Organoid

An organoid is a very small piece of living tissue grown in the lab. It arises from stem cells, meaning cells that can still turn into many different cell types. If you place such cells in a nutrient solution with the appropriate signaling substances, they arrange themselves automatically. In doing so, they form a structure that resembles a real organ, such as a piece of intestinal wall or a section of liver. Most organoids are smaller than a grain of rice, many only half a millimeter in size. So it is not a complete organ, but rather a tiny model of one.

Why mini-organs are meant to replace animal testing

Up to now, the pharmaceutical industry has first tested new active substances on cells in a flat dish, then on animals, then on humans. Both of the first two stages are unreliable. Cells in a flat dish behave differently from cells in real tissue. And a mouse organ often reacts differently than a human one. Roughly nine out of ten drugs that survive animal testing later fail in human trials.

Organoids close this gap to some extent. They consist of human cells and have a three-dimensional structure. That is why they react closer to reality. There is also a practical advantage: organoids can be grown from the cells of a single patient. For certain types of cancer, doctors first test several therapies on such mini-tumors and only then choose the treatment.

This is why the field is interesting to investors. Whoever lets drugs fail earlier saves billions. An active substance that only fails in the final test phase has often cost more than one billion euros by that point.

How cells organize themselves into tissue

The crucial trick is called self-organization. You do not assemble the tissue yourself, but merely create the conditions under which the cells do it themselves. To do this, they are placed in a soft gel that mimics the supporting structure between real cells. Growth factors, i.e. messenger substances that dictate the cells' role, are added to the nutrient solution. Depending on the mixture, intestinal, kidney, or brain tissue is formed.

The cells themselves come from two sources. Either tissue stem cells are taken directly from an organ. Or normal body cells, for example from the skin, are taken and reprogrammed back into a stem-cell-like state using certain gene switches. This second method was awarded the Nobel Prize in 2012 and makes it possible to create organoids from almost any human.

An important limitation: organoids have no blood vessels. Nutrients must migrate in from outside. That is why the interior dies off as soon as an organoid reaches a few millimeters in size. A real, transplantable organ cannot be produced this way so far. Organoids should also not be confused with organ-on-a-chip systems. There, pieces of tissue are perfused through artificial channels, which is more of a technical apparatus than a self-grown structure.

Organoids in research, stock market news, and ethics debates

In the news, organoids usually appear in three contexts. First, in drug testing: companies like Emulate or Hubrecht Organoid Technology sell organoid models to pharmaceutical companies. Second, in basic research, for example when researchers use brain organoids to investigate how viruses or genetic diseases disrupt brain development. Third, in genetic engineering, where genes are altered in the organoid and the consequences are observed directly.

The connection to artificial intelligence is also growing. Organoids generate huge amounts of image data, because they are observed under the microscope over days. Learning programs evaluate these recordings and identify which active substance changes the tissue. Some laboratories go further and connect brain organoids to electrodes in order to compute with living cells. This field is called Organoid Intelligence and is still in its infancy.

This is precisely where the ethical debate begins. Brain organoids show measurable electrical activity, similar to very early brain tissue. Whether they could ever feel anything remains open, and expert panels are already discussing rules for this. For now, the rule is: organoids are research tools, not replacement organs for the operating room.