Targetless T cells in cancer immunotherapy

Features of the immunosuppressive tumor microenvironment in endometrial cancer based on molecular subtype

Endometrial cancer (EC) is one of the three most prevalent gynecological tumors affecting women and is the most prevalent gynecological malignancy in the developed world. Its incidence is rapidly increasing worldwide, mostly affecting postmenopausal women, whereas recently its prevalence has increased in younger people. EC is an immune gene disease and many studies have shown that the tumor-immunosuppressive microenvironment plays an important role in cancer progression. In recent years, findings regarding the immunosuppressive tumor microenvironment (ITME) of EC have included immune evasion mechanisms and immunotherapy, which are mostly immune checkpoint inhibitors (ICI) for EC. Recently studies on the ITME of different molecular types of EC have found that different molecular types may have different ITME. With the research on the immune microenvironment of EC, a new immunophenotype classification based on the immune microenvironment has been carried out in recent years. However, the impact of the ITME on EC remains unclear, and the immunophenotype of EC remains limited to the research stage. Our review describes recent findings regarding the ITME features of different EC molecular types. The advent of immunotherapy has brought hope for improved efficacy and prognosis in patients with advanced or recurrent EC. The efficacy and safety of ICIs combination therapy remains the focus of future research.

Association of HLA-A, B, and C alleles and cancer susceptibility in 179 solid malignancies

BACKGROUND

The major histocompatibility complex (MHC) genes are known to be capable of influencing the susceptibility of many cancers. All mammalian cells, including cancer cells, express MHC class I molecules consisting of human leukocyte antigens (HLA) A, B, and C. The tumor susceptibility of HLA-A, B, and C alleles has not been studied extensively in solid tumors.

METHODS

HLA-A, B, and C genotypes of 179 solid tumors were collected from Caris Comprehensive Tumor Profiling reports, including 45 GU, 44 GI, 28 pancreaticobiliary, 21 thoracic, 15 breast, 13 Gyn, among others. The tumors were mainly from Caucasians (82%). The HLA allele frequencies in the tumors were compared to those of respective ethnic populations in the US National Marrow Donor Program (NMDP) database. Fisher's exact tests were performed, adjusted P values were calculated using Benjamini-Hochberg's method for false discovery rate (FDR), and Prevalence ratios (PRs) were calculated to quantify associations.

RESULTS

Twenty-one alleles were not listed in the NMDP. Among them, A*11:303 alone was present in 11 carcinomas, and B*08:222 was seen in 4 tumors. Among the alleles listed in the NMDP, C*08:02, B*14:02, A*03:02, and B*44:06 were significantly associated with tumors in Caucasian Americans (PR: 2.50-170), while B*44:02 appeared protective (PR: 0.36). Alleles with less significant associations were listed.

CONCLUSIONS

From the HLA-A, B, and C data of the 179 tumors, we identified several susceptible alleles and one protective allele. Of interest, 21 alleles were not listed in the NMDP. The limited cases prevented our analysis from identifying cancer-susceptible alleles in other races.

Deregulation of HLA-I in cancer and its central importance for immunotherapy

It is now well accepted that many tumors undergo a process of clonal selection which means that tumor antigens arising at various stages of tumor progression are likely to be represented in just a subset of tumor cells. This process is thought to be driven by constant immunosurveillance which applies selective pressure by eliminating tumor cells expressing antigens that are recognized by T cells. It is becoming increasingly clear that the same selective pressure may also select for tumor cells that evade immune detection by acquiring deficiencies in their human leucocyte antigen (HLA) presentation pathways, allowing important tumor antigens to persist within cells undetected by the immune system. Deficiencies in antigen presentation pathway can arise by a variety of mechanisms, including genetic and epigenetic changes, and functional antigen presentation is a hard phenomenon to assess using our standard analytical techniques. Nevertheless, it is likely to have profound clinical significance and could well define whether an individual patient will respond to a particular type of therapy or not. In this review we consider the mechanisms by which HLA function may be lost in clinical disease, we assess the implications for current immunotherapy approaches using checkpoint inhibitors and examine the prognostic impact of HLA loss demonstrated in clinical trials so far. Finally, we propose strategies that might be explored for possible patient stratification.

Distinct Responsiveness of Tumor-Associated Macrophages to Immunotherapy of Tumors with Different Mechanisms of Major Histocompatibility Complex Class I Downregulation

Simple Summary

Tumor-associated macrophages (TAMs) are one of the major cell subpopulations in the tumor microenvironment (TME) where they can either be pro-tumorigenic or contribute to an anti-tumor immunity. The TME and TAM phenotype were analyzed after combined immuno-therapy (IT) in tumor models characterized by distinct expression of major histocompatibility class I complex (MHC-I) molecules, i.e., tumors induced with TC-1 (MHC-I-proficient), TC-1/A9 (reversibly downregulated), and TC-1/dB2m (irreversibly downregulated) cells. We found out that combined IT highly activated immune reactions in the TME of TC-1 and TC-1/A9 tumors, but the TME of TC-1/dB2m tumors remained almost unchanged. Correspondingly, TAMs from TC-1/A9 tumors were able to destroy tumor cells in vitro, while TAMs isolated from TC-1/dB2m tumors showed profoundly decreased cytotoxicity. Hence, various capabilities of TAMs in tumors with distinct expression of MHC-I molecules should be considered when applying IT, particularly IT focused on TAMs.

Abstract

Tumor-associated macrophages (TAMs) plentifully infiltrate the tumor microenvironment (TME), but their role in anti-tumor immunity is controversial. Depending on the acquired polarization, they can either support tumor growth or participate in the elimination of neoplastic cells. In this study, we analyzed the TME by RNA-seq and flow cytometry and examined TAMs after ex vivo activation. Tumors with normal and either reversibly or irreversibly decreased expression of major histocompatibility complex class I (MHC-I) molecules were induced with TC-1, TC-1/A9, and TC-1/dB2m cells, respectively. We found that combined immunotherapy (IT), composed of DNA immunization and the CpG oligodeoxynucleotide (ODN) ODN1826, evoked immune reactions in the TME of TC-1- and TC-1/A9-induced tumors, while the TME of TC-1/dB2m tumors was mostly immunologically unresponsive. TAMs infiltrated both tumor types with MHC-I downregulation, but only TAMs from TC-1/A9 tumors acquired the M1 phenotype upon IT and were cytotoxic in in vitro assay. The anti-tumor effect of combined IT was markedly enhanced by a blockade of the colony-stimulating factor-1 receptor (CSF-1R), but only against TC-1/A9 tumors. Overall, TAMs from tumors with irreversible MHC-I downregulation were resistant to the stimulation of cytotoxic activity. These data suggest the dissimilarity of TAMs from different tumor types, which should be considered when utilizing TAMs in cancer IT.

Virus-specific T cells for malignancies - then, now and where to?

Purpose of Review

Virus-associated malignancies are a global health burden, constituting 10-12% of cancers worldwide. As these tumors express foreign viral antigens that can elicit specific T cell responses, virus-directed immunotherapies are a promising treatment strategy. Specifically, adoptive cell transfer of virus-specific T cells (VSTs) has demonstrated the potential to eradicate cancers associated with certain viruses.

Recent Findings

Initial studies in 1990s first showed that VSTs specific for the Epstein-Barr virus (EBVSTs) can induce complete remissions in patients with post-transplant lymphoproliferative disease. Since then, studies have validated the specificity and safety of VSTs in multiple lymphomas and solid malignancies. However, challenges remain to optimize this platform for widespread use, including enhancing potency and persistence, overcoming the immunosuppressive tumor microenvironment, and streamlining manufacturing processes that comply with regulatory requirements.

Summary

This review focuses on data from clinical trials evaluating VSTs directed against three viruses (EBV, HPV and MCPyV), as well as recent preclinical and clinical advances, and potential future directions.

HLA class I loss in colorectal cancer: implications for immune escape and immunotherapy

T cell-mediated immune therapies have emerged as a promising treatment modality in different malignancies including colorectal cancer (CRC). However, only a fraction of patients currently respond to treatment. Understanding the lack of responses and finding biomarkers with predictive value is of great importance. There is evidence that CRC is a heterogeneous disease and several classification systems have been proposed that are based on genomic instability, immune cell infiltration, stromal content and molecular subtypes of gene expression. Human leukocyte antigen class I (HLA-I) plays a pivotal role in presenting processed antigens to T lymphocytes, including tumour antigens. These molecules are frequently lost in different types of cancers, including CRC, resulting in tumour immune escape from cytotoxic T lymphocytes during the natural history of cancer development. The aim of this review is to (i) summarize the prevalence and molecular mechanisms behind HLA-I loss in CRC, (ii) discuss HLA-I expression/loss in the context of the newly identified CRC molecular subtypes, (iii) analyze the HLA-I phenotypes of CRC metastases disseminated via blood or the lymphatic system, (iv) discuss strategies to recover/circumvent HLA-I expression/loss and finally (v) review the role of HLA class II (HLA-II) in CRC prognosis.

The SPPL3-Defined Glycosphingolipid Repertoire Orchestrates HLA Class I-Mediated Immune Responses

HLA class I (HLA-I) glycoproteins drive immune responses by presenting antigens to cognate CD8+ T cells. This process is often hijacked by tumors and pathogens for immune evasion. Because options for restoring HLA-I antigen presentation are limited, we aimed to identify druggable HLA-I pathway targets. Using iterative genome-wide screens, we uncovered that the cell surface glycosphingolipid (GSL) repertoire determines effective HLA-I antigen presentation. We show that absence of the protease SPPL3 augmented B3GNT5 enzyme activity, resulting in upregulation of surface neolacto-series GSLs. These GSLs sterically impeded antibody and receptor interactions with HLA-I and diminished CD8+ T cell activation. Furthermore, a disturbed SPPL3-B3GNT5 pathway in glioma correlated with decreased patient survival. We show that the immunomodulatory effect could be reversed through GSL synthesis inhibition using clinically approved drugs. Overall, our study identifies a GSL signature that inhibits immune recognition and represents a potential therapeutic target in cancer, infection, and autoimmunity.

Implications of Tumor-Immune Coevolution on Cancer Evasion and Optimized Immunotherapy

Cancer represents a diverse collection of diseases characterized by heterogeneous cell populations that dynamically evolve in their environment. As painfully evident in cases of treatment failure and recurrence, this general feature makes identifying long-term successful therapies difficult. It is now well-established that the adaptive immune system recognizes and eliminates cancer cells, and various immunotherapeutic strategies have emerged to augment this effect. These therapies, while promising, often fail as a result of immune-specific cancer evasion. Increasingly available empirical evidence details both cancer and immune system populations pre- and post-treatment, providing rich opportunity for mathematical models of the tumor-immune interaction and subsequent co-evolution. Integrated mathematical and experimental efforts bear immediate relevance for optimized therapies and will undoubtedly accelerate our understanding of this emergent field.

Identification of novel prognosis-related genes in the endometrial cancer immune microenvironment

The incidence of endometrial cancer is increasing each year, and treatment effects are poor for patients with advanced and specific subtypes. Exploring immune infiltration-related factors in endometrial cancer can aid in the prognosis of patients and provide new immunotherapy targets. We downloaded immune metagene and functional data of patients with different subtypes of endometrial cancer from The Cancer Genome Atlas database and selected the lymphocyte-specific kinase (LCK) metagene as a representative genetic marker of the immune microenvironment in endometrial cancer. The results showed that LCK metagene expression is related to the prognosis of patients with endometrioid endometrial adenocarcinoma subtypes and highly correlated with the PTEN and PIK3CA mutational status. A search for LCK-related modules returned seven independent genetic predictors of survival in patients with endometrial cancer. The TIMER algorithm showed that the expression of these seven genes was positively correlated with the infiltration levels of six types of immune cells. The diagnostic value of these markers was validated using real-time quantitative PCR and immunohistochemical methods. Our results identified CD74, HLA-DRB5, CD52, HLA-DPB1 and HLA-DRB1 as possible valuable genetic markers for the diagnosis and prognosis of endometrial cancer and provided a theoretical basis for immunotherapy targets for its clinical treatment.

Total HLA Class I Antigen Loss with the Downregulation of Antigen-Processing Machinery Components in Two Newly Established Sarcomatoid Hepatocellular Carcinoma Cell Lines

Limited information is currently available concerning HLA class I antigen abnormalities in sarcomatoid hepatocellular carcinoma (sHCC). Here, we have analyzed the growth characteristics and HLA class I antigen status of four sHCC cell lines (sHCC29, sHCC63, sHCC74, and SAR-HCV); the first three were newly established in this study. Among the four, sHCC29 showed the highest growth rate in vitro and tumorigenicity in NOD-SCID mice. Unlike sHCC74 and SAR-HCV, both sHCC29 and sHCC63 had no detectable surface HLA class I antigen expression, alongside undetected intracellular β₂-microglobulin (β₂m) and marked HLA class I heavy chain and selective antigen-processing machinery (APM) component downregulation. The loss of β₂m in sHCC29 and sHCC63 was caused by a >49 kb deletion across the B2M locus, while their downregulation of APM components was transcriptional, reversible by IFN-γ only in several components. β₂m was also undetected in the primary HCC lesions of the patients involved, indicating its in vivo relevance. We report for the first time HLA class I antigen loss with underlying B2M gene deficiency and APM defects in 50% (2 of 4) of the sHCC cell lines tested. These findings may have implications for a proper design of T cell immunotherapy for the treatment of sHCC patients.

Introduction

This chapter focuses on the discovery of the Major Histocompatibility Complex (MHC) in mice (H-2) and in humans (HLA), and on the role played by the International HLA Workshops in the analysis and characterization of this complex genetic system. The early days of Tumour Immunology and the importance of the definition of Tumour Associated Transplantation Antigens (TATA) are also discussed. Today we know that tumour cells can be killed by T lymphocytes by recognizing tumour antigenic peptides presented by MHC molecules and they can also escape this recognition by losing the expression of MHC molecules. This important phenomenon has been profoundly studied for many years both in my lab in Granada and in other laboratories. The results of this research have important implications for the new generation of cancer immunotherapy that boosts T cell responses. A historical perspective of major discoveries is presented in this chapter, with the names of the scientists that have made a significant contribution to the enormous progress made in the field of Tumour Immunology.

HLA Class-I Expression and Cancer Immunotherapy

The impact of HLA class I loss in cancer immunotherapy is carefully analyzed. Why some metastatic lesions regress and other progress after immunotherapy? Are T lymphocytes responsible for tumour rejection and how these responses can be boosted? These questions are discussed in the context of the molecular mechanisms responsible for MHC/HLA class I alterations. If the metastatic tumour cells harbor "irreversible/hard" HLA lesions, they will escape and kill the host. In contrast, if the molecular lesion is "reversible/soft", tumor cells can potentially recover HLA-class I expression and can finally be destroyed. These important new concepts are integrated together and gain a great importance in the new era of "immune checkpoint antibodies". Finally, the ability to recover HLA-I expression in tumours harboring "structural-irreversible-hard" genetic lesions is seen as a challenge for the future investigation.

Stochastic modeling of tumor progression and immune evasion

It is now well-established that the host's adaptive immune system plays an important role in identifying and eliminating cancer cells in much the same way that intracellular pathogens are cleared during an adaptive immune response to infection. From a therapeutic standpoint, the adaptive immune system is unique in that it can co-evolve alongside a developing tumor. Tumor acquisition of immune evasive phenotypes, such as class-I MHC down-regulation, remains a major limitation of successful T-cell immunotherapy. Here, we consider a population dynamical model coupling tumor and adaptive immune compartments in order to study the dynamics and survival of an evolving threat when faced with adaptive immune pressure. We demonstrate that predicted optimal growth strategies depend on whether or not the threat may acquire an immune-evasive phenotype as well as the mode of immune detection. We parameterize adaptive immune functioning by T-cell turnover and repertoire diversity and predict that decreases in the latter quantity which occur in advanced age may substantially affect the ability to recognize, and therefore control, an immune evasive threat like cancer. This framework recapitulates general features of age-dependent AML incidence, thereby providing a probable association between cancer frequency and adaptive immune functioning. Lastly, we quantify therapeutic efficacy of adjuvant immunotherapeutic strategies, and predict their benefits and limitations with regard to handling immune evasion. Our model generates survival behavior consistent with known growth-dependent characteristics, and serves as a first attempt at modeling stochastic cancer evolution alongside an adaptive immune compartment.

The transition from HLA-I positive to HLA-I negative primary tumors: the road to escape from T-cell responses

MHC/HLA class I loss in cancer is one of the main mechanisms of tumor immune escape from T-cell recognition and destruction. Tumor infiltration by T lymphocytes (TILs) and by other immune cells was first described many years ago, but has never been directly and clearly linked to the destruction of HLA-I positive and selection of HLA-I negative tumor cells. The degree and the pattern of lymphocyte infiltration in a tumor nest may depend on antigenicity and the developmental stages of the tumors. In addition, it is becoming evident that HLA-I expression and tumor infiltration have a direct correlation with tumor tissue reorganization. We observed that at early stages (permissive Phase I) tumors are heterogeneous, with both HLA-I positive and HLA-negative cancer cells, and are infiltrated by TILs and M1 macrophages as a part of an active anti-tumor Th1 response. At later stages (encapsulated Phase II), tumor nests are mostly HLA-I negative with immune cells residing in the peri-tumoral stroma, which forms a granuloma-like encapsulated tissue structure. All these tumor characteristics, including tumor HLA-I expression pattern, have an important clinical prognostic value and should be closely and routinely investigated in different types of cancer by immunologists and by pathologists. In this review we summarize our current viewpoint about the alterations in HLA-I expression in cancer and discuss how, when and why tumor HLA-I losses occur. We also provide evidence for the negative impact of tumor HLA-I loss in current cancer immunotherapies, with the focus on reversible ('soft') and irreversible ('hard') HLA-I defects.

HLA class I loss and PD-L1 expression in lung cancer: impact on T-cell infiltration and immune escape

Immune-checkpoint inhibitors show encouraging results in cancer treatment, but the clinical benefit is limited exclusively to a subset of patients. We analyzed the density and composition of tumor T-cell infiltration in non-small-cell lung carcinoma (NSCLC) in relation to PD-L1 and HLA class I (HLA-I) expression. We found that positive HLA-I expression, independently on PD-L1 status, is the key factor determining the increased density of the immune infiltrate. When both markers were analyzed simultaneously, we identified four phenotypes of HLA-I and PD-L1 co-expression. They demonstrated different patterns of tumor infiltration and clinicopathologic characteristics, including the tumor size and lymphatic spread. All HLA-I+/PD-L1+ tumors had a high degree of intratumoral infiltration with CD8+T-lymphocytes, whereas HLA-I loss was associated with a significantly reduced number of tumor infiltrating T-lymphocytes mostly restrained in the stroma surrounding the tumor nest. HLA-I-negative/PD-L1-positive tumors had bigger size (T) and lower grade of infiltration with CD8+T-cells. It represents a cancer immune escape phenotype that combines two independent mechanisms of immune evasion: loss of HLA-I and upregulation of PD-L1. Using GCH-array analysis of human lung cancer cell lines we found that the loss of heterozygosity (LOH) with complete or partial deletion of HLA-I genes is the principal mechanism of HLA-I alterations. This irreversible defect, which could potentially decrease the clinical efficacy of lung cancer immunotherapy, appears to be underestimated. In conclusion, our results suggest that the analysis of HLA-I is very important for the selection of potential responders to cancer immunotherapy.

Mutational and putative neoantigen load predict clinical benefit of adoptive T cell therapy in melanoma

Adoptive T-cell therapy (ACT) is a highly intensive immunotherapy regime that has yielded remarkable response rates and many durable responses in clinical trials in melanoma; however, 50-60% of the patients have no clinical benefit. Here, we searched for predictive biomarkers to ACT in melanoma. Whole exome- and transcriptome sequencing and neoantigen prediction were applied to pre-treatment samples from 27 patients recruited to a clinical phase I/II trial of ACT in stage IV melanoma. All patients had previously progressed on other immunotherapies. We report that clinical benefit is associated with significantly higher predicted neoantigen load. High mutation and predicted neoantigen load are significantly associated with improved progression-free and overall survival. Further, clinical benefit is associated with the expression of immune activation signatures including a high MHC-I antigen processing and presentation score. These results improve our understanding of mechanisms behind clinical benefit of ACT in melanoma.

A review of immune therapy in cancer and a question: can thermal therapy increase tumor response?

Immune therapy is a successful cancer treatment coming into its own. This is because checkpoint molecules, adoptive specific lymphocyte transfer and chimeric antigen T-cell (CAR-T) therapy are able to induce more durable responses in an increasing number of malignancies compared to chemotherapy. In addition, immune therapies are able to treat bulky disease, whereas standard cytotoxic therapies cannot treat large tumour burdens. Checkpoint inhibitor monoclonal antibodies are becoming widely used in the clinic and although more complex, adoptive lymphocyte transfer and CAR-T therapies show promise. We are learning that there are nuances to predicting the successful use of the checkpoint inhibitors as well as to specific-antigen adoptive and CAR-T therapies. We are also newly aware of a here-to-fore unrealised natural force, the status of the microbiome. However, despite better understanding of mechanisms of action of the new immune therapies, the best responses to the new immune therapies remain 20-30%. Likely the best way to improve this somewhat low response rate for patients is to increase the patient's own immune response. Thermal therapy is a way to do this. All forms of thermal therapy, from fever-range systemic thermal therapy, to high-temperature HIFU and even cryotherapy improve the immune response pre-clinically. It is time to test the immune therapies with thermal therapy in vivo to test for optimal timing of the combinations that will best enhance tumour response and then to begin to test the immune therapies with thermal therapy in the clinic as soon as possible.

Building proteomic tool boxes to monitor MHC class I and class II peptides

Major histocompatibility complex Class I (MHCI) and Class II (MHCII) presented peptides powerfully modulate T cell immunity and play a vital role in generating effective anti-tumor and anti-viral immune responses in mammals. Characterizing these MHCI or MHCII presented peptides can help generate therapeutic treatments, afford information on T cell mediated biomarkers, provide insight into disease progression, and reduce adverse anti-drug side effects from engineered biotherapeutics. Here, we explore the tools and techniques commonly employed to discover both MHCI- and MHCII-presented peptides. We describe complementary strategies that enhance the characterization of these peptides and the informatics tools employed for both predicting and characterizing MHCI- and MHCII-presented epitopes. The evolution of methodologies for isolating MHC-presented peptides is discussed, as are the mass spectrometric workflows that can be employed for their characterization. We provide a perspective on where this field is headed, and how these tools may be applicable to the discovery and monitoring of epitopes in a variety of scenarios.

HLA-mediated tumor escape mechanisms that may impair immunotherapy clinical outcomes via T-cell activation

Although the immune system provides protection from cancer by means of immunosurveillance, which serves a major function in eliminating cancer cells, it may also lead to cancer immunoediting, molding tumor immunogenicity. Cancer cells exploit several molecular mechanisms to thwart immune-mediated death by disabling cellular components of the immune system associated with tumor recognition and rejection. Human leukocyte antigen (HLA) molecules are mandatory for the immune recognition and subsequent killing of neoplastic cells by the immune system, as tumor antigens must be presented in an HLA-restricted manner to be recognized by T-cell receptors. Impaired HLA-I expression prevents the activation of cytotoxic immune mechanisms, whereas impaired HLA-II expression affects the antigen-presenting capability of antigen presenting cells. Aberrant HLA-G expression by cancer cells favors immune escape by inhibiting the activities of virtually all immune cells. The development of cancer therapies based on T-cell activation must consider these HLA-associated immune evasion mechanisms, as alterations in their expression occur early and frequently in the majority of types of cancer, and have an adverse impact on the clinical response to immunotherapy. Herein, the concept of altered HLA expression as a mechanism exploited by tumors to escape immune control and induce an immunosuppressive environment is reviewed. A number of novel clinical immunotherapeutic approaches used for cancer treatment are also reviewed, and strategies for overcoming the limitations of these immunotherapeutic interventions are proposed.

Acquired Immune Resistance Follows Complete Tumor Regression without Loss of Target Antigens or IFNγ Signaling

Cancer immunotherapy can result in durable tumor regressions in some patients. However, patients who initially respond often experience tumor progression. Here, we report mechanistic evidence of tumoral immune escape in an exemplary clinical case: a patient with metastatic melanoma who developed disease recurrence following an initial, unequivocal radiologic complete regression after T-cell-based immunotherapy. Functional cytotoxic T-cell responses, including responses to one mutant neoantigen, were amplified effectively with therapy and generated durable immunologic memory. However, these immune responses, including apparently effective surveillance of the tumor mutanome, did not prevent recurrence. Alterations of the MHC class I antigen-processing and presentation machinery (APM) in resistant cancer cells, but not antigen loss or impaired IFNγ signaling, led to impaired recognition by tumor-specific CD8⁺ T cells. Our results suggest that future immunotherapy combinations should take into account targeting cancer cells with intact and impaired MHC class I-related APM. Loss of target antigens or impaired IFNγ signaling does not appear to be mandatory for tumor relapse after a complete radiologic regression. Personalized studies to uncover mechanisms leading to disease recurrence within each individual patient are warranted. Cancer Res; 77(17); 4562-6. ©2017 AACR.

Biopolymers codelivering engineered T cells and STING agonists can eliminate heterogeneous tumors

Therapies using T cells that are programmed to express chimeric antigen receptors (CAR T cells) consistently produce positive results in patients with hematologic malignancies. However, CAR T cell treatments are less effective in solid tumors for several reasons. First, lymphocytes do not efficiently target CAR T cells; second, solid tumors create an immunosuppressive microenvironment that inactivates T cell responses; and third, solid cancers are typified by phenotypic diversity and thus include cells that do not express proteins targeted by the engineered receptors, enabling the formation of escape variants that elude CAR T cell targeting. Here, we have tested implantable biopolymer devices that deliver CAR T cells directly to the surfaces of solid tumors, thereby exposing them to high concentrations of immune cells for a substantial time period. In immunocompetent orthotopic mouse models of pancreatic cancer and melanoma, we found that CAR T cells can migrate from biopolymer scaffolds and eradicate tumors more effectively than does systemic delivery of the same cells. We have also demonstrated that codelivery of stimulator of IFN genes (STING) agonists stimulates immune responses to eliminate tumor cells that are not recognized by the adoptively transferred lymphocytes. Thus, these devices may improve the effectiveness of CAR T cell therapy in solid tumors and help protect against the emergence of escape variants.

Rejection versus escape: the tumor MHC dilemma

Most tumor cells derive from MHC-I-positive normal counterparts and remain positive at early stages of tumor development. T lymphocytes can infiltrate tumor tissue, recognize and destroy MHC class I (MHC-I)-positive cancer cells ("permissive" phase I). Later, MHC-I-negative tumor cell variants resistant to T-cell killing emerge. During this process, tumors first acquire a heterogeneous MHC-I expression pattern and finally become uniformly MHC-I-negative. This stage (phase II) represents a "non-permissive" encapsulated structure with tumor nodes surrounded by fibrous tissue containing different elements including leukocytes, macrophages, fibroblasts, etc. Molecular mechanisms responsible for total or partial MHC-I downregulation play a crucial role in determining and predicting the antigen-presenting capacity of cancer cells. MHC-I downregulation caused by reversible ("soft") lesions can be upregulated by TH1-type cytokines released into the tumor microenvironment in response to different types of immunotherapy. In contrast, when the molecular mechanism of the tumor MHC-I loss is irreversible ("hard") due to a genetic defect in the gene/s coding for MHC-I heavy chains (chromosome 6) or beta-2-microglobulin (B2M) (chromosome 15), malignant cells are unable to upregulate MHC-I, remain undetectable by cytotoxic T-cells, and continue to grow and metastasize. Based on the tumor MHC-I molecular analysis, it might be possible to define MHC-I phenotypes present in cancer patients in order to distinguish between non-responders, partial/short-term responders, and likely durable responders. This highlights the need for designing strategies to enhance tumor MHC-I expression that would allow CTL-mediated tumor rejection.

Increased PD-L1 and T-cell infiltration in the presence of HLA class I expression in metastatic high-grade osteosarcoma: a rationale for T-cell-based immunotherapy

Introduction

Immunotherapy may be an excellent choice for treating osteosarcoma given its exceptionally high genomic instability, potentially generating neoantigens. In this study, we aim to investigate the HLA class I expression, PD-L1 and tumour-infiltrating lymphocytes in primary osteosarcomas and relapses/metastases, as well as their changes during disease progression.

Materials and methods

Tumour samples from multiple stages of the disease (pretreatment biopsies, surgical resections of primary osteosarcomas, relapses and metastases) were collected and stained for HLA-A (HCA2), HLA-B/C (HC10), β2-microglobulin and PD-L1 using immunohistochemistry on whole sections. Density and type of T-cell infiltrate were characterised by a triple immunofluorescent staining CD3-CD8-FOXP3.

Results

Overall, 85 formalin-fixed, paraffin-embedded blocks from 25 osteosarcoma patients were included. HLA class I expression was detected in 94% of osteosarcomas (strongly positive in 56%, heterogeneous in 38%) and negative or weakly positive in 6%, without differences between the stages of the disease. HLA-A expression was more frequently negative than HLA-B/C. Tumour-infiltrating lymphocytes were highly heterogeneous and mainly observed in tumour areas with expression of HLA class I. Density of T cells was significantly higher in metastases than in primary tumours and local relapses (p = 0.0003). Positive PD-L1 expression was found in 13% of primary tumours, 25% of relapses and 48% of metastases and correlated with a high T-cell infiltrate (p = 0.002).

Conclusion

An increased number of tumour-infiltrating T cells and PD-L1 expression in metastases compared with primary tumours, suggesting accessibility for T cells, could imply that osteosarcoma patients with metastatic disease may benefit from T-cell-based immunotherapy.

Electronic supplementary material

The online version of this article (doi:10.1007/s00262-016-1925-3) contains supplementary material, which is available to authorized users.