Potent clinical predictive and systemic adjuvant therapeutic value of plasma fractalkine in PD-L1/PD-1 blockade immunotherapy for lung cancer

Recent studies highlight the importance of baseline functional immunity for efficacious immune checkpoint blockade therapies. High-dimensional systemic immune profiling was performed in a discovery cohort of 112 non-small cell lung cancer patients undergoing PD-L1/PD-1 blockade immunotherapy. Responders showed high baseline phenotypic diversity of myeloid cell types in peripheral blood, in which elevated activated monocytic cells and decreased granulocytic phenotypes were potent predictive biomarkers. High-throughput profiling of soluble factors in plasma identified fractalkine (FKN), a chemokine involved in immune chemotaxis and adhesion, as a biomarker of myeloid cell diversity in human patients and in murine models, which was found significantly increased in objective responders. Secreted FKN inhibited adenocarcinoma and squamous cell carcinoma growth in vivo through a prominent contribution of systemic effector NK cells, enhanced tumor infiltration with immunostimulatory immune cells and inhibition of MDSCs within tumors. A synergy between FKN and PD-L1/PD-1 blockade immunotherapy was found in murine lung cancer models refractory to anti-PD-L1/anti-PD-1 treatment. Transcriptional data from 515 human lung adenocarcinoma samples independently confirmed the results from the discovery cohort. Importantly, recombinant FKN and tumor expressed-FKN were efficacious in delaying tumor growth in vivo with significant abscopal effects, indicating a potential therapeutic use of FKN in combination with immunotherapies. One Sentence Summary Serum fractalkine as a biomarker of response to immune checkpoint blockade. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This research was supported by the Spanish Association against Cancer (AECC, PROYE16001ESCO, IDEAS211016AJON); Instituto de Salud Carlos III (ISCIII)-FEDER Project grants FIS PI17/02119, FIS PI20/00010, FIS PI20/00419; COV20/00000, and TRANSPOCART ICI19/00069; Biomedicine Project Grant from the Department of Health of the Government of Navarre-FEDER funds (BMED 050-2019, 51-2021); strategic projects from the Department of Industry, Government of Navarre (AGATA, Ref. 0011-1411-2020-000013; LINTERNA, Ref. 0011-1411-2020-000033; DESCARTHES, 0011-1411-2019-000058); European Project Horizon 2020 Improved Vaccination for Older Adults (ISOLDA; ID: 848166). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The current prospective observational study was approved by the Ethics Committee of Clinical Investigations at the University Hospital of Navarre. Informed consent was obtained from all subjects and all experiments conformed to the principles set out in the WMA Declaration of Helsinki and the Department of Health and Human Services Belmont Report. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors.