Immune Characterization of the Programmed Death Receptor Pathway in High Risk Prostate Cancer

Programmed cell death-1 (PD-1), a T-cell inhibitory receptor, and its ligand, PD-L1, have been reported to be expressed in many tumor types, and this expression has led to the development of many drugs targeting the PD-1 pathway. The objective of this study was to determine the expression of PD-1 and PD-L1 in high-grade prostate cancer tissues, and correlate the expression with disease and patient characteristics.

Immunohistochemistry for PD-1 (CD279), PD-L1 (B7-H1), and CD3 was performed and scored from 0 to 5 on prostatectomy/biopsy tissue samples taken from 25 men with high-grade prostate cancer. Charts were then retrospectively reviewed for numerous patient and disease characteristics. Statistical analyses were done to investigate the association of these patient and disease characteristics with PD-1, PD-L1, and CD3 expression.

A score of 3 to 5 on the semiquantitative 0 to 5 score was deemed "high" expression whereas a score of 0 to 2 was deemed "low" expression. Of the 25 samples, 2 (8%) scored high for PD-1 expression, 2 (8%) scored high for PD-L1 expression, and 18 (72%) scored high for CD3 expression. There was no statistically significant difference between high and low expression groups of PD-1, PD-L1, or CD3 for any of the variables we collected.

An overall low expression of PD-1 and PD-L1, and a concurrent high expression of CD3+ T cells was found in high-risk prostate cancer tissue. No significant association was found between expression of PD-1, PD-L1, or CD3, and patient or disease characteristics. Because of this, one might be able to question the role of PD-L1 in local immune suppression in prostate cancer.