Prospects for chimeric antigen receptor-modified T cell therapy for solid tumors.
ABSTRACT: The potential for adoptive cell immunotherapy as a treatment against cancers has been demonstrated by the remarkable response in some patients with hematological malignancies using autologous T cells endowed with chimeric antigen receptors (CARs) specific for CD19. Clinical efficacy of CAR-T cell therapy for the treatment of solid tumors, however, is rare due to physical and biochemical factors. This review focuses on different aspects of multiple mechanisms of immunosuppression in solid tumors. We characterize the current state of CAR-modified T cell therapy and summarize the various strategies to combat the immunosuppressive microenvironment of solid tumors, with the aim of promoting T cell cytotoxicity and enhancing tumor cell eradication.
Project description:Chimeric antigen receptor (CAR) T cells are engineered constructs composed of synthetic receptors that direct T cells to surface antigens for subsequent elimination. Many CAR constructs are also manufactured with elements that augment T-cell persistence and activity. To date, CAR T cells have demonstrated tremendous success in eradicating hematological malignancies (e.g., CD19 CARs in leukemias). This success is not yet extrapolated to solid tumors, and the reasons for this are being actively investigated. Here in this mini-review, we discuss some of the key hurdles encountered by CAR T cells in the solid tumor microenvironment.
Project description:Chimeric antigen receptors (CAR) are engineered fusion proteins constructed from antigen recognition, signaling, and costimulatory domains that can be expressed in cytotoxic T cells with the purpose of reprograming the T cells to specifically target tumor cells. CAR T-cell therapy uses gene transfer technology to reprogram a patient's own T cells to stably express CARs, thereby combining the specificity of an antibody with the potent cytotoxic and memory functions of a T cell. In early-phase clinical trials, CAR T cells targeting CD19 have resulted in sustained complete responses within a population of otherwise refractory patients with B-cell malignancies and, more specifically, have shown complete response rates of approximately 90% in patients with relapsed or refractory acute lymphoblastic leukemia. Given this clinical efficacy, preclinical development of CAR T-cell therapy for a number of cancer indications has been actively investigated, and the future of the CAR T-cell field is extensive and dynamic. Several approaches to increase the feasibility and safety of CAR T cells are currently being explored, including investigation into the mechanisms regulating the persistence of CAR T cells. In addition, numerous early-phase clinical trials are now investigating CAR T-cell therapy beyond targeting CD19, especially in solid tumors. Trials investigating combinations of CAR T cells with immune checkpoint blockade therapies are now beginning and results are eagerly awaited. This review evaluates several of the ongoing and future directions of CAR T-cell therapy.
Project description:T cells engineered to express CD19-specific chimeric antigen receptors (CARs) have shown breakthrough clinical successes in patients with B-cell lymphoid malignancies. However, similar therapeutic efficacy of CAR T cells in solid tumors is yet to be achieved. In this study we systematically evaluated a series of CAR constructs targeting glypican-3 (GPC3), which is selectively expressed on several solid tumors. We compared GPC3-specific CARs that encoded CD3? (Gz) alone or with costimulatory domains derived from CD28 (G28z), 4-1BB (GBBz), or CD28 and 4-1BB (G28BBz). All GPC3-CARs rendered T cells highly cytotoxic to GPC3-positive hepatocellular carcinoma, hepatoblastoma, and malignant rhabdoid tumor cell lines in vitro. GBBz induced the preferential production of Th1 cytokines (interferon ?/granulocyte macrophage colony-stimulating factor) while G28z preferentially induced Th2 cytokines (interleukin-4/interleukin-10). Inclusion of 4-1BB in G28BBz could only partially ameliorate the Th2-polarizing effect of CD28. 4-1BB induced superior expansion of CAR T cells in vitro and in vivo. T cells expressing GPC3-CARs incorporating CD28, 4-1BB, or both induced sustained tumor regressions in two xenogeneic tumor models. Thus, GBBz CAR endows T cells with superior proliferative potential, potent antitumor activity, and a Th1-biased cytokine profile, justifying further clinical development of GBBz CAR for immunotherapy of GPC3-positive solid tumors.
Project description:Uniform and strong expression of CD19, a cell surface antigen, on cells of B-cell lineage is unique to hematologic malignancies. Tumor-associated antigen (TAA) targets in solid tumors exhibit heterogeneity with regards to intensity and distribution, posing a challenge for chimeric antigen receptor (CAR) T-cell therapy. Novel CAR designs, such as dual TAA-targeted CARs, tandem CARs, and switchable CARs, in conjunction with inhibitory CARs, are being investigated as means to overcome antigen heterogeneity. In addition to heterogeneity in cancer-cell antigen expression, the key determinants for antitumor responses are CAR expression levels and affinity in T cells. Herein, we review CAR T-cell therapy clinical trials for patients with lung or pancreatic cancers, and provide detailed translational strategies to overcome antigen heterogeneity.
Project description:Despite high remission rates following CAR-T cell therapy in B-ALL, relapse due to loss of the targeted antigen is increasingly recognized as a mechanism of immune escape. We hypothesized that simultaneous targeting of CD19 and CD22 may reduce the likelihood of antigen loss, thus improving sustained remission rates. A systematic approach to the generation of CAR constructs incorporating two target-binding domains led to several novel CD19/CD22 bivalent CAR constructs. Importantly, we demonstrate the challenges associated with the construction of a bivalent CAR format that preserves bifunctionality against both CD19 and CD22. Using the most active bivalent CAR constructs, we found similar transduction efficiency compared to that of either CD19 or CD22 single CARs alone. When expressed on human T cells, the optimized CD19/CD22 CAR construct induced comparable interferon γ and interleukin-2 in vitro compared to single CARs against dual-antigen-expressing as well as single-antigen-expressing cell lines. Finally, the T cells expressing CD19/CD22 CAR eradicated ALL cell line xenografts and patient-derived xenografts (PDX), including a PDX generated from a patient with CD19- relapse following CD19-directed CAR therapy. The CD19/CD22 bivalent CAR provides an opportunity to test whether simultaneous targeting may reduce risk of antigen loss.
Project description:Anti-CD19 chimeric antigen receptor (CAR) T cells have caused remissions of B cell malignancies, but problems including cytokine-mediated toxicity and short persistence of CAR T cells in vivo might limit the effectiveness of anti-CD19 CAR T cells. Anti-CD19 CARs that have been tested clinically had single-chain variable fragments (scFvs) derived from murine antibodies. We have designed and constructed novel anti-CD19 CARs containing a scFv with fully human variable regions. T cells expressing these CARs specifically recognized CD19+ target cells and carried out functions including degranulation, cytokine release, and proliferation. We compared CARs with CD28 costimulatory moieties along with hinge and transmembrane domains from either the human CD28 molecule or the human CD8? molecule. Compared with T cells expressing CARs with CD28 hinge and transmembrane domains, T cells expressing CARs with CD8? hinge and transmembrane domains produced lower levels of cytokines and exhibited lower levels of activation-induced cell death (AICD). Importantly, CARs with hinge and transmembrane regions from either CD8? or CD28 had similar abilities to eliminate established tumors in mice. In anti-CD19 CARs with CD28 costimulatory moieties, lower levels of inflammatory cytokine production and AICD are potential clinical advantages of CD8? hinge and transmembrane domains over CD28 hinge and transmembrane domains.
Project description:Most B-cell malignancies express CD19, and a majority of patients with B-cell malignancies are not cured by current standard therapies. Chimeric antigen receptors (CARs) are fusion proteins consisting of antigen recognition moieties and T-cell activation domains. T cells can be genetically modified to express CARs, and adoptive transfer of anti-CD19 CAR T cells is now being tested in clinical trials. Effective clinical treatment with anti-CD19 CAR T cells was first reported in 2010 after a patient with advanced-stage lymphoma treated at the NCI experienced a partial remission of lymphoma and long-term eradication of normal B cells. Additional patients have subsequently obtained long-term remissions of advanced-stage B-cell malignancies after infusions of anti-CD19 CAR T cells. Long-term eradication of normal CD19(+) B cells from patients receiving infusions of anti-CD19 CAR T cells demonstrates the potent antigen-specific activity of these T cells. Some patients treated with anti-CD19 CAR T cells have experienced acute adverse effects, which were associated with increased levels of serum inflammatory cytokines. Although anti-CD19 CAR T cells are at an early stage of development, the potent antigen-specific activity observed in patients suggests that infusions of anti-CD19 CAR T cells might become a standard therapy for some B-cell malignancies.
Project description:Chimeric antigen receptors (CAR)-T cell therapy has recently made promising advances towards treatment of B-cell malignancies. This approach makes use of an antibody-derived single chain variable fragment (scFv)-based CAR to target the CD19 antigen. Currently scFvs are the most common strategy for creation of CARs, but tumor cells can also be targeted using non-antibody based approaches with designs focused on the interaction between natural receptors and their ligands. This emerging strategy has been used in unique ways to target multiple tumor types, including solid and haematological malignancies. In this review, we will highlight the performance of receptor-ligand combinations as designs for CARs to treat cancer, with a particular focus on haematologic malignancies.
Project description:Impressive results have been achieved by adoptively transferring T-cells expressing CD19-specific CARs with binding domains from murine mAbs to treat B-cell malignancies. T-cell mediated immune responses specific for peptides from the murine scFv antigen-binding domain of the CAR can develop in patients and result in premature elimination of CAR T-cells increasing the risk of tumor relapse. As fully human scFv might reduce immunogenicity, we generated CD19-specific human scFvs with similar binding characteristics as the murine FMC63-derived scFv using human Ab/DNA libraries. CARs were constructed in various formats from several scFvs and used to transduce primary human T-cells. The resulting CD19-CAR T-cells were specifically activated by CD19-positive tumor cell lines and primary chronic lymphocytic leukemia cells, and eliminated human lymphoma xenografts in immunodeficient mice. Certain fully human CAR constructs were superior to the FMC63-CAR, which is widely used in clinical trials. Imaging of cell surface distribution of the human CARs revealed no evidence of clustering without target cell engagement, and tonic signaling was not observed. To further reduce potential immunogenicity of the CARs, we also modified the fusion sites between different CAR components. The described fully human CARs for a validated clinical target may reduce immune rejection compared with murine-based CARs.
Project description:Chimeric antigen receptor (CAR)-engineered T cells (CAR-T cells) have been shown to have unprecedented efficacy in B cell malignancies, most notably in B cell acute lymphoblastic leukemia (B-ALL) with up to a 90% complete remission rate using anti-CD19 CAR-T cells. However, CAR T-cell therapy for solid tumors currently is faced with numerous challenges such as physical barriers, the immunosuppressive tumor microenvironment and the specificity and safety. The clinical results in solid tumors have been much less encouraging, with multiple cases of toxicity and a lack of therapeutic response. In this review, we will discuss the current stats and challenges of CAR-T cell therapy for solid tumors, and propose possibl e solutions and future perspectives.