Summary Characterization of host immune cell parameters prior to treatment is expected to identify biomarkers predictive of clinical outcome as well as to elucidate why some patients fail to respond to immunotherapy. We monitored blood immune cells from 58 patients with non‐small‐ cell lung cancer (NSCLC) undergoing surgery of the primary tumor and from 50 age‐matched healthy volunteers. Complete leukocyte blood count, the number of circulating dendritic cells (DC), HLA‐DRlow monocytes and several lymphocytic subpopulations were determined by eight‐color flow cytometry. Furthermore, the prognostic value of the immune cell parameters investigated was evaluated by patients’ survival analysis. Compared to the control group, blood of NSCLC patients contained more neutrophils resulting in a higher neutrophil‐to‐lymphocyte ratio (NLR), but a lower number of blood DC, in particular of plasmacytoid DC (pDC), natural killer (NK) cells and naive CD4+ and CD8+ T cells. Furthermore, a higher frequency of CD4+ regulatory T cells (Treg) and HLA‐DRlow monocytes was detected, and smoking had a significant impact on these values. HLA‐DRlow monocytes were positively correlated to the number of neutrophils, monocytes and NLR, but negatively associated with the number of pDC and naive CD4+ T cells. The frequency of Treg, HLA‐DRlow monocytes and naive CD4+ and CD8+ T cells as well as the ratios of CD4/HLA‐DRlow monocytes and HLA‐DRlow monocytes/pDC correlated with patient’s overall survival. Next to Treg, HLA‐DRlow monocytes and naive T cells represent prognostic markers for NSCLC patients and might be useful for monitoring of patients’ responses to immunotherapies in future studies.

A group of European FOCIS Centers of Excellence adapted panels of the Human Immunophenotyping Consortium (HIPC) for whole blood analysis. Using four core panels [T/regulatory T cell/B/natural killer (T/T reg /B/NK) and myeloid cells] the main leukocyte populations were analyzed in a clinical-diagnostic setting in a harmonized manner across different platforms. As a first step, the consortium presents here the absolute and relative frequencies of the leukocyte subpopulations in the peripheral blood of more than 300 healthy volunteers across six different European centers.