Analyse der zellulären und löslichen Immuncheckpoint-Komponenten PD-L1 und sPD-L1 beim Nierenzellkarzinom

Renal cell carcinoma (RCC) is one of the ten most common cancers in Germany. Whilst tumors localized within the kidney may be successfully treated by surgical tumor resection, untreated metastatic disease leads to death within a few weeks. The introduction of drug therapy using immune checkpoint inhibitors (e.g. Pembrolizumab, anti-PD-1-antibody or Avelumab, anti-PD-L1-antibody), which target specific co-inhibitory receptors at the tumor (PD-L1) or immune cell (PD-1) levels, has significantly increased the life expectancy of these patients. However, a sig-nificant number of patients do not benefit from this therapy or suffer serious immune-related adverse events, hence finding reliable predictive biomarkers would be of crucial importance for choosing the right therapeutic agent. In this study, the expression and regulation of PD-L1 by cytokines was investigated in different cell lines of RCC and the amount of soluble PD-L1 (sPD-L1) released from the cells into the cell supernatant was measured. In addition, the levels of sPD-L1 were measured in the serum of patients with renal tumors before and after tumor resection. In the clear cell RCC cell lines (A498, CaKi-1, Cal54), the typical induction of PD-L1 by Interferon-γ (IFN-γ) was found, with an increase of sPD-L1 levels in the cell supernatant. Knock-down of PD-L1 by siRNA resulted in the downregulation of PD-L1, and a decrease in sPD-L1 levels in the corresponding cell su-pernatant, suggesting that ccRCC cells secrete sPD-L1. In the papillary RCC cell line (CaKi-2), PD-L1 could be measured but there was no increase in IFN-γ. This data indicates that the ex-pression and regulation of PD-L1 as measured by secreted sPD-L1 may vary in different types of RCC cells. Heterogeneous levels of sPD-L1 were detected in the blood of patients with RCC. Interestingly, there was a significant increase in sPD-L1 after tumor resection compared with paired blood levels before tumor resection, indicating a primarily non-tumor derived origin of sPD-L1 in blood. Further analysis showed a significant correlation of sPD-L1 with the inflammatory mark-er C-reactive protein (CRP). Like sPD-L1, CRP was elevated in the post- versus pre-tumor resec-tion samples, as expected due to the surgical insult. Furthermore, there was a correlation of sPD-L1 in serum with PD-L1 mRNA measured in whole blood. These results indicate that IFN-γ dependent regulation of PD-L1 in RCC cells may be an im-portant factor in the responsiveness of patients towards immune checkpoint blockade (ICB) therapy and that there may be differences between ccRCC and pRCC cell lines. This hypothesis needs to be further investigated using appropriate patient cohorts. The sPD-L1 levels measured in blood may consist of sPD-L1 released from tumor cells and of sPD-L1 formed in immune cells. The significance of sPD-L1 as a biomarker for ICB therapy is therefore complex and re-quires further investigation using different patient cohorts with a range of inflammatory parame-ters.