Animal-free perspectives for organoid culture – PhD Defense Joost Wijnakker

The need for animal-free organoid culture

Organoids are mini-organs grown in the lab from human stem cells. They allow researchers to study how organs function, how diseases develop, and to test new medicines. Until now, organoids were almost always grown using Matrigel, a gel derived from mouse tumors. This material is expensive, varies from batch to batch, and is unsuitable for clinical use in humans. These limitations have hindered progress in the field for many years.

The key role of integrins

“To grow organoids without animal-derived materials, we first had to understand exactly which signals stem cells need to grow,” Joost explains. “Integrins turned out to be a very important factor.” Integrins are receptors that cells use to sense their surroundings. In collaboration with integrin expert Timothy Springer and organoid expert Wim de Lau, existing antibodies were used to pinpoint which integrins are essential for organoid growth. Together, they discovered that integrin β1 is particularly crucial for organoid growth, cell orientation, and cell survival. This insight formed the foundation for Joost’s search for an animal-free alternative to Matrigel.

An unexpected solution: the bacterial protein Invasin

That search led to a surprising discovery. Joost found that a small fragment of the bacterial protein Invasin can activate multiple integrin β1 receptors at once. “Natural matrix proteins usually activate only one type of receptor, but Invasin works like a kind of universal activator of several integrins,” he explains. “This means it mimics different aspects of the extracellular matrix at the same time.” Later studies revealed that Invasin is even more potent than some existing molecules: a so-called super-agonist. The first results appeared in 2024, when Joost showed that Invasin enables organoids to grow in 2D on flat surfaces. This work was summarized in an earlier news item from the Hubrecht Institute.

From 2D to 3D in a fully synthetic system

Building on this discovery, Joost combined Invasin with a fully synthetic gel, the PIC hydrogel developed by Professor Paul Kouwer. This made it possible to grow organoids in 3D, comparable to earlier methods using Matrigel. These findings were recently described in this news article. Organoids grown in the PIC–Invasin gel grew well, maintained their structure, and could be cultured over extended periods. Joost: “When we saw that organoids could truly grow using Invasin alone, we knew: this can change the way organoids are cultured.”