IMMU-33. MULTI-ANTIGEN RECOGNITION CIRCUITS OVERCOME CHALLENGES OF SPECIFICITY, HETEROGENEITY, AND DURABILITY IN T-CELL THERAPY FOR GLIOBLASTOMA

Treatment of solid cancers with chimeric antigen receptor (CAR) T-cells is challenging because of a lack of target antigens that are both tumor-specific and homogenously expressed. While epidermal growth factor receptor (EGFR)vIII represents a glioblastoma (GBM)-specific antigen, its expression is heterogeneous within the tumor resulting in tumor escape. In contrast, more homogenously expressed GBM-associated antigens (GAA), such as EphA2, are non-ideal because of expression in other normal organs, yielding potential cross-reactive toxicity. As a way to safely target GAAs in the tumor without attacking normal cells expressing the same GAAs outside of the brain, we adapted a novel synthetic Notch (synNotch) receptor system and established a “prime and kill” sequential two-receptor CAR circuit. A synNotch receptor recognizes a specific priming antigen; the heterogeneous GBM neoantigen EGFRvIII or a brain tissue-specific antigen to prime the local expression of a CAR that mediates cytotoxicity against a GAA (e.g. EphA2). In orthotopic GBM6 glioma model, a patient-derived xenograft (PDX) with heterogeneous expression of EGFRvIII, intravenous infusion of T-cells transduced with EGFRvIII synNotch→anti-IL-13Rα2/EphA2 tandem CAR circuit resulted in long-term (over 100 days) survival and eradication of the heterogeneous tumor in all of 12 mice in two independent experiments. In contrast, constitutive CARs targeting EGFRvIII or IL-13Rα2/EphA2 (as a tandem CAR) failed to exhibit long-term anti-tumor response. Moreover, T-cells transduced with synNotch-regulated CAR maintain a less differentiated state which is associated with higher durability compared with ones with constitutive CAR in vivo. T-cells transduced with a synNotch→CAR circuit primed by a brain-specific antigen, myelin oligodendrocyte glycoprotein (MOG), exhibited a precise and potent local control of intracranial PDX without evidence of priming in extracranial organs. These data support the utility of synNotch→CAR circuits in EGFRvIII-negative GBM cases. By integrating multiple imperfect but complementary antigens, we improve both the specificity and persistence of T-cells directed against GBM.

Pooled Knockin Targeting for Genome Engineering of Cellular Immunotherapies

Adoptive transfer of genetically modified immune cells holds great promise for cancer immunotherapy. CRISPR knockin targeting can improve cell therapies, but more high-throughput methods are needed to test which knockin gene constructs most potently enhance primary cell functions in vivo. We developed a widely adaptable technology to barcode and track targeted integrations of large non-viral DNA templates and applied it to perform pooled knockin screens in primary human T cells. Pooled knockin of dozens of unique barcoded templates into the T cell receptor (TCR)-locus revealed gene constructs that enhanced fitness in vitro and in vivo. We further developed pooled knockin sequencing (PoKI-seq), combining single-cell transcriptome analysis and pooled knockin screening to measure cell abundance and cell state ex vivo and in vivo. This platform nominated a novel transforming growth factor β (TGF-β) R2-41BB chimeric receptor that improved solid tumor clearance. Pooled knockin screening enables parallelized re-writing of endogenous genetic sequences to accelerate discovery of knockin programs for cell therapies.

IMMU-21. SEQUENTIAL TWO-RECEPTOR PRIMING CAR SYSTEM TO OVERCOME HETEROGENEOUS ANTIGEN EXPRESSION

Heterogeneous expression of target antigens allows tumor escape from chimeric antigen receptor-transduced T-cell (CART) therapy targeting a single antigen. While epidermal growth factor receptor (EGFR)vIII represents a glioblastoma (GBM)-specific antigen, its expression is heterogeneous within the tumor. On the other hand, most other antigens expressed more uniformly in GBMs are non-mutated, glioma-associated antigens (GAAs), such as EphA2. Although these GAAs are not expressed in the normal brain, they are expressed at low levels in other normal organs. As a way to safely target GAAs in the tumor without attacking normal cells expressing the same GAAs outside of the brain, we adapted a novel synthetic Notch (synNotch) receptor system, and established a “prime and kill” sequential two-receptor CAR circuit: the first is a transcriptional CAR against EGFRvIII, and the second is a CAR against a GAA (e.g. EphA2). When the first CAR binds to EGFRvIII, it induces the expression of the second CAR against GAA. While the first CAR does not trigger the cytotoxic function itself, the second CAR mediates the cytotoxicity upon recognition of the target GAA. We validated this system in vitro using the mixture of U87 GBM cells and those transduced with EGFRvIII. SynNotch CART effectively lysed both EGFRvIII+ and EGFRvIII-negative U87 cells when they are mixed, but never lysed EGFRvIII-negative cells in the absence of EGFRvIII+ cells. SynNotch CART cells exhibited precise local effect in vivo, sparing EGFRvIII-negative subcutaneous tumor while efficiently clearing intracranial EGFRvIII heterogeneous tumor. In the orthotopic GBM6 model, which is a patient-derived xenograft with heterogeneous expression of EGFRvIII, intravenous infusion of synNotch CART resulted in long-term (over 50 days) survival and eradication of the heterogeneous tumor in 6 of 6 mice, while the conventional anti-EGFRvIII CART failed to do so. These data provide a strong basis for developing synNotch CART therapy for GBM.

Enhancement of anti-tumor CD8 immunity by IgG1-mediated targeting of Fc receptors

Dendritic cells (DCs) function as professional antigen presenting cells and are critical for linking innate immune responses to the induction of adaptive immunity. Many current cancer DC vaccine strategies rely on differentiating DCs, feeding them tumor antigens ex vivo, and infusing them into patients. Importantly, this strategy relies on prior knowledge of suitable “tumor-specific” antigens to prime an effective anti-tumor response. DCs express a variety of receptors specific for the Fc region of immunoglobulins, and antigen uptake via Fc receptors is highly efficient and facilitates antigen presentation to T cells. Therefore, we hypothesized that expression of the mouse IgG1 Fc region on the surface of tumors would enhance tumor cell uptake by DCs and other myeloid cells and promote the induction of anti-tumor T cell responses. To test this, we engineered a murine lymphoma cell line expressing surface IgG1 Fc and discovered that such tumor cells were taken up rapidly by DCs, leading to enhanced cross-presentation of tumor-derived antigen to CD8+ T cells. IgG1-Fc tumors failed to grow in vivo and prophylactic vaccination of mice with IgG1-Fc tumors resulted in rejection of unmanipulated tumor cells. Furthermore, IgG1-Fc tumor cells were able to slow the growth of an unmanipulated primary tumor when used as a therapeutic tumor vaccine. Our data demonstrate that engagement of Fc receptors by tumors expressing the Fc region of IgG1 is a viable strategy to induce efficient and protective anti-tumor CD8+ T cell responses without prior knowledge of tumor-specific antigens.

Mania-like behavior induced by disruption of CLOCK

Circadian rhythms and the genes that make up the molecular clock have long been implicated in bipolar disorder. Genetic evidence in bipolar patients suggests that the central transcriptional activator of molecular rhythms, CLOCK, may be particularly important. However, the exact role of this gene in the development of this disorder remains unclear. Here we show that mice carrying a mutation in the Clock gene display an overall behavioral profile that is strikingly similar to human mania, including hyperactivity, decreased sleep, lowered depression-like behavior, lower anxiety, and an increase in the reward value for cocaine, sucrose, and medial forebrain bundle stimulation. Chronic administration of the mood stabilizer lithium returns many of these behavioral responses to wild-type levels. In addition, the Clock mutant mice have an increase in dopaminergic activity in the ventral tegmental area, and their behavioral abnormalities are rescued by expressing a functional CLOCK protein via viral-mediated gene transfer specifically in the ventral tegmental area. These findings establish the Clock mutant mice as a previously unrecognized model of human mania and reveal an important role for CLOCK in the dopaminergic system in regulating behavior and mood.