Recent reports on the impressive efficacy of adoptively transferred T cells to challenge cancer in early phase clinical trials have significantly raised the profile of T cell therapy. Concomitantly, ...general expectations are also raised by these reports, with the natural aspiration to deliver this therapy over a wide range of tumor indications. Chimeric antigen receptors (CARs) endow T cell populations with defined antigen specificities that function independently of the natural T cell receptor and permit targeting of T cells towards virtually any tumor. Here, we review the current clinical application of CAR–T cells and relate clinical efficacy and safety of CAR–T cell trials to parameters considered critical for CAR engineering, classified as the three T's of CAR–T cell manipulation.
The primary aim of this clinical trial was to determine the feasibility of delivering first-generation CAR T cell therapy to patients with advanced, CEACAM5
+
malignancy. Secondary aims were to ...assess clinical efficacy, immune effector function and optimal dose of CAR T cells. Three cohorts of patients received increasing doses of CEACAM5
+
-specific CAR T cells after fludarabine pre-conditioning plus systemic IL2 support post T cell infusion. Patients in cohort 4 received increased intensity pre-conditioning (cyclophosphamide and fludarabine), systemic IL2 support and CAR T cells. No objective clinical responses were observed. CAR T cell engraftment in patients within cohort 4 was significantly higher. However, engraftment was short-lived with a rapid decline of systemic CAR T cells within 14 days. Patients in cohort 4 had transient, acute respiratory toxicity which, in combination with lack of prolonged CAR T cell persistence, resulted in the premature closure of the trial. Elevated levels of systemic IFNγ and IL-6 implied that the CEACAM5-specific T cells had undergone immune activation in vivo but only in patients receiving high-intensity pre-conditioning. Expression of CEACAM5 on lung epithelium may have resulted in this transient toxicity. Raised levels of serum cytokines including IL-6 in these patients implicate cytokine release as one of several potential factors exacerbating the observed respiratory toxicity. Whilst improved CAR designs and T cell production methods could improve the systemic persistence and activity, methods to control CAR T ‘on-target, off-tissue’ toxicity are required to enable a clinical impact of this approach in solid malignancies.
The last few years have seen the transfer of two decades of research into Chimeric Antigen Receptors (CARs) into clinical trials. Despite this extensive research, there is still a great deal of ...debate into the optimal design strategy for these, primarily, anti-cancer entities. The archetypal CAR consists of a single-chain antibody fragment, specific to a tumour-associated antigen, fused to a component of the T-cell receptor complex (typically CD3zeta) which on antigen binding primes the engrafted T-cell for anti-tumour activity. The modular nature of these artificial receptors has enabled researchers to modify aspects of their structure, including the extracellular spacer, transmembrane and cytoplasmic domain, to achieve laboratory defined optimal activity. Despite this there is no consensus on the optimal structure, a problem exacerbated by conflicting results using identical receptors. In this review, we provide a structural overview of CAR development and highlight areas that require further refinement. We also attempt to identify possible reasons for conflicting results in the hope that this information will inspire future rational design strategies for optimal tumour targeting using CARs.
Summary
Blockbuster antibody therapies have catapulted immune‐based approaches to treat cancer into the consciousness of mainstay clinical research. On the back of this, other emerging immune‐based ...therapies are providing great promise. T‐cell therapy is one such area where recent trials using T cells genetically modified to express an antibody‐based chimeric antigen receptor (CAR) targeted against the CD19 antigen have demonstrated impressive responses when adoptively transferred to patients with advanced chronic lymphocytic leukemia. The general concept of the CAR T cell was devised some 20 years ago. In this relatively short period of time, the technology to redirect T‐cell function has moved at pace facilitating clinical translation; however, many questions remain with respect to developing the approach to improve CAR T‐cell therapeutic activity and also to broaden the range of tumors that can be effectively targeted by this approach. This review highlights some of the underlying principles and compromises of CAR T‐cell technology using the CD19‐targeted CAR as a paradigm and discusses some of the issues that relate to targeting solid tumors with CAR T cells.
NKG2D ligands are widely expressed in solid and hematologic malignancies but absent or poorly expressed on healthy tissues. We conducted a phase I dose-escalation study to evaluate the safety and ...feasibility of a single infusion of NKG2D-chimeric antigen receptor (CAR) T cells, without lymphodepleting conditioning in subjects with acute myeloid leukemia/myelodysplastic syndrome or relapsed/refractory multiple myeloma. Autologous T cells were transfected with a γ-retroviral vector encoding a CAR fusing human NKG2D with the CD3ζ signaling domain. Four dose levels (1 × 10
-3 × 10
total viable T cells) were evaluated. Twelve subjects were infused 7 acute myeloid leukemia (AML) and 5 multiple myeloma. NKG2D-CAR products demonstrated a median 75% vector-driven NKG2D expression on CD3
T cells. No dose-limiting toxicities, cytokine release syndrome, or CAR T cell-related neurotoxicity was observed. No significant autoimmune reactions were noted, and none of the ≥ grade 3 adverse events were attributable to NKG2D-CAR T cells. At the single injection of low cell doses used in this trial, no objective tumor responses were observed. However, hematologic parameters transiently improved in one subject with AML at the highest dose, and cases of disease stability without further therapy or on subsequent treatments were noted. At 24 hours, the cytokine RANTES increased a median of 1.9-fold among all subjects and 5.8-fold among six AML patients. Consistent with preclinical studies, NKG2D-CAR T cell-expansion and persistence were limited. Manufactured NKG2D-CAR T cells exhibited functional activity against autologous tumor cells
, but modifications to enhance CAR T-cell expansion and target density may be needed to boost clinical activity.
Chimeric antigen receptor (CAR) T cells represent a novel targeted approach to overcome both quantitative and qualitative shortfalls of the host immune system relating to the detection and subsequent ...destruction of tumors. The identification of antigens expressed specifically on the surface of tumor cells is a critical first step in the ability to utilize CAR T cells for the treatment of cancer. The 5T4 is a tumor-associated antigen which is expressed on the cell surface of most solid tumors including ovarian cancer. Matched blood and tumor samples were collected from 12 patients with ovarian cancer; all tumors were positive for 5T4 expression by immunohistochemistry. Patient T cells were effectively transduced with 2 different anti-5T4 CAR constructs which differed in their affinity for the target antigen. Co-culture of CAR T cells with matched autologous tumor disaggregates resulted in antigen-specific secretion of IFN-gamma. Furthermore, assessment of the efficacy of anti-5T4 CAR T cells in a mouse model resulted in therapeutic benefit against established ovarian tumors. These results demonstrate proof of principle that 5T4 is an attractive target for immune intervention in ovarian cancer and that patient T cells engineered to express a 5T4-specific CAR can recognize and respond physiologically to autologous tumor cells.
The adoptive transfer of chimeric antigen receptor (CAR)-expressing T cells is a relatively new but promising approach in the field of cancer immunotherapy. This therapeutic strategy is based on the ...genetic reprogramming of T cells with an artificial immune receptor that redirects them against targets on malignant cells and enables their destruction by exerting T cell effector functions. There has been an explosion of interest in the use of CAR T cells as an immunotherapy for cancer. In the pre-clinical setting, there has been a considerable focus upon optimizing the structural and signaling potency of the CAR while advances in bio-processing technology now mean that the clinical testing of these gene-modified T cells has become a reality. This review will summarize the concept of CAR-based immunotherapy and recent clinical trial activity and will further discuss some of the likely future challenges facing CAR-modified T cell therapies.
Chimeric antigen receptor-T cells (CAR-Ts) are an exciting new cancer treatment modality exemplified by the recent regulatory approval of two CD19-targeted CAR-T therapies for certain B cell ...malignancies. However, this success in the hematological setting has yet to translate to a significant level of objective clinical responses in the solid tumor setting. The reason for this lack of translation undoubtedly lies in the substantial challenges raised by solid tumors to all therapies, including CAR-T, that differ from B cell malignancies. For instance, intravenously infused CAR-Ts are likely to make rapid contact with cancerous B cells since both tend to reside in the same vascular compartments within the body. By contrast, solid cancers tend to form discrete tumor masses with an immune-suppressive tumor microenvironment composed of tumor cells and non-tumor stromal cells served by abnormal vasculature that restricts lymphocyte infiltration and suppresses immune function, expansion, and persistence. Moreover, the paucity of uniquely and homogeneously expressed tumor antigens and inherent plasticity of cancer cells provide major challenges to the specificity, potency, and overall effectiveness of CAR-T therapies. This review focuses on the major preclinical and clinical strategies currently being pursued to tackle these challenges in order to drive the success of CAR-T therapy against solid tumors.
Epithelial ovarian cancer (EOC) is the leading cause of gynaecological cancer-related death in Europe. Although most patients achieve an initial complete response with first-line treatment, ...recurrence occurs in more than 80% of cases. Thus, there is a clear unmet need for novel second-line treatments. EOC is frequently infiltrated with T lymphocytes, the presence of which has been shown to be associated with improved clinical outcomes. Adoptive T-cell therapy (ACT) using ex vivo-expanded tumour-infiltrating lymphocytes (TILs) has shown remarkable efficacy in other immunogenic tumours, and may represent a promising therapeutic strategy for EOC. In this preclinical study, we investigated the efficacy of using anti-CD3/anti-CD28 magnetic beads and IL-2 to expand TILs from freshly resected ovarian tumours. TILs were expanded for up to 3 weeks, and then subjected to a rapid-expansion protocol (REP) using irradiated feeder cells. Tumours were collected from 45 patients with EOC and TILs were successfully expanded from 89.7% of biopsies. Expanded CD4
+
and CD8
+
subsets demonstrated features associated with memory phenotypes, and had significantly higher expression of key activation and functional markers than unexpanded TILs. Expanded TILs produced anti-tumour cytokines when co-cultured with autologous tumour cells, inferring tumour cytotoxicity. Our findings demonstrate that it is possible to re-activate and expand tumour-reactive T cells from ovarian tumours. This presents a promising immunotherapy that could be used sequentially or in combination with current therapeutic strategies.
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