Three-Year Safety and Efficacy of the INCRAFT Endograft for Treatment of Abdominal Aortic Aneurysms: Results of the INSIGHT Study.

PURPOSE: Preliminary results of the INSIGHT study showed that the low-profile INCRAFT Abdominal Aortic Aneurysm (AAA) Stent-Graft System was safe and effective in the endovascular aneurysm repair (EVAR). This study aimed to assess the durability and the midterm effectiveness of EVAR using the INCRAFT System in the framework of a multicenter, prospective, open-label, post-approval study. MATERIALS AND METHODS: Between 2015 and 2016, 150 subjects from 23 European centers treated with the INCRAFT System for an infrarenal AAA were included. Clinical and radiologic data were prospectively collected and analyzed using protocol-specified, monitored follow-up clinic visits at 1, 6, and 12 months post-implantation and annually after that. The clinical success at 3 years was determined. Freedom from overall and aneurysm-related mortality, type I endoleak, secondary interventions, and aneurysm sac enlargement through 3 years were evaluated. Kaplan-Meier estimates were used for late outcomes. An independent clinical events committee reviewed all events. The CT (computed tomography) scans through 1 year were reviewed by an independent core laboratory. RESULTS: The primary clinical success rate at 3 years was 84.0% (126/150). There were no aneurysm-related deaths, endograft migration, or aneurysm-related ruptures through 3 years. Stent fracture was detected in 2 subjects (1.3%) without clinical sequelae. Over 3 years, freedom from overall mortality was 89.4%, freedom from secondary interventions was 80%, and freedom from aneurysm sac enlargement was 96.5%. The 3-year freedom from type IA and IB endoleaks was 93.3% and 98.6%, respectively. CONCLUSIONS.: In a multicenter real-world study setting, the use of a low-profile INCRAFT device for AAA is associated with sustained clinical success and low rates of reinterventions through 3 years. CLINICAL IMPACT: Low-profile endografts have broadened the spectrum of patients with anatomic suitability for endovascular repair of abdominal aortic aneurysms (AAA). However, questions remain regarding the durability of the repair. The INSIGHT study evaluated the use of the INCRAFT System in routine real-world clinical practice, including patients with complex anatomies. The treatment was safe and effective. The results showed sustained clinical success over 3 years, with no aneurysm-related deaths or ruptures, and a high rate of intervention-free survival at 3 years. Despite the low-profile design of the endograft, the midterm results demonstrate the durability of AAA repair using the INCRAFT System.ClinicalTrials.gov Identifier: NCT02477111.

One-year results of the INSIGHT study on endovascular treatment of abdominal aortic aneurysms.

OBJECTIVE: Endovascular repair of abdominal aortic aneurysms (AAAs) using the INCRAFT AAA Stent Graft System was safe and effective in regulatory approval studies. We herein report on the 1-year results of a real-world clinical study. METHODS: The INSIGHT study is a multi-center, prospective, open label, post-approval study conducted to continually evaluate the safety and performance of the INCRAFT System. Between 2015 and 2016, 150 consecutive patients with AAA at 23 centers in Europe were treated with the device in routine clinical practice. The primary endpoint was freedom from major adverse events (MAEs), namely death, myocardial infarction, cerebrovascular accident, and renal failure, within 30 days of the index procedure. End point data were assessed by a core laboratory. The secondary end points included technical success at the conclusion of the procedure and clinical success. RESULTS: All 150 patients studied (mean age, 73.6 ± 8.0 years; 89.3% men) met the primary end point without MAEs at 30-day follow-up. Technical success was achieved in 99.3% of patients without stent fractures at 30 days. Among the 146 patients eligible for 1-year follow-up, the MAE rate was 8.2% (ie, 12 patients suffered 13 MAEs: cerebrovascular accident in 8, myocardial infarction in 1, and 4 died, resulting in a 2.7% all-cause mortality rate). There were no reports of new onset renal failure requiring dialysis. Only 2.7% of patients had type I endoleak, and no type III endoleaks were identified through 1 year. The rate of clinical success at 1 year was 91.8%. CONCLUSIONS: The 1-year results of this multicenter real-world study underscore the safety and effectiveness of endovascular treatment of AAA with the INCRAFT System in routine clinical practice.

Repair of an Autologous Saphenous Vein Graft Aneurysm Ten Years after Renal Artery Reconstruction during Live Donor Renal Transplantation.

Saphenous vein graft (SVG) aneurysms (SVGA) after renal transplantation represents a rare vascular complication with subsequent challenging multidisciplinary treatment. We present a case of a 30-year-old female who received a live donor kidney transplantation for end-stage renal disease that was caused due to the hemolytic uremic syndrome. Postoperatively, an insufficient graft perfusion due to an arterial kinking was noted and repaired using an autologous SVG interposition. Ten years later, a 3-cm aneurysm of the SVG at the anastomotic site with the common iliac artery was discovered. Multidisciplinary surgical exploration with excision of the aneurysm-carrying vein graft and interposition of a new autologous SVG was successfully carried out with preservation of renal allograft's function. Treatment of SVGA after rental transplantation with a new autologous SVG is challenging but feasible, requiring a multidisciplinary approach in order to guarantee successful rates and to prevent allograft loss.

Vessel wall morphology is equivalent for different artery types and localizations of advanced human aneurysms.

Aneurysm formation occurs most frequently as abdominal aortic aneurysm (AAA), but is also seen in other localizations like thoracic or peripheral aneurysm. While initial mechanisms for aneurysm induction remain elusive, observations from AAA samples show transmural inflammation with proteolytic imbalance and repair mechanisms triggered by the innate immune system. However, limited knowledge exists about aneurysm pathology, especially for others than AAA. We compared 42 AAA, 15 popliteal, 3 ascending aortic, five iliac, two femoral, two brachial, one visceral and two secondary aneurysms to non-aneurysmatic controls by histologic analysis, immunohistochemistry and cytokine expression. Muscular and elastic type arteries show a uniform way of aneurysm formation. All samples show similar morphology. The changes compared to controls are distinct and include matrix remodeling with smooth muscle cell phenotype switch and angiogenesis, adventitial lymphoid cell accumulation and M1 macrophage homing together with neutrophil inflammation. Inflammatory cytokines are up-regulated accordingly. Comparative analysis of different disease entities can identify characteristic pathomechanisms. The phenotype of human advanced aneurysm disease is observed for elastic and muscular type arteries, does not differ between disease localizations and might, thus, be a unique response of the vasculature to the still unknown trigger of aneurysm formation.

Heterogeneous histomorphology, yet homogeneous vascular smooth muscle cell dedifferentiation, characterize human aneurysm disease.

OBJECTIVE: Abdominal aortic aneurysm (AAA) is a frequent, potentially life-threatening, disease that can only be treated by surgical means such as open surgery or endovascular repair. No alternative treatment is currently available, and despite expanding knowledge about the pathomechanism, clinical trials on medical aneurysm abrogation have led to inconclusive results. The heterogeneity of human AAA based on histologic examination is thereby generally neglected. In this study we aimed to further elucidate the role of these differences in aneurysm disease. METHODS: Tissue samples from AAA and popliteal artery aneurysm patients were examined by histomorphologic analysis, immunohistochemistry, Western blot, and polymerase chain reaction. The results were correlated with clinical data such as aneurysm diameter and laboratory results. RESULTS: The morphology of human AAA vessel wall probes varies tremendously based on the grade of inflammation. This correlates with increasing intima/media thickness and upregulation of the vascular endothelial growth factor cascade but not with any clinical parameter or the aneurysm diameter. The phenotypic switch of vascular smooth muscle cells occurred regardless of the inflammatory state and expressional changes of the transcription factors Kruppel-like factor-4 and transforming growth factor-ß lead to differential protein localization in aneurysmal compared with control arteries. These changes were in similar manner also observed in samples from popliteal artery aneurysms, which, however, showed a more homogenous phenotype. CONCLUSIONS: Heterogeneity of AAA vessel walls based on inflammatory morphology does not correlate with AAA diameter yet harbors specific implications for basic research and possible aneurysm detection.

Extra- and Intraluminal Elastase Induce Morphologically Distinct Abdominal Aortic Aneurysms in Mice and Thus Represent Specific Subtypes of Human Disease.

Topical application of elastase to induce arterial aneurysm formation is an emerging murine model of vascular disease. In the context of aortic abdominal aneurysm (AAA), angiotensin II infusion and porcine pancreatic elastase perfusion models are commonly used today. This study, therefore, compares matrix remodeling, inflammation, and angiogenesis as distinct features of aneurysms in two models treated with intra-/extraluminal elastase. C57BL/6 mice underwent intra-/extraluminal elastase application via laparotomy and were followed up for 4 weeks. Basic histology and immunohistochemistry were performed at different time points along with transmission electron microscopy, PCR analysis, TUNEL assays, and blood analysis. Both models did not differ in aneurysm growth rate, but they showed distinct features and results depending on the way of elastase application. Extraluminal aneurysm induction preserved endothelial cell function and elastic fibers but showed ongoing acute inflammation, mainly in the adventitia. The destruction of elastic layers followed by chronic inflammation was a characteristic of intraluminal elastase perfusion, as well as medial angiogenesis, a key feature in human AAA. Different animal models harbor different features of human AAA and must, therefore, be chosen wisely. External elastase application mimics an acute inflammatory aneurysm, whereas intraluminal elastase perfusion shows chronic inflammation with angiogenesis and endothelial destruction, thus better mimicking human disease.

Aneurysm miRNA Signature Differs, Depending on Disease Localization and Morphology.

Limited comprehension of aneurysm pathology has led to inconclusive results from clinical trials. miRNAs are key regulators of post-translational gene modification and are useful tools in elucidating key features of aneurysm pathogenesis in distinct entities of abdominal and popliteal aneurysms. Here, surgically harvested specimens from 19 abdominal aortic aneurysm (AAA) and 8 popliteal artery aneurysm (PAA) patients were analyzed for miRNA expression and histologically classified regarding extracellular matrix (ECM) remodeling and inflammation. DIANA-based computational target prediction and pathway enrichment analysis verified our results, as well as previous ones. miRNA-362, -19b-1, -194, -769, -21 and -550 were significantly down-regulated in AAA samples depending on degree of inflammation. Similar or inverse regulation was found for miR-769, 19b-1 and miR-550, -21, whereas miR-194 and -362 were unaltered in PAA. In situ hybridization verified higher expression of miR-550 and -21 in PAA compared to AAA and computational analysis for target genes and pathway enrichment affirmed signal transduction, cell-cell-interaction and cell degradation pathways, in line with previous results. Despite the vague role of miRNAs for potential diagnostic and treatment purposes, the number of candidates from tissue signature studies is increasing. Tissue morphology influences subsequent research, yet comparison of distinct entities of aneurysm disease can unravel core pathways.

Neointimal hyperplasia in allogeneic and autologous venous grafts is not different in nature.

Neointimal hyperplasia, transplant rejection and thus immunogenicity of allografts are possible reasons for poorer patency rates in cryopreserved venous allografts for peripheral bypass surgery in comparison with autologous venous grafts. To expand the limited knowledge from human allografts, we histologically investigated allogeneic and autologous venous grafts in arterial location. Specimens of allogeneic and autologous venous graft stenosis, harvested 6 months after bypass implantation, were immunohistochemically characterized. Examination of the lesions showed a uniform morphological pattern. A continuous endothelial layer, tissue fibrosis and a thickened neointima with monocytes and dedifferentiated vascular smooth muscle cells were seen in both conduits with very low cell turnover and the absence of acute and chronic inflammation. Neoangiogenesis with CD34-positive endothelium was abundant in the vessel media. The morphological patterns of allogeneic and autologous neointima formation are similar. Consequently, neointimal hyperplasia in venous grafts may reflect a uniform physiological host response of non-immunological factors with the reasons for poorer clinical outcome of cryopreserved allografts yet to be elucidated.

Celiacobihepatic venous bypass for liver revascularization in a patient with intrahepatic contained rupture of a common hepatic artery aneurysm.

Visceral artery aneurysms are rare, often incidental findings due to unspecific or no symptoms. We report a unique case of a 54-year-old patient with a contained rupture of a common hepatic artery aneurysm, without panarteritis nodosa or immunoglobulin G4 association, into the right liver hilum, that led to shock, cholestasis, and liver function impairment. Aneurysm resection and cholecystectomy, followed by revascularization with a great saphenous vein celiacobihepatic bypass and Roux-en-Y hepaticojejunostomy were performed. The patient was discharged 13 days later. Liver function was normal, and the revascularization patency was confirmed at follow-up at 3 and 12 months.

Endovascular treatment of popliteal artery segments P1 and P2 in patients with critical limb ischemia: initial experience using a helical nitinol stent with increased radial force.

PURPOSE: To evaluate efficacy, safety, and midterm patency of a helical, self-expanding nitinol stent after failed percutaneous transluminal angioplasty (PTA) of popliteal artery segments P1 and P2 in patients with chronic critical limb ischemia (CLI) or lifestyle-limiting claudication. METHODS: Between February 2009 and March 2011, 40 patients (23 men; mean age 77±10 years) classified as Rutherford category 3 (n = 10) or 4/5 (n = 30) underwent PTA of the proximal and mid popliteal artery followed by implantation of a SUPERA stent for elastic recoil, residual stenosis, or flow-limiting dissection. All patients had an elevated operative risk. Before and after the procedure and during the 12-month follow-up, a clinical investigation, ankle-brachial-index (ABI) measurement, and color-coded duplex sonography and/or digital subtraction angiography were performed. Primary endpoints were limb salvage and anatomical patency at 12 months. RESULTS: Stent implantation was successful in all patients. The major complication rate was 7.5% (an access-site pseudoaneurysm, 2 retroperitoneal hematomas, and 1 death from retroperitoneal bleeding). Mean follow-up was 15.9 months (range 0.5-27.9). The mean baseline ABI of 0.37 significantly increased to 0.91 at 12 months (p<0.01). Three (7.5%) patients underwent bypass surgery owing to lack of clinical improvement (<0.10 improvement in ABI). Primary and secondary patency rates at 12 months in the 34 patients eligible for follow-up were 68.4% and 79.8%, respectively. The major amputation rate was 5% at 1 year. Five (12.5%) in-stent stenoses and 1 of 2 (5.0%) in-stent occlusions were successfully recanalized (the second occlusion was asymptomatic). CONCLUSION: Implantation of this helical stent into segments of the popliteal artery at the knee joint in CLI patients is a safe and clinically effective bailout method with acceptable intermediate patency.

Endovascular treatment of acute limb ischemia secondary to fracture of a popliteal artery stent.

The authors report the case of a patient with acute lower limb ischemia (category IIa) after occlusion of the popliteal artery due to fracture of a long indwelling stent. The patient refused surgical therapy for religious reasons, and an interventional revascularization was performed as acute rescue therapy. After reentry into the distal popliteal artery was achieved, the artery was dilated, and the fragmented stent was crushed, followed by implantation of two helical nitinol stents with high radial force and a third self-expandable nitinol stent. Sufficient primary technical success was achieved, and stent patency was present at midterm follow-up.

Interdisciplinary complication management of dislodged lumbar interbody spacer in pulmonary artery.

We report the case of an intraoperatively dislodged transforaminal lumbar interbody fusion spacer with creation of a traumatic arteriovenous fistula and device migration to the pulmonary artery. Successful minimally invasive angiographic retrieval of the spacer is discussed with special reference to angiographic and surgical treatment strategies and pitfalls.

Proximal occlusion of unaffected internal iliac artery versus distal occlusion of aneurysmatic internal iliac artery prior to EVAR: a comparative evaluation of efficacy and clinical outcome.

OBJECTIVE: Occlusion of the internal iliac artery (IIA) may be necessary prior to endovascular aneurysm repair (EVAR) to prevent endoleak Type II. We compared efficacy and clinical outcome after proximal occlusion of an unaffected IIA (ProxEmbx) using an Amplatzer vascular plug (AVP) I vs distal occlusion of aneurysmatic IIA with coils and plugs (DistEmbx). METHODS: Between 2009 and 2012, 22 patients underwent EVAR. In 9 patients with unaffected IIA, occlusion was performed by a single AVP. In 13 patients with aneurysmatic IIA, more distal embolization (DistEmbX) was conducted by using several coils and additional AVPs. Retrospectively, technical success, clinical outcome and complications were evaluated. RESULTS: Embolization of the IIA was successful in all patients. Three patients with more DistEmbX of aneurysmatic IIAs suffered from new onset of sexual dysfunction after occlusion without statistically significant difference (p > 0.05). Transient buttock claudication was observed in three patients in each group. Bowel ischaemia did not occur. The procedure time (p = 0.013) and fluoroscopy time (p = 0.038) was significantly lower in the ProxEmbx group than in the DistEmbx group. CONCLUSION: Proximal occlusion of an unaffected IIA and more distal occlusion of an aneurysmatic IIA prior to EVAR had the same technical and clinical outcome. However, proximal plug embolization of an unaffected IIA prior to EVAR was associated with shorter procedure and fluoroscopy time in comparison with more DistEmbX of aneurysmatic IIAs. Advances in knowledge: Proximal embolization of unaffected IIA and DistEmbX of aneurysmatic IIA before EVAR are both effective in preventing Type II endoleaks and have the same technical and clinical outcome.

Monoclonal antibody against beta7 integrins, but not beta7 deficiency, attenuates intestinal allograft rejection in mice.

BACKGROUND: beta7 integrins mediate homing and retention of lymphocytes to the normal and inflamed small bowel in a tissue-selective fashion. In the present study, we investigated the expression of beta7 integrins after small bowel transplantation (SBT) and tested the effects of blocking beta7-mediated pathways by using monoclonal antibody (mAb) or knockout mice. METHODS: Heterotopic SBT from BALB/c to C57BL/6 (B6) was used as a surgical model. Expression of beta7 integrins was measured on recipient lymphocytes (CD4 and CD8 ) in spleen, blood, and mesenteric lymph nodes (MLN) using flow cytometry. To analyze the effects of blocking beta7 integrins on graft survival, either beta7-deficient B6 or wild-type B6 mice that were treated with mAb against beta7 were studied. RESULTS: After allogeneic SBT, there were markedly increased levels of alpha4beta7 recipient CD8 lymphocytes in MLN, blood, and spleen as early as 3 days postoperatively. In contrast, alpha4beta7 integrin levels in isograft recipients were similar to those of normal mice. Mean survival time of intestinal allografts was not affected by beta7 deficiency (7.3+/-1 days) compared with wild-type mice (7.5+/-0.8 days). However, mAb against beta7 integrins significantly prolonged graft survival (12.8+/-1 days) compared with treatment with control mAb (7.3+/-1 days, <0.001). Histologic changes of SBT rejection were significantly attenuated when mice were given mAb against beta7. CONCLUSION: As indicated by the increased levels of alpha4beta7 CD8 lymphocytes, activation of this integrin contributes to the immune response in SBT rejection. Furthermore, blocking beta7 integrins with mAb provides a suitable target for immunosuppressive therapy. The discrepancy in survival data obtained by mAb and beta7 deficiency may be a result of the more rapid activation of compensatory mechanisms in the knockout mice.

Intragraft distribution of lymphocytes expressing beta7 integrins after small bowel transplantation in mice.

Lymphocytes with activated beta7 integrins (alphaEbeta7 and alpha4beta7) contribute to inflammatory reactions in the small bowel. Since the selective recruitment of lymphocytes to the lymphoid compartments of the small bowel is controlled by distinct adhesion molecule interactions, a compartment-dependent use of beta7 integrins may influence the rejection response within intestinal transplants. To further delineate the nature of beta7 integrin-mediated graft infiltration, we analysed their expression on T lymphocytes in the heterotopically transplanted small bowel of BALB/c and C57BL/6 mice. Lymphocytes isolated from the epithelium, lamina propria (LP), Peyer's patches (PP), and mesenteric lymph nodes (MLN) were analysed by three-color fluorescence flow cytometry using monoclonal antibodies (mAb) to integrin the subunits, lymphocyte markers, and MHC I of the donor and recipient strains. On postoperative day 5 (POD) after allogeneic small bowel transplantation (SBT), 43% of intraepithelial lymphocytes (IEL) and 63% of LP, 93% of MLN, and 93% of PP lymphocytes were of host origin. In the MLN and PP of allografts, a major infiltrating lymphocyte population consisted of CD8+ cells with increased expression of alpha4beta7 and decreased expression of L-selectin, an adhesion molecule profile characteristic of intestinal effector cell phenotypes. An increase in alpha4beta7 levels was also found on CD8+ host lymphocytes in the LP. The integrin profile of a number of host IEL suggests an ongoing transition from the phenotype of graft infiltrating lymphocytes with high levels of alpha4beta7 and low levels of alphaepsilonbeta7 to that of resident IEL with high levels of alphaepsilonbeta7 and low levels of alpha4beta7. The importance of beta7-mediated lymphocyte trafficking to the graft is attested by the significant reduction in the host lymphocyte population in the LP, PP, and epithelium following the administration of a beta7-blocking mAb to allograft recipients. In conclusion, while the infiltration patterns of lymphocytes may vary between the lymphoid compartments of intestinal allografts, host CD8+ lymphocytes with high levels of alpha4beta7 constitute a major effector cell population that affects the entire graft.

Vitamin A metabolism is altered in brown Norway and long-Evans rats infused with naftidrofuryl or erythromycin intravenously.

Enzymatic retinyl ester hydrolysis is a key reaction for maintaining cellular retinol homeostasis. The ability of naftidrofuryl and erythromycin to inhibit retinol liberation by retinyl ester hydrolase (REH) in vitro suggests an ability to interfere with vitamin A metabolism in vivo, particularly during hepatic processing. To address this question, systemic and local response to these agents were studied in Brown Norway (BN) and Long-Evans (LE) rats. The study was conducted in two parts: a drug-loading phase and a washout phase. Analysis of variance of the time course changes in plasma retinol during the post-treatment period (Days 10-18) showed rat strain (p < 0.04) and time (p < 0.001; strain-by-time interactive effect, p < 0.001) to be significant factors, but drug exposure (p = 0.19) was not significant. Endpoints included hepatic REH activity, size and composition of the liver vitamin A stores, and retinoid content of the kidneys. Rats recovering from naftidrofuryl dosing demonstrated a lower REH activity than did animals recovering from erythromycin treatment (p < 0.009). The major side effect of erythromycin is vitamin A accumulation in the liver (p < 0.001) and reductions in retinol reserves (p < 0.02) were among the consequences of naftidrofuryl treatment. In the kidney of LE rats, there were higher concentrations of vitamin A (p < 0.003) secondary to naftidrofuryl exposure. Together our data suggest that clinically achievable concentrations of the drugs, given as a continuous infusion, produce aberrations in vitamin A metabolism.

Femoral vein obturator bypass revascularization in groin infectious bleeding: two case reports and review of the literature.

INTRODUCTION: Groin infections resulting in arterial bleeding due to bacterial vessel destruction are a severe challenge in vascular surgery. Patients with them most often present as emergencies and therefore need individualized reconstruction solutions. CASE PRESENTATION: Case 1 is a 67-year-old man with infectious bleeding after an autologous reconstruction of the femoral bifurcation with greater saphenous vein due to infection of a bovine pericard patch after thrombendarterectomy. Case 2 is a 35-year-old male drug addict and had severe femoral bleeding and infection after repeated intravenous and intra-arterial substance abuse. Both patients were treated with an autologous obturator bypass of the superficial femoral vein. We review the current literature and highlight our therapeutic concept of this clinical entity. CONCLUSIONS: Treatment should include systemic antibiotic medication, surgical control of the infectious site, revascularization and soft tissue repair. An extra-anatomical obturator bypass with autologous superficial femoral vein should be considered as the safest revascularization procedure in infections caused by highly pathogenic bacteria.

Bilateral patellar tendon rupture without predisposing systemic disease or steroid use: a case report and review of the literature.

Simultaneous bilateral patella tendon ruptures are very rare injuries of the knee extensor complex often associated with systemic disorders such as lupus erythematosus or rheumatoid arthritis. We describe the case of a 34-year-old man without concomitant systemic disease or steroid use and provide the most comprehensive review of the German and English literature. Furthermore, we discuss the predisposing factors and causal mechanisms as well as current diagnostic procedures and treatment options. In the literature review, only a few patients without systemic disorder or steroid medication present with potential predisposing factors that may be responsible for degenerative changes of the patella tendon, weakening its stability. In addition, in most of these cases, it remains difficult to explain the bilateral and simultaneous nature of this injury.

Comparison of in vivo lymphocyte proliferation between allogeneic and xenogeneic heart transplantation in mice.

There are controversial in vitro data comparing the strength of the cellular immune response between allogeneic and xenogeneic stimulator/responder combinations. The present study therefore compares in vivo lymphocyte proliferation using heart transplantation (HTx) models in mice. Heterotopic HTx into BALB/c mice was performed using donor organs from mice (BALB/c and C57BL/6) or Lewis rats. Intraperitoneally given bromodeoxyuridine (BrdU) was incorporated into the DNA and was subsequently analyzed by flow cytometry. On postoperative days 3 and 5, proliferation of splenocytes, CD4(+) T-lymphocytes, and CD19(+) B-lymphocytes was significantly higher after xenogeneic than after allogeneic and isogeneic HTx. No significant difference was observed when proliferation of CD8(+) lymphocytes was determined. The increased in vivo proliferation after xenotransplantation may reflect an earlier and probably stronger cellular immune response compared to allogeneic transplantation. The higher CD4(+) lymphocyte proliferation underscores the importance of this cell population in xenograft rejection.