Letermovir in lung transplant recipients with cytomegalovirus infection: A retrospective observational study.

Letermovir is a new antiviral drug approved for the prophylaxis of CMV infection in allogeneic stem cell transplants. The aim of the study was to assess the therapeutic efficacy of letermovir in difficult to treat CMV infections in lung transplant recipients. All lung transplant recipients between March 2018 and August 2020, who have been treated with letermovir for ganciclovir-resistant or refractory CMV infection were included in the study and analysed retrospectively. In total, 28 patients were identified. CMV disease was present in 15 patients (53.6%). In 23 patients (82.1%), rapid response was noticed, and CMV-viral load could be significantly decreased (>1 log10 ) after a median of 17 [14-27] days and cleared subsequently in all of these patients. Five patients (17.9%) were classified as non-responder. Thereof, development of a mutation of the CMV UL56 terminase (UL-56-Gen: C325Y) conferring letermovir resistance could be observed in three patients (60%). Common side effects were mild and mostly of gastrointestinal nature. Mild adjustments of the immunosuppressive drugs were mandatory upon treatment initiation with letermovir. In addition to other interventions, letermovir was effective in difficult to treat CMV infections in lung transplant recipients. However, in patients with treatment failure mutation conferring letermovir, resistance should be taken into account.

Association of CMV-specific T-cell immunity and risk of CMV infection in lung transplant recipients.

BACKGROUND: Protecting against CMV infection and maintaining CMV in latent state are largely provided by CMV-specific T-cells in lung transplant recipients. The aim of the study was to assess whether a specific T-cell response is associated with the risk for CMV infection in seronegative patients who are at high risk for delayed CMV infection. METHODS: All CMV-seronegative recipients (R-) from CMV-seropositive donors (D+) between January 2018 and April 2019 were included and retrospectively screened for CMV infection before and after assessment of CMV-specific cell-mediated immunity. RESULTS: Thirty-one of the 50 patients (62%) developed early-onset CMV infection. Lower absolute neutrophil counts were significantly associated with early-onset CMV infection. Antiviral prophylaxis was ceased after 137.2 ± 42.8 days. CMV-CMI were measured at a median of 5.5 months after LTx. 19 patients experienced early and late-onset CMV infection after prophylaxis withdrawal within 15 months post transplantation. Positive CMV-CMI was significantly associated with lower risk of late-onset CMV infection after transplantation in logistic and cox-regression analysis (OR=0.05, p = .01; OR=2,369, p = .026). CONCLUSION: D+/R- lung transplant recipients are at high risk of developing early and late-onset CMV infection. Measurement of CMV-CMI soon after transplantation might further define the CMV infection prediction risk in LTx recipients being at high risk for CMV viremia.

Pirfenidone exerts beneficial effects in patients with IPF undergoing single lung transplantation.

Pirfenidone demonstrated pleiotropic antiinflammatory effects in various experimental and clinical settings. The aim of this study was to assess the impact of previous treatment with pirfenidone on short-term outcomes after single lung transplantation (SLTx). Therefore, patients with idiopathic pulmonary fibrosis (IPF) who were undergoing SLTx were screened retrospectively for previous use of pirfenidone and compared to respective controls. Baseline parameters and short-term outcomes were recorded and analyzed. In total, 17 patients with pirfenidone were compared with 26 patients without antifibrotic treatment. Baseline characteristics and severity of disease did not differ between groups. Use of pirfenidone did not increase blood loss, wound-healing, or anastomotic complications. Severity of primary graft dysfunction at 72 hours was less (0.3 ± 0.6 vs 1.4 ± 1.3, P = .002), and length of mechanical ventilation (37.5 ± 34.8 vs 118.5 ± 151.0 hours, P = .016) and intensive care unit (ICU) stay (6.6 ± 7.1 vs 15.6 ± 20.3, P = .089) were shorter in patients with pirfenidone treatment. An independent beneficial effect of pirfenidone was confirmed by regression analysis while controlling for confounding variables (P = .016). Finally, incidence of acute cellular rejections within the first 30 days after SLTx was lower in patients with previous pirfenidone treatment (0.0% vs 19.2%; P = .040). Our data suggest a beneficial role of previous use of pirfenidone in patients with IPF who were undergoing SLTx.

Association between donor age and risk of graft failure after liver transplantation: an analysis of the Eurotransplant database.

Grafts from elderly donors are increasingly used for liver transplantation. As of yet there is no published systematic data to guide the use of specific age cutoffs the effect of elderly donors on patient outcomes must be clarified. This study analyzed the Eurotransplant database (01/01/2000-31/07/2014; N = 26 294) out of whom 8341 liver transplantations were filtered to identify for this analysis. 2162 of the grafts came from donors >60 including 203 from octogenarians ≥80 years. Primary outcome was the risk of graft failure according to donor age using a confounder adjusted Cox-Regression model with frailty terms (or random effects). The proportion of elderly grafts increased during the study period [i.e., octogenarians 0.1% (n = 1) in 2000 to 3.4% (n = 45) in 2013]. Kaplan-Meier and Cox-analyses revealed a reduced survival and a higher risk for graft failure with increasing donor age. Although the age effect was allowed to vary non-linearly, a linear association hazard ratio (HR = 1.1 for a 10 year increase in donor age) was evident. The linearity of the association suggests that there is no particular age at which the effect increases more rapidly, providing no evidence for a cutoff age. In clinical practice, the combination of high donor age with HU-transplantations, hepatitis C, high MELD-scores and long cold ischemic time should be avoided.

Renal volume assessed by magnetic resonance imaging volumetry correlates with renal function in living kidney donors pre- and postdonation: a retrospective cohort study.

Renal function of potential living kidney donors is routinely assessed with scintigraphy. Kidney anatomy is evaluated by imaging techniques such as magnetic resonance imaging (MRI). We evaluated if a MRI-based renal volumetry is a good predictor of kidney function pre- and postdonation. We retrospectively analyzed the renal volume (RV) in a MRI of 100 living kidney donors. RV was correlated with the tubular excretion rate (TER) of MAG3-scintigraphy, a measured creatinine clearance (CrCl), and the estimated glomerular filtration rate (eGFR) by Cockcroft-Gault (CG), CKD-EPI, and modification of diet in renal disease (MDRD) formula pre- and postdonation during a follow-up of 3 years. RV correlated significantly with the TER (total: r = 0.6735, P < 0.0001). Correlation between RV and renal function was the highest for eGFR by CG (r = 0.5595, P < 0.0001), in comparison with CrCl, MDRD-GFR, and CKD-EPI-GFR predonation. RV significantly correlated with CG-GFR postdonation and predicted CG-GFR until 3 years after donation. MRI renal volumetry might be an alternative technique for the evaluation of split renal function and prediction of renal function postdonation in living kidney donors.

Heart re-transplantation in Eurotransplant.

Internationally 3% of the donor hearts are distributed to re-transplant patients. In Eurotransplant, only patients with a primary graft dysfunction (PGD) within 1 week after heart transplantation (HTX) are indicated for high urgency listing. The aim of this study is to provide evidence for the discussion on whether these patients should still be allocated with priority. All consecutive HTX performed in the period 1981-2015 were included. Multivariate Cox' model was built including: donor and recipient age and gender, ischaemia time, recipient diagnose, urgency status and era. The study population included 18 490 HTX, of these 463 (2.6%) were repeat transplants. The major indications for re-HTX were cardiac allograft vasculopathy (CAV) (50%), PGD (26%) and acute rejection (21%). In a multivariate model, compared with first HTX hazards ratio and 95% confidence interval for repeat HTX were 2.27 (1.83-2.82) for PGD, 2.24 (1.76-2.85) for acute rejection and 1.22 (1.00-1.48) for CAV (P < 0.0001). Outcome after cardiac re-HTX strongly depends on the indication for re-HTX with acceptable outcomes for CAV. In contrast, just 47.5% of all hearts transplanted in patients who were re-transplanted for PGD still functioned at 1-month post-transplant. Alternative options like VA-ECMO should be first offered before opting for acute re-transplantation.

Benefit in liver transplantation: a survey among medical staff, patients, medical students and non-medical university staff and students.

BACKGROUND: The allocation of any scarce health care resource, especially a lifesaving resource, can create profound ethical and legal challenges. Liver transplant allocation currently is based upon urgency, a sickest-first approach, and does not utilize capacity to benefit. While urgency can be described reasonably well with the MELD system, benefit encompasses multiple dimensions of patients' well-being. Currently, the balance between both principles is ill-defined. METHODS: This survey with 502 participants examines how urgency and benefit are weighted by different stakeholders (medical staff, patients on the liver transplant list or already transplanted, medical students and non-medical university staff and students). RESULTS: Liver transplant patients favored the sickest-first allocation, although all other groups tended to favor benefit. Criteria of a successful transplantation were a minimum survival of at least 1 year and recovery of functional status to being ambulatory and capable of all self-care (ECOG 2). An individual delisting decision was accepted when the 1-year survival probability would fall below 50%. Benefit was found to be a critical variable that may also trigger the willingness to donate organs. CONCLUSIONS: The strong interest of stakeholder for successful liver transplants is inadequately translated into current allocation rules.

De novo donor-specific anti-HLA antibodies after kidney transplantation are associated with impaired graft outcome independently of their C1q-binding ability.

Many aspects of post-transplant monitoring of donor-specific (DSA) and non-donor-specific (nDSA) anti-HLA antibodies on renal allograft survival are still unclear. Differentiating them by their ability to bind C1q may offer a better risk assessment. We retrospectively investigated the clinical relevance of de novo C1q-binding anti-HLA antibodies on graft outcome in 611 renal transplant recipients. Acute rejection (AR), renal function, and graft survival were assessed within a mean follow-up of 6.66 years. Post-transplant 6.5% patients developed de novo DSA and 11.5% de novo nDSA. DSA (60.0%; P < 0.0001) but not nDSA (34.1%, P = 0.4788) increased rate of AR as compared with controls (27.4%). C1q-binding anti-HLA antibodies did not alter rate of AR in both groups. Renal function was only significantly diminished in patients with DSAC1q+ . However, DSA significantly impaired 5-year graft survival (65.2%; P < 0.0001) in comparison with nDSA (86.7%; P = 0.0054) and controls (90.7%). While graft survival did not differ between DSAC1q- and DSAC1q+ recipients, 5-year allograft survival was reduced in nDSAC1q+ (80.9%) versus nDSAC1q- (90.7%, P = 0.0251). De novo DSA independently of their ability to bind C1q are associated with diminished graft survival.

Rescue management of early complications after liver transplantation-key for the long-term success.

PURPOSE: Postoperative complications may have not only immediate but also long-term effects on the outcomes. Here, we analyzed the effect of postoperative complications requiring a reoperation (grade 3b) within the first 30 days on patients' and graft survival following liver transplantation. METHODS: Graft and patient survival in relation to donor and recipient variables and the need of reoperation for complications of 277 consecutive liver transplants performed from January 2007 to December 2012 were analyzed. RESULTS: Two hundred seventy-seven liver transplants were performed in 252 patients. Overall patient and graft survival at 1, 2, and 3 years were significantly reduced in patients requiring a reoperation. The labMELD score was significantly elevated (p = 0.04) and cold ischemia time was prolonged (p = 0.03) in recipients undergoing reoperations. Kaplan-Meier curves indicate that complications impact the outcome primarily within the first 3 months after transplantation. In multivariate analyses, the actual need of reoperation (p < 0.001), the labMELD score (p = 0.05), cold ischemia time (p = 0.02), and the need for hemodialysis pre-transplant (p = 0.05) were the only variables which correlated with the overall survival. CONCLUSION: Postoperative complications resulting in reoperations have a significant impact on the outcome primarily in the early phase after liver transplantation. Successful management of postoperative complications is key to every successful liver transplant program.

SDF-1/CXCR4/CXCR7 is pivotal for vascular smooth muscle cell proliferation and chronic allograft vasculopathy.

Chronic rejection remains a major obstacle in transplant medicine. Recent studies suggest a crucial role of the chemokine SDF-1 on neointima formation after injury. Here, we investigate the potential therapeutic effect of inhibiting the SDF-1/CXCR4/CXCR7 axis with an anti-SDF-1 Spiegelmer (NOX-A12) on the development of chronic allograft vasculopathy. Heterotopic heart transplants from H-2bm12 to B6 mice and aortic transplants from Balb/c to B6 were performed. Mice were treated with NOX-A12. Control animals received a nonfunctional Spiegelmer (revNOX-A12). Samples were retrieved at different time points and analysed by histology, RT-PCR and proliferation assay. Blockade of SDF-1 caused a significant decrease in neointima formation as measured by intima/media ratio (1.0 ± 0.1 vs. 1.8 ± 0.1, P < 0.001 AoTx; 0.35 ± 0.05 vs. 1.13 ± 0.27, P < 0.05 HTx). In vitro treatment of primary vascular smooth muscle cells with NOX-A12 showed a significant reduction in proliferation (0.42 ± 0.04 vs. 0.24 ± 0.03, P < 0.05). TGF-ß, TNF-α and IL-6 levels were significantly reduced under SDF-1 inhibition (3.42 ± 0.37 vs. 1.67 ± 0.33, P < 0.05; 2.18 ± 0.37 vs. 1.0 ± 0.39, P < 0.05; 2.18 ± 0.26 vs. 1.6 ± 0.1, P < 0.05). SDF-1/CXCR4/CXCR7 plays a critical role in the development of chronic allograft vasculopathy (CAV). Therefore, pharmacological inhibition of SDF-1 with NOX-A12 may represent a therapeutic option to ameliorate chronic rejection changes.

The Munich Lung Transplant Group: Intraoperative Extracorporeal Circulation in Lung Transplantation.

BACKGROUND: This retrospective single-center study aimed to analyze transfusion requirements, coagulation parameters, and outcome parameters in patients undergoing lung transplantation (LuTx) with intraoperative extracorporeal circulatory support, comparing cardiopulmonary bypass (CPB), and extracorporeal membrane oxygenation (ECMO). METHODS: Over a 3-year period, 49 of a total of 188 LuTx recipients were identified being set intraoperatively on either conventional CPB (n = 22) or ECMO (n = 27). Intra- and postoperative transfusion and coagulation factor requirements as well as early outcome parameters were analyzed. RESULTS: LuTx patients on CPB had significantly higher intraoperative transfusion requirements when compared with ECMO patients, that is, packed red cells (9 units [5-18] vs. 6 units [4-8], p = 0.011), platelets (3.5 units [2-4] vs. 2 units [0-3], p = 0.034), fibrinogen (5 g [4-6] vs. 0 g [0-4], p = 0.013), prothrombin complex concentrate (3 iU [2-5] vs. 0 iU [0-2], p = 0.001), and tranexamic acid (2.5 mg [2-5] vs. 2.0 mg [1-3], p = 0.002). Also, ventilator support requirements (21 days [7-31] vs. 5 days [3-21], p = 0.013) and lengths of ICU stays (36 days [14-62] vs. 15 days [6-44], p = 0.030) were markedly longer in CPB patients. There were no differences in 30-day and 1-year mortality rates. CONCLUSION: These data indicate a perioperative advantage of ECMO usage with low-dose heparinization over conventional CPB for extracorporeal circulatory support during LuTx. Long-term outcome is not affected.

Pediatric heart allocation and transplantation in Eurotransplant.

Pediatric heart allocation in Eurotransplant (ET) has evolved over the past decades to better serve patients and improve utilization. Pediatric heart transplants (HT) account for 6% of the annual transplant volume in ET. Death rates on the pediatric heart transplant waiting list have decreased over the years, from 25% in 1997 to 18% in 2011. Within the first year after listing, 32% of all infants (<12 months), 20% of all children aged 1-10 years, and 15% of all children aged 11-15 years died without having received a heart transplant. Survival after transplantation improved over the years, and in almost a decade, the 1-year survival went from 83% to 89%, and the 3-year rates increased from 81% to 85%. Improved medical management of heart failure patients and the availability of mechanical support for children have significantly improved the prospects for children on the heart transplant waiting list.

The use of extended-release tacrolimus twice a day might be beneficial for selected kidney transplant recipients: a case report.

The calcineurin inhibitor tacrolimus, which is available as an immediate- or extended-release formulation, is the standard-of-care immunosuppression after kidney transplantation with low rejection rates, especially in the first year after transplantation. However, its highly variable metabolism rate, narrow therapeutic window, and nephrotoxic side effects require close drug monitoring and individual dosing. Here, we describe first the application of extended-release tacrolimus (ER-Tac) twice daily with beneficial effects in a kidney transplant recipient under extensive therapeutic drug monitoring. A 47-year-old female kidney transplant recipient, who was identified as a fast metabolizer for tacrolimus, presented with declining allograft function and low tacrolimus through levels over time and 8 years after a second kidney transplantation despite the administration of high doses of ER-Tac once daily. Therefore, the area under the concentration-time curve (AUC) showed exceedingly high blood levels of ER-Tac. The latest biopsy of the kidney transplant showed arteriolar hyalinosis with pole vessel stenosis as a sign of chronic transplant vasculopathy and transplant glomerulopathy as a sign of chronic humoral rejection. After the exclusion of other options for immunosuppressive therapy due to the patient's high immunological risk, the patient was switched from ER-Tac once daily to ER-Tac twice daily. After switching to ER-Tac twice daily, the AUC for oral tacrolimus decreased and the transplant function improved despite higher tacrolimus trough levels and a lower total dose administered. This case highlights the importance of careful therapeutic drug monitoring with the performance of an AUC in the follow-up management of kidney transplant recipients.

Unique 40-year survival after heart transplantation with normal graft function and spontaneous operational tolerance.

Unique 40-year survival after heart transplantation with normal graft function and spontaneous operational tolerance.

BK virus-associated nephropathy: neutrophil gelatinase-associated lipocalin as a new diagnostic tool?

INTRODUCTION: BK nephropathy has emerged as an important cause for allograft failure in renal transplant patients. The kidney tubules are the main target of BK virus infiltration. Neutrophil gelatinase-associated lipocalin (NGAL) has been proven to be a powerful biomarker for tubular damage. Therefore, we investigated the suitability of plasma NGAL as new diagnostic tool in patients with BK infection. MATERIAL AND METHODS: We retrospectively analyzed 240 renal transplant recipients. Systematic BKV screening by plasma PCR was performed one month after transplantation and every three month thereafter for two yr. Plasma NGAL concentration was investigated using a commercial ELISA. Medical records and electronic databases were reviewed for clinical parameters. RESULTS: BK viremia (BKV+) was diagnosed in 5.0% (12/240) and BK nephropathy in 3.3% (8/240) of our patients. BKV+ patients received more induction therapy (p = 0.03) and experienced a higher rate of biopsy-proven rejections compared to 13 control patients with similar graft function but negative BKV PCR. Contrary to our hypothesis, there was no difference in plasma NGAL expression between both groups (128.6 vs. 172.2 ng/mL; p = 0.68). CONCLUSIONS: Intensified immunosuppressive therapy is associated with an increased risk for BK nephropathy. Plasma NGAL is neither suitable for diagnosing BK nephropathy nor helpful in predicting the individual course of patients with BKV infection.

Impact of surgical training and surgeon's experience on early outcome in kidney transplantation.

PURPOSE: The purpose of this study was to assess the impact of surgical training and surgeon's experience on surgical quality and early outcome parameters. METHODS: The outcomes of 184 deceased donor kidney transplant procedures were retrospectively reviewed. Intraoperative quality parameters, complication rates, and early outcome parameters were analyzed with respect to surgeon's experience. Surgeons were grouped according to their level of experience: trainees (n = 5), who were senior residents in their transplant rotation; low-experience surgeons (n = 4), who had an individual caseload of at least 30 supervised procedures; medium-experience surgeons (n = 5), who had an individual caseload of a minimum of 30 unsupervised (+30 supervised) procedures; and high-experience surgeons (n = 2), who had an individual caseload of more than 200 procedures. RESULTS: Surgical training was offered in 20 % of all cases. Surgeons with a high experience in kidney transplantation had a significantly lower warm ischemic time (30 versus 35 min, p = 0.01) and total operation time (135 versus 155 min, p = 0.43) as compared to the other study groups. However, this did not translate into a better outcome after transplantation. The complication rate and early outcome parameters such as length of hospital stay, serum creatinine at discharge, and graft and patient survival at 3 months post TX did not show any significant difference between the groups. CONCLUSION: We conclude that hands-on training of residents in kidney transplantation is feasible and surgical experience can be safely gained within a staged surgical training program.

Gender does matter: gender-specific outcome analysis of 67,855 heart transplants.

BACKGROUND: Gender differences between donor and recipient might have an impact on the outcome after heart transplantation (HT). Data of more than 67,000 patients registered at the International Society of Heart Lung Transplantation (ISHLT) were reviewed focusing on the influence of gender differences on short- and long-term outcome after HT. METHODS: We performed a retrospective analysis of 67,855 cardiac allograft recipients. They received orthotopic HT between January 1, 1980 and June 30, 2009. In contrast to other studies the data for gender differences (donor gender and recipient gender) were calculated with respect to actuarial and conditional survival (without 30-day mortality). RESULTS: One-year survival was highest in male recipients of male donor hearts (mR/mD: 83.74%). The lowest 1-year outcome showed male recipients of female donor organs (mR/fD: 78.95%). Best 5-year survival rates were shown by male recipients with male donor organs (70.75%, p < 0.0001). These differences disappeared in survival conditional to 1 year, indicating that gender predominantly influences short-term outcome. CONCLUSIONS: The combination male recipient/female donor carries a higher risk for early mortality, whereas female recipients/male donor reveals favorable short-term results. Gender-matched HT would be ideal, but not suitable in practice because of the shortage of organs.

Impact of ILD-Specific Therapies on Perioperative Course in Patients with Progressive Interstitial Lung Disease Undergoing Lung Transplantation.

Immunosuppressants and antifibrotics are currently used to treat patients with various interstitial lung diseases, which may undergo lung transplantation (LTx). The retrospective study aimed to evaluate the potential effects of therapeutic regimen on the perioperative course in patients with idiopathic pulmonary fibrosis (IPF) or progressive pulmonary fibrosis (PPF) undergoing LTx. All patients with IPF and PPF undergoing LTx between January 2014 and December 2021 were included. We retrospectively screened for previous use of immunosuppressants and antifibrotic therapy. We analyzed perioperative courses, short-term outcomes, and safety retrospectively. In total, 286 patients with diagnosis of IPF or PPF were analyzed. According to the treatment regimen before LTx, the study cohort was divided into four groups and compared. No differences between antifibrotic monotherapy, combined antifibrotic and immunosuppressive therapy with regard to postoperative complications were observed. Length of mechanical ventilation was shorter in patients with antifibrotics prior to LTx. Pretreatment with antifibrotic monotherapy and a combination of antifibrotic drugs with immunosuppressive therapy, lower body mass index (BMI) and lower blood loss, were independently associated with primary graft dysfunction grades 0-3 72 hours after LTx (p < 0.001). Finally, patients with antifibrotic monotherapy developed significantly less de novo donor-specific antibodies (DSA) (p = 0.009). Higher intraoperative blood loss, etiology of interstitial lung disease (ILD) and older age were independently associated with shorter survival after LTx. Use of antifibrotic monotherapy and a combination of antifibrotic drugs with immunosuppressive therapy in IPF/PPF patients undergoing LTx, proved to be safe and might lead to beneficial effects after LTx.

Frequent Follow-Up of Delisted Liver Transplant Candidates Is Necessary: An Observational Study about Characteristics and Outcomes of Delisted Liver Transplant Candidates.

This observational study focuses on the characteristics and survival of patients taken off of the liver transplant waiting list. Assessment of post-delisting survival and a frequent follow-up of patients after delisting are important keys to improve the survival rate of patients with liver failure after being delisted. Within this study, delisted liver transplant candidates were divided into the following groups: (1) "too good" (54%) or (2) "too sick" (22%) for transplantation, (3) adherence issues (12%) or (4) therapy goal changed (11%). The 5-year survival after delisting within these groups was 84%, 9%, 50%, and 68%, respectively. Less than 3% of the delisted patients had to be relisted again. The clinical expert decision of the multidisciplinary transplant team was sufficiently accurate to differentiate between patients requiring liver transplantation and those who were delisted after a stable recovery of liver function. The assessment of post-delisting survival may serve as a complementary metric to assess differences in center practices and to estimate cumulative post-delisting mortality risk.

CD4+CD25+FoxP3+ regulatory T cells enhance the allogeneic activity of endothelial-specific CD8+/CD28-CTL.

Numerous data indicate that CD4+CD25+FoxP3+ regulatory T cells (Treg cells) can attenuate alloresponses of conventional T lymphocytes against professional antigen-presenting cells and thus qualify for clinical use in various transplant settings. However, it is unknown whether Treg cells also influence T cell-endothelial cell interactions. CD8+ PBMC (CD8+ PBMC, CTL) from healthy human donors were stimulated for 7 days with an allogeneic microvascular endothelial cell line (CDC/EU. HMEC-1, an immortalized human microvascular endothelial cell line, further referred to as HMEC) and additional endothelial cell types and analysed for their lytic activity against these target cells in the presence or absence of Treg cells. Addition of Treg cells (1:1:1) to the CTL/HMEC co-cultures in the efferent immune phase (day -1 prior to the assay) led to an increased cytotoxicity against HMEC. In contrast, Treg cells alone did not lyse HMEC. Treg cell-mediated enhancement of CTL activity was endothelial cell specific since lysis of HLA-matched Epstein-Barr virus-transformed B lymphoblastoid cells (B-LCL) was not influenced by the addition of Treg cells. Further analysis of CD28-positive and CD28-negative CTL sub-populations revealed that only the CD28-negative CTL showed an increased activity against HMEC after Treg cell co-culture. Although there is no doubt about the potential therapeutic efficacy of Treg cells to ameliorate outcome of allogeneic transplants, the endothelium might require additional protective interventions to prevent endothelial cell type-specific alloreactivity.