The effects of brain death and ischemia on tolerance induction are organ-specific

We have previously shown that 12 days of high-dose calcineurin inhibition induced tolerance in MHC inbred miniature swine receiving MHC-mismatched lung, kidney, or co-transplanted heart/kidney allografts. However, if lung grafts were procured from donation after brain death (DBD), and transplanted alone, they were rejected within 19-45 days. Here, we investigated whether donor brain death with or without allograft ischemia would also prevent tolerance induction in kidney or heart/kidney recipients. Four kidney recipients treated with 12 days of calcineurin inhibition received organs from donors rendered brain dead for 4 hours. Six heart/kidney recipients also treated with calcineurin inhibition received organs from donors rendered brain dead for 4 hours, 8 hours, or 4 hours with 4 additional hours of cold storage. In contrast to lung allograft recipients, all isolated kidney or heart/kidney recipients that received organs from DBD donors achieved long-term survival (>100 days) without histologic evidence of rejection. Proinflammatory cytokine gene expression was upregulated in lungs and hearts, but not kidney allografts, after brain death. These data suggest that the deleterious effects of brain death and ischemia on tolerance induction are organ-specific, which has implications for the application of tolerance to clinical transplantation.

Pattern specification and immune response transcriptional signatures of pericardial and subcutaneous adipose tissue

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality in the United States. Recent studies suggest that pericardial adipose tissue (PCAT) secretes inflammatory factors that contribute to the development of CVD. To better characterize the role of PCAT in the pathogenesis of disease, we performed a large-scale unbiased analysis of the transcriptional differences between PCAT and subcutaneous adipose tissue, analysing 53 microarrays across 19 individuals. As it was unknown whether PCAT-secreted factors are produced by adipocytes or cells in the supporting stromal fraction, we also sought to identify differentially expressed genes in isolated pericardial adipocytes vs. isolated subcutaneous adipocytes. Using microarray analysis, we found that: 1) pericardial adipose tissue and isolated pericardial adipocytes both overexpress atherosclerosis-promoting chemokines and 2) pericardial and subcutaneous fat depots, as well as isolated pericardial adipocytes and subcutaneous adipocytes, express specific patterns of homeobox genes. In contrast, a core set of lipid processing genes showed no significant overlap with differentially expressed transcripts. These depot-specific homeobox signatures and transcriptional profiles strongly suggest different functional roles for the pericardial and subcutaneous adipose depots. Further characterization of these inter-depot differences should be a research priority.

The indirect alloresponse impairs the induction but not maintenance of tolerance to MHC class I-disparate allografts

We studied the effects of indirect allorecognition on the induction and maintenance phases of tolerance in miniature swine cotransplanted with heart and kidney allografts. MHC class I-mismatched heart and kidney grafts were cotransplanted in recipients receiving CyA for 12 days. Recipients were unimmunized or immunized with a set of donor-derived or control third-party MHC class I peptides either 21 days prior to transplantation or over 100 days after transplantation. T-cell proliferation, delayed type hypersensitivity reaction (DTH) and antibody production were assessed. All animals injected with donor MHC class I peptides developed potent indirect alloresponses specific to the immunizing peptides. While untreated recipients developed stable tolerance, all animals preimmunized with donor allopeptides rejected kidney-heart transplants acutely. In contrast, when peptide immunization was delayed until over 100 days after kidney-heart transplantation, no effects were observed on graft function or in vitro measures of alloimmunity. Donor peptide immunization prevented tolerance when administered to recipients pre transplantation but did not abrogate tolerance when administered to long-term survivors post transplantation. This suggests that the presence of T cells activated via indirect allorecognition represent a barrier to the induction but not the maintenance of tolerance.

Immunosuppression for lung transplantation

As a result of advances in surgical techniques, immunosuppressive therapy, and postoperative management, lung transplantation has become an established therapeutic option for individuals with a variety of end-stage lung diseases. The current 1-year actuarial survival rate following lung transplantation is approaching 80%. However, the 5- year actuarial survival rate has remained virtually unchanged at approximately 50% over the last 15 years due to the processes of acute and chronic lung allograft rejection (1). Clinicians still rely on a vast array of immunosuppressive agents to suppress the process of graft rejection, but find themselves limited by an inescapable therapeutic paradox. Insufficient immunosuppression results in graft loss due to rejection, while excess immunosuppression results in increased morbidity and mortality from opportunistic infections and malignancies. Indeed, graft rejection, infection, and malignancy are the three principal causes of mortality for the lung transplant recipient. One should also keep in mind that graft loss in a lung transplant recipient is usually a fatal event, since there is no practical means of long-term mechanical support, and since the prospects of re-transplantation are low, given the shortage of acceptable donor grafts. This chapter reviews the current state of immunosuppressive therapy for lung transplantation and suggests alternative paradigms for the management of future lung transplant recipients.

In primed allo-tolerance, TIM-3-Ig rapidly suppresses TGFbeta, but has no immediate effect on Foxp3

T-cell immunoglobulin mucin-3 (TIM-3) is only expressed by differentiated TH1 cells following their proliferative response to antigen, functioning to terminate TH1-mediated immunity upon binding to the TIM-3 ligand, galectin-9. This critical regulatory process involves Treg cells via their stable expression of galectin-9. Soluble TIM-3-Ig blocks galectin-9 and prevents induction of peripheral tolerance. Here we have looked for evidence that TIM-3-Ig might also break established regulatory tolerance. Using allo-primed spleen cells cultured ex vivo and challenged with irradiated donor-type stimulator cells either alone or together with 20 microg/ml TIM-3-Ig, we measured daily cytokine release [IL2, inferon gamma (INFgamma), transforming growth factor beta (TGFbeta), IL6, IL10] and cellular Foxp3 protein. In allo-tolerance, a specific effect of TIM-3-Ig was some fourfold reduction in TGFbeta. Foxp3 was induced in the allo-tolerant response to donor and this was not altered by TIM-3-Ig over the 5-day culture period. No Foxp3 was detected in either rejected or donor stimulator cells at any time. Thus, in an ex vivo model of in vivo tolerance to heart allografts, TIM-3-Ig therapy appears to reduce the stable tolerogenic environment by a rapid and specific repression of TGFbeta release.

Mechanisms of chronic rejection in cardiothoracic transplantation

Despite significant improvements in early post-transplantation survival rates, long-term patient and graft survival have remained poor, due in large part to the vexing problem of chronic allograft rejection. Attempts to combat this problem with intensification of immunosuppression have led to concomitant increases in the rates of fatal malignancies and infections. In cardiac transplantation, chronic rejection is manifested primarily by a disease entity known as cardiac allograft vasculopathy, an occlusive narrowing of the coronary vessels. In lung transplantation, chronic rejection is typified by obliterative bronchiolitis, an airflow limiting narrowing of the bronchioles. From an immunologic standpoint, chronic rejection is believed to be the end result of repeated immune and non-immune insults to the graft. This review examines the pathophysiology of heart and lung chronic, with emphasis on both immune and non-immune causes.

Regulatory transplantation tolerance and "stemness": evidence that Foxp3 may play a regulatory role in SOCS-3 gene transcription

Immune self-tolerance is controlled by a subset of T lymphocytes that are regulatory (Treg) and epigenetically programmed to suppress autoreactive immune effector cells in vivo. Treg require expression of Foxp3, a transcription factor that not only represses the interleukin-2 gene promoter, but also sequesters key mediators of T-cell signal transduction by complexing with cytoplasmic NFAT and NFkappaB. We have discovered that expression of Foxp3 is linked to two stem cell-related factors, namely leukemia inhibitory factor (LIF) and axotrophin. Because both LIF and axotrophin each influence Foxp3, we now ask if reciprocal cross-talk occurs; for example, does Foxp3 in turn influence LIF and/or axotrophin? We compared the effect of wt-Foxp3 versus mutant DeltaE251-Foxp3, which lacks transcriptional activity, on transcript levels of axotrophin, LIF, and suppressor of cytokine signaling-3 (SOCS-3; a feedback inhibitor of LIF) in the Jurkat human T-cell line. Unexpectedly, a 50-fold increase in SOCS-3 transcripts occurred in the DeltaE251-Foxp3 cells, coincident with a dramatic decrease in LIF transcription. This implies that, either directly or indirectly, transcription of SOCS-3 is negatively regulated by wt-Foxp3. Suppression of SOCS-3 by Foxp3 would support a model wherein Foxp3 promotes LIF signaling in Treg and is further evidence of reciprocity between Foxp3, LIF, and axotrophin.

A systematic review of randomized trials comparing revascularization rate and graft patency of off-pump and conventional coronary surgery

OBJECTIVE

Although many trials have been conducted to evaluate the benefits of off-pump coronary surgery, few have concentrated on graft patency. We sought to evaluate the impact of off-pump surgery on completeness of revascularization and graft patency compared with conventional surgery.

METHODS

A systematic literature search was undertaken of all randomized trials of off-pump coronary surgery in MEDLINE, EMBASE, the Cochrane Library Controlled Trials Register, the National Research Register, and abstracts from major conferences.

RESULTS

In total, 132 publications were identified. From this number, we excluded 43 without a conventional surgery arm and 80 that did not evaluate graft patency. One trial was excluded for selective angiography and one abstract was excluded because of insufficient information. A total of 7 trials were eligible for overview. On initial analysis, the relative risk of graft patency in off-pump coronary surgery compared with conventional surgery was 0.959 (95% confidence interval 0.936-0.983; P = .001). The analysis was repeated after excluding one specific trial because of clinical and statistical heterogeneity (chi2(6) = 27.78; P < .001), and a relative risk of 0.953 (95% confidence interval 0.927-0.980; P = .001) was obtained with no further evidence of heterogeneity (chi2(5) = 5.35; P = .374). In 5 trials that included the mean number of grafts performed per arm, the standardized mean difference in revascularization comparing off-pump with conventional surgery was -0.164 (-0.286 to -0.043; P = .008).

CONCLUSION

In a meta-analysis of randomized trials, patients undergoing off-pump coronary surgery had a lower rate of revascularization and lower graft patency than did patients undergoing conventional coronary surgery.

Evidence for functional inter-relationships between FOXP3, leukaemia inhibitory factor, and axotrophin/MARCH-7 in transplantation tolerance

In an ex vivo mouse model, regulatory transplantation tolerance is not only linked to Foxp3, but also to release of leukaemia inhibitory factor (LIF) and to expression of axotrophin (also known as MARCH-7), a putative ubiquitin E3 ligase associated with feedback control of T cell activation and of T cell-derived LIF. Given this coordinate correlation with tolerance, we now ask if Foxp3 expression is influenced by LIF or by axotrophin. In spleen cells from allo-rejected mice we found that exogenous LIF reduced interferon gamma release in response to donor antigen by 50%, but LIF had no direct effect on levels of Foxp3 protein in allo-primed cells that were either tolerant, or aggressive, for donor antigen. However, we did find an effect of axotrophin on Foxp3: in the axotrophin null mouse, thymic Foxp3 transcripts were reduced compared to axotrophin wildtype littermates. To test whether these findings in the mouse were of potential significance in man we measured transcript levels of axotrophin and LIF in peripheral blood cell samples collected for a recently published clinical study concerning haematopoietic stem cell recipients. In controls, human peripheral blood CD4+CD25+cells contained significantly more FOXP3 and axotrophin than CD4+CD25-cells. In bone marrow autograft recipients, where peripheral blood cell samples directly represent both the grafted tissue and the immune response, both FOXP3 and axotrophin negatively correlated with graft versus host disease (GVHD). These data suggest that (i) thymic Foxp3+T cell development is influenced by axotrophin; and (ii) clinical auto-GVHD inversely correlates with axotrophin transcript expression as has been previously reported for FOXP3.

Vascular Endothelium Does Not Activate CD4+ Direct Allorecognition in Graft Rejection

Expression of MHC class II by donor-derived APCs has been shown to be important for allograft rejection. It remains controversial, however, whether nonhemopoietic cells, such as vascular endothelium, possess Ag-presenting capacity to activate alloreactive CD4(+) T lymphocytes. This issue is important in transplantation, because, unlike hemopoietic APCs, allogeneic vascular endothelium remains present for the life of the organ. In this study we report that cytokine-activated vascular endothelial cells are poor APCs for allogeneic CD4(+) T lymphocytes in vitro and in vivo despite surface expression of MHC class II. Our in vitro observations were extended to an in vivo model of allograft rejection. We have separated the allostimulatory capacity of endothelium from that of hemopoietic APCs by using bone marrow chimeras. Hearts that express MHC class II on hemopoietic APCs are acutely rejected in a mean of 7 days regardless of the expression of MHC class II on graft endothelium. Alternatively, hearts that lack MHC class II on hemopoietic APCs are acutely rejected at a significantly delayed tempo regardless of the expression of MHC class II on graft endothelium. Our data suggest that vascular endothelium does not play an important role in CD4(+) direct allorecognition and thus does not contribute to the vigor of acute rejection.

Surrogate markers and risk factors for chronic lung allograft dysfunction

Obliterative bronchiolitis (OB) is the histologic correlate of chronic allograft dysfunction in pulmonary transplantation. The histologic diagnosis of OB is challenging, therefore a physiologic definition, bronchiolitis obliterans syndrome (BOS) based on pulmonary function tests has been used as a surrogate marker for OB for the last decade. BOS has proven to be the best available surrogate marker for OB and is predictive of the ultimate endpoints of graft and patient survival. Multiple other clinical markers have been reported and proposed as alternates for or complements to BOS grade, but all need further evaluation and validation in large, prospective clinical trials. Lastly, given the early occurrence and high incidence of chronic allograft dysfunction, the easily measurable endpoint of BOS grade, and our lack of understanding of ways to prevent or alter the course of BOS, lung transplant recipients represent an ideal population for clinical trials targeting prevention and treatment of chronic allograft dysfunction.

Fetal Liver as a Source of Autologous Progenitor Cells for Perinatal Tissue Engineering

Mesenchymal progenitor cells, isolated from adult bone marrow, have been shown to have utility for autologous tissue engineering. The possibility of isolating from the fetal hematopoietic system a cell population with similar potential, which could be used for autologous reconstruction of prenatally diagnosed congenital anomalies, has not been explored to date. Liver stromal cells isolated from a portion of the right lateral hepatic lobe of midgestation fetal lambs were expanded in vitro. Passage 1 cells displayed a uniform fibroblast-like morphology but could be induced to differentiate into skeletal muscle, adipocytes, chondrocytes, and endothelial cells by selective medium supplementation. By manipulating the extracellular matrix in vitro, spontaneously contracting cardiac myocyte-like cells could be generated as well. Multilineage differentiation was confirmed by morphology, protein expression, and upregulation of lineage-specific mRNA. The potential for engineering myocardial tissue was then investigated by transplanting early-passage progenitor cells, organized on a three-dimensional matrix, into the ventricle of an immunocompromised rat utilizing a previously described model of left ventricular tissue engineering. Survival, incorporation into the host myocardium, and cardiomyocytic differentiation of the transplanted cells were confirmed. We have demonstrated that mesenchymal progenitor cells with multilineage potential can be isolated from the fetal liver and have potential utility for autologous tissue engineering.

Homeostatic proliferation is a barrier to transplantation tolerance

Despite the ease of inhibiting immune responses by blockade of T-cell costimulation in naive rodent models, it is difficult to suppress those responses in animals with memory cells. Studies demonstrating the importance of alloreactive T-cell deletion during tolerance induction have promoted use of peritransplant T-cell-depleting therapies in clinical trials. But potentially complicating wide-scale, nonspecific T-cell depletion is the finding that extensive T-cell proliferation can occur under conditions of lymphopenia. This process, termed homeostatic proliferation, may induce acquisition of functional memory T cells. Here, using clinically relevant mouse models of peripheral T-cell depletion, we show that residual nondepleted T cells undergo substantial homeostatic expansion. In this setting, costimulatory blockade neither significantly suppresses homeostatic proliferation nor prevents allograft rejection. In addition, T cells that have completed homeostatic proliferation show dominant resistance to tolerance when adoptively transferred into wild-type recipients, consistent with known properties of memory cells in vivo. These findings establish the importance of homeostatic proliferation in clinically relevant settings, demonstrate the barrier that homeostatic proliferation can present to the induction of transplantation tolerance, and have important implications for transplantation protocols that use partial or complete peripheral T-cell depletion.

Myocardial tissue engineering and regeneration as a therapeutic alternative to transplantation

Ischemic cardiomyopathy leading to congestive heart failure remains the leading source of morbidity and mortality in Western society and medical management of this condition offers only palliative treatment. While allogeneic heart transplantation can both extend and improve the quality of life for patients with end-stage heart failure, this therapeutic option is limited by donor organ shortage. Even after successful transplantation, chronic cardiac rejection in the form of cardiac allograft vasculopathy can severely limit the lifespan of the transplanted organ. Current experimental efforts focus on cellular cardiomyoplasty, myocardial tissue engineering, and myocardial regeneration as alternative approaches to whole organ transplantation. Such strategies may offer novel forms of therapy to patients with end-stage heart failure within the near future.

Clinical risk factors for primary graft failure following lung transplantation

STUDY OBJECTIVE

s: Primary graft failure (PGF) is a devastating acute lung injury syndrome following lung transplantation. We sought to identify donor, recipient, and operative risk factors for its development.

DESIGN

We conducted a cohort study of 255 consecutive lung transplant procedures performed between October 1991 and July 2000. We defined PGF as follows: (1) diffuse alveolar opacities exclusively involving allograft(s) and developing within 72 h of transplant, (2) a ratio of PaO(2) to fraction of inspired oxygen < 200 beyond 48 h postoperatively, and (3) no other secondary cause of graft dysfunction identified. Risk factors were assessed individually and adjusted for confounding using multivariable logistic regression models.

SETTING

Tertiary-care academic medical center.

RESULTS

The overall incidence was 11.8% (95% confidence interval [CI], 7.9 to 15.9). Following multivariable analysis, the risk factors independently associated with development of PGF were as follows: a recipient diagnosis of primary pulmonary hypertension (PPH; adjusted odds ratio [OR], 4.52; 95% CI, 1.29 to 15.9; p = 0.018), donor female gender (adjusted OR, 4.11; 95% CI, 1.17 to 14.4; p = 0.027), donor African-American race (adjusted OR, 5.56; 95% CI, 1.57 to 19.8; p = 0.008), and donor age < 21 years (adjusted OR, 4.06; 95% CI, 1.34 to 12.3; p = 0.013) and > 45 years (adjusted OR, 6.79; 95% CI, 1.61 to 28.5; p = 0.009).

CONCLUSIONS

Recipient diagnosis of PPH, donor African-American race, donor female gender, and donor age are independently and strongly associated with development of PGF.

Hormonal resuscitation yields more transplanted hearts, with improved early function

BACKGROUND

Brain death results in cardiovascular instability and poor organ perfusion in many brain-dead donors. Hormonal resuscitation stabilizes certain brain-dead donors and is associated with significant increases in the numbers of organs transplanted per donor. The goal of this study was to examine the quality of hearts recovered from donors treated with hormonal resuscitation.

METHODS

A retrospective analysis of 4,543 recipients of hearts recovered from brain-dead donors, reported to the United Network for Organ Sharing/Organ Procurement and Transplantation Network database between November 1, 1999, and December 31, 2001, was conducted. Hormonal resuscitation consisted of a methylprednisolone bolus and infusions of vasopressin and either triiodothyronine or l-thyroxine. Univariate and multivariate analyses were used to evaluate the quality of hearts from donors who received three-drug hormonal resuscitation (3HR) treatment versus donors who did not receive all three drugs (non-3HR). Death within 30 days and early graft dysfunction were used as endpoints.

RESULTS

Hearts from 3HR donors demonstrated a 1-month survival rate of 96.2%, compared with a 92.1% survival rate for non-3HR donor hearts (P<0.01). Early graft dysfunction occurred in 5.6% of 3HR donor hearts and 11.6% of non-3HR donor hearts (P<0.01). Multivariate results demonstrated a 46% reduced odds of death within 30 days and a 48% reduced odds of early graft dysfunction. Steroids alone and steroids plus triiodothyronine/l-thyroxine also significantly reduced prolonged graft dysfunction.

CONCLUSIONS

This study suggests that 3HR treatment of brain-dead donors results in increased numbers of transplanted hearts, with improved short-term graft function.

Temporal changes in left ventricular systolic function in heart donors: results of serial echocardiography

BACKGROUND

Heart donor availability continues to limit cardiac transplantation rates and many donor hearts are not transplanted because of left ventricular dysfunction. The aim of this study was to determine whether intensive donor management results in improved left ventricular systolic function as measured by serial echocardiography.

METHODS

Using the California Transplant Donor Network Database, all donors who underwent serial echocardiography during donor management (from 1996 to 2000) were identified. The study includes those donors with ejection fractions <50% or regional wall-motion abnormalities shown on the initial echocardiogram. The database provides clinical data describing donor characteristics, treatments, and recipient outcomes. The mean ejection fractions at the first and second echocardiograms were compared using the Wilcoxon signed rank test.

RESULTS

In 13 of 16 subjects, initial ejection fractions were <50% and improved in 12 subjects after intensive donor management. Seventy-five percent of the donors received high-dose corticosteroids, 15 of 16 received dopamine, and none received thyroid hormone. In 12 subjects, the donor hearts were transplanted with a survival rate of 92% at an average follow-up of 16 months.

CONCLUSIONS

This pilot study indicates that in some cases, intensive donor management is associated with improved donor left ventricular function. Prospective studies are indicated to determine the predictors of improved donor left ventricular dysfunction and of recipient survival when sub-optimal hearts are transplanted.

Aggressive pharmacologic donor management results in more transplanted organs

BACKGROUND

Brain death results in adverse pathophysiologic effects in many cadaveric donors, resulting in cardiovascular instability and poor organ perfusion. Hormonal resuscitation (HR) has been reported to stabilize and improve cardiac function in brain-dead donors. The goal of this study was to examine the effect of HR on the brain-dead donor on the number of organs transplanted per donor.

METHODS

A retrospective analysis of all brain-dead donors recovered in the United States from January 1, 2000, to September 30, 2001, was conducted. HR consisted of a methylprednisolone bolus and infusions of vasopressin and either triiodothyronine or L-thyroxine. Univariate analyses and multivariate logistic regression analyses were used to detect differences between the HR group and those donors who did not receive HR.

RESULTS

Of 10,292 consecutive brain-dead donors analyzed, 701 received three-drug HR. Univariate analysis showed the mean number of organs from HR donors (3.8) was 22.5% greater than that from nonhormonal resuscitation donors (3.1) (P <0.001). Multivariate analyses showed that HR was associated with the following statistically significant increased probabilities of an organ being transplanted from a donor: kidney 7.3%, heart 4.7%, liver 4.9%, lung 2.8%, and pancreas 6.0%. Extrapolation of these probabilities to the 5,921 brain-dead donors recovered in 2001 was calculated to yield a total increase of 2,053 organs.

CONCLUSION

HR stabilizes certain brain-dead donors and is associated with significant increases in organs transplanted per donor.

Mouse vascular endothelium activates CD8+ T lymphocytes in a B7-dependent fashion

Despite several studies examining the contribution of allorecognition pathways to acute and chronic rejection of vascularized murine allografts, little data describing activation of alloreactive T cells by mouse vascular endothelium exist. We have used primary cultures of resting or IFN-gamma-activated C57BL/6 (H-2(b)) vascular endothelial cells as stimulators and CD8(+) T lymphocytes isolated from CBA/J (H-2(k)) mice as responders. Resting endothelium expressed low levels of MHC class I, which was markedly up-regulated after activation with IFN-gamma. It also expressed moderate levels of CD80 at a resting state and after activation. Both resting and activated endothelium were able to induce proliferation of unprimed CD8(+) T lymphocytes, with proliferation noted at earlier time points after coculture with activated endothelium. Activated endothelium was also able to induce proliferation of CD44(low) naive CD8(+) T lymphocytes. Activated CD8(+) T lymphocytes had the ability to produce IFN-gamma and IL-2, acquired an effector phenotype, and showed up-regulation of the antiapoptotic protein Bcl-x(L). Treatment with CTLA4-Ig led to marked reduction of T cell proliferation and a decrease in expression of Bcl-x(L). Moreover, we demonstrate that nonhemopoietic cells such as vascular endothelium induce proliferation of CD8(+) T lymphocytes in a B7-dependent fashion in vivo. These results suggest that vascular endothelium can act as an APC for CD8(+) direct allorecognition and may, therefore, play an important role in regulating immune processes of allograft rejection.

Mechanism of T cell-mediated endothelial apoptosis

BACKGROUND

Cytotoxic T lymphocyte (CTL)-mediated destruction of allogeneic vascular endothelium is important in the pathogenesis of both acute and chronic allograft rejection. Despite the importance of this phenomenon, the effector mechanisms responsible for endothelial cell killing are not well defined, and conflicting conclusions have been reached based on variation in experimental methodology.

METHODS

We used a recently described method for isolating mouse vascular endothelium to evaluate endothelial cell lysis by CTLs. Endothelial cell destruction was assessed in vitro both by 51Cr release and DNA fragmentation using wild-type and lpr (Fas deficient) endothelium of C3H/HeJ (H2(k)) mice by MHC alloantigen-specific T cells of wild-type, gld (Fas ligand deficient), and perforin-deficient mice on a C57BL/6 (H2(b)) background.

RESULTS

Although maximal lysis of 56.6+/-0.8% was seen when using wild-type targets and effectors, only a moderate decrease in apoptosis to 37.6+/-4.0% was detected when the Fas/Fas ligand death receptor pathway was eliminated. This decrease in cytotoxicity occurred despite the preserved functional capacity of this pathway. Alternatively, a significant decrease in cytotoxicity to 17.4+/-4.7% was seen when the perforin/granzyme exocytosis pathway was eliminated.

CONCLUSIONS

These data indicate that CTLs destroy vascular endothelium primarily by the perforin/granzyme exocytosis pathway with only a minor contribution to apoptosis by the Fas/Fas ligand death receptor pathway. These data are critical for the proper interpretation of studies evaluating acute and chronic allograft rejection and for the design of rational strategies to ameliorate vascular injury concomitant to the rejection process.

Increased transplanted organs from the use of a standardized donor management protocol

The organ shortage has resulted in increasing recipient waiting lists and waiting-list deaths. The increased use of expanded donors has been associated with increased discarding of procured organs because of poor organ function. A structured donor management algorithm or critical pathway was tested to determine its effect on the donor management and procurement process. A pilot study examined donors from 88 critical care units in 10 organ procurement organizations managed under the critical pathway and compared them to retrospective data collected at those same pilot sites. The total number of organs both procured and transplanted per 100 donors was significantly greater (p <0.01) in the critical pathway group when compared to the control group. There was no significant difference in 1-year graft survival for any of the organs recovered, and no significant difference in the rate of delayed graft function in the kidneys transplanted. Use of a structured donor management algorithm results in significant increases in organs procured and organs transplanted without any reduction in the quality of the organs being transplanted.

Left ventricular assist device for right side assistance in patients with transposition

Right (systemic) ventricular dysfunction is well described after Senning operations for transposition of the great arteries, and patients with congenitally corrected transposition of the great arteries. Transplantation remains the only definitive therapy for refractory heart failure, however patients may deteriorate clinically prior to the availability of a donor heart. This report details the implantation of a TCI Heartmate (Thoratec Corp., Pleaston, CA) as a morphologic right ventricular assist device to bridge these patients to transplantation.

Consensus conference report: maximizing use of organs recovered from the cadaver donor: cardiac recommendations, March 28-29, 2001, Crystal City, Va

The shortage of available donor hearts continues to limit cardiac transplantation. For this reason, strict criteria have limited the number of patients placed on the US waiting list to approximately 6000 to 8000 per year. Because the number of available donor hearts has not increased beyond approximately 2500 per year, the transplant waiting list mortality rate remains substantial. Suboptimal and variable utilization of donor hearts has compounded the problem in the United States. In 1999, the average donor yield from 55 US regions was 39%, ranging from 19% to 62%. This report provides the detailed cardiac recommendations from the conference on "Maximizing Use of Organs Recovered From the Cadaver Donor" held March 28 to 29, 2001, in Crystal City, Va. The specific objective of the report is to provide recommendations to improve the evaluation and successful utilization of potential cardiac donors. The report describes the accuracy of current techniques such as echocardiography in the assessment of donor heart function before recovery and the impact of these data on donor yield. The rationale for and specific details of a donor-management pathway that uses pulmonary artery catheterization and hormonal resuscitation are provided. Administrative recommendations such as enhanced communication strategies among transplant centers and organ-procurement organizations, financial incentives for organ recovery, and expansion of donor database fields for research are also described.

Cardiopulmonary bypass for bilateral sequential lung transplantation in patients with chronic obstructive pulmonary disease without adverse effect on lung function or clinical outcome

OBJECTIVE

The use of cardiopulmonary bypass in lung transplantation remains controversial. Previous studies have concluded that cardiopulmonary bypass is deleterious, but these studies were confounded by the inclusion of patients with different diagnoses undergoing single- and double-lung transplantation with elective or emergency use of bypass. The goal of this study was to determine whether cardiopulmonary bypass has deleterious effects on lung function or clinical outcome by analyzing the cases of patients with a single disease entity and elective use of bypass for bilateral sequential lung transplantation.

METHODS

A retrospective review of 50 patients with chronic obstructive pulmonary disease who underwent bilateral sequential lung transplantation was performed. Fourteen patients who underwent elective cardiopulmonary bypass for 218.3 +/- 75.4 minutes were compared to 36 control patients.

RESULTS

After the operation, the bypass and nonbypass groups were not significantly different with respect to median duration of mechanical ventilation (1 day vs 1 day, P =.76), median stay in the intensive care unit (4 days vs 4 days, P =.44), median hospital stay (15.5 days vs 16 days, P =.74), mean increase in serum creatinine level (1.4 +/- 1.9 mg/dL vs 0.9 +/- 1.0 mg/dL, P =.33), and mean ratio of Pao(2) to fraction of inspired oxygen at 1 hour (376.6 +/- 123 vs 357.0 +/- 218, P =.75), at 24 hours (309.9 +/- 92 vs 350.6 +/- 122, P =.26), and at 48 hours (335.0 +/- 144 vs 316.2 +/- 120, P =.64). Late outcome markers compared between the bypass and nonbypass groups were the following: 1-year percentage predicted forced expiratory volume in 1 second (76.1% +/- 17.0% vs 85.3% +/- 21.7%, P =.24), 30-day mortality (7.1% vs 8.3%, P >.999), 1-year survival (85.7% vs 80.1%, P =.66), 3-year survival (64.3% vs 58.3%, P =.70), and the prevalence of bronchiolitis obliterans syndrome (0% vs 36.1%, P =.01).

CONCLUSION

Cardiopulmonary bypass appears to have no deleterious effect on early lung function or clinical outcome. We hope that this pilot study removes some of the unwarranted fear of the use of bypass in lung transplantation for chronic obstructive pulmonary disease.

The role of passenger leukocyte genotype in rejection and acceptance of rat liver allografts

BACKGROUND

Although graft-resident passenger leukocytes are known to mediate acute rejection by triggering direct allorecognition, they may also act in an immunomodulatory fashion and play an important role in tolerance induction. Our purpose in the current study was to utilize rat bone marrow chimeras to evaluate the role of the genotype of passenger leukocytes in both acute rejection and tolerance of liver allografts.

METHODS

The fate of livers bearing donor-type, recipient-type, and third-party passenger leukocytes was evaluated in the MHC class I and II mismatched rejector combination ACI-->LEW and the acceptor combination PVG-->DA.

RESULTS

We report that although treatment of ACI liver donors with lethal irradiation does not lead to prolongation of graft survival in the ACI-->LEW strain combination, ACI livers bearing recipient-type (LEW) or third-party passenger leukocytes (BN) are rejected at a significantly slower rate. We confirm that lethal irradiation of PVG donor animals leads to abrogation of tolerance induction with acute rejection of their livers by DA recipients. However, the majority of PVG livers carrying donor-type (PVG), recipient-type (DA), or third-party (LEW) passenger leukocytes are accepted for >100 days. These DA recipients develop immune tolerance to the donor parenchyma (PVG).

CONCLUSIONS

Our findings demonstrate that long-term acceptance of liver allografts and tolerance induction is not dependent on the presence of donor-type passenger leukocytes and can be achieved with organs carrying donor-type, recipient-type, or third-party passenger leukocytes. The importance of the MHC framework on the surface of passenger leukocytes as a critical regulator of the immune response after transplantation of chimeric organs is substantiated by the delayed tempo of rejection of ACI livers bearing recipient-type or third-party passenger leukocytes in the ACI-->LEW strain combination.

CD3 monitoring of antithymocyte globulin therapy in thoracic organ transplantation

BACKGROUND

Antithymocyte globulin is frequently used as a component of induction therapy in thoracic organ transplantation. This study evaluates the utility of monitoring peripheral CD3 lymphocytes to rationally adjust antithymocyte globulin therapy in this patient population.

METHODS

A total of 17 heart and 19 lung transplant recipients received antithymocyte globulin (ATGAM or thymoglobulin) as induction therapy or to treat steroid-resistant acute or chronic rejection. Absolute CD3 counts were maintained between 50 and 100 cells/microl.

RESULTS

With CD3 monitoring, the doses of antithymocyte globulin were reduced from 10-15 mg/kg to 1-5 mg/kg during the course of therapy. The total amount of antithymocyte globulin given to each CD3 monitored patient was reduced by 48%. Dose reduction did not alter the number of acute rejection or infectious episodes, and hematological side effects were infrequent.

CONCLUSION

CD3 monitoring of antithymocyte globulin therapy in thoracic organ recipients reduced the amount of drug received by each patient, while maintaining CD3 counts less than 100 cells/microl.

Depletion of recipient CD4+ but not CD8+ T lymphocytes prevents the development of cardiac allograft vasculopathy

BACKGROUND

We have described that chimeric rat hearts bearing recipient-type antigen-presenting cells (APCs) do not reject acutely, but develop cardiac allograft vasculopathy (CAV) in untreated recipients. This suggests that CAV is triggered either by CD8+ direct allorecognition or by CD4+ indirect allorecognition. To determine the allorecognition pathway responsible for CAV in this model, recipients of chimeric hearts underwent either CD8+ or CD4+ T cell depletion.

METHODS

Chimeric hearts were created via bone marrow transplantation in two fully major histocompatibility-mismatched rat strain combinations. DA recipients were thymectomized and treated with Ox8 and Ox38 murine monoclonal antibodies, which deplete CD8+ and CD4+ T cells, respectively. Chimeric PVG hearts bearing DA APCs, abbreviated PVG(DA), were heterotopically transplanted into recipients undergoing thymectomy alone or recipients undergoing thymectomy plus either CD4+ or CD8+ T cell depletion.

RESULTS

PVG(DA) allografts survived 100 days, but developed CAV in thymectomized recipients and in those permanently depleted of CD8+ T cells. In contrast, chimeric hearts transplanted into permanently CD4+ T cell-depleted recipients survived 100 days and demonstrated no evidence of CAV.

CONCLUSIONS

In this specific strain combination, recipient CD8+ T cells are neither necessary nor sufficient for the development of CAV, whereas recipient CD4+ T cells are required for the development of CAV. These findings suggest that CAV is dependent on CD4+ indirect allorecognition and that CD8+ direct allorecognition stimulated by nonprofessional APCs plays a minor role.

Non-hematopoietic allograft cells directly activate CD8+ T cells and trigger acute rejection: an alternative mechanism of allorecognition

Despite evidence that human non-hematopoietic cells, such as vascular endothelium, can activate allogeneic T lymphocytes in vitro, the prevailing view has been that hematopoietic antigen-presenting cells are required to trigger alloimmune responses in vivo. Here we report that mouse non-hematopoietic cells activate alloreactive CD8+ T lymphocytes in vitro and in vivo. We also show that vascularized cardiac allografts are acutely rejected via CD8+ direct allorecognition even if the alloantigen is not presented by hematopoietic professional antigen-presenting cells. Because activation of alloreactive CD8+ T cells by donor-type non-hematopoietic cells can continue for the life of the allograft, these findings present a new clinically relevant mechanism of allorecognition and should be taken into consideration when developing strategies to prevent allograft vasculopathy or to induce tolerance.

A novel small animal model of left ventricular tissue engineering

BACKGROUND

Complex congenital cardiac anomalies involving ventricular hypoplasia require either staged palliative reconstruction, converting the circulatory system to a single ventricle based pump, or allogeneic transplantation. Tissue engineering offers the potential for complete reconstruction of these defects, but is limited by the inability to model myocardial tissue engineering in a small animal. Our goal was to develop a small animal model for ventricular tissue engineering using rat heterotopic heart transplantation.

METHODS

Donor hearts were explanted after cardioplegic arrest and the left ventricular volume was augmented by the implantation of a biodegradable engineered construct. The heart was then transplanted heterotopically into syngeneic recipients creating either a volume loaded, functioning left ventricle, or a non-functioning left ventricle. Some of the engineered constructs were seeded with multipotent bone marrow-derived mesenchymal progenitor cells before implantation. Animals were evaluated by echocardiography, morphology, histology, and immunohistochemistry after 1 month.

RESULTS

A scaffolding constructed from polytetrafluoroethylene, polylactide mesh, and type I and IV collagen hydrogel resulted in minimal intracardiac inflammation without aneurysmal dilatation. Successful transplantation and differentiation of mesenchymal progenitor cells was accomplished using this scaffolding. No ventricular arrhythmias resulted from this surgical manipulation and echocardiography revealed both end systolic and diastolic volume augmentation with ventricular expansion.

CONCLUSION

We have developed an in vivo model of ventricular tissue engineering using heterotopic heart transplantation. Future work will focus on construction of ventricular tissue around pre-fabricated vascular networks in order increase cellular engraftment for ventricular reconstruction.

Multiparameter flow cytometric approach for simultaneous evaluation of T lymphocyte-endothelial cell interactions

Since vascular endothelium is now recognized as an immunologically active tissue, a better understanding of the relationship between endothelial cells and T lymphocytes is critical to the field of solid organ transplantation. Investigations of endothelial cell-T cell interactions have been limited by methodology. We developed a flow cytometric method allowing for concurrent investigation of multiple cell populations within the same culture that can be applied to these complex interactions. Allogeneic CD8+ or CD4+ T cells labeled with 5,6-carboxyfluorescein diacetate succinimidyl ester (CFSE) were added to a murine endothelial cell monolayer, in which endothelial proliferation was not inhibited by irradiation or addition of a cell cycle-blocking agent. At specific time points, the coculture was analyzed by flow cytometry. T-cell proliferation could be detected by gating on the T-cell subset and evaluating the CFSE fluorescence peaks. By directly analyzing cellular division, we minimized erroneous interpretation of the data encountered by previous studies, which utilized (3)H-thymidine incorporation as sole measure of proliferation. Further subgating on cells that divided facilitated the study of CD8+ lymphocyte activation, differentiation, and acquisition of effector function. By gating on the endothelial cell population, phenotypic changes such as upregulation of surface MHC molecules or immune-mediated apoptosis could be detected. In conclusion, we present a flow cytometric approach that could have important applications for clinical immunological monitoring in allogeneic or xenogeneic transplantation, and might provide the requisite information to better tailor immunotherapy to prevent chronic rejection.

Bronchogenic carcinoma complicating lung transplantation

BACKGROUND

Malignancy is a well-recognized complication of solid-organ transplantation. Although a variety of malignancies have been reported in lung transplant recipients, a paucity of information exists regarding the incidence and clinical course of bronchogenic carcinoma in this patient population.

METHODS

We conducted a retrospective cohort study of our lung transplant experience at the University of Pennsylvania.

RESULTS

We identified 6 patients with bronchogenic carcinoma detected at the time of, or developing after, transplantation. The incidence of bronchogenic carcinoma was 2.4%. All patients with lung cancer had a history of smoking, with an average of 79 +/- 39 pack-years. A total of 5 patients had chronic obstructive pulmonary disease, and 1 had idiopathic pulmonary fibrosis. Lung cancers were all of non-small-cell histology and first developed in native lungs. Three patients had bronchogenic carcinoma at the time of surgery. The remaining 3 patients were diagnosed between 280 and 1,982 days post-transplantation. Of the 6 patients, 4 presented with a rapid course suggestive of an infectious process. The 1- and 2-year survival rates after diagnosis were 33% and 17%, respectively.

CONCLUSION

Lung transplant recipients are at risk for harboring or developing bronchogenic carcinoma in their native lungs. Rapid progression to locally advanced or metastatic disease commonly occurs, at times mimicking an infection. Bronchogenic carcinoma should be considered in the differential diagnosis of pleuroparenchymal processes involving the native lung.

Characteristics and outcomes of patients with sarcoidosis listed for lung transplantation

STUDY OBJECTIVES

To characterize the course of patients with advanced sarcoidosis who have been listed for lung transplantation and to identify prognostic factors for death while they are on the waiting list.

DESIGN

Retrospective cohort study.

SETTING

Tertiary-care university hospital.

PATIENTS

Forty-three patients with sarcoidosis who have been listed for lung transplantation at the University of Pennsylvania Medical Center.

METHODS

A multivariable explanatory analysis using a Cox proportional hazards model was performed to determine risk factors that are independently associated with mortality while patients await transplantation.

RESULTS

Twenty-three of the 43 patients (53%) died while awaiting transplantation. The survival rate of listed patients (as determined by the Kaplan-Meier method) was 66% at 1 year, 40% at 2 years, and 31% at 3 years. In a univariate analysis, the following factors were significantly associated with death on the waiting list: PaO(2) < or = 60 mm Hg (relative risk [RR], 3.4; 95% confidence interval [CI], 1.2 to 9.3); mean pulmonary artery pressure > or = 35 mm Hg (RR, 3.2; 95% CI, 1.1 to 9.5); cardiac index < or = 2 L/min/m(2) (RR, 2.8; 95% CI, 1.2 to 6.6), and right atrial pressure (RAP) > or = 15 mm Hg (RR, 7.6; 95% CI, 3.0 to 19.3). Multivariable analysis revealed that RAP > or = 15 mm Hg was the only independent prognostic variable (RR, 5.2; 95% CI, 1.6 to 16.7; p = 0.006). Twelve patients underwent lung transplantation. Survival after transplantation determined by the Kaplan-Meier method was 62% at both 1 and 2 years, and 50% at 3 years.

CONCLUSIONS

Patients with advanced sarcoidosis awaiting lung transplantation have a high mortality rate with a median survival of < 2 years. Mortality is most closely linked to elevated RAP. While earlier referral may diminish the mortality rate of patients on the waiting list for transplantation, further improvements in posttransplantation outcomes will be necessary to ensure that this procedure truly bestows a survival benefit.

A simple method for culturing mouse vascular endothelium

Vascular endothelium is an important site for a wide array of immunological processes such as inflammation, atherosclerosis and allograft rejection. Culture methods of mouse vascular endothelium would provide an important in vitro correlate to immunological murine in vivo models. We describe a simple method to culture mouse vascular endothelium from thoracic aorta. Our cultured cells express typical phenotypic (CD105, CD31, CD106), morphological and ultrastructural (intercellular junctions, Weibel-Palade bodies) markers of vascular endothelium. They also possess functional receptors for uptake and processing of acetylated low-density lipoproteins. The mouse vascular endothelium within our system expresses high levels of MHC class I and MHC class II after activation with IFN-gamma. In addition, these cells express the accessory molecules CD80 and CD54, while they lack constitutive expression of CD86 and CD40, providing them the means to function as antigen presenting cells. Alloreactive CD4(+) and CD8(+) T lymphocytes demonstrate evidence of DNA synthesis after co-culture with activated vascular endothelium indicating their commitment to proliferation. In conclusion, we describe a simple culture system to isolate and grow mouse vascular endothelium, which provides a powerful tool to study biological interactions in vitro.

Application of "double bridge mechanical" resuscitation for profound cardiogenic shock leading to cardiac transplantation

BACKGROUND

In patients with acute profound cardiogenic circulatory failure unresponsive to conventional resuscitation, we instituted immediate aggressive application of extracorporeal membrane oxygenation (ECMO) to restore circulatory stability. Long-term hemodynamic support was accomplished with an early "bridge" to ventricular assist device (VAD) before definitive treatment with cardiac transplantation.

METHODS

A respective review of ECMO and VAD data registries was instituted.

RESULTS

From May 1996 to July 2000, 23 patients were placed on ECMO support for profound cardiogenic circulatory failure. Eleven patients (47%) were withdrawn from support due to severe neurologic injury or multisystem organ failure. Three patients (13%) were weaned off ECMO with good outcome. Nine patients (39%) were transferred to a VAD. Two patients expired while on VAD support, and 7 of the VAD-supported patients (78%) survived to transplantation. Overall survival was 43%.

CONCLUSIONS

Emergent ECMO support is a salvage approach for cardiac resuscitation once conventional measures have failed. In neurologically intact patients, the early transfer to a VAD quickly stabilizes hemodynamics, avoids complications, and is essential for long-term circulatory support before definitive treatment with cardiac transplantation.

Emergent lung retransplantation after discovery of two primary malignancies in the donor

A 50-year-old woman underwent single lung transplantation for advanced chronic obstructive pulmonary disease. Shortly after the procedure, it was discovered that the donor suffered from both a renal cell carcinoma and a spindle-cell sarcoma of the ascending aorta, which had metastasized to the spleen. The patient was emergently listed for a retransplantation and underwent bilateral lung transplantation after a new donor became available 4 days after the initial transplantation procedure. After 24 months, the patient is without evidence of malignancy. This case illustrates the role of immediate retransplantation for patients who have inadvertently received thoracic organs from donors harboring occult malignancies.

Donor antigen-presenting cells are important in the development of obliterative airway disease

OBJECTIVE

Obliterative airway disease, which resembles obliterative bronchiolitis histologically, develops in murine heterotopic tracheal allografts. Chimeric tracheas were used to examine whether donor-type antigen-presenting cells are important in the development of obliterative airway disease. To separate the contributions of CD4(+) and CD8(+) direct pathways, we transplanted tracheas from knockout mice lacking major histocompatibility complex (MHC) class I or II antigens.

METHODS

Chimeric tracheas were created via bone marrow transplantation in fully MHC-mismatched combinations. Tracheas from naive B6, autologously reconstituted B6, chimeric B6 bearing recipient-type C3H antigen-presenting cells, MHC class I knockout B6 (B6(I-)), MHC class II knockout B6 (B6(II-)), or C3H mice were transplanted into C3H recipients. The tracheas were harvested at days 14 and 28.

RESULTS

At day 28, isografts showed no occlusion, normal respiratory epithelium, and minimal infiltrates. Naive or autologously reconstituted B6, B6(I-), and B6(II-) tracheas showed minimal occlusion at day 14 but contained intraepithelial infiltrates. By day 28, the naive or autologously reconstituted B6 tracheas had occlusion of 69.5% +/- 11.6% (mean +/- standard error of the mean), and in comparison, B6(I-) and B6(II-) tracheas had occlusions of 53.0% +/- 16.3% and 52.2% +/- 15.9%, respectively (P =. 20,.19). In chimeric B6 tracheas, minimal occlusion was seen at day 14 and remained 33.6% +/- 16.2% (P =.039) at day 28. Subtle epithelial changes and minimal infiltrates were seen.

CONCLUSIONS

Obliterative airway disease appears to involve donor-type antigen-presenting cells and develops in the absence of either MHC class I or II antigens. These findings suggest that either CD8(+) or CD4(+) direct allorecognition is important in the development of obliterative airway disease.

Bilateral versus single lung transplantation for chronic obstructive pulmonary disease: intermediate-term results

BACKGROUND

There is controversy regarding the transplant procedure of choice in chronic obstructive pulmonary disease. We reviewed our intermediate-term outcomes with single lung transplantation (SLT) versus bilateral lung transplantation (BLT).

METHODS

We retrospectively reviewed 130 patients with chronic obstructive pulmonary disease: 84 underwent SLT, 46 BLT. The mean age was 51.1 +/- 1.2 years for those who underwent BLT and 56.2 +/- 0.7 years for those who underwent SLT (p < 0.0001). Male patients represented 65% of the BLT group and 46% of the SLT group (p = 0.04). Spirometry and 6-minute walk tests were obtained preoperatively and at 3- to 6-month intervals. Posttransplant survival and survival from time of onset of bronchiolitis obliterans syndrome were calculated by Kaplan-Meier method. The mean follow-up was 32.4 months.

RESULTS

The 90-day mortality rate was 13.0% For BLT and 15.5% for SLT (p = 0.71). Actuarial survival rates at 1, 3, and 5 years were 82.6%, 74.6%, and 61.9% for BLT and 72.2%, 63.4%, and 57.4% for SLT; the favorable survival trend with BLT did not achieve statistical significance. There were no differences in preoperative spirometry or 6-minute walk tests. The improvements in forced expiratory volume in one second, forced vital capacity (FVC), and 6 MWT were significantly greater following BLT. The incidence of bronchiolitis obliterans syndrome was 22.4% in SLT and 22.2% in BLT; survival following onset of bronchiolitis obliterans syndrome was similar.

CONCLUSIONS

For patients with chronic obstructive pulmonary disease, BLT is associated with superior lung function, exercise tolerance, and a trend toward enhanced survival. Younger candidates may be best suited for BLT. Given the limited donor lungs, SLT remains the preferred alternative for all other patients.

Immune monitoring in xenotransplantation: the multiparameter flow cytometric mixed lymphocyte culture assay

Xenotransplantation requires monitoring of complex cellular interactions in vitro. A tool to monitor cell proliferation in detail would be instrumental in understanding these cellular interactions in heterogeneous xenogeneic lymphocyte cultures and in patients after xenotransplantation. To accomplish this, we used a fluorescent cell proliferation marker, 5,6-carboxyfluorescein diacetate succinimidyl ester (CFSE), in combination with flow cytometry. CFSE, a green fluorescent molecule, binds covalently to intracellular macromolecules. Each cell division reduces the fluorescent intensity per cell by half and shows a characteristic multipeak pattern in flow cytometric analysis. For this study, human lymphocytes were labeled with CFSE and cultured in the presence of irradiated porcine lymphocytes. Cell proliferation was detected in CFSE-labeled lymphocytes in both a single and a multiparameter flow cytometry setting. Concurrently, tritiated ((3)H) thymidine incorporation, a common method to measure gross cell proliferation, was assessed. The kinetics of CFSE-labeled cell proliferation correlated with (3)H-thymidine incorporation in that both methods showed a lag phase for days 1-3 and a log phase for days 4-7. Multiparameter flow cytometric monitoring of mixed lymphocyte cultures allowed phenotyping and assessment of viability of proliferating populations in heterogeneous xenogeneic stimulated human lymphocyte cultures and complemented the classical (3)H-thymidine incorporation assay. The use of this technique will allow a wide array of immunologic parameters to be measured in a heterogeneous xenogeneic mixed lymphocyte culture. The information gained from these assays is essential to understanding the biological significance of xenogeneic cellular interaction and for monitoring the immune status of the xenotransplanted patient.

Replacement of graft-resident donor-type antigen presenting cells alters the tempo and pathogenesis of murine cardiac allograft rejection

BACKGROUND

Graft-resident antigen presenting cells (APCs) are potent stimulators of the alloresponse. To test whether replacement of graft-resident donor-type APCs with those of recipient-type alters allorecognition and the pathogenesis of both acute and chronic rejection, we created chimeric hearts for transplantation into naive recipients.

METHODS

To replace donor-type APCs with those of recipient-type, chimeric animals were created by bone marrow transplantation (BMT) in fully allogeneic mouse and rat strain combinations. The degree of APC replacement in chimeric organs was assessed phenotypically and functionally. Chimeric hearts were transplanted heterotopically into untreated recipients.

RESULTS

Flow cytometric and immunohistochemical analysis did not detect residual bone marrow recipient-type APCs in mouse BMT chimeras. Although semi-quantitative reverse transcription polymerase chain reaction detected 0.001-0.01% residual cells, APCs isolated from chimeric organs were functionally unable to stimulate donor-type cells. When transplanted into naive recipients, chimeric mouse hearts had significantly prolonged survival but were nevertheless rejected acutely. Similar results were obtained in the ACI --> LEW rat strain combination. However, in the PVG --> DA rat model, the majority of chimeric hearts survived >100 days and all long-surviving hearts developed cardiac allograft vasculopathy.

CONCLUSIONS

BMT leads to near complete replacement of organ-resident APCs. The virtual absence of donor-type APCs in chimeric hearts delays or prevents acute rejection in a strain-dependent manner. In contrast, this type of graft modification does not prevent cardiac allograft vasculopathy. This suggests that, although the CD4+ direct pathway may play a role in acute rejection, it is not essential for the development of chronic rejection in rodent cardiac allografts.