CD83 expression characterizes precursor exhausted T cell population.

T cell exhaustion is a main obstacle against effective cancer immunotherapy. Exhausted T cells include a subpopulation that maintains proliferative capacity, referred to as precursor exhausted T cells (T PEX ). While functionally distinct and important for antitumor immunity, T PEX possess some overlapping phenotypic features with the other T-cell subsets within the heterogeneous tumor-infiltrating T-lymphocytes (TIL). Here we explore surface marker profiles unique to T PEX using the tumor models treated by chimeric antigen receptor (CAR)-engineered T cells. We find that CD83 is predominantly expressed in the CCR7 + PD1 + intratumoral CAR-T cells compared with the CCR7 - PD1 + (terminally differentiated) and CAR-negative (bystander) T cells. The CD83 + CCR7 + CAR-T cells exhibit superior antigen-induced proliferation and IL-2 production compared with the CD83 - T cells. Moreover, we confirm selective expression of CD83 in the CCR7 + PD1 + T-cell population in primary TIL samples. Our findings identify CD83 as a marker to discriminate T PEX from terminally exhausted and bystander TIL.