CD28 and glycogen synthase kinase-3 (GSK-3) inhibitor combination therapy generates tumor infiltrating T-cells (TILs) with a reversal of markers for T-cell exhaustion

Abstract

Abstract Immune checkpoint blockade (ICB) of inhibitory receptors such as PD-1 has revolutionized the treatment of cancer. ICB is dependent on CD28 co-receptor expression introducing the question of whether the positive co-receptor could be targeted for the reversal of T-cell exhaustion in immunotherapy. We previously showed that the serine/threonine kinase glycogen synthase kinase-3 (GSK-3) is a central regulator of programmed cell death-1 (PD-1) transcription (Taylor et al., 2016, Immunity) and that small molecule inhibitors of GSK-3 (GSK-3 SMI) are as effective as anti-PD-1 blocking antibody in the control of tumor growth (Taylor et al., 2018, Cancer Research). In this study, we now show that anti-CD28 can synergise with GSK-3α/β inhibitors to regress tumors that are resistant to anti-PD-1 immunotherapy. Combination therapy showed responses in >55% mice with an overall reduction in tumor volume of 70% in responders compared to control mice (182 mm3 vs. 611 mm3). Flow cytometry analysis of tumor infiltrating lymphocytes (TILs) shows that, while non-treated mice were enriched with TOX+TIM3+PD1+CD8+, combination therapy increased tumor infiltration of TOX-negative CD8 T cells with TIM3-PD1int CD8 phenotype. Remarkably, this reversal involved only a single injection of anti-CD28 (PV-1) and GSK-3 SMI (SB415286). These results showed that CD28/GSK-3 combination therapy greatly reduced TOX, TIM-3 and PD1markers indicative of exhaustion. Our findings offer a small molecule approach for synergy with anti-CD28 that leads to an increase tumor infiltration with TOX-negative CD8 T cells that have decrease expression of inhibitory receptors.