Improving CRISPR-Cas specificity with chemical modifications in single-guide RNAs.

CRISPR systems have emerged as transformative tools for altering genomes in living cells with unprecedented ease, inspiring keen interest in increasing their specificity for perfectly matched targets. We have developed a novel approach for improving specificity by incorporating chemical modifications in guide RNAs (gRNAs) at specific sites in their DNA recognition sequence ('guide sequence') and systematically evaluating their on-target and off-target activities in biochemical DNA cleavage assays and cell-based assays. Our results show that a chemical modification (2'-O-methyl-3'-phosphonoacetate, or 'MP') incorporated at select sites in the ribose-phosphate backbone of gRNAs can dramatically reduce off-target cleavage activities while maintaining high on-target performance, as demonstrated in clinically relevant genes. These findings reveal a unique method for enhancing specificity by chemically modifying the guide sequence in gRNAs. Our approach introduces a versatile tool for augmenting the performance of CRISPR systems for research, industrial and therapeutic applications.

A mechanosensitive transcriptional mechanism that controls angiogenesis.

Angiogenesis is controlled by physical interactions between cells and extracellular matrix as well as soluble angiogenic factors, such as VEGF. However, the mechanism by which mechanical signals integrate with other microenvironmental cues to regulate neovascularization remains unknown. Here we show that the Rho inhibitor, p190RhoGAP (also known as GRLF1), controls capillary network formation in vitro in human microvascular endothelial cells and retinal angiogenesis in vivo by modulating the balance of activities between two antagonistic transcription factors, TFII-I (also known as GTF2I) and GATA2, that govern gene expression of the VEGF receptor VEGFR2 (also known as KDR). Moreover, this new angiogenesis signalling pathway is sensitive to extracellular matrix elasticity as well as soluble VEGF. This is, to our knowledge, the first known functional cross-antagonism between transcription factors that controls tissue morphogenesis, and that responds to both mechanical and chemical cues.

Tumor growth and angiogenesis are dependent on the presence of immature dendritic cells.

Dendritic cells (DCs)--immunomodulatory cells that initiate adaptive immune responses--have recently been shown to exert proangiogenic effects when infiltrating the tumor microenvironment. As tumors that escape immune surveillance inhibit DC maturation, we explored whether maturation status determines their ability to promote angiogenesis and whether angiogenesis depends on the presence of DCs. Using mouse xenograft models of human tumors, we show that fast-growing "angiogenic" tumors are infiltrated by a more immature DC population than respective dormant avascular tumors. Accordingly, supplementation of immature DCs, but not mature DCs, enhanced tumor growth. When DCs were mixed with Matrigel and injected subcutaneously into mice, only immature DCs promoted the ingrowth of patent blood vessels. Notably, depletion of DCs in a transgenic mouse model that allows for their conditional ablation completely abrogated basic fibroblast growth factor-induced angiogenesis in Matrigel plugs, and significantly inhibited tumor growth in these mice. Because immature DCs actively promote angiogenesis and tumor growth, whereas DC maturation or ablation suppresses this response, we conclude that angiogenesis is dependent on the presence of immature DCs. Thus, cancer immunotherapies that promote DC maturation may act by both augmenting the host immune response to the tumor and by suppressing tumor angiogenesis.

Micromagnetic-microfluidic blood cleansing device.

Sepsis is a lethal disease caused by a systemic microbial infection that spreads via the bloodstream to overwhelm the body's defenses. Current therapeutic approaches are often suboptimal, in part, because they do not fully eliminate the pathogen, and hence the source of deadly toxins. Here we describe an extracorporeal blood cleansing device to selectively remove pathogens from contaminated blood and thereby enhance the patient's response to antibiotic therapy. Immunomagnetic microbeads were modified to create magnetic opsonins that were used to cleanse flowing human whole blood of Candida albicans fungi, a leading cause of sepsis-related deaths. The micromagnetic-microfluidic blood cleansing device generates magnetic field gradients across vertically stacked channels to enable continuous and high throughput separation of fungi from flowing whole blood. A multiplexed version of the device containing four parallel channels achieved over 80% clearance of fungi from contaminated blood at a flow rate of 20 mL/h in a single pass, a rate 1000 times faster than a previously described prototype micromagnetic-microfluidic cell separation system. These results provide the first proof-of-principle that a multiplexed micromagnetic-microfluidic separation system can be used to cleanse pathogens from flowing human blood at a rate and separation efficiency that is relevant for clinical applications.

An extracorporeal blood-cleansing device for sepsis therapy.

Here we describe a blood-cleansing device for sepsis therapy inspired by the spleen, which can continuously remove pathogens and toxins from blood without first identifying the infectious agent. Blood flowing from an infected individual is mixed with magnetic nanobeads coated with an engineered human opsonin--mannose-binding lectin (MBL)--that captures a broad range of pathogens and toxins without activating complement factors or coagulation. Magnets pull the opsonin-bound pathogens and toxins from the blood; the cleansed blood is then returned back to the individual. The biospleen efficiently removes multiple Gram-negative and Gram-positive bacteria, fungi and endotoxins from whole human blood flowing through a single biospleen unit at up to 1.25 liters per h in vitro. In rats infected with Staphylococcus aureus or Escherichia coli, the biospleen cleared >90% of bacteria from blood, reduced pathogen and immune cell infiltration in multiple organs and decreased inflammatory cytokine levels. In a model of endotoxemic shock, the biospleen increased survival rates after a 5-h treatment.

Mechanochemical control of mesenchymal condensation and embryonic tooth organ formation.

Mesenchymal condensation is critical for organogenesis, yet little is known about how this process is controlled. Here we show that Fgf8 and Sema3f, produced by early dental epithelium, respectively, attract and repulse mesenchymal cells, which cause them to pack tightly together during mouse tooth development. Resulting mechanical compaction-induced changes in cell shape induce odontogenic transcription factors (Pax9, Msx1) and a chemical cue (BMP4), and mechanical compression of mesenchyme is sufficient to induce tooth-specific cell fate switching. The inductive effects of cell compaction are mediated by suppression of the mechanical signaling molecule RhoA, and its overexpression prevents odontogenic induction. Thus, the mesenchymal condensation that drives tooth formation is induced by antagonistic epithelial morphogens that manifest their pattern-generating actions mechanically via changes in mesenchymal cell shape and altered mechanotransduction.

Diffusion of interleukin-2 from cells overlaid with cytocompatible enzyme-crosslinked gelatin hydrogels.

In designing an implantable cell encapsulation construct to continuously deliver therapeutic proteins to a patient, it is critical that the biomaterial be compatible with the encapsulated cells, as well as conducive to the diffusion of desired molecules. As a continuation of our previous work, which demonstrated the cytocompatibility of gelatin hydrogels enzymatically crosslinked by microbial transglutaminase (mTG-gels), this work seeks to elucidate the diffusion properties that are needed for sustained release of therapeutic proteins produced by the engineered cells. HEK293 cells genetically engineered to secrete an anticancer drug, interleukin-2 (hIL2), through 4% mTG-gels used as a 1D diffusion model. Under steady-state conditions, cells secrete hIL2 at a therapeutic rate of 5.0-5.7 ng/cm(2)/h/10(6) cells. The diffusion coefficient of hIL2 through the hydrogels is D(m) = 4.0 x 10(-7) cm(2)/s. This value is comparable with similarly sized proteins through hydrogels and is further verified by modeling nonsteady-state diffusion through various thicknesses of the hydrogels, as well as by acellular diffusion chamber experiments. These findings demonstrate that the enzymatically crosslinked hydrogels are not only cytocompatible but also have suitable transport properties that will facilitate the design of sustained drug release devices.

Counteracting apoptosis and necrosis with hypoxia responsive expression of Bcl-2Delta.

In the encapsulated environment of biohybrid artificial organs, cells often encounter a deficiency in oxygen, which lead to apoptosis, necrosis, and lost of productivity. Two vectors with constitutive CMV promoters were constructed to examine the ability of Bcl-2Delta to help C2C12 mouse myoblasts maintain exogenous protein production under hypoxia. Two additional vectors with hypoxia-inducible promoters (5HRE) that switched on Bcl-2Delta expression based on low oxygen levels (0.0%, 0.5%, 1.0%, 2.0%, 5.0%, or 21.0%) were tested for protein productivity and protection against hypoxic stresses. A yellow fluorescent protein was used as a model protein in all vector constructs. C2C12 cells with Bcl-2Delta consistently produced more protein regardless of the oxygen level or promoter used. Cells utilizing the 5HRE rather than the CMV promoter showed an increased level of protein production as the oxygen was decreased. Among the cells with 5HRE promoters, the presence of Bcl-2Delta also increased viability and decreased apoptosis.

Integrated non-invasive system for quantifying secreted human therapeutic hIL2.

Cell encapsulation has been used to treat diabetes, amyotrophic lateral sclerosis, and other chronic ailments by the secretion of therapeutic proteins in vivo. Detection of these proteins typically requires invasive procedures such as blood sampling or device extraction, however. In this article, a non-invasive means of measuring secreted protein concentration using a co-expressed red fluorescent protein marker is developed. A bicistronic expression vector was constructed for the intracellular production of a red fluorescent protein marker and the secreted production of human interleukin-2 (hIL2). The destabilized red fluorescent protein, DsExDR, was selected for its rapid turnover, as well as its ability to emit red light, which is readily transmitted through mammalian tissue. Transfections of this bicistronic vector into three cell lines C2C12, HEK293, and Jurkat showed linear correlations between the expressed proteins, DsExDR (intracellular) and hIL2 (secreted), with transfection DNA concentration. Correspondingly, there was a linear correlation between secreted product (hIL2) and intracellular marker (DsExDR). As transfection DNA was increased, Jurkat cells were found to increase secreted hIL2 in direct proportion to the accumulated DsExDR. HEK293 and C2C12 cells expressed and secreted significantly more hIL2 than the Jurkat cells, while still maintaining a linear relationship. Thus, all three cell lines were suitable hosts for the bicistronic expression of DsExDR and expression and secretion of therapeutic hIL2. This reporting strategy may find the greatest use in cell encapsulation therapy.