Five-day vascular organoids speed tissue engineering research

Boston Children’s Hospital scientists have unveiled a five-day approach to generate functional vascular organoids capable of supporting blood flow and in vivo engraftment.

Blood vessels are the living conduits that deliver nutrients and oxygen throughout the body, regulate hemostasis, and modulate inflammation. During development, vasculature shapes organ formation and supports postnatal tissue growth and repair, while vascular niches maintain stem cell populations.

Engineering physiologically functional vascular networks in vitro would allow detailed study of human vessel development, high-precision drug testing, and production of pre-vascularized grafts for regenerative medicine.

Recent organoid strategies produced vascular structures but depended on spontaneous mural cell emergence and required prolonged culture periods and extracellular matrix support, constraining scalability and speed required for therapeutic application.

In the study, “Rapid generation of functional vascular organoids via simultaneous transcription factor activation of endothelial and mural lineages,” published in Cell Stem Cell, researchers designed a dual-factor program to co-differentiate induced pluripotent stem cells into endothelial and mural fates for rapid vascular-organoid assembly.

Human induced pluripotent stem cells were guided into mesodermal progenitors, combined at a 1:1 ratio, and aggregated into thousands of 250-µm vascular organoids. Investigators implanted roughly 1,000 organoids beneath the renal capsule of immunodeficient NSG mice.

A separate cohort of diabetic nude mice received the same organoid dose in a hind limb ischemia model. Pancreatic-islet studies paired 1,500 organoids with 500, 300, or 100 islet equivalents in NSG recipients.

Investigators triggered expression of transcription factors ETV2 and NKX3.1 through doxycycline-inducible constructs or chemically modified mRNA, allowing simultaneous endothelial and mural specification inside free-floating spheroids. Flow cytometry, immunofluorescence, bulk and single-cell RNA sequencing, and in-vivo imaging tracked lineage commitment.

Some organoids were embedded in collagen-Matrigel gels to gauge matrix-driven maturation, and functional vascularization was measured by perfusion assays, laser-Doppler flowmetry, and luciferase bioluminescence.

Within five days, about half of the cells in each organoid turned into blood-vessel cells bearing VE-cadherin and CD31, and those cells built hollow, tube-like networks wrapped by smooth-muscle partners.

Dropping the organoids into a collagen–Matrigel gel let them swell to nearly one millimeter and ramped up genes linked to arteries. Short, one-day doxycycline pulses pushed the vessels toward an artery-like identity, yet longer three-day pulses produced a mixed batch of artery- and vein-like cells that sprouted more readily.

After implantation, the organoids tapped into the host’s circulation, restored roughly 50% of lost blood flow in injured limbs, and sharply cut tissue death.

Under the kidney-grafted capsule, organoid-derived human vessels surrounded transplanted mouse islets, letting as few as 100 islet equivalents keep blood sugar normal for 100 days.

Mice that received 300 islet equivalents recovered normal glucose, and about half of those given 100 islet equivalents kept blood sugar normal for 100 days.

The authors conclude that orthogonal transcription-factor programming offers a scalable path to tailor-made vascular organoids capable of rapid engraftment and tissue rescue, suggesting future avenues for treating ischemic injury, improving cell-therapy survival and a potentially durable diabetes therapy.

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