Background
Immune checkpoint expression is promising as a therapeutic modality and reliable biomarkers to predict drug response are lacking. We aimed to define immune signatures by high-dimensional immunophenotyping in cholangiocarcinoma (CCA) patients.

Methods
In this study, using Cytometry Time of Flight (CyTOF), we integrated 16 samples of primary resected CCA patients, either intrahepatic (iCCA, n=7) or perihilar cholangiocarcinoma (pCCA, n=9). We predicted candidate responders to chemotherapy and Durvalumab using transcriptome data from 255 treatment-naïve patients with iCCA and 182 with extrahepatic cholangiocarcinoma (eCCA) and we validated the immune signature by multiplex imaging.

Results
We demonstrated an overactivation of effector memory CD4 T cells with PD-1 and CTLA expression as well as OX40 positive T regulatory cells (Tregs) presented in the tumour tissues. Contrary, cytotoxic effector memory CD8 T cells stayed in the tumour periphery, while central memory CD8 T cells show signs of exhaustion in the tumour niche. In external treatment-naïve cohorts, predicted responders to chemotherapy and Durvalumab were predicted in 2.4% and 5.5% of patients with intrahepatic and extrahepatic tumours, respectively. Validation by multiplex imaging identified 24% (6/24) of the patients with the immune signature predictive of good response.

Conclusion
We have identified a high number of intratumoural PD1-positive memory T cells, which we show are predictive of response to checkpoint blockade in combination with chemotherapy. Screening for this immune signature can be useful in daily clinical care.