues, develop pancreatic intraepithelial neoplasms (PanIN) that progress to pancreatic ductal adenocarcinoma (PDA). We used these mice to study immune suppression in PDA.

METHODS

We immunized KPC and Kras(G12D/+);Pdx-1-Cre mice with attenuated intracellular Listeria monocytogenes (which induces CD4(+) and CD8(+) T-cell immunity) engineered to express Kras(G12D) (LM-Kras). The vaccine was given alone or in sequence with an anti-CD25 antibody (PC61) and cyclophosphamide to deplete T-regulatory (Treg) cells. Survival times were measured; pancreatic and spleen tissues were collected and analyzed by histologic, flow cytometry, and immunohistochemical analyses.

RESULTS

Interferon γ-mediated, CD8(+) T-cell responses were observed in KPC and Kras(G12D/+);Pdx-1-Cre mice given LM-Kras, but not in unvaccinated mice. Administration of LM-Kras to KPC mice 4-6 weeks old (with early stage PanINs), depleted of Treg cells, significantly prolonged survival and reduced PanIN progression (median survival, 265 days), compared with unvaccinated mice (median survival, 150 days; P = .002), mice given only LM-Kras (median survival, 150 days; P = .050), and unvaccinated mice depleted of Treg cells (median survival, 170 days; P = .048). In 8- to 12-week-old mice (with late-stage PanINs), LM-Kras, alone or in combination with Treg cell depletion, did not increase survival time or slow PanIN progression. The combination of LM-Kras and Treg cell depletion reduced numbers of Foxp3(+)CD4(+) T cells in pancreatic lymph nodes, increased numbers of CD4(+) T cells that secrete interleukin 17 and interferon γ, and caused CD11b(+)Gr1(+) cells in the pancreas to acquire an immunostimulatory phenotype.

CONCLUSIONS

Immunization of KPC mice with Listeria monocytogenes engineered to express Kras(G12D), along with depletion of Treg cells, reduces progression of early stage, but not late-stage, PanINs. This approach increases infiltration of the lesion with inflammatory cells. It might be possible to design immunotherapies against premalignant pancreatic lesions to slow or prevent progression to PDA.

Effects of gastric cancer cells on the differentiation of Treg cells

The aim of this study was evaluated the prevalence of Treg cells in peripheral blood in patients with gastric cancer, and investigate the effect of gastric cancer cells on their differentiation. ELISA was employed to assess the concentrations of TGF-β and IL-10 in gastric cancer patients' serum. Then, mouse gastric cancer cells were co-cultured with T lymphocytes or T lymphocytes + anti-TGF-β. Flow cytometric analysis and RT-PCR were then performed to detect Treg cells and TGF-β and IL-10 expression in gastric cancer cells. Our data showed that the expression of TGF-β and IL-10 in the patients with gastric cancer was increased compared to the case with healthy donors. The population of Treg cells and the expression levels of TGF-β and IL-10 in the co-culture group were much higher than in the control group (18.6% vs 9.5%) (P<0.05). Moreover, the population of Treg cells and the expression levels of TGF-β and IL-10 in the co-culture systerm were clearly decreased after addition of anti-TGF-β (7.7% vs 19.6%) (P<0.01). In conclusion, gastric cancer cells may induce Treg cell differentiation through TGF-β, and further promote immunosuppression.

Novel prostate acid phosphatase-based peptide vaccination strategy induces antigen-specific T-cell responses and limits tumour growth in mice

Treatment options for patients with advanced prostate cancer remain limited and rarely curative. Prostatic acid phosphatase (PAP) is a prostate-specific protein overexpressed in 95% of prostate tumours. An FDA-approved vaccine for the treatment of advanced prostate disease, PROVENGE® (sipuleucel-T), has been shown to prolong survival, however the precise sequence of the PAP protein responsible for the outcome is unknown. As the PAP antigen is one of the very few prostate-specific antigens for which there is a rodent equivalent with high homology, preclinical studies using PAP have the potential to be directly relevant to clinical setting. Here, we show three PAP epitopes naturally processed and presented in the context of HHDII/DR1 (114-128, 299-313, and 230-244). The PAP-114-128 epitope elicits CD4(+) and CD8(+) T-cell-specific responses in C57BL/6 mice. Furthermore, when immunised in a DNA vector format (ImmunoBody®), PAP-114-128 prevents and reduces the growth of transgenic adenocarcinoma of mouse prostate-C1 prostate cancer cell-derived tumours in both prophylactic and therapeutic settings. This anti-tumour effect is associated with infiltration of CD8(+) tumour-infiltrating lymphocytes and the generation of high avidity T cells secreting elevated levels of IFN-γ. PAP-114-128 therefore appears to be a highly relevant peptide on which to base vaccines for the treatment of prostate cancer.

The immune system and inflammation in breast cancer

During different stages of tumor development the immune system can either identify and destroy tumors, or promote their growth. Therapies targeting the immune system have emerged as a promising treatment modality for breast cancer, and immunotherapeutic strategies are being examined in preclinical and clinical models. However, our understanding of the complex interplay between cells of the immune system and breast cancer cells is incomplete. In this article, we review recent findings showing how the immune system plays dual host-protective and tumor-promoting roles in breast cancer initiation and progression. We then discuss estrogen receptor α (ERα)-dependent and ERα-independent mechanisms that shield breast cancers from immunosurveillance and enable breast cancer cells to evade immune cell induced apoptosis and produce an immunosuppressive tumor microenvironment. Finally, we discuss protumorigenic inflammation that is induced during tumor progression and therapy, and how inflammation promotes more aggressive phenotypes in ERα positive breast cancers.

Apoptosis-regulated low-avidity cancer-specific CD8(+) T cells can be rescued to eliminate HER2/neu-expressing tumors by costimulatory agonists in tolerized mice

A major barrier to vaccines in cancer treatment is their failure to activate and maintain a complete cancer-specific CD8(+) effector T-cell repertoire. Low-avidity T cells are more likely to escape clonal deletion in the thymus when compared with high-avidity T cells, and therefore comprise the major population of effector T cells available for activation in patients with cancer. However, low-avidity T cells fail to traffic into the tumor microenvironment and function in eradicating tumor under optimal vaccination conditions as opposed to high-avidity T cells that escape clonal deletion and function in tumor killing. We used high- and low-avidity T-cell receptor transgenic CD8(+) T cells specific for the immunodominant epitope HER2/neu (RNEU420-429) to identify signaling pathways responsible for the inferior activity of the low-avidity T cells. Adoptive transfer of these cells into tumor-bearing vaccinated mice identified the members of apoptosis pathways that are upregulated in low-avidity T cells. The increased expression of proapoptotic proteins by low-avidity T cells promoted their own cell death and also that of other tumor-specific CD8(+) T cells within their local environment. Importantly, we show that this proapoptotic effect can be overcome by using a strong costimulatory signal that prevents the activation-induced cell death and enables the low-avidity T cells to traffic into the tumor and assist in tumor clearance. These findings identify new therapeutic opportunities for activating the most potent anticancer T-cell responses.

T cell avidity and tumor immunity: problems and solutions

A potent T cell response is an important component of durable anti-tumor immunity. The quality of the T cell response can, in-part, be measured by the avidity of the T cell for its tumor antigen-expressing target. While convention suggests that raising the avidity of the responding T cells may make for a more potent anti-tumor immune response, the threshold for effective tumor immunity remains unclear, as do some of the adverse effects of an inappropriately high avidity response. In this review, we discuss the relationship between T cell avidity and anti-tumor immunity, considering both experimental model systems as well as human clinical trials.

How numbers, nature, and immune status of foxp3(+) regulatory T-cells shape the early immunological events in tumor development

The influence of CD4(+)CD25(+)Foxp3(+) regulatory T-cells (Tregs) on cancer progression has been demonstrated in a large number of preclinical models and confirmed in several types of malignancies. Neoplastic processes trigger an increase of Treg numbers in draining lymph nodes, spleen, blood, and tumors, leading to the suppression of anti-tumor responses. Treg-depletion before or early in tumor development may lead to complete tumor eradication and extends survival of mice and humans. However this strategy is ineffective in established tumors, highlighting the critical role of the early Treg-tumor encounters. In this review, after discussing old and new concepts of immunological tumor tolerance, we focus on the nature (thymus-derived vs. peripherally derived) and status (naïve or activated/memory) of the regulatory T-cells at tumor emergence. The recent discoveries in this field suggest that the activation status of Tregs and effector T-cells (Teffs) at the first encounter with the tumor are essential to shape the fate and speed of the immune response across a variety of tumor models. The relative timing of activation/recruitment of anti-tumor cells vs. tolerogenic cells at tumor emergence appears to be crucial in the identification of tumor cells as friend or foe, which has broad implications for the design of cancer immunotherapies.

The two sides of HER2/neu: immune escape versus surveillance

The oncogene HER2 is one of the prototypes for targeted immunotherapy of cancer using both monoclonal antibodies as well as T cell based immunotherapies. Effective humoral and cellular immune responses against HER2 can be induced, but these responses can be influenced by the effects of this oncogene on the target tumor cells. The processes involved in HER2-mediated adaptive and innate immunity and the molecular mechanisms underlying the escape of HER2-expressing tumor cells from immune surveillance, particularly from cytotoxic T cells, are discussed. Implementing this knowledge in clinical trials to revert immune evasion may help optimize immunotherapies directed against HER2-expressing tumors.

Effects of cyclophosphamide and IL-2 on regulatory CD4+ T cell frequency and function in melanoma patients vaccinated with HLA-class I peptides: impact on the antigen-specific T cell response

The frequency and function of regulatory T cells (Tregs) were studied in stage II–III melanoma patients who were enrolled in a phase II randomized trial of vaccination with HLA-A*0201-modified tumor peptides versus observation. The vaccinated patients received low-dose cyclophosphamide (CTX) and low-dose interleukin-2 (IL-2). Tregs were analyzed in the lymph nodes (LNs) of stage III patients who were undergoing complete lymph node dissection and in peripheral blood mononuclear cells (PBMCs) collected before vaccination and at different time points during the vaccination period. The LNs of the vaccinated patients, which were surgically removed after two rounds of vaccination and one dose of CTX, displayed a low frequency of Tregs and a less immunosuppressive environment compared with those of the untreated patients. The accurate time-course analysis of the PBMCs of patients enrolled in the vaccination arm indicated a limited and transient modulation in the frequencies of Tregs in PBMCs collected after low-dose CTX administration and a strong Treg boost in those PBMCs collected after low-dose IL-2 administration. However, a fraction of the IL-2-boosted Tregs was functionally modulated to a Th-1-like phenotype in the vaccinated patients. Moreover, low-dose IL-2 promoted the concomitant expansion of conventional activated CD4⁺ T cells. Despite the amplification of Tregs, IL-2 administration maintained or further increased the number of antigen-specific CD8⁺ T cells that were induced by vaccination as demonstrated by the ex vivo human leukocyte antigen-multimer staining and IFN-γ ELISpot assays. Our study suggests that the use of CTX as a Treg modulator should be revised in terms of the administration schedule and of patients who may benefit from this drug treatment. Despite the Treg expansion that was observed in this study, low-dose IL-2 is not detrimental to the functional activities of vaccine-primed CD8⁺ T cell effectors when used in the inflammatory environment of vaccination.

Vaccination for the prevention and treatment of breast cancer with special focus on Her-2/neu peptide vaccines

Immunologic interventions in a subset of breast cancer patients represent a well-established therapeutic approach reflecting individualized treatment modalities. Thus, the therapeutic administration of monoclonal antibodies targeting tumor-associated antigens (TAA), such as Her-2/neu, represents a milestone in cancer treatment. However, passive antibody administration suffers from several drawbacks, including frequency and long duration of treatment. These undesirables may be avoidable in an approach based on generating active immune responses against these same targets. Only recently has the significance of tumors in relation to their microenvironments been understood as essential for creating an effective cancer vaccine. In particular, the immune system plays an important role in suppressing or promoting tumor formation and growth. Therefore, activation of appropriate triggers (such as induction of Th1 cells, CD8+ T cells, and suppression of regulatory cells in combination with generation of antibodies with anti-tumor activity) is a desirable goal. Current vaccination approaches have concentrated on therapeutic vaccines using certain TAA. Many cancer antigens, including breast cancer antigens, have been described and also given priority ranking for use as vaccine antigens by the US National Cancer Institute. One of the TAA antigens which has been thoroughly examined in numerous trials is Her-2/neu. This review will discuss delivery systems for this antigen with special focus on T and B cell peptide vaccines. Attention will be given to their advantages and limitations, as well as the use of certain adjuvants to improve anti-cancer responses.

Limited induction of tumor cross-reactive T cells without a measurable clinical benefit in early melanoma patients vaccinated with human leukocyte antigen class I-modified peptides

PURPOSE

The progressive immune dysfunctions that occur in patients with advanced melanoma make them unlikely to efficiently respond to cancer vaccines. A multicenter randomized phase II trial was conducted to test whether immunization with modified HLA class I tumor peptides in the context of adjuvant therapy results in better immunologic responses and improved clinical outcomes in patients with early melanoma (stages IIB/C-III).

EXPERIMENTAL DESIGN

Forty-three patients were enrolled to undergo vaccination (n = 22) or observation (n = 21). The vaccine included four HLA-A*0201-restricted modified peptides (Melan-A/MART-1([27L]), gp100([210M]), NY-ESO-1([165V]), and Survivin([97M])) emulsified in Montanide ISA51 and injected subcutaneously in combination with cyclophosphamide (300 mg/m(2)) and low-dose IL-2 (3 × 10(6) IU). The immune responses were monitored using ex vivo IFN-γ-ELISpot, HLA/multimer staining, and in vitro short-term peptide sensitization assays.

RESULTS

Vaccination induced a rapid and persistent increase in specific effector memory CD8(+) T cells in 75% of the patients. However, this immunization was not associated with any significant increase in disease-free or overall survival as compared with the observation group. An extensive immunologic analysis revealed a significantly reduced cross-recognition of the corresponding native peptides and, most importantly, a limited ability to react to melanoma cells.

CONCLUSIONS

Adjuvant setting is an appealing approach for testing cancer vaccines because specific CD8(+) T cells can be efficiently induced in most vaccinated patients. However, the marginal antitumor activity of the T cells induced by modified peptides in this study largely accounts for the observed lack of benefit of vaccination. These findings suggest reconsidering this immunization strategy, particularly in early disease.

Regulatory T-cell modulation using cyclophosphamide in vaccine approaches: a current perspective

Regulatory T cells (Treg) have become an important player in regulating anticancer immune responses. In fact, published studies describe a correlation between tumor-infiltrating Tregs and poor prognosis. Once called "suppressor T cells," these T cells evaded isolation because of a lack of known markers that distinguished them from other T cells. However, the biology of these T cells is currently a major focus of immunologic research. Markers have since been discovered that identify these T cells and provide insights into how these T cells are regulated. Despite these advances, much needs to be learned about the subsets of Tregs and their specific roles in regulating immune responses. In addition, specific agents that target Tregs are currently unavailable. Cyclophosphamide has emerged as a clinically feasible agent that can suppress Tregs and allow more effective induction of antitumor immune responses. This review focuses on the use of cyclophosphamide in targeting Tregs to augment cancer vaccine approaches. However, these principles can also be applied to other immunotherapy strategies.