Receptor affinity and extracellular domain modifications affect tumor recognition by ROR1-specific chimeric antigen receptor T cells

The development of CAR design for tumor CAR-T cell therapy

In recent years, the chimeric antigen receptor modified T cells (Chimeric antigen receptor T cells, CAR-T) immunotherapy has developed rapidly, which has been considered the most promising therapy. Efforts to enhance the efficacy of CAR-based anti-tumor therapy have been made, such as the improvement of structures of CAR-T cells, including the development of extracellular antigen recognition receptors, intracellular co-stimulatory molecules and the combination application of CARs and synthetic small molecules. In addition, effects on the function of the CAR-T cells that the space distance between the antigen binding domains and tumor targets and the length of the spacer domains have are also being investigated. Given the fast-moving nature of this field, it is necessary to make a summary of the development of CAR-T cells. In this review, we mainly focus on the present design strategies of CAR-T cells with the hope that they can provide insights to increase the anti-tumor efficacy and safety.

Preclinical Optimization of a CD20-specific Chimeric Antigen Receptor Vector and Culture Conditions

Chimeric antigen receptor (CAR)-based adoptive T-cell therapy is a highly promising treatment for lymphoid malignancies, and CD20 is an ideal target antigen. We previously developed a lentiviral construct encoding a third generation CD20-targeted CAR but identified several features that required additional optimization before clinical translation. We describe here several improvements, including replacement of the immunogenic murine antigen-binding moiety with a fully human domain, streamlining the transgene insert to enhance lentiviral titers, modifications to the extracellular IgG spacer that abrogate nonspecific activation resulting from binding to Fc receptors, and evaluation of CD28, 4-1BB, or CD28 and 4-1BB costimulatory domains. We also found that restimulation of CAR T cells with an irradiated CD20 cell line boosted cell growth, increased the fraction of CAR-expressing cells, and preserved in vivo function despite leading to a reduced capacity for cytokine secretion in vitro. We also found that cryopreservation of CAR T cells did not affect immunophenotype or in vivo antitumor activity compared with fresh cells. These optimization steps resulted in significant improvement in antitumor activity in mouse models, resulting in eradication of established systemic lymphoma tumors in 75% of mice with a single infusion of CAR T cells, and prolonged in vivo persistence of modified cells. These results provide the basis for clinical testing of a lentiviral construct encoding a fully human CD20-targeted CAR with CD28 and 4-1BB costimulatory domains and truncated CD19 (tCD19) transduction marker.

Comparison of T Cell Activities Mediated by Human TCRs and CARs That Use the Same Recognition Domains

Adoptive T cell therapies have achieved significant clinical responses, especially in hematopoietic cancers. Two types of receptor systems have been used to redirect the activity of T cells, normal heterodimeric TCRs or synthetic chimeric Ag receptors (CARs). TCRs recognize peptide-HLA complexes whereas CARs typically use an Ab-derived single-chain fragments variable that recognizes cancer-associated cell-surface Ags. Although both receptors mediate diverse effector functions, a quantitative comparison of the sensitivity and signaling capacity of TCRs and CARs has been limited due to their differences in affinities and ligands. In this study we describe their direct comparison by using TCRs that could be formatted either as conventional αβ heterodimers, or as single-chain fragments variable constructs linked to CD3ζ and CD28 signaling domains or to CD3ζ alone. Two high-affinity TCRs (K_D values of ∼50 and 250 nM) against MART1/HLA-A2 or WT1/HLA-A2 were used, allowing MART1 or WT1 peptide titrations to easily assess the impact of Ag density. Although CARs were expressed at higher surface levels than TCRs, they were 10-100-fold less sensitive, even in the absence of the CD8 coreceptor. Mathematical modeling demonstrated that lower CAR sensitivity could be attributed to less efficient signaling kinetics. Furthermore, reduced cytokine secretion observed at high Ag density for both TCRs and CARs suggested a role for negative regulators in both systems. Interestingly, at high Ag density, CARs also mediated greater maximal release of some cytokines, such as IL-2 and IL-6. These results have implications for the next-generation design of receptors used in adoptive T cell therapies.

Enhanced Expression of Anti-CD19 Chimeric Antigen Receptor in piggyBac Transposon-Engineered T Cells

Adoptive T cell therapy using chimeric antigen receptor (CAR)-modified T cells is a promising cancer immunotherapy. We previously developed a non-viral method of gene transfer into T cells using a piggyBac transposon system to improve the cost-effectiveness of CAR-T cell therapy. Here, we have further improved our technology by a novel culture strategy to increase the transfection efficiency and to reduce the time of T cell manufacturing. Using a CH2CH3-free CD19-specific CAR transposon vector and combining irradiated activated T cells (ATCs) as feeder cells and virus-specific T cell receptor (TCR) stimulation, we achieved 51.4% ± 14% CAR⁺ T cells and 2.8-fold expansion after 14 culture days. Expanded CD19.CAR-T cells maintained a significant fraction of CD45RA⁺CCR7⁺ T cells and demonstrated potent antitumor activity against CD19⁺ leukemic cells both in vitro and in vivo. Therefore, piggyBac-based gene transfer may provide an alternative to viral gene transfer for CAR-T cell therapy.

Wnt signalling pathways in chronic lymphocytic leukaemia and B-cell lymphomas

In this review, we discuss the intricate roles of the Wnt signalling network in the development and progression of mature B-cell-derived haematological malignancies, with a focus on chronic lymphocytic leukaemia (CLL) and related B-cell lymphomas. We review the current literature and highlight the differences between the β-catenin-dependent and -independent branches of Wnt signalling. Special attention is paid to the role of the non-canonical Wnt/planar cell polarity (PCP) pathway, mediated by the Wnt-5-receptor tyrosine kinase-like orphan receptor (ROR1)-Dishevelled signalling axis in CLL. This is mainly because the Wnt/PCP co-receptor ROR1 was found to be overexpressed in CLL and the Wnt/PCP pathway contributes to numerous aspects of CLL pathogenesis. We also discuss the possibilities of therapeutically targeting the Wnt signalling pathways as an approach to disrupt the crucial interaction between malignant cells and their micro-environment. We also advocate the need for research in this direction for other lymphomas, namely, diffuse large B-cell lymphoma, Hodgkin lymphoma, mantle cell lymphoma, Burkitt lymphoma and follicular lymphoma where the Wnt signalling pathway probably plays a similar role.

LINKED ARTICLES

This article is part of a themed section on WNT Signalling: Mechanisms and Therapeutic Opportunities. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.24/issuetoc.

High-Affinity GD2-Specific CAR T Cells Induce Fatal Encephalitis in a Preclinical Neuroblastoma Model

The GD2 ganglioside, which is abundant on the surface of neuroblastoma cells, is targeted by an FDA-approved therapeutic monoclonal antibody and is an attractive tumor-associated antigen for cellular immunotherapy. Chimeric antigen receptor (CAR)-modified T cells can have potent antitumor activity in B-cell malignancies, and trials to harness this cytolytic activity toward GD2 in neuroblastoma are under way. In an effort to enhance the antitumor activity of CAR T cells that target GD2, we generated variant CAR constructs predicted to improve the stability and the affinity of the GD2-binding, 14G2a-based, single-chain variable fragment (scFv) of the CAR and compared their properties in vivo We included the E101K mutation of GD2 scFv (GD2-E101K) that has enhanced antitumor activity against a GD2⁺ human neuroblastoma xenograft in vivo However, this enhanced antitumor efficacy in vivo was concomitantly associated with lethal central nervous system (CNS) toxicity comprised of extensive CAR T-cell infiltration and proliferation within the brain and neuronal destruction. The encephalitis was localized to the cerebellum and basal regions of the brain that display low amounts of GD2. Our results highlight the challenges associated with target antigens that exhibit shared expression on critical normal tissues. Despite the success of GD2-specific antibody therapies in the treatment of neuroblastoma, the fatal neurotoxicity of GD2-specific CAR T-cell therapy observed in our studies suggests that GD2 may be a difficult target antigen for CAR T-cell therapy without additional strategies that can control CAR T-cell function within the CNS. Cancer Immunol Res; 6(1); 36-46. ©2017 AACR.

Development of unique cytotoxic chimeric antigen receptors based on human scFv targeting B7H6

As a stress-inducible natural killer (NK) cell ligand, B7H6 plays a role in innate tumor immunosurveillance and is a fairly tumor selective marker expressed on a variety of solid and hematologic cancer cells. Here, we describe the isolation and characterization of a new family of single chain fragment variable (scFv) molecules targeting the human B7H6 ligand. Through directed evolution of a yeast surface displayed non-immune human-derived scFv library, eight candidates comprising a single family of clones differing by up to four amino acid mutations and exhibiting nM avidities for soluble B7H6-Ig were isolated. A representative clone re-formatted as an scFv-CH1-Fc molecule demonstrated specific binding to both B7H6-Ig and native membrane-bound B7H6 on tumor cell lines with a binding avidity comparable to the previously characterized B7H6-targeting antibody, TZ47. Furthermore, these clones recognized an epitope distinct from that of TZ47 and the natural NK cell ligand NKp30, and demonstrated specific activity against B7H6-expressing tumor cells when expressed as a chimeric antigen receptor (CAR) in T cells.

SLAMF7-CAR T cells eliminate myeloma and confer selective fratricide of SLAMF7+ normal lymphocytes

SLAMF7 is under intense investigation as a target for immunotherapy in multiple myeloma. In this study, we redirected the specificity of T cells to SLAMF7 through expression of a chimeric antigen receptor (CAR) derived from the huLuc63 antibody (elotuzumab) and demonstrate that SLAMF7-CAR T cells prepared from patients and healthy donors confer potent antimyeloma reactivity. We confirmed uniform, high-level expression of SLAMF7 on malignant plasma cells in previously untreated and in relapsed/refractory (R/R) myeloma patients who had received previous treatment with proteasome inhibitors and immunomodulatory drugs. Consequently, SLAMF7-CAR T cells conferred rapid cytolysis of previously untreated and R/R primary myeloma cells in vitro. In addition, a single administration of SLAMF7-CAR T cells led to resolution of medullary and extramedullary myeloma manifestations in a murine xenograft model in vivo. SLAMF7 is expressed on a fraction of normal lymphocytes, including subsets of natural killer (NK) cells, T cells, and B cells. After modification with the SLAMF7-CAR, both CD8⁺ and CD4⁺ T cells rapidly acquired and maintained a SLAMF7^- phenotype and could be readily expanded to therapeutically relevant cell doses. We analyzed the recognition of normal lymphocytes by SLAMF7-CAR T cells and show that they induce selective fratricide of SLAMF7^+/high NK cells, CD4⁺ and CD8⁺ T cells, and B cells. Importantly, however, the fratricide conferred by SLAMF7-CAR T cells spares the SLAMF7^-/low fraction in each cell subset and preserves functional lymphocytes, including virus-specific T cells. In aggregate, our data illustrate the potential use of SLAMF7-CAR T-cell therapy as an effective treatment against multiple myeloma and provide novel insights into the consequences of targeting SLAMF7 for the normal lymphocyte compartment.

Micromolar affinity CAR T cells to ICAM-1 achieves rapid tumor elimination while avoiding systemic toxicity

Adoptive transfer of high-affinity chimeric antigen receptor (CAR) T cells targeting hematological cancers has yielded impressive clinical results. However, safety concerns regarding target expression on healthy tissue and poor efficacy have hampered application to solid tumors. Here, a panel of affinity-variant CARs were constructed targeting overexpressed ICAM-1, a broad tumor biomarker, using its physiological ligand, LFA-1. Anti-tumor T cell potency in vitro was directly proportional to CAR affinity and ICAM-1 density. In a solid tumor mouse model allowing simultaneous monitoring of anti-tumor potency and systemic off-tumor toxicity, micromolar affinity CAR T cells demonstrated superior anti-tumor efficacy and safety compared to their nanomolar counterparts. Longitudinal T cell tracking by PET/CT and concurrent cytokine measurement revealed superior expansion and contraction kinetics of micromolar affinity CAR T cells. Therefore, we developed an ICAM-1 specific CAR with broad anti-tumor applicability that utilized a reduced affinity targeting strategy to significantly boost efficacy and safety.

Development of A Chimeric Antigen Receptor Targeting C-Type Lectin-Like Molecule-1 for Human Acute Myeloid Leukemia

The treatment of patients with acute myeloid leukemia (AML) with targeted immunotherapy is challenged by the heterogeneity of the disease and a lack of tumor-exclusive antigens. Conventional immunotherapy targets for AML such as CD33 and CD123 have been proposed as targets for chimeric antigen receptor (CAR)-engineered T-cells (CAR-T-cells), a therapy that has been highly successful in the treatment of B-cell leukemia and lymphoma. However, CD33 and CD123 are present on hematopoietic stem cells, and targeting with CAR-T-cells has the potential to elicit long-term myelosuppression. C-type lectin-like molecule-1 (CLL1 or CLEC12A) is a myeloid lineage antigen that is expressed by malignant cells in more than 90% of AML patients. CLL1 is not expressed by healthy Hematopoietic Stem Cells (HSCs), and is therefore a promising target for CAR-T-cell therapy. Here, we describe the development and optimization of an anti-CLL1 CAR-T-cell with potent activity on both AML cell lines and primary patient-derived AML blasts in vitro while sparing healthy HSCs. Furthermore, in a disseminated mouse xenograft model using the CLL1-positive HL60 cell line, these CAR-T-cells completely eradicated tumor, thus supporting CLL1 as a promising target for CAR-T-cells to treat AML while limiting myelosuppressive toxicity.

Co-stimulatory signaling determines tumor antigen sensitivity and persistence of CAR T cells targeting PSCA+ metastatic prostate cancer

Advancing chimeric antigen receptor (CAR)-engineered adoptive T cells for the treatment of solid cancers is a major focus in the field of immunotherapy, given impressive recent clinical responses in hematological malignancies. Prostate cancer may be amenable to T cell-based immunotherapy since several tumor antigens, including prostate stem-cell antigen (PSCA), are widely over-expressed in metastatic disease. While antigen selectivity of CARs for solid cancers is crucial, it is problematic due to the absence of truly restricted tumor antigen expression and potential safety concerns with “on-target off-tumor” activity. Here, we show that the intracellular co-stimulatory signaling domain can determine a CAR's sensitivity for tumor antigen expression. A 4-1BB intracellular co-stimulatory signaling domain in PSCA-CARs confers improved selectivity for higher tumor antigen density, reduced T cell exhaustion phenotype, and equivalent tumor killing ability compared to PSCA-CARs containing the CD28 co-stimulatory signaling domain. PSCA-CARs exhibit robust in vivo anti-tumor activity in patient-derived bone-metastatic prostate cancer xenograft models, and 4-1BB-containing CARs show superior T cell persistence and control of disease compared with CD28-containing CARs. Our study demonstrates the importance of co-stimulation in defining an optimal CAR T cell, and also highlights the significance of clinically relevant models in developing solid cancer CAR T cell therapies.

Integrating Proteomics and Transcriptomics for Systematic Combinatorial Chimeric Antigen Receptor Therapy of AML

Chimeric antigen receptor (CAR) therapy targeting CD19 has yielded remarkable outcomes in patients with acute lymphoblastic leukemia. To identify potential CAR targets in acute myeloid leukemia (AML), we probed the AML surfaceome for overexpressed molecules with tolerable systemic expression. We integrated large transcriptomics and proteomics datasets from malignant and normal tissues, and developed an algorithm to identify potential targets expressed in leukemia stem cells, but not in normal CD34⁺CD38^- hematopoietic cells, T cells, or vital tissues. As these investigations did not uncover candidate targets with a profile as favorable as CD19, we developed a generalizable combinatorial targeting strategy fulfilling stringent efficacy and safety criteria. Our findings indicate that several target pairings hold great promise for CAR therapy of AML.

Therapeutic T cell engineering

Genetically engineered T cells are powerful new medicines, offering hope for curative responses in patients with cancer. Chimaeric antigen receptors (CARs) are a class of synthetic receptors that reprogram lymphocyte specificity and function. CARs targeting CD19 have demonstrated remarkable potency in B cell malignancies. Engineered T cells are applicable in principle to many cancers, pending further progress to identify suitable target antigens, overcome immunosuppressive tumour microenvironments, reduce toxicities, and prevent antigen escape. Advances in the selection of optimal T cells, genetic engineering, and cell manufacturing are poised to broaden T-cell-based therapies and foster new applications in infectious diseases and autoimmunity.

Gene Therapy with the Sleeping Beauty Transposon System

The widespread clinical implementation of gene therapy requires the ability to stably integrate genetic information through gene transfer vectors in a safe, effective, and economical manner. The latest generation of Sleeping Beauty (SB) transposon vectors fulfills these requirements, and may overcome limitations associated with viral gene transfer vectors and transient nonviral gene delivery approaches that are prevalent in ongoing clinical trials. The SB system enables high-level stable gene transfer and sustained transgene expression in multiple primary human somatic cell types, thereby representing a highly attractive gene transfer strategy for clinical use. Here, we review the most important aspects of using SB for gene therapy, including vectorization as well as genomic integration features. We also illustrate the path to successful clinical implementation by highlighting the application of chimeric antigen receptor (CAR)-modified T cells in cancer immunotherapy.

Chimeric Antigen Receptor T cells for B Cell Neoplasms: Choose the Right CAR for You

Genetic redirection of T lymphocytes allows us to unleash these potent cellular immune effectors against cancer. Chimeric antigen receptor (CAR) T cells are the best-in-class example that genetic engineering of T cells can lead to deep and durable responses, as has been shown in several clinical trials for CD19+ B cell malignancies. As a consequence, in the last few years, several academic institutions and commercial partners have started developing anti-CD19 CAR T cell products. Although most of these T cell products are highly effective in vivo, basic differences among them can generate different performance characteristics and thereby impact their long-term clinical outcome. Several strategies are being implemented in order to solve the current open issues of CART19 therapy: (i) increasing efficacy against indolent B cell leukemias and lymphomas, (ii) avoiding or preventing antigen-loss relapses, (iii) reducing and managing toxicity, and (iv) bringing this CART therapy to routine clinical practice. The field of CART therapies is thriving, and exciting new avenues are opening for both scientists and patients.

Mining Naïve Rabbit Antibody Repertoires by Phage Display for Monoclonal Antibodies of Therapeutic Utility

Owing to their high affinities and specificities, rabbit monoclonal antibodies (mAbs) have demonstrated value and potential primarily as basic research and diagnostic reagents, but, in some cases, also as therapeutics. To accelerate access to rabbit mAbs bypassing immunization, we generated a large naïve rabbit antibody repertoire represented by a phage display library encompassing >10 billion independent antibodies in chimeric rabbit/human Fab format and validated it by next-generation sequencing. Panels of rabbit mAbs selected from this library against two emerging cancer targets, ROR1 and ROR2, revealed high diversity, affinity, and specificity. Moreover, ROR1- and ROR2-targeting rabbit mAbs demonstrated therapeutic utility as components of chimeric antigen receptor-engineered T cells, further corroborating the value of the naïve rabbit antibody library as a rich and virtually unlimited source of rabbit mAbs.

Quantitative Imaging Approaches to Study the CAR Immunological Synapse

The lytic immunological synapse (IS) is a discrete structural entity formed after the ligation of specific activating receptors that leads to the destruction of a cancerous cell. The formation of an effector cell IS in cytotoxic T lymphocytes or natural killer cells is a hierarchical and stepwise rearrangement of structural and signaling components and targeted release of the contents of lytic granules. While recent advances in the generation and testing of cytotoxic lymphocytes expressing chimeric antigen receptors (CARs) has demonstrated their efficacy in the targeted lysis of tumor targets, the contribution and dynamics of IS components have not yet been extensively investigated in the context of engineered CAR cells. Understanding the biology of the CAR IS will be a powerful approach to efficiently guide the engineering of new CARs and help identify mechanistic problems in existing CARs. Here, we review the formation of the lytic IS and describe quantitative imaging-based measurements using multiple microscopy techniques at a single cell level that can be used in conjunction with established population-based assays to provide insight into the important cytotoxic function of CAR cells. The inclusion of this approach in the pipeline of CAR product design could be a novel and valuable innovation for the field.

'Atypical' CAR T cells: NKG2D and Erb-B as examples of natural receptor/ligands to target recalcitrant solid tumors

Chimeric antigen receptor (CAR) T-cell therapy has recently been recommended for approval for certain B-cell malignancies bringing the approach closer to mainstream cancer treatment. This rapid rise to prominence has been driven by impressive clinical results and the means to successfully commercialize the approach now being actively pursued. The current success of CAR T cells in B-cell malignancies relies upon the absolute lineage specificity of the CD19 antigen. CARs can also be targeted using non-antibody approaches, including the use of receptors and ligands to provide target specificity that have different specificities and binding kinetics. The specific examples of NKG2D and Erb-B are used that provide different characteristics and target profiles for CAR T-cell therapy of cancer.

Promises and limitations of nanoparticles in the era of cell therapy: Example with CD19-targeting chimeric antigen receptor (CAR)-modified T cells

A number of nanoparticles has been developed by chemists for biomedical applications to meet imaging and targeting needs. In parallel, adoptive T therapy with chimeric antigen receptor engineered T cells (CART cells) has recently held great promise in B-cell malignancy treatments thanks to the development of anti-CD19 CAR T cells. Indeed, CD19 is a reliable B cell marker and a validated target protein for therapy. In this perspective article, we propose to discuss the advantages, limits and challenges of nanoparticles and CAR T cells, focusing on CD19 targeting objects: anti-CD19 nanoparticles and anti-CD19 CAR T cells, because those genetically-modified cells are the most widely developed in clinical setting. In the first part, we will introduce B cell malignancies and the CD19 surface marker. Then we will present the positioning of nanomedicine in the topic of B cell malignancy, before exposing CAR T technology. Finally, we will discuss the complementary approaches between nanoparticles and CAR T cells.

Adnectin-Based Design of Chimeric Antigen Receptor for T Cell Engineering

Although chimeric antigen receptor (CAR)-engineered T cell therapy has achieved encouraging clinical trial results for treating hematological cancers, further optimization can likely expand this therapeutic success to more patients and other cancer types. Most CAR constructs used in clinical trials incorporate single chain variable fragment (scFv) as the extracellular antigen recognition domain. The immunogenicity of nonhuman scFv could cause host rejection against CAR T cells and compromise their persistence and efficacy. The limited availability of scFvs and slow discovery of new monoclonal antibodies also limit the development of novel CAR constructs. Adnectin, a class of affinity molecules derived from the tenth type III domain of human fibronectin, can be an alternative to scFv as an antigen-binding moiety in the design of CAR molecules. We constructed adnectin-based CARs targeting epithelial growth factor receptor (EGFR) and found that compared to scFv-based CAR, T cells engineered with adnectin-based CARs exhibited equivalent cell-killing activity against target H292 lung cancer cells in vitro and had comparable antitumor efficacy in xenograft tumor-bearing mice in vivo. In addition, with optimal affinity tuning, adnectin-based CAR showed higher selectivity on target cells with high EGFR expression than on those with low expression. This new design of adnectin CARs can potentially facilitate the development of T cell immunotherapy for cancer and other diseases.

The Affinity of Elongated Membrane-Tethered Ligands Determines Potency of T Cell Receptor Triggering

T lymphocytes are important mediators of adoptive immunity but the mechanism of T cell receptor (TCR) triggering remains uncertain. The interspatial distance between engaged T cells and antigen-presenting cells (APCs) is believed to be important for topological rearrangement of membrane tyrosine phosphatases and initiation of TCR signaling. We investigated the relationship between ligand topology and affinity by generating a series of artificial APCs that express membrane-tethered anti-CD3 scFv with different affinities (OKT3, BC3, and 2C11) in addition to recombinant class I and II pMHC molecules. The dimensions of membrane-tethered anti-CD3 and pMHC molecules were progressively increased by insertion of different extracellular domains. In agreement with previous studies, elongation of pMHC molecules or low-affinity anti-CD3 scFv caused progressive loss of T cell activation. However, elongation of high-affinity ligands (BC3 and OKT3 scFv) did not abolish TCR phosphorylation and T cell activation. Mutation of key amino acids in OKT3 to reduce binding affinity to CD3 resulted in restoration of topological dependence on T cell activation. Our results show that high-affinity TCR ligands can effectively induce TCR triggering even at large interspatial distances between T cells and APCs.

Comprehensive Approach for Identifying the T Cell Subset Origin of CD3 and CD28 Antibody-Activated Chimeric Antigen Receptor-Modified T Cells

The outcome of therapy with chimeric Ag receptor (CAR)-modified T cells is strongly influenced by the subset origin of the infused T cells. However, because polyclonally activated T cells acquire a largely CD45RO+CCR7- effector memory phenotype after expansion, regardless of subset origin, it is impossible to know which subsets contribute to the final T cell product. To determine the contribution of naive T cell, memory stem T cell, central memory T cell, effector memory T cell, and terminally differentiated effector T cell populations to the CD3 and CD28-activated CAR-modified T cells that we use for therapy, we followed the fate and function of individually sorted CAR-modified T cell subsets after activation with CD3 and CD28 Abs (CD3/28), transduction and culture alone, or after reconstitution into the relevant subset-depleted population. We show that all subsets are sensitive to CAR transduction, and each developed a distinct T cell functional profile during culture. Naive-derived T cells showed the greatest rate of proliferation but had more limited effector functions and reduced killing compared with memory-derived populations. When cultured in the presence of memory T cells, naive-derived T cells show increased differentiation, reduced effector cytokine production, and a reduced reproliferative response to CAR stimulation. CD3/28-activated T cells expanded in IL-7 and IL-15 produced greater expansion of memory stem T cells and central memory T cell-derived T cells compared with IL-2. Our strategy provides a powerful tool to elucidate the characteristics of CAR-modified T cells, regardless of the protocol used for expansion, reveals the functional properties of each expanded T cell subset, and paves the way for a more detailed evaluation of the effects of manufacturing changes on the subset contribution to in vitro-expanded T cells.

Tumor Antigen and Receptor Densities Regulate Efficacy of a Chimeric Antigen Receptor Targeting Anaplastic Lymphoma Kinase

We explored the utility of targeting anaplastic lymphoma kinase (ALK), a cell surface receptor overexpressed on pediatric solid tumors, using chimeric antigen receptor (CAR)-based immunotherapy. T cells expressing a CAR incorporating the single-chain variable fragment sequence of the ALK48 mAb linked to a 4-1BB-CD3ζ signaling domain lysed ALK-expressing tumor lines and produced interferon-gamma upon antigen stimulation but had limited anti-tumor efficacy in two xenograft models of human neuroblastoma. Further exploration demonstrated that cytokine production was highly dependent upon ALK target density and that target density of ALK on neuroblastoma cell lines was insufficient for maximal activation of CAR T cells. In addition, ALK CAR T cells demonstrated rapid and complete antigen-induced loss of receptor from the T cell surface via internalization. Using a model that simultaneously modulated antigen density and CAR expression, we demonstrated that CAR functionality is regulated by target antigen and CAR density and that low expression of either contributes to limited anti-tumor efficacy of the ALK CAR. These data suggest that stoichiometric relationships between CAR receptors and target antigens may significantly impact the anti-tumor efficacy of CAR T cells and that manipulation of these parameters could allow precise tuning of CAR T cell activity.

The Multi-Purpose Tool of Tumor Immunotherapy: Gene-Engineered T Cells

A detailed summary of the published clinical trials of chimeric antigen receptor T cells (CAR-T) and TCR-transduced T cells (TCR-T) was constructed to understand the development trend of adoptive T cell therapy (ACT). In contrast to TCR-T, the number of CAR-T clinical trials has increased dramatically in China in the last three years. The ACT seems to be very prosperous. But, the multidimensional interaction of tumor, tumor associated antigen (TAA) and normal tissue exacerbates the uncontrolled outcome of T cells gene therapy. It reminds us the importance that optimizing treatment security to prevent the fatal serious adverse events. How to balance the safety and effectiveness of the ACT? At least six measures can potentially optimize the safety of ACT. At the same time, with the application of gene editing techniques, more endogenous receptors are disrupted while more exogenous receptors are expressed on T cells. As a multi-purpose tool of tumor immunotherapy, gene-engineered T cells (GE-T) have been given different functional weapons. A network which is likely to link radiation therapy, tumor vaccines, CAR-T and TCR-T is being built. Moreover, more and more evidences indicated that the combination of the ACT and other therapies would further enhance the anti-tumor capacity of the GE-T.

Designed Ankyrin Repeat Proteins as Her2 Targeting Domains in Chimeric Antigen Receptor-Engineered T Cells

Chimeric antigen receptor (CAR) engineering is a branch of cancer immunotherapy that equips immune cells to target tumor antigens expressed on the cell surface using antibody-derived single-chain variable fragments (scFvs). However, other antibody mimetics, such as designed ankyrin repeat proteins (DARPins), can also serve as antigen-binding domains in CARs. This study shows that CAR-engineered T (CAR-T) cells utilizing Her2-targeting DARPins G3 and 929 can target human epidermal growth factor receptor 2 (Her2)-overexpressing cancer cells as effectively as CAR-T cells with the scFv 4D5 in vitro, and G3 CAR-T cells can slow or eliminate tumor growth in vivo as effectively as 4D5 CAR-T cells. Some DARPins may offer an attractive alternative to scFv usage in CARs, as they are smaller, thermodynamically stable, poorly immunogenic, and can be generated with different binding properties from DARPin libraries.

Antigen Discovery and Therapeutic Targeting in Hematologic Malignancies

Historically, immune-based therapies have played a leading role in the treatment of hematologic malignancies, with the efficacy of stem cell transplantation largely attributable to donor immunity against malignant cells. As new and more targeted immunotherapies have developed, their role in the treatment of hematologic malignancies is evolving and expanding. Herein, we discuss approaches for antigen discovery and review known and novel tumor antigens in hematologic malignancies. We further explore the role of established and investigational immunotherapies in hematologic malignancies, with a focus on personalization of treatment modalities such as cancer vaccines and adoptive cell therapy. Finally, we identify areas of active investigation and development. Immunotherapy is at an exciting crossroads for the treatment of hematologic malignancies, with further investigation aimed at producing effective, targeted immune therapies that maximize antitumor effects while minimizing toxicity.

A tandem CD19/CD20 CAR lentiviral vector drives on-target and off-target antigen modulation in leukemia cell lines

Background

Clinical success with chimeric antigen receptor (CAR)- based immunotherapy for leukemia has been accompanied by the associated finding that antigen-escape variants of the disease are responsible for relapse. To target hematologic malignancies with a chimeric antigen receptor (CAR) that targets two antigens with a single vector, and thus potentially lessen the chance of leukemic escape mutations, a tandem-CAR approach was investigated.

Methods

Antigen binding domains from the FMC63 (anti-CD19) and Leu16 (anti-CD20) antibodies were linked in differing configurations to transmembrane and T cell signaling domains to create tandem-CARs. Expression on the surface of primary human T cells was induced by transduction with a single lentiviral vector (LV) encoding the tandem-CAR. Tandem-CARs were compared to single antigen targeting CARs in vitro and in vivo, and to an admixture of transduced cells expressing each CAR in vivo in immunodeficient (NSG) disease-bearing mice.

Results

Tandem constructs efficient killed the Raji leukemia cell line both in vitro and in vivo. Tandem CARs generated less cytokine than the CD20 CAR, but similar to CD19 CARs, on their own. In co-culture experiments at low effector to target ratios with both single- and tandem- CAR-T cells, a rapid down-modulation of full-length CD19 expression was seen on leukemia targets. There also was a partial down-modulation of CD22, and to a lesser degree, of CD20. Our data also highlight the extreme sensitivity of the NALM-6 cell line to general lymphocyte-mediated cytotoxicity. While single and tandem constructs were effective in vivo in a standard setting, in a high-disease burden setting, the tandem CAR proved both effective and less toxic than an admixture of transduced T cell populations expressing single CARs.

Conclusion

Tandem CARs are equally effective in standard disease models to single antigen specificity CARs, and may be both more effective and less toxic in a higher disease burden setting. This may be due to optimized cell killing with more moderate cytokine production. The rapid co-modulation of CD19, CD20, and CD22 may account for the ability to rapidly evolve escape mutants by selecting for leukemic clones that not require these target antigens for continued expansion.

Electronic supplementary material

The online version of this article (doi:10.1186/s40425-017-0246-1) contains supplementary material, which is available to authorized users.

A Rational Strategy for Reducing On-Target Off-Tumor Effects of CD38-Chimeric Antigen Receptors by Affinity Optimization

Chimeric antigen receptors (CARs) can effectively redirect cytotoxic T cells toward highly expressed surface antigens on tumor cells. The low expression of several tumor-associated antigens (TAAs) on normal tissues, however, hinders their safe targeting by CAR T cells due to on-target/off-tumor effects. Using the multiple myeloma (MM)-associated CD38 antigen as a model system, here, we present a rational approach for effective and tumor-selective targeting of such TAAs. Using "light-chain exchange" technology, we combined the heavy chains of two high-affinity CD38 antibodies with 176 germline light chains and generated ∼124 new antibodies with 10- to >1,000-fold lower affinities to CD38. After categorizing them into three distinct affinity classes, we incorporated the single-chain variable fragments of eight antibodies from each class into new CARs. T cells carrying these CD38-CARs were extensively evaluated for their on-tumor/off-tumor cytotoxicity as well as CD38-dependent proliferation and cytokine production. We identified CD38-CAR T cells of ∼1,000- fold reduced affinity, which optimally proliferated, produced Th1-like cytokines, and effectively lysed CD38²⁺ MM cells, but spared CD38⁺ healthy hematopoietic cells in vitro and in vivo. Thus, this systematic approach is highly suitable for the generation of optimal CARs for effective and selective targeting of TAAs.

Balance of Anti-CD123 Chimeric Antigen Receptor Binding Affinity and Density for the Targeting of Acute Myeloid Leukemia

Chimeric antigen receptor (CAR)-redirected T lymphocytes are a promising immunotherapeutic approach and object of pre-clinical evaluation for the treatment of acute myeloid leukemia (AML). We developed a CAR against CD123, overexpressed on AML blasts and leukemic stem cells. However, potential recognition of low CD123-positive healthy tissues, through the on-target, off-tumor effect, limits safe clinical employment of CAR-redirected T cells. Therefore, we evaluated the effect of context-dependent variables capable of modulating CAR T cell functional profiles, such as CAR binding affinity, CAR expression, and target antigen density. Computational structural biology tools allowed for the design of rational mutations in the anti-CD123 CAR antigen binding domain that altered CAR expression and CAR binding affinity without affecting the overall CAR design. We defined both lytic and activation antigen thresholds, with early cytotoxic activity unaffected by either CAR expression or CAR affinity tuning but later effector functions impaired by low CAR expression. Moreover, the anti-CD123 CAR safety profile was confirmed by lowering CAR binding affinity, corroborating CD123 is a good therapeutic target antigen. Overall, full dissection of these variables offers suitable anti-CD123 CAR design optimization for the treatment of AML.

Current status and perspectives of chimeric antigen receptor modified T cells for cancer treatment

Chimeric antigen receptor (CAR) is a recombinant immunoreceptor combining an antibody-derived targeting fragment with signaling domains capable of activating cells, which endows T cells with the ability to recognize tumor-associated surface antigens independent of the expression of major histocompatibility complex (MHC) molecules. Recent early-phase clinical trials of CAR-modified T (CAR-T) cells for relapsed or refractory B cell malignancies have demonstrated promising results (that is, anti-CD19 CAR-T in B cell acute lymphoblastic leukemia (B-ALL)). Given this success, broadening the clinical experience of CAR-T cell therapy beyond hematological malignancies has been actively investigated. Here we discuss the basic design of CAR and review the clinical results from the studies of CAR-T cells in B cell leukemia and lymphoma, and several solid tumors. We additionally discuss the major challenges in the further development and strategies for increasing anti-tumor activity and safety, as well as for successful commercial translation.

Increasing the safety and efficacy of chimeric antigen receptor T cell therapy

Chimeric antigen receptor (CAR) T cell therapy is a promising cancer treatment that has recently been undergoing rapid development. However, there are still some major challenges, including precise tumor targeting to avoid off-target or “on-target/off-tumor” toxicity, adequate T cell infiltration and migration to solid tumors and T cell proliferation and persistence across the physical and biochemical barriers of solid tumors. In this review, we focus on the primary challenges and strategies to design safe and effective CAR T cells, including using novel cutting-edge technologies for CAR and vector designs to increase both the safety and efficacy, further T cell modification to overcome the tumor-associated immune suppression, and using gene editing technologies to generate universal CAR T cells. All these efforts promote the development and evolution of CAR T cell therapy and move toward our ultimate goal—curing cancer with high safety, high efficacy, and low cost.

CARs: Synthetic Immunoreceptors for Cancer Therapy and Beyond

Chimeric antigen receptors (CARs) are versatile synthetic receptors that provide T cells with engineered specificity. Clinical success in treating B-cell malignancies has demonstrated the therapeutic potential of CAR-T cells against cancer, and efforts are underway to expand the use of engineered T cells to the treatment of diverse medical conditions, including infections and autoimmune diseases. Here, we review current understanding of the molecular properties of CARs, how this knowledge informs the rational design and characterization of novel receptors, the successes and shortcomings of CAR-T cells in the clinic, and emerging solutions for the continued improvement of CAR-T cell therapy.

Going non-viral: the Sleeping Beauty transposon system breaks on through to the clinical side

Molecular medicine has entered a high-tech age that provides curative treatments of complex genetic diseases through genetically engineered cellular medicinal products. Their clinical implementation requires the ability to stably integrate genetic information through gene transfer vectors in a safe, effective and economically viable manner. The latest generation of Sleeping Beauty (SB) transposon vectors fulfills these requirements, and may overcome limitations associated with viral gene transfer vectors and transient non-viral gene delivery approaches that are prevalent in ongoing pre-clinical and translational research. The SB system enables high-level stable gene transfer and sustained transgene expression in multiple primary human somatic cell types, thereby representing a highly attractive gene transfer strategy for clinical use. Here we review several recent refinements of the system, including the development of optimized transposons and hyperactive SB variants, the vectorization of transposase and transposon as mRNA and DNA minicircles (MCs) to enhance performance and facilitate vector production, as well as a detailed understanding of SB's genomic integration and biosafety features. This review also provides a perspective on the regulatory framework for clinical trials of gene delivery with SB, and illustrates the path to successful clinical implementation by using, as examples, gene therapy for age-related macular degeneration (AMD) and the engineering of chimeric antigen receptor (CAR)-modified T cells in cancer immunotherapy.

From rabbit antibody repertoires to rabbit monoclonal antibodies

In this review, we explain why and how rabbit monoclonal antibodies have become outstanding reagents for laboratory research and increasingly for diagnostic and therapeutic applications. Starting with the unique ontogeny of rabbit B cells that affords highly distinctive antibody repertoires rich in in vivo pruned binders of high diversity, affinity and specificity, we describe the generation of rabbit monoclonal antibodies by hybridoma technology, phage display and alternative methods, along with an account of successful humanization strategies.

Fully human CD19-specific chimeric antigen receptors for T-cell therapy

Impressive results have been achieved by adoptively transferring T-cells expressing CD19-specific CARs with binding domains from murine mAbs to treat B-cell malignancies. T-cell mediated immune responses specific for peptides from the murine scFv antigen-binding domain of the CAR can develop in patients and result in premature elimination of CAR T-cells increasing the risk of tumor relapse. As fully human scFv might reduce immunogenicity, we generated CD19-specific human scFvs with similar binding characteristics as the murine FMC63-derived scFv using human Ab/DNA libraries. CARs were constructed in various formats from several scFvs and used to transduce primary human T-cells. The resulting CD19-CAR T-cells were specifically activated by CD19-positive tumor cell lines and primary chronic lymphocytic leukemia cells, and eliminated human lymphoma xenografts in immunodeficient mice. Certain fully human CAR constructs were superior to the FMC63-CAR, which is widely used in clinical trials. Imaging of cell surface distribution of the human CARs revealed no evidence of clustering without target cell engagement, and tonic signaling was not observed. To further reduce potential immunogenicity of the CARs, we also modified the fusion sites between different CAR components. The described fully human CARs for a validated clinical target may reduce immune rejection compared with murine-based CARs.

Receptor tyrosine kinase-like orphan receptor 1 (ROR-1): An emerging target for diagnosis and therapy of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is characterized by reposition of malignant B cells in the blood, bone marrow, spleen and lymph nodes. It remains the most common leukemia in the Western world. Within the recent years, major breakthroughs have been made to prolong the survival and improve the health of patients. Despite these advances, CLL is still recognized as a disease without definitive cure. New treatment approaches, based on unique targets and novel drugs, are highly desired for CLL therapy. The Identification and subsequent targeting of molecules that are overexpressed uniquely in malignant cells not normal ones play critical roles in the success of anticancer therapeutic strategies. In this regard, ROR family proteins are known as a subgroup of protein kinases which have gained huge popularity in the scientific community for the diagnosis and treatment of different cancer types. ROR1 as an antigen exclusively expressed on the surface of tumor cells can be a target for immunotherapy. ROR-1 targeting using different approaches such as siRNA, tyrosine kinase inhibitors, cell therapy and antibody induces tumor growth suppression in cancer cells. In the current review, we aim to present an overview of the efforts and scientific achievements in targeting ROR family, particularly ROR-1, for the diagnosis and treatment of chronic lymphocytic leukemia (CLL).

Chimaeric antigen receptor T-cell therapy for tumour immunotherapy

Chimaeric antigen receptor (CAR) T-cell therapies, as one of the cancer immunotherapies, have heralded a new era of treating cancer. The accumulating data, especially about CAR-modified T cells against CD19 support that CAR T-cell therapy is a highly effective immune therapy for B-cell malignancies. Apart from CD19, there have been many trials of CAR T cells directed other tumour specific or associated antigens (TSAs/TAAs) in haematologic malignancies and solid tumours. This review will briefly summarize basic CAR structure, parts of reported TSAs/TAAs, results of the clinical trials of CAR T-cell therapies as well as two life-threatening side effects. Experiments in vivo or in vitro, ongoing clinical trials and the outlook for CAR T-cell therapies also be included. Our future efforts will focus on identification of more viable cancer targets and more strategies to make CAR T-cell therapy safer.

Chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is a malignancy of CD5+ B cells that is characterized by the accumulation of small, mature-appearing lymphocytes in the blood, marrow and lymphoid tissues. Signalling via surface immunoglobulin, which constitutes the major part of the B cell receptor, and several genetic alterations play a part in CLL pathogenesis, in addition to interactions between CLL cells and other cell types, such as stromal cells, T cells and nurse-like cells in the lymph nodes. The clinical progression of CLL is heterogeneous and ranges from patients who require treatment soon after diagnosis to others who do not require therapy for many years, if at all. Several factors, including the immunoglobulin heavy-chain variable region gene (IGHV) mutational status, genomic changes, patient age and the presence of comorbidities, should be considered when defining the optimal management strategies, which include chemotherapy, chemoimmunotherapy and/or drugs targeting B cell receptor signalling or inhibitors of apoptosis, such as BCL-2. Research on the biology of CLL has profoundly enhanced our ability to identify patients who are at higher risk for disease progression and our capacity to treat patients with drugs that selectively target distinctive phenotypic or physiological features of CLL. How these and other advances have shaped our current understanding and treatment of patients with CLL is the subject of this Primer.

Targeting O-Acetyl-GD2 Ganglioside for Cancer Immunotherapy

Target selection is a key feature in cancer immunotherapy, a promising field in cancer research. In this respect, gangliosides, a broad family of structurally related glycolipids, were suggested as potential targets for cancer immunotherapy based on their higher abundance in tumors when compared with the matched normal tissues. GD2 is the first ganglioside proven to be an effective target antigen for cancer immunotherapy with the regulatory approval of dinutuximab, a chimeric anti-GD2 therapeutic antibody. Although the therapeutic efficacy of anti-GD2 monoclonal antibodies is well documented, neuropathic pain may limit its application. O-Acetyl-GD2, the O-acetylated-derivative of GD2, has recently received attention as novel antigen to target GD2-positive cancers. The present paper examines the role of O-acetyl-GD2 in tumor biology as well as the available preclinical data of anti-O-acetyl-GD2 monoclonal antibodies. A discussion on the relevance of O-acetyl-GD2 in chimeric antigen receptor T cell therapy development is also included.

Making Better Chimeric Antigen Receptors for Adoptive T-cell Therapy

Chimeric antigen receptors (CAR) are engineered fusion proteins constructed from antigen recognition, signaling, and costimulatory domains that can be expressed in cytotoxic T cells with the purpose of reprograming the T cells to specifically target tumor cells. CAR T-cell therapy uses gene transfer technology to reprogram a patient's own T cells to stably express CARs, thereby combining the specificity of an antibody with the potent cytotoxic and memory functions of a T cell. In early-phase clinical trials, CAR T cells targeting CD19 have resulted in sustained complete responses within a population of otherwise refractory patients with B-cell malignancies and, more specifically, have shown complete response rates of approximately 90% in patients with relapsed or refractory acute lymphoblastic leukemia. Given this clinical efficacy, preclinical development of CAR T-cell therapy for a number of cancer indications has been actively investigated, and the future of the CAR T-cell field is extensive and dynamic. Several approaches to increase the feasibility and safety of CAR T cells are currently being explored, including investigation into the mechanisms regulating the persistence of CAR T cells. In addition, numerous early-phase clinical trials are now investigating CAR T-cell therapy beyond targeting CD19, especially in solid tumors. Trials investigating combinations of CAR T cells with immune checkpoint blockade therapies are now beginning and results are eagerly awaited. This review evaluates several of the ongoing and future directions of CAR T-cell therapy.

Efficacy and toxicity management of CAR-T-cell immunotherapy: a matter of responsiveness control or tumour-specificity?

Chimaeric antigen receptor (CAR)-expressing T-cells have demonstrated potent clinical efficacy in patients with haematological malignancies. However, the use of CAR-T-cells targeting solid tumour-associated antigens (TAAs) has been limited by organ toxicities related to activation of T-cell effector functions through the CAR. Most existing CARs recognize TAAs, which are also found in normal tissues. CAR-T-cell-mediated destruction of normal tissues constitutes a major roadblock to CAR-T-cell therapy, and must be avoided or mitigated. There is a broad range of strategies for modulating antigen responsiveness of CAR-T-cells, with varying degrees of complexity. Some of them might ameliorate the acute and chronic toxicities associated with current CAR constructs. However, further embellishments to CAR therapy may complicate clinical implementation and possibly create new immunogenicity issues. In contrast, the development of CARs targeting truly tumour-specific antigens might circumvent on-target/off-tumour toxicities without adding additional complexity to CAR-T-cell therapies, but these antigens have been elusive and may require novel selection strategies for their discovery.

Redirecting T cells to eradicate B-cell acute lymphoblastic leukemia: bispecific T-cell engagers and chimeric antigen receptors

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.

Humanized Mouse Models of Clinical Disease

Immunodeficient mice engrafted with functional human cells and tissues, that is, humanized mice, have become increasingly important as small, preclinical animal models for the study of human diseases. Since the description of immunodeficient mice bearing mutations in the IL2 receptor common gamma chain (IL2rg^null) in the early 2000s, investigators have been able to engraft murine recipients with human hematopoietic stem cells that develop into functional human immune systems. These mice can also be engrafted with human tissues such as islets, liver, skin, and most solid and hematologic cancers. Humanized mice are permitting significant progress in studies of human infectious disease, cancer, regenerative medicine, graft-versus-host disease, allergies, and immunity. Ultimately, use of humanized mice may lead to the implementation of truly personalized medicine in the clinic. This review discusses recent progress in the development and use of humanized mice and highlights their utility for the study of human diseases.

Acute Myeloid Leukemia Targeting by Chimeric Antigen Receptor T Cells: Bridging the Gap from Preclinical Modeling to Human Studies

Acute myeloid leukemia (AML) still represents an unmet clinical need for adult and pediatric high-risk patients, thus demanding advanced and personalized therapies. In this regard, different targeted immunotherapeutic approaches are available, ranging from naked monoclonal antibodies (mAb) to conjugated and multifunctional mAbs (i.e., BiTEs and DARTs). Recently, researchers have focused their attention on novel techniques of genetic manipulation specifically to redirect cytotoxic T cells endowed with chimeric antigen receptors (CARs) toward selected tumor associated antigens. So far, CAR T cells targeting the CD19 antigen expressed by B-cell origin hematological cancers have gained impressive clinical results, leading to the possibility of translating the CAR platform to treat other hematological malignancies such as AML. However, one of the main concerns in the field of AML CAR immunotherapy is the identification of an ideal target cell surface antigen, being highly expressed on tumor cells but minimally present on healthy tissues, together with the design of an anti-AML CAR appropriately balancing efficacy and safety profiles. The current review focuses mainly on AML target antigens and the related immunotherapeutic approaches developed so far, deeply dissecting methods of CAR T cell safety improvements, when designing novel CARs approaching human studies.

Analysis of ROR1 Protein Expression in Human Cancer and Normal Tissues

Purpose: This study examines cell surface ROR1 expression in human tumors and normal tissues. ROR1 is considered a promising target for cancer therapy due to putative tumor-specific expression, and multiple groups are developing antibodies and/or chimeric antigen receptor-modified T cells to target ROR1. On-target, off-tumor toxicity is a challenge for most nonmutated tumor antigens; however, prior studies suggest that ROR1 is absent on most normal tissues.Experimental Design: Our studies show that published antibodies lack sensitivity to detect endogenous levels of cell surface ROR1 by immunohistochemistry (IHC) in formalin-fixed, paraffin-embedded tissues. We developed a ROR1-specific monoclonal antibody (mAb) targeting the carboxy-terminus of ROR1 and evaluated its specificity and sensitivity in IHC.Results: The 6D4 mAb is a sensitive and specific reagent to detect cell surface ROR1 by IHC. The data show that ROR1 is homogenously expressed on a subset of ovarian cancer, triple-negative breast cancer, and lung adenocarcinomas. Contrary to previous findings, we found ROR1 is expressed on several normal tissues, including parathyroid; pancreatic islets; and regions of the esophagus, stomach, and duodenum. The 6D4 mAb recognizes rhesus ROR1, and ROR1 expression was similar in human and macaque tissues, suggesting that the macaque is a suitable model to evaluate safety of ROR1-targeted therapies.Conclusions: ROR1 is a promising immunotherapeutic target in many epithelial tumors; however, high cell surface ROR1 expression in multiple normal tissues raises concerns for on-target off-tumor toxicities. Clinical translation of ROR1-targeted therapies warrants careful monitoring of toxicities to normal organs and may require strategies to ensure patient safety. Clin Cancer Res; 23(12); 3061-71. ©2016 AACR.

Immunological quality and performance of tumor vessel-targeting CAR-T cells prepared by mRNA-EP for clinical research

We previously reported that tumor vessel-redirected T cells, which were genetically engineered with chimeric antigen receptor (CAR) specific for vascular endothelial growth factor receptor 2 (VEGFR2), demonstrated significant antitumor effects in various murine solid tumor models. In the present study, we prepared anti-VEGFR2 CAR-T cells by CAR-coding mRNA electroporation (mRNA-EP) and analyzed their immunological characteristics and functions for use in clinical research. The expression of anti-VEGFR2 CAR on murine and human T cells was detected with approximately 100% efficiency for a few days, after peaking 6-12 hours after mRNA-EP. Triple transfer of murine anti-VEGFR2 CAR-T cells into B16BL6 tumor-bearing mice demonstrated an antitumor effect comparable to that for the single transfer of CAR-T cells engineered with retroviral vector. The mRNA-EP did not cause any damage or defects to human T-cell characteristics, as determined by viability, growth, and phenotypic parameters. Additionally, two kinds of human anti-VEGFR2 CAR-T cells, which expressed different CAR construction, differentiated to effector phase with cytokine secretion and cytotoxic activity in antigen-specific manner. These results indicate that our anti-VEGFR2 CAR-T cells prepared by mRNA-EP have the potential in terms of quality and performance to offer the prospect of safety and efficacy in clinical research as cellular medicine.

ROR1 is a novel prognostic biomarker in patients with lung adenocarcinoma

Currently, there is no reliable biomarker to clinically predict the prognosis of lung adenocarcinoma (ADC). The receptor-tyrosine-kinase like orphan receptor 1 (ROR1) is reported to be overexpressed and associated with poor prognosis in several tumors. This study aimed to examine the expression of ROR1 and evaluate its prognostic significance in human lung ADC patients. In this present study, Western blot analysis and immunohistochemistry were performed to characterize expression of ROR1 protein in lung ADC patients. The results revealed that ROR1 protein expression was significantly higher in lung ADC tissues than that in their adjacent non-tumor tissues. Patients at advanced stages and those with positive lymph node metastasis expressed higher level of ROR1 (P < 0.001). Moreover, Chi-square test showed that ROR1 expression was correlated to gender (P = 0.028), the 7^th edition of the American Joint Committee on Cancer tumor-node-metastasis (AJCC TNM) staging system and lymph node metastasis (P < 0.001). Kaplan-Meier survival analysis indicated an association of high ROR1 expression with worse overall survival (OS) in lung ADC patients (P < 0.001). Multivariate COX regression analysis further confirmed that ROR1 is an independent prognostic predictor (P < 0.001, HR = 4.114, 95% CI: 2.513–6.375) for OS. Therefore, ROR1 expression significantly correlates with malignant attributes of lung ADC and it may serve as a novel prognostic marker in lung ADC patients.