Single-cell tracking reveals tumor-reactive T cell plasticity during melanoma TIL therapy

Here, we performed longitudinal single-cell RNA and T cell receptor (TCR) sequencing across five timepoints, from baseline tumors through a two-phase ex vivo expansion to post-infusion peripheral blood and tumor biopsies, in seven melanoma patients, generating a high-resolution map of both CD8+ and CD4+ tumor-reactive T cell plasticity.

During early expansion (preREP), tumor-reactive CD8+ T cells were reinvigorated from an exhausted state and acquired distinct HLA-II-high or KLF2-high transcriptional profiles. In-depth characterization of the CD4+ compartment revealed lineage-dependent reinvigoration. After transfer, both CD8+ and CD4+ tumor-reactive clones acquired stem-like profiles and tissue-homing markers before re-infiltrating tumor lesions.