Loss of a unique tumor antigen by cytotoxic T lymphocyte immunoselection from a 3-methylcholanthrene-induced mouse sarcoma reveals secondary unique and shared antigens

Nattokinase-Mediated Regulation of Tumor Physical Microenvironment to Enhance Chemotherapy, Radiotherapy, and CAR-T Therapy of Solid Tumor

The therapy of solid tumors is always hampered by the intrinsic tumor physical microenvironment (TPME) featured with compact and rigid extracellular matrix (ECM) microstructures. Herein, we introduce nattokinase (NKase), a thrombolytic healthcare drug, to comprehensively regulate the TPME for versatile enhancement of various therapy modalities. Intratumoral injection of NKase not only degrades the major ECM component fibronectin but also inhibits cancer-associated fibroblasts (CAFs) in generating fibrosis, resulting in decreased tumor stiffness, enhanced perfusion, and hypoxia alleviation. The NKase-mediated regulation of the TPME significantly promotes the tumoral accumulation of therapeutic agents, leading to efficient chemotherapy without inducing side effects. Additionally, the enhancement of tumor radiotherapy based on radiosensitizers was also achieved by the pretreatment of intratumorally injected NKase, which could be ascribed to the elevated oxygen saturation level in NKase-treated tumors. Moreover, a xenografted human breast MDB-MA-231 tumor model is established to evaluate the influence of NKase on chimeric antigen receptor (CAR)-T cell therapy, illustrating that the pretreatment of NKase could boost the infiltration of CAR-T cells into tumors and thus be a benefit for tumor inhibition. These findings demonstrate the great promise of the NKase-regulated TPME as a translational strategy for universal enhancement of therapeutic efficacy in solid tumors by various treatments.

Modulating tumor physical microenvironment for fueling CAR-T cell therapy

Chimeric antigen receptor (CAR) T cell therapy has achieved unprecedented clinical success against hematologic malignancies. However, the transition of CAR-T cell therapies for solid tumors is limited by heterogenous antigen expression, immunosuppressive microenvironment (TME), immune adaptation of tumor cells and impeded CAR-T-cell infiltration/transportation. Recent studies increasingly reveal that tumor physical microenvironment could affect various aspects of tumor biology and impose profound impacts on the antitumor efficacy of CAR-T therapy. In this review, we discuss the critical roles of four physical cues in solid tumors for regulating the immune responses of CAR-T cells, which include solid stress, interstitial fluid pressure, stiffness and microarchitecture. We highlight new strategies exploiting these features to enhance the therapeutic potency of CAR-T cells in solid tumors by correlating with the state-of-the-art technologies in this field. A perspective on the future directions for developing new CAR-T therapies for solid tumor treatment is also provided.

Challenges targeting cancer neoantigens in 2021: a systematic literature review

Introduction: Cancer neoantigens represent important targets of cancer immunotherapy. The goal of cancer neoantigen vaccines is to induce neoantigen-specific immune responses and antitumor immunity while minimizing the potential for autoimmune toxicity. Advances in sequencing technologies, neoantigen prediction algorithms, and other technologies have dramatically improved the ability to identify and prioritize cancer neoantigens. Unfortunately, results from preclinical studies and early phase clinical trials highlight important challenges to the successful clinical translation of neoantigen cancer vaccines.Areas covered: In this review, we provide an overview of current strategies for the identification and prioritization of cancer neoantigens with a particular emphasis on the two most common strategies used for neoantigen identification: (1) direct identification of peptide ligands eluted from peptide-MHC complexes, and (2) next-generation sequencing combined with neoantigen prediction algorithms. We highlight the limitations of current neoantigen prediction pipelines, and discuss broader challenges associated with cancer neoantigen vaccines including tumor purity/heterogeneity and the immunosuppressive tumor microenvironment.Expert opinion: Despite current limitations, neoantigen prediction is likely to improve rapidly based on advances in sequencing, machine learning, and information sharing. The successful development of robust cancer neoantigen prediction strategies is likely to have a significant impact, with the potential to facilitate cancer neoantigen vaccine design.

Safety and Efficacy of Personalized Cancer Vaccines in Combination With Immune Checkpoint Inhibitors in Cancer Treatment

Cancer immunotherapy can induce sustained responses in patients with cancers in a broad range of tissues, however, these treatments require the optimized combined therapeutic strategies. Despite immune checkpoint inhibitors (ICIs) have lasting clinical benefit, researchers are trying to combine them with other treatment modalities, and among them the combination with personalized cancer vaccines is attractive. Neoantigens, arising from mutations in cancer cells, can elicit strong immune response without central tolerance and out-target effects, which is a truly personalized method. Growing studies show that the combination can elevate the antitumor efficacy with acceptable safety and minimal additional toxicity compared with single agent vaccine or ICI. Herein, we have searched these preclinical and clinical trials and summarized safety and efficacy of personalized cancer vaccines combined with ICIs in several malignancies. Meanwhile, we discuss the rationale of the combination and future challenges.

Radiosurgery and Immunotherapy in the Treatment of Brain Metastases

Radiation therapy represents a mainstay of treatment for patients with brain metastases. Recently, the widespread adoption of immune checkpoint blockade has led to keen interest in treating cancers with checkpoint inhibitors in place of, or as an adjunct to, traditional chemotherapy. However, with the exception of melanoma, immune checkpoint blockade in solid tumors has failed to achieve significant brain control in patients with brain metastases. The possibility of combining immune checkpoint blockade with radiation for the treatment of brain and other metastases represents an exciting new strategy that is in its early stages of investigation. Success with this combinatorial strategy has the potential to result in enhanced rates of brain control, less brain exposure to radiation, and improved cognitive outcomes. In this review, we discuss the mechanisms behind this synergy, describe its limitations, and suggest ways to move the field forward.

Neoantigens Generated by Individual Mutations and Their Role in Cancer Immunity and Immunotherapy

Recent preclinical and clinical studies have proved the long-standing hypothesis that tumors elicit adaptive immune responses and that the antigens driving effective T-cell response are neoantigens, i.e., peptides that are generated from somatically mutated genes. Hence, the characterization of neoantigens and the identification of the immunogenic ones are of utmost importance for improving cancer immunotherapy and broadening its efficacy to a larger fraction of patients. In this review, we first introduce the methods used for the quantification of neoantigens using next-generation sequencing data and then summarize results obtained using these tools to characterize the neoantigen landscape in solid cancers. We then discuss the importance of neoantigens for cancer immunotherapy using checkpoint blockers, vaccination, and adoptive T-cell transfer. Finally, we give an overview over emerging aspects in cancer immunity, including tumor heterogeneity and immunoediting, and give an outlook on future prospects.

Treatment-Induced Mutagenesis and Selective Pressures Sculpt Cancer Evolution

Despite the great progress in our understanding of the molecular basis of human cancer, the heterogeneity of individual tumors and the evolutionary pressures imposed by therapy have hampered our ability to effectively eradicate and control this disease. How, therefore, do cancers evolve under the selective pressures of cancer therapy? Recent studies have linked both primary (or de novo) and acquired treatment resistance to intratumor heterogeneity and clonal evolution. Resistance to targeted therapies often includes mutation of the drug target itself and aberrations of pathways upstream of, downstream from, or parallel to the drug target. For systemic chemotherapies, discrete and recurrent resistance-conferring genetic aberrations have eluded the community, due in part to their wide-ranging mutagenic effects. In this review, we discuss different patterns of clonal evolution during treatment-specific selective pressures and focus on the genetic mechanisms of treatment resistance that have emerged to both targeted therapies and chemotherapies.

Evolution of Neoantigen Landscape during Immune Checkpoint Blockade in Non-Small Cell Lung Cancer

Immune checkpoint inhibitors have shown significant therapeutic responses against tumors containing increased mutation-associated neoantigen load. We have examined the evolving landscape of tumor neoantigens during the emergence of acquired resistance in patients with non-small cell lung cancer after initial response to immune checkpoint blockade with anti-PD-1 or anti-PD-1/anti-CTLA-4 antibodies. Analyses of matched pretreatment and resistant tumors identified genomic changes resulting in loss of 7 to 18 putative mutation-associated neoantigens in resistant clones. Peptides generated from the eliminated neoantigens elicited clonal T-cell expansion in autologous T-cell cultures, suggesting that they generated functional immune responses. Neoantigen loss occurred through elimination of tumor subclones or through deletion of chromosomal regions containing truncal alterations, and was associated with changes in T-cell receptor clonality. These analyses provide insight into the dynamics of mutational landscapes during immune checkpoint blockade and have implications for the development of immune therapies that target tumor neoantigens.Significance: Acquired resistance to immune checkpoint therapy is being recognized more commonly. This work demonstrates for the first time that acquired resistance to immune checkpoint blockade can arise in association with the evolving landscape of mutations, some of which encode tumor neoantigens recognizable by T cells. These observations imply that widening the breadth of neoantigen reactivity may mitigate the development of acquired resistance. Cancer Discov; 7(3); 264-76. ©2017 AACR.See related commentary by Yang, p. 250This article is highlighted in the In This Issue feature, p. 235.

T cell neoepitope discovery in colorectal cancer by high throughput profiling of somatic mutations in expressed genes

OBJECTIVE

Patient-specific (unique) tumour antigens, encoded by somatically mutated cancer genes, generate neoepitopes that are implicated in the induction of tumour-controlling T cell responses. Recent advancements in massive DNA sequencing combined with robust T cell epitope predictions have allowed their systematic identification in several malignancies.

DESIGN

We undertook the identification of unique neoepitopes in colorectal cancers (CRCs) by using high-throughput sequencing of cDNAs expressed by standard cancer cell cultures, and by related cancer stem/initiating cells (CSCs) cultures, coupled with a reverse immunology approach not requiring human leukocyte antigen (HLA) allele-specific epitope predictions.

RESULTS

Several unique mutated antigens of CRC, shared by standard cancer and related CSC cultures, were identified by this strategy. CD8⁺ and CD4⁺ T cells, either autologous to the patient or derived from HLA-matched healthy donors, were readily expanded in vitro by peptides spanning different cancer mutations and specifically recognised differentiated cancer cells and CSC cultures, expressing the mutations. Neoepitope-specific CD8⁺ T cell frequency was also increased in a patient, compared with healthy donors, supporting the occurrence of clonal expansion in vivo.

CONCLUSIONS

These results provide a proof-of-concept approach for the identification of unique neoepitopes that are immunogenic in patients with CRC and can also target T cells against the most aggressive CSC component.

Emerging biomarkers for PD-1 pathway cancer therapy

The field of immuno-oncology has witnessed unprecedented success in recent years, with several PD=1 and PD-L1 inhibitors obtaining US FDA registration and breakthrough drug therapy designation in multiple tumor types. Despite its clear efficacy in certain cancers, treatment with these agents carries a risk of immune-related toxicities and substantial financial burden. It is, therefore, critical to identify patients likely to benefit from such immunotherapies and develop strategies to differentiate responders from nonresponders early during treatment. Here we discuss the development of predictive and treatment response biomarkers for immune checkpoint inhibitors. We first examine the role of PD-L1 expression, the most extensively studied predictive biomarker of response, and further discuss emerging putative predictive biomarkers. We also detail challenges faced in the development of response assessments for immunotherapeutics and propose other biomarkers that may be useful as surrogate intermediate end points of response.

Neoantigens in cancer immunotherapy

The clinical relevance of T cells in the control of a diverse set of human cancers is now beyond doubt. However, the nature of the antigens that allow the immune system to distinguish cancer cells from noncancer cells has long remained obscure. Recent technological innovations have made it possible to dissect the immune response to patient-specific neoantigens that arise as a consequence of tumor-specific mutations, and emerging data suggest that recognition of such neoantigens is a major factor in the activity of clinical immunotherapies. These observations indicate that neoantigen load may form a biomarker in cancer immunotherapy and provide an incentive for the development of novel therapeutic approaches that selectively enhance T cell reactivity against this class of antigens.

Somatically mutated tumor antigens in the quest for a more efficacious patient-oriented immunotherapy of cancer

Although cancer immunotherapy shows efficacy with adoptive T cell therapy (ACT) and antibody-based immune checkpoint blockade, efficacious therapeutic vaccination of cancer patients with tumor-associated antigens (TAAs) remains largely unmet. Current cancer vaccines utilize nonmutated shared TAAs that may have suboptimal immunogenicity. Experimental evidence underscores the strong immunogenicity of unique TAAs derived from somatically mutated cancer proteins, whose massive characterization has been precluded until recently by technical limitations. The development of cost-effective, high-throughput DNA sequencing approaches makes now possible the rapid identification of all the somatic mutations contained in a cancer cell genome. This method, combined with robust bioinformatics platforms for T cell epitope prediction and established reverse immunology approaches, provides us with an integrated strategy to identify patient-specific unique TAAs in a relatively short time, compatible with their potential use in the clinic. Hence, it is now for the first time possible to quantitatively define the patient's unique tumor antigenome and exploit it for vaccination, possibly in combination with ACT and/or immune checkpoint blockade to further increase immunotherapy efficacy.

Vaccination: role in metastatic melanoma

Based on the poor impact on overall survival obtained by systemic chemotherapy in metastatic melanoma and the identification of many melanoma antigens recognized by T cells, in the last decade many efforts have been devoted to the development of active specific immunotherapy as a promising systemic treatment for this neoplastic disease. A number of Phase I-II clinical trials have been performed with different vaccination approaches that included whole tumor cells, antigen peptides, antigen-pulsed dendritic cells, recombinant viruses, plasmids or naked DNA, and heat-shock proteins. Despite some promising immunological and clinical results obtained in these studies, melanoma-specific vaccines have altogether failed to prove their efficacy in the few large Phase III randomized clinical trials performed. Nonetheless, the possibility of activating the human immune system to recognize and destroy tumor cells remains a challenging investigative field, considering that the new knowledge of the intricate cellular and molecular mechanisms that regulate the immune function and tumor-host interactions may allow the development of new clinically relevant melanoma vaccination strategies.

Molecular cancer vaccines: Tumor therapy using antigen-specific immunizations

Vaccination against tumors promises selective destruction of malignant cells by the host's immune system. Molecular cancer vaccines rely on recently identified tumor antigens as immunogens. Tumor antigens can be applied in many forms, as genes in recombinant vectors, as proteins or peptides representing T cell epitopes.Analysis of various aspects indicates some advantage for peptide-based vaccines over the other modalities. Further refinements and extensively monitored clinical trials are necessary to advance molecular cancer vaccines from concepts into powerful therapy.

Tumor-derived autophagosome vaccine: induction of cross-protective immune responses against short-lived proteins through a p62-dependent mechanism

PURPOSE

Tumor-specific antigens of 3-methylcholanthrene (MCA)-induced sarcomas were defined by the narrow immune responses they elicited, which uniquely rejected the homologous tumor, with no cross-reactions between independently derived syngeneic MCA-induced tumors. This study examines whether an autophagosome-enriched vaccine derived from bortezomib-treated sarcomas can elicit an immune response that cross-reacts with other unique sarcomas.

EXPERIMENTAL DESIGN

Mice were vaccinated with either MCA-induced sarcomas or autophagosomes derived from those tumors and later challenged with either homologous or nonhomologous sarcomas. In addition, 293 cells expressing a model antigen were used to understand the necessity of short-lived proteins (SLiP) in this novel vaccine. These findings were then tested in the sarcoma model. Autophagosomes were characterized by Western blotting and fluorescent microscopy, and their ability to generate immune responses was assessed in vitro by carboxyfluorescein succinimidyl ester dilution of antigen-specific T cells and in vivo by monitoring tumor growth.

RESULTS

In contrast to a whole-cell tumor vaccine, autophagosomes isolated from MCA-induced sarcomas treated with a proteasome inhibitor prime T cells that cross-react with different sarcomas and protect a significant proportion of vaccinated hosts from a nonhomologous tumor challenge. Ubiquitinated SLiPs, which are stabilized by proteasome blockade and delivered to autophagosomes in a p62/sequestosome-dependent fashion, are a critical component of the autophagosome vaccine, as their depletion limits vaccine efficacy.

CONCLUSION

This work suggests that common short-lived tumor-specific antigens, not physiologically available for cross-presentation, can be sequestered in autophagosomes by p62 and used as a vaccine to elicit cross-protection against independently derived sarcomas.

Specificity in cancer immunotherapy

From the earliest days in the field of tumor immunology three questions have been asked: do cancer cells express tumor-specific antigens, does the immune system recognize these antigens and if so, what is their biochemical nature? We now know that truly tumor-specific antigens exist, that they are caused by somatic mutations, and that these antigens can induce both humoral and cell-mediated immune responses. Because tumor-specific antigens are exclusively expressed by the cancer cell and are often crucial for tumorigenicity, they are ideal targets for anti-cancer immunotherapy. Nevertheless, the antigens that are targeted today by anti-tumor immunotherapy are not tumor-specific antigens, but antigens that are normal molecules also expressed by normal tissues (so-called "tumor-associated" antigens). If tumor-specific antigens exist and are ideal targets for immunotherapy, why are they not being targeted? In this review, we summarize current knowledge of tumor-specific antigens: their identification, immunological relevance and clinical use. We discuss novel tumor-specific epitopes and propose new approaches that could improve the success of cancer immunotherapy, especially for the treatment of solid tumors.

Unique tumor antigens: evidence for immune control of genome integrity and immunogenic targets for T cell-mediated patient-specific immunotherapy

The molecular identification and characterization of antigenic epitopes recognized by T cells on human cancers has rapidly evolved since the cloning in 1991 of MAGEA1, the first gene reported to encode a CTL-defined human tumor antigen. In the expanding field of human tumor immunology, unique tumor antigens constitute a growing class of T cell-defined epitopes that exhibit strong immunogenicity. Some of these antigens, which often derive from mutation of genes that have relevant biological functions, are less susceptible to immunoselection and may be retained even in advanced tumors. Immunogenicity and constitutive expression of the unique tumor antigens provide a strong rationale for the design of novel, patient-tailored therapies that target such determinants. Here we discuss the immunologic relevance of unique tumor antigens in the light of the prospects for exploiting such epitopes as targets for patient-specific immune intervention strategies.

Mobilizing the low-avidity T cell repertoire to kill tumors

Optimally, T cells destroy infected and transformed cells of the host. To be effective the T cell repertoire must have a sufficiently diverse number of T cell receptors (TCRs) to recognize the abundance of foreign and tumor antigens presented by MHC molecules. The T cell repertoire must also not be reactive toward self-antigens on healthy cells to prevent autoimmunity. Unlike antigens derived from pathogens, most tumor-associated antigens (TAA) are also self-antigens. Therefore, central and peripheral tolerance mechanisms delete or inhibit tumor-reactive T cells. Although there are T cells within the peripheral repertoire that recognize TAA, these T cells are not sufficient to prevent growth of clinically relevant tumors. We will discuss how this dysfunction results, in part, from the low functional avidity of T cells for tumor, or antigen presenting cells (APC) displaying TAA. We discuss the limitations of these low-avidity tumor-reactive T cells and review current immunotherapies aimed at enhancing the avidity and antitumor activity of the tumor-specific T cell repertoire.

Diversity of escape variant mutations in Simian virus 40 large tumor antigen (SV40 Tag) epitopes selected by cytotoxic T lymphocyte (CTL) clones

To better understand the relationship between epitope variation and tumor escape from immune surveillance, SV40 T antigen-transformed B6/K-0 cells were subjected to selection with individual CTL clones specific for the SV40 T antigen H-2D(b)-restricted epitopes I or V. CTL-resistant populations were isolated from a majority of the selection cultures and substituted epitope sequences were identified within most of the resistant populations. Tag sequences deleted of all or portions of the selection-targeted epitope were identified, but in lower numbers compared to epitope sequences bearing single residue substitutions. Relatively few flanking residue substitutions were identified, and only in epitope I-targeted selections. The diversity (numbers and epitope residue locations) of substituted epitope residue positions varied between selections. These findings suggest that the scope of spontaneously occurring mutations that could allow for escape from individual CD8+ T cell clones is large.

Combined chemoimmunotherapy of solid tumours: improving vaccines?

Cytotoxic chemotherapy not only affects the tumour but also targets dividing lymphocytes, the very cells required to develop an immune response. Hence, chemo- and immunotherapy have been seen as antagonistic. It is now clear that the way a chemotherapeutic drug kills a tumour cell determines how that dying cell interacts with the immune system and whether the interaction leads to an immune response. Chemotherapy also depletes regulatory T cells, potentially enhancing immune responses. Furthermore, lymphodepletion triggers homeostatic T cell reconstitution, creating new populations of pre-T cells that need education in the thymic environment. Post-chemotherapy immune system reconstitution may provide a unique opportunity for therapeutic intervention by shaping the repertoire towards reactivity to tumour antigens. An understanding of the underlying cellular and immunological events in both animal models and patients undergoing chemotherapy will guide decisions about which immunomodulatory approaches may be effective with different cytostatic drugs and hence to develop appropriate scheduling for integration of the treatment modalities.

Animal models in oral cancer research

Biologically and clinically relevant animal models are essential in investigation of the progression of diseases and the elaboration of diagnostic or therapeutic protocols. The several rodent models used for in vivo evaluation for oral cancer employ chemical, transplantation and genetic (knockout and transgenic) induction methods. These models are described together with their advantages and disadvantages. Their optimization and application in future research may improve the early detection and treatment of oral cancer.

A listing of human tumor antigens recognized by T cells: March 2004 update

The technological advances occurred in the last few years have led to a great increase in the number of tumor associated antigens (TAA) that are currently available for clinical applications. In this review we provide a comprehensive list of human tumor antigens as reported in the literature updated at February 2004. The list includes all T cell-defined epitopes, while excluding analogs or artificially modified epitopes, as well as virus-encoded and antibodies-recognized antigens. TAAs are listed in alphabetical order along with the epitope sequence and the HLA allele which restricts recognition by T cells. Data on the tissue distribution of each antigen are also provided together with an extensive bibliography that allows a rapid search for any additional information may be needed on each single antigen or epitope. Overall, the updated list is a database tool for clinicians, scientists and students who have an interest in the field of tumor immunology and immunotherapy.

Tumour escape: antitumour effectors too much of a good thing?

Although even "spontaneous" tumours are immunogenic and are commonly infiltrated by tumour antigen-specific T cells (at least in melanoma), most tumours are not completely rejected by the host, and cancer progresses. There is a growing realisation that many responses defined as antitumour effector mechanisms act as double-edged swords and under different conditions either become ineffective or even protumorigenic. Examples are interleukin 2 (also proapoptotic for activated T cells), interferon gamma (by induction of ligands for T and NK cell inhibitory receptors), angiogenesis inhibition (by hypoxia-mediated induction of growth factors promoting metastasis), and macrophage free radical-mediated cytotoxicity (by inhibiting T cells). Immune selection pressure itself, resulting in outgrowth of resistant tumour variants could also be viewed in this light. On the other hand, knowledge of the many tumour escape pathways offers the theoretical possibility of reconstituting antitumour immunity. Tumour escape from immunosurveillance represents the last series of hurdles to be overcome in formulating truly effective cancer immunotherapy, but given the immense plasticity of the tumour cell, and the complex balance between pro- and antitumour activity of the very same effector pathways, this remains a major challenge.

Immunotherapy of melanoma

The rationale for immunotherapy of human melanoma is based on the knowledge acquired in the molecular characterization of T cell defined antigens which are recognized in vitro by patients' lymphocytes. Based on this information, active immunotherapy (vaccination) and adoptive immunotherapy trials were conducted in metastatic melanoma patients. This review highlights the most important clinical studies and discuss their limits, in terms of both immune and clinical response considering the formulation of the vaccine (cellular, peptide/protein; DNA, etc.) or the features of immune cells used in adoptive immunotherapy. This new knowledge, along with that of escape mechanisms, should allow to improve significantly the clinical response rate in the immunotherapy of melanoma.

Therapeutic limitations in tumor-specific CD8+ memory T cell engraftment

BACKGROUND

Adoptive immunotherapy with cytotoxic T lymphocytes (CTL) represents an alternative approach to treating solid tumors. Ideally, this would confer long-term protection against tumor. We previously demonstrated that in vitro-generated tumor-specific CTL from the ovalbumin (OVA)-specific OT-I T cell receptor transgenic mouse persisted long after adoptive transfer as memory T cells. When recipient mice were challenged with the OVA-expressing E.G7 thymoma, tumor growth was delayed and sometimes prevented. The reasons for therapeutic failures were not clear.

METHODS

OT-I CTL were adoptively transferred to C57BL/6 mice 21-28 days prior to tumor challenge. At this time, the donor cells had the phenotypical and functional characteristics of memory CD8+ T cells. Recipients which developed tumor despite adoptive immunotherapy were analyzed to evaluate the reason(s) for therapeutic failure.

RESULTS

Dose-response studies demonstrated that the degree of tumor protection was directly proportional to the number of OT-I CTL adoptively transferred. At a low dose of OT-I CTL, therapeutic failure was attributed to insufficient numbers of OT-I T cells that persisted in vivo, rather than mechanisms that actively suppressed or anergized the OT-I T cells. In recipients of high numbers of OT-I CTL, the E.G7 tumor that developed was shown to be resistant to fresh OT-I CTL when examined ex vivo. Furthermore, these same tumor cells no longer secreted a detectable level of OVA. In this case, resistance to immunotherapy was secondary to selection of clones of E.G7 that expressed a lower level of tumor antigen.

CONCLUSIONS

Memory engraftment with tumor-specific CTL provides long-term protection against tumor. However, there are several limitations to this immunotherapeutic strategy, especially when targeting a single antigen. This study illustrates the importance of administering large numbers of effectors to engraft sufficiently efficacious immunologic memory. It also demonstrates the importance of targeting several antigens when developing vaccine strategies for cancer.

Successful elimination of large established tumors and avoidance of antigen-loss variants by aggressive adoptive T cell immunotherapy

Utilization of ex vivo-expanded epitope-specific cytotoxic T lymphocytes has become a clinical standard in the adoptive immunotherapy of tumors. One of the obstacles faced by T cell-based immunotherapy is the development of tumor immune-escape variants. Using our previously reported CMS5 tumor/DUC18 CD8(+) TCR transgenic system, we sought to investigate whether large established tumors can be successfully eliminated before the development of escape variants. Using BALB/c mice that were s.c. transplanted with two tumors that had been growing for 8 days (double 8-day tumors), we assessed the in vivo anti-tumor activity of in vitro peptide-stimulated DUC18 T cells. A single infusion of activated DUC18 T cells showed a modest effect against the double 8-day tumors, whereas two and three administrations led to regression of both tumors within 10 days. However, in some mice, the tumors re-grew approximately 10 days after the regression. We found these tumors to be antigen-loss variants. These relapsed tumor cells progressively grew in DUC18 transgenic mice and did not express tERK-specific message. When four doses of activated DUC18 T cells were infused, the double 8-day tumors were successfully eliminated and the tumors did not grow out in any mice. Our results demonstrate that mono-specific CD8(+) T cells can effectively eliminate large established tumors before the development of antigen-loss variants when a high number of T cells is rapidly administered.

Autonomous histopathological regression of primary tumours associated with specific immune responses to cancer antigens

Spontaneous histopathological regression of cancer has been reported. The involvement of the immune system in such regression has been advocated, leading to the theory of immunological surveillance against cancer. A prediction of this theory is that common tumour antigens can be recognized upon repeated exposure by cell-mediated immunity, which leads to tumour regression and the subsequent appearance of tumour antigen-loss variants. However, no direct evidence has been provided in non-viral-induced experimental animal models of primary malignancy or in human primary cancer. This study examined two groups of melanoma patients where histopathological regression of the primary tumour was observed. Many of the 23 patients with multiple (> or =3) primary melanomas showed significant regression of their last melanoma (median 33%, mean 40) compared with matched melanomas from patients with a single primary melanoma (median 0%, mean 12) (p=0.0080), or compared with their first primary melanoma (p=0.0013). Regression was consistent with an 'immunization effect' seen in murine tumour transplantation studies, where inoculation with > or =3 asynchronous tumours induces transplantation rejection on subsequent challenge. A significant decrease in the expression of the melanoma common tumour antigen MART-1 in the last primary tumour from multiple melanoma patients (median 8%, mean 24) versus matched single melanoma patients (median 79%, mean 68) (p=0.0041) and in the last versus first tumour in multiple primary patients was found (p=0.0083). Metastases from 17 patients whose primary skin melanomas had completely regressed (occult primary melanoma) also showed significant MART-1 loss (median 0%, mean 11) compared with matched metastases from patients with non-regressing primary melanoma (median 51%, mean 50) (p=0.0013). MART-1 antigen-loss variants observed in the multiple primary and occult primary patients correlated with the presence of peripheral blood MART-1-specific cytotoxic T lymphocytes (CTLs) (p=0.03). No similar effects were observed with two other melanoma antigens, gp100 and CD63. Thus, in two groups of human melanoma patients, evidence is provided for histopathological tumour regression associated with cancer immune surveillance.

Antigenic drift as a mechanism for tumor evasion of destruction by cytolytic T lymphocytes

It is established that mutations in viral antigenic epitopes, or antigenic drifts, allow viruses to escape recognition by both Ab's and T lymphocytes. It is unclear, however, whether tumor cells can escape immune recognition via antigenic drift. Here we show that adoptive therapy with both monoclonal and polyclonal transgenic CTLs, specific for a natural tumor antigen, P1A, selects for multiple mutations in the P1A antigenic epitope. These mutations severely diminish T cell recognition of the tumor antigen by a variety of mechanisms, including modulation of MHC:peptide interaction and TCR binding to MHC:peptide complex. These results provide the first evidence for tumor evasion of T cell recognition by antigenic drift, and thus have important implications for the strategy of tumor immunotherapy.

Paralytic autoimmune myositis develops in nonobese diabetic mice made Th1 cytokine-deficient by expression of an IFN-gamma receptor beta-chain transgene

Nonobese diabetic (NOD) mice and some human type 1 diabetes (T1D) patients manifest low to high levels of other autoimmune pathologies. Skewing their cytokine production from a Th1 (primarily IFN-gamma) to a Th2 (primarily IL-4 and IL-10) pattern is a widely proposed approach to dampen the pathogenicity of autoreactive diabetogenic T cells. However, it is important that altered cytokine balances not enhance any other autoimmune proclivities to dangerous levels. Murine CD4 T cells are characterized by a reciprocal relationship between the production of IFN-gamma and expression of the beta-chain component of its receptor (IFN-gamma RB). Thus, NOD mice constitutively expressing a CD2 promoter-driven IFN-gamma RB transgene in all T cells are Th1-deficient. Unexpectedly, NOD.IFN-gamma RB Tg mice were found to develop a lethal early paralytic syndrome induced by a CD8 T cell-dependent autoimmune-mediated myositis. Furthermore, pancreatic insulitis levels were not diminished in 9-wk-old NOD.IFN-gamma RB Tg females, and overt T1D developed in the few that survived to an older age. Autoimmune-mediated myositis is only occasionally detected in standard NOD mice. Hence, some manipulations diminishing Th1 responses can bring to the forefront what are normally secondary autoimmune pathologies in NOD mice, while also failing to dependably abrogate pancreatic beta cell destruction. This should raise a cautionary note when considering the use of protocols that induce alterations in cytokine balances as a means of blocking progression to overt T1D in at-risk humans.

Immunology of the peritoneal cavity: relevance for host-tumor relation

The peritoneal membrane, formed by a single layer of mesothelial cells, lines the largest cavity of the human body. Anatomic structures of the peritoneal cavity, along with resident leukocyte populations, play an important role in the defense against microorganisms invading by breaching the gut integrity or ascending through the female genital tract. Local immune mechanisms in the peritoneal cavity are also important in patients undergoing peritoneal dialysis and in women with endometriosis. There is now extensive evidence demonstrating the significance of peritoneal immune mechanisms in the control of metastatic spread. Leukocytes belonging to both the innate and adaptive immune systems are present in the peritoneal cavity of normal subjects as well as in patients with intra-abdominal cancer. There is now increased understanding of the mechanisms that not only allow the tumor cells to escape the detection and destruction by the host immune system, but also to use the inflammatory mechanisms to promote tumor growth and spread inside the peritoneal cavity. Malignant ascites represents a model for the study of the interaction between tumor cells and the host immune system as well for the analysis of the tumor microenviroment. The peritoneal immune system may be stimulated by intraperitoneal administration of biologic agents. This peritoneal immunotherapy may be used for palliation of malignant ascites, or as a consolidation strategy in patients with minimal residual disease.

Efficient chromosomal mapping of a methylcholanthrene-induced tumor antigen by CTL immunoselection

It has been difficult to genetically map the genes encoding tumor Ags because they arise as a consequence of somatic mutational events. CTL-mediated immunoselection can impose potent immunoselective pressure against tumor cells, resulting in the survival of rare tumor Ag-loss variants. We subjected a heterozygous 3-methylcholanthrene-induced murine sarcoma cell line to CTL immunoselection, selecting for the loss of a tumor-specific Ag, recognized antigen from MCA-induced tumor 1 (Ram1). Several variants eluded CTL recognition by genetic loss of the hemizygously expressed tumor-specific Ag epitope. A frequently observed genetic escape mechanism was spontaneous mitotic recombination resulting in loss of heterozygosity on chromosome 4. Higher density genetic analyses along with functional confirmation with an independently produced chromosome 4 loss of heterozygosity variant positioned the Ram1 locus to a distal 7.1 cM interval on chromosome 4. This region of the mouse genome is rich in tumor-modifier genes and this positioning of Ram1 may thus provide insight into the genetic basis of 3-methycholanthrene-induced tumor Ags.

Immunological gene therapy with ex vivo gene-modified tumor cells: a critique and a reappraisal

Studies using animal models have demonstrated that transduction of genes encoding different cytokines into tumor cells results in a local recruitment of inflammatory cells that in turn can inhibit tumor growth. This is often accompanied by tumor antigen priming of the host immune system, which becomes resistant to subsequent challenge by the parental, untransduced tumor. Gene-transduced tumor cells have therefore been widely used as vaccines, although in the therapeutic setting their antitumor efficacy was limited to a few animal models. On the basis of this rationale, clinical studies were initiated, results of which are evaluated in this review to identify the reasons for their limited efficacy. We point out problems generated by the use of autologous versus allogeneic gene-transduced vaccines, by the choice of the appropriate cytokine(s), and by patient selection. Results of these studies are also compared with those obtained by peptide-based vaccines in similar groups of patients. Altogether, we conclude that improvements can be made in the construction of gene-modified vaccines by (1) using tumor cells known to express molecularly defined antigens, (2) introducing, in addition to genes encoding cytokines, genes encoding T cell costimulatory molecules, (3) increasing the amount of cytokine released locally by irradiated cells, and (4) coadministering adjuvant cytokines (IL-2 and IL-12) systemically in order to expand the T cell pool activated by vaccines.

Autoimmunity and the immunotherapy of cancer: targeting the "self" to destroy the "other"

It is increasingly clear that immunity to "self"-antigens may result in tumor destruction in mouse and man. But which antigens should be targeted with therapeutic cancer vaccines? In the case of melanoma, recognition of melanocyte differentiation antigens (MDA) can be associated with autoimmune depigmentation (vitiligo). We propose that intersection of protein transport to melanosomes and endosomes allows for the loading of MDA-derived peptides on MHC class II molecules, resulting in the activation of MDA-specific CD4+ "helper" T cells that aid the induction of melanoma-specific CD8+ T cells. Thus, the immunogenicity of MDA may be a consequence of their unique cell biology. Studies of MDA-based vaccines can provide new insight into the development of more effective cancer vaccines.

Expression of Multiple Unique Rejection Antigens on Murine Leukemia BALB/c RL♂1 and the Role of Dominant Akt Antigen for Tumor Escape

Using the pRL1a Ag-loss RL♂1 tumor variant cell line RM2-1, we demonstrated the presence of tumor Ags other than pRL1a that were recognized by CTLs on RL♂1 cells. Semiallogeneic CB6F1 or syngeneic BALB/c CTLs generated against RM2-1 lysed RM2-1 and RL♂1 cells to a similar extent, but no killing was observed with any other tumor or normal cells examined. Clonal analysis and sensitization with reversed phase-HPLC fractions revealed that there were Dd- and Ld-binding peptides recognized by RM2-1 CTLs. Lysis by bulk CTLs stimulated against RL♂1 and limiting dilution analysis suggested that the pRL1a peptide was dominantly recognized to the RM2-1 peptides by CTLs on RL♂1 cells. The rejection response against the parental RL♂1 tumor was much less than that against RM2-1 cells in either CB6F1 or BALB/c mice, suggesting that the presence of altered Akt molecules from which the dominant pRL1a peptide was derived inhibited the rejection response against RL♂1. Depletion of CD4 T cells caused the regression of RL♂1 at the doses in which the tumor grew in untreated mice. The generation of pRL1a CTLs was inhibited in RL♂1-bearing mice. Thus, immunoregulatory CD4 T cells were most likely activated by the altered Akt molecules and inhibited the efficient generation of CTLs against the dominant pRL1a Ag in RL♂1.

Biochemical and Immunogenetic Analysis of an Immunodominant Peptide (B6dom1) Encoded by the Classical H7 Minor Histocompatibility Locus

Of the many minor histocompatibility (H) Ags that have been detected in mice, the ability to induce graft vs host disease (GVHD) after bone marrow transplantation is restricted to a limited number of immunodominant Ags. One such murine Ag, B6dom1, is presented by the H2-Db MHC class I molecule. We present biochemical evidence that the natural B6dom1 peptide is indistinguishable from AAPDNRETF, and we show that this peptide can be isolated from a wide array of tissues, with highest levels from the lymphoid organs and lung. Moreover, we employ a novel, somatic cell selection technique involving CTL-mediated immunoselection coupled with classical genetics, to show that B6dom1 is encoded by the H7 minor H locus originally discovered ∼40 years ago. These studies provide a molecular genetic framework for understanding B6dom1, and exemplify the fact that mouse minor H loci that encode immunodominant CTL epitopes can correspond to classical H loci originally identified by their ability to confer strong resistance to tumor transplantation. Additionally, these studies demonstrate the utility of somatic cell selection approaches toward resolving H Ag immunogenetics.

Shaping the Repertoire of Cytotoxic T-Lymphocyte Responses: Explanation for the Immunodominance Effect Whereby Cytotoxic T Lymphocytes Specific for Immunodominant Antigens Prevent Recognition of Nondominant Antigens

The immunodominance effect, whereby the presence of immunodominant epitopes prevents recognition of nondominant determinants presented on the same antigen-presenting cell (APC) considerably restricts the repertoire of cytotoxic T lymphocyte (CTL) responses. To elucidate the molecular basis of the immunodominance effect, we compared the interactions of a dominant (B6dom1) and a nondominant epitope (H-Y) with their restricting class I molecule (H2-Db), and their ability to trigger cognate CTLs. We found that B6dom1/Db complexes behaved as optimal T-cell receptor (TCR) ligands and triggered a more rapid in vivo expansion of cognate CTLs than H-Y/Db complexes. The superiority of the dominant epitope was explained by its high cell surface density (1,012 copies/cell for B6dom1v 10 copies/cell for H-Y) and its optimal affinity for cognate TCRs. Based on these results, we conclude that dominant class I–associated epitopes are those that have optimal ability to trigger TCR signals in CTLs. We propose that the rapid expansion of CTLs specific for dominant antigens should enable them to compete more successfully than other CTLs for occupancy of the APC surface.

Shaping the Repertoire of Cytotoxic T-Lymphocyte Responses: Explanation for the Immunodominance Effect Whereby Cytotoxic T Lymphocytes Specific for Immunodominant Antigens Prevent Recognition of Nondominant Antigens

The immunodominance effect, whereby the presence of immunodominant epitopes prevents recognition of nondominant determinants presented on the same antigen-presenting cell (APC) considerably restricts the repertoire of cytotoxic T lymphocyte (CTL) responses. To elucidate the molecular basis of the immunodominance effect, we compared the interactions of a dominant (B6dom1) and a nondominant epitope (H-Y) with their restricting class I molecule (H2-Db), and their ability to trigger cognate CTLs. We found that B6dom1/Db complexes behaved as optimal T-cell receptor (TCR) ligands and triggered a more rapid in vivo expansion of cognate CTLs than H-Y/Db complexes. The superiority of the dominant epitope was explained by its high cell surface density (1,012 copies/cell for B6dom1v 10 copies/cell for H-Y) and its optimal affinity for cognate TCRs. Based on these results, we conclude that dominant class I–associated epitopes are those that have optimal ability to trigger TCR signals in CTLs. We propose that the rapid expansion of CTLs specific for dominant antigens should enable them to compete more successfully than other CTLs for occupancy of the APC surface.

Methylcholanthrene causes increased thymocyte apoptosis

The polycyclic aromatic hydrocarbon (PAH), methylcholanthrene (MCA), is a well studied carcinogen and a teratogen. MCA and other PAH cause immune suppression of B cell and T cell responses in mice and MCA had been reported to induce thymus atrophy. Here we show that MCA treatment causes thymus atrophy in adrenalectomized mice and in C57BL/6 and DBA/2 mice which differ in aryl hydrocarbon receptor (AhR) expression. This indicates that MCA-mediated thymus atrophy is mediated, at least in part, by glucocorticoid hormone receptor- and aryl hydrocarbon receptor-independent mechanisms. Assay of thymocytes, both in situ and ex vivo, demonstrate that MCA induces thymocyte apoptosis. Apoptotic thymocytes can be found within or adjacent to thymic Mphi, suggesting rapid phagocytosis. Mice that are deficient in tumor necrosis factor-alpha receptor-1 or p53, or that overexpress bcl-2 are susceptible to MCA-mediated thymus atrophy.

Prospects for adoptive T cell therapy

Since the establishment of methods to isolate genes encoding cytotoxic T lymphocyte defined tumor antigens, several antigens have been identified and characterized for suitability as target antigens for immunotherapy. The development of innovative strategies to generate T cells targeting these antigens and lessons learned from clinical trials of adoptive immunotherapy of viral diseases should facilitate the design of clinical trials for specific adoptive immunotherapy of cancer.

Mutated mitogen-activated protein kinase: a tumor rejection antigen of mouse sarcoma

The molecular basis of the polymorphic tumor rejection antigens of chemically induced sarcomas of inbred mice remains a mystery, despite the discovery of these antigens over 40 years ago and their critical importance to the foundation of tumor immunology. In an analysis of a panel of BALB/c 3-methylcholanthrene-induced tumors, we identified one tumor, CMS5, that elicited a strong cytotoxic T cell response with exquisite specificity for CMS5. A stable cloned line of T cells with this specificity (C18) was used to screen a CMS5 cDNA expression library. The gene encoding the C18-defined antigen was identified as a mutated form of a mouse mitogen-activated protein kinase, ERK2, and a peptide incorporating the resulting amino acid substitution (lysine to glutamine) was efficiently recognized by C18. Vaccination with this peptide elicited specific resistance to CMS5 challenge. Extensive efforts to isolate antigen-loss variants of CMS5 were unsuccessful, suggesting that the mutated mitogen-activated protein kinase is essential for maintenance of the malignant phenotype.