Using cell-attached fucosyltransferase and a biotinylated (Bio+) substrate, Liu, Li, and Chen et al. developed FucoID, a proximity-labeling approach to specifically identify T cells binding to cognate antigen-presenting cells, allowing efficient capture of tumor antigen-specific TILs from multiple murine tumor models. The Bio+-enriched CD8+ T cells were PD-1+, possessed an exhaustion phenotype and a minor population of TCF1+ progenitor exhausted cells, and were more effective in tumor control than ‘bystander’ PD-1+ non-captured cells. Bio+-labeled CD4+ T cells contained target-reactive cells and a CD8+ T cell-suppressing (CD25+; presumably Treg) subpopulation.
Contributed by Ed Fritsch
ABSTRACT: Re-activation and clonal expansion of tumor-specific antigen (TSA)-reactive T cells are critical to the success of checkpoint blockade and adoptive transfer of tumor-infiltrating lymphocyte (TIL)-based therapies. There are no reliable markers to specifically identify the repertoire of TSA-reactive T cells due to their heterogeneous composition. We introduce FucoID as a general platform to detect endogenous antigen-specific T cells for studying their biology. Through this interaction-dependent labeling approach, intratumoral TSA-reactive CD4+, CD8+ T cells, and TSA-suppressive CD4+ T cells can be detected and separated from bystander T cells based on their cell-surface enzymatic fucosyl-biotinylation. Compared to bystander TILs, TSA-reactive TILs possess a distinct T cell receptor (TCR) repertoire and unique gene features. Although exhibiting a dysfunctional phenotype, TSA-reactive CD8+ TILs possess substantial capabilities of proliferation and tumor-specific killing. Featuring genetic manipulation-free procedures and a quick turnover cycle, FucoID should have the potential of accelerating the pace of personalized cancer treatment.