Amongst the distinguishable branches of medicine, one group of people have it harder than most. Neurologists face a daunting problem. While other doctors can easily examine and interact with their organ of concern, neurologists deal with the brain—a hidden enigma. The brain is tucked away behind the skull and layers of protective meninges, making it quite the elusive entity to observe. What adds to the complexity is the ethical dilemma; delving deep into the intricacies of the human brain is constrained by both technological limitations and ethical concerns.
Ever wish we could reverse engineer our brains, construct them from the ground up? Think of scenes reminiscent of a futuristic world, like the Sibyl system in Psycho pass, where brains float in a pale yellow liquid, interconnected to form a parallel supercomputing machine. But presently, we’re far from that vision. Our brain models today are minuscule, mere millimeters in size, resembling insignificant white dots on a petri dish. These miniature structures called brain organoids are theoretically quite simple to make. However the journey to our current understanding is interspersed with a handful of medical advancements, dollops of theories on how we define sentience and a whopping dash of luck.
It was the year of 1907, Dr. Henry Van Peters Wilson was working for the US Bureau of Fisheries where he discovered that sponges when kept in certain conditions degenerated and gave rise to small masses of undifferentiated tissue which in turn grew and differentiated into full sponges. In his paper, he wrote- “This ability to undergo-when the environment is unfavorable but not exceedingly so, regressive changes of differentiation resulting in the production of a simple, more uniform tissue, is something that is plainly useful, i.e adaptive.”. Little did he know that the mass of undifferentiated tissue he observed would set the stage for generations of stem cell research to come.
Fast forwarding 90 years, Dr. James Thomson had successfully figured out how to grow human embryonic stem cells in his lab. This caused quite a stir within the scientific community and the media, splitting opinions into two camps. On one side, there was enthusiasm for this groundbreaking discovery. On the other side, questions arose about the ethical implications. You see, Thomson derived these stem cells from surplus human embryos left from IVF. The process involved extracting stem cells from the blastocyst stage of the developing embryo, essentially leading to the destruction of the embryo. This made a lot of people uneasy.
Thomson faced significant backlash on his research but in 2006, Thomson and a Japanese researcher called Shinya Yamanaka had another breakthrough. They found a way to make stem cells without having to use embryos! According to Merriam-Webster, pluripotent means ‘not fixed in [its] developmental potentialities.’ Yamanaka’s breakthrough involved taking skin cells from adult mice at his clinic. He then introduced a virus carrying 24 scientifically chosen genes into these cells. Remarkably, within just two months, they managed to identify the only 4 genes that were required. This ingenious technique effectively rewound the developmental clock, prompting Yamanaka to coin the cells as induced pluripotent stem cells (iPSCs). Thomson came close to a Nobel Prize, but it eluded him as Yamanaka stole the spotlight. Yamanaka had successfully demonstrated a proof of concept by transforming mouse cells, showcasing cellular reprogramming in a groundbreaking way.
Around 2012, another Japanese researcher Yoshiki Sasai was discovering how to coax embryonic stem cells into becoming neural cells. Sasai’s technique was a blend of science and artistry, as he guided embryonic cell-derived cortical (brain cortex) cells to organically assemble into three-dimensional organoids. The organoids then developed into the cortex by careful administration of growth factors. Some astonishing images from the research even revealed the precursors of eyes within these organoids, a sight to behold. Sasai was hailed as a stem cell Sensei for his groundbreaking work. However, in a tragic turn of events, he faced immense scrutiny and backlash following his co-authoring of two papers which attempted to induce pluripotency in embryonic cells by subjecting them to stressful conditions (like exposure to acid). The papers ended up getting retracted due to errors, and it is said that Sasai, overwhelmed by the fallout, took his own life.
Simultaneously, Madeline Lancaster at Cambridge was trying to form neural rosettes from human embryonic stem cells. She was prodding at the cells to make them stick to the bottom of the plate using a special gel but the floating cells resisted. Instead they stuck together and embedded into the gel forming 3D aggregations. Lancaster wasn’t a stem cell biologist, so intrigued by what she saw she went to her advisor and they discovered that she had accidentally grown a brain organoid. Lancaster in a media interview says that it’s actually quite simple to make brain organoids. According to her, the first decision the stem cell makes is whether it wants to become the brain or everything else. In minimal media, the only cells that survive are the ones who will eventually become a part of the brain.
How accurate are these organoids to the actual tissue architecture of organs? In one study, intestinal organoids were generated from the endocrine cells of the gastrointestinal tract of mice. Analysis showed that the mRNAs of 5 major hormones were expressed in the organoids similar to that of the native tissues. However, in organoids, the cells don’t arrange themselves in the precise natural order as they do in vivo. It’s often likened to having a car assembled with all the parts, but in the wrong order, rendering it non-functional. To address this challenge, researchers have adopted a different strategy: instead of trying to create an entire organ in one go, they focus on separately building models of different parts.
Now that we’re knee-deep in the recipe, the pressing question emerges: do organoids actually work and how so? A team at Stanford transplanted their organoid into a rodent’s visual cortex to see how the tissues integrated with the rodent’s brain. Their test involved flashing light into the rodent’s retina, and to their amazement, the cells within the organoid responded when visualized through imaging. What was even more fascinating was the nuanced functionality observed—specific cells responded to particular types of light, mimicking the workings of the human visual system.
California based company Neurona Therapeutics is in its clinical trial stages with NRTX-1001 which is a single dose treatment designed to decrease seizure activity in the epileptic region of the brain of people with drug-resistant epilepsy. Essentially, the process includes transplanting interneurons that secrete the neurotransmitter gamma-aminobutyric acid (in short, GABA) into the patient’s brain. The interneurons are supposed to integrate with the host’s neural cells and quiet the malfunctioning networks that cause the seizures. The clinical study claims that 2 patients had achieved over 90% decrease in monthly seizure frequency (7 months post treatment) and increased memory performance in cognitive tests. According to the WHO, around 50-million people worldwide suffer from epilepsy. This means that current treatment options which involve surgically removing a part of the brain and its associated side effects such as lost memories and vision could be overcome through this therapy.
Another example of a use case for organoids is drug and gene therapy testing. Researchers who are working on drugs for diabetes, cancer, and numerous other diseases are using organoids because of their close similarity to human organ models compared to animals. One particular area of interest is using CRISPR to introduce genes into the organoid models to study the onset, cause and treatment of diseases.
Researchers at Cortical labs have built ‘Dish Brain’- taking organoids one step further by combining it with high-density multi-electrode arrays (HD-MEAs) and custom software drivers. Their experiments indicate that the brain cells exhibit intelligence by learning and modifying their behavior over time to play a game of simulated “Pong”. The team believes that 2 interrelated processes are required for sentient behavior (which they describe as responsiveness to sensory impressions) in an intelligent system, the first being how the system learns to perceive and act. Secondly, the system must learn when it should adopt a particular activity and what will be the consequence of said activity.
In their experiment, they put to the test a unified brain theory based on the free energy principle. This theory posits that any self-organizing system strives to minimize its variational free energy. In simpler terms, it suggests that the brain continually seeks to minimize the discrepancy between what it predicts and what it observes by adjusting its predictions or taking action to alter the observation.
To train the cells, they followed a specific methodology. When neural activity failed to intercept the ball, an unpredictable electrical stimulus was delivered for a few seconds, causing the ball to restart at a random position vector. On the other hand, successful interception of the ball resulted in a predictable electrical stimulus (100Hz for 100ms) applied across all electrodes simultaneously.
To ensure the experiment was unbiased and that the paddle’s movement wasn’t simply aligned to the ball’s position, they compared different regions of the neural organization. What they found was truly fascinating—distinct areas within the cell culture were actively involved in the process. Some cells directed the paddle upwards, while others moved it downwards. They had to organize themselves effectively to establish precise firing patterns, aligning in a manner that ensured the optimal interception of the ball.
Organoids have the potential to be life-saving therapies and the future of drug testing. Though we’re not there yet, envisioning them as the foundation for an advanced biocomputer is an exciting prospect down the road. However, there are significant hurdles facing the research.
- The system in vitro has no vasculature i.e it lacks the rich network of blood vessels that envelops normal human organs inside the body and pressure from surrounding vessels forcing the cells into the right organization. This means limited growth and a large probability of most of the cell cultures dying in vitro.
- They also lack structures that provide input and exhibit output such as the senses of the human body (sensory input) and motor organs (action output).
- It is also quite expensive. The stem cell approach of making the organoids requires growth factors whose 1 gm cost $750,000.
- The process is time consuming and at this point in time not fast enough for effective and timely therapy.
- Another huge hurdle is getting every researcher across the globe to agree to the same set of quality control standards. Due to the non-existence of a standard protocol, research is difficult to replicate and review.
However, Organoids are a testament to humankind’s relentless pursuit of innovation. The potential applications and the advancements that await are indeed something to look forward to.