IGKV4-1 and neoplasm: For instance, exosomal integrins α6β4 specifically bind to lung-resident fibroblasts and epithelial cells, directing tumor cell metastasis to the lung, and exosomal integrins αvβ5 bind to Kupffer cells, favoring liver tropism, while brain-tropic primary tumor-derived exosomal integrins β3 bind brain-resident endothelial cells, inducing brain metastasis (Hoshino et al., 2015).