Expression pattern of immune checkpoints programmed death (PD-1) and programmed death-ligand (PD-L1) in retinoblastoma and its prognostic significance

Abstract

Background: Retinoblastoma (RB), malignant tumor of the sensory retina, is the most common eye cancer of childhood due to the defect of RB gene. The immune system plays an important role in controlling and eradicating cancer. Recent studies suggest that programmed death-1/programmed death ligand-1 (PD-1/PD-L1) pathway in T-cell activation plays a major role in tumor escape mechanism from host immunity. Therefore, we investigated the expression of PD-1 and PD-L1 in human retinoblastoma cancer to define their clinical significance in patient’s prognosis after enucleation. Methods: We prospectively evaluate the expression of PD-1 and PD-L1 protein in 62 cases of primary enucleated retinoblastoma specimens by immunohistochemistry and further validated by immunoblotting. mRNA levels of PD-1 and PD-L1 genes were quantified in normal retina and tumor samples by quantitative real time PCR (qPCR). Expression of PD-1 and PD-L1 proteins were then correlated with clinicopathological parameters and patient survival by statistical analysis. Results: Immunohistochemistry showed cytoplasmic PD-1 expression in (12/62) 19.3% cases, whereas PD-L1 expressed in 80.6% (50/62) cases. Immunostaining was found in stromal and tumor infiltrating lymphocytes. Immunoreactivity results of target protein were validated by western blotting on representative cases. Protein and mRNA level by IHC and real time qPCR was found to be closely correlated. Expression of PD-L1 showed significant correlation with poor tumour differentiation and tumor invasion (p<0.05). There was also a significant difference in the overall survival of patients with PD-L1 expression. Conclusions: These data suggest that PD-L1 expression may be a new therapeutic immunomarkers for patients with retinoblastoma. This study provides first data for the role of immune checkpoints in retinoblastoma patients. Further translational studies are necessary to confirm this observation and evaluate the predictive value of PD-1 and PD-L1 in retinoblastoma in the context of PD-1 inhibition.