Selective delivery of low-affinity IL-2 to PD-1+ T cells rejuvenates antitumor immunity with reduced toxicity

PD-1 signaling on T cells is the major pathway that limits T cell immunity, but the efficacy of anti-PD-1 therapy has been limited to a small proportion of patients with advanced cancers. We fortuitously observed that anti-PD-1 therapy depends on IL-2 signaling, which raises the possibility that a lack of IL-2 limits anti-PD-1-induced effector T cell expansion. To selectively deliver IL-2 to PD-1+CD8+ tumor-infiltrating lymphocytes (TILs), we engineered a low-affinity IL-2 paired with anti-PD-1 (PD-1-laIL-2), which reduced affinity to peripheral Treg cells but enhanced avidity to PD-1+CD8+ TILs. PD-1-laIL-2 exerted better tumor control and lower toxicity than single or mixed treatments. Mechanistically, PD-1-laIL-2 could effectively expand dysfunctional and tumor-specific CD8+ T cells. Furthermore, we discovered that presumably dysfunctional PD-1+TIM3+ TILs are the dominant tumor-specific T cells responding to PD-1-laIL-2. Collectively, these results highlight that PD-1-laIL-2 can target and reactivate tumor-specific TILs for tumor regression as a unique strategy with stronger efficacy and lower toxicity.