469P Dynamic immunosuppressive activity of circulating monocytes predicts response to immune checkpoint inhibitors (ICIs) in advanced NSCLC

Background: Circulating monocytes (CM) may acquire immunosuppressive activity (IA), contributing to primary/secondary resistance to ICIs.Of note, our group demonstrated that ICIs downregulate cellular FLICE-inhibitory protein (c-FLIP), a mediator of CM IA, in non-progressor NSCLC patients (pts).Methods: Advanced NSCLC pts treated with upfront ICIs, alone (I) or with chemotherapy (CI), were prospectively enrolled.Blood samples were collected at baseline (T0) and after 3 months (T1).Pts were classified as responders (R; progression-free survival (PFS) 6 months) or non-responders (NR; PFS <6 months).CM from pts were isolated and co-cultured with anti-CD3/CD28 activated healthy donor PBMCs to test their IA towards T cells by flow cytometry.Unpaired t tests were used for group comparisons (p<0.05).The FLIP interactome was analyzed by liquid chromatography-mass spectrometry in nuclear and cytoplasmic compartments of FLIP-overexpressing monocytes.Results: From 2021 to 2025, 78 pts were enrolled; 57 evaluable for CD3 + T-cell proliferation at T0, 39 receiving CI (68.4%) and 18 receiving I (31.6%).At T0, 33 (57.9%) were classified as R and 24 (42.1%) as NR.CM from R pts showed higher IA than NR (p = 0.0156); a non-significant trend was observed in CI-treated pts (p = 0.06).At T1, considering specifically pts receiving CI, CM from R pts showed reduced IA after treatment (p = 0,0239), whereas IA increased in NR (p = 0.0237).Characterizing nuclear and cytoplasmic c-FLIP interactome, lactate dehydrogenase (LDH)-A was found to interact with c-FLIP in both compartments.In a subsequent TGCA in silico analysis, high LDH-A levels in the tumor microenvironment correlated with worse survival in lung adenocarcinoma (p < 0.0001).In our cohort, among CI-treated pts with evaluable circulating LDH (44), R had significantly lower baseline LDH than NR (p = 0.0071). Conclusions:Changes in CM IA are associated with response to CI in NSCLC.Moreover, based on potential biological rationale involving the c-FLIP/LDH-A interplay, integration of circulating LDH could refine pts stratification.In a multi-omics framework, body composition and RNA-seq analyses are ongoing.