Background Resident-memory T cells (T_RM) permanently reside in tissues, surveying local environments without recirculating. Surface protein expression (e.g. CD69, CD103) and transcriptional signatures from infection models are used as surrogate markers of T cell residency. Across numerous solid tumor types, T_RM-like phenotypes have been identified and correlated with improved prognosis and responsiveness to immunotherapy. However, the migration properties of CD8⁺tumor infiltrating lymphocytes (TILs) have not been well described, and the reliability of healthy tissue T_RM markers for correlating with CD8⁺ TIL migration properties remains unknown.

Methods In this study, we employed parabiosis migration assays in the context of both acute viral infection and a mouse model of breast cancer. In combination, this system allowed us to simultaneously track both virus-specific memory T cells and tumor-specific T cells.

Results Our migration assays demonstrated that both virus-specific, bystander and tumor-specific CD8⁺ TILs can be resident. Canonical markers of T_RM, including CD69, correlated with tissue residence in healthy mammary tissue, but failed to discriminate between resident cells and recent migrants in tumors. Instead, the expression of markers associated with chronic T cell stimulation (PD-1, CD39, Tim-3) identified a population of resident, tumor-specific cells. We further observed that after tumor entry, Tcf-1⁺PD-1^lo tumor-specific T cells progressively acquired the expression of inhibitory receptors, such as Tim-3, correlating with the phenotypes that represented tumor retention and residence.

Conclusions Thus, T_RM exist within tumors, durable intratumoral residence was not informed by common markers associated with pathogen-specific T_RM that have been described in healthy tissue, but tumor-specific T cells become resident upon tumor antigen recognition and the subsequent upregulation of CD39 and Tim-3. Together with high-dimensional, single-cell transcriptomics, we propose an integrated view of tumor immunosurveillance in which tissue environments and antigen-specific recognition drive distinct residence programs.

Ethics Approval All mice used in experiments were 5–15 weeks of age and used in accordance with the Institutional Animal Care and Use Committees guidelines at the University of Minnesota.