Importance of T cells to accelerated rejection and acceptance of renal allografts in sensitized rat recipients

BACKGROUND: Sensitized recipients often experience fulminant allograft loss by yet ill-defined cellular and/or humoral immune mechanisms. In this study, we analyzed the contribution of cellular elements, in particular T cells, to the accelerated rejection of renal allografts in sensitized rats. METHODS AND RESULTS: LEW rats sensitized with BN skin grafts died of uremia in 3.3+/-0.9 days after transplantation of a BN kidney, similarly to bilaterally nephrectomized animals. Adoptive transfer of 10(6) graft-infiltrating mononuclear cells as well as their CD25+ subset into otherwise normal LEW recipients accelerated rejection of BN test cardiac allografts (5.4+/-0.5 days to 6.6+/-0.4 days vs. 7.8+/-0.8 days in controls, P<0.0007), while the CD25- population was ineffective (8.0+/-0.6 days, NS). Furthermore, alpha/beta-T-cell receptor (TCR)-targeted therapy with R73 monoclonal antibody abrogated accelerated rejection, and produced long-term survival in sensitized animals treated before kidney engraftment (day -7 to day -1). Long-term survival was associated with an up-regulation of intragraft interleukin-4 and interleukin-10 expression in conjunction with depressed Th-1-type cytokines. In addition, alpha/beta-TCR-targeted therapy even in low subtherapeutic dose decreased IgM alloantibody levels, and prevented the switch from IgM to IgG alloantibody response. CONCLUSIONS: This is the first report that documents the striking efficacy of alpha/beta-TCR-targeted therapy in sensitized rat renal transplant recipients. The results provide evidence for a critical role of T cells for both accelerated rejection and long-term graft survival. Up-regulation of Th2-type cytokine profile may, at least in part, contribute to the acquisition of immune unresponsiveness after alpha/beta-TCR-targeted therapy in this well-defined rat renal transplant model.     

Long-term acceptance of skin and cardiac allografts after blocking CD40 and CD28 pathways

The receptor-ligand pairs CD28-B7 and CD40-gp39 are essential for the initiation and amplification of T-cell-dependent immune responses. CD28-B7 interactions provide 'second signals' necessary for optimal T-cell activation and IL-2 production, whereas CD40-gp39 signals co-stimulate B-cell, macrophage, endothelial cell and T-cell activation. Nonetheless, blockade of either of these pathways alone is not sufficient to permit engraftment of highly immunogenic allografts. Here we report that simultaneous but not independent blockade of the CD28 and CD40 pathways effectively aborts T-cell clonal expansion in vitro and in vivo, promotes long-term survival of fully allogeneic skin grafts, and inhibits the development of chronic vascular rejection of primarily vascularized cardiac allografts. The requirement for simultaneous blockade of these pathways for effective inhibition of alloimmunity indicates that, although they are interrelated, the CD28 and CD40 pathways are critical independent regulators of T-cell-dependent immune responses.     

Fas-mediated cytotoxicity is not required for rejection of murine nonvascularized heterotopic cardiac allografts

BACKGROUND: Using mice with loss-of-function mutations in the Fas and Fas ligand (FasL) genes (lpr and gld, respectively) in transplantation experiments has resulted in contradictory findings concerning the role of Fas/FasL-mediated cytotoxicity in allograft rejection. The observation that these mutant mice develop an abnormal lymphocyte phenotype with increasing age that is hyporesponsive in vitro led us to examine the possibility that this characteristic might explain seemingly discordant observations in the literature. Therefore, to distinguish between the effects of Fas/FasL pathway disruption and the effects of immune senescence on in vivo cytotoxicity and allograft rejection, we evaluated the survival of cardiac allografts in gld, lpr, and wild-type mice of varying ages. METHODS: Six- to 21-week-old C3H, C3H/HeJ-Fasl(gld), C57B1/6, and B6.MRL-Fas(lpr) recipients were transplanted with heterotopic, nonvascularized cardiac allografts from neonatal Balb/c, C3H, C57Bl/6, and B6.MRL-Fas(lpr) donors. Mixed lymphocyte reactions were performed in naive gld, lpr, and wild-type animals, 6 and 12 weeks of age. Rejected allografts in gld, lpr, and wild-type recipients and functioning syngeneic transplants were evaluated for intragraft apoptosis by a DNA fragmentation detection assay. RESULTS: Graft survival was not significantly different between 6-week-old gld and lpr recipients and their respective wild-type controls. However, allograft rejection was delayed significantly in older (13-week) gld mice compared with age-matched wild-type mice (P=0.02) or young (6-week) gld animals (P=0.04). Similarly, 21-week-old lpr mice exhibited prolonged graft survival compared with 6-week-old lpr animals (P=0.01). Reduced alloreactive proliferative responses in 12-week-old gld and lpr mice were observed when compared with age-matched wild-type strains. Rejecting allografts displayed a similar level of intragraft apoptotic cells regardless of mutant or wild-type phenotype or age of recipient. CONCLUSIONS: The findings of this study confirm that Fas/FasL-mediated cytotoxicity is not required for murine cardiac allograft rejection. Our findings also demonstrate that the observed delayed graft rejection in lpr and gld mice is a consequence of an age-related alteration of the immune system, specific to gld and lpr mice and associated with an in vivo and in vitro hyporeactivity to alloantigens.     

Chronic rejection and chronic cyclosporin toxicity in renal allografts

Recent evidence indicates that growth factors are critically important in both chronic rejection and chronic cyclosporin A toxicity, suggesting that these two entities share a common pathophysiological pathway, leading to progressive allograft failure. Here, Manuel Pascual and colleagues discuss the relevance of growth factors to chronic allograft nephropathy, and the implications for therapy in view of the great choice of immunosuppressive drugs now available.     

Electrocardiographic and electrophysiologic properties of cardiac allografts

The increasing number of heart transplant patients requires that physicians be able to recognize the electrocardiographic (ECG) and electrophysiologic properties of cardiac allografts. Cardiac allografts are characterized by modifications of resting ECGs and frequent arrhythmias in the postoperative period, and the loss of autonomic nervous control illustrated by permanent tachycardia and loss of heart rate variability during 24-hour ambulatory ECG recording. Some clinical and experimental observations suggest a mid-term reinnervation of the cardiac allograft, but this requires histologic confirmation. The electrophysiologic characteristics of the denervated myocardium are similar to those of the innervated myocardium at rest. However, supersensitivity to circulating catecholamines has been observed in cardiac allografts as in experimentally denervated hearts, which is responsible for a progressive increase in heart rate during exercise and a slow decrease during recovery. Supersensitivity of the denervated heart to acetylcholine may explain the high prevalence of donor sinus dysfunction due to impairment of its automaticity. More often, the sinus node dysfunction is transient and can be treated with an adenosine antagonist, such as theophylline, before permanent implantation of a pacemaker. In the case of pacemaker implantation, synchronization of the donor atria with the recipient atria is desirable, and an endocardial lead implantation is preferred. Several electrophysiologic changes have been observed during acute cardiac allograft rejection. From experimental studies, the most important of these are the disturbance of conduction in the atria and the atrioventricular node and a decrease in the amplitude of the ventricular potential. Initial studies on isolated myocytes show profound changes in membrane conductance during experimental cardiac rejection. The development of new noninvasive detection methods of cardiac allograft rejection, such as intramyocardial voltage electrogram monitoring and high-resolution ECG, could help early diagnosis.     

RANTES chemokine expression is related to acute cardiac cellular rejection and infiltration by CD45RO T-lymphocytes and macrophages

BACKGROUND: Despite the advances made in immunosuppression therapy, episodes of acute cellular rejection may affect graft function and survival. We investigated the role of RANTES in cellular recruitment and in cardiac allograft rejection. METHODS: Endomyocardial biopsies (n = 65) from 30 patients were taken at various times after transplantation. In 4 subjects who died of acute cellular rejection, the profile of RANTES expression was monitored in all biopsy specimens and in postmortem tissue. Myocardial tissue from 10 other transplants was also analyzed. Sections were stained with an anti-human RANTES antibody with the streptavidin-biotin technique. RANTES-positive cells were related to macrophage, CD45RO "memory" T-cell, and eosinophil infiltration. RESULTS: RANTES-positive cells were identified within the cellular infiltrate in 95% of biopsies with moderate/severe rejection and 28% with mild rejection. RANTES-positive, CD45RO-positive, and macrophage cell numbers were higher in subjects who died of acute cellular rejection than of other causes. A highly significant difference in RANTES-positive cell number was observed between moderate/severe, mild, and nonrejection groups (p = .0001) and correlated significantly with macrophage number in both right and left ventricles (r = .693, p < .01; r = .599, p < .05, respectively) and with the number of "memory" T cells (r = .829, p < .001; r = .779, p < .01, respectively). CONCLUSIONS: These findings suggest that local release of RANTES is important in the recruitment of both macrophages and CD45RO T cells in cardiac allograft rejection. RANTES may be an important chemokine to target for therapeutic intervention in heart rejection.     

Tumor necrosis factor-alpha is persistently expressed in cardiac allografts in the absence of histological or clinical evidence of rejection

Plasma exchange (PE) in Guillain-Barré syndrome (GBS) probably removes pathogenic antibodies. Results of a recent clinical study by the French Cooperative Group suggest that at least two sessions of PE are required. As an alternative procedure, we examined the effect of the number of PEs on the reduction of immunoglobulins in 11 patients. A significant immunoglobulin decrease was obtained in the first two sessions but not in subsequent ones. Based on the French trial results and our findings, we conclude that at least two PEs are needed for treating GBS.     

Severe and early alteration of action potential during acute cardiac rejection in rats

INTRODUCTION: Alteration of cardiac action potential and its adaptation to heart rate could contribute to cardiac dysfunction and arrhythmias during acute cardiac rejection. METHODS AND RESULTS: Heterotopic heart transplantation was performed in allogeneic and syngeneic rats in which the action potentials of right and left ventricles were measured at 1, 2.5, 3.3, and 5.7 Hz successively using standard microelectrode techniques and compared with nontransplanted hearts. For each frequency, we measured action potential amplitude, action potential duration, transmembrane resting potential, and Vmax. In the right ventricle, at 1 Hz in the presence of rejection (n = 40), a significant increase was observed in action potential duration at 20%, 50%, and 70% repolarization (82.5%, 75.6%, and 70.8%, respectively) and in action potential amplitude (+17.9 mV), and the resting potential was decreased (-5.3 mV). A lack of adaptation of action potential duration to the driving frequency was observed in the rejecting heart group in contrast to controls (n = 20) and nonrejecting hearts (n = 13). Similar results were observed in the left ventricle and surprisingly in the native hearts (n = 11) of recipients with allografted rejecting hearts in the abdominal position. CONCLUSION: Action potential and its adaptation to the driving frequency is considerably altered during acute rejection. A humoral factor could contribute to cardiac dysfunction.     

Rejection of cardiac allografts by T cells expressing a restricted repertoire of T-cell receptor V beta genes

We have recently shown that T cells infiltrating cardiac allografts early in graft rejection use a limited T-cell receptor (TCR) V beta repertoire. In this study we tested whether this limited repertoire of V beta genes is important for graft rejection. A cell line, AL2-L3, was established from LEW lymphocytes infiltrating ACI heart allografts 2 days after transplantation. This cell line is composed of CD4+ T cells that primarily recognize the class II RTI.B major histocompatibility complex (MHC) molecule expressed by the donor graft. This cell line precipitated acute rejection of donor hearts with a median survival time (MST) of 10.5 days following adoptive transfer to sublethally irradiated LEW recipients. This rate of graft rejection was significantly (P < 0.0007) accelerated when compared with a MST of 60 days for allografts in irradiated control recipients. The AL2-L3-mediated acceleration of graft rejection was donor specific as WF third-party heart allografts were rejected with a delayed tempo (MST = 28.5 days). The V beta repertoire of this cell line was primarily restricted to the expression of V beta 4, 15 and 19 genes. The nucleotide sequence analysis of the beta-chain cDNAs from this cell line demonstrated that the restricted use of the V gene repertoire was not shared with the N, D and J regions. A wide variety of CDR3 loops and J beta genes were used in association with selected V beta genes. These data provide evidence for the role a restricted repertoire of V beta genes plays in cardiac allograft rejection in this model. The restricted usage of the V beta repertoire in an early T-cell response to allografts may provide the opportunity to therapeutically disrupt the rejection reaction by targeting selected T-cell populations for elimination at the time of organ transplantation.     

Expression of fibronectin splicing variants in organ transplantation: a differential pattern between rat cardiac allografts and isografts

Allograft rejection is associated with infiltration of inflammatory cells and deposition of extracellular matrix proteins. The extent to which diversity in the extracellular matrix regulates inflammatory cell function in transplants remains unclear. One group of extracellular matrix proteins, termed fibronectins (FNs), exhibits inherent diversity as a consequence of alternative splicing in three segments: EIIIA, EIIIB, or V. Although the EIIIA segment has documented functions in mesenchymal cell differentiation, neither this segment nor the EIIIB segment have been tested for effects specific to leukocyte functions. By contrast, the V region can include the CS-1 segment to which leukocytes may adhere through alpha 4 beta 1 integrins. In this study, we demonstrate that EIIIA+, EIIIB+, and V+ FN variants are synthesized, primarily by macrophages in distinct temporal and spatial patterns in two rat cardiac transplant models: either with antigenic challenge, allografts, or without challenge, isografts. The ratio of EIIIA inclusion into FN increases by day 1 in allografts and isografts and remains high until allografts are rejected (approximately 7 days) but falls to normal levels in tolerated isografts (day 6). EIIIB+ FN ratios in allografts peak later than do EIIIA+ FNs (day 4). EIIIB+ FN ratios remain relatively low in isografts. Interestingly, EIIIA+ and EIIIB+ FNs are deposited prominently in the myocardium of rejecting allografts in close association with infiltrating leukocytes, and FN expression and deposition are prominent at sites of infarction. By contrast, these FNs are largely restricted to the epicardium and to a lesser degree in the immediately adjacent myocardium in isografts. CS-1+ FNs increase in allografts and isografts at 3 hours after transplantation but are particularly prominent in allografts 1 to 3 days before rejection. Our data suggest that FN splicing variants have a differential role in the effector functions of leukocytes in allografts and isografts and provide a foundation for testing their function on leukocytes and a rationale for FN-based therapeutics to modulate allograft rejection in transplant recipients.     

Experiences of familial acceptance–rejection among transwomen of color.

Because of the stigma associated with transgenderism, many transwomen (biological males who identify as female or transgender) experience rejection or abuse at the hands of their parents and primary caregivers as children and adolescents. The Parental Acceptance–Rejection (PAR) theory indicates that a child’s experience of rejection may have a significant impact on their adult lives. The purpose of this study was to conduct a qualitative analysis of adult transwomen of color’s experiences with caregivers, guided by PAR theory. Twenty transwomen of color completed semi-structured interviews exploring the reaction of their parents and primary caregivers to their gender. While many participants reported that at least one parent or close family member responded with warmth and acceptance, the majority confronted hostility and aggression; reports of neglect and undifferentiated rejection were also common. Many transwomen were forced out of their homes as adolescents or chose to leave, increasing their risk of homelessness, poverty, and associated negative sequelae. Future research is needed to explore how families come to terms with having a transgender child and how best to promote acceptance of such children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anatomic variability of rejection in intestinal allografts after pediatric intestinal transplantation

The internal mammary artery is routinely used for coronary artery bypass grafting because of its optimal long-term patency profile. This vessel can be imaged by angiography, but only the proximal tract at the origin from the succlavian artery can be imaged by conventional echography. The aim of our study was to visualize the intrathoracic course of the native and grafted internal mammary arteries by a new ultrasound equipment which allows high-resolution transthoracic color Doppler imaging of the chest wall vessels and coronary arteries. We studied 35 patients, 16 non operated and 19 operated of coronary surgery with the internal mammary artery grafted to the left anterior descending coronary artery. We used a multifrequency 3.5-7 MHz transducer with a small insonating surface, placed at the second-fifth intercostal space at the left and right sternal border, to image the native mammary arteries. The grafted mammary artery was detected at the fourth-fifth left intercostal space 2-4 cm lateral to the sternal border. The native left internal mammary artery was visualized in all 16 non operated patients, and the right internal mammary artery in 14/16 (87%). The native left internal mammary artery peak flow velocity was 41-160 cm/s (mean 81 +/- 34 cm/s), and the mean flow velocity was 28-89 cm/s (mean 45 +/- 17 cm/s). The right internal mammary artery peak flow velocity was 35-153 cm/s (mean 82 +/- 36 cm/s), and mean flow velocity was 21-82 cm/s (mean 46 +/- 22 cm/s). The grafted left internal mammary artery was visualized in 16/19 patients (84%), evaluated at 6 days to 36 months after surgery. Peak diastolic flow velocity ranged from 24 to 80 cm/s (mean 48 +/- 17 cm/s), and mean diastolic flow velocity ranged from 13 to 57 cm/s (mean 33 +/- 11 cm/s). The left anterior descending peak flow velocity distal to the anastomosis was 22-62 cm/s (mean 37 +/- 15 cm/s) and mean flow velocity was 18-53 cm/s (mean 29 +/- 12 cm/s). We conclude that transthoracic color Doppler echocardiography allows to image the native and grafted mammary arteries, with potential clinical applications in the management of patients with coronary artery disease.     

Hemodynamic follow-up of cardiac allografts from poisoned donors

BACKGROUND: The current shortage of donor organs, combined with an increasing demand for cardiac allografts, means that extended donor criteria are becoming more and more accepted. The use of cardiac allografts for transplantation from donors after acute poisoning is still under discussion; few data are currently available in the medical literature. We describe our experience with 19 orthotopic heart transplant recipients of organs from donors after acute intoxication with different agents. METHODS: Between March 1989 and December 1997, 883 orthotopic heart transplantations were performed at our transplant unit. Within this group, we accepted donor hearts after ethanol intoxication (n=1), benzodiazepine (n=1), alkylphosphate (E 605) in combination with beta-blocker intoxication (n=1), carbon monoxide poisoning (n=5), digitalis (n=1), digitalis/glibenclamide (n=1), chlormethiazole (n=1), propoxyphene (n=1), alkylphosphate (E 605) (n=1), insulin (n=2), neprobamate/ thiocyacide/flurazepam (n=1), paracetamol (n=1), carbamazepine (n=1), and cyanide (n=1) intoxication. At the time of organ explantation, hemodynamic data were available from all patients. RESULTS: Early mortality in this group was 11%; cumulative survival after 5 years was 74%. CONCLUSIONS: Based on our limited experience, cardiac allografts from donors exposed to different kinds of poisons can be transplanted in selected cases. If the donor organ is not hemodynamically compromised, showing regular filling pressures on low or mild inotropic support just before explantation, and if there are no electrocardiographic changes in combination with elevation of the transaminases, cardiac allograft transplantation seems to be a safe and life-saving procedure.