Acute graft versus host disease of the intestine is a serious complication that can occur after a stem cell or bone marrow transplant, where the donated immune cells mistakenly attack the recipient’s digestive system, causing symptoms like diarrhea, abdominal pain, and potentially life-threatening complications.

Understanding Acute Graft Versus Host Disease of the Intestine

When someone undergoes a stem cell transplant (also called bone marrow transplant) to treat conditions like leukemia, lymphoma, or other blood disorders, they receive healthy blood-forming cells from a donor. While this procedure can be lifesaving, it carries the risk of a complication called graft versus host disease, or GVHD. This happens when the immune cells from the donor (the graft) see the recipient’s body (the host) as foreign and begin attacking it^[1].

The intestine, which is part of the gastrointestinal tract, is one of the most commonly affected areas in acute GVHD. When GVHD attacks the intestines, it can cause severe symptoms that significantly impact a patient’s quality of life and overall recovery from transplant. Understanding this condition is crucial for anyone who has undergone or is considering a stem cell transplant^[2].

Epidemiology: How Common Is This Condition?

Acute GVHD is surprisingly common after stem cell transplants. Around 30 to 60 percent of patients who receive an allogeneic transplant (a transplant using cells from another person) will develop some form of acute GVHD^[5]. Among those who develop acute GVHD, the gastrointestinal system is involved in approximately 40 percent of cases^[6].

In one large medical center, among 2,500 patients who underwent their first allogeneic transplant, 63 percent developed GVHD affecting either the gut, liver, or both. Of these, 54 percent experienced GVHD of the gut without liver involvement^[7]. These numbers demonstrate just how prevalent intestinal GVHD is among transplant recipients.

While acute GVHD was once a major cause of death after transplant, advances in prevention and treatment have made a difference. Over the past two decades, the incidence of severe acute GVHD has declined substantially. This is particularly important because historically, only 5 to 20 percent of patients with severe acute GVHD survived^[4].

Most cases of acute GVHD, including intestinal involvement, occur during the first 100 days after transplant. However, symptoms can sometimes appear later, even after this initial period^[5]. Approximately 30 to 50 percent of patients develop acute GVHD, though most cases are mild. About 10 percent of patients experience more severe symptoms that require intensive treatment^[4].

Causes of Acute Intestinal GVHD

The root cause of acute GVHD lies in the immune system’s recognition process. Our bodies have special proteins called human leukocyte antigens, or HLA, on the surface of cells. These proteins work like identification badges, telling the immune system which cells belong to the body and which don’t. In a transplant, the donor’s immune cells may not recognize the recipient’s HLA markers and therefore see the recipient’s tissues as foreign invaders that need to be destroyed^[2].

When immunocompetent T lymphocytes (a type of white blood cell) from the donor graft recognize the recipient’s tissues as foreign due to these histocompatibility differences, they initiate an immune response. This attack typically occurs within the first 100 days after transplant and can lead to tissue damage in various organs, including the intestines^[5].

The development of intestinal GVHD involves a complex series of events. The conditioning regimen (the chemotherapy and sometimes radiation given before transplant to prepare the body) causes initial damage to tissues. This tissue damage releases inflammatory signals called proinflammatory cytokines. These signals activate the donor’s immune cells, which then launch an attack against the recipient’s tissues, particularly targeting the skin, liver, and gastrointestinal tract^[6].

Scientists have discovered that the health of the intestinal microbiome (the community of bacteria and other microorganisms living in the gut) plays an important role in GVHD development. Research has shown that disruption to these helpful gut bacteria can increase the risk of developing intestinal GVHD. The conditioning regimen and antibiotics used during transplant can damage this delicate microbial community^[3].

Risk Factors for Developing Intestinal GVHD

Several factors can increase a person’s likelihood of developing acute GVHD of the intestine after a stem cell transplant. Understanding these risk factors helps patients and medical teams prepare and take appropriate preventive measures.

One significant risk factor involves the type of donor used for the transplant. Transplants from unrelated donors carry a higher risk of GVHD compared to transplants from related donors, such as siblings. Additionally, transplants using peripheral blood stem cells (cells collected from circulating blood) rather than bone marrow have an increased risk of causing GVHD^[10].

The degree of matching between donor and recipient matters greatly. When there is a mismatch in HLA markers, or when the donor and recipient are haplo-identical (sharing only half of their genetic markers), the risk of acute GVHD increases. Having a female donor also raises the odds of developing GVHD^[13].

The intensity of the conditioning regimen before transplant influences GVHD risk. More intensive chemotherapy and radiation, particularly total body irradiation, can increase the likelihood of developing acute GVHD. This is because these treatments cause more tissue damage, which triggers stronger inflammatory responses^[4].

Infections during the transplant period can also heighten the risk. When the body fights off infections, it releases inflammatory signals that can worsen GVHD or trigger its onset. Damage to the gut microbiome from antibiotics or the conditioning regimen makes patients more vulnerable to intestinal GVHD^[4].

Interestingly, researchers have found that patients who have a particular species of bacteria in their gut called Blautia have a lower risk of developing acute GVHD. This suggests that maintaining a healthy and diverse gut microbiome may offer some protection against this complication^[4].

Symptoms and Clinical Presentation

Acute GVHD of the intestine causes symptoms that can range from mild to severe and life-threatening. The gastrointestinal tract, when attacked by GVHD, responds with symptoms that can significantly impact daily life and overall health.

The most common symptom of intestinal GVHD is diarrhea, which can be profuse and watery. This is a secretory diarrhea, meaning the intestines are secreting large amounts of fluid rather than absorbing it properly. Some patients may experience more than a liter of diarrhea per day in severe cases^[1].

Abdominal cramping and pain are frequent complaints. These can range from mild discomfort to severe, debilitating pain that interferes with eating and normal activities. Nausea and vomiting often accompany intestinal GVHD, making it difficult for patients to maintain adequate nutrition and hydration^[2].

Loss of appetite is common and can lead to significant weight loss. Patients may feel full quickly or have no desire to eat at all. This loss of appetite, combined with the body’s inability to properly absorb nutrients due to intestinal damage, can result in malnutrition^[10].

In more severe cases, patients may notice blood in their stool. This occurs when GVHD causes bleeding in the intestinal lining. The intestinal mucosa can become severely inflamed, with erosions and ulcerations forming along its surface. In the most extreme cases, parts of the intestinal lining may slough off completely^[1].

The severity of intestinal GVHD is typically graded from stage 1 (mild) to stage 4 (very severe). Grade 4, the most severe form, causes extensive abdominal symptoms with severe cramping and pain. Patients with severe intestinal GVHD may become so ill that they require hospitalization for intravenous fluids and intensive supportive care^[4].

When describing their experience with intestinal GVHD, patients have reported feeling as though their insides were “on fire,” with alternating waves of pain and nausea. The constant diarrhea can leave patients exhausted and dehydrated, sometimes causing them to lose consciousness. The unpredictability of symptoms can make even simple daily tasks feel overwhelming^[13].

Prevention Strategies

Prevention is the cornerstone of managing acute GVHD of the intestine. Medical teams employ several strategies to reduce the risk of this complication, though it’s important to understand that GVHD cannot always be completely prevented.

The first line of prevention involves careful donor selection. When possible, choosing a donor who is the best HLA match helps minimize the immune system’s response against the recipient’s tissues. Doctors use sophisticated laboratory tests to identify the closest possible match among available donors^[2].

Medications that suppress the immune system are routinely given before and after transplant to prevent GVHD. These prophylactic medications typically include drugs such as calcineurin inhibitors (like cyclosporine or tacrolimus) combined with other agents like methotrexate or mycophenolate mofetil. These medications work to calm the donor immune cells and reduce their tendency to attack the recipient’s tissues^[5].

Some transplant centers use T-cell depletion techniques, where some of the immune cells are removed from the donor graft before transplantation. This can include using anti-thymocyte globulin (ATG) or a technique called post-transplant cyclophosphamide (PTCy). By reducing the number of aggressive immune cells in the graft, these approaches can lower GVHD risk^[8].

Supporting a healthy gut microbiome has emerged as an important preventive strategy. Transplant patients typically have a less diverse gut microbiome because they’ve had extensive chemotherapy and have received many antibiotics. A healthy gut microbiome can be supported through the use of prebiotics (substances that feed beneficial bacteria), though over-the-counter probiotics are generally not sufficient to restore the gut microbiome after transplant^[4].

Fecal microbiota transplant, where stool from a healthy donor is used to restore the recipient’s gut bacteria, represents the most effective way to replace the intestinal microbiome. This procedure transfers all the necessary bacteria, fungi, and other microorganisms. However, this approach comes with risks, including the potential transmission of infections, and is still being studied in clinical trials^[4].

The key to prevention depends on maintaining a healthy gut microbiome, choosing the appropriate GVHD prophylaxis medications, carefully selecting the conditioning regimen, and minimizing damage to the intestinal lining during the transplant process^[4].

How Acute Intestinal GVHD Affects the Body

To understand how acute GVHD affects the intestine, it helps to know what normally happens in a healthy digestive system. The intestines are lined with a layer of epithelial cells that form a protective barrier. These cells absorb nutrients and water while keeping harmful bacteria and toxins out of the bloodstream. The intestinal lining constantly renews itself, with old cells being replaced by new ones every few days.

When acute GVHD attacks the intestines, the donor’s immune cells target and destroy the epithelial cells lining the gut. Under a microscope, doctors can see a characteristic finding: apoptosis (programmed cell death) of the intestinal mucosal epithelium. Individual cells begin dying off, and in severe cases, large sections of the intestinal lining can slough away completely, leaving areas of denudation where there is no protective layer at all^[6].

This destruction disrupts the intestine’s normal functions in several ways. First, the damaged lining cannot properly absorb nutrients, calories, and hydration from food and drink. This leads to malnutrition, weight loss, and dehydration despite adequate intake^[14].

Second, the intestinal barrier breaks down, allowing bacteria and toxins to leak through. This not only causes local inflammation but can also trigger system-wide inflammatory responses. The intestine begins secreting large amounts of fluid rather than absorbing it, resulting in the profuse, watery diarrhea characteristic of intestinal GVHD^[1].

The immune attack also triggers the release of inflammatory molecules called cytokines. These substances amplify the inflammatory response and can cause additional damage to the intestinal tissue. The blood vessels in the intestinal wall become leaky and inflamed, which can lead to bleeding. In severe cases, patients may develop intestinal ulcers or even perforations (holes in the intestinal wall)^[6].

Research has revealed that acute GVHD causes a loss of specialized intestinal cells called neuroendocrine L-cells. These cells normally produce a hormone called glucagon-like peptide-2 (GLP-2), which helps maintain the intestinal lining and supports the function of important cells like Paneth cells and intestinal stem cells. When these cells are lost, the intestine struggles to repair and regenerate itself^[9].

The intestinal stem cells, which are responsible for continuously renewing the gut lining, are particularly vulnerable to GVHD. When these cells are damaged or destroyed, the intestine loses its ability to heal itself effectively. This creates a cycle where damage accumulates faster than the body can repair it^[3].

The inflammation and tissue destruction in the gut also disrupt the intestinal nerves that control movement and sensation. This can affect how food moves through the digestive system, contributing to symptoms like cramping, bloating, and altered bowel patterns^[1].