PD-1-Stimulated T Cell Subsets are Transcriptionally and Functionally Distinct

Abstract

Ligation of the inhibitory receptor PD-1 on T cells results in the inhibition of numerous cellular functions. Despite the overtly inhibitory outcome of PD-1 signaling, an additional series of functions is activated. We have observed that T cells stimulated through the T cell receptor (TCR) and PD-1 primarily do not proliferate, however, there is a population of cells that proliferates more than through TCR stimulation alone. In this study, we performed flow cytometry analysis and RNA sequencing on individual populations of T cells and discovered that unlike the naive T cells, which were inhibited following PD-1 ligation, the T cells that proliferated more following PD-1 ligation were associated with the effector memory (EM) and central memory (CM) phenotypes. Remarkably, we showed that naive, EM, and CM T cell subsets had distinct gene expression profiles following PD-1 ligation. While in the naive and CM T cells, PD-1-regulated-genes were associated with T cell differentiation and metabolism, in the EM cells the genes regulated by PD-1 were coupled to more specific effector functions. Transcription factor analysis identified STAT1 and STAT2 as key mediators of PD-1-induced gene expression, and patients with low STAT1 and STAT2 expression responded favorably to check point blockade. Altogether, the presence of transcriptionally and functionally distinct T cell populations responsive to PD-1 ligation provide novel insights into the biology of PD-1 and suggest the use of T cell subset-specific approaches to improve the clinical outcome observed following therapeutic PD-1 blockade.