Selecting highly affine and well-expressed TCRs for gene therapy of melanoma

Coengineering specificity, safety, and function into T cells for cancer immunotherapy

Adoptive T-cell transfer (ACT) therapies, including of tumor infiltrating lymphocytes (TILs) and T cells gene-modified to express either a T cell receptor (TCR) or a chimeric antigen receptor (CAR), have demonstrated clinical efficacy for a proportion of patients and cancer-types. The field of ACT has been driven forward by the clinical success of CD19-CAR therapy against various advanced B-cell malignancies, including curative responses for some leukemia patients. However, relapse remains problematic, in particular for lymphoma. Moreover, for a variety of reasons, relative limited efficacy has been demonstrated for ACT of non-hematological solid tumors. Indeed, in addition to pre-infusion challenges including lymphocyte collection and manufacturing, ACT failure can be attributed to several biological processes post-transfer including, (i) inefficient tumor trafficking, infiltration, expansion and retention, (ii) chronic antigen exposure coupled with insufficient costimulation resulting in T-cell exhaustion, (iii) a range of barriers in the tumor microenvironment (TME) mediated by both tumor cells and suppressive immune infiltrate, (iv) tumor antigen heterogeneity and loss, or down-regulation of antigen presentation machinery, (v) gain of tumor intrinsic mechanisms of resistance such as to apoptosis, and (vi) various forms of toxicity and other adverse events in patients. Affinity-optimized TCRs can improve T-cell function and innovative CAR designs as well as gene-modification strategies can be used to coengineer specificity, safety, and function into T cells. Coengineering strategies can be designed not only to directly support the transferred T cells, but also to block suppressive barriers in the TME and harness endogenous innate and adaptive immunity. Here, we review a selection of the remarkable T-cell coengineering strategies, including of tools, receptors, and gene-cargo, that have been developed in recent years to augment tumor control by ACT, more and more of which are advancing to the clinic.

Identification of patient-specific CD4+ and CD8+ T cell neoantigens through HLA-unbiased genetic screens

Cancer neoantigens that arise from tumor mutations are drivers of tumor-specific T cell responses, but identification of T cell-recognized neoantigens in individual patients is challenging. Previous methods have restricted antigen discovery to selected HLA alleles, thereby limiting the breadth of neoantigen repertoires that can be uncovered. Here, we develop a genetic neoantigen screening system that allows sensitive identification of CD4⁺ and CD8⁺ T cell-recognized neoantigens across patients' complete HLA genotypes.

RNF31 inhibition sensitizes tumors to bystander killing by innate and adaptive immune cells

Tumor escape mechanisms for immunotherapy include deficiencies in antigen presentation, diminishing adaptive CD8⁺ T cell antitumor activity. Although innate natural killer (NK) cells are triggered by loss of MHC class I, their response is often inadequate. To increase tumor susceptibility to both innate and adaptive immune elimination, we performed parallel genome-wide CRISPR-Cas9 knockout screens under NK and CD8⁺ T cell pressure. We identify all components, RNF31, RBCK1, and SHARPIN, of the linear ubiquitination chain assembly complex (LUBAC). Genetic and pharmacologic ablation of RNF31, an E3 ubiquitin ligase, strongly sensitizes cancer cells to NK and CD8⁺ T cell killing. This occurs in a tumor necrosis factor (TNF)-dependent manner, causing loss of A20 and non-canonical IKK complexes from TNF receptor complex I. A small-molecule RNF31 inhibitor sensitizes colon carcinoma organoids to TNF and greatly enhances bystander killing of MHC antigen-deficient tumor cells. These results merit exploration of RNF31 inhibition as a clinical pharmacological opportunity for immunotherapy-refractory cancers.

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Parallel CRISPR screens in tumor cells identify NK and T cell susceptibility genes

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Ablation of LUBAC ubiquitination complex sensitizes tumors to immune elimination

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Small-molecule RNF31 inhibition sensitizes tumor cells in TNF-dependent fashion

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RNF31 inhibition strongly enhances immune bystander killing

Sequence determinants as key regulators in gene expression of T cells

T cell homeostasis, T cell differentiation, and T cell effector function rely on the constant fine-tuning of gene expression. To alter the T cell state, substantial remodeling of the proteome is required. This remodeling depends on the intricate interplay of regulatory mechanisms, including post-transcriptional gene regulation. In this review, we discuss how the sequence of a transcript influences these post-transcriptional events. In particular, we review how sequence determinants such as sequence conservation, GC content, and chemical modifications define the levels of the mRNA and the protein in a T cell. We describe the effect of different forms of alternative splicing on mRNA expression and protein production, and their effect on subcellular localization. In addition, we discuss the role of sequences and structures as binding hubs for miRNAs and RNA-binding proteins in T cells. The review thus highlights how the intimate interplay of post-transcriptional mechanisms dictate cellular fate decisions in T cells.

Cooperative Targeting of Immunotherapy-Resistant Melanoma and Lung Cancer by an AXL-Targeting Antibody-Drug Conjugate and Immune Checkpoint Blockade

Although immune checkpoint blockade (ICB) has shown remarkable clinical benefit in a subset of patients with melanoma and lung cancer, most patients experience no durable benefit. The receptor tyrosine kinase AXL is commonly implicated in therapy resistance and may serve as a marker for therapy-refractory tumors, for example in melanoma, as we previously demonstrated. Here, we show that enapotamab vedotin (EnaV), an antibody-drug conjugate targeting AXL, effectively targets tumors that display insensitivity to immunotherapy or tumor-specific T cells in several melanoma and lung cancer models. In addition to its direct tumor cell killing activity, EnaV treatment induced an inflammatory response and immunogenic cell death in tumor cells and promoted the induction of a memory-like phenotype in cytotoxic T cells. Combining EnaV with tumor-specific T cells proved superior to either treatment alone in models of melanoma and lung cancer and induced ICB benefit in models otherwise insensitive to anti-PD-1 treatment. Our findings indicate that targeting AXL-expressing, immunotherapy-resistant tumors with EnaV causes an immune-stimulating tumor microenvironment and enhances sensitivity to ICB, warranting further investigation of this treatment combination. SIGNIFICANCE: These findings show that targeting AXL-positive tumor fractions with an antibody-drug conjugate enhances antitumor immunity in several humanized tumor models of melanoma and lung cancer.

Functional differences between low- and high-affinity CD8(+) T cells in the tumor environment

Weak T-cell antigen receptor (TCR)-ligand interactions are sufficient to activate naïve CD8(+) T cells, but generally do not result in tumor eradication. How differences in TCR affinity affect the regulation of T-cell function in an immunosuppressive tumor environment has not been investigated. We have examined the functional differences of high- vs. low-affinity CD8(+) T cells and we observed that infiltration, accumulation, survival and cytotoxicity within the tumor are severely impacted by the strength of TCR-ligand interactions. In addition, high-affinity CD8(+) T cells were found to exhibit lower expression of inhibitory molecules including PD-1, LAG-3 and NKG2A, thus being less susceptible to suppressive mechanisms. Interferon γ and autocrine interleukin-2 were both found to influence the level of expression of these molecules. Interestingly, although high-affinity CD8(+) T cells were superior to low-affinity CD8(+) T cells in their ability to effect tumor eradication, they could be further improved by the presence of tumor specific CD4(+) T cells. These findings illustrate the importance of both TCR affinity and tumor-specific CD4 help in tumor immunotherapy.

Regulatory T cell therapy: Current and future design perspectives

Regulatory T cells (Tregs) maintain immune equilibrium by suppressing immune responses through various multistep contact dependent and independent mechanisms. Cellular therapy using polyclonal Tregs in transplantation and autoimmune diseases has shown promise in preclinical models and clinical trials. Although novel approaches have been developed to improve specificity and efficacy of antigen specific Treg based therapies, widespread application is currently restricted. To date, design-based approaches to improve the potency and persistence of engineered chimeric antigen receptor (CAR) Tregs are limited. Here, we describe currently available Treg based therapies, their advantages and limitations for implementation in clinical studies. We also examine various strategies for improving CAR T cell design that can potentially be applied to CAR Tregs, such as identifying co-stimulatory signalling domains that enhance suppressive ability, determining optimal scFv affinity/avidity, and co-expression of accessory molecules. Finally, we discuss the importance of tailoring CAR Treg design to suit the individual disease.

Reversal of pre-existing NGFR-driven tumor and immune therapy resistance

Melanomas can switch to a dedifferentiated cell state upon exposure to cytotoxic T cells. However, it is unclear whether such tumor cells pre-exist in patients and whether they can be resensitized to immunotherapy. Here, we chronically expose (patient-derived) melanoma cell lines to differentiation antigen-specific cytotoxic T cells and observe strong enrichment of a pre-existing NGFR^hi population. These fractions are refractory also to T cells recognizing non-differentiation antigens, as well as to BRAF + MEK inhibitors. NGFR^hi cells induce the neurotrophic factor BDNF, which contributes to T cell resistance, as does NGFR. In melanoma patients, a tumor-intrinsic NGFR signature predicts anti-PD-1 therapy resistance, and NGFR^hi tumor fractions are associated with immune exclusion. Lastly, pharmacologic NGFR inhibition restores tumor sensitivity to T cell attack in vitro and in melanoma xenografts. These findings demonstrate the existence of a stable and pre-existing NGFR^hi multitherapy-refractory melanoma subpopulation, which ought to be eliminated to revert intrinsic resistance to immunotherapeutic intervention.

Engineering Strategies to Enhance TCR-Based Adoptive T Cell Therapy

T cell receptor (TCR)-based adoptive T cell therapies (ACT) hold great promise for the treatment of cancer, as TCRs can cover a broad range of target antigens. Here we summarize basic, translational and clinical results that provide insight into the challenges and opportunities of TCR-based ACT. We review the characteristics of target antigens and conventional αβ-TCRs, and provide a summary of published clinical trials with TCR-transgenic T cell therapies. We discuss how synthetic biology and innovative engineering strategies are poised to provide solutions for overcoming current limitations, that include functional avidity, MHC restriction, and most importantly, the tumor microenvironment. We also highlight the impact of precision genome editing on the next iteration of TCR-transgenic T cell therapies, and the discovery of novel immune engineering targets. We are convinced that some of these innovations will enable the field to move TCR gene therapy to the next level.

Neoadjuvant immunotherapy leads to pathological responses in MMR-proficient and MMR-deficient early-stage colon cancers

PD-1 plus CTLA-4 blockade is highly effective in advanced-stage, mismatch repair (MMR)-deficient (dMMR) colorectal cancers, yet not in MMR-proficient (pMMR) tumors. We postulated a higher efficacy of neoadjuvant immunotherapy in early-stage colon cancers. In the exploratory NICHE study (ClinicalTrials.gov: NCT03026140), patients with dMMR or pMMR tumors received a single dose of ipilimumab and two doses of nivolumab before surgery, the pMMR group with or without celecoxib. The primary objective was safety and feasibility; 40 patients with 21 dMMR and 20 pMMR tumors were treated, and 3 patients received nivolumab monotherapy in the safety run-in. Treatment was well tolerated and all patients underwent radical resections without delays, meeting the primary endpoint. Of the patients who received ipilimumab + nivolumab (20 dMMR and 15 pMMR tumors), 35 were evaluable for efficacy and translational endpoints. Pathological response was observed in 20/20 (100%; 95% exact confidence interval (CI): 86-100%) dMMR tumors, with 19 major pathological responses (MPRs, ≤10% residual viable tumor) and 12 pathological complete responses. In pMMR tumors, 4/15 (27%; 95% exact CI: 8-55%) showed pathological responses, with 3 MPRs and 1 partial response. CD8⁺PD-1⁺ T cell infiltration was predictive of response in pMMR tumors. These data indicate that neoadjuvant immunotherapy may have the potential to become the standard of care for a defined group of colon cancer patients when validated in larger studies with at least 3 years of disease-free survival data.

Long-distance modulation of bystander tumor cells by CD8+ T cell-secreted IFNγ

T cell-secreted IFNγ can exert pleiotropic effects on tumor cells that include induction of immune checkpoints and antigen presentation machinery components, and inhibition of cell growth. Despite its role as key effector molecule, little is known about the spatiotemporal spreading of IFNγ secreted by activated CD8⁺ T cells within the tumor environment. Using multiday intravital imaging, we demonstrate that T cell recognition of a minor fraction of tumor cells leads to sensing of IFNγ by a large part of the tumor mass. Furthermore, imaging of tumors in which antigen-positive and -negative tumor cells are separated in space reveals spreading of the IFNγ response, reaching distances of >800 µm. Notably, long-range sensing of IFNγ can modify tumor behavior, as both shown by induction of PD-L1 expression and inhibition of tumor growth. Collectively, these data reveal how, through IFNγ, CD8⁺ T cells modulate the behavior of remote tumor cells, including antigen-loss variants.

Targeting Cancer with Genetically Engineered TCR T Cells

The adoptive cell transfer (ACT) of genetically engineered T cell receptor (TCR) T cells is one of the burgeoning fields of immunotherapy, with promising results in current clinical trials. Presently, clinicaltrials.gov has over 200 active trials involving adoptive cell therapy. The ACT of genetically engineered T cells not only allows the ability to select for TCRs with desired properties such as high-affinity receptors and tumor reactivity but to further enhance those receptors allowing for better targeting and killing of cancer cells in patients. Moreover, the addition of genetic material, including cytokines and cytokine receptors, can increase the survival and persistence of the T cell allowing for complete and sustained remission of cancer targets. The potential for improvement in adoptive cell therapy is limitless, with genetic modifications targeting to improve weaknesses of ACT and to thus enhance receptor affinity and functional avidity of the genetically engineered T cells.

Framework engineering to produce dominant T cell receptors with enhanced antigen-specific function

TCR-gene-transfer is an efficient strategy to produce therapeutic T cells of defined antigen specificity. However, there are substantial variations in the cell surface expression levels of human TCRs, which can impair the function of engineered T cells. Here we demonstrate that substitutions of 3 amino acid residues in the framework of the TCR variable domains consistently increase the expression of human TCRs on the surface of engineered T cells.The modified TCRs mediate enhanced T cell proliferation, cytokine production and cytotoxicity, while reducing the peptide concentration required for triggering effector function up to 3000-fold. Adoptive transfer experiments in mice show that modified TCRs control tumor growth more efficiently than wild-type TCRs. Our data indicate that simple variable domain modifications at a distance from the antigen-binding loops lead to increased TCR expression and improved effector function. This finding provides a generic platform to optimize the efficacy of TCR gene therapy in humans.

T-cells "à la CAR-T(e)" - Genetically engineering T-cell response against cancer

The last decade will be remembered as the dawn of the immunotherapy era during which we have witnessed the approval by regulatory agencies of genetically engineered CAR T-cells and of checkpoint inhibitors for cancer treatment. Understandably, T-lymphocytes represent the essential player in these approaches. These cells can mediate impressive tumor regression in terminally-ill cancer patients. Moreover, they are amenable to genetic engineering to improve their function and specificity. In the present review, we will give an overview of the most recent developments in the field of T-cell genetic engineering including TCR-gene transfer and CAR T-cells strategies. We will also elaborate on the development of other types of genetic modifications to enhance their anti-tumor immune response such as the use of co-stimulatory chimeric receptors (CCRs) and unconventional CARs built on non-antibody molecules. Finally, we will discuss recent advances in genome editing and synthetic biology applied to T-cell engineering and comment on the next challenges ahead.

SLFN11 can sensitize tumor cells towards IFN-γ-mediated T cell killing

Experimental and clinical observations have highlighted the role of cytotoxic T cells in human tumor control. However, the parameters that control tumor cell sensitivity to T cell attack remain incompletely understood. To identify modulators of tumor cell sensitivity to T cell effector mechanisms, we performed a whole genome haploid screen in HAP1 cells. Selection of tumor cells by exposure to tumor-specific T cells identified components of the interferon-γ (IFN-γ) receptor (IFNGR) signaling pathway, and tumor cell killing by cytotoxic T cells was shown to be in large part mediated by the pro-apoptotic effects of IFN-γ. Notably, we identified schlafen 11 (SLFN11), a known modulator of DNA damage toxicity, as a regulator of tumor cell sensitivity to T cell-secreted IFN-γ. SLFN11 does not influence IFNGR signaling, but couples IFNGR signaling to the induction of the DNA damage response (DDR) in a context dependent fashion. In line with this role of SLFN11, loss of SLFN11 can reduce IFN-γ mediated toxicity. Collectively, our data indicate that SLFN11 can couple IFN-γ exposure of tumor cells to DDR and cellular apoptosis. Future work should reveal the mechanistic basis for the link between IFNGR signaling and DNA damage response, and identify tumor cell types in which SLFN11 contributes to the anti-tumor activity of T cells.

Generation of CAR-T Cells for Cancer Immunotherapy

T cells engineered with chimeric antigen receptors (CARs) are emerging as powerful cancer immunotherapies. Remarkable efficacies have been demonstrated in treating B-cell malignancies with CAR-T cells, leading to the FDA's first approval of gene therapy. Currently, numerous clinical trials for hematological malignancies and solid tumors are underway worldwide. Production of CAR-T cells with proper qualities is essential for CAR-T success in vivo. Here we detail optimized protocols for the generation of CAR-T cells for preclinical studies using lentiviral gene transfer, expansion of CAR-T cells in culture, detection of CAR expression, and evaluation of CAR-T cellular cytotoxicity in vitro.

Isolation and characterization of NY-ESO-1-specific T cell receptors restricted on various MHC molecules

T immune cells can be engineered to express tumor-specific T cell receptor (TCR) genes and thereby kill cancer cells. This approach—termed TCR gene therapy—is effective but can cause serious adverse events if the target is also expressed in healthy, noncancerous tissue. NY-ESO-1 is a tumor-specific antigen that has been targeted successfully and safely through TCR gene therapies for melanoma, synovial sarcoma, and myeloma. However, trials to date have focused exclusively on a single NY-ESO-1–derived epitope presented on HLA-A*02:01, limiting application to patients expressing that allele. In this work, we isolate TCRs that collectively recognize multiple NY-ESO-1–derived epitopes presented by multiple MHC alleles. We thereby outline a general approach for expanding targeted immunotherapies to more diverse MHC haplotypes.

Tumor-specific T cell receptor (TCR) gene transfer enables specific and potent immune targeting of tumor antigens. Due to the prevalence of the HLA-A2 MHC class I supertype in most human populations, the majority of TCR gene therapy trials targeting public antigens have employed HLA-A2–restricted TCRs, limiting this approach to those patients expressing this allele. For these patients, TCR gene therapy trials have resulted in both tantalizing successes and lethal adverse events, underscoring the need for careful selection of antigenic targets. Broad and safe application of public antigen-targeted TCR gene therapies will require (i) selecting public antigens that are highly tumor-specific and (ii) targeting multiple epitopes derived from these antigens by obtaining an assortment of TCRs restricted by multiple common MHC alleles. The canonical cancer-testis antigen, NY-ESO-1, is not expressed in normal tissues but is aberrantly expressed across a broad array of cancer types. It has also been targeted with A2-restricted TCR gene therapy without adverse events or notable side effects. To enable the targeting of NY-ESO-1 in a broader array of HLA haplotypes, we isolated TCRs specific for NY-ESO-1 epitopes presented by four MHC molecules: HLA-A2, -B07, -B18, and -C03. Using these TCRs, we pilot an approach to extend TCR gene therapies targeting NY-ESO-1 to patient populations beyond those expressing HLA-A2.

Isolation and Characterization of an HLA-DRB1*04-Restricted HPV16-E7 T Cell Receptor for Cancer Immunotherapy

High-risk human papillomavirus (HPV) infection is a causal factor in oropharyngeal and gynecological malignancies, and development of HPV-targeted immunotherapy could be used to treat patients with these cancers. T cell-mediated adoptive immunotherapy targeting E6 and E7, two HPV16 proteins consistently expressed in tumor cells, appears to be both attractive and safe. However, isolation of HPV-specific T cells is difficult owing to the low frequency of these cell precursors in the peripheral blood. In addition, HPV-positive cancer cells often down-regulate major histocompatibility complex (MHC) class I expression ex vivo, limiting the efficacy of MHC class I-restricted approaches. Of particular interest is that both CD4 and CD8 T cells can mediate the responses. Given that CD4 T cells play a critical role in coordinating effective antitumor responses, the generation of a T helper response in patients with HPV16-associated malignancies would unleash the ultimate potential of immunotherapy. In this view, T-cell receptor (TCR) gene transfer could be a relevant strategy to generate HPV16-E7-specific and MHC class II-restricted T cells in sufficient numbers. An HPV16-E7/HLA-DRB1*04 TCR has been isolated from a cancer patient with complete response, and retroviral particles encoding this TCR have been produced. The transgenic TCR is highly expressed in transduced T cells, with a functional inducible caspase-9 suicide gene safety cassette. TCR transgenic T cells are HPV16-E7_70-89 specific and HLA-DRB1*04 restricted, as determined by interferon (IFN)-γ secretion. CD8 and CD4 T cells are equivalently transduced and secrete interleukin-2 and IFN-γ when cultured with appropriate targets. We also demonstrate that TCR transgenic T cells recognize the endogenously processed and presented HPV16-E7_70-89 peptide. In conclusion, our data indicate that the production of MHC class II-restricted HPV16-E7-specific T cells is feasible through TCR gene transfer and could be used for immunotherapy.

A humanized TCR retaining authentic specificity and affinity conferred potent anti-tumour cytotoxicity

The affinity of T-cell receptor (TCR) determines the efficacy of TCR-based immunotherapy. By using human leucocyte antigen (HLA)-A*02 transgenic mice, a TCR was generated previously specific for human tumour testis antigen peptide MAGE-A3_112-120 (KVAELVHFL) HLA-A*02 complex. We developed an approach to humanize the murine TCR by replacing the mouse framework with sequences of folding optimized human TCR variable domains for retaining binding affinity. The resultant humanized TCR exhibited higher affinity and conferred better anti-tumour activity than its parent murine MAGE-A3 TCR (SRm1). In addition, the affinity of humanized TCR was enhanced further to achieve improved T-cell activation. Our studies demonstrated that the human TCR variable domain frameworks could provide support for complementarity-determining regions from a murine TCR, and retain the original binding activity. It could be used as a generic approach of TCR humanization.

Immunotherapies: Exploiting the Immune System for Cancer Treatment

Cancer is a condition that has plagued humanity for thousands of years, with the first depictions dating back to ancient Egyptian times. However, not until recent decades have biological therapeutics been developed and refined enough to safely and effectively combat cancer. Three unique immunotherapies have gained traction in recent decades: adoptive T cell transfer, checkpoint inhibitors, and bivalent antibodies. Each has led to clinically approved therapies, as well as to therapies in preclinical and ongoing clinical trials. In this review, we outline the method by which these 3 immunotherapies function as well as any major immunotherapeutic drugs developed for treating a variety of cancers.

Identification of CMTM6 and CMTM4 as PD-L1 protein regulators

The clinical benefit in patients with diverse types of metastatic cancers that is observed upon blockade of the PD-1 – PD-L1 interaction has highlighted the importance of this inhibitory axis in the suppression of tumor-specific T cell responses1–9. In spite of the key role of PD-L1 expression by cells within the tumor micro-environment, our understanding of the regulation of the PD-L1 protein is limited10–15. Using a haploid genetic screen, we here identify CMTM6, a type 3 transmembrane protein of previously unknown function, as a regulator of the PD-L1 protein. Interference with CMTM6 expression results in impaired PD-L1 protein expression in all tumor cell types tested and in primary human dendritic cells. Furthermore, through both a haploid genetic modifier screen in CMTM6 deficient cells and genetic complementation experiments, we demonstrate that this function is shared by its closest family member CMTM4, but not by all other CMTM members tested. Notably, CMTM6 increases the PD-L1 protein pool without affecting PD-L1 transcript levels. Rather, we demonstrate that CMTM6 is present at the cell surface, associates with the PD-L1 protein, reduces its ubiquitination and increases PD-L1 protein half-life. Consistent with its role in PD-L1 protein regulation, T cell inhibitory capacity of PD-L1 expressing tumor cells is enhanced by CMTM6. Collectively, our data reveal that PD-L1 relies on CMTM6/4 to efficiently carry out its inhibitory function, and suggest potential new avenues to block this pathway.

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

Adoptive Cellular Therapy (ACT) for Cancer Treatment

Adoptive cellular therapy (ACT) with various lymphocytes or antigen-presenting cells is one stone in the pillar of cancer immunotherapy, which relies on the tumor-specific T cell. The transfusion of bulk T-cell population into patients is an effective treatment for regression of cancer. In this chapter, we summarize the development of various strategies in ACT for cancer immunotherapy and discuss some of the latest progress and obstacles in technical, safety, and even regulatory aspects to translate these technologies to the clinic. ACT is becoming a potentially powerful approach to cancer treatment. Further experiments and clinical trials are needed to optimize this strategy.

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.

A Traceless Selection: Counter-selection System That Allows Efficient Generation of Transposon and CRISPR-modified T-cell Products

Recent years have seen major breakthroughs in genome-engineering systems, such as transposon-mediated gene delivery systems and CRISPR-Cas9-mediated genome-editing tools. In these systems, transient expression of auxiliary genes is responsible for permanent genomic modification. For both systems, it would be valuable to select for cells that are likely to undergo stable genome modification. Importantly, in particular for clinical applications of genome-engineered cell products, it will also be of importance to remove those cells that, due to random vector integration, display an unwanted stable expression of the auxiliary gene. Here, we develop a traceless selection system that on the one hand allows efficient enrichment of modified cells, and on the other hand can be used to select against cells that retain expression of the auxiliary gene. The value of this system to produce highly enriched-auxiliary gene-free cell products is demonstrated.

T-cell receptor gene therapy--ready to go viral?

T lymphocytes can be redirected to recognize a tumor target and harnessed to combat cancer by genetic introduction of T-cell receptors of a defined specificity. This approach has recently mediated encouraging clinical responses in patients with cancers previously regarded as incurable. However, despite the great promise, T-cell receptor gene therapy still faces a multitude of obstacles. Identification of epitopes that enable effective targeting of all the cells in a heterogeneous tumor while sparing normal tissues remains perhaps the most demanding challenge. Experience from clinical trials has revealed the dangers associated with T-cell receptor gene therapy and highlighted the need for reliable preclinical methods to identify potentially hazardous recognition of both intended and unintended epitopes in healthy tissues. Procedures for manufacturing large and highly potent T-cell populations can be optimized to enhance their antitumor efficacy. Here, we review the current knowledge gained from preclinical models and clinical trials using adoptive transfer of T-cell receptor-engineered T lymphocytes, discuss the major challenges involved and highlight potential strategies to increase the safety and efficacy to make T-cell receptor gene therapy a standard-of-care for large patient groups.

Human Leukocyte Antigen (HLA) A*1101-Restricted Epstein-Barr Virus-Specific T-cell Receptor Gene Transfer to Target Nasopharyngeal Carcinoma

Infusing virus-specific T cells is effective treatment for rare Epstein-Barr virus (EBV)-associated posttransplant lymphomas, and more limited success has been reported using this approach to treat a far more common EBV-associated malignancy, nasopharyngeal carcinoma (NPC). However, current approaches using EBV-transformed lymphoblastoid cell lines to reactivate EBV-specific T cells for infusion take 2 to 3 months of in vitro culture and favor outgrowth of T cells targeting viral antigens expressed within EBV(+) lymphomas, but not in NPC. Here, we explore T-cell receptor (TCR) gene transfer to rapidly and reliably generate T cells specific for the NPC-associated viral protein LMP2. We cloned a human leukocyte antigen (HLA) A*1101-restricted TCR, which would be widely applicable because 40% of NPC patients carry this HLA allele. Studying both the wild-type and modified forms, we have optimized expression of the TCR and demonstrated high-avidity antigen-specific function (proliferation, cytotoxicity, and cytokine release) in both CD8(+) and CD4(+) T cells. The engineered T cells also inhibited LMP2(+) epithelial tumor growth in a mouse model. Furthermore, transduced T cells from patients with advanced NPC lysed LMP2-expressing NPC cell lines. Using this approach, within a few days large numbers of high-avidity LMP2-specific T cells can be generated reliably to treat NPC, thus providing an ideal clinical setting to test TCR gene transfer without the risk of autoimmunity through targeting self-antigens.

Case Report of a Fatal Serious Adverse Event Upon Administration of T Cells Transduced With a MART-1-specific T-cell Receptor

Here, we describe a fatal serious adverse event observed in a patient infused with autologous T-cell receptor (TCR) transduced T cells. This TCR, originally obtained from a melanoma patient, recognizes the well-described HLA-A*0201 restricted 26-35 epitope of MART-1, and was not affinity enhanced. Patient 1 with metastatic melanoma experienced a cerebral hemorrhage, epileptic seizures, and a witnessed cardiac arrest 6 days after cell infusion. Three days later, the patient died from multiple organ failure and irreversible neurologic damage. After T-cell infusion, levels of IL-6, IFN-γ, C-reactive protein (CRP), and procalcitonin increased to extreme levels, indicative of a cytokine release syndrome or T-cell-mediated inflammatory response. Infused T cells could be recovered from blood, broncho-alveolar lavage, ascites, and after autopsy from tumor sites and heart tissue. High levels of NT-proBNP indicate semi-acute heart failure. No cross reactivity of the modified T cells toward a beating cardiomyocyte culture was observed. Together, these observations suggest that high levels of inflammatory cytokines alone or in combination with semi-acute heart failure and epileptic seizure may have contributed substantially to the occurrence of the acute and lethal event. Protocol modifications to limit the risk of T-cell activation-induced toxicity are discussed.

Scientific contributions toward successful cancer immunotherapy in The Netherlands

This historical overview shows that immunologists and clinicians from The Netherlands have contributed in a major way to better insights in the nature of cancer immunity. This work involved elucidation of the nature of cancer-associated antigens in autologous and allogeneic settings in addition to understanding of the cellular basis of natural immune responses against cancers and of important immune evasion mechanisms. Insight into such basic immunological mechanisms has contributed to the development of innovating therapies.

MHC-restricted phosphopeptides from insulin receptor substrate-2 and CDC25b offer broad-based immunotherapeutic agents for cancer

Cancer cells display novel phosphopeptides in association with MHC class I and II molecules. In this study, we evaluated two HLA-A2-restricted phosphopeptides derived from the insulin receptor substrate (IRS)-2 and the cell-cycle regulator CDC25b. These proteins are both broadly expressed in multiple malignancies and linked to cancer cell survival. Two phosphopeptides, termed pIRS-21097-1105 and pCDC25b38-46, served as targets of strong and specific CD8 T-cell memory responses in normal human donors. We cloned T-cell receptor (TCR) cDNAs from murine CD8 T-cell lines specific for either pIRS-21097-1105 or pCDC25b38-46. Expression of these TCRs in human CD8 T cells imparted high-avidity phosphopeptide-specific recognition and cytotoxic and cytokine-secreting effector activities. Using these cells, we found that endogenously processed pIRS-21097-1105 was presented on HLA-A2(+) melanomas and breast, ovarian, and colorectal carcinomas. Presentation was correlated with the level of the Ser(1100)-phosphorylated IRS-2 protein in metastatic melanoma tissues. The highest expression of this protein was evident on dividing malignant cells. Presentation of endogenously processed pCDC25b38-46 was narrower, but still evident on HLA-A2(+) melanoma, breast carcinoma, and lymphoblastoid cells. Notably, pIRS-21097-1105-specific and pCDC25b38-46-specific TCR-expressing human CD8 T cells markedly slowed tumor outgrowth in vivo. Our results define two new antigens that may be developed as immunotherapeutic agents for a broad range of HLA-A2(+) cancers.

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.

Adoptive immunotherapy for cancer

Recent clinical success has underscored the potential for immunotherapy based on the adoptive cell transfer (ACT) of engineered T lymphocytes to mediate dramatic, potent, and durable clinical responses. This success has led to the broader evaluation of engineered T-lymphocyte-based adoptive cell therapy to treat a broad range of malignancies. In this review, we summarize concepts, successes, and challenges for the broader development of this promising field, focusing principally on lessons gleaned from immunological principles and clinical thought. We present ACT in the context of integrating T-cell and tumor biology and the broader systemic immune response.

Adoptive immunotherapy with genetically modified lymphocytes in allogeneic stem cell transplantation

Hematopoietic stem cell transplantation from a healthy donor (allo-HSCT) represents the most potent form of cellular adoptive immunotherapy to treat malignancies. In allo-HSCT, donor T cells are double edge-swords: highly potent against residual tumor cells, but potentially highly toxic, and responsible for graft versus host disease (GVHD), a major clinical complication of transplantation. Gene transfer technologies coupled with current knowledge on cancer immunology have generated a wide range of approaches aimed at fostering the immunological response to cancer cells, while avoiding or controlling GVHD. In this review, we discuss cell and gene therapy approaches currently tested in preclinical models and in clinical trials.

Antigen-Specific T-Cell Activation Independently of the MHC: Chimeric Antigen Receptor-Redirected T Cells

Adoptive T-cell therapy has recently shown promise in initiating a lasting anti-tumor response with spectacular therapeutic success in some cases. Specific T-cell therapy, however, is limited since a number of cancer cells are not recognized by T cells due to various mechanisms including the limited availability of tumor-specific T cells and deficiencies in antigen processing or major histocompatibility complex (MHC) expression of cancer cells. To make adoptive cell therapy applicable for the broad variety of cancer entities, patient's T cells are engineered ex vivo with pre-defined specificity by a recombinant chimeric antigen receptor (CAR) which consists in the extracellular part of an antibody-derived domain for binding with a "tumor-associated antigen" and in the intracellular part of a T-cell receptor (TCR)-derived signaling moiety for T-cell activation. The specificity of CAR-mediated T-cell recognition is defined by the antibody domain, is independent of MHC presentation and can be extended to any target for which an antibody is available. We discuss the advantages and limitations of MHC-independent T-cell targeting by an engineered CAR in comparison to TCR modified T cells and the impact of the CAR activation threshold on redirected T-cell activation. Finally we review most significant progress recently made in early stage clinical trials to treat cancer.

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).

In vitro generation of mature, naive antigen-specific CD8(+) T cells with a single T-cell receptor by agonist selection

Peripheral blood T cells transduced with a tumor-specific T-cell receptor (TCR) face problems of auto-reactivity and lack of efficacy caused by cross-pairing of exogenous and endogenous TCR chains, as well as short term in vivo survival due to activation and growth factor-induced differentiation. We here studied an alternative strategy for the efficient generation of naive CD8(+) T cells with a single TCR. TCR-transduced human postnatal thymus-derived and adult mobilized blood-derived hematopoietic progenitor cells (HPCs) were differentiated to CD4(+)CD8(+) double-positive T cells using OP9-Delta-like 1 (OP9-DL1) cultures. Addition of the agonist peptide induced double positive cells to cross-present the peptide, leading, in the absence of co-stimulation, to cell cycle arrest and differentiation into mature CD8(+) T cells. Comprehensive phenotypic, molecular and functional analysis revealed the generation of naive and resting CD8(+) T cells through a process similar to thymic positive selection. These mature T cells show a near complete inhibition of endogenous TCRA and TCRB rearrangements and express high levels of the introduced multimer-reactive TCR. Upon activation, specific cytokine production and efficient killing of tumor cells were induced. Using this strategy, large numbers of high-avidity tumor-specific naive T cells can be generated from readily available HPCs without TCR chain cross-pairing.

Immunotherapy for head and neck cancer patients: shifting the balance

Head and neck squamous cell carcinoma is the sixth most common cancer in the western world. Over the last few decades little improvement has been made to increase the relatively low 5-year survival rate. This calls for novel and improved therapies. Here, we describe opportunities in immunotherapy for head and neck cancer patients and hurdles yet to be overcome. Viruses are involved in a subset of head and neck squamous cell carcinoma cases. The incidence of HPV-related head and neck cancer is increasing and is a distinctly different disease from other head and neck carcinomas. Virus-induced tumors express viral antigens that are good targets for immunotherapeutic treatment options. The type of immunotherapeutic treatment, either active or passive, should be selected depending on the HPV status of the tumor and the immune status of the patient.

Adoptive transfer of genetically modified Wilms' tumor 1-specific T cells in a novel malignant skull base meningioma model

BACKGROUND

Meningiomas are the most commonly diagnosed primary intracranial neoplasms. Despite significant advances in modern therapies, the management of malignant meningioma and skull base meningioma remains a challenge. Thus, the development of new treatment modalities is urgently needed for these difficult-to-treat meningiomas. The goal of this study was to investigate the potential of build-in short interfering RNA-based Wilms' tumor protein (WT1)-targeted adoptive immunotherapy in a reproducible mouse model of malignant skull base meningioma that we recently established.

METHODS

We compared WT1 mRNA expression in human meningioma tissues and gliomas by quantitative real-time reverse-transcription polymerase chain reaction. Human malignant meningioma cells (IOMM-Lee cells) were labeled with green fluorescent protein (GFP) and implanted at the skull base of immunodeficient mice by using the postglenoid foramen injection (PGFi) technique. The animals were sacrificed at specific time points for analysis of tumor formation. Two groups of animals received adoptive immunotherapy with control peripheral blood mononuclear cells (PBMCs) or WT1-targeted PBMCs.

RESULTS

High levels of WT1 mRNA expression were observed in many meningioma tissues and all meningioma cell lines. IOMM-Lee-GFP cells were successfully implanted using the PGFi technique, and malignant skull base meningiomas were induced in all mice. The systemically delivered WT1-targeted PBMCs infiltrated skull base meningiomas and significantly delayed tumor growth and increased survival time.

CONCLUSIONS

We have established a reproducible mouse model of malignant skull base meningioma. WT1-targeted adoptive immunotherapy appears to be a promising approach for the treatment of difficult-to-treat meningiomas.

Mimicking homeostatic proliferation in vitro generates T cells with high anti-tumor function in non-lymphopenic hosts

CD8(+) T cells undergoing homeostatic proliferation (HP) in a lymphopenic environment acquire a central memory-like phenotype (CD44(+) CD62L(+) Ly6c(+)). Such cells are readily functional in vitro, with a strong capacity to secrete IFNγ and IL-2 and to lyse target cells upon antigen recognition. In vivo, these memory-like T cells display potent anti-tumor reactivity. When addressing whether these remarkable properties were "acquired" or dependent on sustained HP, we observed, for the first time, that memory-like T cells retained full anti-tumor functions even when removed from their lymphopenic environment and retransferred into non-lymphopenic P14/Rag2(-/-) recipients (where HP is prevented). Moreover, memory-like T cells were superior to in vitro expanded effector T cells. We next sought to determine the conditions required to reproduce such a potent phenotype in vitro, in order to obtain optimal cells for adoptive cell transfer therapy. Assessing ex vivo lymph node cultures, dendritic cells, fibroblastic reticular cells, and HP-associated cytokines, we found that stimulation of naïve T cells with anti-CD3/CD28 beads and IL-15 (IL-7 was dispensable) led to the generation of memory-like T cell with a similar phenotype. Both in vitro and in vivo memory-like T cells retained the capacity to efficiently control tumor growth in non-lymphopenic hosts upon adoptive cell transfer. A similar phenotype could be imparted to human peripheral blood leukocytes with comparable culture conditions. Our data reinforce the idea that in vitro-generated memory-like T cells could benefit adoptive cell transfer therapies.

Improving the efficacy and safety of engineered T cell therapy for cancer

Adoptive T-cell therapy (ACT) using tumor-infiltrating lymphocytes (TILs) is a powerful immunotherapeutics approach against metastatic melanoma. The success of TIL therapy has led to novel strategies for redirecting normal T cells to recognize tumor-associated antigens (TAAs) by genetically engineering tumor antigen-specific T cell receptors (TCRs) or chimeric antigen receptor (CAR) genes. In this manner, large numbers of antigen-specific T cells can be rapidly generated compared with the longer term expansion of TILs. Great efforts have been made to improve these approaches. Initial clinical studies have demonstrated that genetically engineered T cells can mediate tumor regression in vivo. In this review, we discuss the development of TCR and CAR gene-engineered T cells and the safety concerns surrounding the use of these T cells in patients. We highlight the importance of judicious selection of TAAs for modified T cell therapy and propose solutions for potential "on-target, off-organ" toxicity.

How (specific) would like your T-cells today? Generating T-cell therapeutic function through TCR-gene transfer

T-cells are central players in the immune response against both pathogens and cancer. Their specificity is solely dictated by the T-cell receptor (TCR) they clonally express. As such, the genetic modification of T lymphocytes using pathogen- or cancer-specific TCRs represents an appealing strategy to generate a desired immune response from peripheral blood lymphocytes. Moreover, notable objective clinical responses were observed in terminally ill cancer patients treated with TCR-gene modified cells in several clinical trials conducted recently. Nevertheless, several key aspects of this approach are the object of intensive research aimed at improving the reliability and efficacy of this strategy. Herein, we will survey recent studies in the field of TCR-gene transfer dealing with the improvement of this approach and its application for the treatment of malignant, autoimmune, and infectious diseases.

TCR gene transfer: MAGE-C2/HLA-A2 and MAGE-A3/HLA-DP4 epitopes as melanoma-specific immune targets

Adoptive therapy with TCR gene-engineered T cells provides an attractive and feasible treatment option for cancer patients. Further development of TCR gene therapy requires the implementation of T-cell target epitopes that prevent “on-target” reactivity towards healthy tissues and at the same time direct a clinically effective response towards tumor tissues. Candidate epitopes that meet these criteria are MAGE-C2_336-344/HLA-A2 (MC2/A2) and MAGE-A3_243-258/HLA-DP4 (MA3/DP4). We molecularly characterized TCRαβ genes of an MC2/A2-specific CD8 and MA3/DP4-specific CD4 T-cell clone derived from melanoma patients who responded clinically to MAGE vaccination. We identified MC2/A2 and MA3/DP4-specific TCR-Vα3/Vβ28 and TCR-Vα38/Vβ2 chains and validated these TCRs in vitro upon gene transfer into primary human T cells. The MC2 and MA3 TCR were surface-expressed and mediated CD8 T-cell functions towards melanoma cell lines and CD4 T-cell functions towards dendritic cells, respectively. We intend to start testing these MAGE-specific TCRs in phase I clinical trial.

Improving TCR Gene Therapy for Treatment of Haematological Malignancies

Adoptive immunotherapy using TCR gene modified T cells may allow separation of beneficial Graft versus tumour responses from harmful GvHD. Improvements to this include methods to generate high avidity or high affinity TCR, improvements in vector design and reduction in mispairing. Following adoptive transfer, TCR transduced T cells must be able to survive and persist in vivo to give most effective antitumour responses. Central memory or naive T cells have both been shown to be more effective than effector cells at expanding and persisting in vivo. Lymphodepletion may enhance persistence of transferred T cell populations. TCR gene transfer can be used to redirect CD4 helper T cells, and these could be used in combination with CD8+ tumour specific T cells to provide help for the antitumour response. Antigen specific T regulatory T cells can also be generated by TCR gene transfer and could be used to suppress unwanted alloresponses.

Genetically modulating T-cell function to target cancer

The adoptive transfer of tumor-specific T-lymphocytes holds promise for the treatment of metastatic cancer. Genetic modulation of T-lymphocytes using TCR transfer with tumor-specific TCR genes is an attractive strategy to generate anti-tumor response, especially against large solid tumors. Recently, several clinical trials have demonstrated the therapeutic potential of this approach which lead to impressive tumor regression in cancer patients. Still, several factors may hinder the clinical benefit of this approach, such as the type of cells to modulate, the vector configuration or the safety of the procedure. In the present review we will aim at giving an overview of the recent developments related to the immune modulation of the anti-tumor adaptive response using genetically engineered lymphocytes and will also elaborate the development of other genetic modifications to enhance their anti-tumor immune response.

A screening assay to identify agents that enhance T-cell recognition of human melanomas

Although a series of melanoma differentiation antigens for immunotherapeutic targeting has been described, heterogeneous expression of antigens such as Melan-A/MART-1 and gp100 results from a loss of antigenic expression in many late stage tumors. Antigen loss can represent a means for tumor escape from immune recognition, and a barrier to immunotherapy. However, since antigen-negative tumor phenotypes frequently result from reversible gene regulatory events, antigen enhancement represents a potential therapeutic opportunity. Accordingly, we have developed a cell-based assay to screen for compounds with the ability to enhance T-cell recognition of melanoma cells. This assay is dependent on augmentation of MelanA/MART-1 antigen presentation by a melanoma cell line (MU89). T-cell recognition is detected as interleukin-2 production by a Jurkat T cell transduced to express a T-cell receptor specific for an HLA-A2 restricted epitope of the Melan-A/MART-1 protein. This cellular assay was used to perform a pilot screen by using 480 compounds of known biological activity. From the initial proof-of-principle primary screen, eight compounds were identified as positive hits. A panel of secondary screens, including orthogonal assays, was used to validate the primary hits and eliminate false positives, and also to measure the comparative efficacy of the identified compounds. This cell-based assay, thus, yields consistent results applicable to the screening of larger libraries of compounds that can potentially reveal novel molecules which allow better recognition of treated tumors by T cells.

Generating HPV specific T helper cells for the treatment of HPV induced malignancies using TCR gene transfer

Background

Infection with high risk Human Papilloma Virus (HPV) is associated with cancer of the cervix, vagina, penis, vulva, anus and some cases of head and neck carcinomas. The HPV derived oncoproteins E6 and E7 are constitutively expressed in tumor cells and therefore potential targets for T cell mediated adoptive immunotherapy. Effective immunotherapy is dependent on the presence of both CD4+ and CD8+ T cells. However, low precursor frequencies of HPV16 specific T cells in patients and healthy donors hampers routine isolation of these cells for adoptive transfer purposes. An alternative to generate HPV specific CD4+ and CD8+ T cells is TCR gene transfer.

Methods

HPV specific CD4+ T cells were generated using either a MHC class I or MHC class II restricted TCR (from clones A9 and 24.101 respectively) directed against HPV16 antigens. Functional analysis was performed by interferon-γ secretion, proliferation and cytokine production assays.

Results

Introduction of HPV16 specific TCRs into blood derived CD4+ recipient T cells resulted in recognition of the relevant HPV16 epitope as determined by IFN-γ secretion. Importantly, we also show recognition of the endogenously processed and HLA-DP1 presented HPV16E6 epitope by 24.101 TCR transgenic CD4+ T cells and recognition of the HLA-A2 presented HPV16E7 epitope by A9 TCR transgenic CD4+ T cells.

Conclusion

Our data indicate that TCR transfer is feasible as an alternative strategy to generate human HPV16 specific CD4+ T helper cells for the treatment of patients suffering from cervical cancer and other HPV16 induced malignancies.

Transduction of SIV-specific TCR genes into rhesus macaque CD8+ T cells conveys the ability to suppress SIV replication

BACKGROUND

The SIV/rhesus macaque model for HIV/AIDS is a powerful system for examining the contribution of T cells in the control of AIDS viruses. To better our understanding of CD8(+) T-cell control of SIV replication in CD4(+) T cells, we asked whether TCRs isolated from rhesus macaque CD8(+) T-cell clones that exhibited varying abilities to suppress SIV replication could convey their suppressive properties to CD8(+) T cells obtained from an uninfected/unvaccinated animal.

PRINCIPAL FINDINGS

We transferred SIV-specific TCR genes isolated from rhesus macaque CD8(+) T-cell clones with varying abilities to suppress SIV replication in vitro into CD8(+) T cells obtained from an uninfected animal by retroviral transduction. After sorting and expansion, transduced CD8(+) T-cell lines were obtained that specifically bound their cognate SIV tetramer. These cell lines displayed appropriate effector function and specificity, expressing intracellular IFNγ upon peptide stimulation. Importantly, the SIV suppression properties of the transduced cell lines mirrored those of the original TCR donor clones: cell lines expressing TCRs transferred from highly suppressive clones effectively reduced wild-type SIV replication, while expression of a non-suppressing TCR failed to reduce the spread of virus. However, all TCRs were able to suppress the replication of an SIV mutant that did not downregulate MHC-I, recapitulating the properties of their donor clones.

CONCLUSIONS

Our results show that antigen-specific SIV suppression can be transferred between allogenic T cells simply by TCR gene transfer. This advance provides a platform for examining the contributions of TCRs versus the intrinsic effector characteristics of T-cell clones in virus suppression. Additionally, this approach can be applied to develop non-human primate models to evaluate adoptive T-cell transfer therapy for AIDS and other diseases.