Negative Co-stimulation Constrains T Cell Differentiation by Imposing Boundaries on Possible Cell States.

Co-stimulation regulates T cell activation, but it remains unclear whether co-stimulatory pathways also control T cell differentiation. We used mass cytometry to profile T cells generated in the genetic absence of the negative co-stimulatory molecules CTLA-4 and PD-1. Our data indicate that negative co-stimulation constrains the possible cell states that peripheral T cells can acquire. CTLA-4 imposes major boundaries on CD4 + T cell phenotypes, whereas PD-1 subtly limits CD8 + T cell phenotypes. By computationally reconstructing T cell differentiation paths, we identified protein expression changes that underlied the abnormal phenotypic expansion and pinpointed when lineage choice events occurred during differentiation. Similar alterations in T cell phenotypes were observed after anti-CTLA-4 and anti-PD-1 antibody blockade. These findings implicate negative co-stimulation as a key regulator and determinant of T cell differentiation and suggest that checkpoint blockade might work in part by altering the limits of T cell phenotypes. • Negative co-stimulation limits T cell differentiation outcomes • Archetypal analysis identifies phenotypic boundaries of cell states • CTLA-4 imposes major boundaries on CD4 + T cell phenotypes • PD-1 subtly restrains CD8+ T cell phenotypes Negative co-stimulation is a critical regulator of T cell activity. Wei et al. characterize T cells arising in CTLA-4- and PD-1-deficient mice via mass-cytometry and computational approaches. They show that these negative co-stimulatory molecules impose boundaries on T cell phenotypes during peripheral differentiation, suggesting that checkpoint blockade might work in part by altering the limits of T cell phenotypes. [ABSTRACT FROM AUTHOR]