The roles of CD8 central and effector memory T-cell subsets in allograft rejection.

The contribution of secondary lymphoid tissue-homing central memory T cells (T(CM)) and peripheral tissue-homing effector memory T cells (T(EM)) to allograft rejection is not known. We tested whether T(EM) is the principal subset responsible for allograft rejection due to the nonlymphoid location of target antigens. Skin allograft rejection was studied after transferring either CD8 T(CM) or T(EM) to wild-type mice and to mice that lack secondary lymphoid tissues. We found that CD8 T(CM) and T(EM) were equally effective at rejecting allografts in wild-type hosts. However, CD8 T(EM) were significantly better than T(CM) at rejecting allografts in the absence of secondary lymphoid tissues. CD8 T(CM) were dependent upon secondary lymphoid tissues more than T(EM) for optimal differentiation into effectors that migrate into the allograft. Recall of either CD8 T(CM) or T(EM) led to accumulation of T(EM) after allograft rejection. These findings indicate that either CD8 T(CM) or T(EM) mediate allograft rejection but T(EM) have an advantage over T(CM) in immune surveillance of peripheral tissues, including transplanted organs.