Agonizing over the Stimulatory Immune Checkpoint ICOS.

Vopratelimab, an anti-ICOS (inducible costimulator of T cells) agonist, alone and in combination with nivolumab, possesses limited toxicity and modest clinical activity in a large phase I/II trial. This treatment induced ICOS expression of CD4+ T cells, which may enable biomarkers for patient selection. Nevertheless, T-cell agonists as cancer immunotherapies continue to be challenging. See related article by Yap et al., p. 3695.