As reported, members of the CD44 protein family, particularly its variant isoforms, play critical roles in tumor cells metastasis and immune cell infiltration into the brain.[35, 36] CD44v6, a splice variant of the CD44 protein, is highly expressed on cells with strong brain metastasis potential.[7, 35, 37] We studied whether CD44v6 was also the key mediator for the transBBB delivery of sCABs. Here, CD44 is linked to neoplasm.