Virus-reactive T cells expanded in aplastic anemia eliminate hematopoietic progenitor cells by molecular mimicry

ABSTRACT

Acquired aplastic anemia is a bone marrow failure syndrome characterized by hypocellular bone marrow and peripheral blood pancytopenia. Frequent clinical responses to calcineurin inhibition and antithymocyte globulin strongly suggest critical roles for hematopoietic stem/progenitor cell-reactive T-cell clones in disease pathophysiology; however, their exact contribution and antigen specificities remain unclear. We determined differentiation states and targets of dominant T-cell clones along with their potential to eliminate hematopoietic progenitor cells in the bone marrow of 15 patients with acquired aplastic anemia. Single-cell sequencing and immunophenotyping revealed oligoclonal expansion and effector differentiation of CD8+ T-cell compartments. We reexpressed 28 dominant T-cell receptors (TCRs) of 9 patients in reporter cell lines to determine reactivity with (1) in vitro-expanded CD34+ bone marrow, (2) CD34- bone marrow, or (3) peptide pools covering immunodominant epitopes of highly prevalent viruses. Besides 5 cytomegalovirus-reactive TCRs, we identified 3 TCRs that recognized antigen presented on hematopoietic progenitor cells. T cells transduced with these TCRs eliminated hematopoietic progenitor cells of the respective patients in vitro. One progenitor cell-reactive TCR (11A5) also recognized an epitope of the Epstein-Barr virus-derived latent membrane protein 1 (LMP1) presented on HLA-A∗02:01. We identified 2 LMP1-related mimotopes within the human proteome as activating targets of TCR 11A5, providing proof of concept that molecular mimicry of viral and self-epitopes can drive T cell-mediated elimination of hematopoietic progenitor cells in aplastic anemia.

HLA-C*04:09N is expressed at the cell surface and triggers peptide-specific T-cell activation

The null allele HLA-C*04:09N differs from HLA-C*04:01 in a frameshift mutation within its cytoplasmic domain, resulting in translation of 32 additional amino acids that are assumed to prevent cell surface expression. However, we recently identified a multiple myeloma-reactive T-cell receptor (TCR) that appeared to recognize antigen presented on HLA-C*04:09N and encouraged us to ask whether HLA-C*04:09N, albeit not easily detectable at the cell surface, can present antigen sufficient for T-cell activation. We generated two HLA-class I-deficient cell lines, re-expressed HLAC* 04:09N, detected HLA expression by flow cytometry, and tested for T-cell activation using a cytomegalovirus peptide- specific HLA-C*04:01-restricted TCR. In both cell lines, HLA-C*04:09N expression was detectable at the cell surface and could be enhanced by IFN-γ exposure. Recombinant HLA-C*04:09N expression was sufficient for T-cell activation in vitro, which could be blocked by an HLA-class I-specific antibody, suggesting HLA-TCR interaction at the cell surface. Peripheral blood mononuclear cells isolated from an individual who physiologically expressed HLA-C*04:09N triggered peptide-specific T-cell activation, confirming our results with cells with natural HLA expression levels. In conclusion, we present peptide-specific HLA-C*04:09N-restricted T-cell activation and suggest consideration of this allele in the appropriate clinical context, such as allogeneic stem cell transplantation, or in the setting of cellular therapy.

IFNγ binding to extracellular matrix prevents fatal systemic toxicity

Interferon-γ (IFNγ) is an important mediator of cellular immune responses, but high systemic levels of this cytokine are associated with immunopathology. IFNγ binds to its receptor (IFNγR) and to extracellular matrix (ECM) via four positively charged C-terminal amino acids (KRKR), the ECM-binding domain (EBD). Across evolution, IFNγ is not well conserved, but the EBD is highly conserved, suggesting a critical function. Here, we show that IFNγ lacking the EBD (IFNγΔKRKR) does not bind to ECM but still binds to the IFNγR and retains bioactivity. Overexpression of IFNγΔKRKR in tumors reduced local ECM binding, increased systemic levels and induced sickness behavior, weight loss and toxicity. To analyze the function of the EBD during infection, we generated IFNγΔKRKR mice lacking the EBD by using CRISPR-Cas9. Infection with lymphocytic choriomeningitis virus resulted in higher systemic IFNγΔKRKR levels, enhanced sickness behavior, weight loss and fatal toxicity. We conclude that local retention of IFNγ is a pivotal mechanism to protect the organism from systemic toxicity during prolonged immune stimulation.

Generation of TGFβR2(-1) neoantigen-specific HLA-DR4-restricted T cell receptors for cancer therapy

BACKGROUND

Adoptive transfer of patient's T cells, engineered to express a T cell receptor (TCR) with defined novel antigen specificity, is a convenient form of cancer therapy. In most cases, major histocompatibility complex (MHC) I-restricted TCRs are expressed in CD8⁺ T cells and the development of CD4⁺ T cells engineered to express an MHC II-restricted TCR lacks behind. Critical is the choice of the target antigen, whether the epitope is efficiently processed and binds with high affinity to MHC molecules. A mutation in the transforming growth factor β receptor 2 (TGFβR2(-1)) gene creates a frameshift peptide caused by the deletion of one adenine (-1) within a microsatellite sequence. This somatic mutation is recurrent in microsatellite instable colorectal and gastric cancers and, therefore, is a truly tumor-specific antigen detected in many patients.

METHODS

ABabDR4 mice, which express a diverse human TCR repertoire restricted to human MHC II molecule HLA-DRA/DRB1*0401 (HLA-DR4), were immunized with the TGFβR2(-1) peptide and TGFβR2(-1)-specific TCRs were isolated from responding CD4⁺ T cells. The TGFβR2(-1)-specific TCRs were expressed in human CD4⁺ T cells and their potency and safety profile were assessed by co-cultures and other functional assays.

RESULTS

We demonstrated that TGFβR2(-1) neoantigen is immunogenic and elicited CD4⁺ T cell responses in ABabDR4 mice. When expressed in human CD4⁺ T cells, the HLA-DR4 restricted TGFβR2(-1)-specific TCRs induced IFNy expression at low TGFβR2(-1) peptide amounts. The TGFβR2(-1)-specific TCRs recognized HLA-DR4⁺ lymphoblastoid cells, which endogenously processed and presented the neoantigen, and colorectal cancer cell lines SW48 and HCT116 naturally expressing the TGFβR2(-1) mutation. No MHC II alloreactivity or cross-reactivity to peptides with a similar TCR-recognition motif were observed, indicating the safety of the TCRs.

CONCLUSIONS

The data suggest that HLA-DR4-restricted TCRs specific for the TGFβR2(-1) recurrent neoantigen can be valuable candidates for adoptive T cell therapy of a sizeable number of patients with cancer.

Targeting the recurrent Rac1P29S neoepitope in melanoma with heterologous high-affinity T cell receptors

Recurrent neoepitopes are cancer-specific antigens common among groups of patients and therefore ideal targets for adoptive T cell therapy. The neoepitope FSGEYIPTV carries the Rac1P29S amino acid change caused by a c.85C>T missense mutation, which is the third most common hotspot mutation in melanoma. Here, we isolated and characterized TCRs to target this HLA-A*02:01-binding neoepitope by adoptive T cell therapy. Peptide immunization elicited immune responses in transgenic mice expressing a diverse human TCR repertoire restricted to HLA-A*02:01, which enabled isolation of high-affinity TCRs. TCR-transduced T cells induced cytotoxicity against Rac1P29S expressing melanoma cells and we observed regression of Rac1P29S expressing tumors in vivo after adoptive T cell therapy (ATT). Here we found that a TCR raised against a heterologous mutation with higher peptide-MHC affinity (Rac2P29L) more efficiently targeted the common melanoma mutation Rac1P29S. Overall, our study provides evidence for the therapeutic potential of Rac1P29S-specific TCR-transduced T cells and reveal a novel strategy by generating more efficient TCRs by heterologous peptides.

Immune Phenotypes and Target Antigens of Clonally Expanded Bone Marrow T Cells in Treatment-Naïve Multiple Myeloma

Multiple myeloma is a hematologic malignancy of monoclonal plasma cells that accumulate in the bone marrow. Despite their clinical and pathophysiologic relevance, the roles of bone marrow-infiltrating T cells in treatment-naïve patients are incompletely understood. We investigated whether clonally expanded T cells (i) were detectable in multiple myeloma bone marrow, (ii) showed characteristic immune phenotypes, and (iii) whether dominant clones recognized antigens selectively presented on multiple myeloma cells. Single-cell index sorting and T-cell receptor (TCR) αβ sequencing of bone marrow T cells from 13 treatment-naïve patients showed dominant clonal expansion within CD8+ cytolytic effector compartments, and only a minority of expanded T-cell clones expressed the classic immune-checkpoint molecules PD-1, CTLA-4, or TIM-3. To identify their molecular targets, TCRs of 68 dominant bone marrow clones from five selected patients were reexpressed and incubated with multiple myeloma and non-multiple myeloma cells from corresponding patients. Only 1 of 68 TCRs recognized antigen presented on multiple myeloma cells. This TCR was HLA-C-restricted, self-peptide-specific and could be activated by multiple myeloma cells of multiple patients. The remaining dominant T-cell clones did not recognize multiple myeloma cells and were, in part, specific for antigens associated with chronic viral infections. In conclusion, we showed that dominant bone marrow T-cell clones in treatment-naïve patients rarely recognize antigens presented on multiple myeloma cells and exhibit low expression of classic immune-checkpoint molecules. Our data provide experimental context for experiences from clinical immune-checkpoint inhibition trials and will inform future T cell-dependent therapeutic strategies.

H3.3K27M mutation is not a suitable target for immunotherapy in HLA-A2+ patients with diffuse midline glioma

Diffuse midline glioma is the leading cause of solid cancer-related deaths in children with very limited treatment options. A majority of the tumors carry a point mutation in the histone 3 variant (H3.3) creating a potential HLA-A*02:01 binding epitope (H3.3K27M_26-35). Here, we isolated an H3.3K27M-specific T cell receptor (TCR) from transgenic mice expressing a diverse human TCR repertoire. Despite a high functional avidity of H3.3K27M-specific T cells, we were not able to achieve recognition of cells naturally expressing the H3.3K27M mutation, even when overexpressed as a transgene. Similar results were obtained with T cells expressing the published TCR 1H5 against the same epitope. CRISPR/Cas9 editing was used to exclude interference by endogenous TCRs in donor T cells. Overall, our data provide strong evidence that the H3.3K27M mutation is not a suitable target for cancer immunotherapy, most likely due to insufficient epitope processing and/or amount to be recognized by HLA-A*02:01 restricted CD8⁺ T cells.

Abstract 5507: Generating optimal-affinity T cell receptors targeting the shared neoantigen KRAS G12V using the humanized TCR transgenic mouse platform HuTCR

Background T cell receptor (TCR)-engineered T cell therapy (TCR-T) is a promising therapeutic modality to address key limitations of targeting solid tumors. Neoantigens are excellent therapeutic targets for TCR-T cell therapy, because they are highly specific and often homogeneously expressed in the tumor. While most neoantigens are patient-specific, there are rare exceptions of widely shared neoantigens, such as the driver oncogene KRAS containing mutations at position 12. The KRAS mutations G12C, G12D, and G12V are among the most common mutations in solid tumors, including indications with high unmet medical need, such as pancreatic, colorectal, and non-small cell lung cancer. Previous TCR-T approaches targeting KRAS G12V have been primarily focused on HLA-A*02:01, which appeared to be unable to present a mutant KRAS epitope. Here, we aim to generate TCRs of optimal affinity and high specificity to a KRAS G12V epitope in an HLA-agnostic manner using our HuTCR mouse platform.

Experimental procedures HuTCR mice represent a fully humanized TCR-MHC system and bear a diverse TCR repertoire, being transgenic for the entire human TCR alpha and beta gene loci and multiple human HLA class I molecules, while lacking murine TCRs and murine MHC class I molecules. The multi-HLA HuTCR mice were immunized with KRAS G12V peptides or the neoantigen-encoding adenovirus, leading to robust immune responses.

Results Single-cell sequencing of responding T cells revealed HLA-A*11:01-restricted immune responses, indicating that the epitope presented on HLA-A*11:01 was more immunogenic than epitopes presented on other HLA alleles. HLA-A*11:01 is expressed in approximately 11% of the United States and the European Union population and in around 30% of Asian populations. We were able to generate 30 KRAS G12V-specific TCRs, which we characterized for efficacy and safety. We selected a lead candidate, which demonstrated potent anti-tumor efficacy and no detectable off-target toxicity, to be pursued further into the clinic.

Conclusion Using the HuTCR mouse platform, we identified TCRs of optimal affinity and high specificity for the shared oncogenic KRAS G12V mutation. Importantly, the HuTCR platform was a powerful tool enabling us to determine the HLA allele responsible for generating the strongest immune response, and consequently, to define the patient population that may benefit most from targeting KRAS G12V.

Citation Format: Alexei Leliavski, Lorenz Knackstedt, Jennifer Oduro, Claudia Selck, Arunraj Dhamodaran, Thomas Blankenstein, Elisa Kieback, Lucia Poncette. Generating optimal-affinity T cell receptors targeting the shared neoantigen KRAS G12V using the humanized TCR transgenic mouse platform HuTCR [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5507.

IFN-γ-dependent tumor-antigen cross-presentation by lymphatic endothelial cells promotes their killing by T cells and inhibits metastasis

Tumor-associated lymphatic vessels promote metastasis and regulate antitumor immune responses. Here, we assessed the impact of cytotoxic T cells on the local lymphatic vasculature and concomitant tumor dissemination during an antitumor response. Interferon-γ (IFN-γ) released by effector T cells enhanced the expression of immunosuppressive markers by tumor-associated lymphatic endothelial cells (LECs). However, at higher effector T cell densities within the tumor, T cell-based immunotherapies induced LEC apoptosis and decreased tumor lymphatic vessel density. As a consequence, lymphatic flow was impaired, and lymph node metastasis was reduced. Mechanistically, T cell-mediated tumor cell death induced the release of tumor antigens and cross-presentation by tumor LECs, resulting in antigen-specific LEC killing by T cells. When LECs lacked the IFN-γ receptor expression, LEC killing was abrogated, indicating that IFN-γ is indispensable for reducing tumor-associated lymphatic vessel density and drainage. This study provides insight into how cytotoxic T cells modulate tumor lymphatic vessels and may help to improve immunotherapeutic protocols.

95 MAGE-A1 protein expression pattern in > 5,000 tumor and healthy tissue samples: Validation of MAGE-A1 as an ideal target for TCR-based cell therapy

Background

Cancer testis antigens (CTAs) are considered attractive targets for T cell receptor (TCR)-based cellular therapies as their expression in healthy adults is considered restricted to the immune-privileged testis. However, low-level expression of some CTAs in healthy tissue has been observed, resulting in significant on-target/off-cancer toxicity. Melanoma associated antigen 1 (MAGE-A1) is a member of the MAGE-A CTA family, whose members are known to influence cellular signaling pathways through their E3 ubiquitin ligase-binding MAGE homology domain. MAGE-A proteins are frequently expressed in different cancer types, have been linked to oncogenic activity and their expression has been associated with poor prognosis.1 Literature data suggest that in healthy tissues MAGE-A1 is detected in testis, only, with one exception suggesting MAGE-A1 RNA expression in cerebellum and cerebrum.2 Therefore, to evaluate MAGE-A1 as a potential target for cellular immunotherapies, an in-depth analysis of MAGE-A1 expression in > 70 different healthy tissue types and > 5,000 cancer biopsies was conducted, aiming to assess if MAGE-A1 represents a valid and safe target.

Methods

A MAGE-A1 antibody with high specificity (TK-AbMA1P) was identified and characterized for immunohistochemistry. A large panel of > 70 different healthy tissue types and > 5,000 tumor biopsies was explored and scored for MAGE-A1 expression by tissue microarray. Identified cancer entities with relevant MAGE-A1 expression were further investigated to assess spatial intratumoral MAGE-A1 expression distribution and expression consistency between primary tumor and lymph node/distant metastases.

Results

Characterization of TK-AbMA1P demonstrated fully paralog-selective staining for MAGE-A1. Analysis of MAGE-A1 expression in over 70 different healthy tissues confirmed strictly selective expression of MAGE-A1 in testis. An extended analysis of various CNS tissues including cerebellum and cerebrum did not reveal any expression in CNS. The analysis of > 5,000 tumor biopsies showed significant MAGE-A1 expression in distinct subgroups of multiple major tumor types with high unmet medical need. Substantial expression was detected for example in non-small-cell lung cancer, various breast cancer subtypes, gastrointestinal and urogenital cancers, among others. Extended analysis of the MAGE-A1 positive tumors demonstrated highly homogenous and consistent spatial intratumoral distribution of MAGE-A1 expression as well as between primary tumor and metastases.

Conclusions

This analysis confirms that MAGE-A1 is a highly selectively expressed CTA and demonstrates relevant expression in various indications with high unmet medical need, suggesting that MAGE-A1 is an ideal target for highly potent TCR-based adoptive cell therapy.

References

Weon JL, Potts PR. The MAGE protein family and cancer. Curr Opin Cell Biol 2015;37:1–8.

Morgan RA, Chinnasamy N, Abate-Daga D, Gros A, Robbins PF, Zheng Z, Dudley ME, Feldman SA, Yang JC, Sherry RM, Phan GQ, Hughes MS, Kammula US, Miller AD, Hessman CJ, Stewart AA, Restifo NP, Quezado MM, Alimchandani M, Rosenberg AZ, Nath A, Wang T, Bielekova B, Wuest SC, Akula N, McMahon FJ, Wilde S, Mosetter B, Schendel DJ, Laurencot CM, Rosenberg SA. Cancer regression and neurological toxicity following anti-MAGE-A3 TCR gene therapy. J Immunother 2013;36(2):133–51.

Ethics Approval

This study was approved by the Ethics Commission of the Ärztekammer Hamburg; approval number WF-049/09. Participants gave informed consent before taking part.

225 Optimal-affinity MAGE-A1-specific T cell receptors (TCRs) generated using the humanized TCR-transgenic mouse platform HuTCR are superior to human donor-derived TCRs

Background

As cancer-testis antigens are self-antigens, T cells expressing high-affinity TCRs against such antigens are eliminated via negative selection. Therefore, human-derived TCRs are typically of low affinity and exhibit reduced anti-tumor activity. Affinity maturation by mutagenesis is a common tool to increase affinity but may result in reduced specificity and off-target toxicity. Using our proprietary HuTCR mouse platform, which consists of mouse lines carrying the full human TCR-a/ß loci and human HLA alleles, we have isolated naturally optimized high-affinity TCRs specific for the cancer-testis antigen MAGE-A1 and compared them in vitro and in vivo to human-derived MAGE-A1-specific TCRs that are currently reported to be in clinical development.

Methods

MAGE-A1-specific TCRs were isolated from HuTCR mice immunized with the MAGE-1 antigen using scRNAseq or were synthesized based on publicly available databases of human donor-derived MAGE-A1-specific TCRs. All TCRs were re-expressed in primary human T cells as verified using peptide-MHC-multimer staining. Functional activity of the TCRs was analyzed by coculture with T2 target cells loaded with titrated amounts of epitope and measuring cytokine concentration by ELISA. Reactivity of TCRs to endogenously processed MAGE-A1 protein was assessed by coculture with tumor cell lines with variable MAGE-A1 and/or MHC-class-I expression. Tumor rejection potential of TCRs was evaluated in vivo using a syngeneic mouse model (TNA2 mice) expressing MAGE-A1 and HLA-A*02 on syngeneic tumor cells.

Results

Immunization of HuTCR mice with the MAGE-A1 antigen resulted in robust CD8+ T cell responses and several TCR clonotypes were identified by scRNAseq, with the majority of clonotypes being specific to the MAGE-A1-derived peptide KVLEYVIKV and TCR functional avidities ranging from 0.3nM to 3nM. In sharp contrast, human-derived TCRs of the same epitope specificity exhibited lower functional avidity with EC50 from 3nM to 60nM. In addition, HuTCR-mouse-derived TCRs were more sensitive in recognition of tumor cells expressing low MAGE-A1 and/or MHC-class-I. Adoptive T-cell transfer to TNA2-mice with established tumors resulted in complete rejection without relapse of tumors only in mice treated with HuTCR-mouse-derived TCR but not with human-derived or control TCRs.

Conclusions

The HuTCR mouse platform allows for the generation of high-affinity MAGE-A1-specific human TCRs with increased anti-tumor efficacy as compared to human-derived TCRs against the same cancer antigen. The in vitro and in vivo comparative data presented herein highlight the HuTCR-derived MAGE-A1-specific TCR as the most favorable candidate for clinical translation and a clinical trial evaluating its safety and efficacy in a variety of solid malignancies will be initiated November 2021.

Ethics Approval

All animal experiments were performed according to institutional and national guidelines, after approval by the responsible authority (Landesamt für Gesundheit und Soziales, Berlin). Blood collection from healthy human donors was done after prior informed consent and experiments were conducted in accordance with the ethical standards of Declaration of Helsinki.

499 A first-in-human, phase 1/2 clinical trial of TK-8001, a MAGE-A1 directed T cell receptor in patients with advanced-stage solid tumors (The “IMAG1NE”-trial)

Background

Melanoma-associated antigen 1 (MAGE-A1) is a cancer-testis antigen with highly selective expression in testis (which is an immune privileged site) and in multiple high unmet medical need cancers. Therefore, it represents an attractive target for T cell receptor (TCR)-based therapies. TK-8001 is a MAGE-A1 directed TCR with optimized affinity and specificity, derived from the huTCR mouse platform,1 introduced by retroviral transduction into autologous patient-derived CD8+ T cells. The anticipated mode of action of TK-8001 is to bind to MAGE-A1-epitope presenting tumor cells and eliminate them via CD8+ cytotoxic activity and interferon-γ release. Preclinical exploration of the TK-8001 TCR has demonstrated potent antitumor activity, even in low-expressing MAGE-1 positive tumor cells, and favorable benchmarking vs. existing MAGE-A1 directed TCRs derived from human donors. This abstract describes the currently launched phase 1/2 trial for TK-8001.

Methods

The IMAG1NE trial (Immunotherapeutic MAGE-A1 directed Neoplasm Elimination) is a phase 1/2, first-in-human, open-label, accelerated titration, two-part clinical trial of TK-8001 (MAGE-A1-directed TCR-transduced autologous CD8+ T cells) in subjects with HLA-A*02:01 genotype and advanced-stage/metastatic, MAGE-A1+ solid tumors that either have no approved therapeutic alternative(s) or are in non-curable state and have received a minimum of two lines of systemic therapy. Major endpoints for the IMAG1NE trial will be safety, pharmacokinetics, pharmacodynamics (e.g. cytokine profiles) as well as preliminary clinical efficacy (degree of tumor mass reduction and duration of response).In Part 1 of the trial, three different doses of TK-8001 will be explored for safety and preliminary clinical efficacy in an accelerated titration design. The starting dose is set at 1x10E8 MAGE-A1 TCR transduced CD8+ T cells followed by two escalation steps. Part 2 of the trial will enroll up to 30 subjects with advanced-stage, MAGE-A1 positive cancer to confirm safety and efficacy.The study is expected to open for enrolment in Q4/2021. For further information please contact T-knife GmbH at info@t-knife.com.

References

Li, Liang-Ping, J Christoph Lampert, Xiaojing Chen, Catarina Leitao, Jelena Popović, Werner Müller, and Thomas Blankenstein. Transgenic mice with a diverse human T cell antigen receptor repertoire. Nature Medicine 2010;16: 1029–34.

Ethics Approval

In progress, expected 11/2021

The role of CD4 T cells in rejection of solid tumors

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Versatility of CD4 T cells enables different attack modes towards cancer cells.

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Cooperation of CD4 and CD8 T cells renders anti-tumor responses most efficient.

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Integrating CD4 T cells in cancer therapy will improve clinical outcome.

The focus in cancer immunotherapy has mainly been on CD8 T cells, as they can directly recognize cancer cells. CD4 T cells have largely been neglected, because most cancers lack MHC II expression and cannot directly be recognized by CD4 T cells. Yet, tumor antigens can be captured and cross-presented by MHC II-expressing tumor stromal cells. Recent data suggest that CD4 T cells act as a swiss army knife against tumors. They can kill cancer cells, if they express MHC II, induce tumoricidal macrophages, induces cellular senescence of cancer cells, destroy the tumor vasculature through cytokine release and help CD8 T cells in the effector phase. We foresee a great future for CD4 T cells in the clinic, grafted with tumor antigen specificity by T cell receptor gene transfer, either alone or in combination with engineered CD8 T cells.

Thyrotropin Receptor-Specific Lymphocytes in Adenovirus-TSHR-Immunized Native and Human Leukocyte Antigen-DR3-Transgenic Mice and in Graves' Disease Patient Blood

Background: Antigen-specific lymphocytes are increasingly investigated in autoimmune diseases and immune therapies. We sought to identify thyrotropin receptor (TSHR)-specific lymphocytes in mouse models of Graves' disease, including Graves' patient-specific immunotype human leukocyte antigen (HLA)-DR3, and in frozen and thawed Graves' patient blood samples. Methods and Results: Splenic lymphocytes of adenovirus (Ad)-TSHR-immunized BALB/c mice were stimulated with TSHR-specific peptides C, D, or J. Furthermore, CD154-expressing cells were enriched, expanded in vitro, and analyzed for binding of peptide-major histocompatibility complex (MHC) II multimers ("tetramers," immunotype H2-IA^d). Only peptides C and J were able to elicit increased expression/secretion of CD154 and interferon-γ, and tetramers which were loaded with peptide C resulted in antigen-specific signals in splenic lymphocytes from Ad-TSHR-immunized mice. Accordingly, TSHR-specific HLA-DR3-MHC class II tetramers loaded with peptide p10 specifically bound to human HLA-DR3-(allele B1*03:01)-transgenic Bl/6 mouse splenic T lymphocytes. In addition, we fine-tuned a protocol to reliably measure thawed human peripheral blood mononuclear cells (PBMCs), which resulted in reliable recovery after freezing and thawing with regard to vitality and B and T cell subpopulation markers including regulatory T cells (CD3, CD4, CD25, FoxP3, CD25^high, CD127^low). TSHR-specific HLA-DR3-MHC class II tetramers loaded with peptide p10 identified antigen-specific T cells in HLA-DR3-positive Graves' patients' thawed PBMCs. Moreover, stimulation-dependent release of interleukin (IL)-1beta, IL-6, tumor necrosis factor-alpha from thawed PBMCs occurred at the expected levels. Conclusions: Novel MHC II tetramers identified TSHR-specific T lymphocytes in Ad-TSHR-immunized hyperthyroid BALB/c or HLA-DR3-transgenic mice and in thawed human PBMCs from patients with Graves' disease. These assays may contribute to measure both disease severity and effects of novel immune therapies in future animal studies and clinical investigations of Graves' disease.

Generation of a HuTCR mouse platform-derived MAGE-A1-directed high-affinity TCR with superior potency versus human-derived TCRs

e14515

Background: As cancer-testis antigens are self-antigens, T cells expressing high-affinity TCRs against such antigens are suppressed via negative thymic selection. Therefore, patient- or donor-derived TCRs are typically of low affinity and result in a reduced antitumor effect. Using our proprietary HuTCR platform, which consists of mouse lines carrying the full human TCR α/β loci in combination with common human HLA alleles, we have isolated high-affinity TCRs specific for the cancer-testis antigen MAGE-A1 and compared them to human-derived MAGE-A1-specific TCRs that are currently reported to be in clinical development. Furthermore, we validated MAGE-A1 as a potential cancer therapy target by using immunohistochemistry to evaluate expression in several major tumor types and healthy tissue. Methods: Using scRNAseq, TCRs were isolated from HuTCR mice. Human-derived MAGE-A1-specific TCR sequences were obtained from publicly available databases. All TCRs were expressed in primary human T cells as verified using peptide-MHC-multimer staining. Functional avidity of the TCRs was analyzed by coculture with T2 target cells loaded with titrated amounts of epitope peptides and measuring cytokine concentration by ELISA. Reactivity of TCRs to endogenously processed MAGE-A1 protein was assessed by co-culture with a panel of tumor cell lines varying in MAGE-A1 and/or MHC-class-I expression. MAGE-A1 expression on protein level was evaluated by immunohistochemistry. Results: Immunization of HuTCR mice with the antigen resulted in robust CD8+ T cell responses and several TCR clonotypes were identified by scRNAseq, with the majority of clonotypes being specific to the MAGE-A1-derived peptide KVLEYVIKV and TCR affinities ranging from 0.3 nM to 3 nM. By comparison, human-derived TCRs exhibited generally lower functional avidity from 3 nM to 60 nM. In addition, HuTCR-mouse-derived TCRs were more sensitive in recognition of tumor cell lines expressing low MAGE-A1 and/or HLA-A2. Immunohistochemical analysis of MAGE-A1 expression in healthy tissues demonstrated highly selective expression of MAGE-A1 in testis, only. Screening for expression confirmed that a significant proportion of several major cancer types expresses MAGE-A1 as reported by various other groups [reviewed in Curr Opin Cell Biol. 2015 December; 37: 1–8]. Conclusions: The HuTCR mouse platform allows for the generation of high-affinity MAGE-A1-specific TCRs with increased anti-tumor efficacy as compared to human-derived TCRs against the same cancer antigen. In addition, it was confirmed that MAGE-A1 has a highly selective expression pattern in healthy tissues (testis, only), but shows distinct expression in several major human tumor types.

In vitro proteasome processing of neo-splicetopes does not predict their presentation in vivo

Proteasome-catalyzed peptide splicing (PCPS) of cancer-driving antigens could generate attractive neoepitopes to be targeted by T cell receptor (TCR)-based adoptive T cell therapy. Based on a spliced peptide prediction algorithm, TCRs were generated against putative KRASG12V- and RAC2P29L-derived neo-splicetopes with high HLA-A*02:01 binding affinity. TCRs generated in mice with a diverse human TCR repertoire specifically recognized the respective target peptides with high efficacy. However, we failed to detect any neo-splicetope-specific T cell response when testing the in vivo neo-splicetope generation and obtained no experimental evidence that the putative KRASG12V- and RAC2P29L-derived neo-splicetopes were naturally processed and presented. Furthermore, only the putative RAC2P29L-derived neo-splicetopes was generated by in vitro PCPS. The experiments pose severe questions on the notion that available algorithms or the in vitro PCPS reaction reliably simulate in vivo splicing and argue against the general applicability of an algorithm-driven 'reverse immunology' pipeline for the identification of cancer-specific neo-splicetopes.

Long-term in vitro expansion ensures increased yield of central memory T cells as perspective for manufacturing challenges

Adoptive T cell therapy (ATT) has revolutionized the treatment of cancer patients. A sufficient number of functional T cells are indispensable for ATT efficacy; however, several ATT dropouts have been reported due to T cell expansion failure or lack of T cell persistence in vivo. With the aim of providing ATT also to those patients experiencing insufficient T cell manufacturing via standard protocol, we evaluated if minimally manipulative prolongation of in vitro expansion (long-term [LT] >3 weeks with IL-7 and IL-15 cytokines) could result in enhanced T cell yield with preserved T cell functionality. The extended expansion resulted in a 39-fold increase of murine CD8⁺ T central memory cells (Tcm). LT expanded CD8⁺ and CD4⁺ Tcm cells retained a gene expression profile related to Tcm and T memory stem cells (Tscm). In vivo transfer of LT expanded Tcm revealed persistence and antitumor capacity. We confirmed our in vitro findings on human T cells, on healthy donors and diffuse large B cell lymphoma patients, undergoing salvage therapy. Our study demonstrates the feasibility of an extended T cell expansion as a practicable alternative for patients with insufficient numbers of T cells after the standard manufacturing process thereby increasing ATT accessibility.

Regulation of LCoR and RIP140 expression in cervical intraepithelial neoplasia and correlation with CIN progression and dedifferentiation

Purpose

Ligand-dependent corepressor (LCoR) and receptor-interacting protein 140 (RIP140/NRIP1) play an important role in the regulation of multiple oncogenic signaling pathways and the development of cancer. LCoR and RIP140 form a nuclear complex in breast cancer cells and are of prognostic value in further prostate and cervical cancer. The purpose of this study was to analyze the regulation of these proteins in the development of cervical intraepithelial neoplasia (CIN I–III).

Methods

Immunohistochemical analysis was obtained to quantify RIP140 and LCoR expression in formalin-fixed paraffin embedded tissue sections of cervical intraepithelial neoplasia samples. Tissue (n = 94) was collected from patients treated in the Department of Gynecology and Obstetrics, Ludwig-Maximilians-University of Munich, Germany, between 2002 and 2014. Correlations of expression levels with clinical outcome were carried out to assess for prognostic relevance in patients with CIN2 progression. Kruskal–Wallis test and Mann–Whitney U test were used for data analysis.

Results

Nuclear LCoR overexpression correlates significantly with CIN II progression. Nuclear RIP140 expression significantly increases and nuclear LCoR expression decreases with higher grading of cervical intraepithelial neoplasia. Cytoplasmic RIP140 expression is significantly higher in CIN III than in CIN I or CIN II.

Conclusion

A decrease of nuclear LCoR expression in line with an increase of dedifferentiation of CIN can be observed. Nuclear LCoR overexpression correlates with CIN II progression indicating a prognostic value of LCoR in cervical intraepithelial neoplasia. Nuclear and cytoplasmic RIP140 expression increases significantly with higher grading of cervical intraepithelial neoplasia underlining its potential role in the development of pre-cancerous lesions. These findings support the relevance of LCoR and RIP140 in the tumorigenesis indicating a possible role of LCoR and RIP140 as targets for novel therapeutic approaches in cervical intraepithelial neoplasia and cervical cancer.

Identification and ranking of recurrent neo-epitopes in cancer

Background

Immune escape is one of the hallmarks of cancer and several new treatment approaches attempt to modulate and restore the immune system’s capability to target cancer cells. At the heart of the immune recognition process lies antigen presentation from somatic mutations. These neo-epitopes are emerging as attractive targets for cancer immunotherapy and new strategies for rapid identification of relevant candidates have become a priority.

Methods

We carefully screen TCGA data sets for recurrent somatic amino acid exchanges and apply MHC class I binding predictions.

Results

We propose a method for in silico selection and prioritization of candidates which have a high potential for neo-antigen generation and are likely to appear in multiple patients. While the percentage of patients carrying a specific neo-epitope and HLA-type combination is relatively small, the sheer number of new patients leads to surprisingly high reoccurence numbers. We identify 769 epitopes which are expected to occur in 77629 patients per year.

Conclusion

While our candidate list will definitely contain false positives, the results provide an objective order for wet-lab testing of reusable neo-epitopes. Thus recurrent neo-epitopes may be suitable to supplement existing personalized T cell treatment approaches with precision treatment options.

MRI hip findings in asymptomatic professional rugby players, ballet dancers, and age-matched controls

AIM

To investigate hip magnetic resonance imaging (MRI) findings in asymptomatic professional male rugby players and male ballet dancers compared to age-matched controls.

MATERIALS AND METHODS

After ethics committee approval and consent from participants, 11 professional rugby players, 10 professional ballet dancers, and 10 controls completed activity and symptom questionnaires and underwent 3 T MRI of their self-declared dominant hip. Each scan was independently scored by two musculoskeletal radiologists for multiple features, including: joint morphology, acetabular labrum appearance, cartilage loss, and capsular thickness. Clinical and MRI features were assessed for variance by group using one-way analysis of variance (ANOVA) tests and Tukey post-hoc pairwise comparison of means.

RESULTS

Labral tear prevalence was 87% with no significant difference between groups (p>0.05). Rates of paralabral cysts were significantly higher in ballet dancers (50%), compared to rugby players (0%) and controls (10%; p=0.01). Acetabular cartilage loss was present in 54% with no significant differences between groups. Superior capsular thickness was significantly greater in ballet dancers (5.3 mm) compared to rugby players (3.8 mm) and controls (3.8 mm; p=0.03).

CONCLUSION

Despite the difference in type of activity between groups, there were equally high rates of labral tears and acetabular cartilage loss, questioning the role that sport plays in the development of these findings and their relationship to symptoms. The focally increased superior capsular thickness in ballet dancers may be an adaptive response to extreme ranges of movement.

SigsPack, a package for cancer mutational signatures

Background

Mutational signatures are specific patterns of somatic mutations introduced into the genome by oncogenic processes. Several mutational signatures have been identified and quantified from multiple cancer studies, and some of them have been linked to known oncogenic processes. Identification of the processes contributing to mutations observed in a sample is potentially informative to understand the cancer etiology.

Results

We present here SigsPack, a Bioconductor package to estimate a sample’s exposure to mutational processes described by a set of mutational signatures. The package also provides functions to estimate stability of these exposures, using bootstrapping. The performance of exposure and exposure stability estimations have been validated using synthetic and real data. Finally, the package provides tools to normalize the mutation frequencies with respect to the tri-nucleotide contents of the regions probed in the experiment. The importance of this effect is illustrated in an example.

Conclusion

SigsPack provides a complete set of tools for individual sample exposure estimation, and for mutation catalogue & mutational signatures normalization.

Electronic supplementary material

The online version of this article (10.1186/s12859-019-3043-7) contains supplementary material, which is available to authorized users.

Localization-associated immune phenotypes of clonally expanded tumor-infiltrating T cells and distribution of their target antigens in rectal cancer

The degree and type of T cell infiltration influence rectal cancer prognosis regardless of classical tumor staging. We asked whether clonal expansion and tumor infiltration are restricted to selected-phenotype T cells; which clones are accessible in peripheral blood; and what the spatial distribution of their target antigens is. From five rectal cancer patients, we isolated paired tumor-infiltrating T cells (TILs) and T cells from unaffected rectum mucosa (T_UM) using 13-parameter FACS single cell index sorting. TCRαβ sequences, cytokine, and transcription factor expression were determined with single cell sequencing. TILs and T_UM occupied distinct phenotype compartments and clonal expansion predominantly occurred within CD8⁺ T cells. Expanded TIL clones identified by paired TCRαβ sequencing and exclusively detectable in the tumor showed characteristic PD-1 and TIM-3 expression. TCRβ repertoire sequencing identified 49 out of 149 expanded TIL clones circulating in peripheral blood and 41 (84%) of these were PD-1^- TIM-3^-. To determine whether clonal expansion of predominantly tumor-infiltrating T cell clones was driven by antigens uniquely presented in tumor tissue, selected TCRs were reconstructed and incubated with cells isolated from corresponding tumor or unaffected mucosa. The majority of clones exclusively detected in the tumor recognized antigen at both sites. In summary, rectal cancer is infiltrated with expanded distinct-phenotype T cell clones that either i) predominantly infiltrate the tumor, ii) predominantly infiltrate the unaffected mucosa, or iii) overlap between tumor, unaffected mucosa, and peripheral blood. However, the target antigens of predominantly tumor-infiltrating TIL clones do not appear to be restricted to tumor tissue.

Interferon-γ Receptor Signaling in Dendritic Cells Restrains Spontaneous Proliferation of CD4+ T Cells in Chronic Lymphopenic Mice

In lymphopenic mice, T cells become activated and undergo lymphopenia-induced proliferation (LIP). However, not all T cells are equally sensitive to lymphopenia. Several lymphopenia-insensitive T cell clones were described and their non-responsiveness was mainly attributed to clone-specific properties. Here, we provide evidence for an additional, host-dependent mechanism restraining LIP of lymphopenia-insensitive CD4+ T cells. We show that such cells undergo LIP in lymphopenic mice lacking IFN-γ receptor (IFN-γR) expression, a process, which is promoted by the autocrine action of T cell-derived IFN-γ. Additionally, LIP of lymphopenia-insensitive CD4+ T cells requires an intact microflora and is accompanied by the massive accumulation of IL-6 and dendritic cells (DCs). Consistent with these results, IL-6 neutralization and the DC-specific restoration of IFN-γR expression are both sufficient to restrict LIP. Hence, the insensitivity of CD4+ T cells to lymphopenia relies on cell-intrinsic properties and a complex interplay between the commensal microflora, IL-6, IFN-γR+ DCs, and T cell-derived IFN-γ.

Effective NY-ESO-1-specific MHC II-restricted T cell receptors from antigen-negative hosts enhance tumor regression

Adoptive transfer of T cell receptor-engineered (TCR-engineered) T cells is a promising approach in cancer therapy but needs improvement for more effective treatment of solid tumors. While most clinical approaches have focused on CD8+ T cells, the importance of CD4+ T cells in mediating tumor regression has become apparent. Regarding shared (self) tumor antigens, it is unclear whether the human CD4+ T cell repertoire has been shaped by tolerance mechanisms and lacks highly functional TCRs suitable for therapy. Here, TCRs against the tumor-associated antigen NY-ESO-1 were isolated either from human CD4+ T cells or from mice that express a diverse human TCR repertoire with HLA-DRA/DRB1*0401 restriction and are NY-ESO-1 negative. NY-ESO-1-reactive TCRs from the mice showed superior recognition of tumor cells and higher functional activity compared with TCRs from humans. We identified a candidate TCR, TCR-3598_2, which was expressed in CD4+ T cells and caused tumor regression in combination with NY-ESO-1-redirected CD8+ T cells in a mouse model of adoptive T cell therapy. These data suggest that MHC II-restricted TCRs against NY-ESO-1 from a nontolerant nonhuman host are of optimal affinity and that the combined use of MHC I- and II-restricted TCRs against NY-ESO-1 can make adoptive T cell therapy more effective.

Abstract 4679: Rectal cancer-infiltrating T cells show clonal expansion associated with spatially restricted tolerogenic phenotypes

T cell infiltration correlates with prognosis and outcome in colorectal cancer regardless of the tumor stage. However, data on clonal expansion, phenotypes, functions, and spatial distribution of tumor-infiltrating T cells (TILs) are limited.

We hypothesized that subsets of clonally expanded rectal cancer-associated T cells are specifically recruited into the tumor and show characteristic phenotypes and functions.

Paired TILs and T cells from adjacent unaffected mucosa were isolated from five treatment-naïve rectal cancer patients. Although T cell immune phenotypes were heterogeneous, the frequencies of CD38+, PD-1+, and TIM-3+ cells were significantly higher in CD8+ TILs when compared to T cells from unaffected mucosa (p < 0.05). To track clonal expansion and phenotypes at the single cell level, we combined 13-parameter FACS single cell index sorting with next generation T cell receptor (TCR) and phenotype sequencing. Paired TCRαβ sequences were obtained from 1237 TILs (on average 412 TILs per patient) and 1257 T cells infiltrating the unaffected mucosa (on average 419 T cells per patient) from three selected patients. Clonal T cell expansion was not restricted to TILs and occurred predominantly in CD8+ T cells (p < 0.05). Expanded TIL clones were more frequently TIM-3+, PD-1+, and CD38+ (p < 0.05) and occupied characteristic phenotype compartments when compared to T cells from unaffected mucosa with t-stochastic neighbor embedding (t-SNE) visualization. FOXP3 expression was enriched in non-expanded TILs (p < 0.05).

Only 11 out of 179 TIL clones were also detectable in unaffected mucosa of the same patients and these overlapping clones were exclusively PD-1- TIM-3-.

In conclusion, rectal cancer is infiltrated by oligoclonal T cells. Selected clones were exclusively detected in TILs suggesting their expansion and recruitment driven by tumor-associated cues. Tolerance was induced i) in an antigen-specific manner by the expression of immune checkpoint molecules predominantly on clonally expanded TILs, and ii) in an antigen-independent manner by infiltrating polyclonal FOXP3+ regulatory T cells.

Citation Format: Livius Penter, Kerstin Dietze, Felix Aigner, Lars Bullinger, Thomas Blankenstein, Leo Hansmann. Rectal cancer-infiltrating T cells show clonal expansion associated with spatially restricted tolerogenic phenotypes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4679.

Targeting Merkel Cell Carcinoma by Engineered T Cells Specific to T-Antigens of Merkel Cell Polyomavirus

Purpose: The causative agent of most cases of Merkel cell carcinoma (MCC) has been identified as the Merkel cell polyomavirus (MCV). MCV-encoded T antigens (Tag) are essential not only for virus-mediated tumorigenesis but also for maintaining MCC cell lines in vitro MCV Tags are thus an appealing target for viral oncoprotein-directed T-cell therapy for MCC. With this study, we aimed to isolate and characterize Tag-specific T-cell receptors (TCR) for potential use in gene therapy clinical trials.Experimental Design: T-cell responses against MCV Tag epitopes were investigated by immunizing transgenic mice that express a diverse human TCR repertoire restricted to HLA-A2. Human lymphocytes genetically engineered to express Tag-specific TCRs were tested for specific reactivity against MCC cell lines. The therapeutic potential of Tag-specific TCR gene therapy was tested in a syngeneic cancer model.Results: We identified naturally processed epitopes of MCV Tags and isolated Tag-specific TCRs. T cells expressing these TCRs were activated by HLA-A2-positive cells loaded with cognate peptide or cells that stably expressed MCV Tags. We showed cytotoxic potential of T cells engineered to express these TCRs in vitro and demonstrated regression of established tumors in a mouse model upon TCR gene therapy.Conclusions: Our findings demonstrate that MCC cells can be targeted by MCV Tag-specific TCRs. Although recent findings suggest that approximately half of MCC patients benefit from PD-1 pathway blockade, additional patients may benefit if their endogenous T-cell response can be augmented by infusion of transgenic MCV-specific T cells such as those described here. Clin Cancer Res; 24(15); 3644-55. ©2018 AACR.

ERAP1-Dependent Antigen Cross-Presentation Determines Efficacy of Adoptive T-cell Therapy in Mice

Cytotoxic T lymphocytes can reject established tumors if their target peptide is efficiently presented by MHC class I molecules (pMHC-I) on the surface of cancerous cells. Therapeutic success upon adoptive T-cell transfer (ATT), however, requires additional cross-presentation of the same pMHC-I on noncancerous cells. Endoplasmic reticulum aminopeptidase 1 (ERAP1) is an enzyme that customizes the N-terminus of proteasome-generated peptides so they can be loaded onto MHC-I molecules in the endoplasmic reticulum (ER). We show here that ERAP1 is critically involved in the process of tumor rejection and assumes a dual role by independently operating on both sides. Direct presentation of two MHC-I-restricted epitopes of a cancer-driving transplantation rejection antigen through ERAP1 moderately affected tumor rejection by adoptively transferred T-cell receptor gene-modified T cells in each case. ERAP1 expression by antigen cross-presenting cells of the ATT recipients was critical for expansion of therapeutic monospecific T cells and correlated with tumor rejection. Specifically, lack of ERAP1 expression in the ATT recipient's noncancerous cells enabled progression of pMHC-I-positive, IFNγ-responsive tumors, despite the presence of antigen-specific functional cytotoxic T lymphocytes. These data reveal a decisive role for ERAP1 in T-cell-mediated tumor rejection and will enhance the choice of MHC-I-restricted epitopes targeted by adoptive T-cell transfer.Significance: This study demonstrates a role of ERAP1 in the efficacy of adoptive T-cell transfer and has potential to improve personalized T-cell therapy for solid tumors. Cancer Res; 78(12); 3243-54. ©2018 AACR.

A Transgenic Dual-Luciferase Reporter Mouse for Longitudinal and Functional Monitoring of T Cells In Vivo

Adoptive T-cell therapy (ATT) efficacy is limited when targeting large solid tumors. The evaluation of ATT outcomes using accessory treatment would greatly benefit from an in vivo monitoring tool, allowing the detection of functional parameters of transferred T cells. Here, we generated transgenic bioluminescence imaging of T cells (BLITC) mice expressing an NFAT-dependent click-beetle luciferase and a constitutive Renilla luciferase, which supports concomitant in vivo analysis of migration and activation of T cells. Rapid transferability of our system to preestablished tumor models was demonstrated in the SV40-large T antigen model via both crossbreeding of BLITC mice into a T-cell receptor (TCR)-transgenic background and TCR transduction of BLITC T cells. We observed rapid tumor infiltration of BLITC CD8⁺ T cells followed by a burst-like activation that mirrored rejection kinetics. Using the BLITC reporter in the clinically relevant H-Y model, we performed female to male transfers and detected H-Y-specific alloreactivity (graft-versus-host disease) in vivo In an H-Y solid tumor model, we found migration of adoptively transferred H-Y TCR-transgenic CD4⁺ T cells into the tumor, marked by transient activation. This suggests a rapid inactivation of infiltrating T cells by the tumor microenvironment, as confirmed by their expression of inhibitory receptors. In summary, the BLITC reporter system facilitates analysis of therapeutic parameters for ATT, is rapidly transferable to models of interest not restricted to tumor research, and is suitable for rapid screening of TCR clones for tumor rejection kinetics, as well as off-target effects. Cancer Immunol Res; 6(1); 110-20. ©2018 AACR.

The immune system prevents recurrence of transplanted but not autochthonous antigenic tumors after oncogene inactivation therapy

Targeted oncogene inactivation by small molecule inhibitors can be very effective but tumor recurrence is a frequent problem in the clinic. Therapy by inactivation of the cancer-driving oncogene in transplanted tumors was shown to be augmented in the presence of T cells. However, these experiments did not take into account the long-term, usually tolerogenic, interaction of de novo malignancies with the immune system. Here, we employed mice, in which SV40 large T (Tag) and firefly luciferase (Luc) as fusion protein (TagLuc) could be regulated with the Tet-on system and upon activation resulted in tumors after a long latency. TagLuc inactivation induced profound tumor regression, demonstrating sustained oncogene addiction. While tumor relapse after TagLuc inactivation was prevented in immunocompetent mice bearing transplanted tumors, autochthonous tumors relapsed or recurred after therapy discontinuation indicating that the immune system that coevolved with the malignancy over an extended period of time lost the potency to mount an efficient anti-tumor immune response. By contrast, adoptively transferred CD8⁺ T cells targeting the cancer-driving oncogene eradicated recurrent autochthonous tumors, highlighting a suitable therapy option in a clinically relevant model.

Human TCR-MHC coevolution after divergence from mice includes increased nontemplate-encoded CDR3 diversity

Chen et al. demonstrate that human MHC selects a larger human TCR repertoire than mouse MHC. They show how humans optimized TCR diversity and suggest that CDR3 length adjusts for different V segment–MHC affinity.

For thymic selection and responses to pathogens, T cells interact through their αβ T cell receptor (TCR) with peptide–major histocompatibility complex (MHC) molecules on antigen-presenting cells. How the diverse TCRs interact with a multitude of MHC molecules is unresolved. It is also unclear how humans generate larger TCR repertoires than mice do. We compared the TCR repertoire of CD4 T cells selected from a single mouse or human MHC class II (MHC II) in mice containing the human TCR gene loci. Human MHC II yielded greater thymic output and a more diverse TCR repertoire. The complementarity determining region 3 (CDR3) length adjusted for different inherent V-segment affinities to MHC II. Humans evolved with greater nontemplate-encoded CDR3 diversity than did mice. Our data, which demonstrate human TCR–MHC coevolution after divergence from rodents, explain the greater T cell diversity in humans and suggest a mechanism for ensuring that any V–J gene combination can be selected by a single MHC II.

CTLA4 Promotes Tyk2-STAT3-Dependent B-cell Oncogenicity

CTL-associated antigen 4 (CTLA4) is a well-established immune checkpoint for antitumor immune responses. The protumorigenic function of CTLA4 is believed to be limited to T-cell inhibition by countering the activity of the T-cell costimulating receptor CD28. However, as we demonstrate here, there are two additional roles for CTLA4 in cancer, including via CTLA4 overexpression in diverse B-cell lymphomas and in melanoma-associated B cells. CTLA4-CD86 ligation recruited and activated the JAK family member Tyk2, resulting in STAT3 activation and expression of genes critical for cancer immunosuppression and tumor growth and survival. CTLA4 activation resulted in lymphoma cell proliferation and tumor growth, whereas silencing or antibody-blockade of CTLA4 in B-cell lymphoma tumor cells in the absence of T cells inhibits tumor growth. This inhibition was accompanied by reduction of Tyk2/STAT3 activity, tumor cell proliferation, and induction of tumor cell apoptosis. The CTLA4-Tyk2-STAT3 signal pathway was also active in tumor-associated nonmalignant B cells in mouse models of melanoma and lymphoma. Overall, our results show how CTLA4-induced immune suppression occurs primarily via an intrinsic STAT3 pathway and that CTLA4 is critical for B-cell lymphoma proliferation and survival. Cancer Res; 77(18); 5118-28. ©2017 AACR.

T-cell Receptors for Clinical Therapy: In Vitro Assessment of Toxicity Risk

Adoptive therapy with T-cell receptor (TCR)-engineered T cells has shown promising results in the treatment of patients with tumors, and the number of TCRs amenable for clinical testing is expanding rapidly. Notably, adoptive therapy with T cells is challenged by treatment-related side effects, which calls for cautious selection of target antigens and TCRs that goes beyond their mere ability to induce high T-cell reactivity. Here, we propose a sequence of in vitro assays to improve selection of TCRs and exemplify risk assessments of on-target as well as off-target toxicities using TCRs directed against cancer germline antigens. The proposed panel of assays covers parameters considered key to safety, such as expression of target antigen in healthy tissues, determination of a TCR's recognition motif toward its cognate peptide, and a TCR's cross-reactivity toward noncognate peptides. Clin Cancer Res; 23(20); 6012-20. ©2017 AACR.

Tumour ischaemia by interferon-γ resembles physiological blood vessel regression

The relative contribution of the effector molecules produced by T cells to tumour rejection is unclear, but interferon-γ (IFNγ) is critical in most of the analysed models. Although IFNγ can impede tumour growth by acting directly on cancer cells, it must also act on the tumour stroma for effective rejection of large, established tumours. However, which stroma cells respond to IFNγ and by which mechanism IFNγ contributes to tumour rejection through stromal targeting have remained unknown. Here we use a model of IFNγ induction and an IFNγ-GFP fusion protein in large, vascularized tumours growing in mice that express the IFNγ receptor exclusively in defined cell types. Responsiveness to IFNγ by myeloid cells and other haematopoietic cells, including T cells or fibroblasts, was not sufficient for IFNγ-induced tumour regression, whereas responsiveness of endothelial cells to IFNγ was necessary and sufficient. Intravital microscopy revealed IFNγ-induced regression of the tumour vasculature, resulting in arrest of blood flow and subsequent collapse of tumours, similar to non-haemorrhagic necrosis in ischaemia and unlike haemorrhagic necrosis induced by tumour necrosis factor. The early events of IFNγ-induced tumour ischaemia resemble non-apoptotic blood vessel regression during development, wound healing or IFNγ-mediated, pregnancy-induced remodelling of uterine arteries. A better mechanistic understanding of how solid tumours are rejected may aid the design of more effective protocols for adoptive T-cell therapy.

Prevalence of human papillomavirus infection of the anal canal in women: A prospective analysis of high-risk populations

Infection with certain types of human papillomavirus (HPV) has been associated with the development of cervical and anal cancer. Worldwide, the incidence of anal cancer has increased markedly. The present study aimed to evaluate the prevalence of HPV infection of the uterine cervix and anal canal in human immunodeficiency virus (HIV)- and non-HIV-infected risk populations. Cervical and anal HPV swabs and cytology samples were collected from 287 patients at the University Hospital of Munich, Germany between 2011 and 2013. Patients were divided into HIV-negative controls (G1) and two risk groups, including HIV-negative patients with cytological abnormalities of the cervix (G2) and HIV-infected patients (G3). Data, including clinical parameters, were analysed. The risk groups had significantly more positive results for HPV in the anus (71.03 and 83.15% for G2 and G3, respectively), as compared with G1. The predominant HPV genotypes found in the anus were high-risk HPV genotypes, which were significantly correlated with concomittant cervical HPV findings. In the risk groups, a significant association between the cytological findings and HPV detection in the cervix was found, while the results of the anus revealed no significance. The results of the present study suggested that the prevalence of HPV infection in the anal canal of risk populations is high. Furthermore, patients with abnormal cervical cytology results and HIV-infected women, irrespective of their individual cervical findings, may have a risk of concomittant anal high-risk HPV infection. Based on the predominant HPV genotypes found in the study, HPV vaccination could reduce the incidence of anal cancer. Nevertheless, high-risk patients should be intensively screened for anal squamous intraepithelial abnormalities to avoid invasive cancer stages.

Tumor-Infiltrating Merkel Cell Polyomavirus-Specific T Cells Are Diverse and Associated with Improved Patient Survival

Tumor-infiltrating CD8+ T cells are associated with improved survival of patients with Merkel cell carcinoma (MCC), an aggressive skin cancer causally linked to Merkel cell polyomavirus (MCPyV). However, CD8+ T-cell infiltration is robust in only 4% to 18% of MCC tumors. We characterized the T-cell receptor (TCR) repertoire restricted to one prominent epitope of MCPyV (KLLEIAPNC, "KLL") and assessed whether TCR diversity, tumor infiltration, or T-cell avidity correlated with clinical outcome. HLA-A*02:01/KLL tetramer+ CD8+ T cells from MCC patient peripheral blood mononuclear cells (PBMC) and tumor-infiltrating lymphocytes (TIL) were isolated via flow cytometry. TCRβ (TRB) sequencing was performed on tetramer+ cells from PBMCs or TILs (n = 14) and matched tumors (n = 12). Functional avidity of T-cell clones was determined by IFNγ production. We identified KLL tetramer+ T cells in 14% of PBMC and 21% of TIL from MCC patients. TRB repertoires were strikingly diverse (397 unique TRBs were identified from 12 patients) and mostly private (only one TCRb clonotype shared between two patients). An increased fraction of KLL-specific TIL (>1.9%) was associated with significantly increased MCC-specific survival P = 0.0009). T-cell cloning from four patients identified 42 distinct KLL-specific TCRa/b pairs. T-cell clones from patients with improved MCC-specific outcomes were more avid (P < 0.05) and recognized an HLA-appropriate MCC cell line. T cells specific for a single MCPyV epitope display marked TCR diversity within and between patients. Intratumoral infiltration by MCPyV-specific T cells was associated with significantly improved MCC-specific survival, suggesting that augmenting the number or avidity of virus-specific T cells may have therapeutic benefit. Cancer Immunol Res; 5(2); 137-47. ©2017 AACR.

Preventing tumor escape by targeting a post-proteasomal trimming independent epitope

Blankenstein and colleagues describe a novel strategy to avoid tumor escape from adoptive T cell therapy.

Adoptive T cell therapy (ATT) can achieve regression of large tumors in mice and humans; however, tumors frequently recur. High target peptide-major histocompatibility complex-I (pMHC) affinity and T cell receptor (TCR)-pMHC affinity are thought to be critical to preventing relapse. Here, we show that targeting two epitopes of the same antigen in the same cancer cells via monospecific T cells, which have similar pMHC and pMHC-TCR affinity, results in eradication of large, established tumors when targeting the apparently subdominant but not the dominant epitope. Only the escape but not the rejection epitope required postproteasomal trimming, which was regulated by IFN-γ, allowing IFN-γ–unresponsive cancer variants to evade. The data describe a novel immune escape mechanism and better define suitable target epitopes for ATT.

Interleukin-7 Modulates Anti-Tumor CD8+ T Cell Responses via Its Action on Host Cells

The adoptive transfer of antigen-specific CD8+ T cells is a promising approach for the treatment of chronic viral and malignant diseases. In order to improve adoptive T cell therapy (ATT) of cancer, recent strategies aim at the antibody-based blockade of immunosuppressive signaling pathways in CD8+ T cells. Alternatively, adjuvant effects of immunostimulatory cytokines might be exploited to improve therapeutic CD8+ T cell responses. For example, Interleukin-7 (IL-7) is a potent growth, activation and survival factor for CD8+ T cells that can be used to improve virus- and tumor-specific CD8+ T cell responses. Although direct IL-7 effects on CD8+ T cells were studied extensively in numerous models, the contribution of IL-7 receptor-competent (IL-7R+) host cells remained unclear. In the current study we provide evidence that CD8+ T cell-mediated tumor rejection in response to recombinant IL-7 (rIL-7) therapy is strictly dependent on IL-7R+ host cells. On the contrary, CD8+ T cell expansion is independent of host IL-7R expression. If, however, rIL-7 therapy and peptide vaccination are combined, host IL-7R signaling is crucial for CD8+ T cell expansion. Unexpectedly, maximum CD8+ T cell expansion relies mainly on IL-7R signaling in non-hematopoietic host cells, similar to the massive accumulation of dendritic cells and granulocytes. In summary, we provide evidence that IL-7R+ host cells are major targets of rIL-7 that modulate therapeutic CD8+ T cell responses and the outcome of rIL-7-assisted ATT. This knowledge may have important implications for the design and optimization of clinical ATT protocols.

Expression of Activin During and After Chemotherapy in Peripheral Blood of Patients with Primary Breast Cancer

BACKGROUND/AIM

Activins are dimeric glycoproteins that play a significant role in reproduction and in endocrine-active tumors. The aim of this study was to evaluate the potential correlation between the concentration of activins (activin A, activin B, and activin AB) in patients receiving adjuvant chemotherapy for breast cancer.

PATIENTS AND METHODS

The serum concentration of activins in 30 patients receiving chemotherapy within the German SUCCESS A study was analyzed using different enzyme-linked immunosorbent assays at three time points: After primary surgery, but before chemotherapy; 4 weeks after the end of chemotherapy; and 2 years after chemotherapy during recurrence-free follow-up.

RESULTS

The activin concentration decreased in all patients after chemotherapy. Premenopausal patients had significantly lower concentrations of activin AB during follow-up than postmenopausal women (p=0.037). Thirteen out of 16 premenopausal patients developed chemotherapy-related amenorrhea (CRA) but did not significantly differ in their activin concentrations compared to the other premenopausal women. A positive human epidermal growth factor receptor 2/neu status was associated with a significant reduction of activin AB concentration (p=0.02), and trastuzumab treatment correlated with significantly decreased activin A concentration (p=0.012).

CONCLUSION

Serial measurements of activin A concentration might be used for monitoring trastuzumab treatment. A sudden increase of activin concentration could be an early indicator of disease recurrence.