Honors & Awards

  • HFSP Postdoctoral Fellowship, Human Frontier Science Program (07/01/2021)
  • NSERC Postdoctoral Fellow, Natural Sciences and Engineering Research Council of Canada (04/01/2021)

Stanford Advisors


  • Alex Vlahos, Xiaojing Gao, Jeewoo Kang. "United States Patent 17/985,624 Protease-controlled Secretion and Display of Intercellular Signals", Leland Stanford Junior University

Lab Affiliations

All Publications

  • Compact Programmable Control of Protein Secretion in Mammalian Cells BioRxiv Vlahos, A. E., Call, C. C., Kadaba, S. E., Guo, S., Gao, X. J. 2023
  • Protease-controlled secretion and display of intercellular signals. Nature communications Vlahos, A. E., Kang, J., Aldrete, C. A., Zhu, R., Chong, L. S., Elowitz, M. B., Gao, X. J. 2022; 13 (1): 912


    To program intercellular communication for biomedicine, it is crucial to regulate the secretion and surface display of signaling proteins. If such regulations are at the protein level, there are additional advantages, including compact delivery and direct interactions with endogenous signaling pathways. Here we create a modular, generalizable design called Retained Endoplasmic Cleavable Secretion (RELEASE), with engineered proteins retained in the endoplasmic reticulum and displayed/secreted in response to specific proteases. The design allows functional regulation of multiple synthetic and natural proteins by synthetic protease circuits to realize diverse signal processing capabilities, including logic operation and threshold tuning. By linking RELEASE to additional sensing and processing circuits, we can achieve elevated protein secretion in response to "undruggable" oncogene KRAS mutants. RELEASE should enable the local, programmable delivery of intercellular cues for a broad variety of fields such as neurobiology, cancer immunotherapy and cell transplantation.

    View details for DOI 10.1038/s41467-022-28623-y

    View details for PubMedID 35177637

  • Endothelialized collagen based pseudo-islets enables tuneable subcutaneous diabetes therapy BIOMATERIALS Vlahos, A. E., Kinney, S. M., Kingston, B. R., Keshavjee, S., Won, S., Martyts, A., Chan, W. W., Sefton, M. V. 2020; 232: 119710


    Pancreatic islets are fragile cell clusters and many isolated islets are not suitable for transplantation. Furthermore, following transplantation, islets will experience a state of hypoxia and poor nutrient diffusion before revascularization, which is detrimental to islet survival; this is affected by islet size and health. Here we engineered tuneable size-controlled pseudo-islets created by dispersing de-aggregated islets in an endothelialized collagen scaffold. This supported subcutaneous engraftment, which returned streptozotocin-induced diabetic mice to normoglycemia. Whole-implant imaging after tissue clearing demonstrated pseudo-islets regenerated their vascular architecture and insulin-secreting β-cells were within 5 μm of a perfusable vessel - a feature unique to this approach. By using an endothelialized collagen scaffold, this work highlights a novel "bottom-up" approach to islet engineering that provides control over the size and composition of the constructs, while enabling the critical ability to revascularize and engraft when transplanted into the clinically useful subcutaneous space.

    View details for DOI 10.1016/j.biomaterials.2019.119710

    View details for Web of Science ID 000514748200021

    View details for PubMedID 31901691

  • A scalable device-less biomaterial approach for subcutaneous islet transplantation Biomaterials Vlahos, A. E., Tailor-Volodarsky, I., Kinney, S. M., Sefton, M. V. 2020
  • Modular tissue engineering for the vascularization of subcutaneously transplanted pancreatic islets PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Vlahos, A. E., Cober, N., Sefton, M. V. 2017; 114 (35): 9337–42


    The transplantation of pancreatic islets, following the Edmonton Protocol, is a promising treatment for type I diabetics. However, the need for multiple donors to achieve insulin independence reflects the large loss of islets that occurs when islets are infused into the portal vein. Finding a less hostile transplantation site that is both minimally invasive and able to support a large transplant volume is necessary to advance this approach. Although the s.c. site satisfies both these criteria, the site is poorly vascularized, precluding its utility. To address this problem, we demonstrate that modular tissue engineering results in an s.c. vascularized bed that enables the transplantation of pancreatic islets. In streptozotocin-induced diabetic SCID/beige mice, the injection of 750 rat islet equivalents embedded in endothelialized collagen modules was sufficient to restore and maintain normoglycemia for 21 days; the same number of free islets was unable to affect glucose levels. Furthermore, using CLARITY, we showed that embedded islets became revascularized and integrated with the host's vasculature, a feature not seen in other s.c.Collagen-embedded islets drove a small (albeit not significant) shift toward a proangiogenic CD206+MHCII-(M2-like) macrophage response, which was a feature of module-associated vascularization. While these results open the potential for using s.c. islet delivery as a treatment option for type I diabetes, the more immediate benefit may be for the exploration of revascularized islet biology.

    View details for DOI 10.1073/pnas.1619216114

    View details for Web of Science ID 000408536000043

    View details for PubMedID 28814629

    View details for PubMedCentralID PMC5584405

  • Degradable methacrylic acid-based synthetic hydrogel for subcutaneous islet transplantation. Biomaterials Kinney, S. M., Ortaleza, K., Vlahos, A. E., Sefton, M. V. 2021; 281: 121342


    Islet transplantation is a promising regenerative therapy that would reduce the dependence of type 1 diabetic patients on insulin injections. However, islet transplantation is not yet widely available, in part because there is no ideal transplant site. The subcutaneous space has been highlighted as a promising transplant site, but it does not have the vasculature required to support an islet graft. In this study we demonstrate that islets engraft in the subcutaneous space when injected in an inherently vascularizing, degradable methacrylic acid-polyethylene glycol (MAA-PEG) hydrogel; no vascularizing cells or growth factors were required. In streptozotocin-induced diabetic mice, injection of 600 rodent islet equivalents in MAA-PEG hydrogels was sufficient to reverse diabetes for 70 days; a PEG gel without MAA had no benefit. MAA-PEG hydrogel scaffolds degraded over the course of a week and were replaced by a host-derived, vascularized, innervated matrix that supported subcutaneous islets. The survival of islet grafts through the inflammatory events of subcutaneous transplantation, hydrogel degradation, and islet revascularization underscore the benefits of the MAA biomaterial. Our findings establish the MAA-PEG hydrogel as a platform for subcutaneous islet transplantation.

    View details for DOI 10.1016/j.biomaterials.2021.121342

    View details for PubMedID 34995903

  • Endothelialized collagen modules for islet tissue engineering Transplantation, Bioengineering, and Regeneration of the Endocrine Pancreas Vlahos, A. E., Sefton, M. V. Elsevier Inc.. 2019: 277–287
  • Interpenetrating Alginate-Collagen Polymer Network Microspheres for Modular Tissue Engineering. ACS biomaterials science & engineering Mahou, R., Vlahos, A. E., Shulman, A., Sefton, M. V. 2018; 4 (11): 3704-3712


    The lack of vascularization limits the creation of engineered tissue constructs with clinically relevant sizes. We pioneered a bottom-up process (modular tissue engineering) in which constructs with intrinsic vasculature were assembled from endothelialized building blocks. In this study, we prepared an interpenetrating polymer network (IPN) hydrogel from a collagen-alginate blend and evaluated its use as microspheres in modular tissue engineering. Ionotropic gelation of alginate was combined with collagen fibrillogenesis, and the resulting hydrogel was stiffer and had greater resistance to enzymatic degradation relative to that of collagen alone; the viability of embedded mesenchymal stromal cells (adMSC) was unaltered. IPN microspheres were fabricated by a coaxial air-flow technique, and an additional step of collagen coating was required to have human umbilical vein endothelial cells (HUVEC) attach and proliferate. When implanted subcutaneously in SCID/bg mice, adMSC-HUVEC microspheres promoted more blood vessels at day 7 relative to microspheres without adMSC but coated with HUVEC. Perfusion studies confirmed that these vessels were connected to the host vasculature. Fewer vessels were detected in both groups at day 21, but in adMSC-HUVEC explants, more smooth muscle cells had wrapped around vessels, and CLARITY processing of whole explants revealed a restricted leakage of blood. The capacity for rapid gelation and high throughput production are promising features for the use of these microspheres in modular tissue engineering.

    View details for DOI 10.1021/acsbiomaterials.7b00356

    View details for PubMedID 33429609

  • Interpenetrating Alginate-Collagen Polymer Network Microspheres for Modular Tissue Engineering ACS BIOMATERIALS SCIENCE & ENGINEERING Mahou, R., Vlahos, A. E., Shulman, A., Sefton, M. V. 2018; 4 (11): 3704–12
  • Muted fibrosis from protected islets NATURE BIOMEDICAL ENGINEERING Vlahos, A. E., Sefton, M. V. 2018; 2 (11): 791–92

    View details for DOI 10.1038/s41551-018-0316-9

    View details for Web of Science ID 000449679300002

    View details for PubMedID 31015616

  • Injectable and inherently vascularizing semi-interpenetrating polymer network for delivering cells to the subcutaneous space BIOMATERIALS Mahou, R., Zhang, D. Y., Vlahos, A. E., Sefton, M. V. 2017; 131: 27–35


    Injectable hydrogels are suitable for local cell delivery to the subcutaneous space, but the lack of vasculature remains a limiting factor. Previously we demonstrated that biomaterials containing methacrylic acid promoted vascularization. Here we report the preparation of a semi-interpenetrating polymer network (SIPN), and its evaluation as an injectable carrier to deliver cells and generate blood vessels in a subcutaneous implantation site. The SIPN was prepared by reacting a blend of vinyl sulfone-terminated polyethylene glycol (PEG-VS) and sodium polymethacrylate (PMAA-Na) with dithiothreitol. The swelling of SIPN was sensitive to the PMAA-Na content but only small differences in gelation time, permeability and stiffness were noted. SIPN containing 20 mol% PMAA-Na generated a vascular network in the surrounding tissues, with 2-3 times as many vessels as was obtained with 10 mol% PMAA-Na or PEG alone. Perfusion studies showed that the generated vessels were perfused and connected to the host vasculature as early as seven days after transplantation. Islets embedded in SIPN were viable and responsive to glucose stimulation in vitro. In a proof of concept study in a streptozotocin-induced diabetic mouse model, a progressive return to normoglycemia was observed and the presence of insulin positive islets was confirmed when islets were embedded in SIPN prior to delivery. Our approach proposes a biomaterial-mediated strategy to deliver cells while enhancing vascularization.

    View details for DOI 10.1016/j.biomaterials.2017.03.032

    View details for Web of Science ID 000401393600003

    View details for PubMedID 28371625

  • Using Del-1 to Tip the Angiogenic Balance in Endothelial Cells in Modular Constructs TISSUE ENGINEERING PART A Ciucurel, E. C., Vlahos, A. E., Sefton, M. V. 2014; 20 (7-8): 1222–34


    Modular tissue engineering is a method of building vascularized tissue-engineered constructs. Submillimeter-sized collagen pieces (modules) coated with a layer of endothelial cells (EC; vascular component), and with embedded functional cells, are self-assembled into a larger, three-dimensional tissue. In this study, we examined the use of developmental endothelial locus-1 (Del-1), an extracellular matrix protein with proangiogenic properties, as a means of tipping the angiogenic balance in human umbilical vein endothelial cells incorporated in modular tissue-engineered constructs. The motivation was to enhance the vascularization of these constructs upon transplantation in vivo, in this case, without the use of exogenous mesenchymal stromal cells. EC were transduced using a lentiviral construct to overexpress Del-1. The Del-1 EC formed more sprouts in a fibrin gel sprouting assay in vitro compared with eGFP (control) transduced EC, as expected. Del-1 EC had a distinct profile of gene expression (upregulation of matrix metalloproteinase-9 [MMP-9], urokinase-type plasminogen activator [uPA/PLAU], vascular endothelial growth factor [VEGF-A], and intercellular adhesion molecule-1 [ICAM-1]; downregulation of angiopoietin-2 [Ang2]), also supporting the notion of "tipping the angiogenic balance". On the other hand, contrary to our expectations, when Del-1 EC-coated modules were implanted subcutaneously in a severe combined immunodeficient/beige animal model, the proangiogenic effect of Del-1 was less remarkable. There was only a small increase in the number of blood vessels formed in Del-1 implants compared with the eGFP implants, and only few blood vessels formed at the implant site in both cases. This was presumed due to limited EC survival after transplantation. We speculate that if we could improve EC survival in our study (for example, by adding other prosurvival factors or supporting cells), we would see a greater Del-1-induced angiogenic benefit in vivo as a consequence of increased Del-1 secretion by a higher number of surviving cells.

    View details for DOI 10.1089/ten.tea.2013.0241

    View details for Web of Science ID 000334110000011

    View details for PubMedID 24138448

    View details for PubMedCentralID PMC3993075