Mechanisms of Healing

Time doesn’t heal all wounds - the immune system does.

It rushes in when the body is injured to repair the wall of epithelial cells that make up our skin and line our lungs and intestines. At the same time, it defends against bacteria and other pathogens as they try to enter our bodies through the wound.

One of the immune system’s most powerful components following an injury is the cytokine interleukin-22 (IL-22).

“IL-22 has evolved to mediate two essential functions to handle a wound or injury,” says Nico Ghilardi, Associate Director and Senior Scientist in the Department of Immunology at Genentech. “On the one hand, it has healing properties that can repair the wound. On the other, it helps fight off bacteria that can enter through the wound and cause an infection. It’s like if IL-22 worked as a doctor and a bodyguard at the same time.”

Since IL-22 was discovered in 2000, researchers at Genentech and elsewhere have dreamed of using it to repair wounds that refuse to heal on their own. Over the last few years, Genentech scientists have overcome a host of challenges to produce IL-22Fc, a modified version of the IL-22 molecule that might have use as a new treatment option. In theory, IL-22Fc may have potential in a wide variety of wound-healing applications, including diabetic foot ulcers, inflammatory bowel disease, and other conditions where there is significant epithelial tissue damage.

But we’re getting ahead of ourselves; let’s start at the beginning – how the immune system helps to heal injuries.

The Basic Immune Response

The first line of defense against pathogens is at the surface of our bodies, where tightly connected epithelial cells keep pathogens out.

“A type of epithelial cell, called keratinocytes, makes up the skin’s outermost protective barrier,” said Dimitry Danilenko, Principal Scientist-Pathologist in Developmental Sciences at Genentech. “This layer works to protect us from dehydration, ultraviolet radiation and the onslaught of bacteria.”

When a cut or other injury disrupts the epithelial barrier, the immune system goes on high alert, taking aim at two equally important goals:

  1. 1. Stopping the invader: Specialized immune cells recognize pathogens and start producing proteins called cytokines and chemokines. These alarm signals increase blood flow to the area and recruit other immune cells (these processes also lead to swelling and redness, referred to as inflammation). Eventually, the invading bacteria are removed, the immune cells leave, inflammation subsides and the body goes back to its normal state.
  2. 2. Healing: To promote healing, cells of the immune system such as T-helper cells produce the cytokine protein IL-22, which signals the epithelium to re-grow and re-seal the injured site. IL-22 also stimulates production of antimicrobial peptides to further protect the injured area from bacteria.


Putting IL-22 to Work in Diabetes

Given the fundamental role that IL-22 plays in healing, the Genentech team hypothesized that a drug based on the molecule could help people with wounds that never get better. One of these conditions, which seemed surprising at first, was diabetes.

Nerve damage leading to loss of sensation is a common complication of diabetes. So it’s not unusual for diabetic patients to get a cut or scratch and not notice it. Unnoticed small injuries on the feet, for example, grow and with repeated trauma can get infected, leading to diabetic foot ulcers. To make matters worse, poor blood flow to the foot – another complication of diabetes – makes it much more difficult for immune cells to reach the affected area, leaving the body vulnerable to infection.

people worldwide will have diabetes1
of diabetics could have a foot ulcer in their lifetime2
require an amputation2
amputations due to foot ulcers annually1

Constant vigilance is crucial to avoid losing a foot to diabetes, requiring regular clinic visits to remove dead tissue and care for the wound. That vigilance also includes keeping weight off the affected foot to avoid further injury. “It’s a hard regimen to follow and very disruptive to daily living,” says Puneet Arora, Medical Director for Early Clinical Development at Genentech. “There’s a strong sense of unmet need for a potential treatment option that will promote wound closure in slow or non-healing ulcers.”

Why does diabetes cause foot ulcers?

Preclinical results suggest that IL-22 may offer new hope for treating this difficult condition, by promoting wound healing through the stimulation of epithelial cell growth and by helping to clear the infection through the production of antimicrobial peptides. “We believe the two functions of IL-22 are perfectly matched,” says Charlene Liao, the IL-22Fc Project Team Leader at Genentech.

Bacterial Balance for IBD

The skin isn’t the only epithelial surface that comes in contact with bacteria. In fact, our bodies contain at least as many bacterial cells as they do human cells. Most of those bacteria live in our intestines, where they help us process the foods we eat.

“Bacteria are absolutely necessary for our well-being, but they can become dangerous when they cross the epithelial barrier in the intestines,” says Ghilardi. “To keep the bacteria in their place, the body constantly senses their presence and reinforces the intestinal epithelium. In healthy individuals, this results in a tight epithelial barrier and a thick mucus layer to keep bacteria away from their own cells.”

In ulcerative colitis and Crohn's disease, the primary forms of inflammatory bowel disease (IBD), the intestinal walls and the epithelial lining become thin and weak for reasons that are not well understood. The normally helpful bacteria are now able to get through this barrier and enter a place where they shouldn’t be, namely the host tissue. The body now treats this invasion like an infection and responds initially, by trying to flush the bacteria out with torrents of water (also known as diarrhea).

What is IBD?

The two main forms of inflammatory bowel disease (IBD) are ulcerative colitis and Crohn’s disease. Both forms are due to improper inflammatory responses in the gastrointestinal tract.5

At the same time, immune cells in the gut cause inflammation as they combat the bacteria. But in patients with IBD, the immune system never prevails because the weak epithelial barrier continues to admit new bacteria from the gut. The result of this never-ending battle between our immune system and our gut bacteria is perpetual inflammation and irreparable collateral damage to the intestine.

people are affected by IBD5
in most people6
new cases of IBD are diagnosed per year in the U.S.6

Most forms of IBD are treated with immunosuppressive agents to decrease inflammation. “The problem is that once you start, you have to continue forever. It’s difficult to come off these agents,” says Tim Lu, Associate Medical Director for Early Clinical Development at Genentech. And while you’re taking immunosuppressive drugs, he adds, “You’re at increased risk of infection.”

There isn't a single cause for IBD.

More likely, several different factors can influence the onset of the disease. These are the "omes" of IBD.

Gut Microbiome

The types of bacteria inside our gastrointestinal tracts.5


The reactivity of the intestinal immune response.5


The contributions of DNA changes and heritability.5


Environmental factors like diet and geography.5

The good news is that, based on preclinical research, IL-22 works just the same way in the gut as it does in the skin: it promotes epithelial healing and the production of antimicrobial peptides, which act like the body’s homegrown antibiotics and can kill bacteria that come too close.

“If it works, it could potentially give patients the option to reduce or eliminate the use of immunosuppressive drugs and reduce the risk of infection,” Lu says.

Making it Work

To make IL-22-based therapy a reality, Genentech’s manufacturing team first had to turn it into a molecule that could be administered to humans as an investigational medicine — without destroying IL-22’s unique wound-healing and antimicrobial properties. Each step of the manufacturing process for IL-22 posed a new set of challenges that required our scientists to adapt and modify methods for making biologic medicines. For further background on the fascinating and complex science of manufacturing, read our editorial by Genentech’s former Global Head of Pharmaceutical Technical Operations.

The first challenge was durability. Like other cytokines, IL-22 is generally cleared quickly from the body when administered in its natural form, which limits its potential therapeutic utility. To address this problem, our scientists attached IL-22 to a fragment of an antibody (the “stalk” region, known as the Fc domain). The resulting fusion protein, IL-22Fc, combines the biological function of IL-22 with the long half-life and increased stability of an antibody, making it an ideal clinical candidate. Fc fusion proteins can have a half-life of 1-2 weeks, long enough to deliver a potential therapeutic effect without the need for daily infusions.


The manufacturing challenges didn’t end there. Because IL-22Fc is a fusion protein, the normal cell-culture process – the growth of biologic medicines in living cells – had to be modified from the procedures used for monoclonal antibodies. “Other steps in the process, like purification and formulation, were also difficult,” says Matt Kalo, Genentech’s Technical Development Leader for IL-22Fc.

To address these challenges, the manufacturing team used ingenuity and adaptation to develop a molecule that persists in the human body, retains the special biological characteristics of IL-22, and has the desired shelf-life as a biologic medicine. Reaching these standards made it possible to advance IL-22Fc into the clinic and potentially help those who need it most.

“We are very excited about this innovative and unconventional way to strengthen our natural mechanism of healing,” Liao says. “If this investigational medicine works as designed, it will be one of a kind, because rather than merely providing relief from disease symptoms, it could actually induce healing. This would be incredibly helpful for many people suffering from difficult-to-treat conditions.”