A human fetal liver-derived infant MLL-AF4 acute lymphoblastic leukemia model reveals a distinct fetal gene expression program

Although 90% of children with acute lymphoblastic leukemia (ALL) are now cured, the prognosis for infant-ALL remains dismal. Infant-ALL is usually caused by a single genetic hit that arises in utero: an MLL/KMT2A gene rearrangement (MLL-r). This is sufficient to induce a uniquely aggressive and treatment-refractory leukemia compared to older children. The reasons for disparate outcomes in patients of different ages with identical driver mutations are unknown. Using the most common MLL-r in infant-ALL, MLL-AF4, as a disease model, we show that fetal-specific gene expression programs are maintained in MLL-AF4 infant-ALL but not in MLL-AF4 childhood-ALL. We use CRISPR-Cas9 gene editing of primary human fetal liver hematopoietic cells to produce a t(4;11)/MLL-AF4 translocation, which replicates the clinical features of infant-ALL and drives infant-ALL-specific and fetal-specific gene expression programs. These data support the hypothesis that fetal-specific gene expression programs cooperate with MLL-AF4 to initiate and maintain the distinct biology of infant-ALL.

WNT5A from the fetal liver vascular niche supports human fetal liver hematopoiesis

The human fetal liver is a critical organ for prenatal hematopoiesis, the study of which offers insights into niche signals that regulate the fates of hematopoietic stem and progenitor cells (HSPCs) during fetal development. Here, we demonstrate that human fetal liver endothelium uniquely supports the maturation and expansion of multilineage HSPCs. Specifically, co-culture of fetal liver-derived immature CD43+CD45− hematopoietic cells with human fetal liver endothelial cells (ECs) led to a profound increase in the numbers of phenotypic CD45+CD34+ HSPCs and multilineage colony-forming progenitors generated in vitro, when compared to co-culture with ECs derived from other organs. We further identified a supportive role for EC-derived WNT5A in this process via gain- and loss-of-function studies within ECs. Our study emphasizes the importance of the organ-specific endothelial niche in supporting hematopoietic development and provides novel insight into signals that may facilitate HSPC expansion in vitro for clinical applications.

Expression Patterns of Analgesic Metabolising Machinery in 1st and 2nd Trimester Human Fetal Liver and Gonads

Use of over-the-counter analgesics during pregnancy is widespread globally. Most analgesic compounds can freely diffuse through the placental feto-maternal interface and reach the developing fetus. Current literature suggests an endocrine disruptor (ED) potential of in utero exposure to these compounds. The liver is the primary site of contact with EDs in the fetus. Exposure of the fetal gonads can also alter reproductive function with potential intergenerational effects. We aimed to characterise the metabolic capability of these fetal organs. RNA sequencing was performed in 80 second trimester human fetal livers and 48 fetal gonads (balanced for fetal age and fetal sex). Samples were collected from elective terminations of normal pregnancies (liver 11-19 weeks, FeGo study: REC 04/S0802/21, and gonads 6-17 weeks, as previously described1. RNA was extracted and Illumina NextSeq was used to produce 76 bp single end (liver) or paired end 2x50 bp (gonads) sequencing reads. Reads were quality controlled, aligned to the human reference genome and quantified at gene regions. Statistical analyses involved an ANOVA model of two-way interactions between fetal sex and fetal age. All organs expressed phase I and II metabolising enzymes and drug transporters involved in the pharmacokinetic and pharmacodynamic pathways of over-the-counter analgesics. The human fetal liver expressed ABCC2, ABCC3, ABCC4 and ABCG2 receptors at similar levels between males and females. Expression of cytochrome p450 enzymes CYP2A6, CYP2C8, CYP2C9, CYP2E1, CYP3A4 involved in metabolism of the analgesics paracetamol and ibuprofen, all increased with gestational age in the liver. Expression of GSTM1, GSTP1, GSTT1, SULT1A1, SULT1A3, SULT1A4, SULT1E1, SULT2A1, UGT2B4, UGT2B7 and UGT2B15 metabolising enzymes also increased during gestation, while fetal hepatic GSTP1 expression showed a significant 2-way interaction between both sex and age. Fetal gonads expressed ABCC4 and ABCG2 transporters, with transcript levels demonstrating significant sex-specific and gestational age differences. Fewer analgesic metabolising enzymes were expressed in the gonads than the fetal liver, including CYP2E1, GSTP1 and SULT1A1, all significantly altered by gestation and fetal sex. Our results reveal expression of major analgesics metabolic and transport components within the human fetal liver, ovaries and testes between gestation weeks 7-19. Significant sex alterations in transcript levels also suggest sexually dimorphic metabolic activity of these organs during fetal life. In conclusion, analgesics can be transported into fetal liver and gonad cells and metabolised into bioactive forms, posing toxicity risks for the developing fetus.1. Lecluze E, Rolland AD, Filis P, et al. Dynamics of the transcriptional landscape during human fetal testis and ovary development. Hum Reprod. 2020;35(5):1099-1119.

A novel human fetal liver-derived model reveals that MLL-AF4 drives a distinct fetal gene expression program in infant ALL

ABSTRACTAlthough 90% of children with acute lymphoblastic leukemia (ALL) are now cured1, the prognosis of infant-ALL (diagnosis within the first year of life) remains dismal2. Infant-ALL is usually caused by a single genetic hit that arises in utero: rearrangement of the MLL/KMT2A gene (MLL-r). This is sufficient to give rise to a uniquely aggressive and treatment-refractory leukemia compared to older children with the same MLL-r3–5. The reasons for disparate outcomes in patients of different ages with identical driver mutations are unknown. This paper addresses the hypothesis that fetal-specific gene expression programs co-operate with MLL-AF4 to initiate and maintain infant-ALL. Using direct comparison of fetal and adult HSC and progenitor transcriptomes we identify fetal-specific gene expression programs in primary human cells. We show that MLL-AF4-driven infant-ALL, but not MLL-AF4 childhood-ALL, displays expression of fetal-specific genes. In a direct test of this observation, we find that CRISPR-Cas9 gene editing of primary human fetal liver cells to produce a t(4;11)/MLL-AF4 translocation replicates the clinical features of infant-ALL and drives infant-ALL-specific and fetal-specific gene expression programs. These data strongly support the hypothesis that fetal-specific gene expression programs co-operate with MLL-AF4 to initiate and maintain the distinct biology of infant-ALL.

A murine model demonstrating reversal of structural and functional correlates of cirrhosis with progenitor cell transplantation

Development of cell transplantation for treating liver cirrhosis hinges critically on the availability of animal models for studying human stem cell transplantation. We report an immune-permissive murine model of liver cirrhosis with full clinical correlates of decompensated liver disease, and allows testing efficacy of stem cell transplantation. Liver cirrhosis was induced in Nod-scid gamma(NSG) mice with oral thioacetamide(TA) and compared to controls over 12 months. 4 month TA treated cirrhotic mice were then transplanted intrasplenically with 2million human fetal liver progenitor cells(HFH) and compared with cirrhotic controls 2 months after transplantation. NSG-TA mice developed shrunken and nodular livers with histological evidence of fibrosis as compared to controls. This was associated with evidence of worsening decompensated liver disease, with jaundice, hypoalbuminemia, coagulopathy, and encephalopathy in NSG-TA mice. Transplantation of HFH resulted in improvement in both fibrosis and markers of decompensated liver disease. We have demonstrated that NSG-TA mice can recapitulate the full clinical picture of structural and functional cirrhosis, both of which can be improved by transplantation of human fetal liver cells. This model serves as a valuable tool for validation of in vivo liver stem cell transplantation and opens up opportunities for studying the mechanism how stem cells reverse fibrosis.