Activity Of Chimeric Antigen Receptor Research Articles

Choice of costimulatory domains and of cytokines determines CAR T-cell activity in neuroblastoma

ABSTRACTChimeric antigen receptor (CAR) T-cell therapy has been shown to be dramatically effective in the treatment of B-cell malignancies. However, there are still substantial obstacles to overcome, before similar responses can be achieved in patients with solid tumors. We evaluated both in vitro and in a preclinical murine model the efficacy of different 2nd and 3rd generation CAR constructs targeting GD2, a disial-ganglioside expressed on the surface of neuroblastoma (NB) tumor cells. In order to address potential safety concerns regarding clinical application, an inducible safety switch, namely inducible Caspase-9 (iC9), was also included in the vector constructs. Our data indicate that a 3rd generation CAR incorporating CD28.4-1BB costimulatory domains is associated with improved anti-tumor efficacy as compared with a CAR incorporating the combination of CD28.OX40 domains. We demonstrate that the choice of 4-1BB signaling results into significant amelioration of several CAR T-cell characteristics, including: 1) T-cell exhaustion, 2) basal T-cell activation, 3) in vivo tumor control and 4) T-cell persistence. The fine-tuning of T-cell culture conditions obtained using IL7 and IL15 was found to be synergic with the CAR.GD2 design in increasing the anti-tumor activity of CAR T cells. We also demonstrate that activation of the suicide gene iC9, included in our construct without significantly impairing neither CAR expression nor anti-tumor activity, leads to a prompt induction of apoptosis of GD2.CAR T cells. Altogether, these findings are instrumental in optimizing the function of CAR T-cell products to be employed in the treatment of children with NB.

CD44v6 as innovative sarcoma target for CAR-redirected CIK cells

ABSTRACTPurpose of our study was to explore a new immunotherapy for high grade soft tissue sarcomas (STS) based on cytokine-induced killer cells (CIK) redirected with a chimeric antigen receptor (CAR) against the tumor-promoting antigen CD44v6. We aimed at generating bipotential killers, combining the CAR specificity with the intrinsic tumor-killing ability of CIK cells (CAR+.CIK). We set a patient-derived experimental platform. CAR+.CIK were generated by transduction of CIK precursors with a lentiviral vector encoding for anti-CD44v6-CAR. CAR+.CIK were characterized and assessed in vitro against multiple histotypes of patient-derived STS. The anti-sarcoma activity of CAR+.CIK was confirmed in a STS xenograft model. CD44v6 was expressed by 40% (11/27) of patient-derived STS. CAR+.CIK were efficiently expanded from patients (n = 12) and killed multiple histotypes of STS (including autologous targets, n = 4). The killing activity was significantly higher compared with unmodified CIK, especially at low effector/target (E/T) ratios: 98% vs 82% (E/T = 10:1) and 68% vs 26% (1:4), (p<0.0001). Specificity of tumor killing was confirmed by blocking with anti-CD44v6 antibody. CAR+.CIK produced higher amounts of IL6 and IFN-γ compared to control CIK. CAR+.CIK were highly active in mice bearing subcutaneous STS xenografts, with significant delay of tumor growth (p<0.0001) without toxicities.We report first evidence of CAR+.CIK's activity against high grade STS and propose CD44v6 as an innovative target in this setting. CIK are a valuable platform for the translation of CAR-based strategies to challenging field of solid tumors. Our findings support the exploration of CAR+.CIK in clinical trials against high grade STS.

Improving T-cell expansion and function for adoptive T-cell therapy using ex vivo treatment with PI3Kδ inhibitors and VIP antagonists

AbstractAdoptive therapy with ex vivo–expanded genetically modified antigen-specific T cells can induce remissions in patients with relapsed/refractory cancer. The clinical success of this therapy depends upon efficient transduction and expansion of T cells ex vivo and their homing, persistence and cytotoxicity following reinfusion. Lower rates of ex vivo expansion and clinical response using anti-CD19 chimeric antigen receptor (CAR) T cells have been seen in heavily pretreated lymphoma patients compared with B-cell acute lymphoblastic leukemia patients and motivate the development of novel strategies to enhance ex vivo T cell expansion and their persistence in vivo. We demonstrate that inhibition of phosphatidylinositol 3-kinase δ (PI3Kδ) and antagonism of vasoactive intestinal peptide (VIP) signaling partially inhibits the terminal differentiation of T cells during anti-CD3/CD28 bead-mediated expansion (mean, 54.4% CD27+CD28+ T cells vs 27.4% in control cultures; P < .05). This strategy results in a mean of 83.7% more T cells cultured from lymphoma patients in the presence of PI3Kδ and VIP antagonists, increased survival of human T cells from a lymphoma patient in a murine xenograft model, enhanced cytotoxic activity of antigen-specific human CAR T cells and murine T cells against lymphoma, and increased transduction and expansion of anti-CD5 human CAR T cells. PI3Kδ and VIP antagonist-expanded T cells from lymphoma patients show reduced terminal differentiation, enhanced polyfunctional cytokine expression, and preservation of costimulatory molecule expression. Taken together, synergistic blockade of these pathways is an attractive strategy to enhance the expansion and functional capacity of ex vivo–expanded cancer-specific T cells.

Antitumor activity of EGFR-specific CAR T cells against non-small-cell lung cancer cells in vitro and in mice

Effective control of non-small-cell lung cancer (NSCLC) remains clinically challenging, especially during advanced stages of the disease. This study developed an adoptive T-cell treatment through expression of a chimeric antigen receptor (CAR) to target human epidermal growth factor receptor (EGFR) in NSCLC. We optimized the non-viral piggyBac transposon system to engineer human T cells for the expression of EGFR-CAR, consisting of EGFR scFv, transmembrane domain, and intracellular 4-1BB-CD3ζ signaling domains. The modified CAR T cells exhibited expansion capability and anticancer efficacy in a time- and antigen-dependent manner in vitro as well as regression of EGFR-positive human lung cancer xenografts in vivo. EGFR-CAR T therapy is a promising strategy to improve the efficacy and potency of the adoptive immunotherapy in NSCLC. Moreover, EGFR-CAR T therapy could become a clinical application for NSCLC patients in the future.

High-Affinity GD2-Specific CAR T Cells Induce Fatal Encephalitis in a Preclinical Neuroblastoma Model.

The GD2 ganglioside, which is abundant on the surface of neuroblastoma cells, is targeted by an FDA-approved therapeutic monoclonal antibody and is an attractive tumor-associated antigen for cellular immunotherapy. Chimeric antigen receptor (CAR)-modified T cells can have potent antitumor activity in B-cell malignancies, and trials to harness this cytolytic activity toward GD2 in neuroblastoma are under way. In an effort to enhance the antitumor activity of CAR T cells that target GD2, we generated variant CAR constructs predicted to improve the stability and the affinity of the GD2-binding, 14G2a-based, single-chain variable fragment (scFv) of the CAR and compared their properties in vivo We included the E101K mutation of GD2 scFv (GD2-E101K) that has enhanced antitumor activity against a GD2+ human neuroblastoma xenograft in vivo However, this enhanced antitumor efficacy in vivo was concomitantly associated with lethal central nervous system (CNS) toxicity comprised of extensive CAR T-cell infiltration and proliferation within the brain and neuronal destruction. The encephalitis was localized to the cerebellum and basal regions of the brain that display low amounts of GD2. Our results highlight the challenges associated with target antigens that exhibit shared expression on critical normal tissues. Despite the success of GD2-specific antibody therapies in the treatment of neuroblastoma, the fatal neurotoxicity of GD2-specific CAR T-cell therapy observed in our studies suggests that GD2 may be a difficult target antigen for CAR T-cell therapy without additional strategies that can control CAR T-cell function within the CNS. Cancer Immunol Res; 6(1); 36-46. ©2017 AACR.

A tale of two receptors

Cancer Despite the explosion of research on chimeric antigen receptor (CAR) T cell therapy, most preclinical studies use transduced human T cells in immunodeficient mice. To determine how CAR activity is affected by T cell receptor (TCR) engagement, Yang et al. used a CAR targeting CD19 and

Enhanced Cancer Immunotherapy by Chimeric Antigen Receptor-Modified T Cells Engineered to Secrete Checkpoint Inhibitors.

Purpose: Despite favorable responses of chimeric antigen receptor (CAR)-engineered T-cell therapy in patients with hematologic malignancies, the outcome has been far from satisfactory in the treatment of solid tumors, partially owing to the development of an immunosuppressive tumor microenvironment. To overcome this limitation, we engineered CAR T cells secreting checkpoint inhibitors (CPI) targeting PD-1 (CAR.αPD1-T) and evaluated their efficacy in a human lung carcinoma xenograft mouse model.Experimental Design: To evaluate the effector function and expansion capacity of CAR.αPD1-T cells in vitro, we measured the production of IFNγ and T-cell proliferation following antigen-specific stimulation. Furthermore, the antitumor efficacy of CAR.αPD1-T cells, CAR T cells, and CAR T cells combined with anti-PD-1 antibody was determined using a xenograft mouse model. Finally, the underlying mechanism was investigated by analyzing the expansion and functional capacity of TILs.Results: Human anti-PD-1 CPIs secreted by CAR.αPD1-T cells efficiently bound to PD-1 and reversed the inhibitory effect of PD-1/PD-L1 interaction on T-cell function. PD-1 blockade by continuously secreted anti-PD-1 attenuated the inhibitory T-cell signaling and enhanced T-cell expansion and effector function both in vitro and in vivo In the xenograft mouse model, we demonstrated that the secretion of anti-PD-1 enhanced the antitumor activity of CAR T cells and prolonged overall survival.Conclusions: With constitutive anti-PD-1 secretion, CAR.αPD1-T cells are more functional and expandable, and more efficient at tumor eradication than parental CAR T cells. Collectively, our study presents an important and novel strategy that enables CAR T cells to achieve better antitumor immunity, especially in the treatment of solid tumors. Clin Cancer Res; 23(22); 6982-92. ©2017 AACR.

Chimeric antigen receptor T-cell therapies for lymphoma.

New therapies are needed for patients with Hodgkin or non-Hodgkin lymphomas that are resistant to standard therapies. Indeed, unresponsiveness to standard chemotherapy and relapse after autologous stem-cell transplantation are indicators of an especially poor prognosis. Chimeric antigen receptor (CAR) T cells are emerging as a novel treatment modality for these patients. Clinical trial data have demonstrated the potent activity of anti-CD19 CAR T cells against multiple subtypes of B-cell lymphoma, including diffuse large-B-cell lymphoma (DLBCL), follicular lymphoma, mantle-cell lymphoma, and marginal-zone lymphoma. Importantly, anti-CD19 CAR T cells have impressive activity against chemotherapy-refractory lymphoma, inducing durable complete remissions lasting >2 years in some patients with refractory DLBCL. CAR-T-cell therapies are, however, associated with potentially fatal toxicities, including cytokine-release syndrome and neurological toxicities. CAR T cells with novel target antigens, including CD20, CD22, and κ-light chain for B-cell lymphomas, and CD30 for Hodgkin and T-cell lymphomas, are currently being investigated in clinical trials. Centrally manufactured CAR T cells are also being tested in industry-sponsored multicentre clinical trials, and will probably soon become a standard therapy. Herein, we review the clinical efficacy and toxicity of CAR-T-cell therapies for lymphoma, and discuss their limitations and future directions with regard to toxicity management, CAR designs and CAR-T-cell phenotypes, conditioning regimens, and combination therapies.

Most Do, but Some Do Not: CD4⁺CD25- T Cells, but Not CD4⁺CD25⁺ Treg Cells, Are Cytolytic When Redirected by a Chimeric Antigen Receptor (CAR).

Evidences are accumulating that CD4+ T cells can physiologically mediate antigen specific target cell lysis. By circumventing major histocompatibility complex (MHC)-restrictions through an engineered chimeric antigen receptor (CAR), CD4+ T cells lyse defined target cells as efficiently as do CD8+ T cells. However, the cytolytic capacity of redirected CD4+CD25− T cells, in comparison with CD4+CD25+ regulatory T (Treg) cells was so far not thoroughly defined. Treg cells require a strong CD28 signal together with CD3ζ for activation. We consequently used a CAR with combined CD28­CD3ζ signalling for redirecting CD4+CD25− T cells and CD4+CD25+ Treg cells from the same donor. CAR redirected activation of these T cell subsets and induced a distinct cytokine pattern with high IL-10 and a lack of IL-2 release by Treg cells. Despite strong antigen-specific activation, CAR Treg cells produced only weak target cell lysis, whereas CD4+CD25− CAR T cells were potent killers. Cytolysis did not correlate with the target cell sensitivity to Fas/FasL mediated killing; CD4+CD25− T cells upregulated perforin and granzyme B upon CAR activation, whereas Treg cells did less. The different cytolytic capacities of CAR redirected conventional CD4+ cells and Treg cells imply their use for different purposes in cell therapy.

327 B7-H3 Chimeric Antigen Receptor Modified T Cells Show Potent Anti-Tumor Activity in a Preclinical Model of Glioblastoma

Abstract INTRODUCTION While initial phase I data suggest efficacy of local delivery of chimeric antigen receptor (CAR) modified T cells against glioblastoma (GBM), their activity remains limited in part by the intensity of antigen expression. Targeting more robust tumor associated antigens (TAAs) may help to improve anti-tumor responses. B7-H3 (CD276), a transmembrane glycoprotein which is overexpressed on many solid cancers including GBM, is a promising target. Here we generate CAR T cells specific for B7-H3 and characterize their function in a preclinical model of glioblastoma. METHODS B7-H3 CAR T cells were generated by retroviral transduction of healthy donor peripheral blood mononuclear cells (PBMCs) using a vector designed by our lab. The CAR modified T cells were tested in vitro for their ability to produce proinflammatory cytokines and kill B7-H3 positive glioma cell lines. In vivo activity of B7-H3 CAR T cells was tested using an orthotopic GBM xenograft mouse model. RESULTS &gt;B7-H3 CAR T cells produced the proinflammatory cytokines interferon-gamma (IFN-g), interleukin-2 (IL-2), and tumor necrosis factor-alpha (TNF-a) when cocultured with B7-H3 positive glioma cell lines. B7-H3 CAR T cells also killed B7-H3 positive glioma cells in an in vitro cytotoxicity assay. Finally, B7-H3 CAR T cells demonstrated potent anti-tumor activity in vivo, producing tumor regression in our mouse model of GBM and significantly improving survival. CONCLUSION B7-H3 CAR T cells effectively target GBM and demonstrate significant anti-tumor activity in our preclinical studies. Efforts to translate this CAR for clinical use are warranted and will add to the armamentarium for treating patients with GBM and other solid cancers.

Chimeric antigen receptor (CAR) T cells genetically engineered to deliver IL-12 to the tumor microenvironment in ovarian cancer.

3050 Background: Chimeric antigen receptor (CAR) T cell therapy for solid tumor malignancies has not shown the same degree of clinical efficacy observed in hematologic malignancies. The presence of an immunosuppressive cytokine and cellular microenvironment has been hypothesized as one reason for the failure of adoptive immunotherapy for solid tumors. In ovarian cancer, the presence of tumor associated macrophages (TAMs) and immunosuppressive cytokines in the ascitic microenvironment have been reported. IL-12 is a proinflammatory cytokine produced by macrophages, dendritic cells (DC) and NK cells, and has been shown to increase proliferation of T cells and enhance antigen presentation by macrophages. We hypothesized that CAR T cells genetically modified to constitutively secrete IL-12 would overcome a hostile tumor microenvironment in a peritoneal carcinomatosis model of ovarian cancer. Methods: CAR T cells were generated from retroviral transduction of second generation and IL-12 modified CAR’s directed to either an irrelevant CD-19 antigen or Muc16ecto. Results: Here we report increased production of IL-12, improved proliferation and cytotoxic activity of 4H1128-IL12 CAR T cells. We show increased levels of inflammatory cytokines at 24 and 48hrs after treatment of tumor-bearing mice, leading to increased survival at advanced stages of disease. Mice treated with 4H1128-IL12 CAR T cells had decreased levels of F4/80+ CD11b+TAM’s. Genetic analysis of recovered TAM’s from the ascites of treated animals showed skewing towards an M1-phenotype via upregulation of cytokines, chemokines, MHC-II and downregulation of Arg1. Recovered 4H1128-IL12 CAR T cells showed upregulation of FAS-L and recovered TAMs showed increased expression of FAS suggesting FAS/FAS-L engagement was responsible for decreased TAMs. Blocking the FAS/FAS-L pathway led to recovery of TAM populations in 4H1128-IL12 treated mice. Finally, clodronate-mediated depletion of TAM’s further enhanced survival in mice treated with 4H1128-IL12 CAR T cells. Conclusions: These results demonstrate the mechanisms of efficacy of localized delivery of IL-12 to the tumor microenvironment by 4H1128-IL12 CAR T cells.

A phase I trial of CD19-targeted EGFRt/19-28z/4-1BBL armored chimeric antigen receptor (CAR) modified T cells in patients with relapsed or refractory chronic lymphocytic leukemia.

TPS7568 Background: Despite the recent progress in the therapy of CLL with BTK, PI3Kδ, and BCL2 inhibitors, CLL remains incurable and patients with high-risk disease features (i.e. del17p, complex karyotype) and patients whose disease progress after treatment with the above targeted agents continue to have extremely poor prognosis. CD19-specific chimeric antigen receptor (CAR) T cell therapy with various 2nd generation CARs (19-28z or 19-41BBz) have demonstrated anti-tumor efficacy in CLL but the complete response (CR) rates in CLL have been suboptimal (20-45%) compared to CR rates in ALL (80-90%). The suboptimal activity of the current 2nd generation CAR T cells can be due to the inhibitory tumor microenvironment (TM) of CLL. We believe one approach to over the hostile TM is through the use of CD19-CAR T cells further modified to express a second costimulatory ligand, 4-1BBL. A binding of 4-1BBL to its cognate receptor enhances T cell proliferation, IL-2 secretion, and survival and cytolytic activity of the T cells compared to 19-28z. 19-41BBz and 1928BBz (Zhao Z et al. Cancer Cell 2015;28:415-428). Methods: This phase I dose escalating trial is a single-center clinical trial (MSKCC) to study the safety and efficacy of autologous EGFRt/19-28z/4-1BBL+ CAR T cells in patients with relapsed CLL. Given the concern for potential systemic toxicity the vector includes a "safety switch" in the form of a gene for the expression of truncated form of human epidermal growth factor receptor (EGFRt). Patients with relapsed CLL are eligible for the trial. Patients will receive conditioning chemotherapy of cyclophosphamide followed by escalating doses of CAR T cells (1x105 – 3x106 CAR T cells/kg). The primary endpoint is safety and maximum tolerated doses of the CAR T ells. Secondary objectives include response assessment by iwCLL criteria. The comprehensive treatment algorithms for CRS and neurotoxicity are based on our CAR T cell experience in other studies. The study will begin enrollment in February 2017 and enroll up to 30 patients. Clinical trial information: Pending.

Development of CAR T cells designed to improve antitumor efficacy and safety.

Chimeric antigen receptor (CAR) T cell therapy has shown promising efficacy against hematologic malignancies. Antitumor activity of CAR T cells, however, needs to be improved to increase therapeutic efficacy in both hematologic and solid cancers. Limitations to overcome are 'on-target, off-tumor' toxicity, antigen escape, short CAR T cell persistence, little expansion, trafficking to the tumor and inhibition of T cell activity by an inhibitory tumor microenvironment. Here we will discuss how optimizing the design of CAR T cells through genetic engineering addresses these limitations and improves the antitumor efficacy of CAR T cell therapy in pre-clinical models.

Engineering Chimeric Antigen Receptors

Chimeric antigen receptors (CARs) are recombinant protein molecules that redirect cytotoxic lymphocytes toward malignant and other target cells. The high feasibility of manufacturing CAR-modified lymphocytes for the therapy of cancer has spurred the development and optimization of new CAR T cells directed against a broad range of target antigens. In this review, we describe the main structural and functional elements constituting a CAR, discuss the roles of these elements in modulating the anti-tumor activity of CAR T cells, and highlight alternative approaches to CAR engineering.

Chimeric antigen receptor (CAR) T cells genetically engineered to deliver IL-12 to the tumor microenvironment in ovarian cancer.

141 Background: Chimeric antigen receptor (CAR) T cell therapy for solid tumor malignancies has not shown the same degree of clinical efficacy observed in hematologic malignancies such as B-ALL. The presence of an immunosuppressive cellular and cytokine microenvironment has been hypothesized as one reason for the failure of adoptive immunotherapy for solid tumors. In ovarian cancer, myeloid derived suppressor cells (MDSC) and immunosuppressive cytokines in the ascitic microenvironment have been reported. IL-12 is a proinflammatory cytokine produced by macrophages, dendritic cells (DC), and NK cells, and it has been shown to increase proliferation of T cells, induce differentiation of type 1 T helper cells, inhibit regulatory T cells, promote maturation of DCs, and enhance antigen presentation by macrophages. We hypothesize that CAR T cells genetically modified to constitutively secrete IL-12 will overcome a hostile tumor microenvironment in a peritoneal carcinomatosis model of ovarian cancer. Methods: CAR T cells were generated from retroviral transduction of second generation and IL-12 modified CAR’s directed to either an irrelevant CD-19 antigen or Muc16ecto. C57BL/6 mice were inoculated i.p with syngeneic ovarian cancer cells and treated with various CAR T cells. Results: Here we report increased production of IL-12, improved proliferation and cytotoxic activity of 4H1128ζ-IL12 CAR T cells. Further, we show increased levels of inflammatory cytokines at 24 and 48hrs after treatment of tumor-bearing mice, leading to increased survival at advanced stages of disease. Animals treated with 4H1128ζ-IL12 CAR T cells had decreased levels of F4/80+ CD11b+MDSCs. Genetic analysis of recovered MDSCs from the ascites of treated animals showed skewing towards an M1-phenotype via upregulation of cytokines, chemokines, MHC-II, and downregulation of Arg1. Furthermore, clodronate-mediated depletion of TAM’s further enhanced survival in mice treated with 4H1128ζ-IL12 CAR T cells. Conclusions: These results demonstrate the mechanisms of efficacy of localized delivery of IL-12 to the tumor microenvironment by 4H1128ζ-IL12 CAR T cells.

Targeting the adenosine 2A receptor enhances chimeric antigen receptor T cell efficacy.

Chimeric antigen receptor (CAR) T cells have been highly successful in treating hematological malignancies, including acute and chronic lymphoblastic leukemia. However, treatment of solid tumors using CAR T cells has been largely unsuccessful to date, partly because of tumor-induced immunosuppressive mechanisms, including adenosine production. Previous studies have shown that adenosine generated by tumor cells potently inhibits endogenous antitumor T cell responses through activation of adenosine 2A receptors (A2ARs). Herein, we have observed that CAR activation resulted in increased A2AR expression and suppression of both murine and human CAR T cells. This was reversible using either A2AR antagonists or genetic targeting of A2AR using shRNA. In 2 syngeneic HER2+ self-antigen tumor models, we found that either genetic or pharmacological targeting of the A2AR profoundly increased CAR T cell efficacy, particularly when combined with PD-1 blockade. Mechanistically, this was associated with increased cytokine production of CD8+ CAR T cells and increased activation of both CD8+ and CD4+ CAR T cells. Given the known clinical relevance of the CD73/adenosine pathway in several solid tumor types, and the initiation of phase I trials for A2AR antagonists in oncology, this approach has high translational potential to enhance CAR T cell efficacy in several cancer types.

Lenalidomide Enhances the Function of CS1 Chimeric Antigen Receptor Redirected-T Cells Against Multiple Myeloma

Multiple myeloma (MM) is an incurable malignancy of plasma cells even with great advances in treatment. Chimeric Antigen Receptor (CAR) directed T cell therapy, which can specifically recognize tumor associated antigens and kill tumor cells in an MHC independent manner, is a promising approach for hematological malignancy. There are several candidate antigens for CAR T cell targeting of multiple myeloma, including BCMA and CS1. Our goal is to develop novel CARs for the treatment of MM and explore the potential benefits of combinatorial therapy of CAR T cells and immunomodulatory drugs (IMiDs) such as lenalidomide. In the present study, we redirected central memory T cells to express second-generation CARs specific for either CS1 or BCMA that incorporate CD28 signaling moieties. Central memory T cells were activated by CD3/CD28 bead stimulation, transduced with lentivirus encoding the CAR construct, and expanded ex vivo. The engineered and expanded CS1 and BCMA CAR T cells exhibited similar phenotypes and comparable in vitro effector function. However, once adoptively transferred into MM tumor-bearing NOD/Scid IL2RγCnull (NSG) mice by intravenous injection of 1x10^6 CAR T cells, CS1 CAR T cells exhibited superior antitumor activity over BCMA CART cells and significantly prolonged mouse survival (P<0.01). To further improve the anti-MM activity of CAR T cell therapy, we investigated the effects of lenalidomide on CS1 CAR T cell function against MM. Central memory T cells were activated and transduced with lentivirus encoding CS1 CAR and then expanded in vitro in the presence of 0, 1 or 10mM lenalidomide for 3-4 weeks and then effector function was evaluated. We found that CD8+ CAR T cells were preferentially expanded over CD4+ CAR T cells in a dose-dependent manner. Lenalidomide-treated CAR T cells secreted higher levels of Th1 cytokines such as IFN-gamma, TNF-alpha, and IL-2, but reduced Th2 cytokines such as IL-4 and IL-10 upon antigen stimulation as compared with untreated CAR T cells. Meanwhile we observed that lenalidomide greatly improved the maintenance of T cell memory markers (CD62L, CD28, and CD27) in the culture and enhanced the formation of immune synapses between CAR T cells and MM cells. RNA-seq analysis revealed that more than 600 genes were differentially expressed among the lenalidomide treated and un-treated CD8+CAR+ T cells. Among those, expression of immune synapse related genes such as cell junction and biological assembly is significantly increased with lenalidomide treatment. Moreover, lenalidomide results in elevated gene transcrips characteristic of memory, homing and cytolytic function of CAR T cells. To test the synergistic effects, MM bearing mice were treated with a single infusion of 1x10^6 CS1 CAR T cells (i.v) on day 0 and/or 5-7.5mgkg-1 of lenalidomide daily (i.p.) initiating on day 0 for 30 days. CS1 CAR T cells and lenalidomide exhibited synergistic anti-MM activity in vivo when MM mice received combinatorial treatment. The combination therapy significantly inhibited tumor growth in vivo, prolonged mouse survival (P<0.01) and improved CAR T cell persistence in mice as compared to single-agent treatment. Taken together, these findings indicate that lenalidomide plays a co-stimulatory role in immune modulation of CAR T cells and strengthens the anti-tumor activity of CS1 CAR T cells in vivo. Rational combination of these immunotherapeutic regimens is an effective strategy and the planned clinical trial will use a combination of lenalidomide and CS1 CAR T cells for increasing treatment efficacy. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Preclinical Development of FLT3-Redirected Chimeric Antigen Receptor T Cell Immunotherapy for Acute Myeloid Leukemia

Background: Outcomes for adults and children with acute myeloid leukemia (AML) are dismal with 20-40% and 60% 5-year event-free survival, respectively. Alternative therapeutic strategies for AML are thus needed to improve outcomes. Chimeric antigen receptor (CAR) T cell immunotherapy has induced remarkable clinical responses in multiple phase 1 clinical trials for patients with relapsed or chemorefractory B cell leukemias, encouraging great interest in developing similar approaches for AML. Prior studies have demonstrated efficacy of CD33 or CD123-redirected CAR T cells in AML models, although the genetic heterogeneity of AML will likely require identification of additional therapeutic targets. In the current studies, we report preliminary in vitro and in vivo efficacy of new CAR T cells targeting the FMS-like tyrosine kinase 3 (FLT3) in human AML. FLT3 mutations via internal tandem duplication or kinase domain point mutations occur in approximately 25% of AML and result in FLT3 surface protein overexpression, suggesting potential efficacy of FLT3-targeting therapies. Both types of FLT3 alterations induce ligand-independent activation of FLT3 signaling, further demonstrating a critical role of FLT3 in AML pathogenesis.Hypothesis: FLT3 is a promising target for CAR T cell immunotherapy based treatment of AML.Results: Quantitative flow cytometric analysis of human AML cell lines demonstrated FLT3 surface expression ranging from 1338 (MOLM-13), 2594 (MOLM-14), and 2710 (MV4;11) receptors/cell versus 623 receptors/cell on negative control U937 cells. We first generated FLT3-redirected CAR construct consisting of a single chain variable fragment (scFv) derived from a well-characterized anti-human FLT3 antibody coupled to T cell 4-1BB (CD137) costimulatory and CD3-zeta activation domains. CD33 CAR T cells based on Gemtuzumab created by identical methodologies were also used as AML CAR T cell controls. In vitro studies verified that human T cells transduced with the FLT3 CAR construct induced interferon-gamma and interleukin-2 production after co-culture with AML cell lines MOLM-13, MOLM-14, and MV4;11. One dose of FLT3 CAR T cells inhibited leukemia proliferation in vivo in NOD-SCID-IL2Rγc-/- (NSG) mice engrafted with FLT3-mutant MOLM-13 or MOLM14 cell lines. These first data demonstrate potent preclinical activity of FLT3 CAR T cells and warrant further study in additional AML models.However, on target/off tumor toxicities can occur with AML antigen-targeted immunotherapies, as previously reported in studies of CD33 and CD123 CAR T cells. Normal expression of FLT3 has been mainly described on CD34+ hematopoietic progenitor stem cell populations, and FLT3-targeted therapies have potential to induce aplastic anemia. To address this question of hematologic toxicity of FLT3 CAR T cells, we created normal human hematopoiesis xenograft models in NOD scid gamma Il3-GM-SF (NSGS) mice engrafted with CD34+ cord blood cells for treatment with anti-AML CAR T cells. No difference in human granulocyte numbers was observed in marrows of engrafted mice treated with FLT3 CAR T cells, CD33 CAR T cells, or non-transduced T cells. A significant reduction in monocytes was observed in FLT3 CAR T cell-treated animals, however (p<0.05 by t test). To determine potential for increased hematologic toxicity in the presence of greater target antigen levels, we injected MOLM-14 into CD34+ cell-engrafted mice, then treated animals with control or anti-AML CAR T cells. We surprisingly found no decrement in defined hematopoietic stem cell (HSC) or granulocyte macrophage progenitor (GMP) populations, but did observe increased multipotent and common myeloid progenitor (MPP, CMP) cell numbers and an increase in total human cell engraftment 5 days after FLT3 CAR treatment in comparison to non-transduced T cell-treated animals. Relative to CD33 CAR T cells, FLT3 CAR T cells induced less toxicity to HSCs and MPPs and equivalent toxicity to CMPs and GMPs, indicating lower hematologic toxicity with FLT3 targeting.Conclusions: Taken together, these initial data demonstrate potent in vitro and in vivo anti-AML activity with limited hematopoietic toxicity of FLT3 CAR T cell immunotherapy. Future studies are focused on testing the effectiveness on other AML cell lines with varying expression of FLT3. DisclosuresNo relevant conflicts of interest to declare.

“Switchable chimeric antigen receptor T cells: a novel universal chimeric antigen receptor platform for a safe control of T-cell activation”

In a recent issue of PNAS, Rodgers et al. present an elegant study describing the development of a bifunctional antibody switch able to control retargeting and activation of chimeric antigen receptor (CAR)—engineered T cells, offering a potential additional safety tool compared to standard CAR platforms (1). Indeed, despite the recent striking responses obtained by adoptive transfer of CAR-T cells in relapsed and refractory patients affected by CD19+ malignancies, difficulties have emerged in the ability of controlling both CAR T-cell pharmacokinetic and pharmacodynamic properties (2-6).

Effective adoptive immunotherapy of triple-negative breast cancer by folate receptor-alpha redirected CAR T cells is influenced by surface antigen expression level.

BackgroundThe poor prognosis and the limited efficacy of targeted therapy in patients with triple-negative breast cancer (TNBC) have raised the need for alternative therapies. Recent studies have demonstrated that folate receptor-alpha (FRα) may represent an ideal tumor-associated marker for immunotherapy for TNBC.MethodsThe aim of the present study was to apply a chimeric antigen receptor (CAR) approach for the targeting of FRα expressed on TNBC cells and evaluate the antitumor activity of CAR-engineered T cells in vitro and in vivo.ResultsWe found that human T cells expressing a FRα-specific CAR were potent and specific killers of TNBC cells that express moderate levels of FRα in vitro and significantly inhibited tumor outgrowth following infusion into immunodeficient mice bearing an MDA-MB-231 tumor xenograft. However, the antitumor activity of the FRα CAR T cells was modest when compared to the same CAR T cells applied in an ovarian tumor xenograft model where FRα expression is more abundant. Notably, FRα CAR T cells induced superior tumor regression in vivo against MDA-MB-231 that was engineered for overexpression of FRα.ConclusionsTaken together, our results show that FRα CAR T cells can mediate antitumor activity against established TNBC tumor, particularly when FRα is expressed at higher levels. These results have significant implications for the pre-selection of patients with high antigen expression levels when utilizing CAR-based adoptive T cell therapies of cancer in future clinical trials.Electronic supplementary materialThe online version of this article (doi:10.1186/s13045-016-0285-y) contains supplementary material, which is available to authorized users.