Project Summary This proposal is significant because we aim to develop novel treatments for secondary lymphedema, a common and morbid complication of cancer treatment. This is important because current therapies for this disease are palliative and inadequate. In our previous studies, we have shown that the pathology of lymphedema is secondary to progressive fibrosis and is mediated by chronic T-helper (CD4+) cell inflammation and T-helper 2 (Th2) differentiation. We have used this information to develop novel therapies for the treatment of secondary lymphedema and have recently translated our work from the bench to the bedside in an investigator-initiated trial using Th2 cytokine neutralizing antibodies. The objective of this application is to identify the cellular mechanisms that initiate CD4+ cell inflammatory responses following lymphatic injury. This objective is a logical extension of our previous work and should identify additional targets that can be targeted pharmacologically to treat/prevent lymphedema. Our long-term objective is to use the information we gain from this basic understanding of lymphedema to develop therapies that disrupt the cycle of events that promote progressive fibrosis and lymphatic dysfunction. Our approach is innovative since we use a combination of mouse models and clinical specimens to dissect the cellular mechanisms of lymphedema pathology. Our group is uniquely positioned to accomplish our goals on the basis of our multidisciplinary team, our access to clinical tissues, and our novel mouse models. We plan to achieve our objectives using 2 specific aims: Aim 1. Determine how lymphatic injury activates CD4+ cells. This aim will use clinical samples and mouse models to test the hypothesis that keratinocytes play a key role in the activation and migration of CD4+ cells to lymphedematous tissues. In addition, we will test the hypothesis that single nucleotide polymorphisms in immune response genes will increase the risk of lymphedema. Aim 3. Determine how inflammation impairs lymphatic function. This aim will test the hypothesis that inflammatory responses in lymphedema impair lymphatic function by multiple effects, including tissue and lymphatic fibrosis, perilymphatic inflammation, and impaired formation of collateral lymphatic vessels.