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Most variants associated with complex traits and diseases identified by genome-wide association studies (GWAS) map to noncoding regions of the genome with unknown effects. Using ancestrally diverse, biobank-scale GWAS data, massively parallel CRISPR screens, and single-cell transcriptomic and proteomic sequencing, we discovered 124 cis -target genes of 91 noncoding blood trait GWAS loci. Using precise variant insertion through base editing, we connected specific variants with gene expression changes. We also identified trans -effect networks of noncoding loci when cis target genes encoded transcription factors or microRNAs. Networks were themselves enriched for GWAS variants and demonstrated polygenic contributions to complex traits. This platform enables massively parallel characterization of the target genes and mechanisms of human noncoding variants in both cis and trans .

The engineering of patient T-cells for adoptive cell therapies has revolutionised the treatment of several cancer types(1). However, further improvements are needed to increase response and cure rates. CRISPR-based loss-of-function screens have been limited to negative regulators of T-cell functions(2-1) and raise safety concerns due to permanent genome modification. Here we identify positive T-cell regulators via overexpression of ~12,000 barcoded human open reading frames (ORFs). The top-ranked genes increased primary human CD4+ and CD8+ T-cell proliferation, activation, and secretion of key cytokines like interleukin-2 and interferon-gamma. In addition, we developed a single-cell genomics method (OverCITE-seq) for high-throughput quantification of the transcriptome and surface antigens in ORF-engineered T-cells. The top-ranked ORF, lymphotoxin beta receptor (LTBR), is typically expressed in myeloid cells but absent in lymphocytes. When overexpressed in T-cells, LTBR induced profound transcriptional and epigenomic remodelling, increasing T-cell effector functions, as well as resistance to exhaustion in chronic stimulation settings, via constitutive activation of the canonical NF-κB pathway. LTBR and other top-ranked genes improved antigen-specific chimeric antigen receptor (CAR) T-cell and γδ T-cell responses, highlighting their potential for future cancer-agnostic therapies(5). Our results provide several strategies for improving next generation T-cell therapies via induction of new synthetic cell programmes.

Genetic risk for autism spectrum disorder (ASD) is associated with hundreds of genes spanning a wide range of biological functions

SHP2 (PTPN11) acts upstream of SOS1/2 to enable RAS activation. Allosteric SHP2 inhibitors (SHP2i) in the clinic prevent SHP2 activation, block proliferation of RTK- or cycling RAS mutant-driven cancers, and overcome “adaptive resistance.” To identify SHP2i resistance mechanisms, we performed genome-wide CRISPR/Cas9 knockout screens on two SHP2i-sensitive cell lines, recovering genes expected to cause resistance (NF1, PTEN, CDKN1B, LZTR1, and RASA2) and novel targets (INPPL1, MAP4K5, epigenetic modifiers). We screened 14 additional lines with a focused CRISPR library targeting common “hits” from the genome-wide screens. LZTR1 deletion conferred resistance in 12/14 lines, followed by MAP4K5 (8/14), SPRED2/STK40 (6/14), and INPPL1 (5/14). INPPL1, MAP4K5, or LZTR1 deletion reactivated ERK signaling. INPPL1-mediated sensitization to SHP2i required its NPXY motif but not lipid phosphatase activity. MAP4K5 acted upstream of MEK through a kinase-dependent target(s); LZTR1 had cell-dependent effects on RIT and RAS stability. INPPL1, MAP4K5, or LZTR1 deletion also conferred SHP2i resistance in vivo. Defining the SHP2i resistance landscape could suggest effective combination approaches.

Pooled CRISPR screens coupled with single-cell RNA-sequencing have enabled systematic interrogation of gene function and regulatory networks. Here, we introduce Cas13 RNA Perturb-seq (CaRPool-seq), which leverages the RNA-targeting CRISPR-Cas13d system and enables efficient combinatorial perturbations alongside multimodal single-cell profiling. CaRPool-seq encodes multiple perturbations on a cleavable CRISPR array that is associated with a detectable barcode sequence, allowing for the simultaneous targeting of multiple genes. We compared CaRPool-seq to existing Cas9-based methods, highlighting its unique strength to efficiently profile combinatorially perturbed cells. Finally, we apply CaRPool-seq to perform multiplexed combinatorial perturbations of myeloid differentiation regulators in an acute myeloid leukemia (AML) model system and identify extensive interactions between different chromatin regulators that can enhance or suppress AML differentiation phenotypes.

CRISPR-Cas transcriptional tools have been widely applied for programmable regulation of complex biological networks. In comparison to eukaryotic systems, bacterial CRISPR activation (CRISPRa) has stringent target site requirements for effective gene activation. While genes may not always have an NGG protospacer adjacent motif (PAM) at the appropriate position, PAM-flexible dCas9 variants can expand the range of targetable sites. Here we systematically evaluate a panel of PAM-flexible dCas9 variants for their ability to activate bacterial genes. We observe that dxCas9-NG provides a high dynamic range of gene activation for sites with NGN PAMs while dSpRY permits modest activity across almost any PAM. Similar trends were observed for heterologous and endogenous promoters. For all variants tested, improved PAM-flexibility comes with the trade-off that CRISPRi-mediated gene repression becomes less effective. Weaker CRISPR interference (CRISPRi) gene repression can be partially rescued by expressing multiple sgRNAs to target many sites in the gene of interest. Our work provides a framework to choose the most effective dCas9 variant for a given set of gene targets, which will further expand the utility of CRISPRa/i gene regulation in bacterial systems.

SHP2 (PTPN11) acts upstream of SOS1/2 to enable RAS activation. Allosteric inhibitors (SHP2is) stabilize SHP2 auto-inhibition, preventing activation by upstream stimuli. SHP2is block proliferation of RTK- or cycling RAS mutant-driven cancers and overcome adaptive resistance to other RAS-ERK pathway drugs. Several SHP2is are in clinical trials. To identify potential SHP2i resistance mechanisms, we performed genome-wide CRISPR/Cas9 knockout screens on two SHP2i-sensitive AML cell lines and recovered genes expected to cause resistance, including tumor suppressor (NF1, PTEN, CDKN1B) and “RASopathy” (LZTR1, RASA2) genes, and several novel targets (INPPL1, MAP4K5, epigenetic modifiers). We then screened 14 cancer lines with a focused CRISPR library targeting common “hits” from the genome-wide screens. LZTR1 deletion conferred resistance in 12/14 lines, followed by MAP4K5 (8/14), SPRED2 (6/14), STK40 (6/14), and INPPL1 (5/14). INPPL1, MAP4K5, or LZTR1 deletion reactivated ERK signaling. INPPL1-mediated sensitization to SHP2i required its NPXY motif but not its lipid phosphatase domain. MAP4K5 acted upstream of MEK via a kinase-dependent target(s), whereas LZTR1 showed cell-dependent effects on RIT and RAS stability. INPPLI, MAP4K5, or LZTR1 deletion also conferred SHP2i resistance in mice. Our results reveal multiple SHP2i resistance genes, emphasizing the need for detailed understanding of the resistance landscape to arrive at effective combinations.

Background Many neurodegenerative diseases develop only later in life, when cells in the nervous system lose their structure or function. In many forms of neurodegenerative diseases, this late-onset phenomenon remains largely unexplained. Results Analyzing single-cell RNA sequencing from Alzheimer’s disease (AD) and Huntington’s disease (HD) patients, we find increased transcriptional heterogeneity in disease-state neurons. We hypothesize that transcriptional heterogeneity precedes neurodegenerative disease pathologies. To test this idea experimentally, we use juvenile forms (72Q; 180Q) of HD iPSCs, differentiate them into committed neuronal progenitors, and obtain single-cell expression profiles. We show a global increase in gene expression variability in HD. Autophagy genes become more stable, while energy and actin-related genes become more variable in the mutant cells. Knocking down several differentially variable genes results in increased aggregate formation, a pathology associated with HD. We further validate the increased transcriptional heterogeneity in CHD8+/− cells, a model for autism spectrum disorder. Conclusions Overall, our results suggest that although neurodegenerative diseases develop over time, transcriptional regulation imbalance is present already at very early developmental stages. Therefore, an intervention aimed at this early phenotype may be of high diagnostic value.

Type VI CRISPR enzymes are RNA-targeting proteins with nuclease activity that enable specific and robust target gene knock-down without altering the genome. To define rules for the design of Cas13d guide RNAs, we conducted massively-parallel screens targeting mRNAs of a green fluorescent protein (GFP) transgene and CD46, CD55 and CD71 cell surface proteins in human cells. In total, we measured the activity of 24,460 guide RNAs with and without mismatches relative to the target sequences. Knock-down efficacy is driven by guide RNA-specific features and target site context. Single mismatches generally reduce knock-down to a modest degree, but spacer nucleotides 15 – 21 are largely intolerant to target site mismatches. We developed a computational model to identify optimal guide RNAs and confirm its generalizability testing 3,979 guides targeting mRNAs of 48 endogenous genes. We show that Cas13 can be used in forward transcriptomic pooled screens and, using our model, predict optimized Cas13 guide RNAs for all protein-coding transcripts in the human genome., Editorial summary Design of optimal guide RNAs for Cas13d-mediated RNA knock-down is enabled by computational modeling of large-scale screening data

With the focus on technology for this issue of Molecular Cell, a group of scientists working in different areas of molecular biology provide their perspective on the most recent important technological advance in their field, where the field is lacking, and their wish list for future technology development.

Adoptive T cell therapies (ACT) have been curative for a limited number of cancer patients. The sensitization of cancer cells to T cell killing may expand the benefit of these therapies for more patients. To this end, we use a three-step approach to identify cancer genes that disfavor T cell immunity. First, we profile gene transcripts upregulated by cancer under selection pressure from T cell killing. Second, we identify potential tumor gene targets and pathways that disfavor T cell killing using signaling pathway activation libraries and genome-wide loss-of-function CRISPR-Cas9 screens. Finally, we implement pharmacological perturbation screens to validate these targets and identify BIRC2, ITGAV, DNPEP, BCL2, and ERRα as potential ACT-drug combination candidates. Here, we establish that BIRC2 limits antigen presentation and T cell recognition of tumor cells by suppressing IRF1 activity and provide evidence that BIRC2 inhibition in combination with ACT is an effective strategy to increase efficacy.

To date the locus with the most robust human genetic association to COVID-19 susceptibility is 3p21.31. Here, we integrate genome-scale CRISPR loss-of-function screens and eQTLs in diverse cell types and tissues to pinpoint genes underlying COVID-19 risk. Our findings identify SLC6A20 and CXCR6 as putative causal genes that mediate COVID-19 risk and highlight the usefulness of this integrative approach to bridge the divide between correlational and causal studies of human biology.

The majority of variants associated with complex traits and common diseases identified by genome-wide association studies (GWAS) map to noncoding regions of the genome with unknown regulatory effects in cis and trans. By leveraging biobank-scale GWAS data, massively parallel CRISPR screens and single cell transcriptome sequencing, we discovered target genes of noncoding variants for blood trait loci. The closest gene was often the target gene, but this was not always the case. We also identified trans-effects networks of noncoding variants when cis target genes encoded transcription factors, such as GFI1B and NFE2. We observed that GFI1B trans-target genes were enriched for GFI1B binding sites and fine-mapped GWAS variants, and expressed in human bone marrow progenitor cells, suggesting that GFI1B acts as a master regulator of blood traits. This platform will enable massively parallel assays to catalog the target genes of human noncoding variants in both cis and trans.

Immune checkpoint blockade (ICB) has transformed the treatment of metastatic cancer but is hindered by variable response rates. A key unmet need is the identification of biomarkers that predict treatment response. To address this, we analyzed six whole exome sequencing cohorts with matched disease outcomes to identify genes and pathways predictive of ICB response. To increase detection power, we focus on genes and pathways that are significantly mutated following correction for epigenetic, replication timing, and sequence-based covariates. Using this technique, we identify several genes (BCLAF1, KRAS, BRAF, andTP53)and pathways (MAPK signaling, p53 associated, and immunomodulatory) as predictors of ICB response and develop the Cancer Immunotherapy Response CLassifiEr (CIRCLE). Compared to tumor mutational burden alone, CIRCLE led to superior prediction of ICB response with a 10.5% increase in sensitivity and a 11% increase in specificity. We envision that CIRCLE and more broadly the analysis of recurrently mutated cancer genes will pave the way for better prognostic tools for cancer immunotherapy.

In pluripotent cells, a delicate activation-repression balance maintains pro-differentiation genes ready for rapid activation. The identity of transcription factors (TFs) that specifically repress pro-differentiation genes remains obscure. By targeting ~1,700 TFs with CRISPR loss-of-function screen, we found that ZBTB11 and ZFP131 are required for embryonic stem cell (ESC) pluripotency. ESCs without ZBTB11 or ZFP131 lose colony morphology, reduce proliferation rate and upregulate transcription of genes associated with three germ layers. ZBTB11 and ZFP131 bind proximally to pro-differentiation genes. ZBTB11 or ZFP131 loss leads to an increase in H3K4me3, NELF complex release, and concomitant transcription at associated genes. Together, our results suggest that ZBTB11 and ZFP131 maintain pluripotency by preventing premature expression of pro-differentiation genes and present a generalizable framework to maintain cellular potency.

Recently, a novel isolate of the SARS-CoV-2 virus carrying a point mutation in the Spike protein (D614G) has emerged and rapidly surpassed others in prevalence, including the original SARS-CoV-2 isolate from Wuhan, China. This Spike variant is a defining feature of the most prevalent clade (A2a) of SARS-CoV-2 genomes worldwide. Using phylogenomic data, several groups have proposed that the D614G variant may confer increased transmissibility leading to positive selection, while others have claimed that currently available evidence does not support positive selection. Furthermore, in the A2a clade, this mutation is in linkage disequilibrium with a ORF1b protein variant (P314L), making it difficult to discern the functional significance of the Spike D614G mutation from population genetics alone. Here, we perform site-directed mutagenesis on a human codon-optimized spike protein to introduce the D614G variant and produce SARS-CoV-2-pseudotyped lentiviral particles (S-Virus) with this variant and with D614 Spike. We show that in multiple cell lines, including human lung epithelial cells, that S-Virus carrying the D614G mutation is up to 8-fold more effective at transducing cells than wild-type S-Virus. This provides functional evidence that the D614G mutation in the Spike protein increases transduction of human cells. Further we show that the G614 variant is more resistant to cleavage in vitro and in human cells, which may suggest a possible mechanism for the increased transduction. Given that several vaccines in development and in clinical trials are based on the initial (D614) Spike sequence, this result has important implications for the efficacy of these vaccines in protecting against this recent and highly-prevalent SARS-CoV-2 isolate.

BackgroundMany neurodegenerative diseases (NDs) develop only later in life, when cells in the nervous system lose their structure or function. In genetic forms of NDs, this late onset phenomenon remains largely unexplained.ResultsAnalyzing single cell RNA sequencing (scRNA-seq) from Alzheimer’s disease (AD) patients, we find increased transcriptional heterogeneity in AD excitatory neurons. We hypothesized that transcriptional heterogeneity precedes ND pathologies. To test this idea experimentally, we used juvenile forms (72Q; 180Q) of Huntington’s disease (HD) iPSCs, differentiated them into committed neuronal progenitors, and obtained single cell expression profiles. We show a global increase in gene expression variability in HD. Autophagy genes become more stable, while energy and actin-related genes become more variable in the mutant cells. Knocking-down several differentially-variable genes resulted in increased aggregate formation, a pathology associated with HD. We further validated the increased transcriptional heterogeneity in CHD8+/- cells, a model for autism spectrum disorder.ConclusionsOverall, our results suggest that although NDs develop over time, transcriptional regulation imbalance is present already at very early developmental stages. Therefore, an intervention aimed at this early phenotype may be of high diagnostic value.

In pluripotent cells, a delicate activation-repression balance maintains pro-differentiation genes ready for rapid activation. The identity of transcription factors (TFs) that specifically repress pro-differentiation genes remains obscure. By targeting ∼1,700 TFs with CRISPR loss-of-function screen, we found that ZBTB11 and ZFP131 are required for embryonic stem cell (ESC) pluripotency. ESCs without ZBTB11 or ZFP131 lose colony morphology, reduce proliferation rate, and upregulate transcription of genes associated with three germ layers. ZBTB11 and ZFP131 bind proximally to pro-differentiation genes. ZBTB11 or ZFP131 loss leads to an increase in H3K4me3, negative elongation factor (NELF) complex release, and concomitant transcription at associated genes. Together, our results suggest that ZBTB11 and ZFP131 maintain pluripotency by preventing premature expression of pro-differentiation genes and present a generalizable framework to maintain cellular potency.

In pluripotent cells, a delicate activation-repression balance maintains pro-differentiation genes ready for rapid activation. The identity of transcription factors (TFs) that specifically repress pro-differentiation genes remains obscure. By targeting ~1,700 TFs with CRISPR loss-of-function screen, we found that ZBTB11 and ZFP131 are required for embryonic stem cell (ESC) pluripotency. ZBTB11 and ZFP131 maintain promoter-proximally paused Polymerase II at pro-differentiation genes in ESCs. ZBTB11 or ZFP131 loss leads to NELF pausing factor release, an increase in H3K4me3, and transcriptional upregulation of genes associated with all three germ layers. Together, our results suggest that ZBTB11 and ZFP131 maintain pluripotency by preventing premature expression of pro-differentiation genes and present a generalizable framework to maintain cellular potency.One-sentence summaryA Transcription Factor-wide CRISPR screen identifies ZBTB11 and ZFP131 maintaining pluripotency by pausing POL II at pro-differentiation genes

Pooled CRISPR screens have been used to identify genes responsible for specific phenotypes and diseases, and, more recently, to connect genetic perturbations with multi-dimensional gene expression profiles. Here, we describe a method to link genome-wide chromatin accessibility to genetic perturbations in single cells. This scalable, cost-effective method combines pooled CRISPR perturbations with a single-cell combinatorial indexing assay for transposase-accessible chromatin (CRISPR-sciATAC). Using a human and mouse species-mixing experiment, we show that CRISPR-sciATAC separates single cells with a low doublet rate. Then, in human myelogenous leukemia cells, we apply CRISPR-sciATAC to target 21 chromatin-related genes that are frequently mutated in cancer and 84 subunits and cofactors of chromatin remodeling complexes, generating chromatin accessibility data for ~30,000 single cells. Using this large-scale atlas, we correlate loss of specific chromatin remodelers with changes in accessibility — globally and at the binding sites of individual transcription factors. For example, we show that loss of the H3K27 methyltransferase EZH2 leads to increased accessibility at heterochromatic regions involved in embryonic development and triggers expression of multiple genes in the HOXA and HOXD clusters. At a subset of regulatory sites, we also analyze dynamic changes in nucleosome spacing upon loss of chromatin remodelers. CRISPR-sciATAC is a high-throughput, low-cost single-cell method that can be applied broadly to study the role of genetic perturbations on chromatin in normal and disease states.

CRISPR-Cas13 mediates robust transcript knockdown in human cells through direct RNA targeting. Compared to DNA-targeting CRISPR enzymes like Cas9, RNA targeting by Cas13 is transcript- and strand-specific: It can distinguish and specifically knock-down processed transcripts, alternatively spliced isoforms and overlapping genes, all of which frequently serve different functions. Previously, we identified optimal design rules for RfxCas13d guide RNAs (gRNAs), and developed a computational model to predict gRNA efficacy for all human protein-coding genes. However, there is a growing interest to target other types of transcripts, such as noncoding RNAs (ncRNAs) or viral RNAs, and to target transcripts in other commonly-used organisms. Here, we predicted relative Cas13-driven knock-down for gRNAs targeting messenger RNAs and ncRNAs in six model organisms (human, mouse, zebrafish, fly, nematode and flowering plants) and four abundant RNA virus families (SARS-CoV-2, HIV-1, H1N1 influenza and MERS). To allow for more flexible gRNA efficacy prediction, we also developed a web-based application to predict optimal gRNAs for any RNA target entered by the user. Given the lack of Cas13 guide design tools, we anticipate this resource will facilitate CRISPR-Cas13 RNA targeting in common model organisms, emerging viral threats to human health, and novel RNA targets.

Clustered Regularly Interspace Short Palindromic Repeats (CRISPR)-Cas9 genome editing methods provide the tools necessary to examine phenotypic impacts of targeted perturbations in high-throughput screens. While these technologies have the potential to reveal functional elements with direct therapeutic applications, statistical techniques to analyze noncoding screen data remain limited. We present CRISPR-Decryptr, a computational tool for the analysis of CRISPR noncoding screens. Our method leverages experimental design: accounting for multiple conditions, controls, and replicates to infer the regulatory landscape of noncoding genomic regions. We validate our method on a variety of mutagenesis, CRISPR activation, and CRISPR interference screens, extracting new insights from previously published data.

The emergence of CRISPR-Cas9 gene-editing technologies and genome-wide CRISPR-Cas9 libraries enables efficient unbiased genetic screening that can accelerate the process of therapeutic discovery for genetic disorders. Here, we demonstrate the utility of a genome-wide CRISPR-Cas9 loss-of-function library to identify therapeutic targets for facioscapulohumeral muscular dystrophy (FSHD), a genetically complex type of muscular dystrophy for which there is currently no treatment. In FSHD, both genetic and epigenetic changes lead to misexpression of DUX4, the FSHD causal gene that encodes the highly cytotoxic DUX4 protein. We performed a genome-wide CRISPR-Cas9 screen to identify genes whose loss-of-function conferred survival when DUX4 was expressed in muscle cells. Genes emerging from our screen illuminated a pathogenic link to the cellular hypoxia response, which was revealed to be the main driver of DUX4-induced cell death. Application of hypoxia signaling inhibitors resulted in increased DUX4 protein turnover and subsequent reduction of the cellular hypoxia response and cell death. In addition, these compounds proved successful in reducing FSHD disease biomarkers in patient myogenic lines, as well as improving structural and functional properties in two zebrafish models of FSHD. Our genome-wide perturbation of pathways affecting DUX4 expression has provided insight into key drivers of DUX4-induced pathogenesis and has identified existing compounds with potential therapeutic benefit for FSHD. Our experimental approach presents an accelerated paradigm towards mechanistic understanding and therapeutic discovery of a complex genetic disease, which may be translatable to other diseases with well-established phenotypic selection assays.

SUMMARY A key limitation of the widely used CRISPR enzyme S. pyogenes Cas9 is the strict requirement of an NGG protospacer-adjacent motif (PAM) at the target site. This constraint can be limiting for genome editing applications that require precise Cas9 positioning. Recently, two Cas9 variants with a relaxed PAM requirement (NG) have been developed (xCas9 and Cas9-NG), but their activity has been measured at only a small number of endogenous sites. Here, we devise a high-throughput Cas9 pooled competition screen to compare the performance of Cas9 variants at thousands of genomic loci for gene knockout, transcriptional activation, and inhibition. We show that PAM flexibility comes at a substantial cost of decreased DNA targeting and cleavage. Of the PAM-flexible variants, we find that Cas9-NG outperforms xCas9 regardless of genome engineering modality or PAM. Finally, we combine xCas9 mutations with those of Cas9-NG, creating a stronger transcriptional modulator than existing PAM-flexible Cas9 variants., In Brief Cas9 requires an NGG protospacer-adjacent motif (PAM) at its DNA target site. Here, Legut et al. benchmark Cas9 and two recently developed PAM-flexible variants, showing that PAM flexibility comes with reduced efficacy. The authors also report a hybrid enzyme combining mutations from both PAM-flexible variants, demonstrating its improved efficacy for transcriptional activation., Graphical Abstract

RNA-targeting CRISPR-Cas13 proteins have recently emerged as a powerful platform to transiently modulate gene expression outcomes. However, protein and CRISPR RNA (crRNA) delivery in human cells can be challenging and knockdown can be transient due to rapid crRNA degradation. Here we compare several chemical RNA modifications at different positions to identify synthetic crRNAs that improve RNA targeting efficiency and half-life in human cells. We show that co-delivery of modified crRNAs and recombinant Cas13 enzyme in ribonucleoprotein (RNP) complexes enables transient gene expression modulation in primary CD4+ and CD8+ T-cells. This system represents a robust and efficient method to transiently modulate transcripts without genetic manipulation.

Type VI CRISPR enzymes have recently been identified as programmable RNA-guided, RNA-targeting Cas proteins with nuclease activity that allow for specific and robust target gene knock-down without altering the genome. However, we currently lack information about optimal Cas13 guide RNA designs for high target RNA knock-down efficacy. To close this gap, we conducted four massively-parallel Cas13 screens targeting the mRNA of a destabilized green fluorescent protein (GFP) transgene and CD46, CD55 and CD71 cell surface proteins in human cells. In total, we measured the activity of 24,460 guide RNA including 6,469 perfect match guide RNAs and a diverse set of guide RNA variants and permutations with mismatches relative to the target sequences.We find that guide RNAs show high diversity in knock-down efficiency driven by crRNA-specific features as well as target site context. Moreover, while single mismatches generally reduce knock-down to a modest degree, we identify a critical region spanning spacer nucleotides 15 – 21 that is largely intolerant to target site mismatches. We developed a computational model to identify guide RNAs with high knock-down efficacy. We confirmed the model’s generalizability across a large number of endogenous target mRNAs and show that Cas13 can be used in forward genetic pooled CRISPR-screens to identify essential genes. Using this model, we provide a resource of optimized Cas13 guide RNAs to target all protein-coding transcripts in the human genome, enabling transcriptome-wide forward genetic screens.

Despite recent therapeutic advances in the management of non-Hodgkin lymphoma (NHL), up to 50% of patients with diffuse large B-cell lymphoma (DLBCL) relapse after first line therapy, and for DLBCL patients who relapse within 12 months after subsequent stem cell transplant (SCT), the median overall survival (OS) is 6.3 months. Recently, chimeric antigen receptor (CAR) T-cell therapy has shown remarkable activity in relapsed DLBCL with complete response (CR) rate of 40% and 54% for the two of the FDA-approved CAR T-cell products, tisagenlecleucel and axicabtagene ciloleucel, respectively. However, at a median follow-up of 18 months, only 36% of patients treated with tisagenlecleucel remained in CR; with longer follow-up for axicabtagene ciloleucel the median progression free survival (PFS) was 5.9 months. Immune escape and immune evasion are primary mechanisms of CAR-T resistance; clearly improvements are needed to increase response rate and cure. While CRISPR-based loss-of-function screens have shown promise for high-throughput identification of genes that modulate T-cell response, these methods have been limited thus far to negative regulators of T-cell functions, and raise safety concerns due to the permanent nature of genome modification. Here we identify positive T-cell regulators via overexpression of ~12,000 barcoded human open reading frames (ORFs). Using this genome-scale ORF screen, we found modulator genes which increased primary human CD4+ and CD8+ T-cell proliferation, including activation markers like CD25 and CD40L, and secretion of key cytokines like interleukin-2 and interferon-gamma. In addition, we developed a single-cell genomics method (OverCITE-seq) for high-throughput quantification of the transcriptome and surface proteome in ORF-engineered T-cells. The top-ranked ORF, lymphotoxin beta receptor (LTBR), is typically expressed in a subset of myeloid cells but absent in lymphocytes. When expressed in T-cells, LTBR induces a profound transcriptional remodelling, resulting in increased resistance to exhaustion and activation-induced apoptosis, as well as upregulation of a plethora of proinflammatory cytokines, co-stimulatory molecules and antigen presentation machinery. In order to investigate the mechanism of action of LTBR, we developed an epistasis assay which allows for simultaneous gene knockout and LTBR overexpression in primary T cells. Thus, LTBR appears to induce both canonical and non-canonical NFkB pathways - but the phenotype observed in T cells is dependent only on the former. Finally, we co-expressed several top-ranked genes, including LTBR, with FDA approved CD19-targeting CARs utilizing either 4-1BB or CD28 co-stimulatory domains. In line with previous results, co-expression of top-ranked ORFs increased proinflammatory cytokine secretion and cytotoxicity against CD19+ positive cancer cell lines. This functional improvement was also observed when top-ranked ORFs and CARs were delivered to T cells isolated from DLBCL patients as shown in Figure 1. Our results provide several strategies for improving next generation CAR T-cell therapies via induction of new synthetic cell programs which may optimize immune activation and enhance the efficacy of these important therapies, a high priority for patients with relapsed and refractory DLBCL and other lymphomas. Figure 1 Figure 1. Disclosures Mimitou: Immunai: Current Employment. Smibert: Immunai: Current Employment. Diefenbach: Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding; IMab: Research Funding; Gilead: Current equity holder in publicly-traded company; Celgene: Research Funding; AbbVie: Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Merck Sharp & Dohme: Consultancy, Honoraria, Research Funding; IGM Biosciences: Research Funding; Morphosys: Consultancy, Honoraria, Research Funding; MEI: Consultancy, Research Funding; Perlmutter Cancer Center at NYU Langone Health: Current Employment; Incyte: Research Funding; Trillium: Research Funding; Seattle Genetics: Consultancy, Honoraria, Research Funding; Genentech, Inc./ F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding. Sanjana: Qiagen: Consultancy; Vertex: Consultancy.

In the race to publish papers and secure funding, science can sometimes seem like a competition. But, in reality, modern science relies on open sharing and collaboration. One unexpected aspect of open science is the role it has played in uplifting the careers of myself and my lab members., Drawing from his personal experience, Neville Sanjana highlights how open science benefits academic careers.

Genome editing technologies such as Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) systems have ushered in a new era of targeted DNA manipulation. The easy programmability of CRISPR using short oligonucleotides enables rapid synthesis of large-scale libraries for functional genetic screens. Here we present fundamental concepts and methods for pooled CRISPR screens and review biological results from recent genome-scale loss-of-function and gain-of-function screens. We also discuss new frontiers in pooled screens, including novel effector domains for functional screens and applications in the noncoding genome.

Recurrent chromosomal translocations producing a chimaeric MLL oncogene give rise to a highly aggressive acute leukaemia associated with poor clinical outcome. The preferential involvement of chromatin-associated factors as MLL fusion partners belies a dependency on transcription control. Despite recent progress made in targeting chromatin regulators in cancer, available therapies for this well-characterized disease remain inadequate, prompting the need to identify new targets for therapeutic intervention. Here, using unbiased CRISPR-Cas9 technology to perform a genome-scale loss-of-function screen in an MLL-AF4-positive acute leukaemia cell line, we identify ENL as an unrecognized gene that is specifically required for proliferation in vitro and in vivo. To explain the mechanistic role of ENL in leukaemia pathogenesis and dynamic transcription control, a chemical genetic strategy was developed to achieve targeted protein degradation. Acute loss of ENL suppressed the initiation and elongation of RNA polymerase II at active genes genome-wide, with pronounced effects at genes featuring a disproportionate ENL load. Notably, an intact YEATS chromatin-reader domain was essential for ENL-dependent leukaemic growth. Overall, these findings identify a dependency factor in acute leukaemia and suggest a mechanistic rationale for disrupting the YEATS domain in disease.

SummaryAll current highly effective anti-tumor immunotherapeutics depend on the activity of T cells, but tumor cells can escape immune recognition by several mechanisms including loss of function in antigen presentation and inflammatory response genes, expression of immunomodulatory proteins and an immunosuppressive tumor microenvironment. In contrast, the comprehensive identification of strategies that sensitize tumor cells to immunotherapy in vivo has remained challenging. Here, we combine a two-cell type (2CT) whole-genome CRISPR-Cas9 screen with dynamic transcriptional analysis (DTA) of tumor upon T cell encounter to identify a set of genes that tumor cells express as an active defense against T cell-mediated killing. We then employed small molecule and biologic screens designed to antagonize gene products employed by tumor cells to actively defend against T cell-mediated tumor destruction and found that the inhibition of BIRC2, ITGAV or DNPEP enhanced tumor cell destruction by T cells. Mechanistically, we found that BIRC2 promoted immunotherapy resistance through inhibiting non-canonical NF-κB signaling and limiting inflammatory chemokine production. These findings show the path forward to improving T cell-mediated tumor destruction in the clinic.

For genome-wide screens and other applications that require the processing of a large number of cells, the immunomagnetic sorting of cells on a microfluidic chip is a scalable, rapid and cost-efficient alternative to fluorescence-activated cell sorting.

CRISPR screens have been used to connect genetic perturbations with changes in gene expression and phenotypes. Here we describe a CRISPR-based, single-cell combinatorial indexing assay for transposase-accessible chromatin (CRISPR–sciATAC) to link genetic perturbations to genome-wide chromatin accessibility in a large number of cells. In human myelogenous leukemia cells, we apply CRISPR–sciATAC to target 105 chromatin-related genes, generating chromatin accessibility data for ~30,000 single cells. We correlate the loss of specific chromatin remodelers with changes in accessibility globally and at the binding sites of individual transcription factors (TFs). For example, we show that loss of the H3K27 methyltransferase EZH2 increases accessibility at heterochromatic regions involved in embryonic development and triggers expression of genes in the HOXA and HOXD clusters. At a subset of regulatory sites, we also analyze changes in nucleosome spacing following the loss of chromatin remodelers. CRISPR–sciATAC is a high-throughput, single-cell method for studying the effect of genetic perturbations on chromatin in normal and disease states. The effects of gene knockouts on chromatin accessibility are measured with single-cell CRISPR screens.

Overexpression of mouse neurogenin ( Neurog) 2 alone or in combination with mouse Neurog2/1 in human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) can rapidly produce high-yield excitatory neurons. Here, we report a detailed characterization of human neuronal networks induced by the expression of human NEUROG2 together with human NEUROG2/1 in hESCs using molecular, cellular, and electrophysiological measurements over 60 d after induction. Both excitatory synaptic transmission and network firing activity increased over time. Strikingly, inhibitory synaptic transmission and GABAergic cells were identified from NEUROG2/1 induced neurons (iNs). To illustrate the application of such iNs, we demonstrated that the heterozygous knock out of SCN2A, whose loss-of-function mutation is strongly implicated in autism risk, led to a dramatic reduction in network activity in the NEUROG2/1 iNs. Our findings not only extend our understanding of the NEUROG2/1-induced human neuronal network but also substantiate NEUROG2/1 iNs as an in vitro system for modeling neuronal and functional deficits on a human genetic background.-Lu, C., Shi, X., Allen, A., Baez-Nieto, D., Nikish, A., Sanjana, N. E., Pan, J. Q. Overexpression of NEUROG2 and NEUROG1 in human embryonic stem cells produces a network of excitatory and inhibitory neurons.

To better understand host-virus genetic dependencies and find potential therapeutic targets for COVID-19, we performed a genome-scale CRISPR loss-of-function screen to identify host factors required for SARS-CoV-2 viral infection of human alveolar epithelial cells. Top-ranked genes cluster into distinct pathways, including the vacuolar ATPase proton pump, Retromer, and Commander complexes. We validate these gene targets using several orthogonal methods such as CRISPR knockout, RNA interference knockdown, and small-molecule inhibitors. Using single-cell RNA-sequencing, we identify shared transcriptional changes in cholesterol biosynthesis upon loss of top-ranked genes. In addition, given the key role of the ACE2 receptor in the early stages of viral entry, we show that loss of RAB7A reduces viral entry by sequestering the ACE2 receptor inside cells. Overall, this work provides a genome-scale, quantitative resource of the impact of the loss of each host gene on fitness/response to viral infection.