Cell therapy with tumor-infiltrating lymphocytes (TILs) has yielded durable responses for multiple cancer types, but the causes of therapeutic resistance remain largely unknown. Here multidimensional analysis was performed on time-serial tumor and blood in a lung cancer TIL therapy trial. Using T cell receptor sequencing on both functionally expanded T cells and neoantigen-loaded tetramer-sorted T cells, we identified tumor antigen-specific T cell receptors. We then mapped clones into individual transcriptomes and found that tumor-reactive clonotypes expressed a dysfunctional program and lacked stem-like features among patients who lacked clinical benefit. Tracking tumor-reactive clonotypes over time, decay of antigen-reactive peripheral T cell clonotypes was associated with the emergence of progressive disease. Further, subclonal neoantigens previously targeted by infused T cells were subsequently absent within tumors at progression, suggesting potential adaptive resistance. Our findings suggest that targeting clonal antigens and circumventing dysfunctional states may be important for conferring clinical responses to TIL therapy.