Claudins interact with LILRB immune inhibitory receptors to promote myeloid immunosuppression in cancer
The mechanisms underlying tumor cell-myeloid cell interactions within the tumor microenvironment (TME) remain unclear, and predictive biomarkers for patient response to myeloid checkpoint blockade are lacking. This study identified specific binding between tight-junction claudins (CLDNs) and leukocyte immunoglobulin-like receptor subfamily B members LILRB2 and LILRB5. In multiple human cancer cohorts, the spatial proximity of LILRB2? macrophages to CLDN-expressing cancer cells correlated with clinical outcomes, nominating this spatial relationship as a potential biomarker. In syngeneic LILRB2-transgenic and humanized mouse models, CLDN18.2–LILRB2 interaction triggered bidirectional signaling, enhanced the immunosuppressive activity of myeloid cells, and accelerated tumor progression. These effects were reversed by LILRB2 blockade. Mechanistically, the CLDN-LILRB2 axis sustained immunosuppression by regulating NF-?B and STAT signaling pathways. Our findings reveal a novel tight junction protein-mediated mechanism of myeloid cell regulation in the TME, offering a rationale for targeting this pathway in cancer therapy. Overall design: NSG-SGM3 mice that had received total body irradiation (250 cGy) were transplanted with 3 x 104 human cord blood CD34+ cells (STEMCELL, # 70008). After 6 weeks, when human immune cell engraftment in mouse peripheral blood was detected, 1 × 106 SK-MEL-5 or 2 × 106 MIA PaCa-2 cells were injected subcutaneously into the right flanks of each mouse. After tumor volumes reached 50 to 60 mm3, mice were randomized into groups and intraperitoneally injected with antibodies (LALAPG-mutated anti-LILRB2 antibody or isotype control) at a dose of 10 milligram per kilogram of bodyweight twice weekly. Liver and spleen metastases were observed 6 to 8 weeks post-tumor implantation. Live, single, tumor-infiltrating human CD45+ cells and  peripheral blood engrafted human CD45+ cells were FACS-enriched at 8 weeks post-implantation and subsequently used for single-cell RNA-sequencing analysis.