Also known as: Cancer cells that act like stem cells
The central mystery: transplant recipients from the same organ donor develop fatal organ failures in different systems. House determines the donor had cancer stem cells that partially differentiated into organ-specific tissue but failed to function properly, causing sudden organ failure. In Apple's case, these cells lodged in her occipital lobe, causing visual processing problems despite a healthy transplanted cornea.
Elderly transplant recipient with intestinal graft who develops fatal pancreatic failure. House attempts to perform a brain biopsy on him to investigate the mystery illness affecting all transplant recipients, but Frank dies before the procedure can provide answers.
Also known as: Heart attack
One of the transplant recipients who died from sudden cardiac failure months after receiving a kidney from the mystery donor.
Also known as: Liver failure
Transplant recipient who received a new heart and lung but died from sudden liver failure, part of the pattern of organ failures in recipients from the same donor.
Also known as: Lung failure
Transplant recipient who received a liver but died from sudden lung failure. Later revealed he was taking methotrexate for arthritis, which temporarily helped manage symptoms related to the cancer stem cells.
Also known as: TLE
Transplant recipient who appeared to die from head trauma during a boxing match, but House discovers through video analysis that he had a temporal lobe seizure moments before being hit, indicating neurological involvement in the mystery illness.
Apple's primary symptom: despite having a successful corneal transplant and healthy eye, she perceives the world as ugly and gray because cancer stem cells in her occipital lobe interfere with proper visual processing. Surgery to remove these cells restores her normal vision.