Research progress of CMTM4 in the tumor immune microenvironment and immunotherapy.

Immunosuppression within the tumor microenvironment (TME) remains a major barrier to durable responses to cancer immunotherapy. CKLF-like MARVEL transmembrane domain-containing 4 (CMTM4), a member of the CMTM family, has emerged as a regulator of tumor immune regulation and membrane protein trafficking. This critical narrative review summarizes the genetic and structural features of CMTM4, its immunological functions under physiological and pathological conditions, and its multifaceted roles within the immune compartment of the TME. The review focuses on three aspects (1): mechanisms by which CMTM4 contributes to programmed death-ligand 1 (PD-L1) stability and interacts with TME-associated membrane proteins (2); cell-type-specific interactions between CMTM4 and immune effector or suppressor cells; and (3) its potential value as a candidate prognostic biomarker and therapeutic target for modulating resistance to immune checkpoint inhibitors (ICIs). This review also discusses unresolved mechanistic questions, limitations of current research models, and challenges in clinical translation. Future studies integrating single-cell multi-omics, spatial transcriptomics, proteomics, and organoid models may help clarify the context-dependent functions of CMTM4 and provide a stronger basis for its translational evaluation.