Tumor-Primed, In Vitro-Activated CD4+ Effector T Cells Establish Long-Term Memory without Exogenous Cytokine Support or Ongoing Antigen Exposure

Tumor-reactive T cells can be primed in vivo, then activated in vitro to provide numerical expansion and uniform acquisiton of effector phenotype and function. Adoptive transfer of effector T cells mediates complete regression of established tumors in animal models. Some experimental models indicate that extensive in vitro proliferation of T cells inhibits efficacy and that central memory T cells (T(CM)) provide greater activity than effector memory T cells (T(EM)). Clinical studies also demonstrate that persistence of adoptively transferred T cells is associated with therapeutic response, thus identifying that conditions to maximize effector cell numbers yet retain memory function are important. In this article, we demonstrate that adoptive transfer of in vitro activated effector CD4(+) T cells into tumor-free congenic mice mediates rejection of tumor challenge 9 mo later, at which time T cells re-express activation markers and undergo rapid proliferation at tumor sites. Analysis of the phenotype of memory cells in lymphoid tissues following adoptive transfer shows high CD44 expression with heterogeneous expression of CD62L, indicating a mixture of T(EM) and T(CM) phenotypes. Memory cells were sorted into two subsets based on CD62L expression levels and then activated in vitro. Although T(EM) cells proliferated more rapidly, T(EM) and T(CM) cells acquired effector phenotype and function. These data indicate that controlled in vitro expansion of tumor-reactive T cells for adoptive immunotherapy also provides a competent memory response.