Adoptive T cell therapy promotes the emergence of genomically altered tumor escape variants

UPP1 promotes lung adenocarcinoma progression through the induction of an immunosuppressive microenvironment

The complexity of the tumor microenvironment (TME) is a crucial factor in lung adenocarcinoma (LUAD) progression. To gain deeper insights into molecular mechanisms of LUAD, we perform an integrative single-cell RNA sequencing (scRNA-seq) data analysis of 377,574 cells from 117 LUAD patient samples. By linking scRNA-seq data with bulk gene expression data, we identify a cluster of prognostic-related UPP1high tumor cells. These cells, primarily situated at the invasive front of tumors, display a stronger association with the immunosuppressive components in the TME. Our cytokine array analysis reveals that the upregulation of UPP1 in tumor cells leads to the increased release of various immunosuppressive cytokines, with TGF-β1 being particularly prominent. Furthermore, this UPP1 upregulation also elevates the expression of PD-L1 through the PI3K/AKT/mTOR pathway, which contributes to the suppression of CD8 + T cells. Cytometry by time-of-flight (CyTOF) analysis provides additional evidence of the role of UPP1 in shaping the immunosuppressive nature of the TME. Using patient-derived organoids (PDOs), we discover that UPP1high tumors exhibit relatively increased sensitivity to Bosutinib and Dasatinib. Collectively, our study highlights the immunosuppressive role of UPP1 in LUAD, and these findings may provide insights into the molecular features of LUAD and facilitate the development of personalized treatment strategies.

Gold Nanoparticle-Carrying T Cells for the Combined Immuno-Photothermal Therapy

Cancer immunotherapy is a promising therapy to treat cancer patients with minimal toxicity, but only a small fraction of patients responded to it as a monotherapy. In this study, a strategy to boost therapeutic efficacy by combining an immunotherapy based on ex vivo expanded tumor-reactive T cells is devised, or adoptive cell therapy (ACT), with photothermal therapy (PTT). Smart gold nanoparticles (sAuNPs), which aggregates to form gold nanoclusters in the cells, are loaded into T cells, and their photothermal effects within T cells are confirmed. When transferred into tumor-bearing mice, large number of sAuNP-carrying T cells successfully infiltrate into tumor tissues and exert anti-tumor activity to suspend tumor growth, but over time tumor cells evade and regrow. Of note, ≈20% of injected doses of sAuNPs are deposited in tumor tissues, suggesting T cells are an efficient nanoparticle tumor delivery vehicle. When T cells no longer control tumor growth, PTT is performed to further eliminate tumors. In this manner, ACT and PTT are temporally coupled, and the combined immuno-photothermal treatment demonstrated significantly greater therapeutic efficacy than the monotherapy.

Parkin Deficiency Suppresses Antigen Presentation to Promote Tumor Immune Evasion and Immunotherapy Resistance

Parkin is an E3 ubiquitin ligase, which plays a key role in the development of Parkinson disease. Parkin defects also occur in numerous cancers, and a growing body of evidence indicates that Parkin functions as a tumor suppressor that impedes a number of cellular processes involved in tumorigenesis. Here, we generated murine and human models that closely mimic the advanced-stage tumors where Parkin deficiencies are found to provide deeper insights into the tumor suppressive functions of Parkin. Loss of Parkin expression led to aggressive tumor growth, which was associated with poor tumor antigen presentation and limited antitumor CD8+ T-cell infiltration and activation. The effect of Parkin deficiency on tumor growth was lost following depletion of CD8+ T cells. In line with previous findings, Parkin deficiency was linked with mitochondria-associated metabolic stress, PTEN degradation, and enhanced Akt activation. Increased Akt signaling led to dysregulation of antigen presentation, and treatment with the Akt inhibitor MK2206-2HCl restored antigen presentation in Parkin-deficient tumors. Analysis of data from patients with clear cell renal cell carcinoma indicated that Parkin expression was downregulated in tumors and that low expression correlated with reduced overall survival. Furthermore, low Parkin expression correlated with reduced patient response to immunotherapy. Overall, these results identify a role for Parkin deficiency in promoting tumor immune evasion that may explain the poor prognosis associated with loss of Parkin across multiple types of cancer.

SIGNIFICANCE

Parkin prevents immune evasion by regulating tumor antigen processing and presentation through the PTEN/Akt network, which has important implications for immunotherapy treatments in patients with Parkin-deficient tumors.

Cellular Therapy in NSCLC: Between Myth and Reality

PURPOSE OF REVIEW

In this paper, we review the current state and modalities of adoptive cell therapies (ACT) in non-small cell lung carcinoma (NSCLC). We also discuss the challenges hampering the use of ACT and the approaches to overcome these barriers.

RECENT FINDINGS

Several trials are ongoing investigating the three main modalities of T cell-based ACT: tumor-infiltrating lymphocytes (TILs), genetically engineered T-cell receptors (TCRs), and chimeric antigen receptor (CAR) T cells. The latter, in particular, has revolutionized the treatment of hematologic malignancies. However, the efficacy against solid tumor is still sparse. Major limitations include the following: severe toxicities, restricted infiltration and activation within the tumors, antigen escape and heterogeneity, and manufacturing issues. ACT is a promising tool to improve the outcome of metastatic NSCLC, but significant translational and clinical research is needed to improve its application and expand the use in NSCLC.

Trap and ambush therapy using sequential primary and tumor escape-selective oncolytic viruses

In multiple models of oncolytic virotherapy, it is common to see an early anti-tumor response followed by recurrence. We have previously shown that frontline treatment with oncolytic VSV-IFN-β induces APOBEC proteins, promoting the selection of specific mutations that allow tumor escape. Of these mutations in B16 melanoma escape (ESC) cells, a C-T point mutation in the cold shock domain-containing E1 (CSDE1) gene was present at the highest frequency, which could be used to ambush ESC cells by vaccination with the mutant CSDE1 expressed within the virus. Here, we show that the evolution of viral ESC tumor cells harboring the escape-promoting CSDE1C-T mutation can also be exploited by a virological ambush. By sequential delivery of two oncolytic VSVs in vivo, tumors which would otherwise escape VSV-IFN-β oncolytic virotherapy could be cured. This also facilitated the priming of anti-tumor T cell responses, which could be further exploited using immune checkpoint blockade with the CD200 activation receptor ligand (CD200AR-L) peptide. Our findings here are significant in that they offer the possibility to develop oncolytic viruses as highly specific, escape-targeting viro-immunotherapeutic agents to be used in conjunction with recurrence of tumors following multiple different types of frontline cancer therapies.

Nanoparticle-based modulation of CD4+ T cell effector and helper functions enhances adoptive immunotherapy

Helper (CD4⁺) T cells perform direct therapeutic functions and augment responses of cells such as cytotoxic (CD8⁺) T cells against a wide variety of diseases and pathogens. Nevertheless, inefficient synthetic technologies for expansion of antigen-specific CD4⁺ T cells hinders consistency and scalability of CD4⁺ T cell-based therapies, and complicates mechanistic studies. Here we describe a nanoparticle platform for ex vivo CD4⁺ T cell culture that mimics antigen presenting cells (APC) through display of major histocompatibility class II (MHC II) molecules. When combined with soluble co-stimulation signals, MHC II artificial APCs (aAPCs) expand cognate murine CD4⁺ T cells, including rare endogenous subsets, to induce potent effector functions in vitro and in vivo. Moreover, MHC II aAPCs provide help signals that enhance antitumor function of aAPC-activated CD8⁺ T cells in a mouse tumor model. Lastly, human leukocyte antigen class II-based aAPCs expand rare subsets of functional, antigen-specific human CD4⁺ T cells. Overall, MHC II aAPCs provide a promising approach for harnessing targeted CD4⁺ T cell responses.

Tumor-infiltrating lymphocytes for adoptive cell therapy: recent advances, challenges, and future directions

INTRODUCTION

Adoptive cell therapy (ACT) with tumor-infiltrating lymphocytes (TILs) is a highly personalized type of cancer immunotherapy. TIL-based ACT exploits naturally occurring TILs, derived from the patients' tumor. This treatment has shown consistent clinical responses in melanoma, and recent results point toward a potential use in multiple cancer diagnoses. However, several limitations have restricted the clinical development and adaptation of TIL-based ACT.

AREAS COVERED

In this review, we present the principles of TIL-based ACT and discuss the most significant limitations for therapeutic efficacy and its widespread application. The topics of therapeutic resistance (both innate and acquired), treatment-related toxicity, and the novel research topic of metabolic barriers in the tumor microenvironment (TME) are covered.

EXPERT OPINION

There are many ongoing areas of research focusing on improving clinical efficacy and optimizing TIL-based ACT. Many strategies have shown great potential, particularly strategies advancing TIL efficacy (such as increasing and harnessing ex vivo the sub-population of tumor-reactive TILs) and manufacturing processes. Novel approaches can help overcome current limitations and potentially result in TIL-based ACT entering the mainstream of cancer therapy across tumor types.

TCR-T Immunotherapy: The Challenges and Solutions

T cell receptor-engineered T cell (TCR-T) therapy is free from the limit of surface antigen expression of the target cells, which is a potential cellular immunotherapy for cancer treatment. Significant advances in the treatment of hematologic malignancies with cellular immunotherapy have aroused the interest of researchers in the treatment of solid tumors. Nevertheless, the overall efficacy of TCR-T cell immunotherapy in solid tumors was not significantly high when compared with hematological malignancies. In this article, we pay attention to the barriers of TCR-T cell immunotherapy for solid tumors, as well as the strategies affecting the efficacy of TCR-T cell immunotherapy. To provide some reference for researchers to better overcome the impact of TCR-T cell efficiency in solid tumors.

Local therapy with an engineered oncolytic adenovirus enables antitumor response in non-injected melanoma tumors in mice treated with aPD-1

Intratumoral immunotherapies are entering clinical use but concerns remain regarding their effects on non-injected tumors. Here, we studied the impact of local treatment with an adenovirus coding for TNFa and IL-2 on systemic antitumor response in animals receiving aPD-1 (anti-programmed cell death protein 1) therapy. Using bilateral murine melanoma models, we tested systemic tumor response to combined therapy with anti-PD-1 and an adenovirus coding for TNFa and IL-2 ("virus"). Virus was given intratumorally (to one of the two tumors only) and aPD-1 monoclonal antibody systemically. We evaluated both tumors' response to treatment, overall survival, metastasis development, and immunological mechanisms involved with response. Consistent tumor control was observed in both injected and non-injected tumors, including complete response in all treated animals receiving aPD-1+ virus therapy. Mechanistically, virus injections enabled potent effector lymphocyte response locally, with systemic effects in non-injected tumors facilitated by aPD-1 treatment. Moreover, adenovirus therapy demonstrated immunological memory formation. Virus therapy was effective in preventing metastasis development. Local treatment with TNFa and IL-2 coding adenovirus enhanced systemic response to aPD-1 therapy, by re-shaping the microenvironment of both injected and non-injected tumors. Therefore, our pre-clinical data support the rationale for a trial utilizing a combination of aPD-1 plus virus for the treatment of human cancer.

Enhancing adoptive CD8 T cell therapy by systemic delivery of tumor associated antigens

Adoptive T-cell transfer (ACT) offers a curative therapeutic option for subsets of melanoma and hematological cancer patients. To increase response rates and broaden the applicability of ACT, it is necessary to improve the post-infusion performance of the transferred T cells. The design of improved treatment strategies includes transfer of cells with a less differentiated phenotype. Such T cell subsets have high proliferative potential but require stimulatory signals in vivo to differentiate into tumor-reactive effector T cells. Thus, combination strategies are needed to support the therapeutic implementation of less differentiated T cells. Here we show that systemic delivery of tumor-associated antigens (TAAs) facilitates in vivo priming and expansion of previously non-activated T cells and enhance the cytotoxicity of activated T cells. To achieve this in vivo priming, we use flexible delivery vehicles of TAAs and a TLR7/8 agonist. Contrasting subcutaneous delivery systems, these vehicles accumulate TAAs in the spleen, thereby achieving close proximity to both cross-presenting dendritic cells and transferred T cells, resulting in robust T-cell expansion and anti-tumor reactivity. This TAA delivery platform offers a strategy to safely potentiate the post-infusion performance of T cells using low doses of antigen and TLR7/8 agonist, and thereby enhance the effect of ACT.

In Situ Programming of CAR T Cells

Gene therapy makes it possible to engineer chimeric antigen receptors (CARs) to create T cells that target specific diseases. However, current approaches require elaborate and expensive protocols to manufacture engineered T cells ex vivo, putting this therapy beyond the reach of many patients who might benefit. A solution could be to program T cells in vivo. Here, we evaluate the clinical need for in situ CAR T cell programming, compare competing technologies, review current progress, and provide a perspective on the long-term impact of this emerging and rapidly flourishing biotechnology field.

Oncolytic virotherapy induced CSDE1 neo-antigenesis restricts VSV replication but can be targeted by immunotherapy

In our clinical trials of oncolytic vesicular stomatitis virus expressing interferon beta (VSV-IFNβ), several patients achieved initial responses followed by aggressive relapse. We show here that VSV-IFNβ-escape tumors predictably express a point-mutated CSDE1P5S form of the RNA-binding Cold Shock Domain-containing E1 protein, which promotes escape as an inhibitor of VSV replication by disrupting viral transcription. Given time, VSV-IFNβ evolves a compensatory mutation in the P/M Inter-Genic Region which rescues replication in CSDE1P5S cells. These data show that CSDE1 is a major cellular co-factor for VSV replication. However, CSDE1P5S also generates a neo-epitope recognized by non-tolerized T cells. We exploit this predictable neo-antigenesis to drive, and trap, tumors into an escape phenotype, which can be ambushed by vaccination against CSDE1P5S, preventing tumor escape. Combining frontline therapy with escape-targeting immunotherapy will be applicable across multiple therapies which drive tumor mutation/evolution and simultaneously generate novel, targetable immunopeptidomes associated with acquired treatment resistance.

The Resistance Mechanisms of Lung Cancer Immunotherapy

Immunotherapy has revolutionized lung cancer treatment in the past decade. By reactivating the host’s immune system, immunotherapy significantly prolongs survival in some advanced lung cancer patients. However, resistance to immunotherapy is frequent, which manifests as a lack of initial response or clinical benefit to therapy (primary resistance) or tumor progression after the initial period of response (acquired resistance). Overcoming immunotherapy resistance is challenging owing to the complex and dynamic interplay among malignant cells and the defense system. This review aims to discuss the mechanisms that drive immunotherapy resistance and the innovative strategies implemented to overcome it in lung cancer.

Eomesodermin Increases Survival and IL-2 Responsiveness of Tumor-specific CD8+ T Cells in an Adoptive Transfer Model of Cancer Immunotherapy

Tumor-specific CD8 T cells often fail to elicit effective antitumor immune responses due to an inability to expand into a substantial effector population and persist long-term in vivo. Using an adoptive transfer model of cancer immunotherapy, we demonstrate that constitutive eomesodermin (Eomes) expression in tumor-specific CD8 T cells improves tumor rejection and survival. The increase in tumor rejection was associated with an increased number and persistence of CD8 T cells in lymphoid tissues during acute tumor rejection, tumor regrowth, and in mice that remained tumor-free. Constitutive Eomes expression increased expression of CD25, and this was associated with enhanced interleukin-2 responsiveness and tumor-specific CD8 T-cell proliferation. Moreover, constitutive Eomes expression improved cell survival. Taken together, our data suggest that constitutive Eomes expression enhances CD8 T-cell proliferation and survival, in part through the enhancement of interleukin-2 responsiveness through CD25 induction.

Acquired resistance during adoptive cell therapy by transcriptional silencing of immunogenic antigens

Immunotherapies such as adoptive cell therapy (ACT) are promising treatments for solid cancers. However, relapsing disease remains a problem and the molecular mechanisms underlying resistance are poorly defined. We postulated that the deregulated epigenetic landscape in cancer cells could underpin the acquisition of resistance to immunotherapy. To address this question, two preclinical models of ACT were employed to study transcriptional and epigenetic regulatory processes within ACT-treated cancer cells. In these models ACT consistently causes robust tumor regression, but resistance develops and tumors relapse. We identified down-regulated expression of immunogenic antigens at the mRNA level correlated with escape from immune control. To determine whether this down-regulation was under epigenetic control, we treated escaped tumor cells with DNA demethylating agents, azacytidine (AZA) and decitabine (DEC). AZA or DEC treatment restored antigen expression in a proportion of the tumor population. To explore the importance of other epigenetic modifications we isolated tumor cells refractory to DNA demethylation and screened clones against a panel of 19 different epigenetic modifying agents (EMAs). The library of EMAs included inhibitors of a range of chromosomal and transcription regulatory protein complexes, however, when tested as single agents none restored further antigen expression. These findings suggest that tumor cells employ multiple epigenetic and genetic mechanisms to evade immune control, and a combinatorial approach employing several EMAs targeting transcription and genome stability may be required to overcome tumor resistance to immunotherapy.

Suboptimal T-cell Therapy Drives a Tumor Cell Mutator Phenotype That Promotes Escape from First-Line Treatment

Antitumor T-cell responses raised by first-line therapies such as chemotherapy, radiation, tumor cell vaccines, and viroimmunotherapy tend to be weak, both quantitatively (low frequency) and qualitatively (low affinity). We show here that T cells that recognize tumor-associated antigens can directly kill tumor cells if used at high effector-to-target ratios. However, when these tumor-reactive T cells were present at suboptimal ratios, direct T-cell-mediated tumor cell killing was reduced and the ability of tumor cells to evolve away from a coapplied therapy (oncolytic or suicide gene therapy) was promoted. This T-cell-mediated increase in therapeutic resistance was associated with C to T transition mutations that are characteristic of APOBEC3 cytosine deaminase activity and was induced through a TNFα and protein kinase C-dependent pathway. Short hairpin RNA inhibition of endogenous APOBEC3 reduced rates of tumor escape from oncolytic virus or suicide gene therapy to those seen in the absence of antitumor T-cell coculture. Conversely, overexpression of human APOBEC3B in tumor cells enhanced escape from suicide gene therapy and oncolytic virus therapy both in vitro and in vivo Our data suggest that weak affinity or low frequency T-cell responses against tumor antigens may contribute to the ability of tumor cells to evolve away from first-line therapies. We conclude that immunotherapies need to be optimized as early as possible so that, if they do not kill the tumor completely, they do not promote treatment resistance.

Enhanced Safety and Efficacy of Oncolytic VSV Therapy by Combination with T Cell Receptor Transgenic T Cells as Carriers

Vesicular stomatitis virus (VSV) represents an attractive oncolytic virotherapy platform because of its potent tumor cell-killing and immune-stimulating properties; yet the clinical translation of VSV faces numerous challenges, such as inefficient systemic delivery and severe side effects such as neurotoxicity. We hypothesized that we could overcome these limitations and simultaneously enhance the therapy, by combining VSV with adoptively transferred T cell receptor (TCR) transgenic T cells as carrier cells. We show that CD8⁺ T central memory cells (CD8⁺ T cm) can be efficiently loaded with VSV, they support intracellular virus production, and they can efficiently transfer VSV to tumor cells without compromising their own viability or antitumor reactivity. Loading VSV onto CD8⁺ T cm not only improves the safety compared with systemic administration of naked virus, but this approach also allows for an effective delivery of virus to its tumor target, resulting in an effective combination therapy in NSG mice bearing subcutaneous human acute myeloid leukemia (AML) tumors. We conclude that the combination of potent tumor debulking provided by the oncolytic VSV with the added effector functions afforded by the cytotoxic immune carrier cells results in a potent and safer immunotherapeutic, which can be further developed for clinical translation.

Betulin silver nanoparticles qualify as efficient antimelanoma agents in in vitro and in vivo studies

The current study was purported to assess the: (i) in vitro toxicity of betulin silver nanoparticles (AgNPs-B), bare and capped with polyethylene glycol (PEG), on two murine melanoma cell lines (B164A5 and B16Ova) and on healthy cell lines (keratinocytes and melanocytes), and (ii) in vivo antitumor efficacy of PEGylated AgNPs-B in an experimental melanoma model. Bare and PEG-capped AgNPs-B were synthesized by a chemical reduction method resulting in stable and non-aggregated spherical AgNPs-B and PEG-AgNPs-B, of narrow size distributions and mean hydrodynamic diameters of 25 nm and 75 nm, respectively. In vitro assessments were achieved by MTT and Annexin V-FITC assays and in vivo evaluation involved non-invasive techniques for the surveillance of the physiological skin parameters changes and histopathological examination of the harvested organs. The in vitro results revealed selective cytotoxicity against melanoma cells, at low doses that are nontoxic to normal cells; higher doses were associated with the loss of selectivity and toxicity for healthy cells. PEGylated formulation of betulin exerted a dose-dependent pro-apoptotic effect, more obvious in the case of B164A5 cells. Histopathological analysis suggested that PEGylated AgNPs-B developed relevant in vivo effects as antimelanoma agents by decreasing the tumor volume and inhibiting the development of secondary tumors.

Acquired resistance to cancer immunotherapy

In recent times, advances in cancer immunotherapy have yielded impressive, durable clinical responses in patients with varied subtypes of cancer. However, a significant proportion of patients who initially demonstrate encouraging tumor regression develop resistance and progress over time. The identification of novel therapeutic approaches to overcome resistance may result in significantly improved clinical outcomes and remains an area of high scientific priority. This review aims to summarize the current knowledge regarding the role of both tumor-intrinsic and tumor-extrinsic factors in the development of resistance to cancer immunotherapy and to discuss current and possible future therapeutic strategies targeting these mechanisms.

Vaccine immunotherapy with ARNAX induces tumor-specific memory T cells and durable anti-tumor immunity in mouse models

Immunological checkpoint blockade therapies benefit a limited population of cancer patients. We have previously shown that vaccine immunotherapy with Toll‐like receptor (TLR)3‐adjuvant and tumor antigen overcomes anti‐programmed death ligand‐1 (PD‐L1) resistance in mouse tumor models. In the present study, 4 different ovalbumin (OVA)‐expressing tumor cell lines were implanted into syngeneic mice and subjected to anti‐tumor immunotherapy using ARNAX and whole OVA protein. ARNAX is a TLR3‐specific agonist that does not activate the mitochondrial antiviral‐signaling protein (MAVS) pathway, and thus does not induce systemic inflammation. Dendritic cell priming and proliferative CTL were induced by ARNAX + OVA, but complete remission was achieved only in a PD‐L1‐low cell line of EG7. Addition of anti‐PD‐L1 antibody to the ARNAX + OVA therapy brought complete remission to another PD‐L1‐high subline of EG7. Tumor shrinkage but not remission was observed in MO5 in that regimen. We analyzed tumor cells and tumor‐infiltrating immune cells to identify factors associated with successful ARNAX vaccine therapy. Tumors that responded to ARNAX therapy expressed high levels of MHC class I and low levels of PD‐L1. The tumor‐infiltrating immune cells in ARNAX‐susceptible tumors contained fewer immunosuppressive myeloid cells with low PD‐L1 expression. Combination with anti‐PD‐L1 antibody functioned not only within tumor sites but also within lymphoid tissues, augmenting the therapeutic efficacy of the ARNAX vaccine. Notably, ARNAX therapy induced memory CD8⁺ T cells and rejection of reimplanted tumors. Thus, ARNAX vaccine + anti‐PD‐L1 therapy enabled permanent remission against some tumors that stably present antigens.

Simultaneous in vitro generation of CD8 and CD4 T cells specific to three universal tumor associated antigens of WT1, survivin and TERT and adoptive T cell transfer for the treatment of acute myeloid leukemia

Previously, we found that most patients with acute myeloid leukemia (AML) expressed at least one of the leukemic associated antigens (LAAs) WT1, survivin and TERT, and different combinations of the three LAAs predicted negative clinical outcomes. Multi-tumor antigen-specific T cells were generated to overcome antigenic variation and may be sufficient to maximize antitumoral effects. To generate triple antigen-specific (Tri)-T cells that recognize three LAAs, dendritic cells (DCs) were transfected with three tumor antigen-encoding RNAs. These DCs were used to stimulate both CD8 and CD4 T cells and to overcome the limitation of known human leukocyte antigen-restricted epitopes. The sum of the antigen-specific T cell frequencies was higher in the Tri-T cells than in the T cells that recognized a single antigen. Furthermore, the Tri-T cells were more effective against leukemic blasts that expressed all three LAAs compared with blasts that expressed one or two LAAs, suggesting a proportional correlation between IFN-γ secretion and LAA expression. Engrafted leukemic blasts in the bone marrow of mice significantly decreased in the presence of Tri-T cells. This technique represents an effective immunotherapeutic strategy in AML.

Nanoparticles: augmenting tumor antigen presentation for vaccine and immunotherapy treatments of cancer

The major goal of immunity is maintaining host survival. Toward this, immune cells recognize and eliminate targets that pose a danger. Primarily, these are external invaders (pathogens) and internal invaders (cancers). Their recognition relies on distinguishing foreign components (antigens) from self-antigens. Since cancer cells are the host's own cells that are harmfully altered, they are difficult to distinguish from normal self. Furthermore, the antigens least resembling the host are often sequestered in parts of the tumor least accessible to immune responses. Therefore, to sufficiently boost immunity, these tumor antigens must be exposed to the immune system. Toward this, nanoparticles provide an innovating means of tumor antigen presentation and are destined to become an integral part of cancer immunotherapy.

CDK4/6 Inhibition Augments Antitumor Immunity by Enhancing T-cell Activation

Immune checkpoint blockade, exemplified by antibodies targeting the PD-1 receptor, can induce durable tumor regressions in some patients. To enhance the efficacy of existing immunotherapies, we screened for small molecules capable of increasing the activity of T cells suppressed by PD-1. Here, we show that short-term exposure to small-molecule inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6) significantly enhances T-cell activation, contributing to antitumor effects in vivo, due in part to the derepression of NFAT family proteins and their target genes, critical regulators of T-cell function. Although CDK4/6 inhibitors decrease T-cell proliferation, they increase tumor infiltration and activation of effector T cells. Moreover, CDK4/6 inhibition augments the response to PD-1 blockade in a novel ex vivo organotypic tumor spheroid culture system and in multiple in vivo murine syngeneic models, thereby providing a rationale for combining CDK4/6 inhibitors and immunotherapies.Significance: Our results define previously unrecognized immunomodulatory functions of CDK4/6 and suggest that combining CDK4/6 inhibitors with immune checkpoint blockade may increase treatment efficacy in patients. Furthermore, our study highlights the critical importance of identifying complementary strategies to improve the efficacy of immunotherapy for patients with cancer. Cancer Discov; 8(2); 216-33. ©2017 AACR.See related commentary by Balko and Sosman, p. 143See related article by Jenkins et al., p. 196This article is highlighted in the In This Issue feature, p. 127.

Subversion of NK-cell and TNFα Immune Surveillance Drives Tumor Recurrence

Understanding how incompletely cleared primary tumors transition from minimal residual disease (MRD) into treatment-resistant, immune-invisible recurrences has major clinical significance. We show here that this transition is mediated through the subversion of two key elements of innate immunosurveillance. In the first, the role of TNFα changes from an antitumor effector against primary tumors into a growth promoter for MRD. Second, whereas primary tumors induced a natural killer (NK)-mediated cytokine response characterized by low IL6 and elevated IFNγ, PD-L1hi MRD cells promoted the secretion of IL6 but minimal IFNγ, inhibiting both NK-cell and T-cell surveillance. Tumor recurrence was promoted by trauma- or infection-like stimuli inducing VEGF and TNFα, which stimulated the growth of MRD tumors. Finally, therapies that blocked PD-1, TNFα, or NK cells delayed or prevented recurrence. These data show how innate immunosurveillance mechanisms, which control infection and growth of primary tumors, are exploited by recurrent, competent tumors and identify therapeutic targets in patients with MRD known to be at high risk of relapse. Cancer Immunol Res; 5(11); 1029-45. ©2017 AACR.

Oncolytic Vesicular Stomatitis Virus as a Viro-Immunotherapy: Defeating Cancer with a "Hammer" and "Anvil"

Oncolytic viruses have gained much attention in recent years, due, not only to their ability to selectively replicate in and lyse tumor cells, but to their potential to stimulate antitumor immune responses directed against the tumor. Vesicular stomatitis virus (VSV), a negative-strand RNA virus, is under intense development as an oncolytic virus due to a variety of favorable properties, including its rapid replication kinetics, inherent tumor specificity, and its potential to elicit a broad range of immunomodulatory responses to break immune tolerance in the tumor microenvironment. Based on this powerful platform, a multitude of strategies have been applied to further improve the immune-stimulating potential of VSV and synergize these responses with the direct oncolytic effect. These strategies include: 1. modification of endogenous virus genes to stimulate interferon induction; 2. virus-mediated expression of cytokines or immune-stimulatory molecules to enhance anti-tumor immune responses; 3. vaccination approaches to stimulate adaptive immune responses against a tumor antigen; 4. combination with adoptive immune cell therapy for potentially synergistic therapeutic responses. A summary of these approaches will be presented in this review.

Effector, Memory, and Dysfunctional CD8(+) T Cell Fates in the Antitumor Immune Response

The adaptive immune system plays a pivotal role in the host's ability to mount an effective, antigen-specific immune response against tumors. CD8(+) tumor-infiltrating lymphocytes (TILs) mediate tumor rejection through recognition of tumor antigens and direct killing of transformed cells. In growing tumors, TILs are often functionally impaired as a result of interaction with, or signals from, transformed cells and the tumor microenvironment. These interactions and signals can lead to transcriptional, functional, and phenotypic changes in TILs that diminish the host's ability to eradicate the tumor. In addition to effector and memory CD8(+) T cells, populations described as exhausted, anergic, senescent, and regulatory CD8(+) T cells have been observed in clinical and basic studies of antitumor immune responses. In the context of antitumor immunity, these CD8(+) T cell subsets remain poorly characterized in terms of fate-specific biomarkers and transcription factor profiles. Here we discuss the current characterization of CD8(+) T cell fates in antitumor immune responses and discuss recent insights into how signals in the tumor microenvironment influence TIL transcriptional networks to promote CD8(+) T cell dysfunction.

Enrichment and Expansion with Nanoscale Artificial Antigen Presenting Cells for Adoptive Immunotherapy

Adoptive immunotherapy (AIT) can mediate durable regression of cancer, but widespread adoption of AIT is limited by the cost and complexity of generating tumor-specific T cells. Here we develop an Enrichment + Expansion strategy using paramagnetic, nanoscale artificial antigen presenting cells (aAPC) to rapidly expand tumor-specific T cells from rare naïve precursors and predicted neo-epitope responses. Nano-aAPC are capable of enriching rare tumor-specific T cells in a magnetic column and subsequently activating them to induce proliferation. Enrichment + Expansion resulted in greater than 1000-fold expansion of both mouse and human tumor-specific T cells in 1 week, with nano-aAPC based enrichment conferring a proliferation advantage during both in vitro culture and after adoptive transfer in vivo. Robust T cell responses were seen not only for shared tumor antigens, but also for computationally predicted neo-epitopes. Streamlining the rapid generation of large numbers of tumor-specific T cells in a cost-effective fashion through Enrichment + Expansion can be a powerful tool for immunotherapy.

Definitive Management of Oligometastatic Melanoma in a Murine Model Using Combined Ablative Radiation Therapy and Viral Immunotherapy

PURPOSE

The oligometastatic state is an intermediate state between a malignancy that can be completely eradicated with conventional modalities and one in which a palliative approach is undertaken. Clinically, high rates of local tumor control are possible with stereotactic ablative radiation therapy (SABR), using precisely targeted, high-dose, low-fraction radiation therapy. However, in oligometastatic melanoma, virtually all patients develop progression systemically at sites not initially treated with ablative radiation therapy that cannot be managed with conventional chemotherapy and immunotherapy. We have demonstrated in mice that intravenous administration of vesicular stomatitis virus (VSV) expressing defined tumor-associated antigens (TAAs) generates systemic immune responses capable of clearing established tumors. Therefore, in the present preclinical study, we tested whether the combination of systemic VSV-mediated antigen delivery and SABR would be effective against oligometastatic disease.

METHODS AND MATERIALS

We generated a model of oligometastatic melanoma in C57BL/6 immunocompetent mice and then used a combination of SABR and systemically administered VSV-TAA viral immunotherapy to treat both local and systemic disease.

RESULTS

Our data showed that SABR generates excellent control or cure of local, clinically detectable, and accessible tumor through direct cell ablation. Also, the immunotherapeutic activity of systemically administered VSV-TAA generated T-cell responses that cleared subclinical metastatic tumors. We also showed that SABR induced weak T-cell-mediated tumor responses, which, particularly if boosted by VSV-TAA, might contribute to control of local and systemic disease. In addition, VSV-TAA therapy alone had significant effects on control of both local and metastatic tumors.

CONCLUSIONS

We have shown in the present preliminary murine study using a single tumor model that this approach represents an effective, complementary combination therapy model that addresses the need for both systemic and local control in oligometastatic melanoma.

Generation of CD8(+) T cells expressing two additional T-cell receptors (TETARs) for personalised melanoma therapy

Adoptive T-cell therapy of cancer often fails due to the tumor cells' immune escape mechanisms, like antigen loss or down-regulation. To anticipate immune escape by loss of a single antigen, it would be advantageous to equip T cells with multiple specificities. To study the possible interference of 2 T-cell receptors (TCRs) in one cell, and to examine how to counteract competing effects, we generated TETARs, CD8(+) T cells expressing two additional T-cell receptors by simultaneous transient transfection with 2 TCRs using RNA electroporation. The TETARs were equipped with one TCR specific for the common melanoma antigen gp100 and one TCR recognizing a patient-specific, individual mutation of CCT6A (chaperonin containing TCP1, subunit 6A) termed "CCT6A(m) TCR." These CD8(+) T cells proved functional in cytokine secretion and lytic activity upon stimulation with each of their cognate antigens, although some reciprocal inhibition was observed. Murinisation of the CCT6A(m) TCR increased and prolonged its expression and increased the lytic capacity of the dual-specific T cells. Taken together, we generated functional, dual-specific CD8(+) T cells directed against a common melanoma-antigen and an individually mutated antigen for the use in personalised adoptive T-cell therapy of melanoma. The intended therapy would involve repetitive injections of the RNA-transfected cells to overcome the transiency of TCR expression. In case of autoimmunity-related side effects, a cessation of treatment would result in a disappearance of the introduced receptors, which increases the safety of this approach.

Favorable alteration of tumor microenvironment by immunomodulatory cytokines for efficient T-cell therapy in solid tumors

Unfavorable ratios between the number and activation status of effector and suppressor immune cells infiltrating the tumor contribute to resistance of solid tumors to T-cell based therapies. Here, we studied the capacity of FDA and EMA approved recombinant cytokines to manipulate this balance in favor of efficient anti-tumor responses in B16.OVA melanoma bearing C57BL/6 mice. Intratumoral administration of IFN-α2, IFN-γ, TNF-α, and IL-2 significantly enhanced the anti-tumor effect of ovalbumin-specific CD8+ T-cell (OT-I) therapy, whereas GM-CSF increased tumor growth in association with an increase in immunosuppressive cell populations. None of the cytokines augmented tumor trafficking of OT-I cells significantly, but injections of IFN-α2, IFN-γ and IL-2 increased intratumoral cytokine secretion and recruitment of endogenous immune cells capable of stimulating T-cells, such as natural killer and maturated CD11c+ antigen-presenting cells. Moreover, IFN-α2 and IL-2 increased the levels of activated tumor-infiltrating CD8+ T-cells concomitant with reduction in the CD8+ T-cell expression of anergy markers CTLA-4 and PD-1. In conclusion, intratumoral administration of IFN-α2, IFN-γ and IL-2 can lead to immune sensitization of the established tumor, whereas GM-CSF may contribute to tumor-associated immunosuppression. The results described here provide rationale for including local administration of immunostimulatory cytokines into T-cell therapy regimens. One appealing embodiment of this would be vectored delivery which could be advantageous over direct injection of recombinant molecules with regard to efficacy, cost, persistence and convenience.

Adenovirus Improves the Efficacy of Adoptive T-cell Therapy by Recruiting Immune Cells to and Promoting Their Activity at the Tumor

Despite the rapid progress in the development of novel adoptive T-cell therapies, the clinical benefits in treatment of established tumors have remained modest. Several immune evasion mechanisms hinder T-cell entry into tumors and their activity within the tumor. Of note, oncolytic adenoviruses are intrinsically immunogenic due to inherent pathogen-associated molecular patterns. Here, we studied the capacity of adenovirus to overcome resistance of chicken ovalbumin-expressing B16.OVA murine melanoma tumors to adoptive ovalbumin-specific CD8(+) T-cell (OT-I) therapy. Following intraperitoneal transfer of polyclonally activated OT-I lymphocytes, control of tumor growth was superior in mice given intratumoral adenovirus compared with control mice, even in the absence of oncolytic virus replication. Preexisting antiviral immunity against serotype 5 did not hinder the therapeutic efficacy of the combination treatment. Intratumoral adenovirus injection was associated with an increase in proinflammatory cytokines, CD45(+) leukocytes, CD8(+) lymphocytes, and F4/80(+) macrophages, suggesting enhanced tumor immunogenicity. The proinflammatory effects of adenovirus on the tumor microenvironment led to expression of costimulatory signals on CD11c(+) antigen-presenting cells and subsequent activation of T cells, thus breaking the tumor-induced peripheral tolerance. An increased number of CD8(+) T cells specific for endogenous tumor antigens TRP-2 and gp100 was detected in combination-treated mice, indicating epitope spreading. Moreover, the majority of virus/T-cell-treated mice rejected the challenge of parental B16.F10 tumors, suggesting that systemic antitumor immunity was induced. In summary, we provide proof-of-mechanism data on combining adoptive T-cell therapy and adenovirotherapy for the treatment of cancer.

Mutated BRAF Emerges as a Major Effector of Recurrence in a Murine Melanoma Model After Treatment With Immunomodulatory Agents

We used a VSV-cDNA library to treat recurrent melanoma, identifying immunogenic antigens, allowing us to target recurrences with immunotherapy or chemotherapy. Primary B16 melanoma tumors were induced to regress by frontline therapy. Mice with recurrent tumors were treated with VSV-cDNA immunotherapy. A Th17 recall response was used to screen the VSV-cDNA library for individual viruses encoding rejection antigens, subsequently targeted using immunotherapy or chemotherapy. Recurrent tumors were effectively treated with a VSV-cDNA library using cDNA from recurrent B16 tumors. Recurrence-associated rejection antigens identified included Topoisomerase-IIα, YB-1, cdc7 kinase, and BRAF. Fourteen out of 16 recurrent tumors carried BRAF mutations (595-605 region) following frontline therapy, even though the parental B16 tumors were BRAF wild type. The emergence of mutated BRAF-containing recurrences served as an excellent target for BRAF-specific immune-(VSV-BRAF), or chemo-(PLX-4720) therapies. Successful PLX-4720 therapy of recurrent tumors was associated with the development of a broad spectrum of T-cell responses. VSV-cDNA technology can be used to identify recurrence specific antigens. Emergence of mutated BRAF may be a major effector of melanoma recurrence which could serve as a target for chemo or immune therapy. This study suggests a rationale for offering patients with initially wild-type BRAF melanomas an additional biopsy to screen for mutant BRAF upon recurrence.

Adaptive Resistance to Immunotherapy Directed Against p53 Can be Overcome by Global Expression of Tumor-Antigens in Dendritic Cells

Immunotherapy of cancer utilizes dendritic cells (DCs) for antigen presentation and the induction of tumor-specific immune responses. However, the therapeutic induction of anti-tumor immunity is limited by tumor escape mechanisms. In this study, immortalized dendritic D2SC/1 cells were transduced with a mutated version of the p53 tumor suppressor gene, p53M234I, or p53C132F/E168G, which are overexpressed in MethA fibrosarcoma tumor cells. In addition, D2SC/1 cells were fused with MethA tumor cells to generate a vaccine that potentially expresses a large repertoire of tumor-antigens. Cellular vaccines were transplanted onto Balb/c mice and MethA tumor growth and anti-tumor immune responses were examined in vaccinated animals. D2SC/1–p53M234I and D2SC/1–p53C132F/E168G cells induced strong therapeutic and protective MethA tumor immunity upon transplantation in Balb/c mice. However, in a fraction of immunized mice MethA tumor growth resumed after an extended latency period. Analysis of these tumors indicated loss of p53 expression. Mice, pre-treated with fusion hybrids generated from D2SC/1 and MethA tumor cells, suppressed MethA tumor growth and averted adaptive immune escape. Polyclonal B-cell responses directed against various MethA tumor proteins could be detected in the sera of D2SC/1–MethA inoculated mice. Athymic nude mice and Balb/c mice depleted of CD4⁺ or CD8⁺ T-cells were not protected against MethA tumor cell growth after immunization with D2SC/1–MethA hybrids. Our results highlight a potential drawback of cancer immunotherapy by demonstrating that the induction of a specific anti-tumor response favors the acquisition of tumor phenotypes promoting immune evasion. In contrast, the application of DC/tumor cell fusion hybrids prevents adaptive immune escape by a T-cell dependent mechanism and provides a simple strategy for personalized anti-cancer treatment without the need of selectively priming the host immune system.

The profile of tumor antigens which can be targeted by immunotherapy depends upon the tumor's anatomical site

Previously, we showed that vesicular stomatitis virus (VSV) engineered to express a cDNA library from human melanoma cells (ASMEL, Altered Self Melanoma Epitope Library) was an effective systemic therapy to treat subcutaneous (s.c.) murine B16 melanomas. Here, we show that intravenous treatment with the same ASMEL VSV-cDNA library was an effective treatment for established intra-cranial (i.c.) melanoma brain tumors. The optimal combination of antigens identified from the ASMEL which treated s.c. B16 tumors (VSV-N-RAS+VSV-CYTC-C+VSV-TYRP-1) was ineffective against i.c. B16 brain tumors. In contrast, combination of VSV-expressed antigens-VSV-HIF-2α+VSV-SOX-10+VSV-C-MYC+VSV-TYRP1-from ASMEL which was highly effective against i.c. B16 brain tumors, had no efficacy against the same tumors growing subcutaneously. Correspondingly, i.c. B16 tumors expressed a HIF-2α(Hi), SOX-10(Hi), c-myc(Hi), TYRP1, N-RAS(lo)Cytc(lo) antigen profile, which differed significantly from the HIF-2α(lo), SOX-10(lo), c-myc(lo), TYRP1, N-RAS(Hi)Cytc(Hi) phenotype of s.c. B16 tumors, and was imposed upon the tumor cells by CD11b(+) cells within the local brain tumor microenvironment. Combining T-cell costimulation with systemic VSV-cDNA treatment, long-term cures of mice with established i.c. tumors were achieved in about 75% of mice. Our data show that the anatomical location of a tumor profoundly affects the profile of antigens that it expresses.

CD8+ T-cell responses rapidly select for antigen-negative tumor cells in the prostate

Stimulation of patients' immune systems for the treatment of solid tumors is an emerging therapeutic paradigm. The use of enriched autologous T cells for adoptive cell therapy or vaccination with antigen-loaded dendritic cells have shown clinical efficacy in melanoma and prostate cancer, respectively. However, the long-term effects of immune responses on selection and outgrowth of antigen-negative tumor cells in specific tumor types must be determined to understand and achieve long-term therapeutic effects. In this study, we have investigated the expression of a tumor-specific antigen in situ after treatment with tumor-specific CD8(+) T cells in an autochthonous mouse model of prostate cancer. After T-cell treatment, aggregates of dead antigen-positive tumor cells were concentrated in the lumen of the prostate gland and were eventually eliminated from the prostate tissue. Despite the elimination of antigen-positive tumor cells, prostate tumor continued to grow in T-cell-treated mice. Interestingly, the remaining tumor cells were antigen negative and downregulated MHC class I expression. These results show that CD8(+) T cells are effective in eliminating antigen-bearing prostate tumor cells but they also can select for the outgrowth of antigen-negative tumor cells. These findings provide insights into the requirements for an effective cancer immunotherapy within the prostate that not only induces potent immune responses but also avoids selection and outgrowth of antigen-negative tumor cells.

Detecting and targeting tumor relapse by its resistance to innate effectors at early recurrence

Tumor recurrence represents a major clinical challenge. Our data show that emergent recurrent tumors acquire a phenotype radically different from that of their originating primary tumors. This phenotype allows them to evade a host-derived innate immune response elicited by the progression from minimal residual disease (MRD) to actively growing recurrence. Screening for this innate response predicted accurately in which mice recurrence would occur. Premature induction of recurrence resensitized MRD to the primary therapy, suggesting a possible paradigm shift for clinical treatment of dormant disease in which the current expectant approach is replaced with active attempts to uncover MRD before evolution of the escape phenotype is complete. By combining screening with second-line treatments targeting innate insensitivity, up to 100% of mice that would have otherwise relapsed were cured. These data may open new avenues for early detection and appropriately timed, highly targeted treatment of tumor recurrence irrespective of tumor type or frontline treatment.

Immunotherapy-induced CD8+ T cells instigate immune suppression in the tumor

Despite clear evidence of immunogenicity, cancer vaccines only provide a modest clinical benefit. To evaluate the mechanisms that limit tumor regression following vaccination, we have investigated the weak efficacy of a highly immunogenic experimental vaccine using a murine melanoma model. We discovered that the tumor adapts rapidly to the immune attack instigated by tumor-specific CD8+ T cells in the first few days following vaccination, resulting in the upregulation of a complex set of biological networks, including multiple immunosuppressive processes. This rapid adaptation acts to prevent sustained local immune attack, despite continued infiltration by increasing numbers of tumor-specific T cells. Combining vaccination with adoptive transfer of tumor-specific T cells produced complete regression of the treated tumors but did not prevent the adaptive immunosuppression. In fact, the adaptive immunosuppressive pathways were more highly induced in regressing tumors, commensurate with the enhanced level of immune attack. Examination of tumor infiltrating T-cell functionality revealed that the adaptive immunosuppression leads to a progressive loss in T-cell function, even in tumors that are regressing. These novel observations that T cells produced by therapeutic intervention can instigate a rapid adaptive immunosuppressive response within the tumor have important implications for clinical implementation of immunotherapies.

Spontaneous regression of metastatic melanoma - clinical evidence of the abscopal effect

INTRODUCTION

Metastatic melanoma is poorly understood. Regression of primary lesions has been associated with poor prognosis, but spontaneous regression of all metastatic disease is clearly beneficial. A patient's own immune responses occasionally appear to stimulate spontaneous regression of metastatic disease in melanoma.

PATIENTS AND METHODS

We present six interesting cases of complete or nearly complete spontaneous regression of metastatic melanoma, suggest possible causes and review the literature.

RESULTS AND CONCLUSIONS

These cases show clear radiological, pathological or clinical evidence of spontaneous regression of metastatic melanoma. This remains a poorly understood phenomena warranting further investigation and may prove useful in the development of immune mediated solutions.

Functional cloning of recurrence-specific antigens identifies molecular targets to treat tumor relapse

Aggressive regrowth of recurrent tumors following treatment-induced dormancy represents a major clinical challenge for treatment of malignant disease. We reported previously that recurrent prostate tumors, which underwent complete macroscopic regression followed by aggressive regrowth, could be cured with a vesicular stomatitis virus (VSV)-expressed cDNA library derived from recurrent tumor cells. By screening the protective, recurrence-derived VSV-cDNA library, here we identify topoisomerase-IIα (TOPO-IIα) as a recurrence-specific tumor antigen against which tolerance can be broken. Tumor recurrences, in two different types of tumor (prostate and melanoma), which had evaded two different frontline treatments (immunotherapy or chemotherapy), significantly overexpressed TOPO-IIα compared with their primary tumor counterparts, which conferred a novel sensitivity to doxorubicin (DOX) chemotherapy upon the recurrent tumors. This was exploited in vivo using combination therapies to cure mice, which would otherwise have relapsed, after suboptimal primary therapy in both models. Our data show that recurrent tumors-across histologies and primary treatments-express distinct antigens compared with the primary tumor which can be identified using the VSV-cDNA library technology. These results suggest that it may be possible to design a few common second-line therapies against a variety of tumor recurrences, in some cases using agents with no obvious activity against the primary tumor.

DARPin-targeting of measles virus: unique bispecificity, effective oncolysis, and enhanced safety

Oncolytic virotherapy is an emerging treatment modality that uses replication-competent viruses to destroy cancers. Many naturally occurring viruses have a preferential, although nonexclusive, tropism for tumors and tumor cells. In addition, specific targeting of cancer cells can be achieved at the virus entry level. We optimized retargeting of cell entry by elongating the measles virus attachment protein with designed ankyrin repeat proteins (DARPins), while simultaneously ablating entry through the natural receptors. DARPin-targeted viruses were strongly attenuated in off-target tissue, thereby enhancing safety, but completely eliminated tumor xenografts. Taking advantage of the unique properties of DARPins of being fused without generating folding problems, we generated a virus simultaneous targeting two different tumor markers. The bispecific virus retained the original oncolytic efficacy, while providing proof of concept for a strategy to counteract issues of resistance development. Thus, DARPin-targeting opens new prospects for the development of personalized, targeted therapeutics.

Systemic combination virotherapy for melanoma with tumor antigen-expressing vesicular stomatitis virus and adoptive T-cell transfer

Oncolytic virotherapy offers the potential to treat tumors both as a single agent and in combination with traditional modalities such as chemotherapy and radiotherapy. Here we describe an effective, fully systemic treatment regimen, which combines virotherapy, acting essentially as an adjuvant immunotherapy, with adoptive cell transfer (ACT). The combination of ACT with systemic administration of a vesicular stomatitis virus (VSV) engineered to express the endogenous melanocyte antigen glycoprotein 100 (gp100) resulted in regression of established melanomas and generation of antitumor immunity. Tumor response was associated with in vivo T-cell persistence and activation as well as treatment-related vitiligo. However, in a proportion of treated mice, initial tumor regressions were followed by recurrences. Therapy was further enhanced by targeting an additional tumor antigen with the VSV-antigen + ACT combination strategy, leading to sustained response in 100% of mice. Together, our findings suggest that systemic virotherapy combined with antigen-expressing VSV could be used to support and enhance clinical immunotherapy protocols with adoptive T-cell transfer, which are already used in the clinic.

MHC-class I-restricted CD4 T cells: a nanomolar affinity TCR has improved anti-tumor efficacy in vivo compared to the micromolar wild-type TCR

Clinical studies with immunotherapies for cancer, including adoptive cell transfers of T cells, have shown promising results. It is now widely believed that recruitment of CD4(+) helper T cells to the tumor would be favorable, as CD4(+) cells play a pivotal role in cytokine secretion as well as promoting the survival, proliferation, and effector functions of tumor-specific CD8(+) cytotoxic T lymphocytes. Genetically engineered high-affinity T-cell receptors (TCRs) can be introduced into CD4(+) helper T cells to redirect them to recognize MHC-class I-restricted antigens, but it is not clear what affinity of the TCR will be optimal in this approach. Here, we show that CD4(+) T cells expressing a high-affinity TCR (nanomolar K (d) value) against a class I tumor antigen mediated more effective tumor treatment than the wild-type affinity TCR (micromolar K (d) value). High-affinity TCRs in CD4(+) cells resulted in enhanced survival and long-term persistence of effector memory T cells in a melanoma tumor model. The results suggest that TCRs with nanomolar affinity could be advantageous for tumor targeting when expressed in CD4(+) T cells.

Adoptive transfer of cytotoxic T lymphocytes targeting two different antigens limits antigen loss and tumor escape

An antitumor T-cell response can lead to tumor control without clearing all tumor cells. As long as residual tumor cells remain, there is a constant risk of escape from that T-cell response. We previously showed that adoptive transfer of anti-ova OT-I T cells into B16ova-bearing mice led to tumor regression followed by escape of tumors that had lost the ova gene, rendering the OT-I T cells ineffective. In this study, we hypothesized that simultaneous transfer of cytotoxic T lymphocytes targeted against two independent antigens would reduce selection for single-antigen-loss cells, thereby limiting tumor escape. Using OT-I and Pmel T cells to treat B16ova tumors, we found that early cotransfer could prevent tumor emergence in most mice, whereas neither T-cell specificity alone was able to do so. When combined with total body irradiation for the treatment of larger 7-day tumors, cotransfer was also better at limiting tumor recurrence, and the tumors that did escape combination therapy continued to express both target antigens. As adoptively transferred T cells also persisted in vivo, even in mice with recurrent tumors, we hypothesized that restimulation of these antitumor T cells would prolong survival of mice with recurrent tumors. Consistent with this hypothesis, administration of a low-dose regimen of cyclophosphamide following tumor escape slowed tumor growth in mice that had previously received T-cell therapy, but not in control-treated mice, an effect that was associated with increased activation of T cells in vitro by low- but not high-dose cyclophosphamide.