The cells of the transplanted organ set off an immunological attack. Killer t cells and antibodies rush to the site, causing organ rejection, and the organ dies.

If this protein is derived from harmless substances inside the cell, immune system components known as killer t cells will bypass the cell, considering it to pose no threat to the body.

Natural killer cells, which are a class of lymphocyte distinct from t cells and B cells, destroy foreign cells (eg, neoplastic cells) even without prior sensitization.