De novo-designed minibinders expand the synthetic biology sensing repertoire.

Synthetic and chimeric receptors capable of recognizing and responding to user-defined antigens have enabled "smart" therapeutics based on engineered cells. These cell engineering tools depend on antigen sensors which are most often derived from antibodies. Advances in the de novo design of proteins have enabled the design of protein binders with the potential to target epitopes with unique properties and faster production timelines compared to antibodies. Building upon our previous work combining a de novo-designed minibinder of the Spike protein of SARS-CoV-2 with the synthetic receptor synNotch (SARSNotch), we investigated whether minibinders can be readily adapted to a diversity of cell engineering tools. We show that the Spike minibinder LCB1 easily generalizes to a next-generation proteolytic receptor SNIPR that performs similarly to our previously reported SARSNotch. LCB1-SNIPR successfully enables the detection of live SARS-CoV-2, an improvement over SARSNotch which can only detect cell-expressed Spike. To test the generalizability of minibinders to diverse applications, we tested LCB1 as an antigen sensor for a chimeric antigen receptor (CAR). LCB1-CAR enabled CD8+ T cells to cytotoxically target Spike-expressing cells. Our findings suggest that minibinders represent a novel class of antigen sensors that have the potential to dramatically expand the sensing repertoire of cell engineering tools.

Human microglia states are conserved across experimental models and regulate neural stem cell responses in chimeric organoids.

Microglia are resident macrophages in the brain that emerge in early development and respond to the local environment by altering their molecular and phenotypic states. Fundamental questions about microglia diversity and function during development remain unanswered because we lack experimental strategies to interrogate their interactions with other cell types and responses to perturbations ex vivo. We compared human microglia states across culture models, including cultured primary and pluripotent stem cell-derived microglia. We developed a "report card" of gene expression signatures across these distinct models to facilitate characterization of their responses across experimental models, perturbations, and disease conditions. Xenotransplantation of human microglia into cerebral organoids allowed us to characterize key transcriptional programs of developing microglia in vitro and reveal that microglia induce transcriptional changes in neural stem cells and decrease interferon signaling response genes. Microglia additionally accelerate the emergence of synchronized oscillatory network activity in brain organoids by modulating synaptic density.

Altered modes of stem cell division drive adaptive intestinal growth.

Throughout life, adult organs continually adapt to variable environmental factors. Adaptive mechanisms must fundamentally differ from homeostatic maintenance, but little is known about how physiological factors elicit tissue remodeling. Here, we show that specialized stem cell responses underlie the adaptive resizing of a mature organ. In the adult Drosophila midgut, intestinal stem cells interpret a nutrient cue to "break homeostasis" and drive growth when food is abundant. Activated in part by niche production of insulin, stem cells direct a growth program through two altered modes of behavior: accelerated division rates and predominance of symmetric division fates. Together, these altered modes produce a net increase in total intestinal cells, which is reversed upon withdrawal of food. Thus, tissue renewal programs are not committed to maintain cellular equilibrium; stem cells can remodel organs in response to physiological triggers.