Secondary lymphedema is a lifelong and occasionally life-threatening disease that often occurs as a consequence of axillary clearance for breast cancer. Regeneration of lymphatic tissues and restoration of lymph flow through a fibrotic scar are two basic essentials for the treatment of secondary lymphedema. Mesenchymal stem cells (MSCs) hold great therapeutic potential due to their effectiveness in stimulating host tissue regeneration via secreting numerous pro-regenerative factors dependent on the specific demands of the type and stage of injury. However, MSCs tend to differentiate and lose their self-renewal ability during the ex vivo expansion. Also, direct delivery of MSCs through injection will lose the function of extracellular matrix (ECM) proteins, which also play an important role in the lymphatic tissue regeneration and which tend to be absent in fibrotic tissues. We propose to use MSCs to fabricate both MSC cell sheet fragments as well as a completely biological tissue-engineered lymphtic collecting vessel (TELCV) under physiologically low oxygen tension, which can effectively promote the ECM production, and maintain the stemness of MSCs and thus their regenerative factor secreting capacity and differentiation ability. Our central hypothesis is that the local administration of MSC fragments, combined with a MSC-based TELCV, will significantly reduce lymphatic edema and improve lymphatic regeneration via the in-site formation of functional lymphatic vasculature and the restoration of lymphatic drainage. The proposed study applies advanced stem cell engineering technology in lymphedema treatment. Upon completion, it will provide an effective treatment of secondary lymphedema, and thereby hold great potential in significantly improving the life quality of women suffering from lymphedema. This Academic Research Enhancement Award (AREA) will also allow us to train undergraduate students with hands-on experience in stem cell and tissue engineering research.