Researchers in Japan and the U.S. have developed a laboratory technique for generating vascularized pancreatic islet tissue that when transplanted into diabetic mice grows a system of mature blood vessels and secretes insulin to control the animals’ blood sugar.
The team, led by Hideki Taniguchi, M.D., Ph.D., and colleagues at the Yokahama City University Graduate School of Medicine in Japan, developed a tissue engineering method, known as self-condensation cell culture, which can generate endothelialized 3D tissue oganoids from multiple types of cells and diverse tissue fragments derived from a variety of organs. They say results from in vivo studies in which bioengineered human and mouse islets were transplanted into diabetic mice indicate that the technology could be used to create vascularized, functional islet tissue transplants for treating type 1 diabetes in humans.
“This method may serve as a principal curative strategy for treating type 1 diabetes, of which there are 79,000 new diagnoses per year,” says Takanori Takebe, M.D., a physician-scientist at the Cincinnati Children's Center for Stem Cell and Organoid Medicine, who is co-author on the researchers’ paper in Cell Reports. “This is a life-threatening disease that never goes away, so developing effective and possibly permanent therapeutic approaches would help millions of children and adults around the world.”
The team describes its developments in a paper released today, which is entitled “Self-Condensation Culture Enables Vascularization of Tissue Fragments for Efficient Therapeutic Transplantation.”
Clinical studies have already shown that human pancreatic islets can be transplanted into patients to treat type 1 diabetes. Stem cell–based technologies could also feasibly provide engineered islet tissue for transplantation. However, in reality donor tissue doesn’t engraft well, at least in part because tissue loses vascularization as it is being processed prior to transplantation. “…future clinical applications of such tissue-based approaches face a critical challenge related to effective transplantation strategies that ensure efficient engraftment through the timely development of vascular networks,” the authors write. Various approaches to improving post-transplant engraftment have been tried, however, as the scientists point out, “transplant vascularization generally takes at least 7 days, and the rapid introduction of vasculature into a transplanted tissue remains a considerable challenge.”
The team had previously developed a self-condensation approach to generating tissue organoids from organ progenitor cells, which they used to create tissue-engineered human liver organoids that became vascularized after transplantation into laboratory mice. In their latest reported studies, the team further tested the ability of the same technology to generate vascularized tissue, in vitro, from either isolated adult mouse or human tissue fragments from a variety of organs, or from human induced pluripotent stem cell (iPSC)-derived tissues, which they co-cultured with human mesenchymal stem cells (MSCs) in a substrate that promotes tissue formation. “The results showed that applying this self-condensation approach to other tissue fragments isolated from adult animals or human pluripotent stem cell-derived tissues led to the successful formation of endothelialized and condensed tissues,” the researchers write. When they then added human umbilical vascular endothelial cells (HUVECs) to the mix, the system generated tissues that could then form functional vasculature in vivo.
The team applied the same approach to engineer pancreatic islets using either mouse or human islet tissue cultured in combination with the MSC and HUVECs. The resulting mini-vascularized mouse islets were first transplanted into immunodeficient diabetic mice. Encouragingly, more than 90% of the animals receiving these mini-vascularized mouse islets survived, the animals put on weight to prehyperglycemia levels, and their blood glucose levels dropped.
Transplantation experiments were then repeated using the human mini-sized vascularized islets. Analyses showed that the recipient diabetic animals exhibited increased serum human insulin concentrations, with insulin secretion responding to glucose levels. When the researchers then tracked vascularization dynamics in transplanted human or mouse islets, they found that reperfusion started 2 to 3 days after transplantation, the HUVECs formed new blood vessels within 7 days, and a vascular network was generated around the islets, with blood circulating in the new vessels.
Studies using islets vascularized by fluorescently labeled HUVECs and human MSCs further showed that the human blood vessels formed by the HUVECs had connected with the host mouse vessels. The developing blood vessels were still immature at 3 days post-transplantation, but by day 7 the vessels were mature enough to reconstruct a nonleaky functional vascular network.
“These findings demonstrate the formation process of stable human vascular networks within mice,” the authors write. “First, vascular endothelial cells migrate, proliferate, and form premature tubes, thereby establishing leaky blood vessels. Then, they underwent extensive remodelling and stabilized by an MSC to become non-leaky mature vessels.”
The team's studies also indicated that the structure of the cell condensation–generated islets and the proportion of different islet cell types in the vascularized tissues were equivalent to the structure and cell type distribution found in normal pancreatic islets. “Here, using multiple types of cells with tissue fragments, we successfully integrated 3D tissue structures with vascular networks by adapting self-condensation culture,” the team concludes. “The present study clearly showed that pancreatic islets isolated from adult mice and humans were capable of establishing vascular networks in vitro, when co-cultured with HUVECs and human MSCs under appropriate conditions.…Our approach enabled drastic improvements in the survival rates in fulminant diabetic mice followed by multiple mechanism of action analyses, including islet engraftment rates, insulin secretion, and glucose responsiveness, highlighting the possibility of halting long-term insulin therapy through the clinical use of vascularized islets.”