Antigen receptor-engineered Tregs inhibit CNS autoimmunity in cell therapy using non-redundant immune mechanisms in mice

CD4⁺FOXP3⁺ Tregs are currently explored to develop cell therapies against immune‐mediated disorders, with an increasing focus on antigen receptor‐engineered Tregs. Deciphering their mode of action is necessary to identify the strengths and limits of this approach. Here, we addressed this issue in an autoimmune disease of the CNS, EAE. Following disease induction, autoreactive Tregs upregulated LAG‐3 and CTLA‐4 in LNs, while IL‐10 and amphiregulin (AREG) were increased in CNS Tregs. Using genetic approaches, we demonstrated that IL‐10, CTLA‐4, and LAG‐3 were nonredundantly required for the protective function of antigen receptor‐engineered Tregs against EAE in cell therapy whereas AREG was dispensable. Treg‐derived IL‐10 and CTLA‐4 were both required to suppress acute autoreactive CD4⁺ T‐cell activation, which correlated with disease control. These molecules also affected the accumulation in the recipients of engineered Tregs themselves, underlying complex roles for these molecules. Noteworthy, despite the persistence of the transferred Tregs and their protective effect, autoreactive T cells eventually accumulated in the spleen of treated mice. In conclusion, this study highlights the remarkable power of antigen receptor‐engineered Tregs to appropriately provide multiple suppressive factors nonredundantly necessary to prevent autoimmune attacks.

Gene Therapy "Made in Germany": A Historical Perspective, Analysis of the Status Quo, and Recommendations for Action by the German Society for Gene Therapy

Gene therapies have been successfully applied to treat severe inherited and acquired disorders. Although research and development are sufficiently well funded in Germany and while the output of scientific publications and patents is comparable with the leading nations in gene therapy, the country lags noticeably behind with regard to the number of both clinical studies and commercialized gene therapy products. In this article, we give a historical perspective on the development of gene therapy in Germany, analyze the current situation from the standpoint of the German Society for Gene Therapy (DG-GT), and define recommendations for action that would enable our country to generate biomedical and economic advantages from innovations in this sector, instead of merely importing advanced therapy medicinal products. Inter alia, we propose (1) to harmonize and simplify regulatory licensing processes to enable faster access to advanced therapies, and (2) to establish novel coordination, support and funding structures that facilitate networking of the key players. Such a center would provide the necessary infrastructure and know-how to translate cell and gene therapies to patients on the one hand, and pave the way for commercialization of these promising and innovative technologies on the other. Hence, these courses of action would not only benefit the German biotech and pharma landscape but also the society and the patients in need of new treatment options.

Generation of Epstein-Barr Virus Antigen-Specific T Cell Receptors Recognizing Immunodominant Epitopes of LMP1, LMP2A, and EBNA3C for Immunotherapy

Epstein-Barr virus (EBV) infections in healthy individuals are usually cleared by immune cells, wherein CD8⁺ T lymphocytes play the most important role. However, in some immunocompromised individuals, EBV infections can lead to the development of cancer in B, T, natural killer (NK) cells and epithelial cells. Most EBV-associated cancers express a limited number of virus-specific antigens such as latent membrane proteins (LMP1 and LMP2) and nuclear proteins (EBNA1, -2, EBNA3A, -B, -C, and EBNA-LP). These antigens represent true tumor-specific antigens and can be considered useful targets for T cell receptor (TCR) gene therapy to treat EBV-associated diseases. We used a TCR isolation platform based on a single major histocompatibility complex class I (MHC I) K562 cell library for the detection, isolation, and re-expression of TCRs targeting immunodominant peptide MHC (pMHC). Mature dendritic cells (mDCs) were pulsed with in vitro-transcribed (ivt) RNA encoding for the selected antigen to stimulate autologous T cells. The procedure allowed the mDCs to select an immunogenic epitope of the antigen for processing and presentation on the cell surface in combination with the most suitable MHC I molecule. We isolated eight EBV-specific TCRs. They recognize various pMHCs of EBV antigens LMP1, LMP2A, and EBNA3C, some of them described previously and some newly identified in this study. The TCR genes were molecularly cloned into retroviral vectors and the resultant TCR-engineered T cells secreted interferon-γ after antigen contact and were able to lyse tumor cells. The EBV-specific TCRs can be used as a basis for the generation of a TCR library, which provides a valuable source of TCRs for the production of EBV-specific T cells to treat EBV-associated diseases in patients with different MHC I types.

CD8-Specific Designed Ankyrin Repeat Proteins Improve Selective Gene Delivery into Human and Primate T Lymphocytes

Adoptive T cell immunotherapy in combination with gene therapy is a promising treatment concept for chronic infections and cancer. Recently, receptor-targeted lentiviral vectors (LVs) were shown to enable selective gene transfer into particular types of lymphocytes both in vitro and in vivo. This approach might facilitate the genetic engineering of a patient's own T lymphocytes, possibly even shifting this concept from personalized medicine to an off-the shelf therapy in future. Here, we describe novel high-affinity binders for CD8 consisting of designed ankyrin repeat proteins (DARPins), which were selected to bind to the CD8 receptor of human and nonhuman primate (NHP) cells. These binders were identified by ribosome display screening of DARPin libraries using recombinant human CD8 followed by receptor binding analysis on primary lymphocytes. CD8-targeted LVs (CD8-LVs) were then generated that delivered genes exclusively and specifically to human and NHP T lymphocytes by using the same targeting domain. These CD8-LVs were as specific for human T lymphocytes as their single-chain variable fragment-based counterpart, but they could be produced to higher titers. Moreover, they were superior in transducing cytotoxic T cells both in vitro and in vivo when equal particle numbers were applied. Since the here described CD8-LVs transduced primary T lymphocytes from NHP and human donors equally well, they offer the opportunity for preclinical studies in different animal models including large animals such as NHPs without the need for modifications in vector design.

ER-aminopeptidase 1 determines the processing and presentation of an immunotherapy-relevant melanoma epitope

Dissecting the different steps of the processing and presentation of tumor-associated antigens is a key aspect of immunotherapies enabling to tackle the immune response evasion attempts of cancer cells. The immunodominant glycoprotein gp100_209-217 epitope, which is liberated from the melanoma differentiation antigen gp100^PMEL17 , is part of immunotherapy trials. By analyzing different human melanoma cell lines, we here demonstrate that a pool of N-terminal extended peptides sharing the common minimal epitope is generated by melanoma proteasome subtypes. In vitro and in cellulo experiments indicate that ER-resident aminopeptidase 1 (ERAP1)-but not ERAP2-defines the processing of this peptide pool thereby modulating the T-cell recognition of melanoma cells. By combining the outcomes of our studies and others, we can sketch the complex processing and endogenous presentation pathway of the gp100_209-217 -containing epitope/peptides, which are produced by proteasomes and are translocated to the vesicular compartment through different pathways, where the precursor peptides that reach the endoplasmic reticulum are further processed by ERAP1. The latter step enhances the activation of epitope-specific T lymphocytes, which might be a target to improve the efficiency of anti-melanoma immunotherapy.

Efficient Non-Viral T-Cell Engineering by Sleeping Beauty Minicircles Diminishing DNA Toxicity and miRNAs Silencing the Endogenous T-Cell Receptors

Transposon-based vectors have entered clinical trials as an alternative to viral vectors for genetic engineering of T cells. However, transposon vectors require DNA transfection into T cells, which were found to cause adverse effects. T-cell viability was decreased in a dose-dependent manner, and DNA-transfected T cells showed a delayed response upon T-cell receptor (TCR) stimulation with regard to blast formation, proliferation, and surface expression of CD25 and CD28. Gene expression analysis demonstrated a DNA-dependent induction of a type I interferon response and interferon-β upregulation. By combining Sleeping Beauty transposon minicircle vectors with SB100X transposase-encoding RNA, it was possible to reduce the amount of total DNA required, and stable expression of therapeutic TCRs was achieved in >50% of human T cells without enrichment. The TCR-engineered T cells mediated effective tumor cell killing and cytokine secretion upon antigen-specific stimulation. Additionally, the Sleeping Beauty transposon system was further improved by miRNAs silencing the endogenous TCR chains. These miRNAs increased the surface expression of the transgenic TCR, diminished mispairing with endogenous TCR chains, and enhanced antigen-specific T-cell functionality. This approach facilitates the rapid non-viral generation of highly functional, engineered T cells for immunotherapy.

Unbiased Identification of T-Cell Receptors Targeting Immunodominant Peptide-MHC Complexes for T-Cell Receptor Immunotherapy

T-cell receptor (TCR) immunotherapy uses T cells engineered with new TCRs to enable detection and killing of cancer cells. Efficacy of TCR immunotherapy depends on targeting antigenic peptides that are efficiently presented by the best-suited major histocompatibility complex (MHC) molecules of cancer cells. However, efficient strategies are lacking to easily identify TCRs recognizing immunodominant peptide-MHC (pMHC) combinations utilizing any of the six possible MHC class I alleles of a cancer cell. We generated an MHC cell library and developed a platform approach to detect, isolate, and re-express TCRs specific for immunodominant pMHCs. The platform approach was applied to identify a human papillomavirus (HPV16) oncogene E5-specific TCR, recognizing a novel, naturally processed pMHC (HLA-B*15:01) and a cytomegalovirus-specific TCR targeting an immunodominant pMHC (HLA-B*07:02). The platform provides a useful tool to isolate in an unbiased manner TCRs specific for novel and immunodominant pMHC targets for use in TCR immunotherapy.

Isolation and functional characterization of hepatitis B virus-specific T-cell receptors as new tools for experimental and clinical use

T-cell therapy of chronic hepatitis B is a novel approach to restore antiviral T-cell immunity and cure the infection. We aimed at identifying T-cell receptors (TCR) with high functional avidity that have the potential to be used for adoptive T-cell therapy. To this end, we cloned HLA-A*02-restricted, hepatitis B virus (HBV)-specific T cells from patients with acute or resolved HBV infection. We isolated 11 envelope- or core-specific TCRs and evaluated them in comprehensive functional analyses. T cells were genetically modified by retroviral transduction to express HBV-specific TCRs. CD8⁺ as well as CD4⁺ T cells became effector T cells recognizing even picomolar concentrations of cognate peptide. TCR-transduced T cells were polyfunctional, secreting the cytokines interferon gamma, tumor necrosis factor alpha and interleukin-2, and effectively killed hepatoma cells replicating HBV. Notably, our collection of HBV-specific TCRs recognized peptides derived from HBV genotypes A, B, C and D presented on different HLA-A*02 subtypes common in areas with high HBV prevalence. When co-cultured with HBV-infected cells, TCR-transduced T cells rapidly reduced viral markers within two days. Our unique set of HBV-specific TCRs with different affinities represents an interesting tool for elucidating mechanisms of TCR-MHC interaction and dissecting specific anti-HBV mechanisms exerted by T cells. TCRs with high functional avidity might be suited to redirect T cells for adoptive T-cell therapy of chronic hepatitis B and HBV-induced hepatocellular carcinoma.

Chimeric PD-1:28 Receptor Upgrades Low-Avidity T cells and Restores Effector Function of Tumor-Infiltrating Lymphocytes for Adoptive Cell Therapy

Inherent intermediate- to low-affinity T-cell receptors (TCR) that develop during the natural course of immune responses may not allow sufficient activation for tumor elimination, making the majority of T cells suboptimal for adoptive T-cell therapy (ATT). TCR affinity enhancement has been implemented to provide stronger T-cell activity but carries the risk of creating undesired cross-reactivity leading to potential serious adverse effects in clinical application. We demonstrate here that engineering of low-avidity T cells recognizing a naturally processed and presented tumor-associated antigen with a chimeric PD-1:28 receptor increases effector function to levels seen with high-avidity T cells of identical specificity. Upgrading the function of low-avidity T cells without changing the TCR affinity will allow a large arsenal of low-avidity T cells previously thought to be therapeutically inefficient to be considered for ATT. PD-1:28 engineering reinstated Th1 function in tumor-infiltrating lymphocytes that had been functionally disabled in the human renal cell carcinoma environment without unleashing undesired Th2 cytokines or IL10. Involved mechanisms may be correlated to restoration of ERK and AKT signaling pathways. In mouse tumor models of ATT, PD-1:28 engineering enabled low-avidity T cells to proliferate stronger and prevented PD-L1 upregulation and Th2 polarization in the tumor milieu. Engineered T cells combined with checkpoint blockade secreted significantly more IFNγ compared with T cells without PD-1:28, suggesting a beneficial combination with checkpoint blockade therapy or other therapeutic strategies. Altogether, the supportive effects of PD-1:28 engineering on T-cell function make it an attractive tool for ATT. Cancer Res; 77(13); 3577-90. ©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.

Domain-swapped T cell receptors improve the safety of TCR gene therapy

T cells engineered to express a tumor-specific αβ T cell receptor (TCR) mediate anti-tumor immunity. However, mispairing of the therapeutic αβ chains with endogenous αβ chains reduces therapeutic TCR surface expression and generates self-reactive TCRs. We report a general strategy to prevent TCR mispairing: swapping constant domains between the α and β chains of a therapeutic TCR. When paired, domain-swapped (ds)TCRs assemble with CD3, express on the cell surface, and mediate antigen-specific T cell responses. By contrast, dsTCR chains mispaired with endogenous chains cannot properly assemble with CD3 or signal, preventing autoimmunity. We validate this approach in cell-based assays and in a mouse model of TCR gene transfer-induced graft-versus-host disease. We also validate a related approach whereby replacement of αβ TCR domains with corresponding γδ TCR domains yields a functional TCR that does not mispair. This work enables the design of safer TCR gene therapies for cancer immunotherapy.

DOI:http://dx.doi.org/10.7554/eLife.19095.001

T cells enable the immune system to recognize invading microbes and diseased cells while ignoring healthy cells. The ability of a T cell to recognize a specific microbe or diseased cell is determined by two proteins that pair to form its “T cell receptor.” The paired receptors are exported to the surface of the T cell, where they bind to infected or cancerous cells. Those T cells that produce receptors that bind healthy cells are eliminated during development.

T cells can generally distinguish between the body’s own cells and the cells of invading bacteria or other microbes. However, cancer cells are more difficult to identify because they are similar to healthy cells. Efforts to develop therapies that enhance the immune system’s ability to recognize cancer cells have had only limited success. One successful approach – known as T cell receptor gene therapy – modifies T cells to destroy cancer cells by arming them with a cancer-specific T cell receptor.

This technique produces T cells possessing two T cell receptors – the cancer-specific receptor and the one it had originally – so it is possible for proteins from the two receptors to mispair. This impedes the correct pairing of the cancer-specific T cell receptor, reducing the effectiveness of the therapy. More importantly, mispaired T cell receptors may cause the immune cells to attack healthy cells in the body, leading to autoimmune disease. To make T cell receptor gene therapy safe, the cancer-specific receptor must not mispair with the resident receptor.

Here, Bethune et al. describe a new strategy to prevent T cell receptors from mispairing. The researchers altered the arrangement of particular regions in a cancer-specific T cell receptor to make a new receptor called a domain-swapped T cell receptor (dsTCR). Like normal T cell receptors, the dsTCRs were exported to the T cell surface and were able to interact with other proteins involved in immune responses. Furthermore, T cells armed with dsTCRs were able to kill cancer cells and prevent tumor growth in mice. Unlike other cancer-specific receptors, dsTCRs did not mispair with the resident T cell receptors in mouse or human cells, and did not cause autoimmune disease in mice.

The findings of Bethune et al. show that the structure of the T cell receptor is unexpectedly robust, in that it still works even if it is modified. The next step is to study dsTCRs in more detail with the aim of optimizing them so that they might be used in human clinical trials in the future.

DOI:http://dx.doi.org/10.7554/eLife.19095.002

Targeting B-cell neoplasia with T-cell receptors recognizing a CD20-derived peptide on patient-specific HLA

T cells engineered to express chimeric antigen receptors (CARs) targeted to CD19 are effective in treatment of B-lymphoid malignancies. However, CARs recognize all CD19 positive (pos) cells, and durable responses are linked to profound depletion of normal B cells. Here, we designed a strategy to specifically target patient B cells by utilizing the fact that T-cell receptors (TCRs), in contrast to CARs, are restricted by HLA. Two TCRs recognizing a peptide from CD20 (SLFLGILSV) in the context of foreign HLA-A*02:01 (CD20p/HLA-A2) were expressed as 2A-bicistronic constructs. T cells re-directed with the A23 and A94 TCR constructs efficiently recognized malignant HLA-A2(pos) B cells endogenously expressing CD20, including patient-derived follicular lymphoma and chronic lymphocytic leukemia (CLL) cells. In contrast, a wide range of HLA-A2(pos)CD20(neg) cells representing different tissue origins, and HLA-A2(neg)CD20(pos) cells, were not recognized. Cytotoxic T cells re-directed with CD20p/HLA-A2-specific TCRs or CD19 CARs responded with similar potencies to cells endogenously expressing comparable levels of CD20 and CD19. The CD20p/HLA-A2-specific TCRs recognized CD20p bound to HLA-A2 with high functional avidity. The results show that T cells expressing CD20p/HLA-A2-specific TCRs efficiently and specifically target B cells. When used in context of an HLA-haploidentical allogeneic stem cell transplantation where the donor is HLA-A2(neg) and the patient HLA-A2(pos), these T cells would selectively kill patient-derived B cells and allow reconstitution of the B-cell compartment with HLA-A2(neg) donor cells. These results should pave the way for clinical testing of T cells genetically engineered to target malignant B cells without permanent depletion of normal B cells.

Abstract 3202: Transgenic antigen-specific, HLA-A*02:01-allo-restricted cytotoxic T cells recognize tumor-associated target antigen STEAP1 with high specificity

Background: Pediatric cancers, including Ewing sarcoma (ES), are only weakly immunogenic and the tumor-patients immune system often is devoid of effector T cells for tumor elimination. Based on expression profiling technology targetable tumor associated antigens (TAA) are identified and exploited for engineered T cell therapy. Here, the specific recognition and lytic potential of transgenic, allo-restricted CD8+ T cells directed against the ES-associated antigen STEAP1 was examined.

Methods: Following repetitive STEAP1130 peptide-driven stimulations with HLA-A*02:01+ dendritic cells, allo-restricted HLA-A*02:01- CD8+ T cells were sorted with HLA-A*02:01/peptide multimers and expanded by limiting dilution. After functional analysis of suitable T cell clones via ELISpot, flow cytometry and xCELLigence assay, TCR α- and β-chains were identified. They were cloned into retroviral vectors, codon optimized, transfected into HLA-A*02:01- primary T cell populations and tested again for specificity and lytic capacity in vitro and in a Rag2-/-γc-/- mouse model.

Results: Initially generated and transgenic T cells specifically recognized STEAP1130-pulsed or transfected cells in the context of HLA-A*02:01 with minimal cross-reactivity as determined by specific IFNγ release. They lysed cells and inhibited growth of HLA-A*02:01+ ES lines more effectively than HLA-A*02:01- ES lines. In vivo tumor growth was inhibited more effective with transgenic STEAP1130-specific T cells than with unspecific T cells.

Conclusion: Our results identify TCRs capable of recognizing and inhibiting growth of STEAP1 expressing HLA-A*02:01+ ES cells in vitro and in vivo in a highly restricted manner. As STEAP1 is overexpressed in a wide variety of cancers, we anticipate these STEAP1-specific TCRs to be potentially useful for immunotherapy of other STEAP1 expressing tumors.

Citation Format: David Schirmer, Richard Klar, Oxana Schmidt, Dirk Wohlleber, Wolfgang Uckert, Uwe Thiel, Felix Bohne, Dirk H. Busch, Angela M. Krackhardt, Stefan Burdach, Günther H. Richter. Transgenic antigen-specific, HLA-A*02:01-allo-restricted cytotoxic T cells recognize tumor-associated target antigen STEAP1 with high specificity. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3202.

ERK1 as a Therapeutic Target for Dendritic Cell Vaccination against High-Grade Gliomas

Glioma regression requires the recruitment of potent antitumor immune cells into the tumor microenvironment. Dendritic cells (DC) play a role in immune responses to these tumors. The fact that DC vaccines do not effectively combat high-grade gliomas, however, suggests that DCs need to be genetically modified specifically to promote their migration to tumor relevant sites. Previously, we identified extracellular signal-regulated kinase (ERK1) as a regulator of DC immunogenicity and brain autoimmunity. In the current study, we made use of modern magnetic resonance methods to study the role of ERK1 in regulating DC migration and tumor progression in a model of high-grade glioma. We found that ERK1-deficient mice are more resistant to the development of gliomas, and tumor growth in these mice is accompanied by a higher infiltration of leukocytes. ERK1-deficient DCs exhibit an increase in migration that is associated with sustained Cdc42 activation and increased expression of actin-associated cytoskeleton-organizing proteins. We also demonstrated that ERK1 deletion potentiates DC vaccination and provides a survival advantage in high-grade gliomas. Considering the therapeutic significance of these results, we propose ERK1-deleted DC vaccines as an additional means of eradicating resilient tumor cells and preventing tumor recurrence. Mol Cancer Ther; 15(8); 1975-87. ©2016 AACR.

Transgenic antigen-specific, HLA-A*02:01-allo-restricted cytotoxic T cells recognize tumor-associated target antigen STEAP1 with high specificity

Pediatric cancers, including Ewing sarcoma (ES), are only weakly immunogenic and the tumor-patients' immune system often is devoid of effector T cells for tumor elimination. Based on expression profiling technology, targetable tumor-associated antigens (TAA) are identified and exploited for engineered T-cell therapy. Here, the specific recognition and lytic potential of transgenic allo-restricted CD8(+) T cells, directed against the ES-associated antigen 6-transmembrane epithelial antigen of the prostate 1 (STEAP1), was examined. Following repetitive STEAP1(130) peptide-driven stimulations with HLA-A*02:01(+) dendritic cells (DC), allo-restricted HLA-A*02:01(-) CD8(+) T cells were sorted with HLA-A*02:01/peptide multimers and expanded by limiting dilution. After functional analysis of suitable T cell clones via ELISpot, flow cytometry and xCELLigence assay, T cell receptors' (TCR) α- and β-chains were identified, cloned into retroviral vectors, codon optimized, transfected into HLA-A*02:01(-) primary T cell populations and tested again for specificity and lytic capacity in vitro and in a Rag2(-/-)γc(-/-) mouse model. Initially generated transgenic T cells specifically recognized STEAP1(130)-pulsed or transfected cells in the context of HLA-A*02:01 with minimal cross-reactivity as determined by specific interferon-γ (IFNγ) release, lysed cells and inhibited growth of HLA-A*02:01(+) ES lines more effectively than HLA-A*02:01(-) ES lines. In vivo tumor growth was inhibited more effectively with transgenic STEAP1(130)-specific T cells than with unspecific T cells. Our results identify TCRs capable of recognizing and inhibiting growth of STEAP1-expressing HLA-A*02:01(+) ES cells in vitro and in vivo in a highly restricted manner. As STEAP1 is overexpressed in a wide variety of cancers, we anticipate these STEAP1-specific TCRs to be potentially useful for immunotherapy of other STEAP1-expressing tumors.

Targeting human melanoma neoantigens by T cell receptor gene therapy

In successful cancer immunotherapy, T cell responses appear to be directed toward neoantigens created by somatic mutations; however, direct evidence that neoantigen-specific T cells cause regression of established cancer is lacking. Here, we generated T cells expressing a mutation-specific transgenic T cell receptor (TCR) to target different immunogenic mutations in cyclin-dependent kinase 4 (CDK4) that naturally occur in human melanoma. Two mutant CDK4 isoforms (R24C, R24L) similarly stimulated T cell responses in vitro and were analyzed as therapeutic targets for TCR gene therapy. In a syngeneic HLA-A2-transgenic mouse model of large established tumors, we found that both mutations differed dramatically as targets for TCR-modified T cells in vivo. While T cells expanded efficiently and produced IFN-γ in response to R24L, R24C failed to induce an effective antitumor response. Such differences in neoantigen quality might explain why cancer immunotherapy induces tumor regression in some individuals, while others do not respond, despite similar mutational load. We confirmed the validity of the in vivo model by showing that the melan-A-specific (MART-1-specific) TCR DMF5 induces rejection of tumors expressing analog, but not native, MART-1 epitopes. The described model allows identification of those neoantigens in human cancer that serve as suitable T cell targets and may help to predict clinical efficacy.

Eradication of Large Solid Tumors by Gene Therapy with a T-Cell Receptor Targeting a Single Cancer-Specific Point Mutation

PURPOSE

Cancers usually contain multiple unique tumor-specific antigens produced by single amino acid substitutions (AAS) and encoded by somatic nonsynonymous single nucleotide substitutions. We determined whether adoptively transferred T cells can reject large, well-established solid tumors when engineered to express a single type of T-cell receptor (TCR) that is specific for a single AAS.

EXPERIMENTAL DESIGN

By exome and RNA sequencing of an UV-induced tumor, we identified an AAS in p68 (mp68), a co-activator of p53. This AAS seemed to be an ideal tumor-specific neoepitope because it is encoded by a trunk mutation in the primary autochthonous cancer and binds with highest affinity to the MHC. A high-avidity mp68-specific TCR was used to genetically engineer T cells as well as to generate TCR-transgenic mice for adoptive therapy.

RESULTS

When the neoepitope was expressed at high levels and by all cancer cells, their direct recognition sufficed to destroy intratumor vessels and eradicate large, long-established solid tumors. When the neoepitope was targeted as autochthonous antigen, T cells caused cancer regression followed by escape of antigen-negative variants. Escape could be thwarted by expressing the antigen at increased levels in all cancer cells or by combining T-cell therapy with local irradiation. Therapeutic efficacies of TCR-transduced and TCR-transgenic T cells were similar.

CONCLUSIONS

Gene therapy with a single TCR targeting a single AAS can eradicate large established cancer, but a uniform expression and/or sufficient levels of the targeted neoepitope or additional therapy are required to overcome tumor escape. Clin Cancer Res; 22(11); 2734-43. ©2015 AACRSee related commentary by Liu, p. 2602.

T Cells Engineered to Express a T-Cell Receptor Specific for Glypican-3 to Recognize and Kill Hepatoma Cells In Vitro and in Mice

BACKGROUND & AIMS

Cancer therapies are being developed based on our ability to direct T cells against tumor antigens. Glypican-3 (GPC3) is expressed by 75% of all hepatocellular carcinomas (HCC), but not in healthy liver tissue or other organs. We aimed to generate T cells with GPC3-specific receptors that recognize HCC and used them to eliminate GPC3-expressing xenograft tumors grown from human HCC cells in mice.

METHODS

We used mass spectrometry to obtain a comprehensive peptidome from GPC3-expressing hepatoma cells after immune-affinity purification of human leukocyte antigen (HLA)-A2 and bioinformatics to identify immunodominant peptides. To circumvent GPC3 tolerance resulting from fetal expression, dendritic cells from HLA-A2-negative donors were cotransfected with GPC3 and HLA-A2 RNA to stimulate and expand antigen-specific T cells.

RESULTS

Peptide GPC3367 was identified as a predominant peptide on HLA-A2. We used A2-GPC3367 multimers to detect, select for, and clone GPC3-specific T cells. These clones bound the A2-GPC3367 multimer and secreted interferon-γ when cultured with GPC3367, but not with control peptide-loaded cells. By genomic sequencing of these T-cell clones, we identified a gene encoding a dominant T-cell receptor. The gene was cloned and the sequence was codon optimized and expressed from a retroviral vector. Primary CD8(+) T cells that expressed the transgenic T-cell receptor specifically bound GPC3367 on HLA-A2. These T cells killed GPC3-expressing hepatoma cells in culture and slowed growth of HCC xenograft tumors in mice.

CONCLUSIONS

We identified a GPC3367-specific T-cell receptor. Expression of this receptor by T cells allows them to recognize and kill GPC3-positive hepatoma cells. This finding could be used to advance development of adoptive T-cell therapy for HCC.

Codon optimization of the human papillomavirus E7 oncogene induces a CD8+ T cell response to a cryptic epitope not harbored by wild-type E7

Codon optimization of nucleotide sequences is a widely used method to achieve high levels of transgene expression for basic and clinical research. Until now, immunological side effects have not been described. To trigger T cell responses against human papillomavirus, we incubated T cells with dendritic cells that were pulsed with RNA encoding the codon-optimized E7 oncogene. All T cell receptors isolated from responding T cell clones recognized target cells expressing the codon-optimized E7 gene but not the wild type E7 sequence. Epitope mapping revealed recognition of a cryptic epitope from the +3 alternative reading frame of codon-optimized E7, which is not encoded by the wild type E7 sequence. The introduction of a stop codon into the +3 alternative reading frame protected the transgene product from recognition by T cell receptor gene-modified T cells. This is the first experimental study demonstrating that codon optimization can render a transgene artificially immunogenic through generation of a dominant cryptic epitope. This finding may be of great importance for the clinical field of gene therapy to avoid rejection of gene-corrected cells and for the design of DNA- and RNA-based vaccines, where codon optimization may artificially add a strong immunogenic component to the vaccine.

Identification of human T-cell receptors with optimal affinity to cancer antigens using antigen-negative humanized mice

Identifying T-cell receptors (TCRs) that bind tumor-associated antigens (TAAs) with optimal affinity is a key bottleneck in the development of adoptive T-cell therapy of cancer. TAAs are unmutated self proteins, and T cells bearing high-affinity TCRs specific for such antigens are commonly deleted in the thymus. To identify optimal-affinity TCRs, we generated antigen-negative humanized mice with a diverse human TCR repertoire restricted to the human leukocyte antigen (HLA) A*02:01 (ref. 3). These mice were immunized with human TAAs, for which they are not tolerant, allowing induction of CD8⁺ T cells with optimal-affinity TCRs. We isolate TCRs specific for the cancer/testis (CT) antigen MAGE-A1 (ref. 4) and show that two of them have an anti-tumor effect in vivo. By comparison, human-derived TCRs have lower affinity and do not mediate substantial therapeutic effects. We also identify optimal-affinity TCRs specific for the CT antigen NY-ESO. Our humanized mouse model provides a useful tool for the generation of optimal-affinity TCRs for T-cell therapy.

IFN-γ regulates CD8+ memory T cell differentiation and survival in response to weak, but not strong, TCR signals

In response to primary Ag contact, naive mouse CD8(+) T cells undergo clonal expansion and differentiate into effector T cells. After pathogen clearance, most effector T cells die, and only a small number of memory T cell precursors (TMPs) survive to form a pool of long-lived memory T cells (TMs). Although high- and low-affinity CD8(+) T cell clones are recruited into the primary response, the TM pool consists mainly of high-affinity clones. It remains unclear whether the more efficient expansion of high-affinity clones and/or cell-intrinsic processes exclude low-affinity T cells from the TM pool. In this article, we show that the lack of IFN-γR signaling in CD8(+) T cells promotes TM formation in response to weak, but not strong, TCR agonists. The IFN-γ-sensitive accumulation of TMs correlates with reduced mammalian target of rapamycin activation and the accumulation of long-lived CD62L(hi)Bcl-2(hi)Eomes(hi) TMPs. Reconstitution of mammalian target of rapamycin or IFN-γR signaling is sufficient to block this process. Hence, our data suggest that IFN-γR signaling actively blocks the formation of TMPs responding to weak TCR agonists, thereby promoting the accumulation of high-affinity T cells finally dominating the TM pool.

CD8 T cell tolerance to a tumor-associated self-antigen is reversed by CD4 T cells engineered to express the same T cell receptor

Ag receptors used for cancer immunotherapy are often directed against tumor-associated Ags also expressed in normal tissues. Targeting of such Ags can result in unwanted autoimmune attack of normal tissues or induction of tolerance in therapeutic T cells. We used a murine model to study the phenotype and function of T cells redirected against the murine double minute protein 2 (MDM2), a tumor-associated Ag that shows low expression in many normal tissues. Transfer of MDM2-TCR–engineered T cells into bone marrow chimeric mice revealed that Ag recognition in hematopoietic tissues maintained T cell function, whereas presentation of MDM2 in nonhematopoietic tissues caused reduced effector function. TCR-engineered CD8⁺ T cells underwent rapid turnover, downmodulated CD8 expression, and lost cytotoxic function. We found that MDM2-TCR–engineered CD4⁺ T cells provided help and restored cytotoxic function of CD8⁺ T cells bearing the same TCR. Although the introduction of the CD8 coreceptor enhanced the ability of CD4⁺ T cells to recognize MDM2 in vitro, the improved self-antigen recognition abolished their ability to provide helper function in vivo. The data indicate that the same class I–restricted TCR responsible for Ag recognition and tolerance induction in CD8⁺ T cells can, in the absence of the CD8 coreceptor, elicit CD4 T cell help and partially reverse tolerance. Thus MHC class I–restricted CD4⁺ T cells may enhance the efficacy of therapeutic TCR-engineered CD8⁺ T cells and can be readily generated with the same TCR.

Abstract 2803: Preclinical models for the development of HER2-specific T-cell therapy

The adoptive transfer of autologous, tumor-reactive T cells to treat cancer patients is a promising tool in immunotherapy. One of our clinical goals is the adoptive transfer of autologous T cells transduced with a human epidermal growth factor receptor 2 (HER2)-directed TCR in patients with advanced breast cancer. We successfully established cytotoxic T-cell clones and CD8+ T cells transduced with a TCR specific for the tumor and self-antigen HER2 and tested their lytic capability in vitro.

Since HER2 is a self antigen that is not only expressed by malignant cells but also in normal tissue, e.g. the heart, we tested the recognition of normal HER2+-cell lines by HER2-directed T cells in vitro. For this purpose HER2-directed CD8+ T cells were used to analyze the recognition and lysis of HLA-A2+ cardiomyocyte cell lines in IFNγ-ELISA and chromium-release-assay. Compared to HER2-overexpressing breast cancer cell lines recognition of the cardiomyocytes by HER2-directed T cells was much lower. From these data we hypothesize that there might be a therapeutic window, which may allow the treatment with HER2-directed T cells without having any unwanted side effects, like cardiac dysfunction.

To further analyse this, we are establishing a mouse model using HLA-A2-transgenic NOD/SCID-HHDII mice. We injected a human breast cancer cell line s.c. into NOD/SCID-HHDII mice, waited until a solid tumor had been established, and evaluated the responsiveness of tumor cells towards adoptive T cell transfer. Our data show an improvement in tumor growth inhibition after adoptive T cell transfer and IL-15 treatment; however, no significant tumor reduction was observed yet. Furthermore, in the NOD/SCID-HHDII mice we are able to detect potential autoimmune reactions. Subsequent experiments will analyze the combination therapy of transferred HER2-directed T cells with HER2-directed antibody treatment (Trastuzumab and/or Pertuzumab) in order to increase the anti-tumor response. These pre-clinical studies, as well as the in vitro tests, are important for the evaluation of possible unwanted side effects after adoptive transfer of TCR-transduced T cells specific for self-antigens like HER2.

Citation Format: Christiane Kreutzer, Heinke Conrad, Peter Meyerhuber, Wolfgang Uckert, Philipp Beckhove, Helga Bernhard. Preclinical models for the development of HER2-specific T-cell therapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2803. doi:10.1158/1538-7445.AM2014-2803

Manufacture of gene-modified human T-cells with a memory stem/central memory phenotype

Advances in genetic engineering have made it possible to generate human T-cell products that carry desired functionalities, such as the ability to recognize cancer cells. The currently used strategies for the generation of gene-modified T-cell products lead to highly differentiated cells within the infusion product, and on the basis of data obtained in preclinical models, this is likely to impact the efficacy of these products. We set out to develop a good manufacturing practice (GMP) protocol that yields T-cell receptor (TCR) gene-modified T-cells with more favorable properties for clinical application. Here, we show the robust clinical-scale production of human peripheral blood T-cells with an early memory phenotype that express a MART-1-specific TCR. By combining selection and stimulation using anti-CD3/CD28 beads for retroviral transduction, followed by expansion in the presence of IL-7 and IL-15, production of a well-defined clinical-scale TCR gene-modified T-cell product could be achieved. A major fraction of the T-cells generated in this fashion were shown to coexpress CD62L and CD45RA, and express CD27 and CD28, indicating a central memory or memory stemlike phenotype. Furthermore, these cells produced IFNγ, TNFα, and IL-2 and displayed cytolytic activity against target cells expressing the relevant antigen. The T-cell products manufactured by this robust and validated GMP production process are now undergoing testing in a phase I/IIa clinical trial in HLA-A*02:01 MART-1-positive advanced stage melanoma patients. To our knowledge, this is the first clinical trial protocol in which the combination of IL-7 and IL-15 has been applied for the generation of gene-modified T-cell products.

Misinitiation of intrathymic MART-1 transcription and biased TCR usage explain the high frequency of MART-1-specific T cells

Immunity to tumor differentiation antigens, such as melanoma antigen recognized by T cells 1 (MART-1), has been comprehensively studied. Intriguingly, CD8(+) T cells specific for the MART-1(26(27)-35) epitope in the context of HLA-A0201 are about 100 times more abundant compared with T cells specific for other tumor-associated antigens. Moreover, MART-1-specific CD8(+) T cells show a highly biased usage of the Vα-region gene TRAV12-2. Here, we provide independent support for this notion, by showing that the combinatorial pairing of different TCRα- and TCRβ- chains derived from HLA-A2-MART-1(26-35) -specific CD8(+) T-cell clones is unusually permissive in conferring MART-1 specificity, provided the CDR1α TRAV12-2 region is used. Whether TCR bias alone accounts for the unusual abundance of HLA-A2-MART-1(26-35) -specific CD8(+) T cells has remained conjectural. Here, we provide an alternative explanation: misinitiated transcription of the MART-1 gene resulting in truncated mRNA isoforms leads to lack of promiscuous transcription of the MART-1(26-35) epitope in human medullary thymic epithelial cells and, consequently, evasion of central self-tolerance toward this epitope. Thus, biased TCR usage and leaky central tolerance might act in an independent and additive manner to confer high frequency of MART-1(26-35) -specific CD8(+) T cells.

Targeting high-grade B cell lymphoma with CD19-specific T cells

Adoptive T cell therapy is an important additional treatment option for malignant diseases resistant to chemotherapy. Using a murine high-grade B cell lymphoma model, we have addressed the question whether the B cell differentiation antigen CD19 can act as rejection antigen. CD19(-/-) mice inoculated with CD19(+) B cell lymphoma cells showed higher survival rates than WT mice and were protected against additional tumor challenge. T cell depletion prior to tumor transfer completely abolished the protective response. By heterotypic vaccination of CD19(-/-) mice against murine CD19, survival after tumor challenge was significantly increased. To define protective epitopes within the CD19 molecule, T cells collected from mice that had survived the tumor transfer were analyzed for IFNγ secretion in response to CD19-derived peptides. The majority of mice exhibited a CD4(+) T cell response to CD19 peptide 27, which was the most dominant epitope after CD19 vaccination. A peptide 27-specific CD4(+) T cell line protected CD19(-/-) mice against challenge with CD19(+) lymphoma and also cured a significant proportion of WT mice from recurrent disease in a model of minimal residual disease after chemotherapy. In conclusion, our data highlight CD19-specific CD4(+) T cells for adoptive T cell therapy of B cell lymphomas.

TCR-engineered T cells: a model of inducible TCR expression to dissect the interrelationship between two TCRs

TCR gene modified T cells for adoptive therapy simultaneously express the Tg TCR and the endogenous TCR, which might lead to mispaired TCRs with harmful unknown specificity and to a reduced function of TCR-Tg T cells. We generated dual TCR T cells in two settings in which either TCR was constitutively expressed by a retroviral promoter while the second TCR expression was regulable by a Tet-on system. Constitutively expressed TCR molecules were reduced on the cell surface depending on the induced TCR expression leading to strongly hampered function. Besides that, using fluorescence resonance energy transfer we detected mispaired TCR dimers and different pairing behaviors of individual TCR chains with a mutual influence on TCR chain expression. The loss of function and mispairing could not be avoided by changing the TCR expression level or by introduction of an additional cysteine bridge. However, in polyclonal T cells, optimized TCR formats (cysteineization, codon optimization) enhanced correct pairing and function. We conclude from our data that (i) the level of mispairing depends on the individual TCRs and is not reduced by increasing the level of one TCR, and (ii) modifications (cysteineization, codon optimization) improve correct pairing but do not completely exclude mispairing (cysteineization).

Plasticity in the contribution of T cell receptor variable region residues to binding of peptide-HLA-A2 complexes

One hypothesis accounting for major histocompatibility complex (MHC) restriction by T cell receptors (TCRs) holds that there are several evolutionary conserved residues in TCR variable regions that contact MHC. While this "germline codon" hypothesis is supported by various lines of evidence, it has been difficult to test. The difficulty stems in part from the fact that TCRs exhibit low affinities for pep/MHC, thus limiting the range of binding energies that can be assigned to these key interactions using mutational analyses. To measure the magnitude of binding energies involved, here we used high-affinity TCRs engineered by mutagenesis of CDR3. The TCRs included a high-affinity, MART-1/HLA-A2-specific single-chain TCR and two other high-affinity TCRs that all contain the same Vα region and recognize the same MHC allele (HLA-A2), with different peptides and Vβ regions. Mutational analysis of residues in CDR1 and CDR2 of the three Vα2 regions showed the importance of the key germline codon residue Y51. However, two other proposed key residues showed significant differences among the TCRs in their relative contributions to binding. With the use of single-position, yeast-display libraries in two of the key residues, MART-1/HLA-A2 selections also revealed strong preferences for wild-type germline codon residues, but several alternative residues could also accommodate binding and, hence, MHC restriction. Thus, although a single residue (Y51) could account for a proportion of the energy associated with positive selection (i.e., MHC restriction), there is significant plasticity in requirements for particular side chains in CDR1 and CDR2 and in their relative binding contributions among different TCRs.

T cells expressing a chimeric antigen receptor that binds hepatitis B virus envelope proteins control virus replication in mice

BACKGROUND & AIMS

Antiviral agents suppress hepatitis B virus (HBV) replication but do not clear the infection. A strong effector T-cell response is required to eradicate HBV, but this does not occur in patients with chronic infection. T cells might be directed toward virus-infected cells by expressing HBV-specific receptors and thereby clear HBV and help to prevent development of liver cancer. In mice, we studied whether redirected T cells can engraft after adoptive transfer, without prior T-cell depletion, and whether the large amounts of circulating viral antigens inactivate the transferred T cells or lead to uncontrolled immune-mediated damage.

METHODS

CD8(+) T cells were isolated from mice and stimulated using an optimized protocol. Chimeric antigen receptors (CARs) that bind HBV envelope proteins (S-CAR) and activate T cells were expressed on the surface of cells using retroviral vectors. S-CAR-expressing CD8(+) T cells, which carried the marker CD45.1, were injected into CD45.2(+) HBV transgenic mice. We compared these mice with mice that received CD8(+) T cells induced by vaccination, cells that express a CAR without a proper signaling domain, or cells that express a CAR that does not bind HBV proteins (controls).

RESULTS

CD8(+) T cells that expressed HBV-specific CARs recognized different HBV subtypes and were able to engraft and expand in immune-competent HBV transgenic mice. After adoptive transfer, the S-CAR-expressing T cells localized to and functioned in the liver and rapidly and efficiently controlled HBV replication compared with controls, causing only transient liver damage. The large amount of circulating viral antigen did not impair or overactivate the S-CAR-grafted T cells.

CONCLUSIONS

T cells with a CAR specific for HBV envelope proteins localize to the liver in mice to reduce HBV replication, causing only transient liver damage. This immune cell therapy might be developed for patients with chronic hepatitis B, regardless of their HLA type.

TCR-ligand koff rate correlates with the protective capacity of antigen-specific CD8+ T cells for adoptive transfer

Adoptive immunotherapy is a promising therapeutic approach for the treatment of chronic infections and cancer. T cells within a certain range of high avidity for their cognate ligand are believed to be most effective. T cell receptor (TCR) transfer experiments indicate that a major part of avidity is hardwired within the structure of the TCR. Unfortunately, rapid measurement of structural avidity of TCRs is difficult on living T cells. We developed a technology where dissociation (koff rate) of truly monomeric peptide-major histocompatibility complex (pMHC) molecules bound to surface-expressed TCRs can be monitored by real-time microscopy in a highly reliable manner. A first evaluation of this method on distinct human cytomegalovirus (CMV)-specific T cell populations revealed unexpected differences in the koff rates. CMV-specific T cells are currently being evaluated in clinical trials for efficacy in adoptive immunotherapy; therefore, determination of koff rates could guide selection of the most effective donor cells. Indeed, in two different murine infection models, we demonstrate that T cell populations with lower koff rates confer significantly better protection than populations with fast koff rates. These data indicate that koff rate measurements can improve the predictability of adoptive immunotherapy and provide diagnostic information on the in vivo quality of T cells.

MHC multimer-guided and cell culture-independent isolation of functional T cell receptors from single cells facilitates TCR identification for immunotherapy

Adoptive therapy using T cells redirected to target tumor- or infection-associated antigens is a promising strategy that has curative potential and broad applicability. In order to accelerate the screening process for suitable antigen-specific T cell receptors (TCRs), we developed a new approach circumventing conventional in vitro expansion-based strategies. Direct isolation of paired full-length TCR sequences from non-expanded antigen-specific T cells was achieved by the establishment of a highly sensitive PCR-based T cell receptor single cell analysis method (TCR-SCAN). Using MHC multimer-labeled and single cell-sorted HCMV-specific T cells we demonstrate a high efficacy (approximately 25%) and target specificity of TCR-SCAN receptor identification. In combination with MHC-multimer based pre-enrichment steps, we were able to isolate TCRs specific for the oncogenes Her2/neu and WT1 even from very small populations (original precursor frequencies of down to 0.00005% of CD3(+) T cells) without any cell culture step involved. Genetic re-expression of isolated receptors demonstrates their functionality and target specificity. We believe that this new strategy of TCR identification may provide broad access to specific TCRs for therapeutically relevant T cell epitopes.

NY-ESO-1 antigen-reactive T cell receptors exhibit diverse therapeutic capability

The cancer-testis antigen NY-ESO-1 has been used as a target for different immunotherapies like vaccinations and adoptive transfer of antigen-specific cytotoxic T cells, as it is expressed in various tumor types and has limited expression in normal cells. The in vitro generation of T cells with defined antigen specificity by T cell receptor (TCR) gene transfer is an established method to create cells for immunotherapy. However, an extensive characterization of TCR which are candidates for treatment of patients is crucial for successful therapies. The TCR has to be efficiently expressed, their affinity to the desired antigen should be high enough to recognize low amounts of endogenously processed peptides on tumor cells, and the TCR should not be cross-reactive to other antigens. We characterized three NY-ESO-1 antigen-reactive cytotoxic T lymphocyte clones which were generated by different approaches of T cell priming (autologous, allogeneic), and transferred their TCR into donor T cells for more extensive evaluations. Although one TCR most efficiently bound MHC-multimers loaded with NY-ESO-1 peptide, T cells expressing this transgenic TCR were not able to recognize endogenously processed antigen. A second TCR recognized HLA-A2 independent of the bound peptide beside its much stronger recognition of NY-ESO-1 bound to HLA-A2. A third TCR displayed an intermediate but peptide-specific performance in all functional assays and, therefore, is the most promising candidate TCR for further clinical development. Our data indicate that multiple parameters of TCR gene-modified T cells have to be evaluated to identify an optimal TCR candidate for adoptive therapy.

Human antitumor CD8+ T cells producing Th1 polycytokines show superior antigen sensitivity and tumor recognition

Adoptive transfer of T cells expressing transgenic TCR with antitumor specificity provides a hopeful new therapy for patients with advanced cancer. To fulfill a large need for TCR with high affinity and specificity for various tumor entities, we sought to identify parameters for rapid selection of CTL clones with suitable characteristics. Twelve CTL clones displaying different Ag sensitivities for the same peptide-MHC epitope of the melanoma-associated Ag tyrosinase were analyzed in detail. Better MHC-multimer binding and slower multimer release are thought to reflect stronger TCR-peptide-MHC interactions; thus, these parameters would seem well suited to identify higher avidity CTL. However, large disparities were found comparing CTL multimer binding with peptide sensitivity. In contrast, CD8(+) CTL with superior Ag sensitivity mediated good tumor cytotoxicity and also secreted the triple combination of IFN-γ, IL-2, and TNF-α, representing a Th1 pattern often missing in lower avidity CTL. Furthermore, recipient lymphocytes were imbued with high Ag sensitivity, superior tumor recognition, as well as capacity for Th1 polycytokine secretion after transduction with the TCR of a high-avidity CTL. Thus, Th1 polycytokine secretion served as a suitable parameter to rapidly demark cytotoxic CD8(+) T cell clones for further TCR evaluation.

Transmitter- and hormone-activated Ca(2+) responses in adult microglia/brain macrophages in situ recorded after viral transduction of a recombinant Ca(2+) sensor

In vitro studies show that microglia, the resident immune cells of the brain, express neurotransmitter and neuropeptide receptors which are linked to Ca(2+) signaling. Here we describe an approach to obtain Ca(2+) recordings from microglia in situ. We injected a retrovirus encoding a calcium sensor into the cortex of mice 2 days after stimulation of microglial proliferation by a stab wound injury. Microglial cells were identified with tomato lectin in acute slices prepared 3, 6, 21 and 42 days after the injury. The membrane current profile and the ameboid morphology indicated that microglial cells were activated at day 6 while at day 42 they resembled resting microglia. We recorded transient Ca(2+) responses to application of ATP, endothelin-1, substance P, histamine and serotonin. The fluorescence amplitude of ATP was increased only at day 6 compared to other time points, while responses to all other ligands did not vary. Only half of the microglial cells that responded to ATP also responded to endothelin-1, serotonin and histamine. Substance P, in contrast, showed a complete overlap with the ATP responding microglial population at day 6, at day 42 this population was reduced to 55%. Cultured cells were less responsive to these ligands. This study shows that in situ microglia consist of heterogeneous populations with respect to their sensitivity to neuropeptides and -transmitters.

MHC-restricted fratricide of human lymphocytes expressing survivin-specific transgenic T cell receptors

The apoptosis inhibitor protein survivin is overexpressed in many tumors, making it a candidate target molecule for various forms of immunotherapy. To explore survivin as a target antigen for adoptive T cell therapy using lymphocytes expressing survivin-specific transgenic T cell receptors (Tg-TCRs), we isolated HLA-A2-allorestricted survivin-specific T cells with high functional avidity. Lymphocytes expressing Tg-TCRs were derived from these T cells and specifically recognized HLA-A2+ survivin+ tumor cells. Surprisingly, HLA-A2+ but not HLA-A2- lymphocytes expressing Tg-TCRs underwent extensive apoptosis over time. This demise was caused by HLA-A2-restricted fratricide that occurred due to survivin expression in lymphocytes, which created ligands for Tg-TCR recognition. Therefore, survivin-specific TCR gene therapy would be limited to application in HLA-A2-mismatched stem cell transplantation. We also noted that lymphocytes that expressed survivin-specific Tg-TCRs killed T cell clones of various specificities derived from HLA-A2+ but not HLA-A2- donors. These results raise a general question regarding the development of cancer vaccines that target proteins that are also expressed in activated lymphocytes, since induction of high-avidity T cells that expand in lymph nodes following vaccination or later accumulate at tumor sites might limit themselves by self-MHC-restricted fratricide while at the same time inadvertently eliminating neighboring T cells of other specificities.

Enhanced T cell receptor gene therapy for cancer

IMPORTANCE OF THE FIELD

Adoptive therapy with T cell receptor- (TCR-) redirected T cells has shown efficacy in mouse tumor models and first responses in cancer patients. One prerequisite to elicit effective anti-tumor reactivity is the transfer of high-avidity T cells. Their generation, however, faces several technical difficulties. Target antigens are often expressed at low levels and their recognition requires the use of high-affine receptors. Yet, mainly low-affinity TCRs have been isolated from tumor-infiltrating lymphocytes. Furthermore, upon transfer into a T cell the introduced receptor has to compete with the endogenous TCR.

AREAS COVERED IN THIS REVIEW

This review discusses how the functional avidity of TCR-modified T cells can be enhanced by i) increasing the amount of introduced TCR heterodimers on the cell surface; and ii) generating receptors with high affinity. Risks of TCR gene therapy and possible safety mechanisms are discussed.

WHAT THE READER WILL GAIN

The reader will gain an overview of the technical developments in TCR and T cell engineering.

TAKE HOME MESSAGE

Despite technical obstacles, many advances have been made in the generation of high-avidity T cells expressing enhanced TCRs. Mouse studies and clinical trials will evaluate the effect of these improvements.

Interleukin-9 (IL-9) and NPM-ALK each generate mast cell hyperplasia as single 'hit' and cooperate in producing a mastocytosis-like disease in mice

Mast cell neoplasms are characterized by abnormal growth and focal accumulation of mast cells (MC) in one or more organs. Although several cytokines, including stem cell factor (SCF) and interleukin-9 (IL-9) have been implicated in growth of normal MC, little is known about pro-oncogenic molecules and conditions triggering differentiation and growth of MC far enough to lead to the histopathological picture of overt mastocytosis. The anaplastic lymphoma kinase (ALK) has recently been implicated in growth of neoplastic cells in malignant lymphomas. Here, we describe that transplantation of NPM-ALK-transplanted mouse bone marrow progenitors into lethally irradiated IL-9 transgenic mice not only results in lymphoma-formation, but also in the development of a neoplastic disease exhibiting histopathological features of systemic mastocytosis, including multifocal dense MC-infiltrates, occasionally with devastating growth in visceral organs. Transplantation of NPM-ALK-transduced progenitors into normal mice or maintenance of IL-9-transgenic mice without NPM-ALK each resulted in MC hyperplasia, but not in mastocytosis. Neoplastic MC in mice not only displayed IL-9, but also the IL-9 receptor, and the same was found to hold true for human neoplastic MC. Together, our data show that neoplastic MC express IL-9 receptors, that IL-9 and NPM-ALK upregulate MC-production in vivo, and that both'hits' act in concert to induce a mastocytosis-like disease in mice. These data may have pathogenetic and clinical implications and fit well with the observation that neoplastic MC in advanced SM strongly express NPM and multiple "lymphoid" antigens including CD25 and CD30.