Generation and Functional Capacity of Polyclonal Alloantigen‐Specific Memory CD4 T Cells

Alloreactive memory T cells can significantly impact graft survival due to their enhanced functional capacities, diverse tissue distribution and resistance to tolerance induction and depletional strategies. However, their role in allograft rejection is not well understood primarily due to the lack of suitable in vivo models. In this study, we use a novel approach to generate long‐lived polyclonal alloreactive memory CD4 T cells from adoptive transfer of alloantigen‐activated precursors into mouse hosts. We demonstrate that CD25 upregulation is a marker for precursors to alloantigen‐specific memory and have created a new mouse model that features an expanded population of polyclonal alloreactive memory T cells that is distinguishable from the naive T‐cell population. Furthermore, we show that alloreactive memory T cells exhibit rapid recall effector responses with predominant IFN‐γ and IL‐2 production, and mediate vigorous allograft rejection. Interestingly, while we found a heterogeneous distribution of allomemory T cells in lymphoid and nonlymphoid tissues, they were all predominantly of the effector‐memory (CD62Llo) phenotype. Our results present a unique model for the generation and tracking of polyclonal allospecific memory CD4 T cells in vivo and reveal insights into the distinct and robust nature of alloreactive T‐cell memory.