Dickkopf 1 Impairs Sensitivity to PD-1 Blockade through CD8+ T Cell Inactivation in dMMR/MSI Colorectal Cancer

Dickkopf 1 (DKK1) could promote tumor progression by suppressing immunity. Therefore, we investigated whether DKK1 influence prognosis and sensitivity to PD-1 blockade in colorectal cancers (CRCs) with defective DNA mismatch repair genes (dMMR) or microsatellite instability (MSI). We found that elevated DKK1 expression was associated with recurrence and dismissed CD8+ T cell infiltrations, and patients with high serum DKK1 had poor anti-PD-1 response. RNA interference or neutralization of DKK1 in CRCs enhanced CD8+ T cell cytotoxicity, and down-regulation of T-bet and E2F1 following GSK3β activation was detected in DKK1-treated CD8+ T cells. In organoid-lymphocyte co-culture model, apoptosis proportions were elevated after individual neutralization of both PD-1 and DKK1, and the combined neutralization resulted in further increases. In conclusion, DKK1 suppresses tumor immunity in dMMR/MSI CRCs by inactivating CD8+ T cells through GSK3β/E2F1/T-bet axis. DKK1 neutralization may improve the sensitivity to PD-1 blockade in dMMR/MSI CRCs.