Robust temporal map of human in vitro myelopoiesis using single-cell genomics.

Myeloid cells are central to homeostasis and immunity. Characterising in vitro myelopoiesis protocols is imperative for their use in research, immunotherapies, and understanding human myelopoiesis. Here, we generate a >470K cells molecular map of human induced pluripotent stem cells (iPSC) differentiation into macrophages. Integration with in vivo single-cell atlases shows in vitro differentiation recapitulates features of yolk sac hematopoiesis, before definitive hematopoietic stem cells (HSC) emerge. The diversity of myeloid cells generated, including mast cells and monocytes, suggests that HSC-independent hematopoiesis can produce multiple myeloid lineages. We uncover poorly described myeloid progenitors and conservation between in vivo and in vitro regulatory programs. Additionally, we develop a protocol to produce iPSC-derived dendritic cells (DC) resembling cDC2. Using CRISPR/Cas9 knock-outs, we validate the effects of key transcription factors in macrophage and DC ontogeny. This roadmap of myeloid differentiation is an important resource for investigating human fetal hematopoiesis and new therapeutic opportunities.

Genome-wide meta-analysis, fine-mapping and integrative prioritization implicate new Alzheimer's disease risk genes.

Genome-wide association studies have discovered numerous genomic loci associated with Alzheimer's disease (AD); yet the causal genes and variants are incompletely identified. We performed an updated genome-wide AD meta-analysis, which identified 37 risk loci, including new associations near CCDC6, TSPAN14, NCK2 and SPRED2. Using three SNP-level fine-mapping methods, we identified 21 SNPs with >50% probability each of being causally involved in AD risk and others strongly suggested by functional annotation. We followed this with colocalization analyses across 109 gene expression quantitative trait loci datasets and prioritization of genes by using protein interaction networks and tissue-specific expression. Combining this information into a quantitative score, we found that evidence converged on likely causal genes, including the above four genes, and those at previously discovered AD loci, including BIN1, APH1B, PTK2B, PILRA and CASS4.

Screening for functional transcriptional and splicing regulatory variants with GenIE.

Genome-wide association studies (GWAS) have identified numerous genetic loci underlying human diseases, but a fundamental challenge remains to accurately identify the underlying causal genes and variants. Here, we describe an arrayed CRISPR screening method, Genome engineering-based Interrogation of Enhancers (GenIE), which assesses the effects of defined alleles on transcription or splicing when introduced in their endogenous genomic locations. We use this sensitive assay to validate the activity of transcriptional enhancers and splice regulatory elements in human induced pluripotent stem cells (hiPSCs), and develop a software package (rgenie) to analyse the data. We screen the 99% credible set of Alzheimer's disease (AD) GWAS variants identified at the clusterin (CLU) locus to identify a subset of likely causal variants, and employ GenIE to understand the impact of specific mutations on splicing efficiency. We thus establish GenIE as an efficient tool to rapidly screen for the role of transcribed variants on gene expression.

ASXL1 mutation correction by CRISPR/Cas9 restores gene function in leukemia cells and increases survival in mouse xenografts.

Recurrent somatic mutations of the epigenetic modifier and tumor suppressor ASXL1 are common in myeloid malignancies, including chronic myeloid leukemia (CML), and are associated with poor clinical outcome. CRISPR/Cas9 has recently emerged as a powerful and versatile genome editing tool for genome engineering in various species. We have used the CRISPR/Cas9 system to correct the ASXL1 homozygous nonsense mutation present in the CML cell line KBM5, which lacks ASXL1 protein expression. CRISPR/Cas9-mediated ASXL1 homozygous correction resulted in protein re-expression with restored normal function, including down-regulation of Polycomb repressive complex 2 target genes. Significantly reduced cell growth and increased myeloid differentiation were observed in ASXL1 mutation-corrected cells, providing new insights into the role of ASXL1 in human myeloid cell differentiation. Mice xenografted with mutation-corrected KBM5 cells showed significantly longer survival than uncorrected xenografts. These results show that the sole correction of a driver mutation in leukemia cells increases survival in vivo in mice. This study provides proof-of-concept for driver gene mutation correction via CRISPR/Cas9 technology in human leukemia cells and presents a strategy to illuminate the impact of oncogenic mutations on cellular function and survival.

CSNK1A1 mutations and gene expression analysis in myelodysplastic syndromes with del(5q).

Mutations of CSNK1A1, a gene mapping to the commonly deleted region of the 5q- syndrome, have been recently described in patients with del(5q) myelodysplastic syndromes (MDS). Haploinsufficiency of Csnk1a1 in mice has been shown to result in ß-catenin activation and expansion of haematopoietic stem cells (HSC). We have screened a large cohort of 104 del(5q) MDS patients and have identified mutations of CSNK1A1 in five cases (approximately 5%). We have shown up-regulation of ß-catenin target genes in the HSC of patients with del(5q) MDS. Our data further support a central role of CSNK1A1 in the pathogenesis of MDS with del(5q).

Phase II trial of syncopated thalidomide, lenalidomide, and weekly dexamethasone in patients with newly diagnosed multiple myeloma.

UNLABELLED: Thalidomide and lenalidomide, in combination with dexamethasone, provide response rates ranging from 63%-79% after 4 cycles of therapy. Because of toxicities such as neuropathy and myelosuppression for thalidomide and lenalidomide, respectively, dose escalation has not been pursued. We evaluated a syncopated regimen of alternating weeks of thalidomide and lenalidomide to determine if a modified schedule allows for fewer dose reductions and, subsequently, superior efficacy. Although well tolerated, this phase II trial did not show superior efficacy compared with conventional dosing and scheduling of these agents. INTRODUCTION: Over the past decade, the novel agents thalidomide, lenalidomide, and bortezomib have emerged as effective treatment in patients with multiple myeloma (MM). Initially used in the relapse setting, these agents have been incorporated into frontline treatment algorithms. They have been combined in doublets with corticosteroids, in triplets with alkylators, or with each other. Because thalidomide and lenalidomide have different clinical activity and toxicity profiles, we designed a trial to evaluate a syncopated schedule of thalidomide and lenalidomide with weekly dexamethasone in patients with newly diagnosed MM to determine response and toxicity. PATIENTS AND METHODS: Twenty-two patients with newly diagnosed MM were treated with syncopated thalidomide (200 mg on days 1-7 and 15-21), lenalidomide (25 mg on days 8-14 and 22-28 for the first cycle and 50 mg on the same schedule for subsequent cycles) with weekly dexamethasone (40 mg). Each cycle lasted 28 days. MM parameters were assessed at the end of each cycle. It was intended that the patients proceed to stem cell mobilization and autologous transplantation after 4 cycles of therapy. RESULTS: The median number of cycles administered was 3.5. The overall response was 68%. The regimen was well tolerated by the majority of the patients; only patient discontinued treatment because of toxicity. CONCLUSION: We conclude that a syncopated schedule of thalidomide and lenalidomide with weekly dexamethasone was tolerated well, with no unexpected toxicities. However the response rate, even using lenalidomide at 50 mg, was not superior to standard dosing of thalidomide or lenalidomide plus dexamethasone.