Glycogen synthase kinase 3 (GSK-3) synergizes with immune-checkpoint blockade (ICB) to overcome tumor resistance due to unique tumor infiltrating T-cell subsets as revealed by mass cytometry (CyTOF)

Abstract We have shown that the serine/threonine kinase glycogen synthase kinase-3 (GSK-3) is a major regulator of programmed cell death-1 (PD-1) transcription and expression in T-cells (Taylor et al., 2016, Immunity). Further, small molecule inhibitors (SMIs) increased Tbx21 transcription for enhanced Tbet expression which suppressed Pdcd1 transcription in CD8+cytolytic T-cells. SMIs against GSK-3 are as effective as anti-PD-1 blocking antibody in the control of spontaneous pulmonary metastasis of B16 melanoma and EL-4 lymphoma cells (Taylor et al., 2018, Cancer Research). This introduced a new chemical approach to down-regulate PD-1 for the treatment of cancer. In addition, GSK-3 effects in Tbet expression can induce the expression of interferon-γ1 (IFNγ1) and granzyme B (GZMB) for enhanced cytolytic T-cell (CTL) killing of tumors suggesting that GSK-3 SMIs might synergize with check-point blockade. We now show that GSK-3α/β inhibition can cooperate with anti-PD-1 blockade to overcome tumor resistance. Using high dimensional profiling of tumor infiltrated lymphocytes (TILs) with mass cytometry (CyTOF), we show that the synergy of GSK-3 SMI and anti-PD-1 is accompanied by 2 specific findings: (i) an increase in the presence of a unique subset of CD8+ TIL effector-memory T-cells beyond that observed with anti-PD-1 alone, and (ii) the significant decrease of a subset of CD4+ suppressor regulatory T-cells (Tregs) not observed with anti-PD-1 alone. Our findings offer a small molecule approach for synergy with anti-PD-1 that leads to an increase in CD8+ T-cells and the marked decrease of Tregs in tumors.