Graft-Versus-Host Disease (GVHD): Donor Immune Attack on the Host
Graft-versus-host disease (GVHD) is a severe immune-mediated condition that occurs when donor immune cells attack the recipient’s tissues following transplantation. Unlike transplant rejection, where the host immune system targets the graft, GVHD represents the reverse immune relationship. It most commonly occurs after allogeneic haematopoietic stem cell transplantation, where donor immune cells are transferred into an immunocompromised host. The condition results from a failure of immune tolerance between donor and recipient.
What You Need to Know
Graft-versus-host disease develops when immunologically active donor T lymphocytes mount an immune response against recipient tissues. This occurs most commonly after allogeneic stem cell or bone marrow transplantation, where donor immune cells are transferred into a host whose immune system is impaired or suppressed. For GVHD to occur, donor immune cells must be viable and capable of activation, the recipient must express antigens that differ from those of the donor, and the recipient must be unable to effectively eliminate donor lymphocytes. When these conditions coexist, donor T cells recognise host tissues as foreign and initiate sustained immune attack.
Once activated, donor T cells proliferate and migrate into multiple organs, releasing inflammatory mediators and recruiting additional immune cells. This immune activity is systemic rather than localised, meaning tissue injury is driven by immune recognition rather than infection, toxicity, or mechanical damage. Organs with high cell turnover or active immune surveillance are particularly vulnerable, which explains why the skin, gastrointestinal tract, and liver are commonly involved. Injury is immune-mediated and progressive, rather than self-limiting, because host antigens remain continuously present.
Several core principles explain the behaviour of GVHD:
donor T cells act as the primary drivers of tissue injury rather than recipient immune cells
immune activation targets normal host tissues rather than pathogens or malignant cells
tissue damage progresses through sustained immune signalling rather than isolated inflammatory events
GVHD exists as a spectrum of disease rather than a single uniform process. Acute and chronic GVHD differ in immune mechanisms, patterns of tissue injury, and clinical behaviour. Acute GVHD is dominated by inflammatory T-cell–mediated injury, while chronic GVHD involves longer-term immune dysregulation, fibrosis, and immune-mediated tissue remodelling. These forms represent distinct pathophysiological patterns rather than sequential stages of the same disease. In both cases, GVHD arises from persistent immune imbalance rather than transient immune activation, which explains its prolonged course and potential for significant morbidity.
Beyond the Basics
Initiation of GVHD: host tissue injury and immune activation
GVHD is initiated by tissue injury in the recipient, most commonly caused by conditioning regimens such as chemotherapy or radiation prior to transplantation. This injury disrupts normal tissue integrity and leads to release of inflammatory mediators and host antigens. Antigen-presenting cells within the recipient become activated in this pro-inflammatory environment and process host antigens for presentation to donor T lymphocytes. The presence of inflammation lowers immune activation thresholds, meaning donor immune cells encounter host antigens in a context that favours immune attack rather than tolerance.
Damaged host tissues generate danger signals that donor T cells interpret as evidence of foreign or abnormal tissue. Instead of remaining quiescent, donor immune cells are primed toward activation. This early inflammatory phase is critical because it determines whether donor immune cells remain controlled or progress to widespread immune activation. Once this priming occurs, downstream immune responses are difficult to contain.
Donor T-cell activation and clonal expansion
Following antigen presentation, donor T cells become activated and undergo clonal expansion. Activated cells differentiate into effector T lymphocytes capable of direct cytotoxic injury and high-level cytokine production. The immune response rapidly amplifies as additional donor immune cells are recruited and activated through cytokine signalling. This process mirrors a normal immune response to infection, but the target is host tissue rather than a pathogen. Activated donor T cells migrate beyond the initial site of activation and circulate systemically. This allows immune injury to occur simultaneously across multiple organs. Because donor immune cells remain viable and persist within the host, immune attack does not resolve spontaneously. Ongoing antigen exposure sustains activation, explaining the progressive and systemic nature of GVHD.
Cytokine-mediated tissue injury
Cytokine signalling plays a central role in GVHD-associated damage. Pro-inflammatory cytokines increase vascular permeability, promote immune cell recruitment, and amplify local inflammation within affected tissues. This creates a self-reinforcing inflammatory environment that intensifies tissue injury. As cells are damaged, additional host antigens are released, further fuelling immune activation. This widespread cytokine activity produces both organ-specific injury and systemic illness. Patients may develop features that resemble severe inflammatory or infectious syndromes, despite the absence of an external pathogen. Sustained cytokine signalling prevents resolution of inflammation and promotes ongoing tissue damage, setting the stage for chronic disease.
Target organ vulnerability
Certain organs are particularly susceptible to GVHD because of their high immune activity and rapid cellular turnover. The skin, gastrointestinal tract, and liver are most commonly affected. In the skin, immune-mediated epithelial injury disrupts barrier integrity and normal regeneration. In the gastrointestinal tract, mucosal damage impairs absorption and compromises barrier function, increasing susceptibility to secondary inflammation and infection. Hepatic involvement arises from immune-mediated injury to bile ducts and surrounding tissue, disrupting normal metabolic and excretory processes. These organs also play important roles in immune regulation and systemic homeostasis. Injury to these systems worsens immune imbalance and contributes to escalation of disease. Organ involvement frequently overlaps, and progression can be rapid once multiple systems are affected.
Chronic GVHD: immune dysregulation and fibrotic disease
Chronic GVHD differs fundamentally from acute GVHD in both mechanism and outcome. Rather than being dominated by overt cytotoxic inflammation, chronic GVHD is characterised by persistent immune dysregulation, abnormal repair processes, and progressive fibrosis. Immune signalling interferes with normal tissue regeneration, leading to excessive scarring and structural distortion. Over time, fibrosis replaces functional tissue, resulting in permanent loss of organ function. Low-grade immune activity persists without re-establishment of immune control, allowing injury to continue even when acute inflammation subsides. This pattern explains why chronic GVHD often resembles autoimmune or fibrotic disease and why functional decline may progress despite apparent inflammatory quiescence.
Why GVHD is unique among immune disorders
GVHD is distinct from other immune-mediated diseases because the immune system attacking the host originates from the donor rather than the recipient. Donor immune cells retain full functional capacity but operate in an environment where normal regulatory mechanisms are absent or ineffective. This creates a profound imbalance in which immune attack proceeds with limited restraint. Because donor immune cells have no intrinsic tolerance to host tissues, immune retraining is not feasible. Prevention and management therefore rely on immune modulation to suppress donor immune activity rather than attempting to restore tolerance. GVHD represents externally imposed immune dysregulation, which explains both its severity and the complexity of long-term control.
Clinical Connections
Graft-versus-host disease often presents with involvement of multiple organ systems and can progress rapidly once donor immune activation is established. Early features commonly include skin changes such as rash or tightening, gastrointestinal symptoms including diarrhoea or abdominal pain, and biochemical or clinical evidence of liver dysfunction. These manifestations arise from donor T-cell–mediated injury to tissues with high immune activity and turnover. In chronic GVHD, presentation is more insidious, with gradual functional decline, fibrosis, and features that resemble autoimmune disease rather than acute inflammation. Although symptoms may fluctuate, immune-mediated tissue injury often continues beneath the surface.
Several clinical patterns raise concern for evolving GVHD:
concurrent changes in skin, gut, and liver function suggesting systemic immune activation
progressive stiffness, dryness, or fibrotic changes indicating chronic immune-driven remodelling
deterioration in organ function without an alternative infectious or toxic explanation
Assessment therefore focuses on coordinated monitoring across systems rather than isolated symptoms. Subtle changes in skin integrity, gastrointestinal tolerance, liver function tests, or functional capacity may signal donor immune activity before severe injury is established. Long-term management centres on sustained immune suppression to limit donor T-cell activity while minimising complications such as infection, metabolic disturbance, and drug toxicity. Preserving organ function depends on early detection of immune-mediated injury and careful adjustment of therapy over time rather than reaction to advanced disease alone.
Concept Check
How does graft-versus-host disease differ immunologically from transplant rejection?
Why is host tissue injury an important trigger for GVHD?
How do donor T cells become activated and sustain immune attack?
Why are the skin, gut, and liver particularly affected in GVHD?
How does chronic GVHD differ pathophysiologically from acute GVHD?