Glycogen synthase kinase (GSK-3) synergizes with PD-1/PDL1 blockade to generate super-armed CD8 killers against tumors

Abstract Immune checkpoint blockade (ICB) of negative co-receptors on T-cells such as programmed cell death-1 (PD-1) is promising for the treatment of cancer. Despite success, the poor prognosis for most patients highlights the need for novel clinical interventions. We have shown that the kinase, glycogen synthase kinase-3 (GSK-3) negatively regulates T-cell activation due to altered PD-1 and LAG-3 expression (Taylor et al., 2016 Immunity; Rudd et al., 2019 Cell Reports). GSK-3 inhibition (GSK-3i) is as effective as anti-PD-1 in controlling the growth of melanoma (Taylor et al., 2017 Can Res; Krueger and Rudd, Immunity 2017; Stelle et al., 2021 iScience). GSK-3i increases Tbet (Tbx21) transcription, which inhibits PD-1/LAG-3 transcription, while increasing granzyme B (GZMB) and interferon gamma (IFNγ). Here, we show that Gsk3−/− mice and small molecule inhibitors (SMIs) synergize with anti-PD-1 to eliminate melanomas that are resistant to anti-PD-1 monotherapy. Transcriptomic profiling showed that GSK-3 × PD-1 cooperativity was characterized by a specific increase in a family of different granzymes (7/12 GZM genes out of a data base of 20,500 potential genes). Some GZMs have been characterized and others not, but as a family, this increased armory of GZMs in CD8+ T-cells is expected to greatly enhance tumor killing. Overall, our data shows the PD-1 × GSK-3 synergy in limiting tumor growth is due to a specific set of cytolysis mediators needed for tumor killing.