14.2 Types of transplant rejection

Transplant rejection poses a significant challenge in organ transplantation. The immune system's response to foreign tissue can lead to three types of rejection: hyperacute, acute, and chronic. Each type has distinct mechanisms, timelines, and clinical manifestations.

Understanding these rejection types is crucial for successful transplantation. Prevention strategies, such as careful donor-recipient matching and immunosuppression, along with prompt management of rejection episodes, are key to improving graft survival and patient outcomes.

Types of Transplant Rejection

Types of transplant rejection

• Hyperacute rejection occurs within minutes to hours after transplantation mediated by preformed antibodies in recipient's blood rapidly attacking donor tissue (kidney, heart)
• Acute rejection develops days to weeks post-transplantation involving T-cell mediated response against donor antigens leading to inflammation and organ dysfunction (liver, lung)
• Chronic rejection occurs months to years after transplantation causing gradual decline in graft function due to ongoing immune responses resulting in fibrosis (cornea, blood vessels)

Mechanisms of rejection

• Hyperacute rejection
  • Preexisting antibodies bind donor endothelial cells triggering complement activation
  • Rapid thrombosis forms in blood vessels
  • Neutrophils infiltrate causing extensive tissue damage
• Acute rejection
  • T cells recognize donor MHC molecules as foreign
  • CD4+ T helper cells activate macrophages and B cells amplifying immune response
  • CD8+ cytotoxic T cells directly attack graft cells causing apoptosis
  • Activated B cells produce antibodies against donor antigens
• Chronic rejection
  • Persistent low-grade inflammation damages graft over time
  • Alloantibody production against donor HLA molecules
  • Fibrosis and tissue remodeling alter organ structure
  • Vascular changes lead to ischemia and progressive dysfunction

Clinical signs of rejection

• Hyperacute rejection
  • Immediate graft failure within minutes to hours post-transplant
  • Cyanosis and mottling of transplanted organ indicate lack of blood flow
  • Absence of blood flow in imaging studies (ultrasound, angiography)
• Acute rejection
  • Onset within days to weeks after transplantation
  • Fever, malaise, and graft tenderness signal immune activation
  • Organ-specific dysfunction (elevated creatinine in kidney transplants, increased liver enzymes)
  • Biopsy shows cellular infiltration and tissue damage confirming diagnosis
• Chronic rejection
  • Gradual onset months to years post-transplant
  • Progressive decline in graft function detected through lab tests
  • Fibrosis and scarring of transplanted organ visible on imaging
  • Organ-specific manifestations (bronchiolitis obliterans in lung transplants, coronary artery disease in heart transplants)

Prevention and management strategies

• Prevention strategies
  • Careful donor-recipient matching (ABO blood type, HLA typing) to minimize immunological differences
  • Pre-transplant crossmatching detects preformed antibodies avoiding hyperacute rejection
  • Immunosuppressive induction therapy at time of transplantation prevents early rejection
• Management of hyperacute rejection
  • Limited treatment options due to rapid onset and severe damage
  • Immediate graft removal if detected to prevent systemic complications
  • Plasmapheresis removes circulating antibodies potentially salvaging graft
• Management of acute rejection
  • High-dose corticosteroids as first-line treatment suppress inflammation
  • T cell-depleting antibodies (antithymocyte globulin) for steroid-resistant cases
  • Adjustment of maintenance immunosuppression regimen (tacrolimus, mycophenolate)
• Management of chronic rejection
  • Regular monitoring of graft function through lab tests and imaging
  • Optimization of immunosuppression balancing rejection risk and side effects
  • Treatment of comorbidities (hypertension, hyperlipidemia) to protect graft function
  • Consideration of retransplantation in advanced cases when graft failure is imminent
• Long-term strategies
  • Patient education on medication adherence emphasizing importance of immunosuppression
  • Regular follow-up and monitoring for signs of rejection (lab tests, biopsies)
  • Minimization of immunosuppression-related side effects (infections, malignancies) through careful dosing