Irreversible chronic vascular rejection occurs only after development of advanced allograft vasculopathy: a comparative study of a rat cardiac allograft model using a retransplantation protocol

Histologic damage of lung allografts according to magnitude of acute rejection in the re-isotransplant model

BACKGROUND

Graft damage due to acute rejection has been reported as one of the risk factors in the chronic stage of cardiac and renal allografts. This study was designed to elucidate the histologic changes of grafts after ongoing acute allograft rejection was discontinued in models of lung re-isotransplantation.

METHODS

WKAH rat lungs were orthotopically transplanted into F344 recipients. Three days (3A group) and 5 days (5A group) after the first allotransplantation, the grafts were re-isotransplanted back into the WKAH rats (3RA and 5RA groups, respectively). Five days (5I group) after the first isotransplantation, the grafts were re-isotransplanted back into the WKAH rats (5RI group). The grafts were removed 30 and 60 days after re-isotransplantation and assessed histologically.

RESULTS

Typical acute allograft rejection developed in the 3A and 5A groups, and the changes were reduced after re-isotransplantation, although they remained significantly greater in the 5RA group than in the 3RA and 5RI groups. For intimal hyperplasia, the graft score 60 days after re-isotransplantation in the 5RA group was significantly higher than in the 5RI and 3RA groups. The changes in airway inflammation were significantly greater in the 5RA group than in the 3RA and 5RI groups at 60 days. Peribronchiolar fibrosis was significantly more frequent in the 5RA and 3RA groups than in the 5RI group.

CONCLUSIONS

Acute rejection and airway inflammation corresponded to the magnitude of rejection before retransplantation. Significant intimal hyperplasia developed in severe acute rejection, and peribronchiolar fibrosis occurred after the first acute rejection.

Cardiac Allograft Vasculopathy: An Update

Allograft vasculopathy remains the nemesis of long-term survival in heart transplantation. Possible modifying risk factors such as obesity, diabetes, and hypertension should continue to be pursued aggressively. All patients should receive statins. Clinical trials will provide the evidence needed to ascertain whether mammalian target of rapamycin inhibitors should be used in de novo cardiac transplant recipients to attenuate cardiac allograft vasculopathy (CAV). Intravascular ultrasound appears to play a key role in the diagnosis and evaluation of new treatments, and may indeed represent a surrogate marker that can be used to tailor management and improve outcomes. A better understanding of CAV is needed to develop targeted preventive therapies. Ongoing research in native atherosclerosis and vascular biology may provide answers within the next decade.

Progression of alloresponse and tissue-specific immunity during graft coronary artery disease

Chronic rejection remains the major obstacle for long-term transplant survival. Both indirect alloresponse and tissue-specific autoimmunity have been implicated in its pathogenesis. The interrelationship between these two types of host anti-graft response remains poorly understood. We have developed an immunosuppression-free mouse model of graft coronary artery disease (GCAD), in which all FVB (H-2(q)) cardiac allografts placed into minor Ag (mHC)-mismatched DBA/1 (H-2(q)) hosts survived more than 112 days, and developed GCAD. We then examined the kinetics of both anti-mHC alloresponse and host autoimmunity against heart-specific antigen, cardiac myosin (CM). At 8 days post-transplantation, recipient mice showed minimal intragraft inflammation and apoptosis, and limited expansion of allo-specific T cells. In addition, we observed early production of anti-myosin IgG1 autoantibodies, which occurred in the absence of activated CM-specific T lymphocytes. By day 56, GCAD indices, the numbers of mHC- and CM-reactive T cells, and the levels of circulating allo- and CM-specific antibodies were all significantly increased. While host alloresponse was exhausted at 112 days post-transplant, T-cell reactivity against CM persisted. Our data suggest that both allo- and tissue-specific immunity might contribute to the induction of GCAD. They indicate that continual autoimmune response against graft tissue antigens may provide for GCAD sustenance.

Rapamycin has no effect on fibrosis-associated gene expression or extracellular matrix accumulation when administered to animals with established or early allograft vasculopathy

BACKGROUND

Most patients with functioning heart transplants have established and progressive chronic allograft vasculopathy, a fibroproliferative process for which there is no effective treatment. Coronary artery disease is characterized by histologic evidence of extracellular matrix accumulation (fibrosis). This study compares the effect of rapamycin administered to rats with established allograft vasculopathy on histologic indices of disease progression, extracellular matrix accumulation (fibrosis), and the expression of genes known to regulate extracellular matrix turnover in this model.

METHODS

Lewis recipients of Fisher 344 rat thoracic to abdominal aorta transplants were administered rapamycin starting at 8, 12, and 16 weeks posttransplant or no treatment. Six grafts in each group were harvested at 24 weeks. Vascular remodeling and collagen accumulation (Sirius red) were measured by computerized histomorphometry of aortic sections. mRNA was extracted from frozen tissue, and the expression of fibrosis-associated genes was studied by means of semiquantitative reverse transcriptase-polymerase chain reaction.

RESULTS

Rapamycin had no effect on the progression of early or established allograft vasculopathy with regard to intimal thickening, remodeling, extracellular matrix accumulation, or profibrotic gene expression, regardless of the time commenced.

CONCLUSION

The attenuation of the fibroproliferative response in rodents by rapamycin is not seen if the onset of rapamycin therapy is delayed.

Chronic liver allograft rejection in a population treated primarily with tacrolimus as baseline immunosuppression: long-term follow-up and evaluation of features for histopathological staging

BACKGROUND

Predisposing factors, long-term occurrence, and histopathological changes associated with recovery or progression to allograft failure from chronic rejection (CR) were studied in adult patients treated primarily with tacrolimus.

METHODS

CR cases were identified using stringent criteria applied to a retrospective review of computerized clinicopathological data and slides.

RESULTS

After 1973 days median follow-up, 35 (3.3%) of 1049 primary liver allograft recipients first developed CR between 16 and 2532 (median 242) days. The most significant risk factors for CR were the number (P<0.001) and histological severity (P<0.005) of acute rejection episodes and donor age >40 years (P<0.03). Other demographic and matching parameters were not associated with CR in this cohort. Ten patients died with, but not of, CR. Eight required retransplantation because of CR at a median of 268 days. Ten resolved either histologically or by normalization of liver injury tests over a median of 548 days. CR persisted for 340 to 2116 days in the remaining seven patients. More extensive bile duct loss (P<0.01), smallarterial loss (P<0.03), foam cell clusters (P<0.01) and higher total bilirubin (P<0.02) and aspartate aminotransferase (P<0.03) were associated with allograft failure from CR.

CONCLUSIONS

Early chronic liver allograft rejection is potentially reversible and a combination of histological, clinical, and laboratory data can be used to stage CR. Unique immunological and regenerative properties of liver allografts, which lead to a low incidence and reversibility of early CR, can provide insights into transplantation biology.

Rapamycin reverses chronic graft vascular disease in a novel cardiac allograft model

BACKGROUND

Chronic graft vascular disease (CGVD) in cardiac allografts has been defined as a slowly evolving vasculopathy unresponsive to conventional immunosuppression. We compared 4 rodent models of CGVD to evaluate the reproducibility of CGVD in heart allografts. Rapamycin (Rapa) and cyclosporine (CSA) were then used to treat CGVD.

METHODS AND RESULTS

Hearts were harvested and placed heterotopically into allogenic recipients. CGVD scores of PVG allografts from ACI recipients treated with CSA on days 1 through 10 were significantly elevated on day 90 (n=16) compared with other models (immunosuppression used): (1) Lewis to F344 recipients (CSA), (2) Brown Norway to Lewis (FK506), and (3) DA to Wistar-Firth (methylprednisolone, azathioprine, CSA). Although delayed (day 60 to 90) CSA treatment had no effect (n=6), delayed Rapa (3 mg. kg-1. d-1 IP) reversed CGVD in PVG grafts (0.22+/-0.19 on day 90, n=6). ACI isografts showed no evidence of CGVD (n=6) at day 90. Immunohistochemistry of PVG grafts revealed perivascular infiltrates consisting of CD4(+) T cells and limited numbers of macrophages persisting up to day 90. Flow cytometry demonstrated increased levels of anti-donor antibody at day 90, which was significantly inhibited by Rapa treatment.

CONCLUSIONS

PVG grafts developed a significant increase in CGVD without evidence of ongoing myocardial rejection. This CGVD appeared to be mediated by both cellular and humoral mechanisms, given CD4(+) perivascular infiltrates and increased levels of anti-donor antibody. The anti-CGVD effectiveness of Rapa during a period in which there was little myocardial cellular infiltrate supports a novel mechanism of effect such as smooth muscle or B-cell inhibition.

Oestrogen and transplant vascular disease

1. The aetiology of chronic rejection is clearly multifactorial and relates to both immunological and non-immunological factors. 2. Our studies suggest that the insulin-like growth factor (IGF)-I ligand and receptor genes are rate limiting in smooth muscle proliferation in the development of transplant arteriosclerosis. 3. Suppressing growth factor ligand or receptor expression could be effective strategies for the prevention or treatment of transplant arteriosclerosis. 4. We consistently find chronic oestradiol treatment of transplant recipients inhibits arteriosclerosis by attenuating both IGF-I expression and the immune response, particularly major histocompatibility complex class II expression. 5. Thus, a cell- or tissue-specific oestrogen with minimal feminizing properties may be an ideal drug for prevention of one of the major causes of loss of transplant function.

Chronic rejection: increasing evidence for the importance of allogen-independent factors

Chronic rejection is a process caused by an interplay of different risk factors. Early injury regardless of type, seems to be an important prognostic event. Later insults appear to contribute. As the individual components of the process are increasingly dissected and understood, means to modulate or normalize them will be forthcoming.