Biology subjects

Kueh, H. Y.

Publications and source records attributed to Kueh, H. Y..

11 recordsLinked to original sources

bioRxiv2025

Design of solubly expressed miniaturized SMART MHCs

The precise recognition of specific peptide-MHC (pMHC) complexes by T-cell receptors (TCRs) plays a key role in infectious disease, cancer and autoimmunity. A critical step in many immunobiological studies is the identification of T-cells expressing TCRs specific to a given pMHC antigen. However, the intrinsic instability of empty class-I MHCs limits their soluble expression in Escherichia coli (E. coli) and makes it very difficult to characterize even a small fraction of possible pMHC/TCR interactions. To overcome this limitation, we designed small proteins which buttress the peptide binding groove of class I MHCs, replacing {beta}2-microglobulin ({beta}2m) and the heavy chain 3 domain, and enable soluble expression of both H-2Db and A*02:01 in E. coli. We demonstrate that these soluble, monomeric, antigen-receptive, truncated (SMART) MHCs retain both peptide- and TCR-binding specificity, and that peptide-bound structures of both allomorphs are similar to their full-length, native counterparts. With extension to the majority of HLA alleles, SMART MHCs should be broadly useful for probing the T-cell repertoire in approaches ranging from yeast display to T-cell staining. SignificanceDespite the critical role that TCR/pMHC interactions play in human health, it has remained difficult to produce reagents necessary to study them. Requirements for refolding or sequence optimization limit immunologists and biochemists ability to characterize diverse pMHC/TCR interactions. Here, we develop a de-novo designed protein domain that stabilizes the H-2Db and A*02:01 class I MHC allomorphs, allowing soluble expression in E. coli without the need for a stabilizing peptide, and improving display on the yeast surface, while maintaining peptide and TCR binding interactions. These features facilitate a wide range of experiments to more fully understand the nature of pMHC/TCR interactions, and pave the way for the development of stabilizing domains for all MHC allomorphs.

biochemistry↗

bioRxiv2024

Potent antitumor activity of a designed interleukin-21 mimic

Long-standing goals of cancer immunotherapy are to activate cytotoxic antitumor T cells across a broad range of affinities while dampening suppressive regulatory T (Treg) cell responses, but current approaches achieve these goals with limited success. Here, we report a de novo IL-21 mimic, 21h10, designed to have augmented stability and high signaling potency in both humans and mice. In multiple animal models and in ex vivo human melanoma patient derived organotypic tumor spheroids (PDOTS), 21h10 showed robust antitumor activity. 21h10 generates significantly prolonged STAT signaling in vivo compared with native IL-21, and has considerably stronger anti-tumor activity. Toxicities associated with systemic administration of 21h10 could be mitigated by TNF blockade without compromising antitumor efficacy. In the tumor microenvironment, 21h10 induced highly cytotoxic antitumor T cells from clonotypes with a range of affinities for endogenous tumor antigens, robustly expanding low-affinity cytotoxic T cells and driving high expression of interferon- (IFN-) and granzyme B compared to native IL-21, while increasing the frequency of IFN-+ Th1 cells and reducing that of Foxp3+ Tregs. As 21h10 has full human/mouse cross-reactivity, high stability and potency, and potentiates low-affinity antitumor responses, it has considerable translational potential.

biochemistry↗

bioRxiv2024

A timed epigenetic switch balances T and ILC lineage proportions in the thymus

How stem and progenitor cells give rise to multiple cell types in defined numbers and proportions is a central question in developmental biology. Epigenetic switches, acting at single gene loci, can generate extended delays in the activation timing of lineage-specifying genes, and thereby impact lineage decisions and cell type output of progenitors. Here, we analyzed a timed epigenetic switch controlling Bcl11b, a transcription factor that drives T cell lineage commitment, but only after a long multi-day time delay in expression. To investigate roles for this delay in controlling lineage decision making, we analyzed progenitors with a deletion in a distal Bcl11b enhancer, that further extends this delay by [~]3 days. Strikingly, delaying Bcl11b activation reduces T cell output but enhances ILC generation in the thymus, and does so by redirecting progenitors to the ILC lineages at the T and ILC developmental branchpoint. Mechanistically, delaying Bcl11b activation promoted ILC redirection by up-regulating a PLZF-dependent ILC transcriptional program in progenitors. Despite up-regulating PLZF, committed ILC progenitors were still capable of later activating Bcl11b, which is also needed for specification of type 2 ILCs. These results show that epigenetic switches, by controlling the activation timing and order of lineage-specifying genes within regulatory networks, can modulate population sizes and proportions of differentiated cell types.

developmental biology↗

bioRxiv2024

Proofreading and single-molecule sensitivity in T-cellreceptor signaling by condensate nucleation

T-cells display the remarkable ability to detect single foreign peptides displayed on target cells, while ignoring highly abundant self peptides. This selectivity has been explained by kinetic proofreading in the T-cell receptor (TCR) signaling pathway, which prevents responses to short-lived binding events regardless of their abundance. However, the biochemical mechanisms that drive kinetic proofreading have remained unclear. Here, using computational modeling, we show that these key signaling properties of the TCR pathway can emerge from the dynamics of LAT phosphorylation, diffusion, and condensation following TCR-pMHC binding. In this model, time delays in LAT condensate nucleation underlie kinetic proofreading, enabling selective signaling responses to high-affinity pMHC ligands. The cooperativity in the nucleation and growth of LAT condensates also provides a mechanism to amplify weak signals from single foreign peptides and for condensates to grow with increasing antigen numbers. In contrast to other models, condensate-nucleation proofreading predicts a dependence of signal strength on pMHC spacing at fixed number, a prediction we validated experimentally using a protein scaffold to present pMHCs at defined intervals. Our results suggest that nucleation-condensation proofreading underlies the remarkable antigen detection capabilities of the TCR signaling pathway. SignificanceTo fight infections and cancer, T-cells must selectively recognize low levels of foreign peptides from pathogens or cancer cells, but the mechanisms that enable these properties have remained unclear.Using mathematical modeling and experiments, we find that T-cells can selectively detect single foreign peptides through a clustering process where a key protein downstream of the T-cell receptor forms condensates containing hundreds of signaling proteins. This condensate nucleation process can explain experimentally observed features of T-cell signaling, including our finding that the size of signaling clusters depends on the distance between foreign peptides. Our work reveals a key role for the condensation of signaling molecules in setting the spatial and temporal thresholds that control the sensitivity and selectivity of T-cells.

biophysics↗

bioRxiv2023

Antigen perception in T cells by long-term Erk and NFAT signaling dynamics.

Immune system threat detection hinges on T cells ability to perceive varying peptide major-histocompatibility complex (pMHC) antigens. As the Erk and NFAT pathways link T cell receptor engagement to gene regulation, their signaling dynamics may convey information about pMHC inputs. To test this idea, we developed a dual reporter mouse strain and a quantitative imaging assay that, together, enable simultaneous monitoring of Erk and NFAT dynamics in live T cells over day-long timescales as they respond to varying pMHC inputs. Both pathways initially activate uniformly across various pMHC inputs, but diverge only over longer (9+ hrs) timescales, enabling independent encoding of pMHC affinity and dose. These late signaling dynamics are decoded via multiple temporal and combinatorial mechanisms to generate pMHC-specific transcriptional responses. Our findings underscore the importance of long timescale signaling dynamics in antigen perception, and establish a framework for understanding T cell responses under diverse contexts. SIGNIFICANCE STATEMENTTo counter diverse pathogens, T cells mount distinct responses to varying peptide-major histocompatibility complex ligands (pMHCs). They perceive the affinity of pMHCs for the T cell receptor (TCR), which reflects its foreignness, as well as pMHC abundance. By tracking signaling responses in single living cells to different pMHCs, we find that T cells can independently perceive pMHC affinity vs dose, and encode this information through the dynamics of Erk and NFAT signaling pathways downstream of the TCR. These dynamics are jointly decoded by gene regulatory mechanisms to produce pMHC-specific activation responses. Our work reveals how T cells can elicit tailored functional responses to diverse threats and how dysregulation of these responses may lead to immune pathologies.

immunology↗

bioRxiv2022

Flexible and scalable control of T cell memory by a reversible epigenetic switch

The immune system encodes information about the severity of a pathogenic threat in the quantity and type of memory cell populations formed in response. This encoding emerges from the decisions of lymphocytes to maintain or lose self-renewal and memory potential during a challenge. By tracking responding CD8 T cells at the single-cell and clonal lineage level using time-resolved transcriptomics and quantitative live imaging, we identify a remarkably flexible decision-making strategy, whereby T cells initially choose whether to maintain or lose memory potential early after antigen recognition, but following pathogen clearance may regain memory potential if initially lost. Mechanistically, this flexibility is implemented by a cis-epigenetic switch that silences the memory regulator TCF1 in a stochastic and reversible manner in response to stimulatory inputs. Mathematical modeling shows how this strategy allows memory T cell numbers to scale robustly with pathogen virulence and immune response magnitudes. We propose that flexibility and stochasticity in cellular decision making ensures optimal immune responses against diverse threats.

immunology↗

bioRxiv2021

Unsupervised discovery of dynamic cell phenotypic states from transmitted light movies

Identification of cell phenotypic states within heterogeneous populations, along with elucidation of their switching dynamics, is a central challenge in modern biology. Conventional single-cell analysis methods typically provide only indirect, static phenotypic readouts. Transmitted light images, on the other hand, provide direct morphological readouts and can be acquired over time to provide a rich data source for dynamic cell phenotypic state identification. Here, we describe an end-to-end deep learning platform, UPSIDE (for Unsupervised Phenotypic State IDEntification), for discovering cell states and their dynamics from transmitted light movies. UPSIDE uses the variational auto-encoder architecture to learn latent cell representations, that are then clustered for state identification, decoded for feature interpretation, and linked across movie frames for transition rate inference. Using UPSIDE, we identified distinct blood cell types in a heterogeneous dataset. From acute myeloid leukemia cell movies, we then identified stem-cell associated morphological states and their inter-conversion rates. UPSIDE opens up use of transmitted light movies for systematic exploration of cell state heterogeneity and dynamics in biology and medicine.

bioinformatics↗

bioRxiv2020

Multiplexed single-cell profiling of chromatin states at genomic loci by expansion microscopy

Proper regulation of genome architecture and activity is essential for the development and function of multicellular organisms. Histone modifications, acting in combination, specify these activity states at individual genomic loci. However, the methods used to study these modifications often require either a large number of cells or are limited to targeting one histone mark at a time. Here, we developed a new method called Single Cell Evaluation of Post-TRanslational Epigenetic Encoding (SCEPTRE) that uses Expansion Microscopy (ExM) to visualize and quantify multiple histone modifications at non-repetitive genomic regions in single cells at a spatial resolution of ~75 nm. Using SCEPTRE, we distinguished multiple histone modifications at a single housekeeping gene, quantified histone modification levels at multiple developmentally-regulated genes in individual cells, and identified a relationship between histone H3K4 trimethylation and the loading of paused RNA polymerase II at individual loci. Thus, SCEPTRE enables multiplexed detection of combinatorial chromatin states at single genomic loci in single cells.

genomics↗

bioRxiv2019

Temporal scaling in developmental gene networks by epigenetic timing control

During development, progenitors follow defined temporal schedules for differentiation, to form organs and body plans with precise sizes and proportions. Across diverse contexts, these developmental schedules are encoded by autonomous timekeeping mechanisms in single cells. These autonomous timers not only operate robustly over many cell generations, but can also operate at different speeds in different species, enabling proportional scaling of temporal schedules and population sizes. By combining mathematical modeling with live-cell measurements, we elucidate the mechanism of a polycomb-based epigenetic timer, that delays activation of the T-cell commitment regulator Bcl11b to facilitate progenitor expansion. This mechanism generates activation delays that are independent of cell cycle duration, and are tunably controlled by transcription factors and epigenetic modifiers. When incorporated into regulatory gene networks, this epigenetic timer enables progenitors to set scalable temporal schedules for flexible size control. These findings illuminate how evolution may set and adjust developmental speed in multicellular organisms.

systems biology↗

bioRxiv2018

A fluorescent reporter enables instantaneous measurement of cell cycle speed in live cells

Cell proliferation changes concomitantly with fate transitions during reprogramming, differentiation, regeneration, and oncogenesis. Methods to resolve cell cycle length heterogeneity in real-time are currently lacking. Here, we describe a genetically encoded fluorescent reporter that captures live cell cycle speed using a single measurement. This reporter is based on the color-changing Fluorescent Timer (FT) protein, which emits blue fluorescence when newly synthesized before maturing into a red fluorescent protein. We generated a mouse strain expressing an H2B-FT fusion reporter from a universally active locus, and demonstrate that faster-cycling cells can be distinguished from slower-cycling ones based on the intracellular fluorescence ratio between the FTs blue and red states. Using this reporter, we reveal the native cell cycle speed distributions of fresh hematopoietic cells, and demonstrate its utility in analyzing cell proliferation in solid tissues. This system is broadly applicable for dissecting functional heterogeneity associated with cell cycle dynamics in complex tissues.

cell biology↗

bioRxiv2018

A stochastic epigenetic switch controls the dynamics of T-cell lineage commitment

Cell fate decisions occur through the switch-like, irreversible activation of fate-specifying genes. These activation events are often assumed to be tightly-coupled to changes in upstream transcription factors, but could also be constrained by cis-epigenetic mechanisms at individual gene loci. Here, we studied the activation of Bcl11b, which controls T-cell fate commitment. To disentangle cis and trans effects, we generated mice where two Bcl11b copies are tagged with distinguishable fluorescent proteins. Quantitative live microscopy of progenitors from these mice revealed that Bcl11b turned on after a stochastic delay averaging multiple days, which varied not only between cells but also between Bcl11b alleles within the same cell. Genetic perturbations, together with mathematical modeling, showed that a distal enhancer controls the rate of epigenetic activation, while a parallel Notch-dependent trans-acting step stimulates expression from activated loci. These results show that developmental fate transitions can be controlled by stochastic cis-acting events on individual loci.

bioinformatics↗