Guideline for Children With Cancer Receiving General Anesthesia for Procedures and Imaging.

Children with cancer and those undergoing hematopoietic stem cell transplantation frequently require anesthesia for imaging as well as diagnostic and therapeutic procedures from diagnosis through follow-up. Due to their underlying disease and side effects of chemotherapy and radiation, they are at risk for complications during this time, yet no published guideline exists for preanesthesia preparation. A comprehensive literature review served as the basis for discussions among our multidisciplinary panel of oncologists, anesthesiologists, nurse practitioners, clinical pharmacists, pediatric psychologists, surgeons and child life specialists at the Children's Hospital of Philadelphia. Due to limited literature available, this panel created an expert consensus guideline addressing anesthesia preparation for this population.

Ligand-Induced Degradation of a CAR Permits Reversible Remote Control of CAR T Cell Activity In Vitro and In Vivo.

Chimeric antigen receptor (CAR)-modified T cells are endowed with novel antigen specificity and are most often administered to patients without an engineered mechanism to control the CAR T cells once infused. "Suicide switches" such as the small molecule-controlled, inducible caspase-9 (iCas9) system afford the ability to selectively eliminate engineered T cells; however, these approaches are designed for all-or-none, irreversible termination of an ongoing immune response. In order to permit reversible and adjustable modulation, we have created a CAR that is capable of on-demand downregulation by fusing the CAR to a previously developed ligand-induced degradation (LID) domain. Addition of a small molecule ligand triggers exposure of a cryptic degron within the LID domain, resulting in proteasomal degradation of the CAR-LID fusion protein and loss of CAR on the surface of T cells. This fusion construct allowed for reversible and "tunable" inhibition of CAR T cell activity in vitro. Delivery of the triggering molecule in CAR-LID-treated tumor-bearing mice temporarily reduced CAR activity through modulation of CAR surface expression. The ability to more flexibly modulate CAR T cell expression through a small molecule provides a platform for controlling possible adverse side effects, as well as preclinical investigations of CAR T cell biology.

Imaging CAR T Cell Trafficking with eDHFR as a PET Reporter Gene.

Cell-based therapeutics have considerable promise across diverse medical specialties; however, reliable human imaging of the distribution and trafficking of genetically engineered cells remains a challenge. We developed positron emission tomography (PET) probes based on the small-molecule antibiotic trimethoprim (TMP) that can be used to image the expression of the Escherichia coli dihydrofolate reductase enzyme (eDHFR) and tested the ability of [18F]-TMP, a fluorine-18 probe, to image primary human chimeric antigen receptor (CAR) T cells expressing the PET reporter gene eDHFR, yellow fluorescent protein (YFP), and Renilla luciferase (rLuc). Engineered T cells showed an approximately 50-fold increased bioluminescent imaging signal and 10-fold increased [18F]-TMP uptake compared to controls in vitro. eDHFR-expressing anti-GD2 CAR T cells were then injected into mice bearing control GD2- and GD2+ tumors. PET/computed tomography (CT) images acquired on days 7 and 13 demonstrated early residency of CAR T cells in the spleen followed by on-target redistribution to the GD2+ tumors. This was corroborated by autoradiography and anti-human CD8 immunohistochemistry. We found a high sensitivity of detection for identifying tumor-infiltrating CD8 CAR T cells, ∼11,000 cells per mm3. These data suggest that the [18F]-TMP/eDHFR PET pair offers important advantages that could better allow investigators to monitor immune cell trafficking to tumors in patients.

ß-synuclein at the "synapse" of encephalitis and neurodegeneration in multiple sclerosis?

Lodygin and colleagues recently identified a candidate grey matter target antigen in a rat model of multiple sclerosis, a disease classically associated with the white matter antigen, myelin.

Enhanced-affinity murine T-cell receptors for tumor/self-antigens can be safe in gene therapy despite surpassing the threshold for thymic selection.

Many of the most promising tumor antigens for T-cell-based cancer immunotherapies are unmodified self-antigens. Unfortunately, the avidity of T cells specific for these antigens is limited by central tolerance during T-cell development in the thymus, resulting in decreased anti-tumor efficacy of these T cells. One approach to overcoming this obstacle is to mutate T-cell receptor (TCR) genes from naturally occurring T cells to enhance the affinity for the target antigen. These enhanced-affinity TCRs can then be developed for use in TCR gene therapy. Although TCRs with significantly enhanced affinity have been generated using this approach, it is not clear whether these TCRs, which bypass the affinity limits imposed by negative selection, remain unresponsive to the low levels of self-antigen generally expressed by some normal tissues. Here we show that 2 variants of a high-affinity WT1-specific TCR with enhanced affinity for WT1 are safe and do not mediate autoimmune tissue infiltration or damage when transduced into peripheral CD8 T cells and transferred in vivo. However, if expressed in developing T cells and subjected to thymic selection, the same enhanced-affinity TCRs signal tolerance mechanisms in the thymus, resulting in T cells with attenuated antigen sensitivity in the periphery.

Structural features of T cell receptor variable regions that enhance domain stability and enable expression as single-chain ValphaVbeta fragments.

The variable (V) domains of antibodies and T cell receptors (TCRs) share sequence homology and striking structural similarity. Single-chain antibody V domain constructs (scFv) are routinely expressed in a variety of heterologous systems, both for production of soluble protein as well as for in vitro engineering. In contrast, single-chain T cell receptor V domain constructs (scTCR) are prone to aggregation and misfolding and are refractory to display on phage or yeast in their wild-type form. However, through random mutagenesis and yeast display engineering, it has been possible to isolate scTCR mutants that are properly folded and displayed on the yeast surface. These displayed mutants can serve not only as a scaffold for further engineering but also as scTCR variants that exhibit favorable biophysical properties in Escherichia coli expression. Thus, a more comprehensive understanding of the V domain mutations that allowed display would be beneficial. Our goal here was to identify generalizable patterns of important mutations that can be applied to different TCRs. We compared five different scTCRs, four from mice and one from a human, for yeast surface display. Analysis of a collection of mutants revealed four distinct regions of TCR V domains that were most important for enabling surface expression: the Valpha-Vbeta interface, the HV4 of Vbeta, and the region of the Valpha and Vbeta domains normally apposed against the constant (C) domains. Consistent with the role of the V-C interface in surface display, reconstitution of this interface, by including the constant domains of each chain, allowed V domain display and alphabeta chain association on the yeast surface, thus providing an alternative TCR scaffold. However, the surface levels of TCR achieved with engineered scTCR mutants were superior to that of the ValphaCalpha/VbetaCbeta constructs. Therefore, we describe further optimization of the current strategy for surface display of the single-chain format in order to facilitate yeast display engineering of a broader range of scTCRs.

Enhancing Chimeric Antigen Receptor T Cell Anti-tumor Function through Advanced Media Design.

Effective chimeric antigen receptor (CAR)-T cell therapy is dependent on optimal cell culture methods conducive to the activation and expansion of T cells ex vivo, as well as infection with CAR. Media formulations used in CAR-T cell manufacturing have not been optimized for gene delivery, cell expansion, and overall potency. Bioactive components and derivatives that support the generation of functionally-competent T cell progeny with long-lasting persistence are largely undefined. Current media formulations rely on fetal bovine serum (FBS) or human serum (HS), which suffer from a lack of consistency or supply issues. We recognize that components of blood cellular fractions that are absent in serum may have therapeutic value. Here we investigate whether a concentrated growth factor extract, purified from human transfusion grade whole blood fractions, and marketed as PhysiologixTM xeno-free (XF) hGFC (Phx), supports CAR-T cell expansion and function. We show that Phx supports T cell proliferation in clinical and research-grade media. We also show that Phx treatment enhances lentiviral-mediated gene expression across a wide range of multiplicity of infections (MOIs). We compared the ability of anti-GD-2 CAR-T cells expanded ex vivo in medium conditioned with either Phx or HS to clear tumor burden in a human xenograft model of neuroblastoma. We show that T cells expanded in Phx have superior engraftment and potency in vivo, as well as CAR-induced cytolytic activity in vitro. Metabolomic profiling revealed several factors unique to Phx that may have relevance for CAR-T cell preclinical discovery, process development, and manufacturing. In particular, we show that carnosine, a biogenic amine modestly enriched in Phx relative to HS, enhances lentiviral gene delivery in activated T cells. By limiting extracellular acidification, carnosine enhances the metabolic fitness of T cells, shifting their metabolic profile from an acidic, stressed state toward an oxidative, energetic state. These findings are very informative regarding potential derivatives to include in medium customized for gene delivery and overall potency for T cell adoptive immunotherapies.

Biosensor detection systems: engineering stable, high-affinity bioreceptors by yeast surface display.

Over the past two decades, the field of biosensors has been developing fast, portable, and convenient detection tools for various molecules of interest, both biological and environmental. Although much attention is paid to the transduction portion of the sensor, the actual bioreceptor that binds the ligand is equally critical. Tight, specific binding by the bioreceptor is required to detect low levels of the relevant ligand, and the bioreceptor must be stable enough to survive immobilization, storage, and in ideal cases, regeneration on the biosensing device. Often, naturally-occurring bioreceptors or antibodies that are specific for a ligand either express affinities that may be too low to detect useful levels, or the proteins are too unstable to be used and reused as a biosensor. Further engineering of these receptors can improve their utility. Here, we describe in detail the use of yeast surface display techniques to carry out directed evolution of bioreceptors to increase both the stability of the molecules and their affinity for the ligands. This powerful technique has enabled the production of stabilized, single-chain antibodies, T cell receptors, and other binding molecules that exhibit affinity increases for their ligands of up to 1 million-fold and expression of stable molecules in E. coli.

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.

Display, engineering, and applications of antigen-specific T cell receptors.

The use of T cell receptors (TCRs) as potential therapeutic agents provides an opportunity to target a greatly expanded array of antigens, compared to those now targeted with monoclonal antibodies. With the advent of new display technologies and TCR formats for in vitro engineering, it should be possible to generate high-affinity TCRs against virtually any peptide antigen that is shown to bind to a major histocompatibility complex (MHC) molecule (e.g. peptides derived from viral antigens or from self proteins that are associated with the transformed phenotype). What remains, however, are challenges associated with effective targeting of very low numbers of cell surface antigens (pepMHC), fewer than the case for conventional monoclonal antibody-based therapies. This hurdle might be overcome with the attachment of more effective payloads for soluble TCR approaches, or by using TCR gene transfer into T cells that can then be adoptively transferred into patients. There is considerable work to be done on the physiological aspects of either approach, including pharmacokinetic studies in the case of soluble TCRs, and T cell trafficking, persistence, and autoreactivity studies in the case of adoptively transferred T cells. As with the field of monoclonal antibodies, it will take time to explore these issues, but the potential benefits of TCR-based therapies make these challenges worth the effort.