Abstract
Tumor infiltrating lymphocytes (TIL) display activation markers and their presence is often associated with a favorable outcome. The role of tumor antigens in T cell recruitment into tumors is unclear. In an attempt to address this issue, we purified lymphocytes from breast tumor or nontumor, mammary tissue from patients, and normal mammary tissue from healthy individuals. In all groups, including healthy individuals, the majority of cells displayed an effector/memory (CD45RA^lo^/CD27^+/−^) phenotype and quite surprisingly the early and transient activation marker CD69, thus, questioning the tumor antigen specificity of TIL. Because the human repertoire is diverse, the T cells found in the tumors could recognize both self/tumor and environmental antigens through cross‐reactivity. To test this hypothesis, we used two anti‐male HY monospecific TCR transgenic mouse models. We found an infiltration of HY negative tumors by the CD4^+^ and CD8^+^ monoclonal T cells after priming with HY positive cells in the periphery. Thus, the presence of activated effector/memory T lymphocytes in tumors can be independent of reactivity against tumor antigens. These results suggest that to find activated effector T cells in a tissue does not always mean that a specific immune response is taking place. © 2005 Wiley‐Liss, Inc.