Geometric parameters that affect the behavior of logic-gated CAR T cells.

Clinical applications of CAR-T cells are limited by the scarcity of tumor-specific targets and are often afflicted with the same on-target/off-tumor toxicities that plague other cancer treatments. A new promising strategy to enforce tumor selectivity is the use of logic-gated, two-receptor systems. One well-described application is termed Tmod™, which originally utilized a blocking inhibitory receptor directed towards HLA-I target antigens to create a protective NOT gate. Here we show that the function of Tmod blockers targeting non-HLA-I antigens is dependent on the height of the blocker antigen and is generally compatible with small, membrane-proximal targets. We compensate for this apparent limitation by incorporating modular hinge units to artificially extend or retract the ligand-binding domains relative to the effector cell surface, thereby modulating Tmod activator and blocker function. By accounting for structural differences between activator and blocker targets, we developed a set of simple geometric parameters for Tmod receptor design that enables targeting of blocker antigens beyond HLA-I, thereby broadening the applications of logic-gated cell therapies.

A carcinoembryonic antigen-specific cell therapy selectively targets tumor cells with HLA loss of heterozygosity in vitro and in vivo.

The CEACAM5 gene product [carcinoembryonic antigen (CEA)] is an attractive target for colorectal cancer because of its high expression in virtually all colorectal tumors and limited expression in most healthy adult tissues. However, highly active CEA-directed investigational therapeutics have been reported to be toxic, causing severe colitis because CEA is expressed on normal gut epithelial cells. Here, we developed a strategy to address this toxicity problem: the Tmod dual-signal integrator. CEA Tmod cells use two receptors: a chimeric antigen receptor (CAR) activated by CEA and a leukocyte Ig-like receptor 1 (LIR-1)-based inhibitory receptor triggered by human leukocyte antigen (HLA)-A*02. CEA Tmod cells exploit instances of HLA heterozygous gene loss in tumors to protect the patient from on-target, off-tumor toxicity. CEA Tmod cells potently killed CEA-expressing tumor cells in vitro and in vivo. But in contrast to a traditional CEA-specific T cell receptor transgenic T cell, Tmod cells were highly selective for tumor cells even when mixed with HLA-A*02-expressing cells. These data support further development of the CEA Tmod construct as a therapeutic candidate for colorectal cancer.

Extensive functional comparisons between chimeric antigen receptors and T cell receptors highlight fundamental similarities.

Though TCRs have been subject to limited engineering in the context of therapeutic design and optimization, they are used largely as found in nature. On the other hand, CARs are artificial, composed of different segments of proteins that function in the immune system. This characteristic raises the possibility of altered response to immune regulatory stimuli. Here we describe a large-scale, systematic comparison of CARs and TCRs across 5 different pMHC targets, with a total of 19 constructs examined in vitro. These functional measurements include CAR- and TCR-mediated activation, proliferation, and cytotoxicity in both acute and chronic settings. Surprisingly, we find no consistent difference between CARs and TCRs as receptor classes with respect to their relative sensitivity to major regulators of T cell activation: PD-L1, CD80/86 and IL-2. Though TCRs often emerge from human blood directly as potent, selective receptors, CARs must be heavily optimized to attain these properties for pMHC targets. Nonetheless, when iteratively improved and compared head to head in functional tests, CARs appear remarkably similar to TCRs with respect to immune modulation.

Re-examination of MAGE-A3 as a T-cell Therapeutic Target.

In 2013, an innovative MAGE-A3-directed cancer therapeutic of great potential value was terminated in the clinic because of neurotoxicity. The safety problems were hypothesized to originate from off-target T-cell receptor activity against a closely related MAGE-A12 peptide. A combination of published and new data led us to test this hypothesis with current technology. Our results call into question MAGE-A12 as the source of the neurotoxicity. Rather, the data imply that an alternative related peptide from EPS8L2 may be responsible. Given the qualities of MAGE-A3 as an onco-testis antigen widely expressed in tumors and largely absent from normal adult tissues, these findings suggest that MAGE-A3 may deserve further consideration as a cancer target. As a step in this direction, the authors isolated 2 MAGE-A3 peptide-major histocompatibility complex-directed chimeric antigen receptors, 1 targeting the same peptide as the clinical T-cell receptor. Both chimeric antigen receptors have improved selectivity over the EPS8L2 peptide that represents a significant risk for MAGE-A3-targeted therapeutics, showing that there may be other options for MAGE-A3 cell therapy.

Potent, Selective CARs as Potential T-Cell Therapeutics for HPV-positive Cancers.

Next-generation T-cell therapies will likely continue to utilize T-cell receptors (TCRs) and chimeric antigen receptors (CARs) because each receptor type has advantages. TCRs often possess exceptional properties even when tested unmodified from patients' T cells. CARs are generally less sensitive, possibly because their ligand-binding domains are grafted from antibodies selected for binding affinity or avidity and not broadly optimized for a functional response. Because of the disconnect between binding and function among these receptor types, the ultimate potential of CARs optimized for sensitivity and selectivity is not clear. Here, we focus on a thoroughly studied immuno-oncology target, the HLA-A*02/HPV-E629-38 complex, and show that CARs can be optimized by a combination of high-throughput binding screens and low-throughput functional assays to have comparable activity to clinical TCRs in acute assays in vitro. These results provide a case study for the challenges and opportunities of optimizing high-performing CARs, especially in the context of targets utilized naturally by TCRs.

c-Myb and p300 regulate hematopoietic stem cell proliferation and differentiation.

Precise control of hematopoietic stem cell (HSC) proliferation and differentiation is needed to maintain a lifetime supply of blood cells. Using genome-wide ENU mutagenesis and phenotypic screening, we have identified a mouse line that harbors a point mutation in the transactivation (TA) domain of the transcription factor c-Myb (M303V), which reduces c-Myb-dependent TA by disrupting its interaction with the transcriptional coactivator p300. The biological consequences of the c-Myb(M303V/M303V) mutation include thrombocytosis, megakaryocytosis, anemia, lymphopenia, and the absence of eosinophils. Detailed analysis of hematopoiesis in c-Myb(M303V/M303V) mice reveals distinct blocks in T cell, B cell, and red blood cell development, as well as a remarkable 10-fold increase in the number of HSCs. Cell cycle analyses show that twice as many HSCs from c-Myb(M303V/M303V) animals are actively cycling. Thus c-Myb, through interaction with p300, controls the proliferation and differentiation of hematopoietic stem and progenitor cells.

Structure-function relationships of chimeric antigen receptors in acute T cell responses to antigen.

Chimeric antigen receptors (CARs) and their parent signaling molecule, the T cell receptor (TCR), are fascinating proteins of increasing relevance to disease therapy. Here we use a collection of 1221 pMHC-directed CAR constructs representing 10 pMHC targets to study aspects of CAR structure-activity relationships (SAR), with particular focus on the extracellular and transmembrane structural components. These experiments that involve pMHC targets whose number/cell can be manipulated by peptide dosing in vitro enable systematic analysis of the SAR of CARs in carefully controlled experimental situations (Harris and Kranz, 2016). We find that CARs tolerate a wide range of structural variation, with the ligand-binding domains (LBDs) dominating the SAR of CAR antigen sensitivity. Notwithstanding the critical role of the LBD, CAR antigen-binding on the cell surface, measured by pMHC tetramer staining, is not an effective predictor of functional sensitivity. These results have important implications for the design and testing of CARs aimed toward the clinic.

Functional arrays of human pluripotent stem cell-derived cardiac microtissues.

To accelerate the cardiac drug discovery pipeline, we set out to develop a platform that would be capable of quantifying tissue-level functions such as contractile force and be amenable to standard multiwell-plate manipulations. We report a 96-well-based array of 3D human pluripotent stem cell (hPSC)-derived cardiac microtissues - termed Cardiac MicroRings (CaMiRi) - in custom 3D-print-molded multiwell plates capable of contractile force measurement. Within each well, two elastomeric microcantilevers are situated above a circumferential ramp. The wells are seeded with cell-laden collagen, which, in response to the gradual slope of the circumferential ramp, self-organizes around tip-gated microcantilevers to form contracting CaMiRi. The contractile force exerted by the CaMiRi is measured and calculated using the deflection of the cantilevers. Platform responses were robust and comparable across wells, and we used it to determine an optimal tissue formulation. We validated the contractile force response of CaMiRi using selected cardiotropic compounds with known effects. Additionally, we developed automated protocols for CaMiRi seeding, image acquisition, and analysis to enable the measurement of contractile force with increased throughput. The unique tissue fabrication properties of the platform, and the consequent effects on tissue function, were demonstrated upon adding hPSC-derived epicardial cells to the system. This platform represents an open-source contractile force screening system useful for drug screening and tissue engineering applications.

Discovery of pyrimidine benzimidazoles as Src-family selective Lck inhibitors. Part II.

A series of 4-amino-6-benzimidazole-pyrimidines was designed to target lymphocyte-specific tyrosine kinase (Lck), a member of the Src-family kinases (SFKs). These type II inhibitors were optimized using a cellular Lck-dependent proliferation assay and are capable of inhibiting Lck at single-digit nanomolar concentrations. This scaffold is likely to serve a valuable template for developing potent inhibitors of a number of SFKs.

Discovery of pyrimidine benzimidazoles as Lck inhibitors: part I.

A series of 4-amino-6-benzimidazole-pyrimidines was designed to target lymphocyte-specific tyrosine kinase (Lck), a member of the Src kinase family. Highly efficient parallel syntheses were devised to prepare analogues for SAR studies. A number of these 4-amino-6-benzimidazole-pyrimidines exhibited single-digit nanomolar IC(50)s against Lck in biochemical and cellular assays. These 4-amino-6-benzimidazole-pyrimidines represent a new class of tyrosine kinase inhibitors.

Isolation and Characterization of a Distinct Subpopulation from the WM115 Cell Line That Resembles In Vitro Properties of Melanoma Cancer Stem Cells.

Despite key advances in cancer therapies, malignant tumors, such as melanoma, continue to be one of the leading causes of mortality. Recent debate on whether cancer can originate from a tumor-initiating subpopulation has permeated oncology and stem cell research. It has been well established that primary and immortalized tumor cells consist of heterogeneous cell populations. The profound effect of tumor heterogeneity on tumor growth and drug resistance remains elusive, but it is highly likely that subpopulations of cancer cells have different capabilities of self-renewal and drug resistance. Discrepancies between excellent in vitro potency and efficacy and poor patient response have been observed on multiple cancer therapeutics. Although this observation can be attributed to many factors, a better understanding of the contribution from subpopulations within a cancer will help bridge the gap between in vitro assay results and patient prognosis. To comprehend this impact, it is critical to isolate and characterize cancer subpopulations that possess higher growth and drug resistance properties so that novel therapeutics can be developed to eventually eradicate all cancer cells. In this article, we describe a method to enrich a subpopulation, CB4, from the melanoma cell line WM115. CB4 exhibited higher anchorage-independent growth, higher survival under serum starvation condition, and lower drug sensitivity to commonly used melanoma treatment compared with WM115. Details of functional properties and gene expression of CB4 compared with WM115 are reported. Our study demonstrates that it is feasible to isolate and enrich a subpopulation that exhibits higher growth capacity and treatment resistance from an immortalized tumor cell line.

Latent membrane protein 1 is critical for efficient growth transformation of human B cells by epstein-barr virus.

The EBV latent membrane protein 1 (LMP1) is an integral membrane protein that acts like a constitutively activated receptor. LMP1 interacts with members of the tumor necrosis factor receptor-associated factor family, as well as with tumor necrosis factor receptor-associated death domain, resulting in induction of nuclear factor-kappaB, the p38 mitogen-activated protein kinase pathway, and the c-Jun NH(2)-terminal kinase activator protein 1-signaling cascade. The binding of Janus kinase 3 results in activation of signal transducers and activators of transcription. The domain structure of LMP1 has been mapped extensively, but the quantitative contribution of distinct LMP1 domains to the efficiency of B-cell proliferation by EBV has not been determined. On the basis of the maxi-EBV system, which allows us to introduce and study mutations in the context of the complete EBV genome, a panel of 10 EBV mutants with alterations in the LMP1 gene locus was established. The mutant EBVs were tested for their efficiency to induce and maintain proliferation of clonal B-cell lines in vitro. Surprisingly and with reduced frequency, EBV mutants which deleted LMP1's COOH terminus, transmembrane domains, or the entire open reading frame were able to generate proliferating B-cell clones that were dependent on the presence of human fibroblast feeder cells. A B-cell clone carrying the LMP1-null mutant EBV genome was also analyzed for oncogenicity in severe combined immunodeficiency mice. Our results demonstrate that LMP1 is critical but not mandatory for the generation of proliferating B cells in vitro. LMP1 functions greatly contribute to EBV's transformation potential and appear essential for its oncogenicity in severe combined immunodeficiency mice.

Inhibition of the Inositol Kinase Itpkb Augments Calcium Signaling in Lymphocytes and Reveals a Novel Strategy to Treat Autoimmune Disease.

Emerging approaches to treat immune disorders target positive regulatory kinases downstream of antigen receptors with small molecule inhibitors. Here we provide evidence for an alternative approach in which inhibition of the negative regulatory inositol kinase Itpkb in mature T lymphocytes results in enhanced intracellular calcium levels following antigen receptor activation leading to T cell death. Using Itpkb conditional knockout mice and LMW Itpkb inhibitors these studies reveal that Itpkb through its product IP4 inhibits the Orai1/Stim1 calcium channel on lymphocytes. Pharmacological inhibition or genetic deletion of Itpkb results in elevated intracellular Ca2+ and induction of FasL and Bim resulting in T cell apoptosis. Deletion of Itpkb or treatment with Itpkb inhibitors blocks T-cell dependent antibody responses in vivo and prevents T cell driven arthritis in rats. These data identify Itpkb as an essential mediator of T cell activation and suggest Itpkb inhibition as a novel approach to treat autoimmune disease.

Structural insights into enzyme regulation for inositol 1,4,5-trisphosphate 3-kinase B.

D-Myoinositol 1,4,5-trisphophate 3-kinases (IP(3)-3Ks) play important roles in metazoan cellular signaling. It has been demonstrated that mice without a functional version of IP(3)-3K isoform B are deficient in peripheral T-cells, indicating that IP(3)-3KB is essential to the developing immune system. The recent apo IP(3)-3KA structure exhibited a helix at the catalytic domain N-terminus exhibited a helix at the N-terminus of the catalytic domain, with a tryptophan indole moiety mimicking the binding mode of the substrate ATP purine ring, suggesting a mechanism of autoinhibition. Here we present the structure of the complete catalytic domain of IP(3)-3KB, including the CaM binding domain in complex with Mg(2+) and ATP. The crystal structure reveals a homodimeric arrangement of IP(3)-3KB catalytic domains, mediated via an intermolecular antiparallel beta-sheet formed from part of the CaM binding region. Residues from the putative autoinhibitory helix are rearranged into a loop configuration, with extensive interactions with the bound ATP. Mutagenesis of residues from this region reveals that substitution of the putative autoinhibitory tryptophan generates a hyperactive enzyme which retains Ca(2+)/CaM sensitivity. The IP(3)-3KB structure suggests a mechanism of enzyme activation, and raises the possibility that an interaction between IP(3)-3KB molecules may occur as part of the catalytic or regulatory cycle.

High physiological levels of LMP1 result in phosphorylation of eIF2 alpha in Epstein-Barr virus-infected cells.

LMP1 is an Epstein-Barr virus (EBV)-encoded membrane protein essential for the proliferation of EBV-infected lymphoblasts (E. Kilger, A. Kieser, M. Baumann, and W. Hammerschmidt, EMBO J. 17:1700-1709, 1998). LMP1 also inhibits gene expression and induces cytostasis in transfected cells when it is expressed at levels as little as twofold higher than the average for EBV-positive lymphoblasts (M. Sandberg, A. Kaykas, and B. Sugden, J. Virol. 74:9755-9761, 2000; A. Kaykas and B. Sugden, Oncogene 19:1400-1410, 2000). We have found that in three different clones of EBV-infected lymphoblasts the levels of expression of LMP1 in individual cells in each clone ranged over 100-fold. This difference is due to a difference in levels of the LMP1 transcript. In these clones, cells expressing high levels of LMP1 incorporated less BrdU. We also found that induction of expression of LMP1 or of a derivative of LMP1 with its transmembrane domain fused to green fluorescent protein instead of its carboxy-terminal signaling domain resulted in phosphorylation of eIF2 alpha in EBV-negative Burkitt's lymphoma cells. This induction of phosphorylation of eIF2 alpha was also detected in EBV-infected lymphoblasts, in which high levels of LMP1 correlated with high levels of phosphorylation of eIF2 alpha. Our results indicate that inhibition of gene expression and of cell proliferation by LMP1 occurs normally in EBV-infected cells.