Nanobody-based characterization of Galectin-13 reveals immunomodulatory and tumor-promoting functions.

Galectin-13 (GAL-13), also known as placental protein 13, is a lectin primarily studied in the context of pregnancy and immune regulation at the maternal-fetal interface. However, its potential roles in other tissues, including cancer, remain largely unknown. In this work, we provide new insights into the role of this protein while developing a comprehensive set of research tools to facilitate future studies. Our transcriptomic analyses reveal that GAL-13 reprograms gene expression in HepG2 liver cells, suggesting functions beyond placental physiology, potentially linked to inflammatory and tumor-related signaling. We generated a panel of 10 high-affinity nanobodies that enable detection, neutralization, and affinity-based purification of GAL-13, overcoming long-standing challenges in obtaining a soluble, functional form of the protein. Importantly, this large nanobody panel also provides an opportunity to map the functional epitopes of GAL-13, including those outside its classical carbohydrate recognition domain (CRD). The purified GAL-13 retains its biological activities, notably inducing apoptosis in Jurkat T cells and stimulating CCL20 expression in HepG2 cells. This de novo induction of CCL20 was inhibited by our nanobodies, demonstrating their utility in dissecting GAL-13-mediated effects. Moreover, we observed extensive cross-reactivity of several nanobodies with GAL-16, reflecting the strong structural similarity between these two placental galectins and underscoring the need for careful validation of reagent specificity. Altogether, by integrating methodological innovation with functional analyses, our study provides essential molecular tools to advance GAL-13 research and reveals an emerging role for this understudied lectin in cancer biology.