Chimaeric T-cell receptors specific to a B-lymphoma idiotype: a model for tumour immunotherapy

Tumor Growth Suppression of Pancreatic Cancer Orthotopic Xenograft Model by CEA-Targeting CAR-T Cells

Chimeric antigen receptor engineered T cell (CAR-T) therapy has high therapeutic efficacy against blood cancers, but it has not shown satisfactory results in solid tumors. Therefore, we examined the therapeutic effect of CAR-T therapy targeting carcinoembryonic antigen (CEA) in pancreatic adenocarcinoma (PDAC). CEA expression levels on the cell membranes of various PDAC cell lines were evaluated using flow cytometry and the cells were divided into high, medium, and low expression groups. The relationship between CEA expression level and the antitumor effect of anti-CEA-CAR-T was evaluated using a functional assay for various PDAC cell lines; a significant correlation was observed between CEA expression level and the antitumor effect. We created orthotopic PDAC xenograft mouse models and injected with anti-CEA-CAR-T; only the cell line with high CEA expression exhibited a significant therapeutic effect. Thus, the therapeutic effect of CAR-T therapy was related to the target antigen expression level, and the further retrospective analysis of pathological findings from PDAC patients showed a correlation between the intensity of CEA immunostaining and tumor heterogeneity. Therefore, CEA expression levels in biopsies or surgical specimens can be clinically used as biomarkers to select PDAC patients for anti-CAR-T therapy.

Chimeric Antigen Receptor-Engineered T Cell Therapy in Acute Myeloid Leukaemia

Acute myeloid leukaemia (AML) is a disease with a very poor outcome and remains an area of significant unmet need, necessitating novel therapeutic strategies. The progress made in the field of immunotherapy, in particular chimeric antigen receptor (CAR)-engineered T cells, has given rise to many hopes for pathologies such as B cell acute lymphoblastic leukaemia and B cell lymphoma, and many studies have attempted to translate these successes to AML. This review summarises the recent advances in, and defines an ideal target for, CAR T cell therapy in AML.

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.

Adoptive immunotherapy for cancer: the next generation of gene-engineered immune cells

Adoptive cellular immunotherapy involving transfer of tumor-reactive T cells has shown some notable antitumor responses in a minority of cancer patients. In particular, transfer of tumor-infiltrating lymphocytes has resulted in long-term objective responses in patients with advanced melanoma. However, the inability to isolate sufficient numbers of tumor-specific T cells from most malignancies has restricted the broad utility of this approach. An emerging approach to circumvent this limitation involves the genetic modification of effector cells with T cell receptor (TCR) transgenes or chimeric single-chain variable fragment (scFv) receptors that can specifically redirect T cells to tumor. There has been much progress in the design of TCR and scFv receptors to enhance the antigen-specific activation of effector cells and their trafficking and persistence in vivo. Considerable effort has been directed toward improving the safety of this approach and reducing the immunogenicity of the receptor. This review discusses the latest developments in the field of adoptive immunotherapy using genetically modified immune cells that have been transduced with either TCR or scFv receptor transgenes and used in preclinical and clinical settings as anticancer agents.

Antitumor activity of chimeric immunoreceptor gene-modified Tc1 and Th1 cells against autologous carcinoembryonic antigen-expressing colon cancer cells

To generate tumor-specific and interferon (IFN)-gamma-producing Tc1 and Th1 cells applicable for many cancer patients, we previously developed a protocol for generating carcinoembryonic antigen (CEA)-specific Tc1 and Th1 cells from healthy human T cells by transduction with a lentivirus containing a chimeric immunoglobulin T-cell receptor (cIgTCR) gene composed of single-chain variable fragments from an anti-CEA-specific monoclonal antibody fused to an intracellular signaling domain of CD28 and CD3zeta. These cells, designated Tc1-T and Th1-T bodies, respectively, showed strong antitumor activity against CEA-expressing tumor cells in RAG2-/- mice when both of them were transferred. However, it remains unclear whether it is possible to generate Tc1-T and Th1-T bodies from cancer patients with defective T-cell function because of significant immunosuppression. Here, we prepared Tc1-T and Th1-T bodies from T cells of a colon cancer patient, and asked whether these T bodies can exert effective T-cell function against autologous tumor cells. These T bodies showed high cytotoxicity and produced IFN-gamma in response to CEA-expressing autologous tumor cells, even in the presence of soluble CEA. It was also demonstrated that Th1-T bodies supported the survival of Tc1-T bodies through cell-to-cell interactions. Furthermore, our protocol utilized retrovirus for cIgTCR transduction to achieve better induction efficiency compared to lentivirus-mediated transduction. Taken together, our findings here indicate that retrovirally transduced Tc1-T and Th1-T bodies will become a promising strategy for adoptive immunotherapy of human cancer.

Cellular immunotherapy for follicular lymphoma using genetically modified CD20-specific CD8+ cytotoxic T lymphocytes

Humoral immunotherapy using the monoclonal anti-CD20 antibody rituximab induces remissions in approximately 60% of patients with relapsed follicular lymphoma; however, most patients eventually relapse despite continued expression of CD20 on lymphoma cells. We have hypothesized that cellular immunotherapy targeting CD20(+) cells might provide a more effective mechanism for eliminating lymphoma cells than anti-CD20 antibodies and are therefore investigating the utility of cytotoxic T lymphocytes (CTL) genetically modified to target the CD20 antigen. Peripheral blood mononuclear cells were activated with anti-CD3 antibody (OKT3) and recombinant human interleukin-2 and electroporated with a plasmid containing a CD20-specific scFvFc:zeta chimeric T cell receptor gene and a neomycin phosphotransferase gene (neo(R)). Transfected cells were selected using the antibiotic G418 and cloned by limiting dilution. Using this approach, we have generated CD8(+) CTL clones with CD20-specific cytotoxicity, which specifically lysed CD20(+) target cells, including actual tumor cells from patients with follicular lymphoma, small lymphocytic lymphoma, splenic marginal zone lymphoma, diffuse large B cell lymphoma, and chronic lymphocytic leukemia. The CTL clones have been expanded to numbers sufficient for therapy ( approximately 10(9) cells). Our data indicate the feasibility of generating and expanding CD20-specific CTL and, for the first time, demonstrate that such CTL exhibit specific cytotoxicity against actual tumor cells isolated from patients with a variety of B lymphoid malignancies. In view of these promising findings, a Phase I clinical trial for relapsed follicular lymphoma is being initiated.

Antibodies and gene therapy: teaching old ‘magic bullets’ new tricks

The emergence of recombinant technologies has revolutionized the selection and production of monoclonal antibodies, allowing the design of fully human antibodies of any specificity and for diverse purposes. Recombinant antibodies can be engineered with optimized properties, such as antigen-binding affinity, molecular architecture and dimerization state, and fused with a vast array of effector moieties to enhance their tumor-targeting ability and potency. The use of gene therapy methods offers additional benefits by achieving sustained and effective concentrations of therapeutic antibodies directly at points of target intervention. This compensates for the rapid blood clearance of antibody fragments and could make the antibody less immunogenic and better tolerated. Furthermore, genetic approaches provide antibody molecules with new functions in unexpected scenarios: expression of antibody domains in precise intracellular locations and grafting of new binding activities to engineered cells. The relevance of these and other emerging concepts for antibody-based cancer therapy is discussed.

An array of immunotherapeutic strategies for B-cell lymphomas

With FDA approval of monoclonal antibodies (mAb) against the B-cell-specific cell surface molecule CD20, immunotherapy in B-cell non-Hodgkin's-lymphomas (NHL) has gained momentum. Since the first description of the CD20 mAb and its use in a single patient, it has taken more than 20 years to implement this in current treatment options. NHLs are of particularly interest to the research community, since a whole array of novel immunotherapeutic strategies are currently in development. Unconjugated and radioconjugated mAbs are either approved, or in Phase III trials with very promising results. Adoptive transfer of polyclonally activated, tumour-specific or antigen-specific T-cells are in Phase I and II trials. Even antisense approaches have reappeared in the treatment of NHL. However, it is not only passive immunotherapy that has evolved. There are several new strategies for vaccination in NHL, whilst older approaches are under revision. Vaccine strategies targeting the tumour cell specific clonal idiotype (Id) have been refined and, with the identification of T-cell responses against shared epitopes, vaccination against the clonal Id might finally become clinically applicable. Significant progress has also been made in the development of cellular vaccines. Malignant B-cells are turned into 'tumour-APC' and are used to stimulate T-cell responses in Phase I trials. Moreover, with the identification of universal tumour antigens, another antigen-specific vaccine for NHL can be envisioned. By combining this array of very promising tools, immunotherapy might finally become a standard modality for the treatment of B-cell malignancies.

Grafting T cells with tumor specificity: the chimeric receptor strategy for use in immunotherapy of malignant diseases

Appreciation of the complementary nature of T-cell- and antibody-based immunotherapy stimulated interest in developing approaches that combine their advantages and minimize their limitations. A recent strategy is based on permanent grafting of cytotoxic T cells with a recombinant chimeric receptor designed for cellular targeting with antibody-like specificity and for cellular activation after binding to antigen. The extracellular moiety of the chimeric receptor consists of an antigen-binding domain derived from an antibody, the intracellular moiety consists of a signalling domain for cellular activation, thus combining the broad specificity of antibody-based and major histocompatibility complex (MHC)-independent recognition with the potent antitumor activity of T cells. By generation of specific T cells against any antigen for which a suitable monoclonal antibody (MAb) exists, the chimeric receptor strategy has the potential to extend the adoptive immunotherapy for a variety of malignant and infectious diseases. However, little is known about the optimized design of this type of receptor. We here discuss our results in grafting T cells with chimeric receptors of various design with regard to efficient cellular activation.

A chimeric receptor that selectively targets membrane-bound carcinoembryonic antigen (mCEA) in the presence of soluble CEA

Chimeric T cell receptors with specificity for tumor-associated antigens are successfully used to target T cells to tumor cells. The efficacy of this approach, however, is reduced by soluble antigen that is frequently present in high serum concentrations. To overcome this situation, we constructed an anti-CEA chimeric receptor whose extracellular moiety is composed of a humanized single chain antibody fragment (scFv) derived from the anti-CEA mAb BW431/26 and the CH2/CH3 constant domains of human IgG. The intracellular moiety consists of the gamma-signaling chain of the human Fc epsilon RI receptor constituting a completely humanized chimeric receptor. After transfection, the humBW431/26 scFv-CH2CH3-gamma receptor is expressed as a homodimer on the surface of MD45 T cells. Co-incubation with CEA+ tumor cells specifically activates grafted MD45 T cells indicated by IL-2 secretion and cytolytic activity against CEA+ tumor cells. Notably, the efficacy of receptor-mediated activation is not affected by soluble CEA up to 25 micrograms/ml demonstrating the usefulness of this chimeric receptor for specific cellular activation by membrane-bound CEA even in the presence of high concentrations of CEA, as found in patients during progression of the disease.

Tyrosine kinase chimeras for antigen-selective T-body therapy

Protein tyrosine kinases (PTKs) transmit activation signals in almost every cell type, including immune effector cells. The aberrant or constitutive activation of PTKs can often cause neoplastic transformation. The use of chimeric receptors based on PTKs may enable us to elucidate the signaling pathways of normal immune cells and other cell types, and the abnormal events that can lead to malignant transformation. In this review, we focus on antigen specific chimeric PTKs in which antibody-derived scFv are joined to the Syk family of PTKs. These chimeric receptors yielded reagents that can selectively redirect immune effector cells and specifically activate them to produce cytokines or lyse their target. The advantages of using such PTK-based chimeras to redirect lymphocytes to tumor targets and their potential as an immunotherapeutic approach to malignant disease is discussed.