Retroviral-mediated gene transfer in primary murine and human T-lymphocytes

Who wins the combat, CAR or TCR?

Chimeric antigen receptor T (CAR-T) cell therapy has drawn increasing attention over the last few decades given its remarkable effectiveness and breakthroughs in treating B cell hematological malignancies. Even though CAR-T cell therapy has outstanding clinical successes, most treated patients still relapse after infusion. CARs are derived from the T cell receptor (TCR) complex and co-stimulatory molecules associated with T cell activation; however, the similarities and differences between CARs and endogenous TCRs regarding their sensitivity, signaling pathway, killing mechanisms, and performance are still not fully understood. In this review, we discuss the parallel comparisons between CARs and TCRs from various aspects and how these current findings might provide novel insights and contribute to improvement of CAR-T cell therapy efficacy.

T-cell counts in peripheral blood at leukapheresis predict responses to subsequent CAR-T cell therapy

Prediction of responses to chimeric antigen receptor (CAR)-T cell therapies is essential to maximize their therapeutic efficacy for diffuse large B-cell lymphoma (DLBCL). While several tumor-intrinsic risk factors of resistance and/or early relapse have been identified, clinically useful markers that determine potential activity of CAR-T cells have not been fully investigated. T-cell property at the time of leukapheresis may serve as such a marker. Therefore, we evaluated the clinical impact of CD3⁺ cell count in peripheral blood at leukapheresis on clinical outcomes of CAR-T cell therapy. In total, 44 patients with relapsed or refractory (r/r) DLBCL who received tisagenlecleucel at Kyoto University Hospital were included. According to CD3⁺ cell counts, patients were categorized into CD3^LOW and CD3^HIGH groups with a threshold of 553/μL, based on receiver operating characteristic curve analysis. 1-year progression-free survival was significantly higher in the CD3^HIGH group than the CD3^LOW group (68.3% vs. 17.3%; adjusted hazard ratio [aHR], 0.37; p = 0.042). Overall survival was also superior in the CD3^HIGH group (aHR, 0.24; p = 0.043). Moreover, higher CD3⁺ cell counts at leukapheresis were associated with significantly higher lymphocyte counts in peripheral blood at day 7 after CAR-T cell infusion (median 860 vs. 420/μL, P = 0.021), suggesting more extensive expansion of infused CAR-T cells in vivo. In conclusion, we demonstrated that the CD3⁺ cell count at leukapheresis predicts both expansion of CAR-T cells after infusion and outcomes of CAR-T cell therapy, and are useful for building comprehensive therapeutic strategies at the time of leukapheresis.

T Cell Fitness and Autologous CAR T Cell Therapy in Haematologic Malignancy

A range of emerging therapeutic approaches for the treatment of cancer aim to induce or augment endogenous T cell responses. Chimeric antigen receptor (CAR) T cell therapy (CTT) is one such approach that utilises the patient’s own T cells, engineered ex vivo to target cell surface antigens, to eliminate haematological malignancies. Despite mediating high rates of responses in some clinical trials, this approach can be limited by dysfunctional T cells if they are present at high frequencies either in the starting material from the patient or the CAR T cell product. The fitness of an individual’s T cells, driven by age, chronic infection, disease burden and cancer treatment, is therefore likely to be a crucial limiting factor of CTT. Currently, T cell dysfunction and its impact on CTT is not specifically quantified when patients are considering the therapy. Here, we review our current understanding of T cell fitness for CTT, how fitness may be impacted by age, chronic infection, malignancy, and treatment. Finally, we explore options to specifically tailor clinical decision-making and the CTT protocol for patients with more extensive dysfunction to improve treatment efficacy. A greater understanding of T cell fitness throughout a patient’s treatment course could ultimately be used to identify patients likely to achieve favourable CTT outcomes and improve methods for T cell collection and CTT delivery.

Incorporation of bacterial immunoevasins to protect cell therapies from host antibody-mediated immune rejection

Cellular therapies are engineered using foreign and synthetic protein sequences, such as chimeric antigen receptors. The frequently observed humoral responses to CAR T cells result in rapid clearance, especially after re-infusions. There is an unmet need to protect engineered cells from host-versus-graft rejection, particularly for the advancement of allogeneic cell therapies. Here, utilizing the IgG protease "IdeS", we programmed CAR T cells to defeat humoral immune attacks. IdeS cleavage of host IgG averted Fc-dependent phagocytosis and lysis, and the residual F(ab')₂ fragments remained on the surface, providing cells with an inert shield from additional IgG deposition. "Shield" CAR T cells efficiently cleaved cytotoxic IgG, including anti-CAR antibodies, detected in patient samples and provided effective anti-tumor activity in the presence of anti-cell IgG in vivo. This technology may be useful for repeated human infusions of engineered cells, more complex engineered cells, and expanding widespread use of "off-the-shelf" allogeneic cellular therapies.

Editing of Endogenous Genes in Cellular Immunotherapies

PURPOSE OF REVIEW

T cell-based cellular and antibody immunotherapies have dramatically altered the landscape of cancer treatment over the past decade. Over the same time span, gene editing technologies have enabled unprecedented degrees of genetic control.

RECENT FINDINGS

Knock-outs of endogenous genes, especially based on electroporation of targetable nucleases such as CRISPR/Cas9, have rapidly proliferated. Simultaneous introduction of large DNA sequences can integrate new synthetic genetic instructions with specific endogenous loci to alter T cell function and specificity. Recently developed discovery technologies to perform genome-wide knock-out and large-scale knock-in screens in T cells can rapidly identify endogenous gene targets and therapeutic knock-in programs. Endogenous gene knock-outs and targeted knock-ins may offer the chance to expand beyond the current limitations of randomly integrating viral vector-based T cell therapies, and extend immunotherapies' therapeutic advances to wider hematologic and solid tumor indications.

Retroviral Transduction and Reporter Assay: Transcription Factor Cooperation in Th9 Cell Development

Naïve CD4+ T cells differentiate into different T helper subsets in response to specific cytokine environment and transcription factors. Th9 cells are induced in response to signals from cytokines, TGF-β and IL-4. Transcription factors that are downstream of these cytokines converge to drive the development of Th9 cells. Retroviral transduction allows the genetic modification in T cells thereby helping us to better understand the molecular mechanisms that control their development as well as function. In this chapter, an optimized protocol for retroviral transduction of murine Th9 cells as well as transient transfection of Th9 cells with luciferase reporter constructs is described.

Immunotherapeutic approaches in prostate cancer: combinations and clinical integration

Despite multiple immunologic approaches with peptide, protein, and DNA vaccines, no single therapy has induced complete remission or maintained durability of response in patients with castration-resistant prostate cancer (CRPC). Historically, immunotherapy has had limited effect on solid tumors with the exception of melanoma and renal cell carcinomas, which have been deemed as immunologic cancers given their potential for remissions either spontaneously or after removal of the primary lesion. There is considerable excitement about using an immunotherapy in combination with biologic agents such as checkpoint inhibitors, cytokines, other vaccines, or chemotherapy. Sipuleucel-T represents one of several novel immunologic therapeutic approaches to treat prostate cancer in addition to other solid tumors. It is the first in its class of autologous cellular therapies to demonstrate safety and an overall survival benefit in patients with asymptomatic or minimally symptomatic CRPC and represents a unique treatment method that may be further enhanced with other agents. Although sipuleucel-T can be used as a foundation on which to build and enhance future immunologic clinical trials, other exciting strategies are in development that may be easily integrated into the algorithm of current care.

Adoptive cellular therapy of cancer: exploring innate and adaptive cellular crosstalk to improve anti-tumor efficacy

ABSTRACT 

The mammalian immune system has evolved to produce multi-tiered responses consisting of both innate and adaptive immune cells collaborating to elicit a functional response to a pathogen or neoplasm. Immune cells possess a shared ancestry, suggestive of a degree of coevolution that has resulted in optimal functionality as an orchestrated and highly collaborative unit. Therefore, the development of therapeutic modalities that harness the immune system should consider the crosstalk between cells of the innate and adaptive immune systems in order to elicit the most effective response. In this review, the authors will discuss the success achieved using adoptive cellular therapy in the treatment of cancer, recent trends that focus on purified T cells, T cells with genetically modified T-cell receptors and T cells modified to express chimeric antigen receptors, as well as the use of unfractionated immune cell reprogramming to achieve optimal cellular crosstalk upon infusion for adoptive cellular therapy.

Dual targeting of ErbB2 and MUC1 in breast cancer using chimeric antigen receptors engineered to provide complementary signaling

PURPOSE

Chimeric antigen receptor (CAR) engineered T-cells occupy an increasing niche in cancer immunotherapy. In this context, CAR-mediated CD3ζ signaling is sufficient to elicit cytotoxicity and interferon-γ production while the additional provision of CD28-mediated signal 2 promotes T-cell proliferation and interleukin (IL)-2 production. This compartmentalisation of signaling opens the possibility that complementary CARs could be used to focus T-cell activation within the tumor microenvironment.

METHODS

Here, we have tested this principle by co-expressing an ErbB2- and MUC1-specific CAR that signal using CD3ζ and CD28 respectively. Stoichiometric co-expression of transgenes was achieved using the SFG retroviral vector containing an intervening Thosea asigna peptide.

RESULTS

We found that "dual-targeted" T-cells kill ErbB2(+) tumor cells efficiently and proliferate in a manner that requires co-expression of MUC1 and ErbB2 by target cells. Notably, however, IL-2 production was modest when compared to control CAR-engineered T-cells in which signaling is delivered by a fused CD28 + CD3ζ endodomain.

CONCLUSIONS

These findings demonstrate the principle that dual targeting may be achieved using genetically targeted T-cells and pave the way for testing of this strategy in vivo.

Chimeric antigen receptors for T-cell based therapy

The Chimeric Antigen Receptor (CAR) consists of an antibody-derived targeting domain fused with T-cell signaling domains that, when expressed by a T-cell, endows the T-cell with antigen specificity determined by the targeting domain of the CAR. CARs can potentially redirect the effector functions of a T-cell towards any protein and nonprotein target expressed on the cell surface as long as an antibody or similar targeting domain is available. This strategy thereby avoids the requirement of antigen processing and presentation by the target cell and is applicable to nonclassical T-cell targets like carbohydrates. This circumvention of HLA-restriction means that the CAR T-cell approach can be used as a generic tool broadening the potential of applicability of adoptive T-cell therapy. Proof-of-principle studies focusing upon the investigation of the potency of CAR T-cells have primarily focused upon the genetic modification of human and mouse T-cells for therapy. This chapter focuses upon methods to modify T-cells from both species to generate CAR T-cells for functional testing.

Effective transduction of primary mouse blood- and bone marrow-derived monocytes/macrophages by HIV-based defective lentiviral vectors

Human immunodeficiency virus type 1-based defective lentiviral vectors (HIV-based vector) efficiently transduce a wide range of mammalian cell types, but little is known with respect to their utility for gene transfer applications involving primary mouse monocytes/macrophages. This may be important for preclinical development of a range of potential gene therapeutic modalities. Present study described the development of an optimized method for viral vector-mediated gene transfer into primary mouse monocytes/macrophages and the establishment of reproducible protocols for cell isolation/cultivation. It has been determined that bone marrow-derived monocytes/macrophages were consistently more susceptible to viral vector-mediated gene transduction, as compared to blood-derived cells. It has also been documented that the efficiency of transduction increased when cells were maintained in vitro, prior to exposure to vector virus. Finally, experiments were conducted to compare the efficiency of gene transfer mediated by HIV-based vectors to that achieved by other lentivirus or retrovirus vector systems. These studies showed that HIV-based vector system was consistently superior. Overall, these results establish a new and efficient method for gene transfer into primary mouse monocytes/macrophages. This may be of utility in the preclinical development of gene therapies that target this important cell type.

Electric field-induced molecular vibration for noninvasive, high-efficiency DNA transfection

Gene delivery is an essential research tool for elucidating gene structure, regulation, and function in biomedical research and is the technological basis for gene therapy. However, the application of nonviral vectors in mammalian cell transfection and gene therapy is limited in that current methods require large amounts of exogenous DNA and/or exhibit high cytotoxicity and low transfection efficiency in primary cells. Here we describe the development of a novel, noninvasive gene delivery protocol using plasmid DNA vectors, based on the principle of electric field-induced molecular vibration. This method enables foreign DNA molecules to penetrate the plasma membrane and enter the cytoplasm of both primary mesenchymal progenitor cells and established cell lines of various species, at high efficiency and with low cell mortality. This procedure requires no special reagents, allows stable expression of transduced DNA, and does not interfere with the normal cellular differentiation activities of human and chick mesenchymal progenitors.

Lentivirus-mediated gene transfer and expression in established human tumor antigen-specific cytotoxic T cells and primary unstimulated T cells

In this report, we evaluated the efficiency of stable gene transfer into established CD8(+) human tumor antigen-specific cytotoxic T cell (CTL) lines and peripheral blood lymphocytes (PBL) by oncoretroviral and lentiviral vectors. In the oncoretroviral vector, the green fluorescent protein (GFP) reporter gene was regulated by the murine stem cell virus (MSCV) promoter. In three human immunodeficiency virus type 1 (HIV-1)-based lentiviral vectors, the GFP transgene was regulated by either a chimeric MSCV/HIV-1 promoter, or cellular promoters from human housekeeping genes PGK and EF1 alpha. We found that several lines of proliferating tumor-specific CTL were poorly (=2%) transduced by the oncoretroviral vector that transduced Jurkat T cell line efficiently (=80%). In contrast, three lentiviral vectors transduced 38-63% of these proliferating CTL. More interestingly, all lentiviral vectors packaged without the HIV-1 accessory proteins transduced human bulk PBL and purified CD4(+) and CD8(+) lymphocyte subsets without prior stimulation. Detailed analysis indicated that the lentiviral vectors containing the EF1 alpha or PGK ubiquitous promoter can transduce unstimulated PBL and achieve low-level transgene expression in the absence of any T-cell activation. However, T-cell activation subsequent to the transduction of unstimulated PBL is required for high-level transgene expression. Transduced PBL expressing transgene delivered by the lentiviral vectors still preserved resting and naïve cell phenotypes. Taken together, prior T cell stimulation and HIV-1 accessory proteins are dispensable for lentivirus-mediated gene transfer into resting naïve and memory T lymphocytes. These results will have significant implications for the study of T-cell biology and for the improvement of clinical gene therapies of acquired immune deficiency syndrome (AIDS) and cancer.

Redirecting T lymphocyte specificity using T cell receptor genes

Redirecting T cells by transferring T cell receptor (TCR) genes from tumor-associated antigen (TAA)-reactive T cell clones into human peripheral blood lymphocytes (PBL) has therapeutic potential for the treatment of diseases, including cancer. T cell specificity can be altered using retroviruses encoding TCRalpha and TCRbeta chain genes, or chimeric immunoglobulin (cIg) genes containing signaling domains of CD3 zeta or Fc epsilon RI-gamma. This review evaluates recent studies using TCRs and cIgs to redirect T cell specificity and discusses some of the technical and biological hurdles that need to be addressed before these approaches can be successfully used to treat patients.

Quantitative imaging of the T cell antitumor response by positron-emission tomography

We describe a noninvasive, quantitative, and tomographic method to visualize lymphocytes within the whole animal. We used positron-emission tomography (PET) to follow the localization of adoptively transferred immune T lymphocytes. Splenic T cells from animals that had rejected a Moloney murine sarcoma virus/Moloney murine leukemia virus (M-MSV/M-MuLV)-induced tumor were marked with a PET reporter gene, injected into tumor-bearing mice, and imaged in a microPET by using a substrate specific for the reporter. Specific localization of immune T cells to the antigen-positive tumor was detected over time, by sequential imaging of the same animals. Naive T cells did not localize to the tumor site, indicating that preimmunization was required. Autoradiography and immunohistochemistry analysis corroborated the microPET data. The method we have developed can be used to assess the effects of immunomodulatory agents intended to potentiate the immune response to cancer, and can also be useful for the study of other cell-mediated immune responses, including autoimmunity.

Efficient transduction of murine primary T cells requires a combination of high viral titer, preferred tropism, and proper timing of transduction

Retroviral vectors have been used exclusively for genetic modification of primary T cells. Most T cell infection protocols have been developed for human T cells, whereas systematic investigations of the optimal conditions for transduction of murine primary T cells are limited. In this study, ecotropic and 10A1-pseudotyped retroviral vectors were compared for their efficiency in infecting murine primary T cell cells, as well as T cell lines. Various factors that affect transduction efficiency were also explored, including virus titer, times of exposure, timing of infection, low-speed centrifugation, and use of fibronectin fragment. Our results showed that up to 80% of murine primary T cells could be infected after a single exposure. Successful infection required a combination of high virus titer (>10(7) CFU/ml), proper timing of infection (within 24 h after mitogen stimulation), and preferred tropism (ecotropic vectors). These optimization results may help to establish a standard protocol for infection of murine primary T cells and provide some insight into the obstacles to retroviral infection of T cells.

Targeting tumours with genetically enhanced T lymphocytes

The genetic modification of T lymphocytes is an important approach to investigating normal T-cell biology and to increasing antitumour immunity. A number of genetic strategies aim to increase the recognition of tumour antigens, enhance antitumour activities and prevent T-cell malfunction. T cells can also be engineered to increase safety, as well as to express markers that can be tracked by non-invasive imaging technologies. Genetically modified T cells are therefore proving to be of great value for basic immunology and experimental 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.

Human T-lymphocyte cytotoxicity and proliferation directed by a single chimeric TCRzeta /CD28 receptor

Artificial receptors provide a promising approach to target T lymphocytes to tumor antigens. However, the receptors described thus far produce either an activation or a co-stimulatory signal alone, thus limiting the spectrum of functions accomplished by the genetically modified cells. Here we show that human primary T lymphocytes expressing fusion receptors directed to prostate-specific membrane antigen (PSMA) and containing combined T-cell receptor-zeta (TCRzeta), and CD28 signaling elements, effectively lyse tumor cells expressing PSMA. When stimulated by cell-surface PSMA, retrovirally transduced lymphocytes undergo robust proliferation, expanding by more than 2 logs in three weeks, and produce large amounts of interleukin-2 (IL-2). Importantly, the amplified cell populations retain their antigen-specific cytolytic activity. These data demonstrate that fusion receptors containing both TCR and CD28 signaling moieties are potent molecules able to redirect and amplify human T-cell responses. These findings have important implications for adoptive immunotherapy of cancer, especially in the context of tumor cells that fail to express major histocompatibility complex antigens and co-stimulatory molecules.

Retroviruses as tools to study the immune system

Retrovirus-based vectors provide an efficient means to introduce and express genes in cells of the immune system and have become a popular tool to study immune function. They are easy to manipulate and provide stable, long-term gene expression because they integrate into the genome. Current retroviral vectors do have limitations that affect their usefulness in certain applications. However, recent advances suggest a number of ways in which these vectors might be improved to extend their utility in immunological research.