Adoptive T-cell therapy based on the infusion of patient’s own immune cells after ex vivo culturing is among the most potent forms of personalized treatment among recent clinical developments for the treatment of cancer. However, despite high rates of successful initial clinical responses, only about 20 % of patients with metastatic melanoma treated with tumor-infiltrating lymphocytes (TILs) enter complete and long-term regression, with the majority either relapsing after initial partial regression or not benefiting at all. Previous studies have shown a positive correlation between the number infused T cells migrating to the tumor and the clinical response, but also that only a small fraction of adoptively transferred Tcells reach the tumor site. In this chapter, we describe a protocol for transfection of TILs with mRNA encoding the chemokine receptor CXCR2 transiently redirecting and improving TILs migration toward tumor-secreted chemokines in vitro.