Lymphatic vessels invade bone in disease but are absent in health and regeneration.

A recent study reported the existence of lymphatic vessels in normal bone and suggested their involvement in bone regeneration after injury. However, this conclusion was based on approaches that do not allow unequivocal identification of the spatial localization of lymphatic endothelial cells (LECs). Here, we employed a Prox1-based genetic tool and a dual-recombinase-mediated LEC-specific labeling system to trace lymphatic vessels with high specificity. We found that LECs are present in the connective tissues, including the periosteum surrounding the bone. However, they do not reside within the bone itself, nor do they penetrate the periosteum to facilitate bone regeneration after injury. By contrast, hyperplastic LECs on the bone surface breach the periosteum and invade bone tissue in mouse models of generalized lymphatic anomaly and Gorham-Stout disease. These data demonstrate that lymphatic vessels are absent from bone during homeostasis and regeneration after injury but invade bone during disease. This Matters Arising paper is in response to Biswas et al. (2023), published in Cell. See also the response by Yang et al. (2026), published in this issue.