NOTCH signaling is required for the arterial specification and formation of hematopoietic stem cells (HSCs) and lympho-myeloid progenitors in the embryonic aorta-gonad-mesonephros region and extraembryonic vasculature from a distinct lineage of vascular endothelial cells with hemogenic potential. However, the role of NOTCH signaling in hemogenic endothelium (HE) specification from human pluripotent stem cell (hPSC) has not been studied. Here, using a chemically defined hPSC differentiation system combined with the use of DLL1-Fc and DAPT to manipulate NOTCH, we discover that NOTCH activation in hPSC-derived immature HE progenitors leads to formation of CD144+CD43−CD73−DLL4+Runx1 + 23-GFP+ arterial-type HE, which requires NOTCH signaling to undergo endothelial-to-hematopoietic transition and produce definitive lympho-myeloid and erythroid cells. These findings demonstrate that NOTCH-mediated arterialization of HE is an essential prerequisite for establishing definitive lympho-myeloid program and suggest that exploring molecular pathways that lead to arterial specification may aid in vitro approaches to enhance definitive hematopoiesis from hPSCs.

SUMMARY SOX17 has been implicated in arterial specification and the maintenance of hematopoietic stem cells (HSCs) in the murine embryo. However, knowledge about molecular pathways and stage-specific effects of SOX17 in humans remains limited. Here, using SOX17-knockout and SOX17-inducible human pluripotent stem cells (hPSCs), paired with molecular profiling studies, we reveal that SOX17 is a master regulator of HOXA and arterial programs in hemogenic endothelium (HE) and is required for the specification of HE with robust lympho-myeloid potential and DLL4 + CXCR4 + phenotype resembling arterial HE at the sites of HSC emergence. Along with the activation of NOTCH signaling, SOX17 directly activates CDX2 expression, leading to the upregulation of the HOXA cluster genes. Since deficiencies in HOXA and NOTCH signaling contribute to the impaired in vivo engraftment of hPSC-derived hematopoietic cells, the identification of SOX17 as a key regulator linking arterial and HOXA programs in HE may help to program HSC fate from hPSCs.

Mycoplasma (M.) hyorhinis and M. hyosynoviae are pathogens known to cause disease in pigs post-weaning. Due to their fastidious nature, there is increased need for culture-independent diagnostic platforms to detect these microorganisms. Therefore, this study was performed to develop and optimize quantitative real-time PCR (qPCR) assays to rapidly detect M. hyorhinis and M. hyosynoviae in pen-based oral fluids as well as nasal and tonsillar fluids as proxies for samples used in swine herd surveillance. Two methods of genomic DNA extraction, automated versus manual, were used to compare diagnostic test performance. A wean-to-finish longitudinal study was also carried out to demonstrate the reproducibility of using pen-based oral fluids. Overall, pen-based oral and tonsillar fluids were more likely to be positive for both types of bacteria whereas only M. hyorhinis was detected in nasal fluids. DNA extraction protocols were shown to significantly influence test result. Although the initial detection time somewhat differed, both organisms were repeatedly detected in the longitudinal study. Overall, this study evaluated two qPCR methods for rapid and specific detection of either mycoplasma. Results from the present investigation can serve as a foundation for future studies to determine the prevalence of the two microorganisms, environmental load, and effectiveness of veterinary interventions for infection control.

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Administration of ex vivo expanded somatic myeloid progenitors has been explored as a way to facilitate a more rapid myeloid recovery and improve overall survival following myeloablation. Recent advances in induced pluripotent stem cell (iPSC) technologies have created alternative platforms for supplying off-the-shelf immunologically compatible myeloid progenitors, including cellular products derived from major histocompatibility complex (MHC) homozygous "superdonors", potentially increasing the availability of MHC- matching cells and maximizing the utility for stem cell banking. However, it is unclear the teratogenic and tumorigenic potential of iPSC-derived progenitor cells and whether they will induce alloreactive antibodies upon transfer. Here, we evaluated the safety and efficacy of using CD34+CD45+ hematopoietic progenitors derived from MHC homozygous iPSCs (iHPs) for treating cytopenia following myeloablative HSC transplants in a Mauritian cynomolgus macaque (MCM) nonhuman primate (NHP) model. We demonstrated that infusing iHPs is well-tolerated and safe, observing no teratomas or tumors in the MCMs up to one year after HSC transplant and iHP infusion. Importantly, the iHPs also did not induce significant levels of alloantibodies in MHC-matched or -mismatched immunocompetent MCMs, even after increasing MHC expression on iHPs with IFNγ. These results suggest feasibility of iHP use in the setting of myeloablation and that iHP products pose a low risk of inducing alloreactive antibodies.

Abstract. The purpose of this study was to determine the in vitro and ex vivo susceptibility of human corneal cells to West Nile virus (WNV) infection and evaluate the ability of the virus to disseminate to the corneas of infected mice. Human corneal epithelial cells were challenged with WNV, incubated for 1-6 days, and tested for evidence of WNV infection. Viral RNA and antigen were detected at every time point, and the virus reached a peak titer of 2.5 × 10 7 plaque-forming units (pfu)/mL at 3 days postinoculation (PI). Corneas procured from donors were incubated in culture dishes containing WNV for 1-5 days and tested for evidence of WNV. Viral RNA and antigen were detected, and the virus reached a mean peak titer of 4.9 × 10 4 pfu/mL at 5 days PI. Mice were inoculated intraperitoneally with WNV, and their eyes were harvested at 2, 5, and 8 days PI and tested for evidence of WNV. Viral RNA was detected in corneas of four of nine systemically infected mice as early as 2 days PI. We conclude that human corneal cells support WNV replication in vitro and ex vivo, and WNV may disseminate into the corneas of experimentally infected mice. These findings indicate that corneal transmission cannot be ruled out as a novel mode of human-to-human WNV transmission and additional experiments should be conducted to assess this risk further.

Recent advances in understanding the major bottlenecks in derivation of engraftable HSCs and lymphoid cells from pluripotent stem cells (PSC), have identified deficiencies in NOTCH and HOXA signaling as contributing factors to the observed functional deficits of PSC-derived hematopoietic progenitors. However, little is known about the mechanisms that are essential for establishing these pathways during PSC differentiation. Here, we revealed the critical role of SOX17 in linking HOXA and NOTCH-mediated arterial programs in hemogenic endothelium (HE) and specification of definitive lympho-myeloid hematopoiesis. Using SOX17-knockout (SOX17-/-) and SOX17 DOX-inducible (iSOX17) hESCs, we found that SOX17-deficiency substantially reduces formation of CD144+CD43-CD73-DLL4+CXCR4+/- arterial HE and definitive lympho-myeloid hematopoiesis, while SOX17 upregulation at mesodermal stage of development causes the opposite effect. Molecular profiling of HE generated from iSOX17 hESCs in DOX+ and DOX- conditions using RNAseq, SOX17 ChIPseq and ATACseq, revealed that SOX17 overexpression upregulates 522 genes enriched in NOTCH, TGFb, HEDGEHOG and WNT signaling, including DLL1, DLL4, NOTCH4, LFNG, WNT5a, WNT5b, GLI3, and genes associated with HSC development, CXCR4,KITLG and ALDH1A2. In addition, we noted significant upregulation of HOXA7,HOXA9, HOXA10, HOXB8, HOXC4 and CDX2 homeobox genes in SOX17-induced cultures, with no expression of HOXA genes observed in HE from SOX17-/- cells. ChIPSeq analysis revealed DOX+ specific SOX17 binding at transcriptional start sites (TSS) of 316 significantly upregulated genes, including ALDH1A2, CDX2, DLL1, DLL4, HEY1, HOXA7, HOXB8, HOXC4 and KITLG, suggesting that upregulation of these genes could be explained by their direct activation by SOX17. Since ALDH1A2 and CDX2 are known to play a role in the activation of HOXA genes, we investigated whether SOX17's effect on HOXA expression could also be mediated by ALDH1A2 and CDX2. We found that adding ALDH1 inhibitor to DOX+ cultures had no effect on arterial HE development and HOXA expression. In contrast, transfection of iSOX17 hPSCs cultures with CDX2 shRNA significantly decreased arterial HE formation and downregulated HOXA7, HOXA9, and HOXA10 expression. Overall, our studies indicate that SOX17 plays a critical role in the activation and integration of arterial and HOXA programs in HE, which is mediated by CDX2. These findings will be important for designing a strategy for direct HSC fate programming from hPSCs. Disclosures Uenishi: Casebia Therapeutics: Employment. Slukvin:Cynata Therapeutics: Consultancy, Other: Founder and Stockholder.

Mycoplasma (M.) hyosynoviae is known to colonize and cause disease in growing-finishing pigs. In this study, two clinical isolates of M. hyosynoviae were compared by inoculating cesarean-derived colostrum-deprived and specific-pathogen-free growing pigs. After intranasal or intravenous inoculation, the proportion and distribution pattern of clinical cases was compared in addition to the severity of lameness. Tonsils were found to be the primary site of colonization, while bacteremia was rarely detected prior to the observation of clinical signs. Regardless of the clinical isolate, route of inoculation, or volume of inocula, histopathological alterations and tissue invasion were detected in multiple joints, indicating an apparent lack of specific joint tropism. Acute disease was primarily observed 7 to 10 days post-inoculation. The variability in the severity of synovial microscopic lesions and pathogen detection in joint cavities suggests that the duration of joint infection may influence the diagnostic accuracy. In summary, these findings demonstrate that diagnosis of M. hyosynoviae-associated arthritis can be influenced by the clinical isolate, and provides a study platform to investigate the colonization and virulence potential of field isolates. This approach can be particularly relevant to auxiliate in surveillance and testing of therapeutic and/or vaccine candidates.