Xiaodong Wang, Junjie Wang, Qianqian Wang, Gouping Ding, Yiping Huang, Yeqian Feng
Immune checkpoint inhibitors (ICIs) can elicit durable remissions, yet most solid tumors show primary non-response or acquired resistance because the tumor microenvironment (TME) limits T-cell priming, trafficking and effector fitness. Cytokines orchestrate these barriers by shaping spatial immune architecture, regulating suppressive myeloid programmes and inducing inhibitory ligands such as PD-L1. In this Review, we synthesize mechanistic and clinical evidence and propose a push-pull framework for cytokine modulation during checkpoint blockade: locally amplifying Th1/CTL-supporting signals (IL-2/IL-12/IL-15 and type I/II interferons) while selectively attenuating dominant suppressive circuits (TGF-β, IL-6/STAT3, IL-8-CXCR1/2, IL-10 and TNF-driven exhaustion). We critically contrast successful and failed cytokine-ICI combinations, highlighting how systemic exposure, network redundancy and counter-regulatory feedback have constrained several engineered agonists and explain why certain blockade strategies can improve efficacy while reducing immune-related toxicity. We discuss next-generation solutions-tumor-activated pro-cytokines, intratumoral gene delivery and immunocytokines-that concentrate activity within resistant niches and widen the therapeutic window. Finally, we outline actionable biomarkers, including transcriptomic signatures, plasma cytokine kinetics, myeloid/neutrophil metrics and spatial TME profiling, to stratify patients and guide dosing, sequencing and adaptive add-on strategies. Rational, biomarker-guided cytokine modulation offers a path to convert immune-excluded tumors into durable ICI responders.