Extracellular domains of CARs reprogramme T cell metabolism without antigen stimulation.

Metabolism is an indispensable part of T cell proliferation, activation and exhaustion, yet the metabolism of chimeric antigen receptor (CAR)-T cells remains incompletely understood. CARs are composed of extracellular domains-often single-chain variable fragments (scFvs)-that determine ligand specificity and intracellular domains that trigger signalling following antigen binding. Here, we show that CARs differing only in the scFv variously reprogramme T cell metabolism. Even without exposure to antigens, some CARs increase proliferation and nutrient uptake in T cells. Using stable isotope tracers and mass spectrometry, we observed basal metabolic fluxes through glycolysis doubling and amino acid uptake overtaking anaplerosis in CAR-T cells harbouring a rituximab scFv, unlike other similar anti-CD20 scFvs. Disparate rituximab and 14G2a-based anti-GD2 CAR-T cells are similarly hypermetabolic and channel excess nutrients to nitrogen overflow metabolism. Modest overflow metabolism of CAR-T cells and metabolic compatibility between cancer cells and CAR-T cells are identified as features of efficacious CAR-T cell therapy.

Advances in promoting chimeric antigen receptor T cell trafficking and infiltration of solid tumors.

T cells engineered to express chimeric antigen receptors (CARs) have demonstrated robust response rates in treating hematological malignancies. However, solid tumors present multiple challenges that hinder the antitumor efficacy of CAR-T cells, including antigen heterogeneity, off-tumor and systemic toxicities, and the immunosuppressive milieu of the tumor microenvironment (TME). Notably, the TME of solid tumors is characterized by chemokine dysregulation and a dense architecture consisting of tumor stroma, extracellular matrix, and aberrant vasculature that impede migration of CAR-T cells to the tumor site as well as infiltration into the solid-tumor mass. In this review, we highlight recent advances to improve CAR-T-cell trafficking to and infiltration of solid tumors to promote effective antigen recognition by CAR-T cells.

Killer fatigue: Transition to NK-cell-like phenotype is a signature of CAR-T cell exhaustion.

Exhaustion of chimeric antigen receptor (CAR)-T cells hinders their therapeutic efficacy, especially in treating solid tumors. In this issue of Cell, Good et al. develop an in vitro model of antigen-driven CAR-T cell exhaustion to characterize signatures of dysfunction, including a transition to a natural killer (NK)-like phenotype, and suggest new gene targets to prevent exhaustion.

Engineering CAR-T Cells for Next-Generation Cancer Therapy.

T cells engineered to express chimeric antigen receptors (CARs) with tumor specificity have shown remarkable success in treating patients with hematologic malignancies and revitalized the field of adoptive cell therapy. However, realizing broader therapeutic applications of CAR-T cells necessitates engineering approaches on multiple levels to enhance efficacy and safety. Particularly, solid tumors present unique challenges due to the biological complexity of the solid-tumor microenvironment (TME). In this review, we highlight recent strategies to improve CAR-T cell therapy by engineering (1) the CAR protein, (2) T cells, and (3) the interaction between T cells and other components in the TME.

Elucidation and refinement of synthetic receptor mechanisms.

Synthetic receptors are powerful tools for engineering mammalian cell-based devices. These biosensors enable cell-based therapies to perform complex tasks such as regulating therapeutic gene expression in response to sensing physiological cues. Although multiple synthetic receptor systems now exist, many aspects of receptor performance are poorly understood. In general, it would be useful to understand how receptor design choices influence performance characteristics. In this study, we examined the modular extracellular sensor architecture (MESA) and systematically evaluated previously unexamined design choices, yielding substantially improved receptors. A key finding that might extend to other receptor systems is that the choice of transmembrane domain (TMD) is important for generating high-performing receptors. To provide mechanistic insights, we adopted and employed a Förster resonance energy transfer-based assay to elucidate how TMDs affect receptor complex formation and connected these observations to functional performance. To build further insight into these phenomena, we developed a library of new MESA receptors that sense an expanded set of ligands. Based upon these explorations, we conclude that TMDs affect signaling primarily by modulating intracellular domain geometry. Finally, to guide the design of future receptors, we propose general principles for linking design choices to biophysical mechanisms and performance characteristics.