Background
The chimeric antigen receptor NK-92 (CAR NK-92) cell targeting the prostate-specific membrane antigen (PSMA) has shown antitumour effects in castration-resistant prostate cancer (CRPC). However, the expression changes of programmed death ligand 1 (PD-L1) and its mechanisms on CAR NK-92 and CRPC cells and the effect of the anti-PD-L1 monoclonal antibody (mAb) on PD-L1 expressed on CAR NK-92 cells remain unknown.
Conclusion
Combined treatment with CAR NK-92 and anti-PD-L1 mAb improved the antitumour efficacy against CRPC, which is of extraordinary translational value in the clinical treatment of CRPC.
Methods
Human dendritic cells and CD8+ T cells were acquired from blood samples of healthy donors and cocultured with C4-2 cells. Changes in PD-L1 expression were detected by flow cytometry. Differential gene expressions were investigated by RNA sequence analysis, while the regulation of PD-L1 molecular signaling was explored using western blotting. In vitro cytotoxicity was evaluated using the Cell Counting Kit-8 assay and the bioluminescent intensity (BLI) of green fluorescent protein-labelled C4-2 cells. CRPC growth in vivo was monitored using callipers and BLI in male NOD/SCID mice subcutaneously injected with C4-2 cells and treated intravenously with anti-PD-L1/PD-1 mAb, CAR NK-92 or cocultured CD8+ T cells.
Results
Significantly upregulated expression of PD-L1k was observed in cocultured C4-2 and CAR NK-92 cells. In addition, upregulation of PD-L1 expression was dependent on interferon-γ in C4-2 cells, while it was dependent on direct cell-to-cell interaction via the NK group 2 member D/ phosphatidylinositol 3-kinase/AKT pathway in CAR NK-92 cells. The anti-PD-L1 mAb directly acted on PD-L1 expressed on CAR NK-92 cells and augmented the cytotoxicity of CAR NK-92 cells against C4-2 and CRPC cells from one patient in vitro. Anti-PD-L1 mAb significantly enhanced the antitumour effect of CAR NK-92 cells against CRPC cells in vivo when compared to treatment with CAR NK-92 cells or combined with anti-PD-1 mAb in the absence or presence of cocultured CD8+ T cells.