Signals through T cell receptor-zeta chain alone are insufficient to prime resting T lymphocytes

CD28 cosignalling does not affect the activation threshold in a chimeric antigen receptor-redirected T-cell attack

Adoptive immunotherapy of cancer using chimeric antigen receptor (CAR)-engineered T cells with redirected specificity showed efficacy in recent trials. In preclinical models, 'second-generation' CARs with CD28 costimulatory domain in addition to CD3ζ performed superior in redirecting T-cell effector functions and survival. Whereas CD28 costimulation sustains physiological T-cell receptor (TCR)-CD3 activation of naïve T cells, the impact of CD28 cosignalling on the threshold of CAR-mediated activation of pre-stimulated T cells without B7-CD28 recruitment remained unclear. Using CARs of different binding affinities, but same epitope specificity, we demonstrate that CD28 cosignalling neither lowered the antigen threshold nor the binding affinity for redirected T-cell activation. 'Affinity ceiling' above which increase in affinity does not increase T-cell activation was not altered. Accordingly, redirected tumor cell killing depended on the binding affinity but was likewise effective for CD3ζ and CD28-CD3ζ CARs. In contrast to CD3ζ, CD28-CD3ζ CAR-driven activation was not increased further by CD28-B7 engagement. However, CD28 cosignalling, which is required for interleukin-2 induction could not be replaced by high-affinity CD3ζ CAR binding or high-density antigen engagement. We conclude that CD28 CAR cosignalling does not alter the activation threshold but redirects T-cell effector functions.

Adoptive T-cell immunotherapy of cancer using chimeric antigen receptor-grafted T cells

Harnessing the power of the immune system to target cancer has long been a goal of tumor immunologists. One avenue under investigation is the modification of T cells to express a chimeric antigen receptor (CAR). Expression of such a receptor enables T-cell specificity to be redirected against a chosen tumor antigen. Substantial research in this field has been carried out, incorporating a wide variety of malignancies and tumor-associated antigens. Ongoing investigations will ensure this area continues to expand at a rapid pace. This review will explain the evolution of CAR technology over the last two decades in addition to detailing the associated benefits and disadvantages. The outcome of recent phase I clinical trials and the impact that these have had upon the direction of future research in this field will also be addressed.

Treatment of lymphoma with adoptively transferred T cells

BACKGROUND

Chemotherapy-resistant lymphomas can be cured with allogeneic hematopoietic cell transplantation, demonstrating the susceptibility of these tumors to T cell mediated immune responses. However, high rates of transplant-related morbidity and mortality limit this approach. Efforts have, therefore, been made to develop alternative T cell based therapies, and there is growing evidence that adoptive therapy with T cells targeted to lymphoma-associated antigens may be a safe and effective new method for treating this group of diseases.

OBJECTIVE/METHODS

We review publications on adoptive therapy with ex vivo expanded T cells targeting viral antigens, as well as genetically modified autologous T cells, as strategies for the treatment of lymphoma, with the goal of providing an overview of these approaches.

RESULTS/CONCLUSIONS

Epstein-Barr virus specific T cell therapy is an effective and safe method of treating Epstein-Barr virus associated lymphomas; however, most lymphoma subtypes do not express EBV antigens. For these diseases, adoptive immunotherapy with genetically modified T cells expressing chimeric T cell receptors targeting lymphoma-associated antigens such as CD19 and CD20 appears to be a promising alternative. Recent innovations including enhanced co-stimulation, exogenous cytokine administration and use of memory T cells promise to overcome many of the limitations and pitfalls initially encountered with this approach.

The T-body approach: redirecting T cells with antibody specificity

"T-bodies" are genetically engineered T cells armed with chimeric receptors whose extracellular recognition unit is comprised of an antibody-derived recognition domain and whose intracellular region is derived from lymphocyte stimulating moiety(ies). The structure of the prototypic chimeric receptor, also known as a chimeric immune receptor, is modular, designed to accomodate various functional domains and thereby to enable choice of specificity and controlled activation of T cells. The preferred antibody-derived recognition unit is a single chain variable fragment (scFv) that combines the specificity and binding residues of both the heavy and light chain variable regions of a monoclonal antibody. The most common lymphocyte activation moieties include a T-cell costimulatory (e.g. CD28) domain in tandem with a T-cell triggering (e.g. CD3zeta) moiety. By arming effector lymphocytes (such as T cells and natural killer cells) with such chimeric receptors, the engineered cell is redirected with a predefined specificity to any desired target antigen, in a non-HLA restricted manner. Chimeric receptor (CR) constructs are introduced ex vivo into T cells from peripheral lymphocytes of a given patient using retroviral vectors. Following infusion of the resulting T-bodies back into the patient, they traffic, reach their target site, and upon interaction with their target cell or tissue, they undergo activation and perform their predefined effector function. Therapeutic targets for the T-body approach include cancer and HIV-infected cells, or autoimmune effector cells. To date, the most investigated area is cancer therapy. Here, the T-bodies are advantageous because their tumor recognition is not HLA-specific and, therefore, the same constructs can be used for a wide spectrum of patients and cancers.

Enhancement of the anti-leukemic activity of cytokine induced killer cells with an anti-CD19 chimeric receptor delivering a 4-1BB-ζ activating signal

OBJECTIVE

There is growing interest in the use of cytokine-induced killer (CIK) cells in cancer therapy. In this study, we sought to maximize the antileukemic activity of anti-CD19 receptor-modified CIK cells against B-lineage acute lymphoblastic leukemia (ALL).

MATERIALS AND METHODS

CIK cells were transduced with retroviral vectors carrying different types of anti-CD19 chimeric receptors: anti-CD19-zeta, anti-CD19-DAP10, anti-CD19-4-1BB-zeta, and anti-CD19-CD28-zeta. A truncated form of the receptor was used as a control. Transduced CIK cells were then analyzed for their cytotoxic activity against ALL cells and for their capability to proliferate and to release cytokines after ALL encounter.

RESULTS

CIK cells were efficiently transduced with all the anti-CD19 retroviral vectors. Anti-CD19 receptor expression conferred powerful killing activity against ALL cells. However, there were clear advantages when receptors containing the co-stimulatory molecules 4-1BB or CD28 were transduced. Such cells had significantly more potent cytotoxicity than cells expressing the anti-CD19-zeta or anti-CD19-DAP10. Moreover, the presence of 4-1BB or CD28 in the receptor increased the production of interleukin (IL)-2, tumor necrosis factor (TNF)-alpha, TNF-beta, IL-5, IL-6, and IL-8 elicited by coculture with ALL cells. Notably, anti-CD19-4-1BB-zeta CIK cells secreted particularly low levels of interleukin-10 and proliferated strongly after contact with ALL cells.

CONCLUSIONS

Anti-CD19 chimeric receptors delivering primary and costimulatory signals render CIK cells powerfully cytotoxic against ALL cells and induce secretion of immunostimulatory cytokines and proliferation. These results support the testing of genetically modified CIK cells in clinical trials.

Preclinical rationale for combining radiation therapy and immunotherapy beyond checkpoint inhibitors (i.e., CART)

An increasing appreciation for the role of the immune system in targeting cancer cells over the last decade has led to the development of several immunomodulatory agents aimed at enhancing the systemic antitumor immune response. One such method is the use of T cells that are genetically engineered to express chimeric antigen receptors (CARs). The remarkable success of this approach in advanced hematologic malignancies has garnered much enthusiasm for using this novel tool in treating other cancers. However, multiple challenges have hampered the application of this therapy to a broader set of solid tumors, most notably lung cancer. Immunotherapy has already shown great success in lung cancer, and is now the first-line treatment in PD-L1 expressing metastatic disease. Given the mounting evidence that radiation therapy plays a crucial role in amplifying the immune response elicited by immunomodulatory agents, there is potential for radiation to help in overcoming some of these challenges. In this review, we describe the basic principles of CAR T cell therapy and examine its successes and challenges to date. We then discuss the preclinical and clinical data supporting the use of radiation with immunomodulatory agents with a focus on preclinical rationale for combining CAR T cells and radiation therapy in future experiments with a focus on lung cancer.

CD28 co-stimulation via tumour-specific chimaeric receptors induces an incomplete activation response in Epstein-Barr virus-specific effector memory T cells

Expression of tumour antigen-specific chimaeric receptors in T lymphocytes can redirect their effector functions towards tumour cells. Integration of the signalling domains of the co-stimulatory molecule CD28 into chRec enhances antigen-specific proliferation of polyclonal human T cell populations. While CD28 plays an essential role in the priming of naive CD4(+) T cells, its contribution to effector memory T cell responses is controversial. We compared the function of the chRec with and without the CD28 co-stimulatory domain, expressing it in peripheral blood T cells or Epstein-Barr virus (EBV)-specific T cell lines. The chimaeric T cell receptors contain an extracellular single-chain antibody domain, to give specificity against the tumour ganglioside antigen G(D2). The transduced cytotoxic T lymphocytes (CTL) maintained their specificity for autologous EBV targets and their capacity to proliferate after stimulation with EBV-infected B cells. Intracellular cytokine staining demonstrated efficient and comparable antigen-specific interferon (IFN)-gamma secretion by CTL following engagement of both the native and the chimaeric receptor, independent of chimaeric CD28 signalling. Furthermore, tumour targets were lysed in an antigen-specific manner by both chRec. However, while antigen engagement by CD28 zeta chRec efficiently induced expansion of polyclonal peripheral blood lymphocytes in an antigen-dependent manner, CD28 signalling did not induce proliferation of EBV-CTL in response to antigen-expressing tumour cells. Thus, the co-stimulatory requirement for the efficient activation response of antigen-specific memory cells cannot be mimicked simply by combining CD28 and zeta signalling. The full potential of this highly cytolytic T cell population for adoptive immunotherapy of cancer requires further exploration of their co-stimulatory requirements.

Target antigen expression on a professional antigen-presenting cell induces superior proliferative antitumor T-cell responses via chimeric T-cell receptors

Human T cells expressing tumor antigen-specific chimeric receptors fail to sustain their growth and activation in vivo, which greatly reduces their therapeutic value. The defective proliferative response to tumor cells in vitro can partly be overcome by concomitant CD28 costimulatory signaling. We investigated whether T-cell activation via chimeric receptors (chRec) can be further improved by ligand expression on antigen-presenting cells of B-cell origin. We generated Epstein-Barr virus (EBV)-specific cytotoxic T lymphocytes (CTLs) expressing a CD19-specific chRec. These CTLs are provided with native receptor stimulation by autologous EBV-transformed B-lymphoblastoid cell lines (LCLs) but exclusively with chRec (CD19-specific) stimulation by allogeneic, human leukocyte antigen (HLA)-mismatched CD19+ LCLs. CD19zeta-transduced EBV-specific CTLs specifically lysed both allogeneic EBV targets and CD19+ tumor cells through the chRec in a major histocompatibility complex-independent manner, while maintaining their ability to recognize autologous EBV targets through the native T-cell receptor. The transduced CTLs failed to proliferate in response to CD19+ tumor targets even in the presence of CD28 costimulatory signaling. By contrast, CD19 expressed on HLA-mismatched LCL-induced T-cell activation and long-term proliferation that essentially duplicated the result from native receptor stimulation with autologous LCLs, suggesting that a deficit of costimulatory molecules on target cells in addition to CD28 is indeed responsible for inadequate chRec-mediated T-cell function. Hence, effective tumor immunotherapy may be favored if engagement of the chRec on modified T cells is complemented by interaction with multiple costimulator molecules. The use of T cells with native specificity for EBV may be one means of attaining this objective.

Engineering T cells for cancer therapy

It is generally accepted that the immune system plays an important role in controlling tumour development. However, the interplay between tumour and immune system is complex, as demonstrated by the fact that tumours can successfully establish and develop despite the presence of T cells in tumour. An improved understanding of how tumours evade T-cell surveillance, coupled with technical developments allowing the culture and manipulation of T cells, has driven the exploration of therapeutic strategies based on the adoptive transfer of tumour-specific T cells. The isolation, expansion and re-infusion of large numbers of tumour-specific T cells generated from tumour biopsies has been shown to be feasible. Indeed, impressive clinical responses have been documented in melanoma patients treated with these T cells. These studies and others demonstrate the potential of T cells for the adoptive therapy of cancer. However, the significant technical issues relating to the production of natural tumour-specific T cells suggest that the application of this approach is likely to be limited at the moment. With the advent of retroviral gene transfer technology, it has become possible to efficiently endow T cells with antigen-specific receptors. Using this strategy, it is potentially possible to generate large numbers of tumour reactive T cells rapidly. This review summarises the current gene therapy approaches in relation to the development of adoptive T-cell-based cancer treatments, as these methods now head towards testing in the clinical trial setting.

A chimeric T cell antigen receptor that augments cytokine release and supports clonal expansion of primary human T cells

The transduction of primary T cells to express chimeric T cell receptors (cTCR) for redirected targeting of tumor cells is an attractive strategy for generating tumor-specific T cells for adoptive therapy. However, tumor cells rarely provide costimulatory signals and hence cTCRs that transmit just a CD3zeta signal can only initiate target cell killing and interferon-gamma release and fail to induce full activation. Although incorporation of a CD28 component results in IL-2 release and limited proliferation, T cell activation remains incomplete. OX40 transmits a potent and prolonged T cell activation signal and is crucial for maintaining an immunological response. We hypothesize that the CD28-OX40-CD3zeta tripartite cytoplasmic domain will provide a full complement of activation, proliferation, and survival signals for enhanced anti-tumor activity.

Redirected primary T cells harboring a chimeric receptor require costimulation for their antigen-specific activation

Chimeric receptor (CR)–redirected lymphocytes (T bodies) have great potential in the eradication of tumor cells. To extend this approach to target cells that do not express surface ligands to costimulatory receptors (eg, cancer cells), we have generated an antibody-based tripartite chimeric receptor (TPCR) that contains scFv linked to the costimulatory molecule, CD28 without its ligand-binding domain, and to the cytoplasmic moiety of the FcRγ subunit. In this study, we tested the ability of 2,4,6-trinitrophenyl (TNP)–specific TPCR to drive primary, naïve T cells derived from CR-transgenic (Tg) mice to undergo full activation. As a control, we used Tg mice expressing a similar transgene but lacking the signaling region of CD28 (Tg-TPCRΔCD28). Only T cells from the TPCR-Tg and not the CD28-truncated TPCR-Tg mice could undergo activation following stimulation on hapten-modified target cells not expressing B7. Moreover, when stimulated with TNP protein displayed on plastic, the TPCR-Tg T cells expressing the entire TPCR gene became fully activated for proliferation, interleukin 2 production, protection from apoptosis, and killing of TNP-modified target cells. Finally, TPCR-Tg mice manifested a delayed-type hypersensitivity response following skin challenge in the absence of priming. Taken together, our results suggest that the TPCR is the receptor configuration of choice for clinical applications using primary T or stem cells.

Genetic modification of T lymphocytes for adoptive immunotherapy

Adoptive transfer of T lymphocytes is a promising therapy for malignancies-particularly of the hemopoietic system-and for otherwise intractable viral diseases. Efforts to broaden the approach have been limited by the physiology of the T cells themselves and by a range of immune evasion mechanisms developed by tumor cells. In this review we show how genetic modification of T cells is being used preclinically and in patients to overcome these limitations, by incorporation of novel receptors, resistance mechanisms, and control genes. We also discuss how the increasing safety and effectiveness of gene transfer technologies will lead to an increase in the use of gene-modified T cells for the treatment of a wider range of disorders.

Human gammadelta T cells as mediators of chimaeric-receptor redirected anti-tumour immunity

Human peripheral blood gammadelta T cells (Vgamma9(+) Vdelta2(+)) can be selectively expanded in vivo by the systemic administration of aminobisphosphonates without prior antigen priming. To assess the potential of human gammadelta T cells to serve as effector cells of specific anti-tumour immunity, we expanded peripheral blood-derived gammadelta T cells and transduced them with recombinant retrovirus encoding G(D2)- or CD19-specific chimaeric receptors. Flow cytometric analysis of T cells from four individual donors cultured in the presence of zoledronate at day 14 of culture showed selective enrichment of the gammadelta T cell population (Vgamma9(+) Vdelta2(+) CD3(+) CD4(-) CD8(-)) to 73-96% of total CD3(+) T cells. Retroviral gene transfer resulted in chimaeric receptor surface expression in 73 +/- 12% of the population. Transduced gammadelta T cells efficiently recognized antigen-expressing tumour cell targets, as demonstrated by target-specific upregulation of CD69 and secretion of interferon-alpha. Moreover, transduced gammadelta T cells efficiently and specifically lysed the antigen-expressing tumour targets. They could be efficiently expanded in vitro and maintained in culture for prolonged periods. Zoledronate-activated human gammadelta T cells expressing chimaeric receptors may thus serve as potent and specific anti-tumour effector cells. Their responsiveness to stimulation with aminobisphosphonates may enable the selective re-expansion of adoptively transferred T cells in vivo, permitting long lasting anti-tumour immune control.

Vaccine and antibody-directed T cell tumour immunotherapy

Clearer evidence for immune surveillance in malignancy and the identification of many new tumour-associated antigens (TAAs) have driven novel vaccine and antibody-targeted responses for therapy in cancer. The exploitation of active immunisation may be particularly favourable for TAA where tolerance is incomplete but passive immunisation may offer an additional strategy where the immune repertoire is affected by either tolerance or immune suppression. This review will consider how to utilise both active and passive types of therapy delivered by T cells in the context of the failure of tumour-specific immunity by presenting cancer patients. This article will outline the progress, problems and prospects of several different vaccine and antibody-targeted approaches for immunotherapy of cancer where proof of principle pre-clinical studies have been or will soon be translated into the clinic. Two examples of vaccination-based therapies where both T cell- and antibody-mediated anti-tumour responses are likely to be relevant and two examples of oncofoetal antigen-specific antibody-directed T cell therapies are described in the following sections: (1) therapeutic vaccination against human papillomavirus (HPV) antigens in cervical neoplasia; (2) B cell lymphoma vaccines including against immunoglobulin idiotype; (3) oncofoetal antigens as tumour targets for redirecting T cells with antibody strategies.

Recombinant immunotoxins and retargeted killer cells: employing engineered antibody fragments for tumor-specific targeting of cytotoxic effectors

Over the past years, monoclonal antibodies have attracted enormous interest as targeted therapeutics, and a number of such reagents are in clinical use. However, responses could not be achieved in all patients with tumors expressing high levels of the respective target antigens, suggesting that other factors such as limited recruitment of endogenous immune effector mechanisms can also influence treatment outcome. This justifies the search for alternative, potentially more effective reagents. Antibody-toxins and cytolytic effector cells genetically modified to carry antibody-based receptors on the surface, represent such tailor-made targeting vehicles with the potential of improved tumor localization and enhanced efficacy. In this way, advances in recombinant antibody technology have made it possible to circumvent problems inherent in chemical coupling of antibodies and toxins, and have allowed construction via gene fusion of recombinant molecules which combine antibody-mediated recognition of tumor cells with specific delivery of potent protein toxins of bacterial or plant origin. Likewise, recombinant antibody fragments provide the basis for the construction of chimeric antigen receptors that, upon expression in cytotoxic T lymphocytes (CTLs) or natural killer (NK) cells, link antibody-mediated recognition of tumor antigens with these effector cells' potent cytolytic activities, thereby making them promising cellular therapeutics for adoptive cancer therapy. Here, general principles for the derivation of cytotoxic proteins and effector cells with antibody-dependent tumor specificity are summarized, and current strategies to employ these molecules and cells for directed cancer therapy are discussed, focusing mainly on the tumor-associated antigens epidermal growth factor receptor (EGFR) and the closely related ErbB2 (HER2) as targets.

Activation of Resting Human Primary T Cells with Chimeric Receptors: Costimulation from CD28, Inducible Costimulator, CD134, and CD137 in Series with Signals from the TCRζ Chain

Chimeric receptors that include CD28 signaling in series with TCRzeta in the same receptor have been demonstrated to activate prestimulated human primary T cells more efficiently than a receptor providing TCRzeta signaling alone. We examined whether this type of receptor can also activate resting human primary T cells, and whether molecules other than CD28 could be included in a single chimeric receptor in series with TCRzeta to mediate the activation of resting human primary T cells. Human CD33-specific chimeric receptors were generated with CD28, inducible costimulator, CD134, or CD137 signaling regions in series with TCRzeta signaling region and transfected by electroporation into resting human primary T cells. Their ability to mediate Ag-specific activation was analyzed in comparison with a receptor providing TCRzeta signaling alone. Inclusion of any of the costimulatory signaling regions in series with TCRzeta enhanced the level of specific Ag-induced IL-2, IFN-gamma, TNF-alpha, and GM-CSF cytokine production and enabled resting primary T cells to survive and proliferate in response to Ag in the absence of any exogenous factors. Inclusion of CD28, inducible costimulator, or CD134 enhanced TCRzeta-mediated, Ag-specific target cell lysis. Chimeric receptors providing B7 and TNFR family costimulatory signals in series with TCRzeta in the same receptor can confer self-sufficient clonal expansion and enhanced effector function to resting human T cells. This type of chimeric receptor may now be used to discover the most potent combination of costimulatory signals that will improve current immunotherapeutic strategies.

Chimeric T-cell receptors for the targeting of cancer cells

Genetic engineering of human T lymphocytes to express tumor antigen-specific chimeric immune receptors is an attractive means for providing large numbers of effector cells for adoptive immunotherapy. Major mechanisms of tumor escape from immune recognition are efficiently bypassed. Although adoptive transfer of chimeric receptor-expressing peripheral blood-derived T lymphocytes has produced some anti-tumor activity in mice, the first clinical studies have revealed a disappointing lack of correlation between in vitro cytotoxicity and therapeutic efficacy. The most pertinent issue is that chimeric T cells fail to expand and rapidly lose their function in vivo. Potential strategies to enhance the therapeutic value of chimeric receptor-modified cells by preventing their functional inactivation in vivo are currently being investigated.

Activation of T cells via tumor antigen specific chimeric receptors: the role of the intracellular signaling domain

T cells engineered to express hybrid receptors with antibody defined specificity can successfully be targeted to tumor cells. In order to select intracellular domains of chimeric receptors capable of efficiently activate T cells in vitro and in vivo, we compared the function of receptors, which share the same extracellular antigen-binding part, joined to different intra-cellular signal transduction units. The antigen binding domain of the receptors was a single-chain fragment of a monoclonal antibody, which recognize a High Molecular Weight Melanoma-Associated Antigen with high affinity. The intracellular tails were derived from the T-cell receptor zeta chain (TCR-zeta), from the B-cell receptor Ig-alpha molecule and from a mutated Ig-alpha molecule able of stronger signal transduction. We compared the activity of the different chimeric receptors at a single-cell level by using a T-cell line that expressed an activation-dependent EGFP-reporter gene. Upon cross-linking with immobilized antibodies, all receptors were able to induce EGFP expression in the majority of the T cells. In contrast, EGFP expression was induced by contact to melanoma cells in vitro only in T cells that expressed the chimeric receptor that contained the TCR-zeta intracellular tail. In these T cells, the co-expression of chimeric receptors that contain a mutated Ig-alpha tail lowers the threshold of T-cell activation and facilitates tumor recognition in vitro and in vivo. Given their specificity and efficiency, T cells grafted with these type of receptors may represent potential candidates for cancer passive immunotherapy.

Genetic engineering of T cell specificity for immunotherapy of cancer

The ultimate goal of immunotherapy of cancer is to make use of the immune system of patients to eliminate malignant cells. Research has mainly focused on the generation of effective antigen specific T-cell responses because of the general belief that T-cell immunity is essential in controlling tumor growth and protection against viral infections. However, the isolation of antigen specific T cells for therapeutic application is a laborious task and it is often impossible to derive autologous tumor specific T cells to be used for adoptive immunotherapy. Therefore, strategies were developed to genetically transfer tumor specific immune receptors into patients T cells. To this end, chimeric receptors were constructed that comprise antibody fragments specific for tumor associated antigens, linked to genes encoding signaling domains of the T-cell receptor (TCR) or Fc receptor. T cells expressing such chimeric antibody receptors recapitulate the immune specific responses mediated by the introduced receptor. Recently, we introduced chimeric TCR genes into primary human T lymphocytes and demonstrated that these T cell transductants acquired the exquisite major histocompatibility complex (MHC) restricted tumor specificity dictated by the introduced TCR. Importantly, the introduction of chimeric TCR bypasses problems associated with the introduction of nonmodified TCR genes, such as pairing of introduced TCR chains with endogenous TCR chains and unstable TCRalpha expression. A novel strategy which is completely independent of available tumor specific T-cell clones for cloning of the TCR genes was recently used to transfer MHC restricted tumor specificity to T cells. Human "TCR-like" Fab fragments obtained by in vitro selection of Fab phages on soluble peptide/MHC complexes were functionally expressed on human T lymphocytes, resulting in MHC restricted, tumor specific lysis and cytokine production. In addition, affinity maturation of the antibody fragment on Fab phages allows improvement of the tumor cell killing capacity of chimeric Fab receptor engrafted T cells. Developments in retroviral transfer technology now enables the generation of large numbers of antigen specific T cells that can be used for adoptive transfer to cancer patients. In this article we summarize the developments in adoptive T cell immunogenetic therapy and discuss the limitations and perspectives to improve this technology toward clinical application.

Rejection of syngeneic colon carcinoma by CTLs expressing single-chain antibody receptors codelivering CD28 costimulation

A new strategy to improve the therapeutic utility of redirected T cells for cancer involves the development of novel Ag-specific chimeric receptors capable of stimulating optimal and sustained T cell antitumor activity in vivo. Given that T cells require both primary and costimulatory signals for optimal activation and that many tumors do not express critical costimulatory ligands, modified single-chain Ab receptors have been engineered to codeliver CD28 costimulation. In this study, we have compared the antitumor potency of primary T lymphocytes expressing carcinoembryonic Ag (CEA)-reactive chimeric receptors that incorporate either TCR-zeta or CD28/TCR-zeta signaling. Although both receptor-transduced T cell effector populations demonstrated cytolysis of CEA(+) tumors in vitro, T cells expressing the single-chain variable fragment of Ig (scFv)-CD28-zeta chimera had a far greater capacity to control the growth of CEA(+) xenogeneic and syngeneic colon carcinomas in vivo. The observed enhanced antitumor activity of T cells expressing the scFv-CD28-zeta receptor was critically dependent on perforin and the production of IFN-gamma. Overall, this study has illustrated the ability of a chimeric scFv receptor capable of harnessing the signaling machinery of both TCR-zeta and CD28 to augment T cell immunity against tumors that have lost expression of both MHC/peptide and costimulatory ligands in vivo.

Single-chain antigen recognition receptors that costimulate potent rejection of established experimental tumors

Tumor cells are usually weakly immunogenic as they largely express self-antigens and can down-regulate major histocompatability complex/peptide molecules and critical costimulatory ligands. The challenge for immunotherapies has been to provide vigorous immune effector cells that circumvent these tumor escape mechanisms and eradicate established tumors. One promising approach is to engineer T cells with single-chain antibody receptors, and since T cells require 2 distinct signals for optimal activation, we have compared the therapeutic efficacy of erbB2-reactive chimeric receptors that contain either T-cell receptor zeta (TCR-zeta) or CD28/TCR-zeta signaling domains. We have demonstrated that primary mouse CD8(+) T lymphocytes expressing the single-chain Fv (scFv)-CD28-zeta receptor have a greater capacity to secrete Tc1 cytokines, induce T-cell proliferation, and inhibit established tumor growth and metastases in vivo. The suppression of established tumor burden by cytotoxic T cells expressing the CD28/TCR-zeta chimera was critically dependent upon their interferon gamma (IFN-gamma) secretion. Our study has illustrated the practical advantage of engineering a T-cell signaling complex that codelivers CD28 activation, dependent only upon the tumor's expression of the appropriate tumor associated antigen.

Redirecting cytotoxic T lymphocyte responses with T-cell receptor transgenes

In cancer and viral diseases, a great deal of research has focused on generating T-cell responses that might prove therapeutic. These efforts stem from our understanding of the immune system. It is known that the natural immune response can protect or suppress some viral infections and it is hoped that a potent T-cell mediated immune response might also be harnessed to fight cancer. Immunotherapy is a particularly attractive candidate therapy for the treatment of metastatic cancer because of the immune systems capacity for body wide surveillance. Since the generation of T cell clones is a laborious task and it is often impossible to derive T cell clones of the desired specificity and function from many individuals, especially in a timely fashion required for therapeutic interventions, T-cell receptor (TCR) gene transfer has a lot of appeal. TCR gene transfer seeks to transfer the antigen specificity of a T cell clone to other T cells. This article will review the last 15 years of research in TCR gene transfer since the first successful TCR gene transfer experiment, and seeks to give an insight into the areas of investigation currently being pursued to improve on current results and move TCR gene transfer into the clinic.

Epstein-Barr virus-specific human T lymphocytes expressing antitumor chimeric T-cell receptors: potential for improved immunotherapy

Primary T cells expressing chimeric receptors specific for tumor or viral antigens have considerable therapeutic potential. Unfortunately, their clinical value is limited by their rapid loss of function and failure to expand in vivo, presumably due to the lack of costimulator molecules on tumor cells and the inherent limitations of signaling exclusively through the chimeric receptor. Epstein-Barr virus (EBV) infection of B lymphocytes is near universal in humans and stimulates high levels of EBV-specific helper and cytotoxic T cells, which persist indefinitely. Our clinical studies have shown that EBV-specific T cells generated in vitro will expand, persist, and function for more than 6 years in vivo. We now report that EBV-specific (but not primary) T cells transduced with tumor-specific chimeric receptor genes can be expanded and maintained long-term in the presence of EBV-infected B cells. They recognize EBV-infected targets through their conventional T-cell receptor and tumor targets through their chimeric receptors. They efficiently lyse both. EBV-specific T cells expressing chimeric antitumor receptors may represent a new source of effector cells that would persist and function long-term after their transfer to cancer patients.

Analysis of the individual role of the TCRzeta chain in transgenic mice after conditional activation with chemical inducers of dimerization

Signaling through the TCR/CD3 complex plays a critical role in T-cell development and activation. Gene-targeted mice lacking particular components of this complex show arrested T-cell development in the thymus. As all TCR/CD3 components are required for efficient surface expression of the complex, it is difficult to assess the specific signaling role of each receptor component. To overcome this problem, we designed a strategy to examine the specific role(s) of individual receptor chains. A chimeric protein, containing binding domains for chemical inducers of dimerization fused to the cytoplasmic tail of TCRzeta, was generated. Activation of the chimeric receptor after stimulation with chemical dimerizers in Jurkat cells showed tyrosine phosphorylation of the TCRzeta chain chimera, recruitment of phosphorylated Zap70, and generation of NFAT in a reporter assay. Analysis of thymocytes from transgenic mice expressing this chimeric receptor showed that intracytoplasmic crosslinking of the chimera induced tyrosine phosphorylation of the protein, as well as a slow and very weak calcium mobilization response. However, this signaling did not lead to increased expression of activation markers, T-cell proliferation, or apoptosis. In addition, stimulation of thymocytes in suspension or in fetal thymic organ cultures with chemical inducers of dimerization did not lead to alterations in positive or negative selection. We conclude that signaling through the TCRzeta chain alone is not sufficient to generate downstream events leading to full T-cell activation or thymocyte selection; instead, additional CD3 components must be required to induce a functional response in primary thymocytes and peripheral T cells.

TCR dynamics on the surface of living T cells

T lymphocyte activation by specific antigen requires prolonged TCR occupancy and sustained signaling. This is accomplished by the formation of a specialized signaling domain, the immunological synapse, at the T cell-antigen-presenting cell contact site. Surface receptors and signaling components are progressively recruited into this domain where they are organized in defined three-dimensional structures. To better understand how TCR are supplied to the signaling domain during the activation process, we measured (using confocal microscopy and photo-bleaching recovery techniques) lateral mobility of GFP-tagged TCR on living Jurkat cell surface. We show that: (i) surface-expressed TCR exhibit an intrinsic, actin cytoskeleton-independent, lateral mobility which allows them to passively diffuse over the entire T cell surface within approximately 60 min and (ii) non-stimulated TCR rapidly enter the signaling domain. Our results indicate that TCR lateral mobility per se is sufficient to ensure TCR supply to the immunological synapse in the course of sustained T cell activation.

Chimeric antigen receptors for the retargeting of cytotoxic effector cells

T lymphocytes recognize specific antigens through interaction of the T cell receptor (TCR) with short peptides presented by major histocompatibility complex (MHC) class I or II molecules. For initial activation and clonal expansion, naïve T cells are dependent on professional antigen-presenting cells (APCs) that provide additional co-stimulatory signals. TCR activation in the absence of co-stimulation can result in unresponsiveness and clonal anergy. To bypass immunization, different approaches for the derivation of cytotoxic effector cells with grafted recognition specificity have been developed. Chimeric antigen receptors have been constructed that consist of binding domains derived from natural ligands or antibodies specific for cell-surface antigens, genetically fused to effector molecules such as the TCR alpha and beta chains, or components of the TCR-associated CD3 complex. Upon antigen binding, such chimeric receptors link to endogenous signaling pathways in the effector cell and generate activating signals similar to those initiated by the TCR complex. Since the first reports on chimeric antigen receptors, this concept has steadily been refined and the molecular design of chimeric receptors has been optimized. Aided by advances in recombinant antibody technology, chimeric antigen receptors targeted to a wide variety of antigens on the surface of cancer cells and of cells infected by human immunodeficiency virus (HIV) have been generated. In initial clinical studies, infusion of such cells into patients proved to be safe and transient therapeutic effects have been observed.

Chimeric Fv-ζ or Fv-ε receptors are not sufficient to induce activation or cytokine production in peripheral T cells

In current clinical trials, chimeric antibody-like receptors fused to signaling domains derived from TCR-ζ or Fc(ε)RIγ-chain are tested for their ability to lyse tumor cells in vivo. In this study, the function of primary T cells expressing such receptors has been investigated in transgenic mice. These receptors cannot induce proliferation of resting T cells or trigger the production of optimal amounts of cytokines. It is further demonstrated that an initial low presence of cytokine message and protein is disappearing rather fast, whereas the triggering of endogenous TCR/CD3 in the same cells leads to normal prolonged cytokine production. The direct clinical relevance of these findings is further underlined by the increased in vivo tumor rejection by T cells expressing chimeric receptors in presence of exogenous interleukin-2. Therefore, adoptive T-cell therapy using primary T cells transfected with single chain receptors might benefit substantially from the accompanying administration of cytokines.

Chimeric Fv-ζ or Fv-ε receptors are not sufficient to induce activation or cytokine production in peripheral T cells

In current clinical trials, chimeric antibody-like receptors fused to signaling domains derived from TCR-ζ or Fc(ε)RIγ-chain are tested for their ability to lyse tumor cells in vivo. In this study, the function of primary T cells expressing such receptors has been investigated in transgenic mice. These receptors cannot induce proliferation of resting T cells or trigger the production of optimal amounts of cytokines. It is further demonstrated that an initial low presence of cytokine message and protein is disappearing rather fast, whereas the triggering of endogenous TCR/CD3 in the same cells leads to normal prolonged cytokine production. The direct clinical relevance of these findings is further underlined by the increased in vivo tumor rejection by T cells expressing chimeric receptors in presence of exogenous interleukin-2. Therefore, adoptive T-cell therapy using primary T cells transfected with single chain receptors might benefit substantially from the accompanying administration of cytokines.

Engineering mouse T lymphocytes specific to type II collagen by transduction with a chimeric receptor consisting of a single chain Fv and TCR zeta

The chimeric cell surface receptor scC2Fv/CD8/zeta was constructed to engineer primary mouse T lymphocytes with antibody-type specificity to type II collagen (CII). Such cells could be used as gene carriers in the anti-inflammatory gene therapy of an autoimmune arthritis. This receptor includes the single chain Fv domain (scFv) of the anti-CII monoclonal antibody (mAb) C2, hinge region of CD8alpha and the transmembrane and cytoplasmic domains of TCRzeta. The scC2Fv/CD8/zeta gene was transduced into T cell hybridomas and primary mouse lymphocytes using retrovirus-mediated gene transfer. The chimeric receptor scC2Fv/CD8/zeta forms covalently bound homodimers, as demonstrated in T cell hybridomas and packaging fibroblasts. It does not associate with endogenous signalling subunits of the TCR complex. When scC2Fv/CD8/zeta-expressing clones of T cell hybridomas MD.45 and HCQ6 were stimulated with CII they produced IL-2. The level of their IL-2 response correlated with the expression level of the chimeric receptor on the cell surface. Splenocytes isolated from DBA/1 mice were stimulated with Con A in vitro to facilitate retrovirus-mediated transfer of the scC2Fv/CD8/zeta gene. As a result of transduction, approximately 4% of the Con A-activated splenocytes expressed the chimeric receptor scC2Fv/CD8/zeta on the cell surface. These cells proliferated in response to stimulation with CII.

Signaling scaffolds in immune cells

Of the past several years progress in understanding TCR signal transduction has led to the discovery of new kinases, adapter molecules and multiple signaling pathways. The study of molecules such as LAT, SLP-76, FYB, SKAP-55 and VAV have revealed multiple mechanisms with which to control the activation of downstream signaling pathways through RAS, PLC gamma-1 and ERK/MAPK. Signaling through SLP-76 can play a role in TCR-induced cytoskeleton changes through activation of effector molecules in the RAC/RHO-family of GTPases. In addition, SLP-76 through its association with FYB/FYN-T appears to play a role in IL-2 gene transcription following TCR activation. Finally, these newly identified adaptor molecules, such as LAT, may be crucial in T-cell activation by enhancing the recruitment of critical kinases to glycolipid-enriched microdomains of the activated T-cell receptor complex.

The TCR ζ-Chain Immunoreceptor Tyrosine-Based Activation Motifs Are Sufficient for the Activation and Differentiation of Primary T Lymphocytes

The TCR complex signals through a set of 10 intracytoplasmic motifs, termed immunoreceptor tyrosine-based activation motifs (ITAMs), contained within the γ-, δ-, ε-, and ζ-chains. The need for this number of ITAMs is uncertain. Limited and contradictory studies have examined the ability of subsets of the TCR’s ITAMs to signal into postthymic primary T lymphocytes. To study signaling by a restricted set of ITAMs, we expressed in transgenic mice a chimeric construct containing the IAs class II MHC extracellular and transmembrane domains linked to the cytoplasmic domain of the TCR ζ-chain. Tyrosine phosphorylation and receptor cocapping studies indicate that this chimeric receptor signals T cells independently of the remainder of the TCR. We show that CD4+ and CD8+ primary T cells, as well as naive and memory T cells, are fully responsive to stimulation through the IAs-ζ receptor. Further, IAs-ζ stimulation can induce primary T cell differentiation into CTL, Th1, and Th2 type cells. These results show that the ζ-chain ITAMs, in the absence of the γ, δ, and ε ITAMs, are sufficient for the activation and functional maturation of primary T lymphocytes. It also supports the isolated use of the ζ-chain ITAMs in the development of surrogate TCRs for therapeutic purposes.

Efficient discrimination between different densities of target antigen by tetracycline-regulatable T bodies

Engineered T cells expressing chimeric T cell receptors (chTCRs) are of interest for cancer gene therapy but many "cancer antigens" are thought to be unsuitable targets because they are expressed at low levels on normal tissues. We therefore sought to determine whether engineered T cells expressing variable surface densities of a high-affinity chTCR could discriminate different concentrations of the targeted antigen. We plotted the relationship between chTCR density and the concentration of target antigen using Jurkat T cells expressing a hapten-binding chTCR whose expression could be modulated by tetracycline. Our analysis reveals that there is a dynamic equilibrium between cell surface density of the chTCR and the antigen density that optimally triggers T cell activation. At a fixed density of target antigen, optimal T cell activation can be achieved only within a certain range of chTCR densities, while excessive TCR signaling triggers apoptosis of the engineered T cells. Our results show that T cells can be engineered to discriminate different antigen densities and that the T cell response to a fixed concentration of antigen can be optimized by tuning the cell surface density of TCRs.

Chimeric Receptors Providing Both Primary and Costimulatory Signaling in T Cells from a Single Gene Product

Single chain Fv chimeric receptors, or T-bodies, are described with intracellular sequences comprising the costimulatory signaling domain of CD28 in series with the ζ-chain from the TCR complex. Using an engineered human single chain Fv derived from P67, an mAb with specificity for human CD33, and a spacer comprising an Ab hinge region with either Fcγ or part of the CD28 extracellular region, fusion molecules were constructed to test the ability of single chain designs to mediate both primary signaling and costimulation from one extracellular binding event. Constructs with the CD28 signaling domain proximal and the ζ-chain distal to the membrane were found to express more efficiently in Jurkat than constructs with the opposite orientation and were capable of mediating up to 20 times more IL-2 production on stimulation with solid phase Ag when compared with transfectants expressing chimeric receptors with ζ-chain intracellular signaling domains only. IL-2 production was specific to Ag challenge and was completely inhibited by incubation with free Ab of the same specificity as the extracellular binding site of the construct, but not by an isotype-matched control Ab. The CD28 intracellular domain of these fusion proteins was shown to be capable of binding the p85 subunit of phosphatidylinositol 3′-kinase. These constructs represent the first of a new generation of single gene multidomain chimeric receptors capable of mediating both primary and costimulatory signaling specifically from a single extracellular recognition event.

A T cell-independent antitumor response in mice with bone marrow cells retrovirally transduced with an antibody/Fc-gamma chain chimeric receptor gene recognizing a human ovarian cancer antigen

In order to treat common cancers with immunotherapy, chimeric receptors have been developed that combine the tumor specificity of antibodies with T-cell effector functions. Previously, we demonstrated that T cells transduced with a chimeric receptor gene against human ovarian cancer were able to recognize ovarian cancer cells in vitro and in vivo. We now report that recipients of bone marrow cells transduced with these genes exhibited significant antitumor activity in vivo. Moreover, in vivo depletion of T cells in reconstituted mice did not affect antitumor activity, suggesting that other immune cells expressing the chimeric receptor gene may play an important role in tumor rejection.

Efficient lysis of CD44v7/8-presenting target cells by genetically engineered cytotoxic T-lymphocytes--a model for immunogene therapy of cervical cancer

Variant proteins of the CD44 surface glycoprotein family are expressed on many different human tumors and their lymph node metastases. An epitope encoded by sequences of variant exons CD44v7 and v8 and recognized by the monoclonal antibody VFF17 is frequently detected in cervical cancer, whereas the normal cervical epithelium lacks expression of this epitope. We have developed an immunotherapeutic approach for cervical cancer based on the expression of this CD44v7/8 epitope. The single chain antigen-binding fragment of VFF17 was fused to a signal transducing protein (zeta-chain) of the T-cell receptor complex (TCR) and was introduced into a retroviral gene transfer vector. Gene transfer was applied to the murine cytotoxic T-cell line cl96. All recombinant clones expressed the fusion protein on their cell surface. Functionality of the recombinant fusion protein was tested by subjection of several recombinant clones to in vitro cytotoxicity assays. CD44v7/8-expressing target cells were killed efficiently by reprogrammed cl96 in an MHC-independent fashion, whereas CD44v7/ 8-negative cells were not affected. These transfected T cell lines will now be tested in vivo using immune-deficient mice bearing CD44v7/8-expressing tumors.

TCR zeta chain in T cell development and selection

Current data suggest that an important function of the multimeric structure of the TCR is to enable the assembly of structurally and functionally different forms of the TCR, the pre-TCR and alphabetaTCR complexes, at different stages in development. Four distinct TCR subunits (the CD3gamma, delta, and epsilon chains and the zeta chain) contain signal transducing motifs; however, the zeta chain is notable for containing three of these elements. These motifs, especially those within the zeta chain, function to amplify signals generated by the TCR, and this property is especially critical during thymocyte selection. The results of several recent experiments argue that positive and negative selection of thymocytes may involve activation of distinct downstream signaling pathways. The outcome of thymocyte selection can also be influenced, however, by quantitative effects such as changes in ligand concentration or direct alteration of the TCR signaling potential. Recent studies pertaining to the kinetics of TCR-ligand interactions may provide insight into how signaling through the TCR can be regulated either quantitatively or qualitatively.

CD3 delta deficiency arrests development of the alpha beta but not the gamma delta T cell lineage

The CD3 complex found associated with the T cell receptor (TCR) is essential for signal transduction following TCR engagement. During T cell development, TCR-mediated signalling promotes the transition from one developmental stage to the next and controls whether a thymocyte undergoes positive or negative selection. The roles of particular CD3 components in these events remain unclear. Indeed, it is unknown whether they have specialized or overlapping roles. However, the multiplicity of CD3 components and their evolutionary conservation suggest that they serve distinct functions. Here the developmental requirement for the CD3 delta chain is analyzed by generating a mouse line specifically lacking this component (delta-/- mice). Strikingly, CD3 delta is shown to be differentially required during development. In particular, CD3 delta is not needed for steps in development mediated by pre-TCR or gamma delta TCR, but is required for further development of thymocytes expressing alpha beta TCR. Absence of CD3 delta specifically blocks the thymic selection processes that mediate the transition from the double-positive to single-positive stages of development.

Apoptosis but not other activation events is inhibited by a mutation in the transmembrane domain of T cell receptor beta that impairs CD3zeta association

The transmembrane domain of T cell receptor (TCR) beta contains a conserved immunoreceptor tyrosine-based activation-like motif consisting of a duplicated YXXL sequence. The motif is also present in TCRgamma, the equivalent chain to TCRbeta in gammadelta T lymphocytes but is absent in TCRalpha and TCRdelta. To determine the putative role of this sequence in TCR.CD3 complex assembly and signal transduction, a TCRbeta chain cDNA was mutated in the C-terminal tyrosine of the motif, cloned in an expression vector, and transfected into TCRbeta-negative Jurkat cells. Transfectants of the mutated chain (MUT) expressed, on average, much less TCR.CD3 complex on the membrane than wild type TCRbeta transfectants. Radiolabeling experiments suggested that the mutation caused a loose association of the CD3zeta chain resulting in a defective assembly. However, stimulation of high TCR.CD3 expressing wild type and MUT clones with monoclonal antibodies and Staphylococcus aureus enterotoxin B resulted in similar levels of CD25 and CD69 expression, interleukin-2 secretion, and TCR.CD3 complex down-regulation. By contrast, MUT cells were clearly resistant to activation-induced cell death, and they did not express CD95-ligand upon activation. These results suggest a differentiated intracellular signaling pathway leading to apoptosis in which Tyr-TM11 of the immunoreceptor tyrosine-based activation motif-like motif and CD3zeta appear to be involved.

Growth retardation of tumors by adoptive transfer of cytotoxic T lymphocytes reprogrammed by CD44v6-specific scFv:zeta-chimera

Variants of the CD44 protein family containing sequences encoded by variant exon 6 (v6) are involved in the metastatic spread of rat and human tumors. The rat-specific antibody 1.1ASML, which recognizes a v6 epitope, interferes with metastatic dissemination of a rat pancreatic carcinoma. The single-chain antigen-binding fragment of this monoclonal antibody was fused to the zeta-chain of the T-cell receptor complex. The appropriate fusion gene was incorporated into a retroviral gene transfer vector. Murine cytotoxic T lymphocytes (CTLs) were infected, and cellular clones which express the single-chain zeta-chain fusion protein on their cell surface were selected. These CTLs are not MHC-restricted in their CD44v6 recognition and exhibit in vitro lytic activity toward cells expressing CD44 variants comprising exon v6. Tumor cell xenografts grown in athymic nude mice are suppressed in their growth upon infusion of the genetically manipulated CTLs. Our data indicate that the CD44v6 epitope is an effective target for immune tumor therapy and demonstrate the efficacy of genetically engineered CTLs in targeting tumors expressing such epitopes.

Redirected cytotoxic effector function. Requirements for expression of chimeric single chain high affinity immunoglobulin e receptors

The aim of this study was to construct a single chain chimeric FcepsilonRIalpha receptor capable of effector function in leukocytes, including cytotoxic lymphocytes. To determine the most effective single chain FcepsilonRIalpha receptor with respect to IgE binding and signaling function, a variety of chimeric gene constructs were transiently transfected into COS-7 cells. The most effective chimera consisted of four parts including: wild-type or mutated extracellular domains (Trp130 --> Ala130, W130A) of FcepsilonRIalpha, membrane proximal and transmembrane regions of FcgammaRIIa, and intracellular CD3zeta (epsilonIIaIIazeta). Scatchard analysis indicated that these FcepsilonRIalpha chimeric receptor bound ligand with an affinity of 0.9 to 2.2 x 10(9) -1. Ligand binding capacity was dramatically reduced with the deletion of 11 membrane proximal amino acids of FcepsilonRIalpha; however, function was restored by substitution with the equivalent region of FcgammaRIIa, suggesting a crucial requirement for a "spacer" segment between the transmembrane and extracellular ligand binding domain. Chimeras that bound IgE effectively also mediated phagocytosis. Chimeric receptors that contained transmembrane zeta were expressed as multimers and consequently did not bind IgE effectively; however, cotransfection of these chimeras with gamma-chain largely reconstituted IgE-mediated phagocytosis. The mouse cytotoxic T lymphocyte cell line, CTLLR8 was stably transfected with epsilonIIaIIazeta, and cloned transfectants were demonstrated to lyse target cells in an anti-FcepsilonRIalpha or IgE antibody-dependent manner. Therefore, functional single chain chimeric FcepsilonRIalpha receptors were expressed in the absence or presence of associated zeta or gamma molecules and were used to redirect killer lymphocytes to target cells.

Redirecting the complete T cell receptor/CD3 signaling machinery towards native antigen via modified T cell receptor

We show that a chimeric T cell receptor (TCR) beta chain consisting of a single-chain Fv portion derived from a monoclonal antibody and the full TCR beta chain is able to assemble functionally with endogenous TCR/CD3 components and transfer the antibody specificity as well as the TCR specificity into TCR beta- as well as into TCR beta+ T cells. This allows the incorporation new non-major histocompatibility complex-restricted ligand specificities into the intact TCR/CD3 complex which can exploit the full range of biological activities of the endogenous TCR signaling machinery. This approach can provide wider opportunities to redirect T cells to virus or tumor antigen-bearing cells.