Immuno-Oncology

O. Michielin, G. Coukos

• Editorial: S. Karger
• Año: 2015
• ISBN:
  9783318055900
• Categoría: Médecine
• Categoría: Génétique en médecine

Over the last decade, immuno-oncology has witnessed an astonishing pace of discovery and innovation translating into unprecedented successes in the clinical setting, arguably representing one of the most profound and transforming revolution in the history of cancer therapy. This book provides a concise and accurate outline of the main developments in major tumor types including melanoma, lung, breast, brain and renal cell cancers. In addition, transversal chapters that describe the commonalities of some of the therapeutic strategies are provided to cover topics like immune checkpoint biology, T cell engineering or rational combination therapies. Each chapter has been authored by senior key opinion leaders in their respective fields to provide the most up-to-date view on cancer immuno-oncology. To reflect on the key translational aspect of immuno-oncology, all chapters are making explicit connections between basic science discoveries and the resulting translational therapeutic strategies. Immuno-Oncology will be an invaluable source of information for scientists interested in the translation of basic immunology into the clinical practice, as well as for clinician interested in deepening their knowledge of current and upcoming immune strategies in the fight against cancers.

Michielin O, Coukos G (eds): Immuno-Oncology.
Prog Tumor Res. Basel, Karger, 2015, vol 42, pp 110-135 (DOI: 10.1159/000437180)

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T Cell Engineering

Magdalena Pircher^a · Thomas Schirrmann^b · Ulf Petrausch^a

^aDepartment of Oncology, University Hospital Zurich, Zurich, Switzerland; ^bInstitute of Biochemistry, Biotechnology and Bioinformatics, Technische Universität Braunschweig, Braunschweig, Germany

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Abstract

T cells are a new and promising antigen-specific therapeutic option for the treatment of malignant diseases. To achieve antigen specificity against tumor antigens, T cells can be manipulated by gene transfer to express chimeric antigen receptors (CARs). CAR-expressing T cells are called redirected T cells. CARs are composed of an extracellular antibody-derived antigen recognition domain, a transmembrane domain and a cytoplasmatic signal domain. Therefore, redirected T cells combine the exchangeable specificity of an antibody with the cytotoxic machinery of a T cell. Early clinical trials with redirected T cells targeting cluster of differentiation (CD) 19 have shown impressive results in CD19-positive hematological cancers. However, for solid cancers only limited clinical experience exists and new and innovative concepts have to be developed to overcome tumor-mediated immune suppression. Herein, we describe the general design of a CAR, the function of the different domains and the different strategies to produce redirected T cells. Furthermore, we summarize and discuss the preclinical and clinical data indicating the tremendous potential of redirected T cells to become a mainstay of cancer immunotherapy.

© 2015 S. Karger AG, Basel

T cells are a new antigen-specific therapeutic option to overcome certain limitations of monoclonal antibodies because they are capable of actively migrating into malignant tumors and directly killing cancer cells. Monoclonal antibodies are often rapidly removed from the tumor cell surface by processes like capping, shedding or endocytosis. Additionally, there is still the large hurdle of inefficient access of macromolecule-like antibodies to poorly vascularized, malignant tumors, which are additionally protected by endothelia, surrounding tissue or the blood-tissue barriers. This results in limitations regarding efficacy and clinical benefit. Even though monoclonal antibodies have revolutionized therapy of certain malignant diseases (e.g. lymphoma or breast cancer) [1] via direct antiproliferative effects by blocking signaling pathways or via the induction of direct cytotoxic effects by the recruitment of complement or Fc receptor-bearing immune cells (antibody-dependent cell-mediated cytotoxicity), nowadays new immunological therapeutic strategies such as genetically modified T cells are being tested to overcome the limitations mentioned above.

Over the last decades multiple lines of experimental data have demonstrated that T cells are involved in the tumor immune surveillance postulated by Burnet [2] and Smyth et al. [3]. T cells are able to kill tumor cells, but they are also suppressed by the tumor microenvironment [4]. To date, only a limited number of T cell receptors (TCRs) targeting antigens expressed on cancer cells are known. Since TCRs only recognize targets in the context of major histocompatibility complexes, the TCR binding is a highly individual process that is difficult to translate into a standardized, therapeutic intervention with a defined antigen-specific T cell population.

To overcome the limitations of antibody and T cell therapies the antigen specificity of antibodies should be combined with the effector properties of cytotoxic T cells. The antibody allows the targeting of a well-defined antigen, whereas the T cell offers direct target cell killing and active migration into malignant tissues. With the help of an antibody, surface antigens can be targeted independently of the major histocompatibility complex. Thereby, T cell therapy becomes broadened to a wider spectrum of antigens independent of the endogenous T cell repertoire. Additionally, the effect can be amplified by T cell proliferation, resulting in an expanded antigen-specific effector cell population. Today, there are two major strategies to redirect T cells towards malignant tumors with antibodies.

First, bispecific antibodies binding to a tumor-associated antigen as well as to signal molecules like CD3 on T cells have been successfully used to specifically redirect and activate T cells against tumor cells [5, 6]. Although bispecific antibodies can extend the natural antibody-mediated cellular cytotoxicity, they suffer from similar limitations as monospecific antibodies, like the need for large amounts of recombinant protein and their inefficient migration into solid tumors [7]. T cells activated by bispecific antibodies can lose their signal transduction and effector properties following target cell recognition [8] and require additional costimulatory signals for full activation [9]. Nevertheless, the CD3 × CD19 bispecific antibody (blinatumomab) first showed activity in phase I and phase II clinical trials for patients with follicular lymphoma, mantle-cell lymphoma and acute lymphoblastic leukemia, and achieved a breakthrough therapy designation by the US Food and Drug Administration (FDA) [10-12].

Second, genetically engineered T cells are redirected against malignant tumors via the expression of a CAR. This approach is discussed later in this chapter. T cells which are genetically engineered by antigen-specific chimeric receptors contain genes consisting of an antigen recognition domain of an antibody and signal domains triggering their cytolytic mechanisms. Importantly, the CAR can be designed to deliver additional costimulatory signals resulting in more efficient and sustained T cell activation and target cell killing. T cells expressing a CAR are called redirected or genetically modified T cells [13]. In this chapter we will focus on the mechanisms and the design of single-chain CARs which have led to the recently published breakthroughs in the development of redirected T cells, pushing the field of adoptive T cell transfer into a new promising era. Specific problems when TCRs are used to redirect T cells will not be covered here. However, we will show and discuss the design and the most important recent experimental and clinical evidence for T cells redirected by CARs.

Chimeric Antigen Receptors

Based on the most recent published data, Rosenberg and colleagues [14] foresee T cell therapy as the therapeutic intervention that can potentially achieve a cure in at least lymphatic leukemia: ‘Although the palliation of cancer is the daily task of the oncologist, its cure is our “fervent hope”. It seems clear that drug-based treatments alone generally do not kill all cancer cells, with the notable exception of germ cell tumors and some hematological malignancies. Residual disease after drug therapy will ultimately grow back, with lethal consequences. However, the immune system is capable of achieving sterilizing immunity and inducing long-term, durable responses that are probably curative. The use of adoptive T cell-based therapies to eradicate cancer is at a rare nexus of basic immunology and clinically meaningful therapy.’

What Is a Chimeric Antigen Receptor?

The general design of a CAR consists of an amino-terminal signal peptide, followed by an extracellular antibody-derived antigen recognition domain, a transmembrane domain and a cytoplasmatic signal domain (fig. 1). These domains are required to enable the cell surface expression of the receptor and to couple the antibody-mediated antigen recognition with the effector function of the gene-modified T cell. Additional domains, in particular extracellular spacer domains between the antigen recognition domain and transmembrane domain, can dramatically improve the expression, antigen binding and signal function of the CAR. Novel CAR designs contain additional motifs of costimulatory receptors or utilize downstream signal molecules to enhance the effector functions of the gene-modified immune cells [15].

How Is a Chimeric Antigen Receptor Built?

During the first attempts of T cell gene modification, chimeric TCR variants were designed by the substitution of both TCR variable (V) regions with those of antibodies [16, 17]. These chimeric TCR chains also interacted with endogenous TCR chains, often resulting in nonfunctional TCR hybrid complexes. The so-called ‘two-chain CARs’ required the transfection of two genes into the same cell resulting in inefficient and variable production of gene-modified T cells. The fusion of antibody V regions to one of the TCR signal chains like the CD3ε or ζ chain or the FcεRI γ chain allowed the construction of the first single-chain CAR. The fusion of the extracellular domain of CD4 to cytoplasmatic domains of the ζ chain resulted in a functional chimeric single chain receptor gene which could be expressed in T cells [18]. These early redirected lymphocytes demonstrated specific cytotoxicity against HIV (human immunodeficiency virus) [18]. Major interest lies in these early HIV-specific redirected T cells since the early data are now used to estimate long-term risks of redirected T cell transfer [19]. The use of Fab fragments fused to the CD3ε, ζ or FcεRI γ chain enhanced the formation of a functional antigen binding domain stabilized by the disulphide bridge between the C_L and C_H1 domain and reduced the interaction with endogenous TCR signa...