Acute graft versus host disease is a serious complication that can occur after receiving donated stem cells during an allogeneic transplant. When donor immune cells mistake the recipient’s body as foreign, they launch an attack against healthy tissues and organs, creating a condition that affects thousands of transplant patients worldwide each year.
Understanding Acute Graft Versus Host Disease
Acute graft versus host disease, commonly shortened to acute GVHD, develops when immune cells from transplanted tissue recognize the recipient’s body as foreign and begin attacking its cells. The term “graft” refers to the transplanted or donated tissue, while “host” refers to the recipient’s own tissues. This condition represents one of the most significant challenges facing patients who undergo allogeneic hematopoietic stem cell transplantation, which is a procedure where stem cells from a donor are transplanted into a patient’s body.[1]
Traditionally, doctors classified acute GVHD based on when symptoms appeared after transplant. The original definition considered any symptoms occurring within the first 100 days as acute GVHD. However, medical understanding has evolved, and healthcare providers now recognize that the timing alone doesn’t tell the complete story. Modern classification considers both the timing and the specific symptoms that patients experience. This means acute GVHD can sometimes develop beyond the 100-day mark, particularly in patients who received less intensive conditioning regimens or donor lymphocyte infusions.[1]
The National Institutes of Health has established updated classifications to better capture the complexity of this condition. These include acute classic GVHD, which presents within 100 days with typical symptoms, and persistent, recurrent, or late-onset acute GVHD, which shows the same characteristic features but appears after the 100-day window. Some patients may even experience overlap syndrome, where features of both acute and chronic GVHD appear together at any point after transplant.[1]
Epidemiology
Acute GVHD affects a substantial number of transplant recipients worldwide. The occurrence of this condition varies considerably depending on several factors, including the type of donor, the closeness of tissue matching, and the preventive treatments used. When patients receive stem cells from an HLA-matched sibling, meaning a brother or sister with very similar tissue markers, acute GVHD develops in approximately 9 to 50 percent of cases. When the donor is unrelated or not as closely matched, the rates climb higher.[5]
Overall statistics suggest that between 35 and 50 percent of patients who undergo hematopoietic stem cell transplantation will develop acute GVHD. This percentage translates to an estimated 5,500 patients per year developing the condition. The exact risk for any individual patient depends on multiple variables that healthcare teams carefully consider before transplant.[4]
Acute GVHD remains a major cause of death and serious complications in the short term following transplant. It directly or indirectly contributes to mortality at the 100-day and one-year marks after transplantation. The condition carries high rates of both illness and death, making it a major health problem for transplant recipients. Furthermore, approximately 50 percent of patients who experience acute GVHD will eventually develop manifestations of chronic GVHD later in their recovery journey.[4][3]
Causes
The fundamental cause of acute GVHD lies in a complex interaction between the donor’s immune system and the recipient’s body. When a patient receives an allogeneic transplant, they are receiving hematopoietic stem cells, which are immature blood cells that eventually mature and create all types of blood cells, including those of the immune system. These donor cells carry genetic information that differs from the recipient’s own cells.[2]
Normally, blood cells in the immune system protect the body by fighting off invaders like viruses and bacteria. They recognize which cells belong to the body by identifying a protein marker called human leukocyte antigens, or HLA. These markers function like name tags that tell immune cells, “this cell belongs here.” When donor immune cells enter the recipient’s body, they may recognize the recipient’s HLA markers as unfamiliar or threatening, even when doctors have carefully matched the donor and recipient as closely as possible.[2]
The development of acute GVHD follows a three-phase process. The first phase involves tissue damage from the conditioning regimen, which includes the chemotherapy or radiation therapy patients receive before transplant to prepare their body. This initial damage activates the recipient’s antigen-presenting cells through molecules released from damaged and dying cells. The second phase, called the afferent phase, involves the activation and multiplication of donor T cells, which are a type of immune cell. In the final effector phase, these activated immune cells cause damage to the recipient’s tissues through various mechanisms, including direct cell killing and the release of inflammatory molecules called cytokines.[5][11]
Risk Factors
Multiple factors can increase a patient’s likelihood of developing acute GVHD after transplant. Understanding these risk factors helps medical teams plan preventive strategies and helps patients know what to expect. One of the most significant risk factors involves the degree of HLA mismatch between donor and recipient. When the donor and recipient have more differences in their HLA markers, the donor immune cells are more likely to recognize the recipient’s body as foreign. Transplants from unmatched or partially matched donors carry higher rates of acute GVHD compared to those from well-matched siblings.[5][7]
Age plays an important role in acute GVHD risk. Older patients tend to develop this complication more frequently than younger recipients. The relationship between donor and recipient sex also matters. When a female donor provides stem cells to a male recipient, particularly if the female donor has previously been pregnant, the risk of acute GVHD increases. This occurs because pregnancy can sensitize the donor’s immune system to recognize male-specific proteins as foreign.[7]
Previous donor alloimmunization, meaning the donor’s immune system has been exposed to foreign tissue in the past, represents another risk factor. The source of stem cells also influences risk. The type of conditioning regimen matters as well. Patients who receive total body irradiation as part of their preparation for transplant face higher rates of acute GVHD. Chemotherapy and radiation therapy cause tissue damage that can trigger the inflammatory processes leading to GVHD development.[5][7]
Interestingly, some factors can lower the risk of developing acute GVHD. The use of cryopreservation, or freezing of the donor marrow before transplant, appears protective. The use of umbilical cord blood as a stem cell source tends to result in lower GVHD rates compared to other sources. Additionally, the strategic use of immunomodulators, which are medications that adjust immune system activity, can reduce the incidence of acute GVHD.[5]
Symptoms
Acute GVHD most commonly affects three main areas of the body: the skin, the gastrointestinal tract, and the liver. The symptoms can range from mild discomfort to severe, life-threatening complications. Understanding what to watch for enables patients and caregivers to report concerns to the medical team promptly, which is crucial for timely treatment.[3][4]
Skin involvement represents the most common manifestation of acute GVHD. The most characteristic symptom is a rash or reddened areas on the skin that many patients describe as resembling a sunburn. These rashes typically begin on specific areas: the neck, shoulders, ears, and notably on the palms of the hands and soles of the feet. From these starting points, the rash can spread to cover other parts of the body. The affected skin may feel painful, itchy, or both. In more severe cases, the skin may develop blistering or begin peeling. Some patients report that the skin feels tight or uncomfortable.[2][9]
When acute GVHD affects the gastrointestinal tract, patients experience a different set of symptoms that can significantly impact daily life. The most common complaints include nausea, vomiting, and diarrhea. The diarrhea associated with GI acute GVHD can be quite severe and may contain blood in more serious cases. Patients often experience crampy abdominal pain that comes and goes. Loss of appetite is common, and some patients struggle to maintain adequate nutrition and hydration. The severity can range from mild discomfort that is manageable at home to severe symptoms requiring hospitalization for intravenous fluids and nutritional support.[2][9]
Liver involvement in acute GVHD manifests differently than skin or GI symptoms. The most visible sign is jaundice, which is a yellowing of the skin and the whites of the eyes. This occurs because the inflamed liver cannot properly process bilirubin, a yellow pigment produced when red blood cells break down. Blood tests typically show elevated liver enzymes and bilirubin levels. Some patients notice their urine becomes darker in color. Unlike skin or GI GVHD, liver involvement may not cause obvious symptoms initially, and changes might only be detected through routine blood work.[2][9][4]
The symptoms of acute GVHD typically develop within the first three months after transplant, often beginning two to three weeks after the stem cells are infused. However, symptoms can appear later, particularly in patients who received reduced-intensity conditioning regimens. Patients may experience involvement of just one organ, two organs, or all three target organs simultaneously. The extent and severity of organ involvement determines the grade of acute GVHD, which ranges from grade 0 (no GVHD) to grade IV (the most severe form).[3][7]
Prevention
Because acute GVHD carries such significant risks, all patients who undergo allogeneic hematopoietic cell transplantation receive preventive treatment, even though these measures don’t always succeed in preventing the condition. The cornerstone of prevention involves immunosuppressive medications that calm or suppress the donor immune cells to reduce the likelihood they will attack the recipient’s tissues.[3][10]
The standard prevention approach combines cyclosporine with a short course of methotrexate. Cyclosporine is a medication that suppresses T-cell activity and is typically continued for six months after transplant. Healthcare providers carefully monitor cyclosporine blood levels to ensure they remain in the therapeutic range, usually above 200 nanograms per milliliter. Methotrexate is given in several doses during the early days and weeks following transplant. This combination has become the criterion standard because it effectively reduces acute GVHD rates without completely eliminating beneficial immune responses.[10]
Many transplant centers substitute tacrolimus for cyclosporine, particularly when the donor is unrelated to the recipient. Studies suggest tacrolimus may provide better control of acute GVHD compared to cyclosporine, though it doesn’t necessarily improve overall survival rates. Some protocols add prednisone, a corticosteroid medication, to the preventive regimen. While adding prednisone reduces the incidence of acute GVHD, it does not change overall survival and comes with its own set of potential side effects.[10]
Another prevention strategy involves using antithymocyte globulin, or ATG, before the stem cell transplant. This medication significantly reduces the risk of developing severe acute GVHD (grades III or IV) and also decreases the likelihood of extensive chronic GVHD developing later. However, ATG doesn’t alter overall survival rates, possibly because it increases the risk of infections by suppressing immune function more broadly.[10]
Other medications being studied or used for GVHD prevention include mycophenolate mofetil, sirolimus, pentostatin, alemtuzumab, and cyclophosphamide given after transplant. Some centers employ T-cell depletion techniques, where donor T cells are removed from the graft before transplant. While this approach reduces GVHD rates, it hasn’t improved overall survival compared to standard prevention methods, and it may increase the risk of other complications like infection or disease relapse.[10]
A specialized procedure called extracorporeal photopheresis represents an innovative prevention approach. In this procedure, doctors collect the patient’s lymphocytes (a type of white blood cell) and mix them with a medication called 8-methoxypsoralen. When these cells are exposed to ultraviolet light, they become susceptible to programmed cell death. The treated cells are then returned to the patient. Some centers use this procedure as part of the conditioning regimen before transplant, with promising results.[10]
Pathophysiology
The biological processes underlying acute GVHD involve a cascade of events that begins even before the donor stem cells are infused and continues as the transplanted immune system establishes itself in the recipient’s body. Understanding these mechanisms helps explain why certain treatments work and why the condition affects specific organs.[1]
The first step in the pathophysiology involves tissue damage from the conditioning regimen. The chemotherapy or radiation therapy patients receive before transplant serves the important purpose of making space for donor cells and suppressing the recipient’s immune system so it won’t reject the graft. However, this conditioning also damages tissues throughout the body, particularly rapidly dividing cells in the skin, gut lining, and other organs. Damaged and dying cells release molecules called pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). These molecules act as danger signals that activate the recipient’s remaining immune cells.[5][11]
In the second phase, called the afferent phase, the damage signals activate antigen-presenting cells. These specialized cells display bits of the recipient’s proteins to donor T cells that arrive with the transplanted stem cells. When donor T cells encounter these displayed antigens and recognize them as foreign, they become activated. Once activated, donor T cells multiply rapidly, producing large populations of cells primed to attack the recipient’s tissues. This recognition and activation process represents the core immunological mismatch driving acute GVHD.[5]
The third and final phase, known as the effector phase, is when actual tissue damage occurs. Activated donor T cells use multiple mechanisms to destroy recipient cells. Some T cells directly kill target cells by releasing toxic substances or triggering programmed cell death pathways. Other T cells release inflammatory cytokines, which are signaling molecules that recruit additional immune cells and amplify the inflammatory response. Key cytokines involved in acute GVHD include tumor necrosis factor-alpha, interleukin-1, and interferon-gamma. These molecules create a highly inflammatory environment that damages epithelial cells, which are the cells lining surfaces like skin and the digestive tract.[5][11]
The body attempts to counterbalance this aggressive immune response through regulatory mechanisms. Regulatory T cells and certain types of suppressor cells try to dampen the inflammatory cascade, but in acute GVHD, the balance tips toward immune activation rather than regulation. The disturbed equilibrium between immune activation and immune tolerance, combined with impaired tissue repair capacity, determines the severity of clinical damage patients experience.[11]
The target organs in acute GVHD share certain characteristics that make them vulnerable to this immune attack. The skin, gastrointestinal tract, and liver all contain epithelial tissues that are regularly exposed to foreign antigens and therefore maintain active immune surveillance. These organs also undergo constant cell turnover, making them more susceptible to damage when immune cells attack. The gut, in particular, harbors trillions of bacteria that can contribute to inflammation when the intestinal barrier is compromised by GVHD, potentially worsening the condition through bacterial products entering the bloodstream.[3]
