An expanded peripheral T cell population to a cytotoxic T lymphocyte (CTL)-defined, melanocyte-specific antigen in metastatic melanoma patients impacts on generation of peptide-specific CTLs but does not overcome tumor escape from immune surveillance in metastatic lesions

Histopathologic regression in patients with primary cutaneous melanoma undergoing sentinel lymph node biopsy is associated with favorable survival and, after metastasis, with improved progression-free survival on immune checkpoint inhibitor therapy: A single-institutional cohort study

BACKGROUND

Histopathologic regression of cutaneous melanoma is considered a favorable prognostic factor, but its significance in clinical practice remains controversial.

OBJECTIVE

To investigate the prognostic importance of regression in patients with primary cutaneous melanoma undergoing sentinel lymph node (SLN) biopsy and to assess its significance in patients progressing to an unresectable stage requiring systemic therapy.

METHODS

We retrospectively reviewed patients with newly diagnosed melanoma undergoing SLN biopsy between 2010 and 2015 and available information on histopathologic regression (n = 1179). Survival data and associations of clinical variables with SLN status were assessed.

RESULTS

Patients with regressive melanoma showed favorable relapse-free (hazard ratio [HR], 0.52; P = .00013), distant metastasis-free (HR, 0.56; P = .0020), and melanoma-specific survival (HR, 0.35; P = .00053). Regression was associated with negative SLN (odds ratio, 0.48; P = .0077). In patients who progressed to an unresectable stage, regression was associated with favorable progression-free survival under immune checkpoint inhibition (HR, 0.43; P = .031) but not under targeted therapy (HR, 1.14; P = .73) or chemotherapy (HR, 3.65; P = .0095).

LIMITATIONS

Retrospective, single-institutional design.

CONCLUSIONS

Regression of cutaneous melanoma is associated with improved prognosis in patients eligible for SLN biopsy as well as in patients with unresectable disease receiving systemic therapy with immune checkpoint inhibitors.

Cancer neoepitopes viewed through negative selection and peripheral tolerance: a new path to cancer vaccines

A proportion of somatic mutations in tumors create neoepitopes that can prime T cell responses that target the MHC I-neoepitope complexes on tumor cells, mediating tumor control or rejection. Despite the compelling centrality of neoepitopes to cancer immunity, we know remarkably little about what constitutes a neoepitope that can mediate tumor control in vivo and what distinguishes such a neoepitope from the vast majority of similar candidate neoepitopes that are inefficacious in vivo. Studies in mice as well as clinical trials have begun to reveal the unexpected paradoxes in this area. Because cancer neoepitopes straddle that ambiguous ground between self and non-self, some rules that are fundamental to immunology of frankly non-self antigens, such as viral or model antigens, do not appear to apply to neoepitopes. Because neoepitopes are so similar to self-epitopes, with only small changes that render them non-self, immune response to them is regulated at least partially the way immune response to self is regulated. Therefore, neoepitopes are viewed and understood here through the clarifying lens of negative thymic selection. Here, the emergent questions in the biology and clinical applications of neoepitopes are discussed critically and a mechanistic and testable framework that explains the complexity and translational potential of these wonderful antigens is proposed.

Low MxA Expression Predicts Better Immunotherapeutic Outcomes in Glioblastoma Patients Receiving Heat Shock Protein Peptide Complex 96 Vaccination

Heat shock protein peptide complex 96 (HSPPC-96) has been proven to be a safe and preliminarily effective therapeutic vaccine in treating newly diagnosed glioblastoma multiforme (GBM) (NCT02122822). However, the clinical outcomes were highly variable, rendering the discovery of outcome-predictive biomarkers essential for this immunotherapy. We utilized multidimensional immunofluorescence staining to detect CD4+ CD8+ and PD-1+ immune cell infiltration levels, MxA and gp96 protein expression in pre-vaccination GBM tissues of 19 patients receiving HSPPC-96 vaccination. We observed low MxA expression was associated with longer OS than high MxA expression (48 months vs. 20 months, p=0.038). Long-term survivors (LTS) exhibited significantly lower MxA expression than short-term survivors (STS) (p= 0.0328), and ROC curve analysis indicated MxA expression as a good indicator in distinguishing LTS and STS (AUC=0.7955, p=0.0318). However, we did not observe any significant impact of immune cell densities or gp96 expression on patient outcomes. Finally, we revealed the association of MxA expression with prognosis linked to a preexisting TCR clone (CDR3-2) but was independent of the peripheral tumor-specific immune response. Taken together, low MxA expression correlated with better survival in GBM patients receiving HSPPC-96 vaccination, indicating MxA as a potential biomarker for early recognition of responsive patients to this immunotherapy.

Clinical Trial Registration: ClinicalTrials.gov (NCT02122822) http://www. chictr.org.cn/enindex.aspx (ChiCTR-ONC-13003309).

An unbiased approach to defining bona fide cancer neoepitopes that elicit immune-mediated cancer rejection

Identification of neoepitopes that are effective in cancer therapy is a major challenge in creating cancer vaccines. Here, using an entirely unbiased approach, we queried all possible neoepitopes in a mouse cancer model and asked which of those are effective in mediating tumor rejection and, independently, in eliciting a measurable CD8 response. This analysis uncovered a large trove of effective anticancer neoepitopes that have strikingly different properties from conventional epitopes and suggested an algorithm to predict them. It also revealed that our current methods of prediction discard the overwhelming majority of true anticancer neoepitopes. These results from a single mouse model were validated in another antigenically distinct mouse cancer model and are consistent with data reported in human studies. Structural modeling showed how the MHC I-presented neoepitopes had an altered conformation, higher stability, or increased exposure to T cell receptors as compared with the unmutated counterparts. T cells elicited by the active neoepitopes identified here demonstrated a stem-like early dysfunctional phenotype associated with effective responses against viruses and tumors of transgenic mice. These abundant anticancer neoepitopes, which have not been tested in human studies thus far, can be exploited for generation of personalized human cancer vaccines.

The Cancer Epitope Database and Analysis Resource: A Blueprint for the Establishment of a New Bioinformatics Resource for Use by the Cancer Immunology Community

Recent years have witnessed a dramatic rise in interest towards cancer epitopes in general and particularly neoepitopes, antigens that are encoded by somatic mutations that arise as a consequence of tumorigenesis. There is also an interest in the specific T cell and B cell receptors recognizing these epitopes, as they have therapeutic applications. They can also aid in basic studies to infer the specificity of T cells or B cells characterized in bulk and single-cell sequencing data. The resurgence of interest in T cell and B cell epitopes emphasizes the need to catalog all cancer epitope-related data linked to the biological, immunological, and clinical contexts, and most importantly, making this information freely available to the scientific community in a user-friendly format. In parallel, there is also a need to develop resources for epitope prediction and analysis tools that provide researchers access to predictive strategies and provide objective evaluations of their performance. For example, such tools should enable researchers to identify epitopes that can be effectively used for immunotherapy or in defining biomarkers to predict the outcome of checkpoint blockade therapies. We present here a detailed vision, blueprint, and work plan for the development of a new resource, the Cancer Epitope Database and Analysis Resource (CEDAR). CEDAR will provide a freely accessible, comprehensive collection of cancer epitope and receptor data curated from the literature and provide easily accessible epitope and T cell/B cell target prediction and analysis tools. The curated cancer epitope data will provide a transparent benchmark dataset that can be used to assess how well prediction tools perform and to develop new prediction tools relevant to the cancer research community.

Old dogs, new trick: classic cancer therapies activate cGAS

The discovery of cancer immune surveillance and immunotherapy has opened up a new era of cancer treatment. Immunotherapies modulate a patient’s immune system to specifically eliminate cancer cells; thus, it is considered a very different approach from classic cancer therapies that usually induce DNA damage to cause cell death in a cell-intrinsic manner. However, recent studies have revealed that classic cancer therapies such as radiotherapy and chemotherapy also elicit antitumor immunity, which plays an essential role in their therapeutic efficacy. The cytosolic DNA sensor cyclic GMP-AMP synthase (cGAS) and the downstream effector Stimulator of Interferon Genes (STING) have been determined to be critical for this interplay. Here, we review the antitumor roles of the cGAS-STING pathway during tumorigenesis, cancer immune surveillance, and cancer therapies. We also highlight classic cancer therapies that elicit antitumor immune responses through cGAS activation.

Melanoma and Vitiligo: In Good Company

Cutaneous melanoma represents the most aggressive form of skin cancer, whereas vitiligo is an autoimmune disorder that leads to progressive destruction of skin melanocytes. However, vitiligo has been associated with cutaneous melanoma since the 1970s. Most of the antigens recognized by the immune system are expressed by both melanoma cells and normal melanocytes, explaining why the autoimmune response against melanocytes that led to vitiligo could be also present in melanoma patients. Leukoderma has been also observed as a side effect of melanoma immunotherapy and has always been associated with a favorable prognosis. In this review, we discuss several characteristics of the immune system responses shared by melanoma and vitiligo patients, as well as the significance of occurrence of leukoderma during immunotherapy, with special attention to check-point inhibitors.

Mass spectrometry driven exploration reveals nuances of neoepitope-driven tumor rejection

Neoepitopes are the only truly tumor-specific antigens. Although potential neoepitopes can be readily identified using genomics, the neoepitopes that mediate tumor rejection constitute a small minority, and there is little consensus on how to identify them. Here, for the first time to our knowledge, we use a combination of genomics, unbiased discovery mass spectrometry (MS) immunopeptidomics, and targeted MS to directly identify neoepitopes that elicit actual tumor rejection in mice. We report that MS-identified neoepitopes are an astonishingly rich source of tumor rejection-mediating neoepitopes (TRMNs). MS has also demonstrated unambiguously the presentation by MHC I, of confirmed tumor rejection neoepitopes that bind weakly to MHC I; this was done using DCs exogenously loaded with long peptides containing the weakly binding neoepitopes. Such weakly MHC I–binding neoepitopes are routinely excluded from analysis, and our demonstration of their presentation, and their activity in tumor rejection, reveals a broader universe of tumor-rejection neoepitopes than presently imagined. Modeling studies show that a mutation in the active neoepitope alters its conformation such that its T cell receptor–facing surface is substantially altered, increasing its exposed hydrophobicity. No such changes are observed in the inactive neoepitope. These results broaden our understanding of antigen presentation and help prioritize neoepitopes for personalized cancer immunotherapy.

Neoepitopes identified by mass spectrometry are a rich source of tumor rejection antigens, including those with a weak binding to MHC I.

Roles of the cGAS-STING Pathway in Cancer Immunosurveillance and Immunotherapy

Cyclic GMP-AMP synthase (cGAS) is a cytosolic DNA sensor that initiates innate immune responses. DNA-bound cGAS produces cyclic GMP-AMP (cGAMP), which activates stimulator of interferon genes (STING) to induce inflammatory cytokines and other immune mediators. cGAS detects DNA without sequence specificity and responds to both cytosolic foreign DNA from pathogens and self-DNA leaked into the cytosol due to genome instability or cellular damage. Because of the diverse sources of cytosolic DNA, the cGAS-STING pathway plays a critical role during infection, autoimmune diseases, and senescence. Moreover, cGAS detects tumor-derived DNA and stimulates endogenous antitumor immunity. Thus, the cGAS-STING pathway is a promising target for cancer immunotherapy. Here, we review the role of the cGAS-STING pathway in various diseases and highlight various approaches targeting the cGAS-STING pathway for cancer therapy.

Tumor Microenvironment: What have we Learned Studying the Immune Response in this Puzzling Battlefield?

Recent developments hallmark the progress in the understanding of tumor immunology and related therapeutic strategies. The administration of interleukin-2 (IL-2) to patients with cancer has shown that immune manipulation can mediate the regression of established cancers. The identification of the genes encoding cancer antigens and the development of means for effectively immunizing against these antigens has opened new avenues for the development of active immunization of patients with cancer. However, an efficient immune response against tumor comprises an intricate molecular network still poorly understood. Only when the code governing immune responsiveness of cancer will be deciphered, new therapeutic strategies could be designed to fit biologically defined mechanisms of immune rejection of cancer.

In this review, we propose that the mechanisms regulating tumor rejection in response to vaccination will be more efficiently identified by following the evolution of treatment induced events within the tumor microenvironment taking advantage of recently developed technological tools. As a model, we will discuss the observed immune response to tumor antigen -specific immunization and its relationship with the systemic administration of IL-2.

Systematic evaluation of immune regulation and modulation

Cancer immunotherapies are showing promising clinical results in a variety of malignancies. Monitoring the immune as well as the tumor response following these therapies has led to significant advancements in the field. Moreover, the identification and assessment of both predictive and prognostic biomarkers has become a key component to advancing these therapies. Thus, it is critical to develop systematic approaches to monitor the immune response and to interpret the data obtained from these assays. In order to address these issues and make recommendations to the field, the Society for Immunotherapy of Cancer reconvened the Immune Biomarkers Task Force. As a part of this Task Force, Working Group 3 (WG3) consisting of multidisciplinary experts from industry, academia, and government focused on the systematic assessment of immune regulation and modulation. In this review, the tumor microenvironment, microbiome, bone marrow, and adoptively transferred T cells will be used as examples to discuss the type and timing of sample collection. In addition, potential types of measurements, assays, and analyses will be discussed for each sample. Specifically, these recommendations will focus on the unique collection and assay requirements for the analysis of various samples as well as the high-throughput assays to evaluate potential biomarkers.

Innate immune recognition of cancer

The observation that a subset of cancer patients show evidence for spontaneous CD8+ T cell priming against tumor-associated antigens has generated renewed interest in the innate immune pathways that might serve as a bridge to an adaptive immune response to tumors. Manipulation of this endogenous T cell response with therapeutic intent-for example, using blocking antibodies inhibiting PD-1/PD-L1 (programmed death-1/programmed death ligand 1) interactions-is showing impressive clinical results. As such, understanding the innate immune mechanisms that enable this T cell response has important clinical relevance. Defined innate immune interactions in the cancer context include recognition by innate cell populations (NK cells, NKT cells, and γδ T cells) and also by dendritic cells and macrophages in response to damage-associated molecular patterns (DAMPs). Recent evidence has indicated that the major DAMP driving host antitumor immune responses is tumor-derived DNA, sensed by the stimulator of interferon gene (STING) pathway and driving type I IFN production. A deeper knowledge of the clinically relevant innate immune pathways involved in the recognition of tumors is leading toward new therapeutic strategies for cancer treatment.

Targeting WNT1-inducible signaling pathway protein 2 alters human breast cancer cell susceptibility to specific lysis through regulation of KLF-4 and miR-7 expression

The molecular basis for the resistance of tumor cells to cell-mediated cytotoxicity remains poorly understood and thus poses a major challenge for cancer immunotherapy. The present study was designed to determine whether the WNT1-inducible signaling pathway protein 2 (WISP2, also referred to as CCN5), a key regulator of tumor cell plasticity, interferes with tumor susceptibility to cytotoxic T-lymphocyte (CTL)-mediated lysis. We found that silencing WISP2 signaling in human breast adenocarcinoma MCF7 cells impairs CTL-mediated cell killing by a mechanism involving stem cell marker Kruppel-like factor-4 (KLF-4) induction and microRNA-7 (miR-7) downregulation. Inhibition of transforming growth factor beta (TGF-β) signaling using the A83-01 inhibitor in MCF7-shWISP2 cells resulted in a significant reversal of the epithelial-to-mesenchymal-transitioned (EMT) phenotype, the expression of KLF-4 and a partial recovery of target susceptibility to CTLs. More importantly, we showed that silencing KLF-4 was accompanied by a reduction in MCF7-shWISP2 resistance to CTLs. Using human breast cancer tissues, we demonstrated the coexpression of KLF-4 with EMT markers and TGF-β pathway signaling components. More importantly, we found that KLF-4 expression was accompanied by miR-7 inhibition, which is partly responsible for impairing CTL-mediated lysis. Thus, our data indicate that WISP2 has a role in regulating tumor cell susceptibility through EMT by inducing the TGF-β signaling pathway, KLF-4 expression and miR-7 inhibition. These studies indicate for the first time that WISP2 acts as an activator of CTL-induced killing and suggests that the loss of its function promotes evasion of immunosurveillance and the ensuing progression of the tumor.

A broad profile of co-dominant epitopes shapes the peripheral Mycobacterium tuberculosis specific CD8+ T-cell immune response in South African patients with active tuberculosis

We studied major histocompatibility complex (MHC) class I peptide-presentation and nature of the antigen-specific CD8+ T-cell response from South African tuberculosis (TB) patients with active TB. 361 MHC class I binding epitopes were identified from three immunogenic TB proteins (ESAT-6 [Rv3875], Ag85B [Rv1886c], and TB10.4 [Rv0288], including amino acid variations for Rv0288, i.e., A10T, G13D, S27N, and A71S for MHC allotypes common in a South African population (e.g., human leukocyte antigen [HLA]-A*30, B*58, and C*07). Inter-allelic differences were identified regarding the broadness of the peptide-binding capacity. Mapping of frequencies of Mycobacterium tuberculosis (M. tb) antigen-specific CD8+ T-cells using 48 different multimers, including the newly constructed recombinant MHC class I alleles HLA-B*58:01 and C*0701, revealed a low frequency of CD8+ T-cell responses directed against a broad panel of co-dominant M. tb epitopes in the peripheral circulation of most patients. The antigen-specific responses were dominated by CD8+ T-cells with a precursor-like phenotype (CD45RA+CCR7+). The data show that the CD8+ T-cell response from patients with pulmonary TB (prior to treatment) is directed against subdominant epitopes derived from secreted and non-secreted M. tb antigens and that variant, natural occurring M. tb Rv0288 ligands, have a profound impact on T-cell recognition.

Immune system targeting by biodegradable nanoparticles for cancer vaccines

The concept of therapeutic cancer vaccines is based on the activation of the immune system against tumor cells after the presentation of tumor antigens. Nanoparticles (NPs) have shown great potential as delivery systems for cancer vaccines as they potentiate the co-delivery of tumor-associated antigens and adjuvants to dendritic cells (DCs), insuring effective activation of the immune system against tumor cells. In this review, the immunological mechanisms behind cancer vaccines, including the role of DCs in the stimulation of T lymphocytes and the use of Toll-like receptor (TLR) ligands as adjuvants will be discussed. An overview of each of the three essential components of a therapeutic cancer vaccine - antigen, adjuvant and delivery system - will be provided with special emphasis on the potential of particulate delivery systems for cancer vaccines, in particular those made of biodegradable aliphatic polyesters, such as poly(lactic-co-glycolic acid) (PLGA) and poly-ε-caprolactone (PCL). Some of the factors that can influence NP uptake by DCs, including size, surface charge, surface functionalization and route of administration, will also be considered.

Epithelial-to-mesenchymal transition and autophagy induction in breast carcinoma promote escape from T-cell-mediated lysis

Epithelial-to-mesenchymal transition (EMT) mediates cancer cell invasion, metastasis, and drug resistance, but its impact on immune surveillance has not been explored. In this study, we investigated the functional consequences of this mode of epithelial cell plasticity on targeted cell lysis by cytotoxic T lymphocytes (CTL). Acquisition of the EMT phenotype in various derivatives of MCF-7 human breast cancer cells was associated with dramatic morphologic changes and actin cytoskeleton remodeling, with CD24(-)/CD44(+)/ALDH(+) stem cell populations present exhibiting a higher degree of EMT relative to parental cells. Strikingly, acquisition of this phenotype also associated with an inhibition of CTL-mediated tumor cell lysis. Resistant cells exhibited attenuation in the formation of an immunologic synapse with CTLs along with the induction of autophagy in the target cells. This response was critical for susceptibility to CTL-mediated lysis because siRNA-mediated silencing of beclin1 to inhibit autophagy in target cells restored their susceptibility to CTL-induced lysis. Our results argue that in addition to promoting invasion and metastasis EMT also profoundly alters the susceptibility of cancer cells to T-cell-mediated immune surveillance. Furthermore, they reveal EMT and autophagy as conceptual realms for immunotherapeutic strategies to block immune escape.

Type I interferon response and innate immune sensing of cancer

Unexpectedly, many cancers appear to induce a spontaneous adaptive T cell response. The presence of a T cell infiltrate has been linked to favorable clinical outcome in multiple cancer types. However, the innate immune pathways that bridge to an adaptive immune response under sterile conditions are poorly understood. Recent data have indicated that tumors can induce type I interferon (IFN) production by host antigen-presenting cells (APCs), which is required for a spontaneous T cell response in vivo. The innate immune sensing pathways that trigger type I IFN production are being elucidated. Host type I IFNs are also required for optimal therapeutic efficacy with radiation. This recently uncovered role for host type I IFNs for antitumor immunity has important fundamental and clinical implications.

PD-1 expression on Melan-A-reactive T cells increases during progression to metastatic disease

Programmed death 1 (PD-1) is known as an important factor for the development of tolerogenicity. This has been proven in chronic viral infections and different tumor models. To address the role of PD-1 and its ligand programmed death ligand 1 (PD-L1) in different stages of malignant melanoma, we investigated peripheral blood and tumor tissues in regard to overall survival (OS) and prognostic relevance. One hundred samples of peripheral blood mononuclear cells from HLA-A2(+) patients with malignant melanoma (Stages I-IV) were analyzed in seven color FACS combined with multimer analyses for the immunodominant epitope of Melan-A (peptide A2/Melan-A(p26-35mod) ). Corresponding formalin-fixed paraffin-embedded tissues of primary tumor and distant organ metastases from 37 cases were analyzed by immunohistochemistry for Melan-A, PD-L1 and PD-1 expression. Compared to the total CD8(+) T cell population, PD-1 expression by A2/Melan-A(+) CD8(+) T cells was over-represented in melanoma stages III and IV (p < 0.001). Although elevation of PD-1(+) Melan-A(+) CD8(+) T cells had no significant influence on OS, a positive correlation was observed between PD-L1 expression on melanoma cells and OS (p = 0.05). Correlation of advanced tumor stage with increased A2/Melan-A-multimer(+) PD-1(+) T cells in the peripheral blood suggest that blocking of PD-1 could have therapeutic potential in advanced stage melanoma.

A screening assay to identify agents that enhance T-cell recognition of human melanomas

Although a series of melanoma differentiation antigens for immunotherapeutic targeting has been described, heterogeneous expression of antigens such as Melan-A/MART-1 and gp100 results from a loss of antigenic expression in many late stage tumors. Antigen loss can represent a means for tumor escape from immune recognition, and a barrier to immunotherapy. However, since antigen-negative tumor phenotypes frequently result from reversible gene regulatory events, antigen enhancement represents a potential therapeutic opportunity. Accordingly, we have developed a cell-based assay to screen for compounds with the ability to enhance T-cell recognition of melanoma cells. This assay is dependent on augmentation of MelanA/MART-1 antigen presentation by a melanoma cell line (MU89). T-cell recognition is detected as interleukin-2 production by a Jurkat T cell transduced to express a T-cell receptor specific for an HLA-A2 restricted epitope of the Melan-A/MART-1 protein. This cellular assay was used to perform a pilot screen by using 480 compounds of known biological activity. From the initial proof-of-principle primary screen, eight compounds were identified as positive hits. A panel of secondary screens, including orthogonal assays, was used to validate the primary hits and eliminate false positives, and also to measure the comparative efficacy of the identified compounds. This cell-based assay, thus, yields consistent results applicable to the screening of larger libraries of compounds that can potentially reveal novel molecules which allow better recognition of treated tumors by T cells.

Host type I IFN signals are required for antitumor CD8+ T cell responses through CD8{alpha}+ dendritic cells

The generation of antitumor CD8⁺ T cell responses requires type I interferon responsiveness in host antigen-presenting cells

Despite lack of tumor control in many models, spontaneous T cell priming occurs frequently in response to a growing tumor. However, the innate immune mechanisms that promote natural antitumor T cell responses are undefined. In human metastatic melanoma, there was a correlation between a type I interferon (IFN) transcriptional profile and T cell markers in metastatic tumor tissue. In mice, IFN-β was produced by CD11c⁺ cells after tumor implantation, and tumor-induced T cell priming was defective in mice lacking IFN-α/βR or Stat1. IFN signaling was required in the hematopoietic compartment at the level of host antigen-presenting cells, and selectively for intratumoral accumulation of CD8α⁺ dendritic cells, which were demonstrated to be essential using Batf3^−/− mice. Thus, host type I IFNs are critical for the innate immune recognition of a growing tumor through signaling on CD8α⁺ DCs.

Tumor-infiltrating lymphocytes: apparently good for melanoma patients. But why?

Tumor-infiltrating T lymphocytes (TILs) are observed in a number of human primary or metastatic tumors. Recently, gene expression profiling experiments suggested that the presence of T cells in metastatic melanomas before vaccinating the patients with tumor antigens could be a biomarker for clinical benefit from the vaccines. In this context, we review results pertaining to TILs in human melanomas, their prognostic value, and some possible reasons why their presence could help in selecting melanoma patients for vaccination against tumor-specific antigens.

Immune suppression in tumors as a surmountable obstacle to clinical efficacy of cancer vaccines

Human tumors are usually not spontaneously eliminated by the immune system and therapeutic vaccination of cancer patients with defined antigens is followed by tumor regressions only in a small minority of the patients. The poor vaccination effectiveness could be explained by an immunosuppressive tumor microenvironment. Because T cells that infiltrate tumor metastases have an impaired ability to lyse target cells or to secrete cytokine, many researchers are trying to decipher the underlying immunosuppressive mechanisms. We will review these here, in particular those considered as potential therapeutic targets. A special attention will be given to galectins, a family of carbohydrate binding proteins. These lectins have often been implicated in inflammation and cancer and may be useful targets for the development of new anti-cancer therapies.

Association between natural killer cells and regression in melanocytic lesions

Mortality from melanoma, the deadliest of skin cancers, continues to increase in all age groups. A small number of melanomas spontaneously regress. In vitro studies suggest a role for the natural killer cell in effecting regression. In this study, the goal was to determine if natural killer cells are preferentially involved in the cytotoxic response in regressing lesions. Forty-two cases were selected: nevi with regression, nonregressing melanoma with brisk inflammation, and regressing melanoma. Sections were stained with hematoxylin and eosin and immunostained for CD8, CD56, and T-cell intracytoplasmic antigen 1. Numbers of total lymphocytes, CD8-positive lymphocytes, and T-cell intracytoplasmic antigen 1-positive lymphocytes did not differ among the 3 populations or based on location. CD56 positivity was significantly different among the 3 populations. Regressing melanomas showed the greatest CD56 activity, followed by regressing nevi, whereas inflamed, nonregressing melanomas showed the least. CD56(+) lymphocytes were mostly counted in areas of early regression. The natural killer cell could plausibly play a role in the occurrence of regression as a cytotoxic effector cell or as a mediator of the cytotoxic mechanism.

Human leukocyte antigens A*3001 and A*3002 show distinct peptide-binding patterns of the Mycobacterium tuberculosis protein TB10.4: consequences for immune recognition

High-tuberculosis (TB)-burden countries are located in sub-Saharan Africa. We examined the frequency of human leukocyte antigen (HLA) alleles, followed by recombinant expression of the most frequent HLA-A alleles, i.e., HLA-A*3001 and HLA-A*3002, to study differences in mycobacterial peptide presentation and CD8(+) T-cell recognition. We screened a peptide library (9-mer peptides with an 8-amino-acid overlap) for binding, affinity, and off-rate of the Mycobacterium tuberculosis-associated antigen TB10.4 and identified only three TB10.4 peptides with considerable binding to HLA-A*3001. In contrast, 22 peptides bound to HLA-A*3002. This reflects a marked difference in the binding preference between the two alleles, with A*3002 tolerating a more promiscuous peptide-binding pattern and A*3001 accommodating only a very selective peptide repertoire. Subsequent analysis of the affinity and off-rate of the binding peptides revealed a strong affinity (8 nM to 7 μM) and moderate off-rate (20 min to 3 h) for both alleles. Construction of HLA-A*3001 and HLA-A*3002 tetramers containing selected binding peptides from TB10.4, including a peptide which was shared among both alleles, QIMYNYPAM (TB10.4(3-11)), allowed us to enumerate epitope-specific T cells in HLA-A*3001- and HLA-A*3002-typed patients with active TB. HLA-A*3001 and HLA-A*3002 major histocompatibility complex-peptide complexes were recognized in individuals with active TB, irrespective of their homozygous HLA-A*3001 or HLA-A*3002 genetic background. The antigen-specific T cells exhibited the CD45RA(+) CCR7(+) precursor phenotype and the interleukin-7 receptor (CD127), which were different from the phenotype and receptor exhibited by the parental CD8(+) T-cell population.

Immune surveillance of human cancer: if the cytotoxic T-lymphocytes play the music, does the tumoral system call the tune?

Accumulating evidence indicates that the innate and adaptive immune systems participate in the recognition and destruction of cancer cells by a process known as cancer immunosurveillance. Tumor antigen-specific cytotoxic T-lymphocytes (CTL) are the major effectors in the immune response against tumor cells. The identification of tumor-associated antigen (TAA) recognized primarily by CD 8(+) T-lymphocytes has led to the development of several vaccination strategies that induce or potentiate specific immune responses. However, large established tumors, which are associated with the acquisition of tumor resistance to specific lysis, are usually not fully controlled by the immune system. Recently, it has become clear that the immune system not only protects the host against tumor development but also sculpts the immunogenic phenotype of a developing tumor and can favor the emergence of resistant tumor cell variants. Moreover, it has become obvious that the evasion of immunosurveillance by tumor cells is under the control of the tumor microenvironment complexity and plasticity. In this review, we will focus on some new mechanisms associated with the acquisition of tumor resistance to specific lysis during tumor progression, involving genetic instability, structural changes in cytoskeleton, and hypoxic stress. We will also discuss the interaction between CTLs and tumor endothelial cells, a major component of tumor stroma.

Impaired interferon signaling is a common immune defect in human cancer

Immune dysfunction develops in patients with many cancer types and may contribute to tumor progression and failure of immunotherapy. Mechanisms underlying cancer-associated immune dysfunction are not fully understood. Efficient IFN signaling is critical to lymphocyte function; animals rendered deficient in IFN signaling develop cancer at higher rates. We hypothesized that altered IFN signaling may be a key mechanism of immune dysfunction common to cancer. To address this, we assessed the functional responses to IFN in peripheral blood lymphocytes from patients with 3 major cancers: breast cancer, melanoma, and gastrointestinal cancer. Type-I IFN (IFN-alpha)-induced signaling was reduced in T cells and B cells from all 3 cancer-patient groups compared to healthy controls. Type-II IFN (IFN-gamma)-induced signaling was reduced in B cells from all 3 cancer patient groups, but not in T cells or natural killer cells. Impaired-IFN signaling was equally evident in stage II, III, and IV breast cancer patients, and downstream functional defects in T cell activation were identified. Taken together, these findings indicate that defects in lymphocyte IFN signaling arise in patients with breast cancer, melanoma, and gastrointestinal cancer, and these defects may represent a common cancer-associated mechanism of immune dysfunction.

Signaling defects in anti-tumor T cells

The immune response to cancer has been long recognized, including both innate and adaptive responses, showing that the immune system can recognize protein products of genetic and epigenetic changes in transformed cells. The accumulation of antigen-specific T cells within the tumor, the draining lymph node, and the circulation, either in newly diagnosed patients or resultant from experimental immunotherapy, proves that tumors produce antigens and that priming occurs. Unfortunately, just as obviously, tumors grow, implying that anti-tumor immune responses are either not sufficiently vigorous to eliminate the cancer or that anti-tumor immunity is suppressed. Both possibilities are supported by current data. In experimental animal models of cancer and also in patients, systemic immunity is usually not dramatically suppressed, because tumor-bearing animals and patients develop T-cell-dependent immune responses to microbes and to either model antigens or experimental cancer vaccines. However, inhibition of specific anti-tumor immunity is common, and several possible explanations of tolerance to tumor antigens or tumor-induced immunesuppression have been proposed. Inhibition of effective anti-tumor immunity results from the tumor or the host response to tumor growth, inhibiting the activation, differentiation, or function of anti-tumor immune cells. As a consequence, anti-tumor T cells cannot respond productively to developmental, targeting, or activation cues. While able to enhance the number and phenotype of anti-tumor T cells, the modest success of immunotherapy has shown the necessity to attempt to reverse tolerance in anti-tumor T cells, and the vanguard of experimental therapy now focuses on vaccination in combination with blockade of immunosuppressive mechanisms. This review discusses several potential mechanisms by which anti-tumor T cells may be inhibited in function.

Tumor resistance to specific lysis: a major hurdle for successful immunotherapy of cancer

Research over the past decade in tumor immunology has shown that immune reactivity to tumor antigens can decrease tumor growth in experimental models. These observations have been translated into clinical studies involving both passive and active forms of immunotherapy. Immunotherapy, an alternative treatment for cancer, is confronted to a major hurdle: tumor escape of specific lysis. Cancer antigen-specific cytotoxic T lymphocytes (CTL) are the major effectors used in immunotherapy against cancer cells. However, large established tumors are usually not fully controlled by CTL. These effector cells could indeed have a dual activity, which allow cancer cells to escape destruction. In this review, we will focus on the essential role of the p53 tumor suppressor gene in the dynamic regulation of tumor cell death induced by cytotoxic T lymphocytes and the involving of structural changes of cytoskeleton in the acquisition of tumor resistance.

Validation of a HLA-A2 tetramer flow cytometric method, IFNgamma real time RT-PCR, and IFNgamma ELISPOT for detection of immunologic response to gp100 and MelanA/MART-1 in melanoma patients

BACKGROUND

HLA-A2 tetramer flow cytometry, IFNgamma real time RT-PCR and IFNgamma ELISPOT assays are commonly used as surrogate immunological endpoints for cancer immunotherapy. While these are often used as research assays to assess patient's immunologic response, assay validation is necessary to ensure reliable and reproducible results and enable more accurate data interpretation. Here we describe a rigorous validation approach for each of these assays prior to their use for clinical sample analysis.

METHODS

Standard operating procedures for each assay were established. HLA-A2 (A*0201) tetramer assay specific for gp100209(210M) and MART-126-35(27L), IFNgamma real time RT-PCR and ELISPOT methods were validated using tumor infiltrating lymphocyte cell lines (TIL) isolated from HLA-A2 melanoma patients. TIL cells, specific for gp100 (TIL 1520) or MART-1 (TIL 1143 and TIL1235), were used alone or spiked into cryopreserved HLA-A2 PBMC from healthy subjects. TIL/PBMC were stimulated with peptides (gp100209, gp100pool, MART-127-35, or influenza-M1 and negative control peptide HIV) to further assess assay performance characteristics for real time RT-PCR and ELISPOT methods. Validation parameters included specificity, accuracy, precision, linearity of dilution, limit of detection (LOD) and limit of quantification (LOQ). In addition, distribution was established in normal HLA-A2 PBMC samples. Reference ranges for assay controls were established.

RESULTS

The validation process demonstrated that the HLA-A2 tetramer, IFNgamma real time RT-PCR, and IFNgamma ELISPOT were highly specific for each antigen, with minimal cross-reactivity between gp100 and MelanA/MART-1. The assays were sensitive; detection could be achieved at as few as 1/4545-1/6667 cells by tetramer analysis, 1/50,000 cells by real time RT-PCR, and 1/10,000-1/20,000 by ELISPOT. The assays met criteria for precision with %CV < 20% (except ELISPOT using high PBMC numbers with %CV < 25%) although flow cytometric assays and cell based functional assays are known to have high assay variability. Most importantly, assays were demonstrated to be effective for their intended use. A positive IFNgamma response (by RT-PCR and ELISPOT) to gp100 was demonstrated in PBMC from 3 melanoma patients. Another patient showed a positive MART-1 response measured by all 3 validated methods.

CONCLUSION

Our results demonstrated the tetramer flow cytometry assay, IFNgamma real-time RT-PCR, and INFgamma ELISPOT met validation criteria. Validation approaches provide a guide for others in the field to validate these and other similar assays for assessment of patient T cell response. These methods can be applied not only to cancer vaccines but to other therapeutic proteins as part of immunogenicity and safety analyses.

Cytotoxic T lymphocytes directed to the preferentially expressed antigen of melanoma (PRAME) target chronic myeloid leukemia

The cancer testis antigen (CTA) preferentially expressed antigen of melanoma (PRAME) is overexpressed in many hematologic malignancies, including chronic myeloid leukemia (CML). The sensitivity of CML to donor lymphocyte infusion after allogeneic stem cell transplantation suggests this tumor can be highly susceptible to cellular immunotherapy targeted to tumor associated antigens. We therefore tested whether functional PRAME-specific cytotoxic T lymphocytes (PRAME CTLs) could be generated and expanded from healthy donors and CML patients, or whether the limited immunogenicity of this CTA coupled with tumor-associated anergy would preclude this approach. Using optimized culture conditions and HLA-A*02-restricted PRAME-peptides, we have consistently generated PRAME CTLs from 8/9 healthy donors and 5/6 CML patients. These CTLs released IFNgamma in response to PRAME peptides (between 113 +/- 8 and 795 +/- 23 spot forming cells/10(5) T cells) and lysed PRAME peptide-loaded cells (45 +/- 19% at an effector:target [E:T] ratio of 20:1) in a MHC-restricted fashion. Importantly, these CTLs recognized and had cytotoxic activity against HLA-A*02(+)/PRAME(+) tumor cell lines, and could recognize and respond to primary CML cells. PRAME CTLs were generated almost exclusively from the naive T-cell compartment, and clonal analysis showed these cells could have high alphabetaTCR-peptide avidity. PRAME CTLs or vaccines may thus be of value for patients with CML.

Downregulation of IFN-gammaR in association with loss of Fas function is linked to tumor progression

The host immune system functions as an intrinsic surveillance network in the recognition and destruction of tumor cells, and it has been demonstrated that lymphocytes and IFN-gamma are the primary tumor suppressors of the immune system. However, the immune system can concurrently select for tumor variants with reduced immunogenicity and aggressive phenotypes. We report here that tumor escape variants that have survived CTL adoptive immunotherapy exhibited decreased expression levels of both Fas and IFN-gammaR in vitro. Furthermore, examination of spontaneously arising mouse primary mammary carcinoma and lung metastases revealed that both Fas and IFN-gammaR protein levels were dramatically lower in lung metastases than in primary tumors in vivo. Functional disruption of either the Fas- or the IFN-gamma signaling pathway enhanced the colonization efficiency of preexisting metastatic tumor cells, whereas disruption of both Fas and IFN-gammaR pathways resulted in synergistic augmentation of the colonization efficiency of the preexisting metastatic tumor cells, as determined by experimental lung metastases assay. Gene expression profiling revealed that altered expression of genes involved in immediate IFN-gammaR signaling, the interferon primary response, apoptosis and tumor colonization is associated with loss of IFN-gammaR function and enhanced metastatic potential. Interestingly, disruption of IFN-gammaR function did not alter tumor cell susceptibility to CTL-mediated cytotoxicity, but is linked to enhanced infiltration of endogenous T cells in the tumor microenvironment in vivo. These findings suggest that coordinate downregulation of Fas and IFN-gammaR, 2 key components of cancer immunosurveillance system on tumor cells, leads to a more aggressive metastatic phenotype.

An ex vivo readout for evaluation of dendritic cell-induced autologous cytotoxic T lymphocyte responses against esophageal cancer

Esophageal cancer is a highly malignant disease that despite surgery and adjuvant therapies has an extremely poor outcome. Dendritic cell (DC) immunotherapy as a novel promising strategy could be an alternative for treating this malignancy. Effective DC-mediated immune responses can be achieved by raising cytotoxic T lymphocyte (CTL) response against multiple antigens through loading DCs with total tumor RNA. However, the efficacy of this strategy first needs to be evaluated in a pre-clinical setting. The aim of the study was to set up an ex vivo autologous human readout assay for assessing the effects of DC-mediated cytotoxic responses, using total tumor RNA as an antigen load. Biopsy specimens of seven esophageal cancer patients were used to establish primary cultures of normal and cancer cells and to obtain autologous RNA for loading DCs. Mature DCs loaded with either normal or tumor RNA were obtained and subsequently used to raise various lymphocytes populations. Apoptosis levels of the autologous cultures were measured before and after incubating the cultures with the different lymphocytes populations. The mean apoptosis levels in the tumor cell cultures, induced by lymphocytes instructed by DCs loaded with tumor RNA, significantly increased with 15.6% +/-2.9 SEM (range 3.4-24.5%, t-test, P < 0.05). Incubation of the normal cultures with the lymphocytes populations showed a mean non-significant increase in apoptosis of 0.4% +/-3.4 SEM (range -13.9 to 9.8%, t-test, P = 0.7). Here, we introduce a practical, patient-specific autologous readout assay for pre-clinical testing of DC-mediated cytotoxic responses. Additionally, we demonstrated that the use of autologous tumor RNA as a strategy for raising cytotoxic responses against multiple tumor antigens could be effective for treating esophageal cancer.

Granzyme B-induced cell death involves induction of p53 tumor suppressor gene and its activation in tumor target cells

In this study we investigated the involvement of p53 in cytotoxic T-lymphocyte (CTL)-induced tumor target cell killing mediated by the perforin/granzymes pathway. For this purpose we used a human CTL clone (LT12) that kills its autologous melanoma target cells (T1), harboring a wild type p53. We demonstrated initially that LT12 kills its T1 target in a perforin/granzymes-dependent manner. Confocal microscopy and Western blot analysis indicated that conjugate formed between LT12 and T1 resulted in rapid cytoplasmic accumulation of p53 and its activation in T1 target cells. Cytotoxic assay using recombinant granzyme B (GrB) showed that this serine protease is the predominant factor inducing such accumulation. Furthermore, RNA interference-mediated lowering of the p53 protein in T1 cells or pifithrin-alpha-induced p53-specific inhibition activity significantly decreased CTL-induced target killing mediated by CTL or recombinant GrB. This emphasizes that p53 is an important determinant in granzyme B-induced apoptosis. Our data show furthermore that when T1 cells were treated with streptolysin-O/granzyme B, specific phosphorylation of p53 at Ser-15 and Ser-37 residues was observed subsequent to the activation of the stress kinases ataxia telangiectasia mutated (ATM) and p38K. Treatment of T1 cells with pifithrin-alpha resulted in inhibition of p53 phosphorylation at these residues and in a significant decrease in GrB-induced apoptotic T1 cell death. Furthermore, small interference RNAs targeting p53 was also accompanied by an inhibition of streptolysin-O/granzyme B-induced apoptotic T1 cell death. The present study supports p53 induction after CTL-induced stress in target cells. These findings provide new insight into a potential role of p53 as a component involved in the dynamic regulation of the major pathway of CTL-mediated cell death and may have therapeutic implications.

Targeting Molecular and Cellular Inhibitory Mechanisms for Improvement of Antitumor Memory Responses Reactivated by Tumor Cell Vaccine

Development of effective vaccination approaches to treat established tumors represents a focus of intensive research because such approaches offer the promise of enhancing immune system priming against tumor Ags via restimulation of pre-existing (memory) antitumoral helper and effector immune cells. However, inhibitory mechanisms, which function to limit the recall responses of tumor-specific immunity, remain poorly understood and interfere with therapies anticipated to induce protective immunity. The mouse renal cell carcinoma (RENCA) tumor model was used to investigate variables affecting vaccination outcomes. We demonstrate that although a whole cell irradiated tumor cell vaccine can trigger a functional antitumor memory response in the bone marrows of mice with established tumors, these responses do not culminate in the regression of established tumors. In addition, a CD103+ regulatory T (Treg) cell subset accumulates within the draining lymph nodes of tumor-bearing mice. We also show that B7-H1 (CD274, PD-L1), a negative costimulatory ligand, and CD4+ Treg cells collaborate to impair the recall responses of tumor-specific memory T cells. Specifically, mice bearing large established RENCA tumors were treated with tumor cell vaccination in combination with B7-H1 blockade and CD4+ T cell depletion (triple therapy treatment) and monitored for tumor growth and survival. Triple treatment therapy induced complete regression of large established RENCA tumors and raised long-lasting protective immunity. These results have implications for developing clinical antitumoral vaccination regimens in the setting in which tumors express elevated levels of B7-H1 in the presence of abundant Treg cells.

Treatment-enhanced CD4+Foxp3+ glucocorticoid-induced TNF receptor family related high regulatory tumor-infiltrating T cells limit the effectiveness of cytokine-based immunotherapy

Regulatory T cells can suppress activated CD4+ and CD8+ T effector cells and may serve as an impediment to spontaneous or therapeutic type 1 antitumor immunity. In a previous study, we observed minimal therapeutic impact, but significantly enhanced T cell cross-priming and lesional infiltration of tumor-reactive CD8+ T cells into established CMS4 sarcomas after combined treatment of BALB/c mice with rFLt3 ligand (rFL) and recombinant GM-CSF (rGM-CSF). In this study, we show that this cytokine regimen also results in the profound enhancement of CD4+ tumor-infiltrating lymphocytes (TIL) expressing FoxP3, IL-10, and TGF-beta mRNA, with 50 or 90% of CD4+ TIL coexpressing the CD25 and glucocorticoid-induced TNFR family related molecules, respectively. Intracellular staining for Foxp3 protein revealed that combined treatment with rFL plus rGM-CSF results in a significant increase in CD4+Foxp3+ T cells in the spleen of both control and tumor-bearing mice, and that nearly half of CD4+ TIL expressed this marker. In addition, CD4+ TIL cells were of an activated/memory (ICOS(high)CD62L(low)CD45RB(low)) phenotype and were capable of suppressing allospecific T cell proliferation and IFN-gamma production from (in vivo cross-primed) anti-CMS4 CD8+ T cells in vitro, via a mechanism at least partially dependent on IL-10 and TGF-beta. Importantly, in vivo depletion of CD4+ T cells resulted in the ability of previously ineffective, rFL plus rGM-CSF therapy-induced CD8+ T cells to now mediate tumor regression.

Down-regulation of the interferon signaling pathway in T lymphocytes from patients with metastatic melanoma

BACKGROUND

Dysfunction of the immune system has been documented in many types of cancers. The precise nature and molecular basis of immune dysfunction in the cancer state are not well defined.

METHODS AND FINDINGS

To gain insights into the molecular mechanisms of immune dysfunction in cancer, gene expression profiles of pure sorted peripheral blood lymphocytes from 12 patients with melanoma were compared to 12 healthy controls. Of 25 significantly altered genes in T cells and B cells from melanoma patients, 17 are interferon (IFN)-stimulated genes. These microarray findings were further confirmed by quantitative PCR and functional responses to IFNs. The median percentage of lymphocytes that phosphorylate STAT1 in response to interferon-alpha was significantly reduced (Delta = 16.8%; 95% confidence interval, 0.98% to 33.35%) in melanoma patients (n = 9) compared to healthy controls (n = 9) in Phosflow analysis. The Phosflow results also identified two subgroups of patients with melanoma: IFN-responsive (33%) and low-IFN-response (66%). The defect in IFN signaling in the melanoma patient group as a whole was partially overcome at the level of expression of IFN-stimulated genes by prolonged stimulation with the high concentration of IFN-alpha that is achievable only in IFN therapy used in melanoma. The lowest responders to IFN-alpha in the Phosflow assay also showed the lowest gene expression in response to IFN-alpha. Finally, T cells from low-IFN-response patients exhibited functional abnormalities, including decreased expression of activation markers CD69, CD25, and CD71; TH1 cytokines interleukin-2, IFN-gamma, and tumor necrosis factor alpha, and reduced survival following stimulation with anti-CD3/CD28 antibodies compared to controls.

CONCLUSIONS

Defects in interferon signaling represent novel, dominant mechanisms of immune dysfunction in cancer. These findings may be used to design therapies to counteract immune dysfunction in melanoma and to improve cancer immunotherapy.

In melanoma changes of immature and mature dendritic cell expression correlate with tumor thickness:an immunohistochemical study

Cells with a dendritic morphology and/or expression of dendritic cell (DC) markers have been repeatedly described in several human tumors, but the distribution and density of melanoma-associated DCs have not yet been reported. The aim of the present study is to analyze the density and topographical distribution of melanoma-associated DCs and their relation with CD3(+), CD4(+) and CD8(+) T lymphocytes in forty cases of cutaneous human melanoma. In melanocytic tumours different pools of DCs were recognised in the epidermis and in the dermis, particularly in intimate relation with lymphocyte clusters inside the melanocytic proliferation, and more often at the edges of tumours. The number of Langerin-positive DCs showed an inverse correlation with tumour depth (correlation coefficient r= -0.59, P=0.0001) and was significantly lower in thick melanomas compared to thin and intermediate ones (P<0.0005). The density of CD83(+) DCs was significantly lower in thick melanomas compared to thin and intermediate ones (P<0.009). A significant correlation was found between the density of the two DCs subsets (r=0.57, p<0.0001). The number of CD3(+) lymphocytes was inversely correlated to the depth of infiltration (r=-0.596, P<0.0001): melanoma cases with II-III Clark level showed a higher T lymphocyte mean density compared to cases with IV-V Clark level (P<0.0001). T lymphocyte density was significantly lower in thick melanomas compared to thin and intermediate melanomas (P<0.0005). In conclusion, our study indicates a progressive loss of DCs and T lymphocytes in the neoplastic progression of melanomas; further identification of the molecular pathways involved in the functional impairment of these immunitary cells may lead to new immunotherapeutic approaches for melanoma patients that would improve the clinical outcome of the patients.

Melanoma immunology: past, present and future

PURPOSE OF REVIEW

Metastatic melanoma is a disease for which no effective therapeutic options have been developed during the last 30 years with the possible exception of high dose interferon-alpha in the adjuvant setting of stage III patients. The immunotherapy approach was initiated decades ago using cell-based vaccines and adoptive immunotherapy with functionally ill-defined lymphocytes. This paper aims to evaluate the last three decades of research in melanoma immunotherapy and to provide insights in the future of this strategy.

RECENT FINDINGS

Thanks to the development of knowledge in basic and applied immunology, clinical studies of immunotherapy have been followed by trials based on molecular characterization of melanoma antigens and availability of ex-vivo assays allowing the quantitative assessment of the immune response against the given vaccine and against patient tumor cells. This second generation of immunotherapy trials, along with additional preclinical studies, while not yet resulting in a convincing clinical outcome, provided a wealth of data on immunogenicity of different melanoma antigens, mechanism of antigen presentation and factors that impair immune recognition of melanoma cells.

SUMMARY

We discuss how this information will be exploited for designing new and more successful clinical trials of both active and adoptive antigen-specific immunotherapy of metastatic melanoma patients.

Angiogenesis meets immunology: Cytokine gene therapy of cancer

Delivery of cytokine genes at the tumor site in pre-clinical models has been shown to recruit host inflammatory cells followed by inhibition of tumor growth. This local effect is often accompanied by systemic protection mediated by the immune system, mainly by CD8(+) T and NK cells. On this basis, cytokine gene-transduced tumor cells have widely been used as vaccines in clinical trials, which have shown good safety profiles and some local responses but substantial lack of systemic efficacy. Are these findings the end of the story? Possibly not, if major improvements will be attained in the coming years. These should be directed at the level of gene selection and delivery, in order to identify the optimal cytokine and achieve efficient and durable cytokine expression, and at the level of improving immune stimulation, i.e. by co-administration of co-stimulatory molecules including B7 and CD40, or boosting the expression of tumor antigens or MHC class I molecules. Interestingly, some of the cytokines which have shown encouraging anti-tumor activity, including IFNs, IL-4, IL-12 and TNF-alpha, are endowed with anti-angiogenic or vasculotoxic effects, which may significantly contribute to local tumor control. Therapeutic exploitation of this property may result in the design of novel approaches which, by maximizing immune-stimulating and anti-angiogenic effects, could possibly lead to starvation of established tumors in patients.

Inhibitory effect of tumor cell-derived lactic acid on human T cells

A characteristic feature of tumors is high production of lactic acid due to enhanced glycolysis. Here, we show a positive correlation between lactate serum levels and tumor burden in cancer patients and examine the influence of lactic acid on immune functions in vitro. Lactic acid suppressed the proliferation and cytokine production of human cytotoxic T lymphocytes (CTLs) up to 95% and led to a 50% decrease in cytotoxic activity. A 24-hour recovery period in lactic acid-free medium restored CTL function. CTLs infiltrating lactic acid-producing multicellular tumor spheroids showed a reduced cytokine production. Pretreatment of tumor spheroids with an inhibitor of lactic acid production prevented this effect. Activated T cells themselves use glycolysis and rely on the efficient secretion of lactic acid, as its intracellular accumulation disturbs their metabolism. Export by monocarboxylate transporter-1 (MCT-1) depends on a gradient between cytoplasmic and extracellular lactic acid concentrations and consequently, blockade of MCT-1 resulted in impaired CTL function. We conclude that high lactic acid concentrations in the tumor environment block lactic acid export in T cells, thereby disturbing their metabolism and function. These findings suggest that targeting this metabolic pathway in tumors is a promising strategy to enhance tumor immunogenicity.

Induction of cytolytic T lymphocytes against pediatric solid tumors in vitro using autologous dendritic cells pulsed with necrotic primary tumor

PURPOSE

Effective and generally applicable methods for generating cancer vaccines in children have not been defined. Dendritic cells (DCs) are the most potent professional antigen-presenting cells capable of activating primary cytolytic T cells. We tested the ability of DCs generated from pediatric patients' peripheral blood monocytes and pulsed with a necrotic tumor to activate autologous tumor-specific cytolytic T cells.

METHODS

Tumor and peripheral blood cells were obtained from pediatric patients undergoing biopsy or resection for advanced solid tumors according to an institutional research board-approved protocol and after acquiring informed consent from them. To generate DCs, we treated peripheral blood monocytes with granulocyte-macrophage colony stimulating factor and interleukin (IL)-4. Maturation was induced with a cytokine cocktail (CC) containing tumor necrosis factor-alpha, IL-6, IL-1beta, and prostaglandin E2. The DC phenotype was assayed using flow cytometry. Tumor necrosis was induced by exposure to UV-B irradiation (1000 mJ). Dendritic cells pulsed with a UV-B-treated primary tumor and matured with CC were used to stimulate autologous peripheral blood lymphocytes weekly. Tumor-specific cytolytic activity was assayed using 4-hour 51Cr release.

RESULTS

Peripheral blood monocytes isolated from pediatric patients differentiated into immature DCs (CD14-, MHCII+ [major histocompatibility complex], CD80(low), CD86(low)) in the presence of granulocyte-macrophage colony stimulating factor and IL-4. Cytokine cocktail induced maturation of DCs, as characterized by increased expressions of MHCII, CD83, CD80, and CD86. Patients' peripheral blood lymphocytes stimulated in vitro with DCs loaded with a necrotic primary tumor and matured with CC specifically lysed autologous neuroblastoma in 7 of 9 patients.

CONCLUSION

Dendritic cells generated from the peripheral blood of children with advanced solid tumors and pulsed with a necrotic primary tumor undergo maturation and effectively stimulate autologous tumor-specific cytolytic T cells in vitro. We describe a simple method for generating a vaccine capable of activating cytotoxic T cells against pediatric solid tumors that does not require the genetic identification of tumor-associated antigens.

A phase-I trial using a universal GM-CSF-producing and CD40L-expressing bystander cell line (GM.CD40L) in the formulation of autologous tumor cell-based vaccines for cancer patients with stage IV disease

BACKGROUND

Significant antitumor T-cell responses are generated in vitro when human lymphocytes are stimulated with autologous tumor cells in the presence of bystander cells transfected with CD40L and GM-CSF. Our goal was to test this bystander-based vaccine strategy in vivo in cancer patients with stage IV disease.

METHODS

Patients received three intradermal vaccine injections (irradiated autologous tumor cells plus GM.CD40L bystander cells) at 28-day intervals. Patients with no disease progression received three additional vaccines at 4, 12, and 24 months. Patients were monitored for toxicity, tumor response, and tumor-specific immune responses.

RESULTS

Twenty-one patients received at least three vaccine injections, with no toxicity attributable to the vaccine. Immunohistochemistry of vaccine injection site biopsies with CD1a and CD86 antibodies confirmed recruitment and activation of dendritic cells. There was no tumor regression after vaccination, but many patients had stable disease, including six of ten melanoma patients. Four patients developed tumor-specific T-cell responses on ELISPOT testing. One patient, who had stable disease for 24 months, demonstrated an increase in MART-1-specific T-cells by tetramer analysis after re-immunization; biopsy of the tumor that progressed 2 years after the onset of vaccination revealed a massive peritumoral and intratumoral T-cell infiltrate.

CONCLUSIONS

Vaccination of cancer patients with autologous tumor cells and GM.CD40L bystander cells (engineered to express GM-CSF and CD40L) is safe, can recruit and activate dendritic cells, and can elicit tumor-specific T-cell responses. Phase-II trials are underway to evaluate the impact of bystander-based vaccines on melanoma and mantle cell lymphoma.

Isoaspartyl post-translational modification triggers anti-tumor T and B lymphocyte immunity

A hallmark of the immune system is the ability to ignore self-antigens. In attempts to bypass normal immune tolerance, a post-translational protein modification was introduced into self-antigens to break T and B cell tolerance. We demonstrate that immune tolerance is bypassed by immunization with a post-translationally modified melanoma antigen. In particular, the conversion of an aspartic acid to an isoaspartic acid within the melanoma antigen tyrosinase-related protein (TRP)-2 peptide-(181-188) makes the otherwise immunologically ignored TRP-2 antigen immunogenic. Tetramer analysis of iso-Asp TRP-2 peptide-immunized mice demonstrated that CD8+ T cells not only recognized the isoaspartyl TRP-2 peptide but also the native TRP-2 peptide. These CD8+ T cells functioned as cytotoxic T lymphocytes, as they effectively lysed TRP-2 peptide-pulsed targets both in vitro and in vivo. Potentially, post-translational protein modification can be utilized to trigger strong immune responses to either tumor proteins or potentially weakly immunogenic pathogens.

Relating TCR-peptide-MHC affinity to immunogenicity for the design of tumor vaccines

One approach to enhancing the T cell response to tumors is vaccination with mimotopes, mimics of tumor epitopes. While mimotopes can stimulate proliferation of T cells that recognize tumor-associated antigens (TAAs), this expansion does not always correlate with control of tumor growth. We hypothesized that vaccination with mimotopes of optimal affinity in this interaction will improve antitumor immunity. Using a combinatorial peptide library and a cytotoxic T lymphocyte clone that recognizes a TAA, we identified a panel of mimotopes that, when complexed with MHC, bound the TAA-specific TCR with a range of affinities. As expected, in vitro assays showed that the affinity of the TCR-peptide-MHC (TCR-pMHC) interaction correlated with activity of the T cell clone. However, only vaccination with mimotopes in the intermediate-affinity range elicited functional T cells and provided protection against tumor growth in vivo. Vaccination with mimotopes with the highest-affinity TCR-pMHC interactions elicited TAA-specific T cells to the tumor, but did not control tumor growth at any of the peptide concentrations tested. Further analysis of these T cells showed functional defects in response to the TAA. Thus, stimulation of an antitumor response by mimotopes may be optimal with peptides that increase but do not maximize the affinity of the TCR-pMHC interaction.

Coexpression of NRASQ61Rand BRAFV600Ein Human Melanoma Cells Activates Senescence and Increases Susceptibility to Cell-Mediated Cytotoxicity

Activating mutations in BRAF and NRAS oncogenes in human melanomas are mutually exclusive. This finding has suggested an epistatic relationship but is consistent even with synthetic lethality. To evaluate the latter possibility, a mutated NRAS(Q61R) oncogene was expressed, under a constitutive or a doxycycline-regulated promoter, in a metastatic melanoma clone (clone 21) harboring an activated BRAF(V600E) oncogene. After the first 10 to 12 in vitro passages, the constitutive NRAS(Q61R) transfectant displayed progressive accumulation in G(0)-G(1) phase of the cell cycle and stained for the senescence-associated beta-galactosidase activity (SA-beta-Gal). Inducible expression of NRAS(Q61R), by the Tet-Off system, in clone 21 cells (21NRAS(61ON)) led to overactivation of the RAS/RAF/mitogen-activated protein kinase signaling pathway and, after the 10th in vitro passage, led to promotion of senescence. This was documented by reduced proliferation, flattened cell morphology, reduced growth in Matrigel, positive staining for SA-beta-Gal, and expression of AMP-activated protein kinase and of the cell cycle inhibitor p21(waf1/Cip1). These effects were detected neither in 21 cells with silenced NRAS(Q61R) (21NRAS(61OFF)) nor in cells transfected with an inducible wild-type NRAS gene (21NRAS(WTON)). In addition, when compared with parental 21 cells, or with 21NRAS(61OFF), 21NRAS(61ON) and constitutive NRAS(Q61R) transfectants cells showed increased susceptibility to cytotoxicity by both HLA class I antigen-restricted and nonspecific T cells and up-regulation of several MHC class I antigen processing machinery components. These results suggest a relationship of synthetic lethality between NRAS and BRAF oncogenes, leading to selection against "double-mutant" cells.

Melanoma-specific tumor-infiltrating lymphocytes but not circulating melanoma-specific T cells may predict survival in resected advanced-stage melanoma patients

PURPOSE

To study the effect of autologous tumor cell vaccinations on the presence and numbers of circulating CD8+ T cells specific for tumor-associated antigens (TAA) in metastatic melanoma patients. To investigate the correlation between the presence of tumor-infiltrating lymphocytes (TIL) and circulating TAA-specific CD8+ T cells before and after autologous tumor cell vaccination with overall survival.

EXPERIMENTAL DESIGN

Twenty-five stage III and resected stage IV metastatic melanoma patients were adjuvantly treated with a series of intracutaneously injected autologous tumor cell vaccinations, of which the first two contained BCG as an immunostimulatory adjuvant. Tumor samples and blood samples obtained before and after vaccination of these patients were studied for the presence of TAA-specific T cells using HLA-tetramers and results were correlated with survival.

RESULTS

In 5 of 17 (29%) melanoma patients, circulating TAA-specific T cells were detectable prior to immunizations. No significant changes in the frequency and specificity were found during the treatment period in all patients. Presence of circulating TAA-specific T cells was not correlated with survival (log rank, P=0.215). Inside melanoma tissue, TAA-specific TIL could be detected in 75% of 16 available tumor samples. In case of detectable TAA-specific TIL, median survival was 22.5 months compared to median survival of 4.5 months in case of absence of TAA-specific T cells (log rank, P=0.0094). In none of the patients, TAA-specific T cells were found both in tumor tissue and blood at the same time.

CONCLUSIONS

These data suggest that the presence of TAA-specific TILs forms a prognostic factor, predicting improved survival in advanced-stage melanoma patients. The absence of TAA-specific T cells in the circulation suggests that homing of the tumor-specific T cell population to the tumor site contributes to the effectiveness of antitumor immunity.

Frequency of telomerase-specific CD8+ T lymphocytes in patients with cancer

Telomerase is considered a universal tumor-associated antigen (TAA) due to its high rate of expression by cancers (≈90%), and clinical trials are in progress to test the immunotherapeutical efficacy of antitelomerase immunization in patients with cancer. However, the data concerning frequency and functional activity of telomerase-specific cytotoxic T lymphocytes (CTLs) in patients with cancer are few and conflicting, although their knowledge would be mandatory to predict the efficacy of telomerase-specific immunotherapy in selected patients. We performed this study to analyze frequency and cytolytic function of circulating CD8+ T lymphocytes specific for the p540 telomerase peptide in a series of human leukocyte antigen (HLA)–A2+ cancer patients. The results show that most patients with cancer have circulating telomerase-specific CD8+ T lymphocytes, but a high frequency of telomerase-specific CTLs are present only in a fraction of them. Furthermore, CTL lines able to kill telomerase-positive tumor cells, including autologous cancer cells, can be expanded ex vivo from some, but not all, patients with cancer. In conclusion, the results of the study support the development of clinical protocols using telomerase peptides as an immunizing agent. However, they underline the necessity to study single patients immunologically before undergoing vaccination, to select the patients adequately, and to eventually adapt the immunization schedule to the patient's immunologic status.

Culture of melanoma cells in 3-dimensional architectures results in impaired immunorecognition by cytotoxic T lymphocytes specific for Melan-A/MART-1 tumor-associated antigen

OBJECTIVE

To assess the effects of the culture of melanoma cells in 3-dimensional (3D) architectures on their immunorecognition by cytotoxic T lymphocytes (CTLs) specific for tumor-associated antigens.

SUMMARY BACKGROUND DATA

Growth in 3D architectures has been shown to promote the resistance of cancers to treatment with drugs, cytokines, or irradiation, thereby potentially playing an important role in tumor expansion. We investigated the effects of 3D culture on the recognition of melanoma cells by antigen-specific HLA class I-restricted CTLs.

METHODS

Culture of HBL melanoma cells expressing Melan-A/Mart-1 tumor-associated antigen and HLA-A0201 on poly-2-hydroxyethyl methacrylate (polyHEMA)-coated plates resulted in the generation of aggregates of 400- to 500-microm diameters containing on average 30,000 cells and characterized by slower proliferation, as compared with monolayer (2-dimensional) cultures. HLA-A0201 restricted Melan-A/Mart-127-35-specific CTL clones were used to evaluate tumor cell immunorecognition measured as specific IFN-gamma production. Comparative gene and protein expression in 2D and 3D cultures was studied by real-time PCR and flow cytometry, respectively. Overall differences in gene expression profiles between 2D and 3D cultures were evaluated by high-density oligonucleotide array hybridization.

RESULTS

HLA-A0201 restricted Melan-A/Mart-127-35 specific CTL clones produced high amounts of IFN-gamma upon short-term (4-24 hours) coincubation with HBL cells cultured in 2D but not in 3D, thus suggesting altered antigen recognition. Indeed, Melan-A/Mart-1 expression, at both gene and protein levels, was significantly decreased in 3D as compared with 2D cultures. Concomitantly, a parallel decrease of HLA class I molecule expression was also observed. Differential gene profiling studies on HBL cells showed an increased expression of genes encoding molecules involved in intercellular adhesion, such as junctional adhesion molecule 2 and cadherin-like 1 (>20- and 8-fold up-regulated, respectively) in 3D as compared with 2D cultures.

CONCLUSIONS

Taken together, our data suggest that mere growth of melanoma cells in 3D architectures, in the absence of immunoselective pressure, may result in defective recognition by tumor-associated antigen-specific CTL.

Qualitative difference between the cytotoxic T lymphocyte responses to melanocyte antigens in melanoma and vitiligo

Vitiligo is a skin disorder characterized by depigmented macules secondary to melanocyte loss. An unusual facet is its relation to melanoma: cytotoxic T lymphocytes directed to melanocyte antigens are found in both conditions and imply a breakdown of tolerance, yet the resulting immune reaction is the opposite. The mechanisms at the basis of these opposite effects are not known. Here, we performed a direct comparison of whole melanocyte-specific T cell populations in the two diseases. We demonstrate that neither precursor frequencies of Melan-A/MART-1-specific T lymphocytes nor their status of activation differ significantly. However, by using a tetramer-based T cell receptor down-regulation assay, we documented a higher affinity of vitiligo T cells. We calculated that the peptide concentration required for 50% of maximal receptor down-regulation differed by 6.5-fold between the two diseases. Moreover, only vitiligo T cells were capable of efficient receptor down-regulation and IFN-gamma production in response to HLA-matched melanoma cells, suggesting that this difference in receptor affinity is physiologically relevant. The differences in receptor affinity and tumor reactivity were confirmed by analyzing Melan-A/MART-1-specific clones established from the two diseases. Our results suggest that the quality, and not the quantity, of the melanocyte-specific cytotoxic responses differs between the two pathologies.