Background: Although the current literature indicates that age should not be a deterring factor in postmastectomy breast reconstruction, the true impact of increasing age on postoperative outcomes remains unknown. The purpose of this study is to understand the impact of age on complications and patient-reported outcomes (PROs) using the BREAST-Q longitudinally 5 years after postmastectomy breast reconstruction. Methods: The authors conducted a retrospective analysis of patients who underwent autologous (ABR) or implant-based reconstruction (IBR). Age was studied as both a categorical and a continuous variable. Outcome measures included complications and BREAST-Q scores preoperatively, at 6 months, and 1 to 5 years postoperatively. Results: A total of 4730 patients were included, of which 1536 (32.5%) underwent ABR and 3194 (67.5%) underwent IBR. Older age was significantly associated with increased risk of developing mastectomy skin flap/nipple necrosis, infection, and seroma. Older age was negatively correlated with Satisfaction with Breasts (beta = -0.06 [95% CI, -0.12 to -0.01]; P = 0.033) and positively correlated with Psychosocial Well-being (beta = 0.14 [95% CI, 0.09 to 0.20]; P < 0.001). Older age was not correlated with Physical Well-being of the Chest (beta = -0.03 [95% CI, 0.08 to 0.02]; P = 0.2) or Sexual Well-being (beta = -0.04 [95% CI, -0.12 to 0.02]; P = 0.2). Subgroup analyses of ABR and IBR patients demonstrated different complications and PRO profiles. Conclusions: The authors' analysis of the impact of age on surgical outcomes and PROs suggests that complication rates increase with age, and older age is negatively correlated with Satisfaction with Breasts but positively correlated with Psychosocial Well-being. Overall, older patients should be informed about the potential associated risks and anticipated PROs. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, II.

Background: Frailty, defined as decreased physiological reserve and resistance to stressors, has a significant impact on outcomes among surgical patients. The 5-item modified frailty index (mFI-5) was developed to measure frailty and it has been shown to be a powerful predictor of complications after breast reconstruction, especially after autologous-based reconstruction (ABR). However, its utility in predicting patient-reported outcome measures has not been assessed. The purpose of this study was to evaluate the importance of mFI-5 in predicting BREAST-Q scores among ABR patients. Methods: All female patients who underwent ABR after mastectomy for cancer between 2017-2022 at a National Cancer Institute designated cancer center were eligible for inclusion. BREAST-Q domains assessed included Physical Well-being of the Chest, Satisfaction with Breasts, Psychosocial Well-being, and Sexual Well-being. mFI-5 is comprised of hypertension requiring medication, diabetes mellitus, chronic obstructive pulmonary disease or a diagnosis of pneumonia within 30 days, functional status, and congestive heart failure. It was dichotomized into two categories: low frailty (<2) and high frailty (2). A minimally clinically important difference (MCID) of 4 for BREAST-Q was considered clinically significant. Results: 2,160 patients were included in the analysis. The median age at surgery was 51 (interquartile range: 44, 57). 1,933 (89%) had mFI-5 score <2 and 227 (11%) had scores 2. With all other variables controlled for, the mFI-5 had a significantly negative impact on Physical Well-being of the Chest (beta=-4.2, 95% CI: -6.6, -1.8, p<0.001) and on Psychosocial Well-being (beta=-4.1, 95% CI: -5.8, -1.4, p=0.003). Both met the MCID of 4, suggesting the clinical importance of mFI-5 on Physical and Psychosocial Well-being. However, mFI-5 was not significantly associated with Sexual Well-being (beta=-1.2, 95% CI: -4.3, 2.0, p=0.5) or with Satisfaction with Breasts (beta=-2.3, 95% CI: -5.1, 0.50, p=0.11). Conclusion: In this present study, we found that mFI-5 is significantly associated with two BREAST-Q domains, Physical Well-being of the Chest and Psychosocial Well-being, among patients who undergo ABR. Patients with high frailty has clinically lower scores than those with low frailty. Thus, our findings suggest that mFI-5 can be utilized as a strong prognostic indicator of ABR patients' BREAST-Q scores. We encourage providers to incorporate the index score as a frailty assessment to counsel patients about their quality of life and help set expectations.

Lymphedema is a chronic disease that results in swelling and decreased function due to abnormal lymphatic fluid clearance and chronic inflammation. In Western countries, lymphedema most commonly develops following an iatrogenic injury to the lymphatic system during cancer treatment. It is estimated that as many as 10 million patients suffer from lymphedema in the United States alone. Current treatments for lymphedema are palliative in nature, relying on compression garments and physical therapy to decrease interstitial fluid accumulation in the affected extremity. However, recent discoveries have increased the hopes of therapeutic interventions that may promote lymphatic regeneration and function. The purpose of this review is to summarize current experimental pharmacological strategies in the treatment of lymphedema.

Figure S1, S2, S3, S4, S5, S6 and S7

Background Mitotic rate (MR) is considered an important prognostic factor for melanoma but is not currently used for staging because its nuanced effect is not yet well-delineated. We sought to determine if T category-specific MR is predictive of sentinel lymph node (SLN) positivity, recurrence, and melanoma-specific mortality (MSM). Methods A retrospective review of patients with primary cutaneous melanoma from 1994 to 2020 at a single academic center was performed. Patient demographics and tumor characteristics were recorded. MR was considered elevated for each AJCC8-defined T category if it was ≥2 mitoses/mm2 for T1, ≥4 mitoses/mm2 for T2, ≥6 mitoses/mm2 for T3, or ≥7 mitoses/mm2 for T4. Statistical analysis was performed to assess the predictive accuracy of MR on selected outcomes while controlling for ulceration. Results Data from 2,984 patients with complete records were analyzed. Along with Breslow thickness and ulceration, elevated MR was associated with higher risk of MSM (HR 1.816, P=0.0001). There was no difference among patients with ulcerated T1 or T2 tumors regardless of MR, but those with non-ulcerated T1 or T2 tumors and elevated MR were more likely to have positive SLNs (P<0.0001 and P=0.0043, respectively) and recurrence (P=0.0007 and P=0.0004, respectively) compared to counterparts with low MR. There were no notable differences for T3 or T4 tumors based on MR. Conclusions Elevated MR is associated with SLN positivity and recurrence in thin melanomas, independent of ulceration. SLN biopsy should therefore be strongly considered for patients with non-ulcerated lesions <0.8 mm thick if the MR is ≥2 mitoses/mm2.

Purpose: TGF-B1-a growth factor that regulates inflammation and fibrosis—is a key regulator of secondary lymphedema development. Angiotensin-converting enzyme (ACE) activity regulates TGF-B1 signaling in other organ systems; however, it is not known if ACE signaling plays an important role in lymphedema. The purpose of this study was therefore to analyze the expression of ACE in clinical samples, and determine if ACE inhibition is effective for treating the disease in a mouse model. Methods: Matched upper extremity biopsies were collected from patients with unilateral breast cancer-related lymphedema (BCRL) and analyzed using immunofluorescence and qPCR. In addition, we used mouse models to analyze fibrosis, inflammation, lymphatic pumping, and lymphangiogenesis in animals treated with a topical formulation of Captopril, an ACE inhibitor. Results: ACE expression was significantly increased in lymphedematous tissues of patients and in mouse models of lymphedema. Topical Captopril markedly decreased lymphedematous changes in the mouse tail by decreasing TGF-B1 expression and decreasing swelling, fibro adipose deposition, and inflammation. Captopril-treated animals also had significantly increased lymphatic collecting vessel pumping and collateral lymphatic formation. Conclusions: Topical Captopril significantly attenuates the pathological changes of lymphedema in a preclinical model. The use of topical formulations may help avoid systemic effects and holds promise in the clinical setting.

As the surgical community continues to work towards greater diversity, equity, and inclusion, the need for buy-in from all surgeons—including those of the White majority—becomes increasingly apparent. This article invites all surgeons to aid in diversity, equity, and inclusion efforts as “allies,” “upstanders,” and “champions for change,” and provides 2 specific frameworks for enacting allyship within the surgical field. Overt and conscious efforts to embrace allyship are imperative as we seek to fulfill our professional responsibilities to patients and will help create a workplace environment where all persons feel accepted, valued, welcomed, and respected.

PURPOSE: TGF-B1-a growth factor that regulates inflammation and fibrosis—is a key regulator of secondary lymphedema development. Angiotensin-converting enzyme (ACE) activity regulates TGF-B1 signaling in other organ systems; however, it is not known if ACE signaling plays an important role in lymphedema. The purpose of this study was therefore to analyze the expression of ACE in clinical samples, and determine if ACE inhibition is effective for treating the disease in a mouse model. METHODS: Matched upper extremity biopsies were collected from patients with unilateral breast cancer-related lymphedema (BCRL) and analyzed using immunofluorescence and qPCR. In addition, we used mouse models to analyze fibrosis, inflammation, lymphatic pumping, and lymphangiogenesis in animals treated with a topical formulation of Captopril, an ACE inhibitor. RESULTS: ACE expression was significantly increased in lymphedematous tissues of patients and in mouse models of lymphedema. Topical Captopril markedly decreased lymphedematous changes in the mouse tail by decreasing TGF-B1 expression and decreasing swelling, fibroadipose deposition, and inflammation. Captopril-treated animals also had significantly increased lymphatic collecting vessel pumping and collateral lymphatic formation. CONCLUSION: Topical Captopril significantly attenuates the pathological changes of lymphedema in a preclinical model. The use of topical formulations may help avoid systemic effects and holds promise in the clinical setting.

AbstractBackgroundSecondary lymphedema is a common complication of cancer treatment, and previous studies have shown that the expression of transforming growth factor‐beta 1 (TGF‐β1), a pro‐fibrotic and anti‐lymphangiogenic growth factor, is increased in this disease. Inhibition of TGF‐β1 decreases the severity of the disease in mouse models; however, the mechanisms that regulate this improvement remain unknown.MethodsExpression of TGF‐β1 and extracellular matrix molecules (ECM) was assessed in biopsy specimens from patients with unilateral breast cancer‐related lymphedema (BCRL). The effects of TGF‐β1 inhibition using neutralizing antibodies or a topical formulation of pirfenidone (PFD) were analyzed in mouse models of lymphedema. We also assessed the direct effects of TGF‐β1 on lymphatic endothelial cells (LECs) using transgenic mice that expressed a dominant‐negative TGF‐β receptor selectively on LECs (LECDN‐RII).ResultsThe expression of TGF‐β1 and ECM molecules is significantly increased in BCRL skin biopsies. Inhibition of TGF‐β1 in mouse models of lymphedema using neutralizing antibodies or with topical PFD decreased ECM deposition, increased the formation of collateral lymphatics, and inhibited infiltration of T cells. In vitro studies showed that TGF‐β1 in lymphedematous tissues increases fibroblast, lymphatic endothelial cell (LEC), and lymphatic smooth muscle cell stiffness. Knockdown of TGF‐β1 responsiveness in LECDN‐RII resulted in increased lymphangiogenesis and collateral lymphatic formation; however, ECM deposition and fibrosis persisted, and the severity of lymphedema was indistinguishable from controls.ConclusionsOur results show that TGF‐β1 is an essential regulator of ECM deposition in secondary lymphedema and that inhibition of this response is a promising means of treating lymphedema.

BACKGROUND:Numerous studies have evaluated the effect of post-mastectomy radiotherapy (PMRT) on autologous breast reconstruction, but the variability of PMRT regimens and inadequate controls have made results difficult to interpret. Therefore, in this study, irradiated free-flaps are compared to non-irradiated internal controls in patients who underwent immediate bilateral reconstruction followed by unilateral PMRT to better delineate the effect of PMRT. The role of regional nodal irradiation (RNI) is also specifically assessed.METHODS:Appropriate patients were identified through retrospective review. Complications such as fat necrosis, fibrosis, infection, delayed healing, and flap loss, as well as revision surgeries, among the irradiated free-flaps were compared to those on the contralateral non-irradiated side. Additional analyses were performed to evaluate the effect of patient demographics and treatment characteristics, such as RNI, on complications involving the irradiated free-flaps.RESULTS:Seventy-three women were included. There was no significant difference between complication rates for the irradiated and non-irradiated free-flaps (39.7% vs. 38.4%, p = .78), although irradiated free-flaps were more likely to have fibrosis (17.0% vs. 0.0%; p < .0001) and multiple complications (9.6% vs. 0.0%; p = .02). Both groups underwent a similar number of revision surgeries (42.5% vs. 41.1%; p = .29). Looking at the irradiated free-flaps, internal mammary node (IMN) irradiation was the only factor predictive of complications (IRR 3.80, CI 1.32-10.97; p = .01).CONCLUSIONS:PMRT may contribute to free-flap fibrosis, but does not appear to affect the overall risk of complications or revision surgeries. However, additional counseling is warranted if IMN irradiation is likely, as it is potentially associated with increased complications.

Exogenous administration of lymphangiogenic growth factors is widely used to study changes in lymphatic function in pathophysiology. However, this approach can result in off-target effects, thereby generating conflicting data. To circumvent this issue, we modulated intracellular VEGF-C signaling by conditionally knocking out the lipid phosphatase PTEN using the Vegfr3 promoter to drive the expression of Cre-lox in lymphatic endothelial cells (LECs). PTEN is an intracellular brake that inhibits the downstream effects of the activation of VEGFR3 by VEGF-C. Activation of Cre-lox recombination in adult mice resulted in an expanded functional lymphatic network due to LEC proliferation that was independent of lymphangiogenic growth factor production. Furthermore, compared with lymphangiogenesis induced by VEGF-C injection, LECPTEN animals had mature, nonleaky lymphatics with intact cell-cell junctions and reduced local tissue inflammation. Last, compared with wild-type or VEGF-C-injected mice, LECPTEN animals had an improved capacity to resolve inflammatory responses. Our findings indicate that intracellular modulation of lymphangiogenesis is effective in inducing functional lymphatic networks and has no off-target inflammatory effects.

Background: Facial asymmetry from unilateral condylar hyperplasia (UCH) may be definitively treated in the presence of active disease (with high condylectomy and concurrent orthognathic surgery) or after waiting for disease inactivity (orthognathic surgery alone). There is currently no consensus on the standard of care. In this study, we sought to compare functional and esthetic outcomes, as well as treatment duration, between these 2 management options. Methods: Patients who underwent treatment for UCH were identified through retrospective review. Pre- and postoperative 3-dimensional (3D) images were obtained. Short- and long-term operative outcomes of those treated during the active (group 1) were compared to those treated in the inactive phase (group 2). Total treatment time, operative time, and length of hospital stay were evaluated. Facial asymmetry was also assessed by laypersons using a Likert scale. Results: Fifteen patients (mean 25.6 years, range 14-56) were included: 6 in group 1 and 9 in group 2. All surgical outcomes were statistically independent of procedure type. Treatment time was significantly longer in the group 2 (P = 0.03). Both groups demonstrated significant improvement in facial asymmetry scores postoperatively with no significant difference in pre- or postoperative asymmetry between groups (P = 0.64). Conclusions: In patients with active UCH, high condylectomy and orthognathic surgery is a procedure that restores facial symmetry and improves jaw function while halting mandibular growth. Good esthetic and functional outcomes, as well as reduced treatment time and disease burden, support the use of this treatment option for this population.

Nonhematopoietic stromal cells in lymph nodes such as fibroblastic reticular cells (FRCs) can support the survival of plasmablasts and plasma cells [together, antibody-forming cells (AFCs)]. However, a regulatory function for the stromal compartment in AFC accumulation has not been appreciated. Here, we show that chemokine ligand 2 (CCL2)-expressing stromal cells limit AFC survival. FRCs express high levels of CCL2 in vessel-rich areas of the T cell zone and the medulla, where AFCs are located. FRC CCL2 is up-regulated during AFC accumulation, and we use lymph node transplantation to show that CCL2 deficiency in BP3(+) FRCs and lymphatic endothelial cells increases AFC survival without affecting B or germinal center cell numbers. Monocytes are key expressers of the CCL2 receptor CCR2, as monocyte depletion and transfer late in AFC responses increases and decreases AFC accumulation, respectively. Monocytes express reactive oxygen species (ROS) in an NADPH oxidase 2 (NOX2)-dependent manner, and NOX2-deficient monocytes fail to reduce AFC numbers. Stromal CCL2 modulates both monocyte accumulation and ROS production, and is regulated, in part, by manipulations that modulate vascular permeability. Together, our results reveal that the lymph node stromal compartment, by influencing monocyte accumulation and functional phenotype, has a regulatory role in AFC survival. Our results further suggest a role for inflammation-induced vascular activity in tuning the lymph node microenvironment. The understanding of stromal-mediated AFC regulation in vessel-rich environments could potentially be harnessed to control antibody-mediated autoimmunity.

Lymphedema may be characterized by a progressive clinical course and limitations in improvement despite multi-modality treatment. In westernized countries, it most commonly presents as an undesirable complication of cancer treatment, particularly breast cancer. In the past several decades, surgical treatments for lymphedema have advanced, alongside developments in microsurgery. Lymphovenous anastomosis (LVA) and lymph node transplantation are physiological therapies that may reduce lymphedema through addressing its route cause. Ablative techniques such as liposuction and subcutaneous excision aid in resolving the accumulation of proteinaceous adipose and fibrotic tissue seen in advanced lymphedema. The goal of this review is to examine the outcomes and limitations of current surgical techniques used in lymphedema management.

Objective: Obesity results in lymphatic dysfunction, but the cellular mechanisms that mediate this effect remain largely unknown. Previous studies in obese mice have shown that inducible nitric oxide synthase-expressing (iNOSthorn) inflammatory cells accumulate around lymphatic vessels. In the current study, we therefore tested the hypothesis that increased expression of iNOS results in nitrosative stress and injury to the lymphatic endothelial cells (LECs). In addition, we tested the hypothesis that lymphatic injury, independent of obesity, can modulate glucose and lipid metabolism. Methods: We compared the metabolic changes and lymphatic function of wild-type and iNOS knockout mice fed a normal chow or high-fat diet for 16 weeks. To corroborate our in vivo findings, we analyzed the effects of reactive nitrogen species on isolated LECs. Finally, using a genetically engineered mouse model that allows partial ablation of the lymphatic system, we studied the effects of acute lymphatic injury on glucose and lipid metabolism in lean mice. Results: The mesenteric lymphatic vessels of obese wild-type animals were dilated, leaky, and surrounded by iNOSthorn inflammatory cells with resulting increased accumulation of reactive nitrogen species when compared with lean wild-type or obese iNOS knockout animals. These changes in obese wild-type mice were associated with systemic glucose and lipid abnormalities, as well as decreased mesenteric LEC expression of lymphatic-specific genes, including vascular endothelial growth factor receptor 3 (VEGFR-3) and antioxidant genes as compared with lean wild type or obese iNOS knockout animals. In vitro experiments demonstrated that isolated LECs were more sensitive to reactive nitrogen species than blood endothelial cells, and that this sensitivity was ameliorated by antioxidant therapies. Finally, using mice in which the lymphatics were specifically ablated using diphtheria toxin, we found that the interaction between metabolic abnormalities caused by obesity and lymphatic dysfunction is bidirectional. Targeted partial ablation of mesenteric lymphatic channels of lean mice resulted in increased accumulation of iNOSthorn inflammatory cells and increased reactive nitrogen species. Lymphatic ablation also caused marked abnormalities in insulin sensitivity, serum glucose and insulin concentrations, expression of insulin-sensitive genes, lipid metabolism, and significantly increased systemic and mesenteric white adipose tissue (M-WAT) inflammatory responses. Conclusions: Our studies suggest that increased iNOS production in obese animals plays a key role in regulating lymphatic injury by increasing nitrosative stress. In addition, our studies suggest that obesity-induced lymphatic injury may amplify metabolic abnormalities by increasing systemic and local inflammatory responses and regulating insulin sensitivity. These findings suggest that manipulation of the lymphatic system may represent a novel means of treating metabolic abnormalities associated with obesity. (c) 2020 The Authors. Published by Elsevier GmbH. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Background: Facial asymmetry caused by unilateral condylar hyperplasia requires treatment to address facial and occlusal imbalances. There is no definitive evidence to suggest that a single intervention strategy (during either active condylar overgrowth or the burnt-out phase) results in better/more symmetric correction. This study sought to quantify preoperative and postoperative facial asymmetry in unilateral condylar hyperplasia patients comparing treatment for active versus burnt-out disease. Methods: Preoperative and postoperative three-dimensional photographs were obtained. Images were compared to those of unaffected controls as a standard for normal facial symmetry. Facial asymmetry was assessed using root-mean-square deviation. Paired t tests were performed to compare the root-mean-square deviations of preoperative and postoperative images between the unilateral condylar hyperplasia groups and against controls. Results: Forty patients were included (11 active, nine burnt-out, and 20 controls) and 60 three-dimensional images were evaluated. Preoperatively, patients in the burnt-out group had worse asymmetry than those with active unilateral condylar hyperplasia (p = 0.011). Both groups demonstrated significantly improved symmetry postoperatively (active, p = 0.0069; burnt-out, p = 1.74E-4). However, burnt-out patients remained with some residual asymmetry (p = 4.75E-4), whereas their active counterparts showed no significant difference compared to unaffected controls (p = 0.089). Conclusions: Patients with end-stage unilateral condylar hyperplasia have more severe facial asymmetry that is more difficult to normalize compared to earlier intervention during active unilateral condylar hyperplasia. These findings suggest that, if possible, corrective intervention is preferable during active unilateral condylar hyperplasia. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, II.

Abstract Proliferation of aberrant, dysfunctional lymphatic vessels around solid tumors is a common histologic finding. Studies have shown that abnormalities in lymphatic function result in accumulation of inflammatory cells with an immunosuppressive profile. We tested the hypothesis that dysfunctional lymphatic vessels surrounding solid tumors regulate changes in the tumor microenvironment and tumor-specific immune responses. Using subcutaneously implanted mouse melanoma and breast cancer tumors in a lymphatic endothelial cell–specific diphtheria toxin receptor transgenic mouse, we found that local ablation of lymphatic vessels increased peritumoral edema, as compared with controls. Comparative analysis of the peritumoral fluid demonstrated increases in the number of macrophages, CD4+ inflammatory cells, F4/80+/Gr-1+ (myeloid-derived suppressor cells), CD4+/Foxp3+ (Tregs) immunosuppressive cells, and expression of inflammatory cytokines such as TNFα, IFNγ, and IL1β following lymphatic ablation. Tumors grown in lymphatic ablated mice exhibited reduced intratumoral accumulation of cytotoxic T cells and increased tumor PD-L1 expression, causing rapid tumor growth, compared with tumors grown in nonlymphatic-ablated mice. Our study suggests that lymphatic dysfunction plays a role in regulating tumor microenvironments and may be therapeutically targeted in combination with immunotherapy to prevent tumor growth and progression.

Background: Genetic mutations and obesity increase the risk of secondary lymphedema, suggesting that impaired lymphatic function before surgical injury may contribute to disease pathophysiology. Previous studies show that obesity not only decreases lymphatic function, but also markedly increases pathologic changes, such as swelling, fibroadipose deposition, and inflammation. However, although these reports provide circumstantial evidence supporting the hypothesis that baseline lymphatic defects amplify the effect of lymphatic injury, the mechanisms regulating this association remain unknown. Methods: Baseline lymphatic morphology, leakiness, pumping, immune cell trafficking, and local inflammation and fibroadipose deposition were assessed in wild-type and Prox1-haploinsufficient (Prox1+/-) mice, which have previously been shown to have abnormal vasculature without overt evidence of lymphedema. In subsequent experiments, wild-type and Prox1+/- mice underwent popliteal lymph node dissection to evaluate the effect of lymphatic injury. Repeated testing of all variables was conducted 4 weeks postoperatively. Results: At baseline, Prox1+/- mice had dilated, leaky lymphatic vessels corresponding to low-grade inflammation and decreased pumping and transport function, compared with wild-type mice. Popliteal lymph node dissection resulted in evidence of lymphedema in both Prox1+/- and wild-type mice, but popliteal lymph node dissection–treated Prox1+/- mice had increased inflammation and decreased lymphatic pumping. Conclusions: Subclinical lymphatic dysfunction exacerbates the pathologic changes of lymphatic injury, an effect that is multifactorial and related to increased lymphatic leakiness, perilymphatic accumulation of inflammatory cells, and impaired pumping and transport capacity. These findings suggest that preoperative testing of lymphatic function may enable clinicians to more accurately risk-stratify patients and design targeted preventative strategies.

T cell-mediated responses have been implicated in the development of fibrosis, impaired lymphangiogenesis, and lymphatic dysfunction in secondary lymphedema. Here we show that CD4(+) T cells are necessary for lymphedema pathogenesis by utilizing adoptive transfer techniques in CD4 knockout mice that have undergone tail skin and lymphatic excision or popliteal lymph node dissection. We also demonstrate that T cell activation following lymphatic injury occurs in regional skin-draining lymph nodes after interaction with antigen-presenting cells such as dendritic cells. CD4(+) T cell activation is associated with differentiation into a mixed T helper type 1 and 2 phenotype, as well as upregulation of adhesion molecules and chemokines that promote migration to the skin. Most importantly, we find that blocking T cell release from lymph nodes using a sphingosine-1-phosphate receptor modulator prevents lymphedema, suggesting that this approach may have clinical utility.