Tumor-infiltrating lymphocyte (TIL) therapy has shown recent promise in the treatment of advanced melanoma. However, current manufacturing pipelines make use of bulk-expanded TILs, without the ability to select for bona fide tumor-reactive clonotypes. Thus, new methodologies are required to enhance the selectivity and potency of autologous TILs, while leaving bystander T cells untouched. Here, we demonstrate an approach to target recently-activated T cells via display of agonistic ligands that bind to a marker of early T cell activation (4-1BB, CD137) on the surface of a lentiviral (LV) particle. These pseudotyped LV vectors specifically recognize human 4-1BB in cell lines and primary T cells, promoting the selective activation and expansion of antigen-specific T cells from rare starting populations after antigen stimulation. Moreover, anti-4-1BB LVs specifically transduce antigen-specific T cells with userdefined genetic cargoes that can be used to both track individual clonotypes via single-cell sequencing and enhance their cytotoxic function to extend survival in a xenograft model of human melanoma. We also demonstrate that anti-4-1BB LVs can be directly added to tumor-associated lymphocytes and TILcontaining tumor fragments, promoting the transduction of patient-specific T cells ex vivo. Overall, this platform offers the ability to target antigen-specific T cells (CD4+, CD8+) in an antigen-agnostic, MHCindependent manner with potential applications in adoptive cell therapy manufacturing pipelines and TCR identification efforts.