Aging-associated regulatory B-like cells establish a lung-selective immunosuppressive niche to promote pulmonary metastasis

While aging is the primary risk factor for cancer development and a critical driver of metastasis, yet how aging selectively remodels specific distant organs to favor tumor colonization remains unclear. Here, we demonstrate that host aging selectively enhances susceptibility to lung metastasis in an inflammation-dependent manner, without uniformly affecting other organs. Single-cell RNA sequencing reveals that the aged lung accumulates PD-L1CTLA-4IgMIgD- regulatory B (Breg)-like cells, representing the immune population most amplified by the cooperative effects of aging and tumor burden. Trajectory analysis delineates their differentiation from naive B cells, driven by Il10, Ctla4, Cd274, and Egr1 upregulation. This program is evolutionarily conserved, increasing progressively with human chronological lung age. Mechanistically, aged CD140a adventitial fibroblasts drive CXCL13-dependent B-cell reprogramming into a senescent state. These Breg-like cells directly impair natural killer cell cytotoxicity and CD4 T-cell responses, accelerating pulmonary colonization. Our findings reveal a targetable, lung-specific age-associated stromal-immune axis driving metastatic organotropism.