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Tumors undergo dynamic immunoediting as part of a process that balances immunologic sensing of emerging neoantigens and evasion from immune responses. Tumor-infiltrating lymphocytes (TIL) comprise heterogeneous subsets of peripheral T cells characterized by diverse functional differentiation states and dependence on T-cell receptor (TCR) specificity gained through recombination events during their development. We hypothesized that within the tumor microenvironment (TME), an antigenic milieu and immunologic interface, tumor-infiltrating peripheral T cells could reexpress key elements of the TCR recombination machinery, namely, Rag1 and Rag2 recombinases and Tdt polymerase, as a potential mechanism involved in the revision of TCR specificity. Using two syngeneic invasive breast cancer transplantable models, 4T1 and TS/A, we observed that Rag1, Rag2 , and Dntt in situ mRNA expression characterized rare tumor-infiltrating T cells. In situ expression of the transcripts was increased in coisogenic Mlh1 -deficient tumors, characterized by genomic overinstability, and was also modulated by PD-1 immune-checkpoint blockade. Through immunolocalization and mRNA hybridization analyses, we detected the presence of rare TDT + RAG1/2 + cells populating primary tumors and draining lymph nodes in human invasive breast cancer. Analysis of harmonized single-cell RNA-sequencing data sets of human cancers identified a very small fraction of tumor-associated T cells, characterized by the expression of recombination/revision machinery transcripts, which on pseudotemporal ordering corresponded to differentiated effector T cells. We offer thought-provoking evidence of a TIL microniche marked by rare transcripts involved in TCR shaping., (©2021 American Association for Cancer Research.)

MR1 is an MHC class I-like molecule with unique structural and biological features that make it an important member among the molecules involved in antigen presentation to T cells. Distinctive features include ubiquitous expression of the MR1 gene and its monomorphism. Another relevant property is that the MR1 protein appears at very low levels on the plasma membrane and its surface expression is regulated by antigen binding. Finally, the nature of presented antigens differs from those that bind other presenting molecules and includes small metabolites of microbial and self-origin, small drugs and tumor-associated antigens. This opinion paper describes in detail some of those features and discusses recent literature in the field., (Copyright © 2020 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Chimeric antigen receptor (CAR) T-cell immunotherapy is rapidly emerging as a promising novel treatment for malignancies. To broaden the success of CAR T-cell treatment for chronic myeloid leukaemia (CML), we attempted to construct a CD26 CAR T-cell product to target tyrosine kinase inhibitor-insensitive leukaemia stem cells (LSCs), which have been a challenge to cure for several decades and can be discriminated from healthy stem cells by the robust biomarker CD26. Of additional interest is that CD26 has also been reported to be a multi-purpose therapeutic target for other malignancies. Here, we constructed CD26 CAR T cells utilizing lentiviral transduction methods and verified them by flow cytometry analysis and RNA-seq. We found that the initial expansion of CD26 CAR-transduced T cells was delayed due to transient fratricide, but subsequent expansion was accelerated. CD26 CAR T cells exhibited cytotoxicity against the CD26 + T-cell lymphoma cell line Karpas 299, CD26-overexpressing K562 cells and primary CML LSCs, activated multiple effector functions in co-culture assays, and limited tumour progression in a mouse model; but there was some off-tumour cytotoxicity towards activated lymphocytes. In conclusion, these results establish the feasibility of using CD26 as an antigen for CAR T cells targeting CD26 + tumour cells.

High-throughput 3' single-cell RNA-sequencing (scRNA-seq) allows cost-effective, detailed characterization of individual immune cells from tissues. Current techniques, however, are limited in their ability to elucidate essential immune cell features, including variable sequences of T cell antigen receptors (TCRs) that confer antigen specificity. Here, we present a strategy that enables simultaneous analysis of TCR sequences and corresponding full transcriptomes from 3'-barcoded scRNA-seq samples. This approach is compatible with common 3' scRNA-seq methods, and adaptable to processed samples post hoc. We applied the technique to identify transcriptional signatures associated with T cells sharing common TCRs from immunized mice and from patients with food allergy. We observed preferential phenotypes among subsets of expanded clonotypes, including type 2 helper CD4 + T cell (T H 2) states associated with food allergy. These results demonstrate the utility of our method when studying diseases in which clonotype-driven responses are critical to understanding the underlying biology.

High-throughput T cell receptor (TCR) sequencing allows the characterization of an individual's TCR repertoire and directly queries their immune state. However, it remains a non-trivial task to couple these sequenced TCRs to their antigenic targets. In this paper, we present a novel strategy to annotate full TCR sequence repertoires with their epitope specificities. The strategy is based on a machine learning algorithm to learn the TCR patterns common to the recognition of a specific epitope. These results are then combined with a statistical analysis to evaluate the occurrence of specific epitope-reactive TCR sequences per epitope in repertoire data. In this manner, we can directly study the capacity of full TCR repertoires to target specific epitopes of the relevant vaccines or pathogens. We demonstrate the usability of this approach on three independent datasets related to vaccine monitoring and infectious disease diagnostics by independently identifying the epitopes that are targeted by the TCR repertoire. The developed method is freely available as a web tool for academic use at tcrex.biodatamining.be., (Copyright © 2019 Gielis, Moris, Bittremieux, De Neuter, Ogunjimi, Laukens and Meysman.)

The experimental autoimmune encephalomyelitis (EAE) model is indispensable for autoimmunity research, but model-specific T cell dynamics are sparsely studied. We used next-generation immunosequencing across lymphoid organs, blood and spinal cord in response to immunization with myelin basic protein (MBP) to study T cell repertoires and migration patterns. Surprisingly, most spinal cord T cells were unique to the individual animal despite the existence of shared MBP-specific clones, suggesting a previously underestimated T cell diversity. Almost complete emigration of pathogenic clones from blood to spinal cord indicates that blood is not a suitable compartment to study EAE-mediating T cells., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Adoptive immunotherapy based on chimeric antigen receptor-modified T (CAR-T) cells has been demonstrated as one of the most promising therapeutic strategies in the treatment of malignancies. However, CAR-T cell therapy has shown limited efficacy for the treatment of solid tumors. This is, in part, because of tumor heterogeneity and a hostile tumor microenvironment, which could suppress adoptively transferred T cell activity. In this study, we, respectively, engineered human- or murine-derived-armored glypican-3 (GPC3)-specific CAR-T cells capable of inducibly expressing IL-12 (GPC3-28Z-NFAT-IL-12) T cells. The results showed that GPC3-28Z-NFAT-IL-12 T cells could lyse GPC3 + tumor cells specifically and increase cytokine secretion compared with GPC3-28Z T cells in vitro. In vivo, GPC3-28Z-NFAT-IL-12 T cells augmented the antitumor effect when encountering GPC3 + large tumor burdens, which could be attributed to IL-12 increasing IFN-γ production, favoring T cells infiltration and persistence. Furthermore, in immunocompetent hosts, low doses of GPC3-m28Z-mNFAT-mIL-12 T cells exerted superior antitumor efficacy without prior conditioning in comparison with GPC3-m28Z T cells. Also, mIL-12 secretion decreased regulatory T cell infiltration in established tumors. In conclusion, these findings demonstrated that the inducible expression of IL-12 could boost CAR-T function with less potential side effects, both in immunodeficient and immunocompetent hosts. The inducibly expressed IL-12-armored GPC3-CAR-T cells could broaden the application of CAR-T-based immunotherapy to patients intolerant of lymphodepletion chemotherapy and might provide an alternative therapeutic strategy for patients with GPC3 + cancers., (Copyright © 2019 by The American Association of Immunologists, Inc.)

Although the adaptive immune system can detect and eliminate malignant cells, patients with intact and fully functional immune systems develop head and neck cancer. How is this paradox explained? Manuscripts published in the English language from 1975 to 2018 were reviewed using search inputs related to tumor cell antigenicity and immunogenicity, immunodominance, cancer immunoediting and genomic alterations present within carcinomas. Early in tumor development, T cell responses to immunodominant antigens may lead to the elimination of cancer cells expressing these antigens and a tumor composed to tumor cells expressing only immunorecessive antigens. Conversely, other tumor cells may acquire genomic or epigenetic alterations that result in an antigen processing or presentation defect or other inability to be detected or killed by T cells. Such T cell insensitive tumor cells may also be selected for in a progressing tumor. Tumors harboring subpopulations of cells that cannot be eliminated by T cells may require non-T cell-based treatments, such as NK cell immunotherapies. Recognition of such tumor cell populations within a heterogeneous cancer may inform the selection of treatment for HNSCC in the future., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

CD20 is an effective immunotherapy target for CD20 + B-cell malignant cells. Monoclonal antibody, especially rituximab, has been a conventional strategy in the treatment of B-cell malignancies such as non-Hodgkin's lymphoma. However, treatment with monoclonal antibodies has not been enough to overcome the refractory/relapse problems. Chimeric antigen receptor engineered T (CAR-T) cells have exhibited excellent therapeutic effect on lymphocytic leukemia in recent years. In this study, a CD20-specific CAR was constructed and the cytotoxic efficacy of CD20 CAR-T cells on B-cell malignant cells was evaluated by CD107a degranulation, pro-inflammation cytokine production, and true lytic ability in vitro and in vivo. It was found that CD20 CAR-T cells possessed stronger cytotoxic ability against CD20 highly expressed cells. Furthermore, when histone deacetylase inhibitor was used to enhance the expression of CD20 antigen on the surface of B-cell malignant cells via inducing acetylation of H3K9 on CD20 promoter site, it revealed that the cytotoxicity of CD20 CAR-T cells against histone deacetylase inhibitor-treated B-cell malignant cells was significantly enhanced.

The antigenic specificity of T cells occurs via generation and rearrangement of different gene segments producing a functional T cell receptor (TCR). High-throughput sequencing (HTS) allows in-depth assessment of TCR repertoire patterns. There are limited data concerning whether TCR repertoires are altered in inflammatory bowel disease. We hypothesized that pediatric ulcerative colitis (UC) patients possess unique TCR repertoires, resulting from clonotypical expansions in the gut. Paired blood and rectal samples were collected from nine newly diagnosed treatment-naive pediatric UC patients and four healthy controls. DNA was isolated to determine the TCR-β repertoire by HTS. Significant clonal expansion was demonstrated in UC patients, with inverse correlation between clinical disease severity and repertoire diversity in the gut. Using different repertoire variables in rectal biopsies, a clear segregation was observed between patients with severe UC, those with mild-moderate disease and healthy controls. Moreover, the overlap between autologous blood-rectal samples in UC patients was significantly higher compared with overlap among controls. Finally, we identified several clonotypes that were shared in either all or the majority of UC patients in the colon. Clonal expansion of TCR-β-expressing T cells among UC patients correlates with disease severity and highlights their involvement in mediating intestinal inflammation., (© 2018 British Society for Immunology.)

Background: Merkel cell carcinoma (MCC) is an aggressive skin cancer that frequently responds to anti-PD-1 therapy. MCC is associated with sun exposure and, in 80% of cases, Merkel cell polyomavirus (MCPyV). MCPyV-specific T and B cell responses provide a unique opportunity to study cancer-specific immunity throughout PD-1 blockade therapy., Methods: Immune responses were assessed in patients (n = 26) with advanced MCC receiving pembrolizumab. Peripheral blood mononuclear cells (PBMC) were collected at baseline and throughout treatment. MCPyV-oncoprotein antibodies were quantified and T cells were assessed for MCPyV-specificity via tetramer staining and/or cytokine secretion. Pre-treatment tumor biopsies were analyzed for T cell receptor clonality., Results: MCPyV oncoprotein antibodies were detectable in 15 of 17 (88%) of virus-positive MCC (VP-MCC) patients. Antibodies decreased in 10 of 11 (91%) patients with responding tumors. Virus-specific T cells decreased over time in patients who had a complete response, and increased in patients who had persistent disease. Tumors that were MCPyV(+) had a strikingly more clonal (less diverse) intratumoral TCR repertoire than virus-negative tumors (p = 0.0001)., Conclusions: Cancer-specific T and B cell responses generally track with disease burden during PD-1 blockade, in proportion to presence of antigen. Intratumoral TCR clonality was significantly greater in VP-MCC than VN-MCC tumors, suggesting expansion of a limited number of dominant clones in response to fewer immunogenic MCPyV antigens. In contrast, VN-MCC tumors had lower clonality, suggesting a diverse T cell response to numerous neoantigens. These findings reveal differences in tumor-specific immunity for VP-MCC and VN-MCC, both of which often respond to anti-PD-1 therapy.

Patients with high risk neuroblastoma have a poor prognosis and survivors are often left with debilitating long term sequelae from treatment. Even after integration of anti-GD2 monoclonal antibody therapy into standard, upftont protocols, 5-year overall survival rates are only about 50%. The success of anti-GD2 therapy has proven that immunotherapy can be effective in neuroblastoma. Adoptive transfer of chimeric antigen receptor (CAR) T cells has the potential to build on this success. In early phase clinical trials, CAR T cell therapy for neuroblastoma has proven safe and feasible, but significant barriers to efficacy remain. These include lack of T cell persistence and potency, difficulty in target identification, and an immunosuppressive tumor microenvironment. With recent advances in CAR T cell engineering, many of these issues are being addressed in the laboratory. In this review, we summarize the clinical trials that have been completed or are underway for CAR T cell therapy in neuroblastoma, discuss the conclusions and open questions derived from these trials, and consider potential strategies to improve CAR T cell therapy for patients with neuroblastoma.

IgE is the key mediator of allergic responses. Omalizumab, an IgE-specific monoclonal antibody that depletes IgE, is effective for treating severe allergic asthma. The need for frequent administration of the expensive drug, however, limits its applications. Taking advantage of T cell memory, adoptive T cell therapy (ACT) targeting IgE-producing cells has the potential to achieve long-term suppression of IgE and relief of symptoms for severe allergic diseases. The transmembrane form of IgE (mIgE), which is present on all IgE-producing cells, serves as an excellent molecular target for ACT that employs chimeric antigen receptors (CARs). Here, we designed and tested CARs that use the extracellular domain of high affinity IgE receptor, FcεRIα, for mIgE recognition. When expressed on Jurkat T cells, FcεRIα-based CARs mediated robust responses in terms of CD69 upregulation to U266 myeloma cells expressing low levels of mIgE. FcεRIα-based CARs specifically recognized cells expressing mIgE, but not cells with secreted IgE captured through Fcε receptors. CAR + Jurkat cells did not respond to LAD2 mast cells with secreted IgE bound through FcεRI or Ramos cells with secreted IgE bound through FcεRII. Co-culture of CAR + Jurkat cells and LAD2 mast cells with IgE bound did not trigger LAD2 cell degranulation. The activity of CAR using wild type FcεRIα for mIgE binding was inhibited by the presence secreted IgE, which likely blocked CAR-mIgE interaction. The activities of CARs using low affinity mutants of FcεRIα, however, tolerated secreted IgE at relatively high concentrations. Moreover, primary human CD8 + T cells expressing a low affinity mutant CAR responded to U266 cells with INFγ production and cytotoxicity despite the presence of secreted IgE. The potency, specificity, and robustness of our CAR design, combined with repaid advances in the safety of ACT, hold promise for novel and highly effective cell-based therapies against severe allergic diseases.

Engineering T cells with chimeric antigen receptors (CARs) is an effective method for directing T cells to attack tumors, but may cause adverse side effects such as the potentially lethal cytokine release syndrome. Here the authors show that the T cell antigen coupler (TAC), a chimeric receptor that co-opts the endogenous TCR, induces more efficient anti-tumor responses and reduced toxicity when compared with past-generation CARs. TAC-engineered T cells induce robust and antigen-specific cytokine production and cytotoxicity in vitro, and strong anti-tumor activity in a variety of xenograft models including solid and liquid tumors. In a solid tumor model, TAC-T cells outperform CD28-based CAR-T cells with increased anti-tumor efficacy, reduced toxicity, and faster tumor infiltration. Intratumoral TAC-T cells are enriched for Ki-67 + CD8 + T cells, demonstrating local expansion. These results indicate that TAC-T cells may have a superior therapeutic index relative to CAR-T cells.

During infections and cancer, the composition of the T-cell receptor (TCR) repertoire of antigen-specific CD8 + T cells changes over time. TCR avidity is thought to be a major driver of this process, thereby interacting with several additional regulators of T-cell responses to form a composite immune response architecture. Infections with latent viruses, such as cytomegalovirus (CMV), can lead to large T-cell responses characterized by an oligoclonal TCR repertoire. Here, we review the current status of experimental studies and theoretical models of TCR repertoire evolution during CMV infection. We will particularly discuss the degree to which this process may be determined through structural TCR avidity. As engineered TCR-redirected T cells have moved into the spotlight for providing more effective immunotherapies, it is essential to understand how the key features of a given TCR influence T-cell expansion and maintenance in settings of infection or malignancy. Deeper insights into these mechanisms will improve our basic understanding of T-cell immunology and help to identify optimal TCRs for immunotherapy., (© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The unique capabilities of gamma-delta (γδ) T cells to recognize cells under stressed conditions, particularly infected or transformed cells, and killing them or regulating the immune response against them, paved the way to the development of promising therapeutic strategies for cancer and infectious diseases. From a mechanistic standpoint, numerous studies have unveiled a remarkable flexibility of γδ T cells in employing their T cell receptor and/or NK cell receptors for target cell recognition, even if the relevant ligands often remain uncertain. Here, we review the accumulated knowledge on the diverse mechanisms of target cell recognition by γδ T cells, focusing on human γδ T cells, to provide an integrated perspective of their therapeutic potential in cancer and infectious diseases.

The adoptive transfer of neoantigen-reactive tumor-infiltrating lymphocytes (TILs) can result in tumor regression in patients with metastatic cancer. To improve the efficacy of adoptive T cell therapy targeting these tumor-specific mutations, we have proposed a new therapeutic strategy, which involves the genetic modification of autologous T cells with neoantigen-specific T cell receptors (TCRs) and the transfer of these modified T cells back to cancer patients. However, the current techniques to isolate neoantigen-specific TCRs are labor intensive, time consuming, and technically challenging, not suitable for clinical applications. To facilitate this process, a new approach was developed, which included the co-culture of TILs with tandem minigene (TMG)-transfected or peptide-pulsed autologous antigen-presenting cells (APCs) and the single-cell RNA sequencing (RNA-seq) analysis of T cells to identify paired TCR sequences associated with cells expressing high levels of interferon-γ (IFN-γ) and interleukin-2 (IL-2). Following this new approach, multiple TCRs were identified, synthesized, cloned into a retroviral vector, and then transduced into donor T cells. These transduced T cells were shown to specifically recognize the neoantigens presented by autologous APCs. In conclusion, this approach provides an efficient procedure to isolate neoantigen-specific TCRs for clinical applications, as well as for basic and translational research., (Published by Elsevier Inc.)

The generation of allergen-specific TCR transgenic animals allows for the characterization of allergen-specific T-cell responses in vivo and in vitro and is a powerful tool to study adaptive immunity to allergens. Here we describe an approach starting from the isolation of antigen-specific T-cell hybridomas and using PCR, flow cytometric, and co-culture methods to obtain antigen-specific MHC class II-restricted CD4 + TCR transgenic mice on the Rag2 -/- background.

Refractory or relapsed B lymphoblastic leukemia (B-ALL) patients have a dismal outcome with current therapy. We treated 42 primary refractory/hematological relapsed (R/R) and 9 refractory minimal residual disease by flow cytometry (FCM-MRD + ) B-ALL patients with optimized second generation CD19-directed CAR-T cells. The CAR-T-cell infusion dosages were initially ranged from 0.05 to 14 × 10 5 /kg and were eventually settled at 1 × 10 5 /kg for the most recent 20 cases. 36/40 (90%) evaluated R/R patients achieved complete remission (CR) or CR with incomplete count recovery (CRi), and 9/9 (100%) FCM-MRD + patients achieved MRD - . All of the most recent 20 patients achieved CR/CRi. Most cases only experienced mild to moderate CRS. 8/51 cases had seizures that were relieved by early intervention. Twenty three of twenty seven CR/CRi patients bridged to allogeneic hematopoietic stem cell transplantation (allo-HCT) remained in MRD - with a median follow-up time of 206 (45-427) days, whereas 9 of 18 CR/CRi patients without allo-HCT relapsed. Our results indicate that a low CAR-T-cell dosage of 1 × 10 5 /kg, is effective and safe for treating refractory or relapsed B-ALL, and subsequent allo-HCT could further reduce the relapse rate.

Measles is an acute viral disease associated both with immune suppression and development of life-long immunity. Clearance of measles virus (MeV) involves rapid elimination of infectious virus during the rash followed by slow elimination of viral RNA. To characterize cellular immune responses during recovery, we analyzed the appearance, specificity and function of MeV-specific T cells for 6 months after respiratory infection of rhesus macaques with wild type MeV. IFN-γ and IL-17-producing cells specific for the hemagglutinin and nucleocapsid proteins appeared in circulation in multiple waves approximately 2-3, 8 and 18-24 weeks after infection. IFN-γ-secreting cells were most abundant early and IL-17-secreting cells late. Both CD4 + and CD8 + T cells were sources of IFN-γ and IL-17, and IL-17-producing cells expressed RORγt. Therefore, the cellular immune response evolves during MeV clearance to produce functionally distinct subsets of MeV-specific CD4 + and CD8 + T cells at different times after infection.

Progress in our understanding of basic immunology along with the advent of bioengineering technologies have made possible the production of human T-cells expressing Chimeric Antigen Receptors (CAR T-cells). These CAR T-cells are designed to target specific antigens presented by cancer cells. Once CARs are bound to these antigens, CAR T-cells get activated and can initiate potent anti-tumor effects. We will here overview the bioengineering advances which made possible the clinical application of CAR T-cell therapy. We will review the data to date regarding anti-CD19 CAR T-cell therapy for acute lymphoblastic leukemia, non-Hodgkin lymphomas, and chronic lymphocytic leukemia. Besides CD19, CAR T-cells directed against the B-cell maturation antigen have also shown encouraging results to treat patients with refractory multiple myeloma. The more limited body of clinical research in the field of solid tumors will also be reviewed. Moreover, we will elaborate on the main toxicities of limitations of CAR T-cell therapy, namely cytokine release syndrome and neurotoxicity. While enjoying an undeniable hype, CAR T-cell therapy bears significant limitations. We will conclude by exposing the possible approaches to make CAR T-cells safer and more efficient beyond the CD19 target., (Copyright © 2017 Elsevier Masson SAS. All rights reserved.)

The diversity of T-cell receptors recognizing foreign pathogens is generated through a highly stochastic recombination process, making the independent production of the same sequence rare. Yet unrelated individuals do share receptors, which together constitute a "public" repertoire of abundant clonotypes. The TCR repertoire is initially formed prenatally, when the enzyme inserting random nucleotides is downregulated, producing a limited diversity subset. By statistically analyzing deep sequencing T-cell repertoire data from twins, unrelated individuals of various ages, and cord blood, we show that T-cell clones generated before birth persist and maintain high abundances in adult organisms for decades, slowly decaying with age. Our results suggest that large, low-diversity public clones are created during pre-natal life, and survive over long periods, providing the basis of the public repertoire.

Based on the success in animal models of type 1 diabetes (T1D), clinical trials of adoptive regulatory T cell (Treg) therapy are underway using ex vivo expanded polyclonal Tregs. However, pre-clinical data also demonstrate that islet-specific Tregs are more potent than polyclonal Tregs at reversing T1D. Translation of this approach into man will require methods to generate large populations of islet-specific Tregs which, to date, has proved to be a major hurdle. Here we demonstrate the feasibility of lentiviral-mediated T cell receptor (TCR) gene transfer to confer antigen specificity on polyclonal human Tregs. Targeting has been achieved using TCRs isolated from human islet-specific and viral-specific CD4 + T cell clones. Engineered T cells demonstrated expression of ectopically-delivered TCRs, resulting in endowment of cognate antigen-specific responses. This enabled antigen-specific suppression at increased potency compared to polyclonal Tregs. However, cells transduced with islet-specific TCRs were less responsive to cognate antigen than viral-specific TCRs, and in some cases, required additional methods to isolate functional antigen-specific Tregs. This study demonstrates the potential of TCR gene transfer to develop islet-specific Treg therapies for effective treatment of T1D, but also highlights that additional optimisation may be required to achieve its full potential., (Crown Copyright © 2017. Published by Elsevier Ltd. All rights reserved.)

Recent advances in antibody technology to harness T cells for cancer immunotherapy, particularly in the difficult-to-treat setting of relapsed/refractory acute lymphoblastic leukemia (r/r ALL), have led to innovative methods for directing cytotoxic T cells to specific surface antigens on cancer cells. One approach involves administration of soluble bispecific (or dual-affinity) antibody-based constructs that temporarily bridge T cells and cancer cells. Another approach infuses ex vivo-engineered T cells that express a surface plasma membrane-inserted antibody construct called a chimeric antigen receptor (CAR). Both bispecific antibodies and CARs circumvent natural target cell recognition by creating a physical connection between cytotoxic T cells and target cancer cells to activate a cytolysis signaling pathway; this connection allows essentially all cytotoxic T cells in a patient to be engaged because typical tumor cell resistance mechanisms (such as T-cell receptor specificity, antigen processing and presentation, and major histocompatibility complex context) are bypassed. Both the bispecific T-cell engager (BiTE) antibody construct blinatumomab and CD19-CARs are immunotherapies that have yielded encouraging remission rates in CD19-positive r/r ALL, suggesting that they might serve as definitive treatments or bridging therapies to allogeneic hematopoietic cell transplantation. With the introduction of these immunotherapies, new challenges arise related to unique toxicities and distinctive pathways of resistance. An increasing body of knowledge is being accumulated on how to predict, prevent, and manage such toxicities, which will help to better stratify patient risk and tailor treatments to minimize severe adverse events. A deeper understanding of the precise mechanisms of action and immune resistance, interaction with other novel agents in potential combinations, and optimization in the manufacturing process will help to advance immunotherapy outcomes in the r/r ALL setting.

It is widely accepted that central and effector memory CD4 + T cells originate from naïve T cells after they have encountered their cognate antigen in the setting of appropriate co-stimulation. However, if this were true the diversity of T cell receptor (TCR) sequences within the naïve T cell compartment should be far greater than that of the memory T cell compartment, which is not supported by TCR sequencing data. Here we demonstrate that aged mice with far fewer naïve T cells, respond to the model antigen, hen eggwhite lysozyme (HEL), by utilizing the same TCR sequence as their younger counterparts. CD4 + T cell repertoire analysis of highly purified T cell populations from naive animals revealed that the HEL-specific clones displayed effector and central "memory" cell surface phenotypes even prior to having encountered their cognate antigen. Furthermore, HEL-inexperienced CD4 + T cells were found to reside within the naïve, regulatory, central memory, and effector memory T cell populations at similar frequencies and the majority of the CD4 + T cells within the regulatory and memory populations were unexpanded. These findings support a new paradigm for CD4 + T cell maturation in which a specific clone can undergo a differentiation process to exhibit a "memory" or regulatory phenotype without having undergone a clonal expansion event. It also demonstrates that a foreign-specific T cell is just as likely to reside within the regulatory T cell compartment as it would the naïve compartment, arguing against the specificity of the regulatory T cell compartment being skewed towards self-reactive T cell clones. Finally, we demonstrate that the same set of foreign and autoreactive CD4 + T cell clones are repetitively generated throughout adulthood. The latter observation argues against T cell-depleting strategies or autologous stem cell transplantation as therapies for autoimmunity-as the immune system has the ability to regenerate pathogenic clones., (Published by Elsevier Ltd.)

Lymphocytic choriomeningitis virus clone 13 (LCMV13) infection of mice is a widely used model for investigating the mechanisms driving persistent viral infection in humans. LCMV13 disrupts splenic architecture early during infection, but this returns to normal within a few weeks. However, the long-term effects of LCMV13 infection on splenic structure have not been reported. Here, we report that persistent infection with LCMV13 results in sustained splenic atrophy that persists for at least 500 days following infection, whereas infection with the acutely infecting LCMV Armstrong is associated with a return to preinfection spleen weights. Splenic atrophy is associated with loss of T, B, and non-B non-T cells, with B cells most significantly affected. These effects were partly ameliorated by anti-NK1.1 or anti-CD8 antibody treatment. Antigen presentation was detectable at the time of contraction of the spleen, but no longer detected at late time points, suggesting that continued antigen presentation is not required to maintain splenic atrophy. Immunity to Salmonella infection and influenza vaccination were decreased after the virus was no longer detected. Thus splenic atrophy following LCMV13 infection is irreversible and may contribute to impaired immunity following clearance of LCMV13., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Regulatory T cells (Treg) can interfere with the generation and function of anti-tumor immune effectors. Accordingly, ways that could block Treg function would be useful in cancer immunotherapy. We have previously shown that incorporation of CD4+CD25-ve T cells in an in vitro cytolytic T lymphocyte (CTL) generation assay leads to generation of induced regulatory T cells (iTregs), and that these iTreg block the generation of productive CTL response (Chattopadhyay et al., 2006). We here show that human CD4 T cells engineered to express MHC class I-restricted human melanoma associated epitope, MART-127-35, specific T cell receptor (TCR), that can simultaneously exhibit helper as well as cytolytic effector functions (Chhabra et al., 2008, Ray et al., 2010), can interfere with the generation of inducible Treg, block iTreg-mediated suppression, and allow the activation and expansion of MART-127-35 specific CTL responses, in vitro. We also show that mitigation of Treg generation by TCR engineered CD4 T cells is not mediated by a soluble factor and may involve "licensing/conditioning" of the dendritic cells (DC). Our data offer novel insights on the biology of MHC class I restricted TCReng CD4 T cells and have translational implications., (Copyright © 2016 American Society for Histocompatibility and Immunogenetics. Published by Elsevier Inc. All rights reserved.)

T-cell polyspecificity, predicting that individual T cells recognize a continuum of related ligands, implies that multiple antigens can tolerize T cells specific for a given self-antigen. We previously showed in C57BL/6 mice that part of the CD4(+) T-cell repertoire specific for myelin oligodendrocyte glycoprotein (MOG) 35-55 also recognizes the neuronal antigen neurofilament medium (NF-M) 15-35. Such bi-specific CD4(+) T cells are frequent and produce inflammatory cytokines after stimulation. Since T cells recognizing two self-antigens would be expected to be tolerized more efficiently, this finding prompted us to study how polyspecificity impacts tolerance. We found that similar to MOG, NF-M is expressed in the thymus by medullary thymic epithelial cells, a tolerogenic population. Nevertheless, the frequency, phenotype, and capacity to transfer experimental autoimmune encephalomyelitis (EAE) of MOG35-55 -reactive CD4(+) T cells were increased in MOG-deficient but not in NF-M-deficient mice. We found that presentation of NF-M15-35 by I-A(b) on dendritic cells is of short duration, suggesting unstable MHC class II binding. Consistently, introducing an MHC-anchoring residue into NF-M15-35 (NF-M15-35 T20Y) increased its immunogenicity, activating a repertoire able to induce EAE. Our results show that in C57BL/6 mice bi-specific encephalitogenic T cells manage to escape tolerization due to inefficient exposure to two self-antigens., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Regulatory T (Treg) cells expressing Foxp3 transcripton factor are essential for immune homeostasis. They arise in the thymus as a separate lineage from conventional CD4(+)Foxp3(-) T (Tconv) cells. Here, we show that the thymic development of Treg cells depends on the expression of their endogenous cognate self-antigen. The formation of these cells was impaired in mice lacking this self-antigen, while Tconv cell development was not negatively affected. Thymus-derived Treg cells were selected by self-antigens in a specific manner, while autoreactive Tconv cells were produced through degenerate recognition of distinct antigens. These distinct modes of development were associated with the expression of T cell receptor of higher functional avidity for self-antigen by Treg cells than Tconv cells, a difference subsequently essential for the control of autoimmunity. Our study documents how self-antigens define the repertoire of thymus-derived Treg cells to subsequently endow this cell type with the capacity to undermine autoimmune attack., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Objective: Developing a vaccine that is cross-reactive between HCV genotypes requires data on T cell antigenic targets that extends beyond genotype-1. We characterised T cell immune responses against HCV genotype-3, the most common infecting genotype in the UK and Asia, and assessed within genotype and between genotype cross-reactivity., Design: T cell targets were identified in 140 subjects with either acute, chronic or spontaneously resolved HCV genotype-3 infection using (1) overlapping peptides and (2) putative human leucocyte antigens (HLA)-class-I wild type and variant epitopes through the prior assessment of polymorphic HCV genomic sites associated with host HLA, in IFNγ-ELISpot assays. CD4+/CD8+ T cell subsets were defined and viral variability at T cell targets was determined through population analysis and viral sequencing. T cell cross-reactivity between genotype-1 and genotype-3 variants was assessed., Results: In resolved genotype-3 infection, T cells preferentially targeted non-structural proteins at a high magnitude, whereas in chronic disease T cells were absent or skewed to target structural proteins. Additional responses to wild type but not variant HLA predicted peptides were defined. Major sequence viral variability was observed within genotype-3 and between genotypes 1 and 3 HCV at T cell targets in resolved infection and at dominant epitopes, with limited T cell cross-reactivity between viral variants. Overall 41 CD4/CD8+ genotype-3 T cell targets were identified with minimal overlap with those described for HCV genotype-1., Conclusions: HCV T cell specificity is distinct between genotypes with limited T cell cross-reactivity in resolved and chronic disease. Therefore, viral regions targeted in natural HCV infection may not serve as attractive targets for a vaccine that aims to protect against multiple HCV genotypes., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/)

Genetics tools, and especially the ability to enforce, by transgenesis, or disrupt, by homologous recombination, gene expression in a cell-specific manner, have revolutionized the study of immunology and propelled the laboratory mouse as the main model to study immune responses. Perhaps more than any other aspect of immunology, the study of T cell development has benefited from these technologies. This brief chapter summarizes genetic tools specific to T cell development studies, focusing on mouse strains with lineage- and stage-specific expression of the Cre recombinase, or expressing unique antigen receptor specificities. It ends with a broader discussion of strategies to enforce ectopic lineage and stage-specific gene expression.

Monitoring antigen-specific T cells is critical for the study of immune responses and development of biomarkers and immunotherapeutics. We developed a novel multiplex assay that combines conventional immune monitoring techniques and immune receptor repertoire sequencing to enable identification of T cells specific to large numbers of antigens simultaneously. We multiplexed 30 different antigens and identified 427 antigen-specific clonotypes from 5 individuals with frequencies as low as 1 per million T cells. The clonotypes identified were validated several ways including repeatability, concordance with published clonotypes, and high correlation with ELISPOT. Applying this technology we have shown that the vast majority of shared antigen-specific clonotypes identified in different individuals display the same specificity. We also showed that shared antigen-specific clonotypes are simpler sequences and are present at higher frequencies compared to non-shared clonotypes specific to the same antigen. In conclusion this technology enables sensitive and quantitative monitoring of T cells specific for hundreds or thousands of antigens simultaneously allowing the study of T cell responses with an unprecedented resolution and scale.

The systematic assessment of the human immune system bears huge potential to guide rational development of novel immunotherapies and clinical decision making. Multiple assays to monitor the quantity, phenotype, and function of Ag-specific T cells are commonly used to unravel patients' immune signatures in various disease settings and during therapeutic interventions. When compared with tests measuring soluble analytes, cellular immune assays have a higher variation, which is a major technical factor limiting their broad adoption in clinical immunology. The key solution may arise from continuous control of assay performance using TCR-engineered reference samples. We developed a simple, stable, robust, and scalable technology to generate reference samples that contain defined numbers of functional Ag-specific T cells. First, we show that RNA-engineered lymphocytes, equipped with selected TCRs, can repetitively deliver functional readouts of a controlled size across multiple assay platforms. We further describe a concept for the application of TCR-engineered reference samples to keep assay performance within or across institutions under tight control. Finally, we provide evidence that these novel control reagents can sensitively detect assay variation resulting from typical sources of error, such as low cell quality, loss of reagent stability, suboptimal hardware settings, or inaccurate gating., (Copyright © 2015 by The American Association of Immunologists, Inc.)

Natural killer (NK) and CD8(+) T cells play a crucial role in the control of mouse cytomegalovirus (MCMV) infection. These effector cells exert their functions by releasing antiviral cytokines and by cytolytic mechanisms including perforin activation. In addition to their role in virus control, NK cells play an immunoregulatory role since they shape the CD8(+) T cell response to MCMV. To investigate the role of perforin-dependent cytolytic mechanism in NK cell modulation of CD8(+) T cell response during acute MCMV infection, we have used perforin-deficient C57BL/6 mice (Prf1(-/-)) and have shown that virus control by CD8(+) T cells in Prf1(-/-) mice is more efficient if NK cells are activated by the engagement of the Ly49H receptor with the m157 MCMV protein. A lack of perforin results in severe liver inflammation after MCMV infection, which is characterized by immunopathological lesions that are more pronounced in Prf1(-/-) mice infected with virus unable to activate NK cells. This immunopathology is caused by an abundant infiltration of activated CD8(+) T cells. The depletion of CD8(+) T cells has markedly reduced pathohistological lesions in the liver and improved the survival of Prf1(-/-) mice in spite of an increased viral load. Altogether, the results of our study suggest that a lack of perforin and absence of the specific activation of NK cells during acute MCMV infection lead to an unleashed CD8(+) T cell response that is detrimental for the host.

The ease of sequencing the cancer genome, identifying all somatic mutations and grafting mutation-specific T cell receptor (TCR) genes into T cells for adoptive transfer allow, for the first time, a truly tumor-specific and effective therapy. Mutation-specific TCR gene therapy might achieve optimal efficacy with least possible toxicity. Recent clinical data confirm the long-standing evidence from experimental cancer models that antigens encoded by the tumor-specific somatic mutations are potentially the best targets for adoptive T cell therapy. Open questions are, how many somatic mutations create suitable epitopes, whether only individual-specific or also recurrent somatic mutations qualify as suitable epitopes and how neoantigen-specific TCRs are most efficiently obtained. Tumor heterogeneity needs to be considered; therefore, it will be important to identify immunogenic driver mutations that occurred early, are essential for cancer cell survival and present in all cancer cells., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Genetic approaches identified THEMIS as a critical element driving positive selection of CD4(+)CD8(+) thymocytes towards maturation. THEMIS is expressed only in the T-cell lineage, and is recruited to the proximity of signaling T-cell antigen receptors (TCR) by association with the membrane scaffold LAT. However, its molecular role remained an enigma until recently. Conventionally positively-selected T-cells are lacking in THEMIS-deficient mice, leading to the initial hypothesis that THEMIS positively regulates TCR signaling. Recent data show that THEMIS deficiency increases rather than decreases TCR signaling, leading to augmented apoptosis. The finding that THEMIS is constitutively bound to the tyrosine phosphatases SHP1 or SHP2, provides a mechanism for THEMIS action. When recruited onto LAT, THEMIS-SHP promotes immediate dephosphorylation of TCR-proximal signaling components. This negative feedback is central in setting sharp signaling thresholds and helps explain the exquisite ligand discrimination by the TCR, particularly during thymocyte selection., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Bispecific T-cell engagers (BiTEs) are a new class of immunotherapeutic molecules intended for the treatment of cancer. These molecules enhance the patient's immune response to tumors by retargeting T cells to tumor cells. BiTEs are constructed of two single-chain variable fragments (scFv) connected in tandem by a flexible linker. One scFv binds to a T-cell-specific molecule, usually CD3, whereas the second scFv binds to a tumor-associated antigen. This structure and specificity allows a BiTE to physically link a T cell to a tumor cell, ultimately stimulating T-cell activation, tumor killing and cytokine production. BiTEs have been developed, which target several tumor-associated antigens, for a variety of both hematological and solid tumors. Several BiTEs are currently in clinical trials for their therapeutic efficacy and safety. This review examines the salient structural and functional features of BiTEs, as well as the current state of their clinical and preclinical development.

Expansion of human regulatory T cells (Tregs) for clinical applications offers great promise for the treatment of undesirable immune responses in autoimmunity, transplantation, allergy, and antidrug antibody responses, including inhibitor responses in hemophilia A patients. However, polyclonal Tregs are nonspecific and therefore could potentially cause global immunosuppression. To avoid this undesirable outcome, the generation of antigen-specific Tregs would be advantageous. Herein, we report the production and properties of engineered antigen-specific Tregs, created by transduction of a recombinant T-cell receptor obtained from a hemophilia A subject's T-cell clone, into expanded human FoxP3(+) Tregs. Such engineered factor VIII (FVIII)-specific Tregs efficiently suppressed the proliferation and cytokine production of FVIII-specific T-effector cells. Moreover, studies with an HLA-transgenic, FVIII-deficient mouse model demonstrated that antibody production from FVIII-primed spleen cells in vitro were profoundly inhibited in the presence of these FVIII-specific Tregs, suggesting potential utility to treat anti-FVIII inhibitory antibody formation in hemophilia A patients.

Purpose: Adoptive transfer of autologous tumor infiltrating lymphocytes (TIL) can mediate durable cancer regression in selected patients with metastatic melanoma. However, the tumor antigens associated with these favorable responses remain unclear. We hypothesized that a clinical strategy involving the iterative adoptive transfer of selected autologous antigen-specific T-cell clones could help systematically define immunologic targets associated with successful cancer therapy, without the interpretative ambiguity of transferring polyclonal populations. Here, we evaluated the clinical efficacy of CD8(+) T-cell clones specific for the melanocyte differentiation antigens (MDA), gp100 and MART-1, respectively., Experimental Design: We conducted two consecutive phase II clinical trials involving the adoptive transfer of highly selected autologous antigen-specific CD8(+) T-cell clones against gp100 and MART-1, respectively. Fifteen patients with HLA-A2(+) treatment-refractory metastatic melanoma received highly avid MDA-specific CD8(+) T-cell clones specific for either gp100 (n = 10) or MART-1 (n = 5) with or without intravenous interleukin-2 (IL2) after a lymphodepleting myeloablative preparative regimen., Results: Of the 15 treated patients, we observed immune-mediated targeting of skin melanocytes in 11 patients (73%) and clonal engraftment in eight patients (53%) after cell transfer. There were only transient minor tumor regressions observed, but no objective tumor responses based on Response Evaluation Criteria in Solid Tumor (RECIST) criteria., Conclusions: Despite successful clonal repopulation and evidence of in vivo antigen targeting, the poor therapeutic efficacy after the adoptive transfer of autologous MDA-specific T cells raises significant concerns regarding future immunotherapy efforts targeting this class of tumor antigens., (©2014 American Association for Cancer Research.)

The effectiveness of chimeric Ag receptor (CAR)-transduced T (CAR-T) cells has been attributed to supraphysiological signaling through CARs. Second- and later-generation CARs simultaneously transmit costimulatory signals with CD3ζ signals upon ligation, but may lead to severe adverse effects owing to the recognition of minimal Ag expression outside the target tumor. Currently, the threshold target Ag density for CAR-T cell lysis and further activation, including cytokine production, has not yet been investigated in detail. Therefore, we determined the threshold target Ag density required to induce CAR-T cell responses using novel anti-CD20 CAR-T cells with a CD28 intracellular domain and a CD20-transduced CEM cell model. The newly developed CD20CAR-T cells demonstrated Ag-specific lysis and cytokine secretion, which was a reasonable level as a second-generation CAR. For lytic activity, the threshold Ag density was determined to be ∼200 molecules per target cell, whereas the Ag density required for cytokine production of CAR-T cells was ∼10-fold higher, at a few thousand per target cell. CD20CAR-T cells responded efficiently to CD20-downregulated lymphoma and leukemia targets, including rituximab- or ofatumumab-refractory primary chronic lymphocytic leukemia cells. Despite the potential influence of the structure, localization, and binding affinity of the CAR/Ag, the threshold determined may be used for target Ag selection. An Ag density below the threshold may not result in adverse effects, whereas that above the threshold may be sufficient for practical effectiveness. CD20CAR-T cells also demonstrated significant lytic activity against CD20-downregulated tumor cells and may exhibit effectiveness for CD20-positive lymphoid malignancies., (Copyright © 2015 by The American Association of Immunologists, Inc.)

Chimeric antigen receptor (CAR) based immunotherapy has been under development for the last 25 years and is now a promising new treatment modality in the field of cancer immunotherapy. The approach involves genetically engineering T cells to target malignant cells through expression of a bespoke fusion receptor that couples an HLA-independent antigen recognition domain to one or more intracellular T-cell activating modules. Multiple clinical trials are now underway in several centers to investigate CAR T-cell immunotherapy of diverse hematologic and solid tumor types. The most successful results have been achieved in the treatment of patients with B-cell malignancies, in whom several complete and durable responses have been achieved. This review focuses on the preclinical and clinical development of CAR T-cell immunotherapy of solid cancers, targeted against members of the ErbB family.

Purpose: The aim of our study is to elucidate whether T cells expressing GPC3-targeted chimeric antigen receptor (CAR) can efficiently eliminate GPC3-positive HCC cells and their potential in the treatment of HCC., Experimental Design: T cells expressing a first-generation and third-generation GPC3-targeted CAR were prepared using lentiviral vector transduction. The in vitro and in vivo cytotoxic activities of the genetically engineered CAR T cells were evaluated against various HCC cell lines., Results: GPC3-targeted CAR T cells could efficiently kill GPC3-positive HCC cells but not GPC3-negative cells in vitro. These cytotoxic activities seemed to be positively correlated with GPC3 expression levels in the target cells. In addition, T cells expressing the third-generation GPC3-targeted CAR could eradicate HCC xenografts with high level of GPC3 expression and efficiently suppress the growth of HCC xenografts with low GPC3 expression level in vivo. The survival of the mice bearing established orthotopic Huh-7 xenografts was significantly prolonged by the treatment with the third-generation GPC3-targeted CAR T cells., Conclusions: GPC3-targeted CAR T cells could potently eliminate GPC3-positive HCC cells, thereby providing a promising therapeutic intervention for GPC3-positive HCC., (©2014 American Association for Cancer Research.)

Adoptive cell transfer (ACT) is emerging as a powerful modality of cancer treatment. While ACT has proved able to induce massive clinical responses, genetic modification of T lymphocytes further improved clinical responses obtained. One of the major current limitations of ACT is the inability to discern healthy from malignant cells, leading to on target/off tumor responses that can limit its application. We here discuss some of the approaches currently under development and potential solutions to circumvent these limitations and extend this potentially curative therapy to different tumors by targeting a variety of antigens.

Fucoidan, a sulfated polysaccharide purified from brown algae, has a variety of immune-modulation effects, including promoting antigen uptake and enhancing anti-viral and anti-tumor effects. However, the effect of fucoidan in vivo, especially its adjuvant effect on in vivo anti-tumor immune responses, was not fully investigated. In this study, we investigated the effect of fucoidan on the function of spleen dendritic cells (DCs) and its adjuvant effect in vivo. Systemic administration of fucoidan induced up-regulation of CD40, CD80 and CD86 expression and production of IL-6, IL-12 and TNF-α in spleen cDCs. Fucoidan also promoted the generation of IFN-γ-producing Th1 and Tc1 cells in an IL-12-dependent manner. When used as an adjuvant in vivo with ovalbumin (OVA) antigen, fucoidan promoted OVA-specific antibody production and primed IFN-γ production in OVA-specific T cells. Moreover, fucoidan enhanced OVA-induced up-regulation of MHC class I and II on spleen cDCs and strongly prompted the proliferation of OVA-specific CD4 and CD8 T cells. Finally, OVA immunization with fucoidan as adjuvant protected mice from the challenge with B16-OVA tumor cells. Taken together, these results suggest that fucoidan can function as an adjuvant to induce Th1 immune response and CTL activation, which may be useful in tumor vaccine development.

T cells genetically modified to stably express immunoreceptors are being assessed for therapeutic potential in clinical trials. T cells expressing a chimeric antigen receptor (CAR) are endowed with a new specificity to target tumor-associated antigen (TAA) independent of major histocompatibility complex. Our approach to nonviral gene transfer in T cells uses ex vivo numeric expansion of CAR T cells on irradiated artificial antigen presenting cells (aAPC) bearing the targeted TAA. The requirement for aAPC to express a desired TAA limits the human application of CARs with multiple specificities when selective expansion through coculture with feeder cells is sought. As an alternative to expressing individual TAAs on aAPC, we expressed 1 ligand that could activate CAR T cells for sustained proliferation independent of specificity. We expressed a CAR ligand (designated CARL) that binds the conserved IgG4 extracellular domain of CAR and demonstrated that CARL aAPC propagate CAR T cells of multiple specificities. CARL avoids technical issues and costs associated with deploying clinical-grade aAPC for each TAA targeted by a given CAR. Using CARL enables 1 aAPC to numerically expand all CAR T cells containing the IgG4 domain, and simplifies expansion, testing, and clinical translation of CAR T cells of any specificity.

Extensive diversity in the human repertoire of TCRs for Ag is both a cornerstone of effective adaptive immunity that enables host protection against a multiplicity of pathogens and a weakness that gives rise to potential pathological self-reactivity. The complexity arising from diversity makes detection and tracking of single Ag-specific CD4 T cells (ASTs) involved in these immune responses challenging. We report a tandem, multistep process to quantify rare TCRβ-chain variable sequences of ASTs in large polyclonal populations. The approach combines deep high-throughput sequencing (HTS) within functional CD4 T cell compartments, such as naive/memory cells, with shallow, multiple identifier-based HTS of ASTs identified by activation marker upregulation after short-term Ag stimulation in vitro. We find that clonotypes recognizing HLA class II-restricted epitopes of both pathogen-derived Ags and self-Ags are oligoclonal and typically private. Clonotype tracking within an individual reveals private AST clonotypes resident in the memory population, as would be expected, representing clonal expansions (identical nucleotide sequence; "ultraprivate"). Other AST clonotypes share CDR3β amino acid sequences through convergent recombination and are found in memory populations of multiple individuals. Tandem HTS-based clonotyping will facilitate studying AST dynamics, epitope spreading, and repertoire changes that arise postvaccination and following Ag-specific immunotherapies for cancer and autoimmune disease.

Recent clinical trials have shown that evasion of CD8(+) T-cell responses against viral capsid is critical for successful liver-directed gene therapy with adeno-associated viral (AAV) vectors for hemophilia. Preclinical models to test whether use of alternate serotypes or capsid variants could avoid this deleterious response have been lacking. Here, the ability of CD8(+) T cells ("cap-CD8," specific for a capsid epitope presented by human B*0702 or murine H2-L(d) molecules) to target AAV-infected hepatocytes was investigated. In a murine model based on adoptive transfer of ex vivo expanded cap-CD8, AAV2-transduced livers showed CD8(+) T-cell infiltrates, transaminitis, significant reduction in factor IX transgene expression, and loss of transduced hepatocytes. AAV8 gene transfer resulted in prolonged susceptibility to cap-CD8, consistent with recent clinical findings. In contrast, using an AAV2(Y-F) mutant capsid, which is known to be less degraded by proteasomes, preserved transgene expression and largely avoided hepatotoxicity. In vitro assays confirmed reduced major histocompatibility complex class I presentation of this capsid and killing of human or murine hepatocytes compared with AAV2. In conclusion, AAV capsids can be engineered to substantially reduce the risk of destruction by cytotoxic T lymphocytes, whereas use of alternative serotypes per se does not circumvent this obstacle.

Modulation of T-cell responses by HIV occurs via distinct mechanisms, 1 of which involves inactivation of T cells already at the stage of virus-cell fusion. Hydrophobic portions of the gp41 protein of the viral envelope that contributes to membrane fusion may modulate T-cell responsiveness. Here we found a highly conserved sequence (termed "ISLAD") that is associated with the membranotropic gp41 loop region. We showed that ISLAD has the ability to bind the T-cell membrane and to interact with the T-cell receptor (TCR) complex. Furthermore, ISLAD inhibited T-cell proliferation and interferon-γ secretion that resulted from TCR engagement through antigen-presenting cells. Moreover, administering ISLAD (10 µg per mouse) to an experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis reduced the severity of the disease. This was related to the inhibition of pathogenic T-cell proliferation and to reduced pro-inflammatory cytokine secretion in the lymph nodes of ISLAD-treated EAE mice. The data suggest that T-cell inactivation by HIV during membrane fusion may lie in part in this conserved sequence associated with the gp41 loop region.

Immunotherapy with innate immune cells has recently evoked broad interest as a novel treatment option for cancer patients. γ9δ2T cells in particular are emerging as an innate cell population with high frequency and strong antitumor reactivity, which makes them and their receptors promising candidates for immune interventions. However, clinical trials have so far reported only limited tumor control by adoptively transferred γ9δ2T cells. As a potential explanation for this lack of efficacy, we found unexpectedly high variability in tumor recognition within the physiologic human γ9δ2T-cell repertoire, which is substantially regulated by the CDR3 domains of individual γ9δ2TCRs. In the present study, we demonstrate that the reported molecular requirements of CDR3 domains to interact with target cells shape the physiologic γ9δ2T-cell repertoire and, most likely, limit the protective and therapeutic antitumor efficacy of γ9δ2T cells. Based on these findings, we propose combinatorial-γδTCR-chain exchange as an efficient method for designing high-affinity γ9δ2TCRs that mediate improved antitumor responses when expressed in αβT cells both in vitro and in vivo in a humanized mouse model.